UNIVERSIDADE ESTADUAL DE CAMPINAS FACULDADE DE ENGENHARIA DE ALIMENTOS
BIANCA CRISTINA NOGUEIRA FERNANDES
DESENVOLVIMENTO DE EMBALAGENS TERMOATIVAS:
ESTUDO DA VIABILIDADE DA INCORPORAÇÃO DE
PARTÍCULAS EM EMBALAGEM CELULÓSICA
THERMOACTIVE PACKAGING DEVELOPMENT:
FEASIBILITY STUDY OF THE INCORPORATION OF
PARTICLES IN CELLULOSIC PACKAGING
Campinas - SP Fevereiro/2020
BIANCA CRISTINA NOGUEIRA FERNANDES
DESENVOLVIMENTO DE EMBALAGENS TERMOATIVAS:
ESTUDO DA VIABILIDADE DA INCORPORAÇÃO DE
PARTÍCULAS EM EMBALAGEM CELULÓSICA
THERMOACTIVE PACKAGING DEVELOPMENT:
FEASIBILITY STUDY OF THE INCORPORATION OF
PARTICLES IN CELLULOSIC PACKAGING
Dissertação apresentada à Faculdade de Engenharia de Alimentos da Universidade Estadual de Campinas, como parte dos requisitos exigidos para obtenção do título de Mestra em Engenharia de Alimentos.
Master thesis presented to the Faculty of Food Engineering of the University of Campinas in fulfillment of the requirements for the degree of Master in Food Engineering.
Orientadora: ANA SILVIA PRATA
ESTE EXEMPLAR CORRESPONDE À VERSÃO FINAL DA DISSERTAÇÃO DEFENDIDA PELA ALUNA BIANCA CRISTINA NOGUEIRA FERNANDES E ORIENTADA PELA PROFA. DRA. ANA SILVIA PRATA.
Campinas Fevereiro/2020
Agência (s) de fomento e nº (s) de processos: CNPq, 130100/2018-8.
Ficha catalográfica
Universidade Estadual de Campinas
Biblioteca da Faculdade de Engenharia de Alimentos Claudia Aparecida Romano - CRB 8/5816
Fernandes, Bianca Cristina Nogueira, 1992-
F391t Thermoactive packaging development: feasibility study of the incorporation of particles in cellulosic packaging / Bianca Cristina Nogueira Fernandes. – Campinas, SP: [s.n.], 2020.
Orientador: Ana Silvia Prata.
Dissertação (mestrado) – Universidade Estadual de Campinas, Faculdade de Engenharia de Alimentos.
1. Embalagem ativa. 2. Material de mudança de fase. 3. Cera de carnaúba. 4. Encapsulação. 5. Calor - Transferência. I. Prata, Ana Silvia. II.
Universidade Estadual de Campinas. Faculdade de Engenharia de Alimentos. III. Título.
Informações para Biblioteca Digital
Título em outro idioma: Desenvolvimento de embalagens termoativas: estudo daviabilidade da incorporação de partículas em embalagem celulósica
Palavras-chave em inglês: Active packaging; Phase Change Materials; Carnauba wax, Encapsulation, Heat - Transfer.
Área de concentração: Engenharia de Alimentos Titulação: Mestra em Engenharia de Alimentos Banca examinadora:
Ana Silvia Prata [Orientadora] Francys Kley Vieira Moreira
Henriqueta Talita Guimarães Barboza Data de defesa: 27-02-2020
Programa de Pós-Graduação: Engenharia de Alimentos
Identificação e informações acadêmicas do(a) aluno(a) - ORCID do autor: https://orcid.org/0000-0001-7593-464X - Currículo Lattes do autor: http://lattes.cnpq.br/6008110551425536
BANCA EXAMINADORA
________________________________________ Profa. Dra. Ana Silvia Prata - Orientadora Faculdade de Engenharia de Alimentos – UNICAMP
________________________________________ Prof. Francys Kley Vieira Moreira– Membro Titular
Departamento de Engenharia de Materiais - UFSCar
________________________________________
Dra. Henriqueta Talita Guimarães Barboza – Membro Titular Embrapa Agroindústria de Alimentos
A ata da defesa com as respectivas assinaturas dos membros encontra-se no processo de vida acadêmica do aluno.
Aos meus pais e meus irmãos, pelo amor, apoio e incentivo. Ao Natan, pelo companheirismo diário.
AGRADECIMENTOS
A Deus pelo dom da vida, pelas oportunidades improváveis colocadas em meu percurso e pela iluminação em mais uma etapa vencida.
À Profa. Dra. Ana Silvia Prata, pela orientação conduzida com competência, dedicação, dinamismo e atenção irretocáveis. Pelas oportunidades oferecidas e confiança depositada, expresso os meus mais sinceros e sentidos agradecimentos.
Aos membros da Banca Examinadora, pelas valiosas contribuições para o enriquecimento deste trabalho.
À Universidade Estadual de Campinas (UNICAMP) e à Faculdade de Engenharia de Alimentos (FEA), aos professores e funcionários, por todos os ensinamentos que contribuíram para a minha formação científica e acadêmica, e crescimento profissional. Ao Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq, 130100/2018-8) pelo suporte financeiro que possibilitou a realização deste trabalho.
Ao Prof. Dr. Eduardo A. C. Batista pela disponibilidade em ajudar com análises críticas durante o delineamento experimental.
Ao técnico Izaías Cunha “Zazá” pela disponibilidade e por toda ajuda durante a fase experimental.
À equipe do Laboratório de Inovação em Alimentos (LINA), pelo agradável convívio, momentos de descontração, ajuda e apoio imensuráveis.
Aos amigos que acompanharam a trajetória do desenvolvimento deste trabalho, sempre dispostos a contribuir, pelo apoio recíproco e pelos momentos eternos.
À minha família, em especial a minha mãe, ao meu pai, aos meus irmãos e sobrinhos, pelo amor incondicional que me têm dedicado, pelo exemplo de seres humanos vencedores com integridade, honestidade e respeito, pelo permanente incentivo aos estudos e por nunca medirem esforços para proporcionar o melhor a mim.
Ao Natan por todo companheirismo, compreensão, paciência e amor. Por ser esta pessoa tão especial e que me faz muito feliz.
A todos que contribuíram, direta ou indiretamente, para a realização deste trabalho.
O presente trabalho foi realizado com apoio da Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - Brasil (CAPES) - Código de Financiamento 001.
