The aim of fruit processing is to transform fresh fruits into preserved products. Therefore, the selection and elimination of components unsuitable for human con- sumption, lead to by-products and wastes. There is no sharp limit between the two categories as indus- tries processing substances of biological origin are in close cooperation; the by-product of one industry can be a valuable secondary raw material for another.
Apple processing is a good example for the afore- mentioned principle. Although apples (canned ap- ples, apple juice, etc.) are the finished product, and the by-product, apple pomace, is the secondary raw material of pectin production. However, if this by- product goes to the refuse, it becomes waste and pol- lutes the environment. Generally, in Hungary as well as the rest of the world, the majority (60–65%) of
10 Fruit Processing Waste Management 175 food industry by-products become waste and a bur-
den to the environment (Szenes, 1995).
In order to meet stringent environmental require- ments, modern fruit processing should minimize the amount of by-products and waste, decrease energy utilization, produce high-quality foodstuffs without polluting the soil, air, and spas (Barta et al., 1997).
Fruit processing wastes differ from other wastes rthey are organic and therefore, decompose. Most
go back into the soil, due to natural biomass circulation, or decompose without pollution;
rthey are large in volume with high water content.
In spite of the high volume their origin is scattered, making gathering and utilization difficult and expensive; and
rthey tend to deteriorate, thus limiting the storage period, even under appropriate circumstances, which include low temperatures, controlled humidity, and storage in dark and dry places.
Apart from the main finished product, unused sub- stances are considered as waste and by-products.
These can be utilized in different ways depending on their texture and content.
Certain by-products can be valuable resources for human nutrition if special technologies are used.
They include
rprecooling techniques (Brosnan and Sun, 2001) rsolid-state production (Zheng and Shetty, 2000) rGas chromatic evaluation of residues (Pugliese
et al., 2004)
rthe beneficial effects of grinding, soaking, and cooking on the degradation of dangerous matters in fruit waste (Tuncel et al., 1995)
rOthers
Some examples are rpectin from apple pomace
raromas and coloring agents from fruit waste roils from seeds
rtartaric acid from wine lees
Also, further processing of by-products can trans- fer their valuable compounds into new products:
rDistillery wastes can be added to feed after appropriate treatment.
rHousehold and gardening wastes are utilized for soil improvements.
rAll organic by-products can be utilized in a profitable way, if used for biogas production (methane production) or burning (especially if
combined with recovery) (Prema Viswanath et al., 1992; Mahadevaswamy and Venkataraman, 1990).
Pollution Prevention and Control in Fruit Processing
Reductions in wastewater volumes up to 95% have been reported through implementation of good prac- tices. Where possible, adopt the following measures:
rUse clean raw fruit, reducing the concentration of dirt and organics (including pesticides) in the effluent.
rUse dry methods such as vibration or air jets to clean raw fruit. Dry peeling methods reduce the effluent volume (up to 35%) and pollutant concentration (organic load reduced up to 25%).
rSeparate and recirculate processed wastewaters.
rUse countercurrent systems where washing is necessary.
rUse steam instead of hot water to reduce the quantity of wastewater to be treated.
rRemove solid wastes without the use of water.
rReuse concentrated wastewaters and solid wastes for production of by-products.
As an example, recirculation of processed water from fruit preparation reduces the organic load by 75% and water consumption by 95%. Similarly, the liquid waste load (in terms of biochemical oxygen demand, BOD) from apple juice processing can be reduced by 80%.
Good water management should be adopted, where feasible, to achieve the levels of consumption pre- sented in Table 10.1 (Anon, 1998).
Target Pollution Loads
Implementation of cleaner production processes and pollution prevention measures can yield both
Table 10.1. Water Usage in the Fruit Processing Industry
Water Use (cubic meters Product Category per metric ton of product)
Canned fruit 2.5–4.0
Frozen fruit 5.0–6.0
Fruit juices 6.5
Jams 6.0
Baby food 6.0–9.0
Source: Anon, 1998.
Table 10.2. Target Loads Per Unit of Production, Fruit Processing Industry Fruit
Waste Volume Solid Waste
Product (m3/U) BOD (kg/U) (kg/t product)
Apricots 29.0 15.0
Apples 90
All products 3.7 5.0
All except juice 5.4 6.4
Juice 2.9 2.0
Cranberries 5.8 2.8 10
Citrus 10.0 3.2
Sweet cherries 7.8 9.6
Sour cherries 12.0 17.0
Bing cherries 20.0 22.0
Dried fruit 13.0 12.0
Grapefruit
Canned 72.0 11.0
Pressed 1.6 1.9
Olives 38.0 44.0 20
Peaches 180
Canned 13.0 14.0
Frozen 5.4 12.0 200
Pears 12.0 21.0
Pineapples 13.0 10.0
Plums 5.0 4.1
Raisins 2.8 6.0
Strawberries 13.0 5.3 60
Source:Anon, 1998.
economic and environmental benefits. The target loads per unit of production are shown in Table 10.2 (Anon, 1998). The data refer to the waste loads aris- ing from the production processes before the imple- mentation of pollution control measures. These levels are derived from the average loads recorded in a major study of the industry and should be used as maximum levels of unit pollution in the design of new plants.