RESUMO
As embalagens de alimentos não possuem mais um papel passivo na proteção e comercialização de um produto alimentar. Embalagens ativas e inteligentes oferecem inúmeras e inovadoras soluções para manter, melhorar ou monitorar a qualidade e a segurança de produtos alimentícios. Muitos dos avanços deste setor já foram empregados e estão disponíveis comercialmente, mas considerando a importância da manutenção da temperatura em produtos alimentícios, o desenvolvimento de embalagens termoativas ainda é incipiente. Além da qualidade do produto em si, tais embalagens desempenham um papel implícito no impacto ambiental, por permitir a conversão de produtos comuns, como o papel cartonado, em embalagens de elevado desempenho, com uma forte componente tecnológica, vislumbrando a substituição de materiais não renováveis e não biodegradáveis. Nesta perspectiva, Materiais de Mudança de Fase (PCM), foram utilizados pois possuem a capacidade de liberar ou absorver grande quantidade de energia térmica durante transição de fases. Neste projeto foi desenvolvida uma embalagem celulósica com função termoativa a partir da incorporação de um PCM encapsulado. O papelão tratado com partículas de PCM com ponto de fusão a 79° C, apresentou uma diferença marcante no processo de resfriamento em relação à embalagem celulósica original, mantendo a temperatura do produto por mais tempo. Foram realizados experimentos variando as frações de massa das partículas (10 e 20 g), e a resposta térmica foi diretamente proporcional à quantidade de partículas de PCM. Comparado com o material convencional, o material tratado com PCM levou cerca de 10 minutos, a mais, para atingir a temperatura final. Esse tempo reflete a quantidade de energia armazenada durante a transição de fase, e isso permitiu que o material tratado mantivesse a temperatura mais alta até 6° C durante o resfriamento. A importância do uso de partículas estruturadas de PCM também foi destacada. Estas partículas exibiram um calor latente de 168,9 J / g, ponto de fusão a 79 °C, estabilidade térmica até 230 °C, mantendo-se intactas, resistindo à variação de temperatura. Os resultados apresentados neste trabalho expandem a aplicabilidade de partículas de PCM em condições extremas de processamento de embalagens e abrem novas oportunidades para materiais termoativos.
Palavras-chave: Embalagem ativa, material de mudança de fase, cera de carnaúba encapsulação, transferência de calor.
ABSTRACT
Nowadays, food packaging plays an important role in the food product protection and commercialization of foodatuffs. Active and intelligent packaging offer many innovative solutions to maintain, improve or track the quality and safety of food products. Many advances in this sector were already employed and they are commercially available; however, considering the importance of maintaining the temperature in food products, the development of thermoactive packaging is still incipient. In addition to the product quality, packaging plays an implicit role in environmental impact by allowing the conversion of common products, such as cardboard, into high performance materials with a strong technological component, being able to replace renewable and non-biodegradable substances. In this perspective, Phase Change Materials (PCMs) can be used as they have the ability to release or absorb large amounts of thermal energy during the phase transition. Here, we report that cardboard treated with PCM particles with melting point at 79 °C, presented a remarkable difference in the cooling process regarding to the original cellulose, maintaining the temperature of the product for a longer period. We systematically performed kinetic experiments varying the mass fractions of particles, and the thermal response was directly proportional to the amount of PCM particles. Compared to the conventional material, the charging time of material treated with PCM was higher, taking about 10 minutes to reach the final temperature. This time reflects on the amount of energy stored during phase transition, allowing the treated material to maintain the temperature higher up to 6 °C during the cooling. The importance of using structured particles of PCM was also highlighted. These particles exhibited a latent heat of 168.9 J/g, melting point at 79 °C, thermal stability up to 230 °C, and they kept intact after the experiments, resisting to the temperature variation. The results presented in this work expand the applicability of PCM particles in extreme packaging processing conditions and open up new opportunities for thermo-active materials.
Keywords: Active packaging, Phase Change Materials, carnauba wax, encapsulation, heat transfer.
SUMÁRIO
INTRODUÇÃO ... 13
OBJETIVOS ... 16
Objetivo Geral ... 16
Objetivos específicos ... 16
Capítulo 1 - PROSPECTION OF THE USE OF ENCAPSULATION IN FOOD PACKAGING ... 17
1.1 Introduction ...18
1.2 Designing and active packaging ...20
1.2.1 Fundamentals of release, absorption and permeation ...21
1.2.2 Packaging to promote the release ...26
1.2.3 Packaging to promote absorption ...30
1.2.4 Packaging to improve barrier and mechanical properties ...32
1.3 Trends for new packaging ...34
1.3.1 Packaging with particles for thermoregulation ...34
1.3.2 Particles for intelligent packaging ...36
1.4 Conclusions ...38
1.5 References ...38
Capítulo 2 - DEVELOPMENT OF BIODEGRADABLE THERMOACTIVE PACKAGING USING PHASE CHANGE MATERIAL PARTICLES ONTO CELLULOSIC MATERIALS ... 52
2.1 Introduction ...53
2.2 Materials and Methods ... 54
2.2.1 Materials ... 54
2.2.2 Methodology ... 55
2.2.2.1 PCM particles characterization ... 55
2.2.2.2 Incorporation of the encapsulated PCM into the packaging material ... 55
2.2.2.3 Packaging characterization and performance ... 56
2.3 Results and discussion ... 57
2.3.1 Characterization of the particle ... 57
2.3.2 Packaging performance ... 59
2.5. References ... 66
DISCUSSÃO GERAL ... 71
CONCLUSÃO GERAL ... 73
INTRODUÇÃO
Segundo a Associação Brasileira de Embalagem (ABRE, 2017), o setor de embalagens movimenta mundialmente mais de US$ 500 bilhões por ano, representando, dentre 1% e 2,5% do PIB de cada país. Apenas a nível nacional, a movimentação de R$ 47 bilhões por ano, gera mais de 200 mil empregos. No entanto, também é o setor que mais preocupa ambientalistas já que cerca de 40% das embalagens de alimentos são plásticos (SARANTÓPOULOS; REGO, 2012) produzidos a partir de fontes não renováveis e não biodegradáveis, o que causa um significativo impacto ambiental. A possibilidade de converter produtos comuns e biodegradáveis, como os derivados celulósicos, em embalagens de elevado desempenho, com uma forte componente tecnológica pode reduzir o consumo de materiais como o poliestireno expandido, e optar pelo uso de materiais menos nocivos ao meio ambiente.
Nos últimos quinze anos, a indústria de materiais deu um salto, e muitos dos avanços obtidos com o desenvolvimento de novos materiais vem sendo aplicados ao setor de embalagens, permitindo contornar vários inconvenientes através da diversificação de matérias primas. Associado a estes avanços, as embalagens de alimentos não possuem mais um papel passivo na proteção e comercialização de um produto alimentar. Modificações em embalagens permitem que se funcionalize um substrato convencional e este passe a desempenhar funções antes inviáveis. Novos conceitos de embalagens, como as ativas e inteligentes, oferecem inúmeras e inovadoras soluções para prolongar a vida útil dos produtos, manter e monitorar a qualidade dos alimentos durante a cadeia de suprimentos ou consumo (DOBRUCKA, 2014).
Embalagens inteligentes são aquelas capazes de informar uma situação anormal ocorrida no produto. Neste tipo de embalagem é comum o uso de sensores, indicadores de tempo-temperatura, corantes de detecção de gás, indicadores de crescimento microbiano, indicadores de choque físico e numerosos exemplos de tecnologias anti-falsificação e anti-roubo. Além disso, sistemas de embalagem inteligentes conectados como etiquetas, incorporados ou impressos em um material de embalagem de alimentos oferecem possibilidades aprimoradas para monitorar a
qualidade do produto, rastrear os pontos críticos e fornecer informações mais detalhadas ao longo da cadeia de suprimentos (DOBRUCKA, 2014).
Já embalagens ativas, possuem compostos que interagem ou reagem, com o ambiente ou produto, para evitar que uma condição - na maior parte das vezes, indesejável - ocorra. Embalagens ativas atuam sobre o produto, por exemplo embalagens absorvedoras ou liberadoras de aromas, de metais, de umidade e de gases (DOBRUCKA, 2014). Uma medida opcional e vantajosa para o desenvolvimento de embalagens ativas é quando se pode incorporar materiais ativos na matriz original, seja pela funcionalização da superfície ou durante a formação da embalagem (extrusão, por exemplo). Neste sentido, existem substâncias capazes de liberar ou absorver grandes quantidades de energia térmica, chamados de Materiais de Mudança de Fase (PCMs), que quando adicionados a uma embalagem podem transformá-la em termoativa. Porém, uma das limitações com o uso de PCM é a expansão volumétrica que ocorre durante a mudança de fase sólido para líquido e a consequente adesão sobre o material onde estão dispostos, que finalmente reduzem sua eficácia durante os ciclos de aquecimento e resfriamento. Assim, a propagação através de uma partícula protetora oferece novas fronteiras de aplicações para os PCMs. A encapsulação de PCMs vem sendo citada como uma alternativa que pode permitir a contenção volumétrica do PCM durante a mudança de fase e adicionalmente aumentar a área para transferência de calor, minimizando tempo de contato e tornando a transferência mais eficiente (MILIÁN et al., 2017).
A funcionalização de embalagens com partículas pode ser realizada com princípio similar ao aplicado para a funcionalização de fibras têxteis, isto é, as partículas podem ser integradas ao material de embalagem ou aplicadas como revestimento após sua fabricação. As embalagens viáveis de serem funcionalizadas pertencem à classe de polímeros: celulósicos ou termoplásticos, que possuem uma temperatura de fabricação de até 230ºC.
Materiais celulósicos são obtidos após tratamento químico da fibra celulósica e são conformados mecanicamente. Desta forma, partículas de PCMs podem ser aplicadas superficialmente através da utilização de materiais adesivos. Este método pode ser mais conveniente pela facilidade de implementação a um
processo de produção já existente, pela flexibilidade da alteração da propriedade multifuncional desejada e por reduzir a chance de deterioração da partícula, já que esta é aplicada a temperatura próxima do ambiente.
A proposta deste trabalho foi estudar a viabilidade da incorporação de partículas de cera de carnaúba em embalagem celulósica, na expectativa de manter a temperatura quente de um produto alimentício e substituir, a longo prazo, copos descartáveis de poliestireno expandido ou desenvolver materiais duráveis.
OBJETIVOS
Objetivo Geral
Desenvolver uma embalagem termoativa como alternativa para preservar produtos alimentícios aquecidos por mais tempo.
Objetivos específicos
I. Analisar os principais conceitos sobre transferência de calor na funcionalização de embalagens de alimentos.
II. Avaliar a estabilidades das partículas de PCM a altas temperaturas.
III. Avaliar a eficiência térmica de um material de embalagem celulósica como função da quantidade de partículas de PCM adicionadas.
IV. Avaliar a performance da embalagem com PCM em relação a embalagem celulósica comum.
CAPÍTULO 1 - PROSPECTION OF THE USE OF ENCAPSULATION IN FOOD PACKAGING
Prospection of the use of encapsulation in food packaging
Bianca Cristina Nogueira Fernandes1; Bruna Barbon Paulo1, Claire Isabel Grigoli de Luca
Sarantopoulos2, Ana Silvia Prata1*
1 Department of Food Engineering, School of Food Engineering, State University of Campinas - UNICAMP, 13083-862, Campinas, Brazil, Phone: +55 (19) 3521-0069
2 Instituto de Tecnologia de Alimentos – ITAL, 13070-178, Campinas, Brazil, Phone: +55 (19) 3743-1700
Submitted to “Food Engineering Reviews”
ABSTRACT
Food safety and extended shelf life linked to the convenience were the major reasons for the development of the packaging field. However, advances in material science and the widespread encapsulation technologies are allowing the establishment of new concepts for packages, such as intelligent and active packages. Particulate systems have been developed in recent years for the most diverse area with several purposes that can be employed to improve packaging performance mainly focusing on the modification of barrier properties. This review analyzes the recent developments using encapsulation in food packaging and the main concepts about mass transfer evolved in the functionality of these packages, as well as discusses the research challenges faced by the food packaging sector. The fundamental understanding of how release, migration, absorption and permeation processes occur is crucial for the selection of the packaging material with optimized barrier properties, evaluation of the migration of toxic compounds to the food and more than ever, for the comprehension of how to design package materials with new functionalities.
Keywords: microencapsulation, intelligent packaging, active packaging, smart packaging, food
1.1. Introduction
The trend observed throughout the evolution of packaging systems would indicate that the package has a function apart from being a storage recipient for further commercialization. In the mid-40s (Fig. 1) polymeric materials have emerged following the development of the plastic industry.
Fig. 1 Packaging time-line evolution.
Plastic packages followed the change in retail and distribution practices associated with globalization (SONNEVELD, 2000; VERMEIREN et al., 1999) which resulted in the replacement of glass bottles, papers, and metallic cans packages and supplied demands of the society for end-use convenience products such as fresh-cut (GHIDELLI; PÉREZ-GAGO, 2018), ready-to-eat (MIR et al., 2018; PAULSEN et al., 2018; WIECZYŃSKA; CAVOSKI, 2018) and ready-to-cook (PÉREZ-PALACIOS et al., 2018).
Nowadays, packages must also answer for environmental claims and concerns about waste generation (DILKES-HOFFMAN et al., 2018; INGRAO et al., 2015; SOUZA; FERNANDO, 2016; XU et al., 2015), and serve for establishing a communication channel at the consumer level (KUORWEL et al., 2015; OTONI et al., 2016a).
In the last fifteen years, materials Industry made a leap forward, and many of the advances for new materials have been applied to the packaging sector, allowing that raw materials could be improved to overcome several of these inconveniences.
Associated with these advances, food packaging plays an important role in the protection and commercialization of a food product.
New packaging concepts have been introduced seeking innovative solutions to extend shelf life, maintain and monitor food quality throughout the supply chain or consumption. These goals can be reached when substances or even electronic devices are incorporated into traditional materials, and have designated intelligent and active packaging (VILELA et al., 2018).
Intelligent packaging is used to express, for example, a warning about undesirable contaminations in the food product (BIJI; RAVISHANKAR; MOHAN, 2015; FANG et al., 2017; KERRY; O’GRADY; HOGAN, 2006; REALINI; MARCOS, 2014; SOHAIL; SUN; ZHU, 2018). Often, indicators and sensors are employed to interact with internal (food components, metabolites and gases in the headspace) and/or external factors (environmental) providing a dynamic feedback to the consumers/retailers/manufactures on the actual quality of the product, that normally occurs in the form of color change or, an electrical signal related to the state of the food product (POYATOS-RACIONERO et al., 2018).
In contrast, active packaging acts to avoid that these undesirable reactions occur. Thus, the main active food packaging technologies are designed to counteract a wide range of deleterious quality and safety limiting effects, including rancidity, color loss/change, nutrient loss, dehydration, microbial proliferation, senescence, gas build-up and off-odors (SINGH; ABAS WANI; SAENGERLAUB, 2011) assisting to maintain, improve or extend the product quality and its shelf-life (FANG; VITRAC, 2017; KERRY; O ’GRADY; HOGAN, 2006; REALINI; MARCOS, 2014; YILDIRIM et al., 2018).
An active package can be made through the incorporation of certain compounds into conventional plastic-based packaging and the major part of these roles cited above can be reached when using encapsulation processes.
The encapsulation technology in food processing involves the coating or entrapment of an active material, which may be accomplished by micro or macro encapsulation (GIBBS et al., 1999). Microencapsulation is defined as a technology of packaging solids, liquids, or gaseous materials in micrometer scale (DESAI; PARK, 2005).