By-product Treatment and
Utilization in the Case of Certain Fruit-based Products
The processing of fruits produces two types of waste:
solid waste [e.g., peel/skin (Larrauri et al., 1997; Negi et al., 2003; Fern´andez et al., 2004), seeds (Noguchi and Tanaka, 2004), and stones (Lussier et al., 1994)]
and liquid waste [juice (Gil et al., 2000) and wash water]. A serious waste disposal problem can attract flies and rats in the processing room, if not corrected properly. If there is no plan to use the waste products, they should be buried or fed to animals in distant locations.
Solid Fruit Wastes
There are possible ways to use some solid fruit wastes, which are discussed below. However, it is stressed that a full financial evaluation should be done before the implementation of any of the suggestions.
One major goal in using fruit wastes is to ensure a reasonable microbiological quality in them. This means that one should process waste products on the same day that they become available. It is not ad- visable to store wastes until the end of the week’s production before processing them. Even with this precaution, the wastes being used will most likely contain moldy fruit (discarded during processing), insects, leaves, stems, soils, etc. This will contami- nate any products derived from such wastes.
Therefore, some preliminary separation is needed during processing, such as
rpeel and waste pulp in one bin
rmoldy parts, leaves, soil, etc in a second bin, which may be discarded
rstones, seeds, etc., in a third bin
10 Fruit Processing Waste Management 177 Possible Products
The six main products from wastes include rcandied peel
roils rpectin
rre-formed fruit pieces renzymes
rwine/vinegar
Each is discussed below.
Candied Peel. Peel from citrus fruits (orange, lemon, and grapefruit) can be candied for use in, for example, baked goods and snack food. In addition, shreds of peel are used in marmalades, similar to the process of candying. That is, boil the slices or shreds of peel in a 20%-sugar syrup for 15–21 min and progressively increase the sugar concentration in the syrup to 65–70 Brix (percentage of sugar moni- tored by a refractometer) during soaking of the food for 4–5 days. It is then removed, rinsed, and given a final drying in the sun or in the hot air drier. This can serve as a secondary product for a fruit juice or jam processor. This assumes that a large food company is interested in buying the candied peel as an ingredient for their products. In one application, candied melon skin has been used to substitute for sultanas in baked goods and, in another, candied root vegetables have found a similar market.
Oils. The stones of some fruits (e.g., mango, apri- cot, and peach) contain appreciable quantities of oil or fat, some of which have specialized markets for culinary or perfumery/toiletry applications. Palm ker- nel oil is well known as a cooking and industrial oil.
In addition, some seeds (e.g., grape, papaya, and pas- sion fruit) contain oil with a specialized market. Of course, for any commercial product in any country, the goal is to identify the import/export agents in- terested in such products. After that, the processor’s responsibility is to produce the oil to satisfy the cus- tomer in terms of sufficient quantity and stringent quality standards. Obviously, the manufacturer has to secure proper equipment to produce the oils at a reasonable cost.
The process involves grinding the seeds and nuts to release the oil without a significant rise in temper- ature, which would spoil their delicate flavors, with the exception of palm kernel oil. Generally, a powered hammer mill is needed for nut and kernels. A press is needed to extract the oil. Since the existing manual presses have not been tried for this application, a cer-
tain amount of experimentation is needed to establish oil yields and suitability of the equipment. Solvent extraction is not recommended for small-scale appli- cations. However, steam distillation of citrus peel oils is well established for small-scale operations.
The crude oil may be sold to be refined elsewhere, but it is likely that the producer is responsible for the initial refining.
Pectin. This is a gelling agent used in jams and some sweets and occurs in most fruits, ranging from a low to a high level. Commercially, pectin is extracted from citrus peel and apple pomace, the residue left af- ter apple juice has been removed. Other tropical fruits may contain high levels of pectin, passion fruit be- ing a notable example. The utilization of the “shells”
remaining after pulp removal may permit pectin ex- traction.
In most developing countries, pectin is imported from Europe or United States. This may look like a good market or opportunity for processors in these countries to provide pectin locally to substitute for imports. However, there are major problems:
rIn countries where this has been tried, it has not been possible to produce pectin at a cost lower than that for imported products.
rIt is difficult to produce pectin powder on a small scale, although liquid pectin is possible.
rThere are many types of pectin, each with specific properties suitable for a particular application.
For example, pectin for jams as a preserve differs from that used in jam as an ingredient in baked goods.
Re-formed Fruit Pieces. Fruit pulp can be recov- ered and formed into fruit pieces. Although the pro- cess is relatively simple, the demand for this product is low. Therefore, a thorough evaluation of the poten- tial market is recommended before investing in the enterprise (Kilham, 1997).