The resulting microcapsules/microparticles are already used to provide protection, controlled release or mask some unpleasant effects of an active compound
(GOUIN, 2004) in several area of application such as pharmaceutical, food, textiles, automobile, paints and so on. As consequence of the isolation of a specific component, also known as core material or active compound, the addition of these particles into the packaging open new possibilities for development of active packages as it has been related to improvements in overall performance including enhanced mechanical, thermal, and barrier properties, apart from providing new functionalities to the packaging (ECHEGOYEN et al., 2017; OZDEMIR; CEVIK, 2007; SOUZA; FERNANDO, 2016; YILDIRIM et al., 2018). For these reasons, the inclusion of particles also makes possible the use of biopolymers, contributing to the development of a more sustainable and ecological packaging system (SOUZA; FERNANDO, 2016). The selection of the microencapsulation process is governed by physical and chemical properties of core and coating materials and the intended application of the active material. In the food field, the encapsulation processes commonly used are spray-drying, spray-cooling, spray-chilling, fluidized-bed, extrusion, lyophilization, and coacervation, and co-crystallization (DESAI; PARK, 2005) because the restriction of the safety of raw materials.
Although some works are advancing constantly in the encapsulation area as well as in the development of active or intelligent packaging, there is scarce research about encapsulation applied to the packaging system. Thus, in this review we analyze the possibility of developments using encapsulation for food packaging, as well as a discussion about the research challenges faced by the food packaging sector.
1.2. Designing of active packaging
For designing an effective packaging system with delayed adverse environmental effects on food products, it is crucial to understand how the permeation process occurs.
Basically, packages are employed due to their barrier properties which are aimed to extend the shelf-life of a product. These properties are already studied to allow or not the exchange of gases/vapor with the environment and are based on fundamentals of mass transfer. In the same way, to provide some new functionalities as well as to make a strict selection of the materials or particles for designing an active package, the theoretical knowledge of the mass transfer is the utmost importance. The controlled release of an active compound or most of the degradation reactions that
occur in stored food and beverage include the phenomena of mass transfer. For example, lipid oxidation, color change, nutritional losses, off-flavor formation, are related to the permeation of oxygen or small molecules. Further gases also are produced by breathing and maturation processes of the food product, such as dioxide carbon and ethylene. In this case, if these gases remain inside the package, they accelerate the degradation of the stored food product. Also, the food product is in direct contact with the packaging material, increasing the susceptibility of toxic compounds migration from the package material (BOTT; STÖRMER; ALBERS, 2018; SOUZA; FERNANDO, 2016). Thus, a theoretical approach is firstly given and after it has been made a discussion about the prospection for development of active packages through the encapsulation.
1.2.1 Fundamentals of release, absorption and permeation
Release, migration, absorption and permeation processes are driven by the same mass transfer fundamentals. In general, the permeation process of molecules across a membrane occurs in three steps as outlined in Figure 2, namely, the sorption of the compounds from external environment onto polymer surface (C1 to
A); the diffusion of these compounds through the bulk polymer (B) and the desorption of the diffused molecules from the polymer surface (film) into food volume (fluid or not) (C to C2). Besides, after the permeation through the film, the transport of the
compounds to the product occurs even when the film is not in contact with the product. Anyway, a partitioning coefficient can control the distribution of molecules between headspace gas or food product, represented by the discontinued line in the interface environment-film and film-product. On food, mass diffusion combined with convection may also occur (FANG; VITRAC, 2017).
Fig. 2 The permeation process of molecules through a barrier with mass flux (JA) from the higher (C1)
to the lower concentration (C2). Environment-polymer surface (A); Bulk polymer (packaging layer) (B)
and polymer-food product surface (C).
In the schematic illustration from Fig. 2, a concentration gradient is established, and mass flux (JA) occurs from the higher (C1) to the lower (C2)
concentration. According to the localization of this zone, different cases can be named: Case 1- migration and release from B to C and further from C to C2, respectively), Case
2 – absorption (from C1 to A), and Case 3 – permeation (from A to C). All these
situations can be modified for improving the functionality of the package, as showed below.
Case 1 and case 2 are basically diffusional processes starting within the barrier to the food product (or vice versa)
Case 1 - Migration and release from packaging to food product: undesirable
migration of plasticizers, plastic monomers, metallic salts or other additives incorporated into packaging to improve lifetime or mechanical properties, can harm the consumer safety. Thus, adequate material composition or other approaches to controlling these undesirable releases must be employed (COLTRO; MACHADO, 2011). Another type of migration is related to the intentional release of compounds. Several active compounds, such as antimicrobials, colorants, antioxidants, flavor, can be incorporated into the packaging to increase the shelf life of the food or give supplementary functionality, regarding the safety and quality of the product at
consumption (GÓMEZ-ESTACA et al., 2014; OTONI et al., 2016b; RIBEIRO-SANTOS et al., 2017; SANCHES-SILVA et al., 2014).
Case 2 - Absorption by the packaging: some materials, known as
scavengers, have the ability to absorb organic gases and vapors that permeate the packaging or are present in the packaging headspace. When incorporated in the packaging, they can promote the selective removal of certain undesirable components in contact with the food product. The most developed application is oxygen scavengers, regarding that high levels of oxygen are responsible for microbial growth, off flavors and odors development, color changes and nutritional losses (CHARLES; SANCHEZ; GONTARD, 2006; KERRY; O ’GRADY; HOGAN, 2006; LEE et al., 2018).
Case 3 - Permeation from food product to environment or vice versa:
permeation is a combination of sorption and diffusion and refers to the complete passage of compounds through this inert barrier. This mechanism is important for increasing the shelf life of fresh products, like fruits and vegetables, by allowing the exit of carbon dioxide and ethylene internally generated. The CO2 is produced due to
the respiration of such foods, and if it stands inside the container, it will cause stuffing of package material and deterioration of the product (CHARLES; SANCHEZ; GONTARD, 2006). Contrarily, high permeation rates of gases from the environment, as oxygen and vapor, could damage the food product. As mentioned in Case 2, the entrance of oxygen and humidity accelerates the degradation reactions. Thus, the barrier properties must be selective to allow certain substances outgoing without other substances to enter. One way to improve the barrier properties of packages consists in adding reinforcing fillers to the matrix, reducing the solubility and diffusivity of the gas molecules, and consequently, their permeability. The reduction of diffusivity is related to the increase of tortuosity of the pathway which extends the diffusion path (BELTRA et al., 2014; CERISUELO; GAVARA; HERNÁNDEZ-MUÑOZ, 2015).
The permeation cited previously can be described by the diffusion equation. Many mathematical models of mass transfer through the packaging have been formulated (BUONOCORE et al., 2003; PIRINGER et al., 1998) based on general equations developed earlier by Crank (1975), and they will be discussed briefly as follow.
The understanding of the main factors that influence the diffusion process is important for designing packaging systems adapted according to the need.
The assumption of the flow of the compounds through the packaging film is a diffusive phenomenon (Equation 1), and it occurs in steady-state conditions, regarding that the transient state is very short (LAURINDO, 2002) when compared to the purpose of a package to improve a product shelf life. Also, besides being a three-dimensional phenomenon, the area where the transfer occurs is large compared to the thickness, so that one-dimensional flux (JA) can be considered:
𝐽𝐴 = −𝐷𝐴𝐵( 𝜕𝐶 𝜕𝑧) =
𝐷
𝛿(𝐶1− 𝐶2) (1)
Where 𝜕𝑧 is the position. The concentration difference at the polymer film boundaries is due to the film thickness (𝛿) and diffusion coefficient (𝐷𝐴𝐵, S.I. unit m2/s).
The resistance caused by the wall thickness, although easily manipulated, is not as effective as the proper material selection, characterized by the diffusion coefficient, due to the difference of magnitude order from both.
The diffusion coefficient represents the ability of certain molecules (component A in DAB) diffuse through a material medium (component B in DAB) that
can be solid or not. Thus, clearly, it depends on the nature of both substances and their interactions. Regarding the type of molecules, gases have higher diffusivities than liquids due to the size and the weaker interaction force between them. The diffusion coefficient is also more dependent on pressure and temperature for gases because these parameters can modify the degree of agitation of these molecules.
When the 𝐷𝐴𝐵 analysis is restricted to the material medium (component B),
the diffusion through the polymeric material depends on the degree of polymer crystallinity and on the solubility of the molecule in the polymer. From Figure 2, the equilibrium between the gas molecule from the environment and the polymeric membrane (region A) establishes the amount of gas molecule that can enter in the package system. This equilibrium can be described, under restricted conditions, based on Henry’s law of solubility (Equation 2).
𝐶𝐴 = 𝑘𝑃𝐴 (2)
Where CA is the concentration of the permeating species (A) in the polymer
surface in equilibrium with the total concentration, i.e., the partial pressure of the species A in the gaseous phase (PA). The coefficient 𝑘 represents the affinity of the
molecule diffused with the concentrated phase and it is dependent on the pressure and temperature.
However, if occurs sorption of the gas molecule in micro voids causing an interaction with the packaging material, the sorption behavior suffers a deviation from Law’s Henry and tends to follow a logarithmic non-linear relationship according to Langmuir-type sorption (HOWSMON; PEPPAS, 1986). Moreover, the desorption process may also be influenced by plasticization of the contact layer (FANG; VITRAC, 2017).
Another way to express the partition coefficient (𝑘) is replacing it by the solubility coefficient (S) that defines the number of molecules that can be absorbed or desorbed. Then, combining the equilibrium concentration of permeant dissolved in the packaging material (Equation 2) with Fick´s law (Equation 1) gives:
𝐽𝐴 = −𝐷𝐴𝐵(𝜕𝐶 𝜕𝑧) = 𝐷𝐴𝐵 𝛿 𝑆(𝑃𝐴1− 𝑃𝐴2) = 𝑃 𝛿(𝑃𝐴1− 𝑃𝐴2) (3)
Since we observe distinct behavior between diffusivity and solubility with the particle size, the permeability term is preferred to be used to characterize the gas transfer through a film. Thus, the Equation (3) can be used under the same steady-state conditions and assuming diffusion (𝐷𝐴𝐵) and solubility (or partition) coefficients to be independent on concentration.
The gas permeation and diffusion through the polymer barrier is often a complex process, especially when the solute is highly soluble in the polymer, as is the case of the penetration of water vapor into hydrophilic polymers. Therefore, the choice of a packaging material passes through the evaluation of the barrier type required, due to the high sensitivity of many food products to oxygen degradation and to moisture stimulus to microbial growth and the requirements to aroma retention to maintain food quality (BELTRA et al., 2014).
Traditionally, the packaging materials are chosen regarding the solubility of the gas, vapors and flavorings molecules, which is directly related to the affinity with the polymer matrix, as affirmed by Zeman and Kubik (2007). However, the barrier depends also on the degree of polymer crystallinity, and in turn of temperature, pressure and plasticizing effect of the permeant. Consequently, the effective protection or selective barrier is a difficult task to be achieve for only one material. For this reason, multilayers of different materials have been commonly used to improve the benefits of packaging systems. However, they work contrarily to the worldwide trend that aims to recycle non-biodegradable waste (GRUMEZESCU, 2016).
Alternatively, particles produced with biopolymers can be incorporated for promoting the selective barrier or even for reinforcing materials to improve durability and ensure the biodegradability. These topics are being discussed on item 2.4., but also, encapsulation is a rising technological trend toward packaging materials because it enables the enlargement of functionalities for conventional packaging materials leading to higher spectrum of use for renewable source material such as cellulose-derivate products. These functionalities include the release of active compound to the product (item 2.2) or packages able to absorb substances from the product (item 2.3).
1.2.2 Packaging to promote the release
Currently, only one type of packaging has been developed for releasing a substance and refers to antimicrobial ones. The use of antimicrobial packages has increased the consumer safety, since the bactericide compounds are included in the packaging structure instead of being added directly into the food (MIHINDUKULASURIYA; LIM, 2014). The main potential applications of antimicrobials include meat, fish, poultry, bread, cheese, fruits and vegetables (VERMEIREN et al., 1999) that, due to high water activity, are more susceptible to growth of pathogen agents.
Leceta et al. (2015) developed chitosan-based coatings and evaluated their efficacy in maintaining the quality of baby carrots over time. The chitosan-based coatings delayed microbial spoilage without causing adverse impacts on the quality attributes of baby carrots. Coatings also exhibited positive effects on product color and texture. Sensory analysis showed that overall acceptability of coated baby carrots was similar to freshly uncoated samples. In the work of Ghidelli and Pérez-Gago (2018) there are a compilation of studies presenting edible coating application to extend the shelf life of fresh-cut fruits and vegetables.
Eco-friendly microbial agents are already employed for food packaging including essential oils (AYALA-ZAVALA; GONZÁLEZ-AGUILAR, 2010; LEE; SEO; PARK, 2017), inorganic compounds, organic acids (AKBAR; ANAL, 2014; LUZI et al., 2016), bacteriophage (LONE et al., 2016) and allyl isothiocyanate (DIAS et al., 2013; SEO et al., 2012). The criteria used for the selection of the most appropriate microbial agent is based on the mechanism of action of these compounds and its activity against
a target microorganism. A very complete description of microbial agents normally used for food packaging can be found in the works of Vilela et al (2018) and Han (2005).
In general, organic acids, such as sorbic and benzoic acids, increase the acidity of a food, thereby creating an unfavorable environment for microorganisms, which is an effective mean of limiting microbial growth (LÓPEZ-CARBALLO et al., 2012), essential oils have a wide spectrum of antimicrobial activity, against food-borne pathogens and spoilage bacteria (GUTIERREZ; BARRY-RYAN; BOURKE, 2008, 2009). The antimicrobial activity of plant essential oils is due to their chemical structure, in particular to the presence of hydrophilic functional groups, such as hydroxyl groups of phenolic components and/or lipophilicity of some essential oil components (DORMAN; DEANS, 2000). These compounds may be lethal to microbial cells or they might inhibit the production of metabolites, e.g., mycotoxins (GRUMEZESCU, 2016).
On the other hand, metallic ions such as titanium oxide, zinc oxide, copper, copper oxide and silver (PATHAKOTI; MANUBOLU; HWANG, 2017), release their ionic form (MORONES et al., 2005) that act as microbial agent by degrading the bacterial membrane (SONDI; SALOPEK-SONDI, 2004), or by damaging the DNA (SILVESTRE; DURACCIO; CIMMINO, 2011). Sulfur dioxide, SO2 is used as
preservative agents that have been proven to strongly retard the growth of pathogenic fungi (Botrytis cinerea, Cladosporium spp., Rhizopus spp., etc.) and to inhibit the activity of polyphenol oxidase in fruits (XU et al., 2010).
However, many of the above substances are susceptible. Organic acids are prone to thermal degradation (QIU et al., 2018), the biological action of essential oils is mainly due to volatile molecules (RIBEIRO-SANTOS et al., 2017) and some metallic or inorganic salts can migrate to the product harming the consumer safety (KASSOUF et al., 2013). All these disadvantages can be overcome through the encapsulation helping to add safety, economic and environmental advantages (SILVESTRE; DURACCIO; CIMMINO, 2011).
Another advantage refers to the release behavior provided by the particles inside the packaging. As mentioned before, the release from the packaging to the product is related to diffusion coefficients in the packaging material, that indirectly is related to solubility, size and branching of the active compound, but also, it depends on the initial load of the active compound. Some molecules are just prevented from
migrating because they have relatively low diffusion coefficients in relation to the bulk matrix or they may be distributed in packaging systems with very low initial concentrations.
Depending on the solubility of the active compound in the media, or its mobility in the food product, two release behavior to the products can be observed, as demonstrated in Fig. 3. In this Figure, the left side indicates the packaging barrier containing the active compound to be released in the food product, which is in contact with the packaging film. The first release behavior (Fig. 3A) refers to the consumption of all active compound through to the product film-interface. This occurs because the substance migrates immediately from the surface to the product and the diffusion in the product is very high. In this case, the diffusion inside the product plays an essential role, and the concentration in the film-product interface will be reduced following its internal migration. This situation is very common for semi-solids and solids foodstuffs and corresponds to the direct incorporation of active agents into food resulting in an immediate but short-term reduction of microbial growth.
The second case (Fig. 3B) is commonly found when particles are inserted in the packaging material. The encapsulation of active compounds contributes to an additional barrier in the diffusion process, reducing its diffusivity in the packaging material. In this case, the diffusion coefficient in the product can be neglected and diffusion inside packaging material is the limiting mechanism as soon as the concentration profile in the packaging layer is not uniform. Although the concentration of the active agent on the food surface is much lower than its concentration in the package, it tends to have more uniform value, which corresponds to the maximum solubility of the compound in the food product. For example, the antimicrobial activity is kept constant even with the reduction of the amount of the antimicrobial agent inside the package. This system has a longer period above the Minimum Inhibitory Concentration (MIC) compared to system from Figure 3A, because the migration to the surface is slower.
Fig. 3 The schematic release profile of a compound in the package toward the product. C1, C2, and C3
are the concentrations with the time in the surface of the product (A) or in the surface of packaging (B); MIC is the Minimum Inhibitory Concentration. Modified from Han (2005).
In this perspective, encapsulation provides two advantages: 1) to require a smaller amount of active compound than the direct addition to the food, as the migration from packaging film to the food matrix results in longer storage times (RODRIGUEZ et al., 2013) and 2) to provide an additional protective effect to some bactericides, that present some kind of lability (FUCIÑOS et al., 2012).
Encapsulation techniques have been widely used to improve the release of bioactive molecules (OTONI et al., 2016b) in food products.
Gonçalves et al. (2017) applied thyme (Thymus vulgaris) essential oil encapsulated in a complex coacervation matrix in cakes samples. They verified that the particles could protect the oil against the volatilization and control its release, enabling a minimum shelf life of 30 days without the use of synthetic preservatives. Akbar and Anal (2014) developed active film of calcium alginate loaded with these zinc oxide nanoparticles and applied in ready-to-eat poultry meat for protection against two
foodborne pathogens (Salmonella typhimurium and Staphylococcus aureus), and the number of inoculated target bacteria was reduced within 10 days of its incubation.
Many examples of particles and mechanisms of drug delivery have been reported (ESMAEILI; KHODAEI, 2018; GOLDBERG; LANGER; JIA, 2007; MORGAN et al., 2008; ZHANG; WANG; NGAI, 2017; ZHUANG et al., 2014) and these effective action of particles evidences the applicability to package field. Dias et al. (2013) developed an antimicrobial packaging containing allyl isothiocyanate encapsulated in carbon nanotubes that was effective in reducing microbial contamination with
Salmonella Choleraesuis in chicken meat.
In addition to antimicrobial compounds, encapsulation has been employed for controlling oxidative reactions and to promote flavor release to minimize losses of quality of a food restoring the original flavor inside the package (SAJILATA et al., 2007). Encapsulated flavors may also provide a means for masking odors or to improving the organoleptic quality of the product, emitting desirable flavors/aromas in the food (VERMEIREN et al., 1999).
1.2.3 Packaging to promote absorption
Technological design for food packaging may play the role to remove undesirable substances from the environmental in contact with the product. Scavengers or absorbers have been applied in conventional packaging to promote absorption of some gases and extend the shelf life of food products.
Oxygen, for example, is responsible for many undesirable reactions in food products, as the reaction with lipid radical producing peroxide radicals and rancidity (MIN; AHN, 2005); binding to myoglobin in meat products, increasing the browning; (MEYDAV; SAGUY; KOPELMAN, 1977); and the growth of aerobic bacteria and molds (EIROA; JUNQUEIRA; SCHMIDT, 1999). For these reasons, the most widespread kind of active packaging system is oxygen absorbers.
By removing any residual oxygen present in the package, oxygen scavengers had already been successfully employed to prevent lipid oxidation (BOLUMAR et al., 2016; MU et al., 2013) microbial growth (UPASEN; WATTANACHAI, 2018), texture, odor and color changes (HUTTER; RÜEGG; YILDIRIM, 2016; LIMBO et al., 2013; SÄNGERLAUB et al., 2013), formation of toxic aldehydes and nutritional losses, respiration and the production of ethylene in fresh
fruits and vegetables (MARANGONI JÚNIOR et al., 2018; YILDIRIM et al., 2018; ZERDIN; ROONEY; VERMUË, 2003).
There are a large number of oxygen absorbers and the action mechanism is generally based on substances prone to capture oxygen by oxidation reactions, reducing O2 levels from 0.3 – 3 % to less than 0.01% in the food container
(CHAEMSANIT; MATAN; MATAN, 2018). The most commonly applied oxygen absorber are enzymes (HERVÁS PÉREZ; LÓPEZ-CABARCOS; LÓPEZ-RUIZ, 2008; WINESTRAND et al., 2013), catechol (CHARLES; SANCHEZ; GONTARD, 2006; DOMBRE; GUILLARD; CHALIER, 2015; OZDEMIR; FLOROS, 2004), iron and silver powders (BUSOLO et al., 2010; FOLTYNOWICZ et al., 2017; MU et al., 2013; SÄNGERLAUB et al., 2013), and ascorbic acid (ZERDIN; ROONEY; VERMUË, 2003). Enzymes used as scavengers allow that different types of reactions take place for removing oxygen. For example, glucose oxidase (EC 1.1.3.4) catalyzes the oxidation of glucose (HERVÁS PÉREZ; LÓPEZ-CABARCOS; LÓPEZ-RUIZ, 2008) and oxalate oxidase (EC 1.2.3.4) catalyzes the conversion of oxalic acid and molecular oxygen to carbon dioxide and hydrogen peroxide (WINESTRAND et al., 2013). Although many based-microorganism scavengers present heat sensitivity, and high conditions of temperature and pressure are employed for production of plastic-based packages, the most common way to incorporate these compounds in the packaging materials is by direct entrapment in the film forming matrix (ALTIERI et al., 2004; BUSOLO et al., 2010; BUSOLO; LAGARON, 2012; GRANDA-RESTREPO et al., 2009; JOHNSON; INCHINGOLO; DECKER, 2018; UPASEN; WATTANACHAI, 2018; WINESTRAND et al., 2013). Additionally, the kinetics of the oxygen trapping and the sensitivity to physicochemical factors, such as pH, water activity, salt concentration, temperature are limiting factors for the effectiveness of this class of oxygen scavengers (BOLUMAR et al., 2016).
Encapsulation can provide a homogeneous distribution of the enzyme in the particles, with defined concentration and an optimized porosity and surface area for reaction (HERVÁS PÉREZ; LÓPEZ-CABARCOS; LÓPEZ-RUIZ, 2008; HERVÁS PÉREZ; LÓPEZ-RUIZ; LÓPEZ-CABARCOS, 2016). Moreover, dried particles seem to be more appropriate for avoiding changes in the polymeric matrix and consequently the original properties. Wrona et al. (2017) incorporated green tea entrapped by inorganic capsules as a free radical scavenger into melted packaging material and
extruded for developing a new active packaging for extending the product shelf-life. Then, quality parameters such as color, myoglobin concentration and sensory evaluation were evaluated, and the results showed that the increase of shelf-life of fresh minced pork meat was successfully achieved.
Also, some limitations are observed for metallic-based oxygen scavengers. They act through organic redox reactions, but there is a trend for migration into the food due to their reduced size, leading to an unpleasant taste to the product. The encapsulation may be an alternative to protect these kind of metallic oxygen scavengers, reducing the migration rate from the polymers to the food, which is particularly important in the case of iron scavengers (BOLUMAR et al., 2016; CHAUDHARI; NITIN, 2015; SOUZA; FERNANDO, 2016). Moreover, it increases the exposed surface area to the reaction media which consequently turn faster organic reduction reactions.
Carbon dioxide, moisture, flavor substances and ethylene are examples of other substances that can be absorbed by classes of scavengers for extending the product shelf-life. CO2 scavengers, for example, can be composed of physical (zeolite
or active carbon powder) or chemical (calcium hydroxide, Na2CO3, Mg(OH)2, etc.)
absorbers and they are applied into packaging to avoid the accumulation of gas pressure within rigid packages or volume expansion in flexible packaging (CHARLES; SANCHEZ; GONTARD, 2006). Aday et. al (2011) applied carbon dioxide scavengers to maintain the quality attributes of fresh strawberries and their effectiveness was proven by the reduced accumulation of carbon dioxide and lower consumption of oxygen inside the active packaging.
Moisture and ethylene scavengers have been applied into packaging films to reduce the degradation reactions in fresh products (CHAUHAN et al., 2006; EXAMA et al., 1993; MANGARAJ et al., 2012; MURMU; MISHRA, 2017, 2018). Furthermore, flavors absorbers minimize the loss of quality in packaged food by absorbing undesirable flavors (off-flavor) (AHMED et al., 2017; VERMEIREN et al., 1999).
1.2.4 Packaging to improve barrier and mechanical properties
Biobased polymers such as thermoplastics starches, cellulose, chitin, and bio-synthetic materials have been employed in the food packaging market, but they lack mechanical and barrier properties. The incorporation of particles is a strategy
employed to design food-packages with an inert barrier to gases and water vapor and additionally enables to improve the mechanical performance for creation of a sustainable packaging chain and to reduce the dependence of petroleum-synthetic polymers.
Small particles ranging from nano to micro sizes act as reinforcements, partially transferring the internal tension in the polymeric matrix to the particles through the interface (DALMAS et al., 2007; SAMIR et al., 2004). The reduced size leads to a small number of defects in the matrix (AZEREDO, 2009). Then the uniform dispersion of reinforcing materials results in a very large matrix/filler interfacial area, which restricts the molecular mobility of the matrix, and improves its mechanical properties.
Moreover they might change the initial barrier properties of the packaging materials by closing small void volumes or interacting with the matrix (AZEREDO, 2009; RHIM; PARK; HA, 2013). The reduction in particle size increases the number of filler particles, bringing them closer to one another; thus, the interface layers from adjacent particles overlap, altering more significantly the matrix properties (JORDAN et al., 2005).
Thus, the strategy of adding nanoparticles allows tuning the polymer barrier properties through a relatively simple approach (GRUMEZESCU, 2016) which is especially important for biodegradable polymers. This tool opens new possibilities for improving not only their properties, but also their cost-price efficiency (SORRENTINO; GORRASI; VITTORIA, 2007) because the resultant materials are more efficient regarding to manufacturing cost and recycling than conventional multilayers food packages (MITRANO et al., 2015).
The most used reinforcing fillers in food packaging are: clay, chitosan, starch, carbon, silicate, cellulose and silica particles. By designing particles with these materials in appropriate dimensions and incorporating an active compound inside, one can improve not only the barrier properties but also incorporate some additional functionality to the final material.
1.3. Trends for new packaging
1.3.1. Packaging with particles for thermoregulation
Biological products such as food, beverages, pharmaceutical products, blood derivates (CHALCO-SANDOVAL et al., 2017; ORÓ et al., 2012; SARI et al., 2009; ZALBA et al., 2003), are highly sensitive to temperature changes. Aiming to ensure their microbiological, biochemical, physiological, sensory and physical quality is necessary to restrain the thermal variation during the cold chain of distribution. The main concern of environmentalists in relation to packages used with this goal consists in minimize the waste and the use of packages based on crude oil which includes expanded polystyrene.
The development of thermoactive packages for controlling thermal variations is essential to minimize food waste and contamination occurring during exposure to both cold and heat (FREY, 2014; SINGH et al., 2017), and, also, to keep the temperature of warm beverages and meals during consumption.
Some examples of thermoactive packaging are already available commercially using normally substances that undergo exothermic or endothermic reactions.
Examples of exothermic reactions include the dissolution in water of inorganic salts such as quicklime, calcium chloride, and super corroding alloys/salt. Many commercial self-heating thermals have failed, which represent an opportunity to improve this type of packaging. During 2001 in the UK, Nestle tried to commercialize a self-heating can for coffee claiming reach 40 °C by shaking for 3 minutes, but they were withdrawn from the market, because the coffee did not get hot enough during the winter months. However, other self-heating technologies are marketed as HotCan™ (UK), Vitcho (France), Sonoco (USA), Steam to Go™ (UK), KPS Technologies (Korea), Caldo Caldo (Italy), Pressto™ (USA) and Tempra Technologies (USA). The advances observed in the encapsulation field can be employed to improve the performance of thermo-active packages, by controlling the dissolution rate of the substances, isolating corrosive materials, or increasing the effective time of the packaging.
The use of refrigerant gas for cooling is yet the most efficient way to cool down the equipment. A self-cooling can be based on this principle was introduced
briefly into the market with the name of Chill Can™ (The Joseph Company, USA). The removal from the market was related to concerns about the environmental impact of the refrigerant gas. Other alternatives for cooling can be explored. Endothermic dissolution reactions can be provided by ammonium nitrate and chloride in water. IC™ (Instant Cool), developed by Tempra Technology in partnership with Crown Cork & Seal (USA), uses this kind of reaction to 15 ºC within 3 minutes. The Italian self-cooling coffee – ‘Freddo Freddo’ employs the endothermic reaction between sodium thiosulfate pentahydrate and water. Also, theoretically, water evaporation can be a powerful cooling process, as evaporation of 10 ml of water can cool 330 ml of water by 18 ◦C (BUTLER, 2008).
In the last years, substances called Phase Change Materials (PCMs) or temperature-regulating material (TRM) (SINGH et al., 2017) have also been employed for development of thermoactive packaging. These substances have high fusion heat, which gives them the capacity to absorb, store and release large amounts of heat during the phase change. This characteristic allows thermal energy storage and also thermoregulation, when adjusting the melting point of the PCM to the desired temperature variations or temperature of application (CABEZA et al., 2015; GIRO-PALOMA et al., 2016; JACOB; BRUNO, 2015; SHARMA et al., 2009). When incorporated into the structure of the packaging material, they increase its thermal capacity (HOANG et al., 2015b). However, these materials can gradually leak to the surface where they are applied during the transition solid-liquid (HONG; XIN-SHI, 2000; JAMEKHORSHID; SADRAMELI; FARID, 2014), which may interfere in its handling and packaging. Therefore, encapsulated PCMs can be applied directly to packaging structures for smart packaging and can help control temperature fluctuations.
Recently there are several studies of PCM encapsulation, but among these, a few studies are dedicated to the application in food packaging. Some researchers
evaluated the influence of packaging on the product temperature evolution along the cold chain, using paraffin PCM with transition temperature varying from -1.5 ºC to 5 ºC (CHALCO-SANDOVAL et al., 2014, 2015a, 2015b, 2017, HOANG et al., 2015a, 2017). These researches evidenced the applicability of PCM to improve the thermal protection of perishable products. They made a new insight on the development of heat management polymeric materials of interest in food packaging applications.
A recent work has coated PCM from carnauba wax. The study allowed a coating process of PCM particles in the fluidized bed, with potential application to other PCMs and to food packages. The transition temperature of carnauba wax is around 80 ºC, which can be used to keep hot food or beverages (PAULO et al., 2019).
1.3.2 Particles for intelligent packaging
Intelligent packaging is a different class of packaging because it reacts to the environmental conditions. The occurrence of an abnormal condition triggers reactions for production of warning signals to advise the consumer or for release of a substance to repair the abnormal condition stablished. The first example appoints the color indicators, normally named as sensors.
Indicators were raised to solve concerns about the security of selling fresh and quality products. Inadequate storage conditions by which the food product is submitted such as a failed cool chain, microbial growth in the food product and defects in vacuum packages can be detected by irreversible color changing. These smart packages can indicate the end of the shelf-life of the product, avoiding wastes or inadequate consumption.
Color indicators work especially under changing of time-temperature, and gas presence, by chemical or physical reactions, like the formation of complexes or polymerization, respectively.
Gas sensors are freshness indicators by monitoring mainly amines or gaseous ammonia produced by food spoilage. Usually, these sensors are based on metal oxides or, more recently, on conducting polymer nanocomposites (ARSHAK et al., 2007). Closely related amines in complex odor can even be distinguished when placing a range of polymeric nanoparticles containing sensing dyes (SOGA et al., 2013).
For oxygen sensors many substances have been tested. Indigo and methylene blue are normally used as redox dyes, changing from the colorless leucon form to the blue oxidized form in the presence of oxygen. Some enzymes and metallic ions can also be used as oxygen sensors (BIJI; RAVISHANKAR; MOHAN, 2015; MILLS; GROSSHANS; HAZAFY, 2010; POYATOS-RACIONERO et al., 2018; REALINI; MARCOS, 2014; SOHAIL; SUN; ZHU, 2018). Thiazines are used as
indicators of oxygen but also relative humidity changing from blue to purple depending on the concentration of the substances (MILLS; GROSSHANS; HAZAFY, 2010).
Despite the precondition for the substance serve as an indicator is the time required to form the chromophore and the irreversibility of the reaction, concerns about toxicity and luminescence power are also considered. Long luminescence decay times detect the presence of very low partial pressure (pO2) and they are indicated when designing trace oxygen sensors or it should be employed with polymers with low gas permeability.
Luminescence of the dye depends on the media conditions such as the presence of water or ionic species and on the diffusion coefficient of the oxygen in polymers (QUARANTA; BORISOV; KLIMANT, 2012). For these reasons, the use of an inert carrier for holding the light-sensitive dye molecules, for suppressing dye migration and to control the permeability of reactant species is an important approach. Alternative non-toxic sources of oxygen sensors have been developed. Mills, Grosshans and Hazafy (2010) tested the efficiency of a series of encapsulated UV-activated oxygen sensitive inks. O2 indicator is preliminary photobleached upon
exposure to UV light and under the presence of oxygen is able to recovery its original color. Vu and Won (2013) developed an oxygen indicator based on zein as a redox dye, a sacrificial electron donor, UV-absorbing semiconducting photocatalyst, and alginate as an encapsulating polymer.
Sensors-based packages in a simplified way are passive packages. Smart packages can also be designed to interact with the food inside and promote some alteration or repair an undesirable condition. In this context, the use of microencapsulation technology allows to embody multiple micro-compartments for mutual and dynamic interactions according to the environmental conditions. Using this concept, different active compounds in the particle may be alternatively released according several triggers as microbial load, pH, water concentration.
Self-healing agents are able to repair microcracks in the polymers, composite or metal packages avoiding mechanical or barrier damages in the structure. The healing agent is released from the particle by the same trigger that caused the crack and plasticizes the surrounding coating matrix hindering further propagation of the crack. Andersson et al. (2009) developed a self-healing capsule for treat the
surface of paperboard. The treated paper presents a reduced tendency for deteriorated barrier properties and local termination of cracks formed upon creasing.
1.4. Conclusions
Food packaging plays an important role in the protection and commercialization of food products and recently, numerous developments have been made in the field of active and intelligent packaging.
The fundamental understanding of how release, migration, absorption and permeation processes occurs is crucial for the selection of the packaging material with optimized barrier properties, evaluation the migration of toxic compounds to the food and more than ever, for the comprehension of how to design package materials with new functionalities.
Often, the functionalities are related to increase shelf life of product that depends not only on the own product but also on supposed condition of distribution and storage. Temperature abuse in the cold chain or sealing defects in packaging systems can lead to faster degradation food products. Then, packages may be designed with an effective packaging system to release flavour, antimicrobials and antioxidants substances, to absorb undesirable gases, to detect spoilage-related changes, and chemical contaminants, and to repair an abnormal condition.
Encapsulation has been increasingly researched for many fields and presents a huge potential for application in packages. Its promising future is due to the possibility to overcome many inconvenient aspects observed for the compounds freely employed. Through the encapsulation of a small amount of active compound, the slower migration from the packaging film to the food matrix results in longer storage times, an additional protective barrier can be added to active compounds presenting some kind of lability and, finally, an homogeneous distribution of the active compound can be achieved. Furthermore, the incorporation of particles is a strategy employed to design food-packages to improve the mechanical performance for creation of a sustainable packaging chain and to reduce the dependence of petroleum-synthetic polymers.
Acknowledgements
This work was supported by grant from the National Council for Scientific and Technological Development (CNPq).
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