The process involves preparing a concentrate by boiling the fruit pulp, followed by sterilization. Sugar may also be added. A gelling agent, sodium alginate, is then combined with the cooled pulp and then mixed with a strong solution of calcium chloride. All ingre- dients are safe for human consumption, being legal food additives in most countries. The calcium and the alginate combine to form a solid gel structure and the pulp can therefore be re-formed into fruit pieces.
The most common way is to pour the mixture into fruit-shaped moulds and allow it to set.
It is also possible to allow drops of the fruit/alginate mixture to fall into a bath of calcium chloride solu- tion where they form small grains of re-formed fruit, which can be used in baked goods. Commercially, the most common product of this type is glaced cherries.
Enzymes. Commercially, the three most important enzymes from fruit are papain (from papaya), brome- lain (from pineapple), and ficin (from figs). Each is a protein-degrading enzyme used in such applications as meat tenderizers, and washing powders and is also used in leather tanning and beer brewing. However, it is unlikely to be economical to harvest these en- zymes from fruit processing waste. Currently, even the more efficient process of collecting enzymes from fresh whole fruit is no longer economical. Changes in both large-scale production with higher quality standards and use of biotechnology to produce “syn- thetic” enzymes mean that small-scale producers will be unlikely to compete effectively. In addition, there are proposals to phase out the use of these enzymes in food products in Europe and United States. Their market is therefore declining. Consequently, it is not cost effective to harvest enzymes from fruits process- ing waste.
Wine/Vinegar. Although products such as wine or vinegar should be produced from fresh, high-quality fruit juices in order to obtain high-quality products, it is technically feasible to produce them from both solid and liquid fruit wastes. Solid wastes should be shredded and then boiled for 20–30 min to extract the sugars from the fruit and to sterilize the liquid.
Several batches of waste may be boiled in the same liquid to increase the sugar concentration. This is then filtered through boiled cloth to remove the solids and cooled in preparation for inoculation with yeast. Liq- uid wastes should be separated during production to ensure that fruit juice is kept separate from wash wa- ter. For example, the juice could be drained from a peeling/slicing table into a separate drum. The juice is then boiled for 10–15 min and treated as above.
The liquid is then inoculated with “wine” yeast and not bread or beer yeast and fermented in the normal way for wine production. This can then undergo the standard second fermentation to produce fruit vinegar.
In summary, each of the above uses of fruit waste requires
ra good knowledge of the potential market for the products and the quality standards required
ran assessment of the economics of production ra basic familiarity with the production technique ra reasonable capital investment in equipment ra fairly large amount of waste available to make
utilization or harvesting worthwhile
For small-scale operations, where reducing pollu- tion or increasing waste disposal is more important than process economics, the most likely solution is to use wastes as animal feeds.
Some Example of Research Areas for the Utilization Opportunities of Fruit Processing By-products
Several valuable substances—fibers, coloring agents, gelling agents—can be extracted from the wastes of fruit-based products. The way and goal of utilization is determined by the economic efficiency of extrac- tion and the market potential. It is not easy to collect data about the quantity of fruit waste and widespread treatment techniques.
The following literatures review the types of by-products, modern treatment technologies, and approaches of utilization. It does not deal with tra- ditional methods, which can be found in standard literature:
rFruit stones constitute a significant waste disposal problem for the fruit processing industry.
High-quality activated carbon can be produced from waste cherry stones (Lussier et al., 1994).
rFruit processing wastes including apple, cranberry, and strawberry pomace were used as substrates for polygalacturonase production by Lentinus edodesthrough solid-state fermentation (Zheng and Shetty, 2000).
rWatermelon peel constitutes 44% of the whole fruit weight. In the study of Madhuri and Kamini-Devi (2003), the potential to produce preserved products such as pickles, tutti-fruiti, vadiyams, and cheese using the white portion of watermelon rind was investigated.
rFruit wastes (pineapple, mixed fruit, and maosmi) were investigated as possible substrates for citric acid production by solid-state fermentation using Aspergillus niger(Kumar et al., 2003).
rIn 1996, a laboratory study was conducted by Hammond et al., to assess ethanol production potential from banana waste.
rCitrus junosis one of the important citrus fruits in Japan. The fruit juice is an ingredient used in sauces and salad dressings for its special flavor.
10 Fruit Processing Waste Management 179 After juice extraction, the fruit pulp is usually
dumped as waste at a large cost. The
manipulation of food processing wastes is now becoming a very serious environmental issue. The peel ofC. junosfruit was found to possess potent allelopathic activity and a methanol extract of the peel inhibited the growth of several weed species (Fujihara and Shimizu, 2003).
rA method is described by Drunen and
Hranisavljevic (2003) for the enrichment of fruit products with beneficial substances (e.g., antioxidants) extracted from processing waste, e.g., fruit peel.
rProgress is described in an ongoing project in European Union (EU) (QLKI-1999-00124) on anthocyanin bioactivities. The investigation covers the functional properties and the effects of anthocyanins and anthocyanin-rich food
ingredients on heart disease. This study aims to use such compounds as colorants and in the development of new anthocyanin-rich functional foods (Anon, 2002).
Successful Waste Utilization in Wine Making Among food industry by-products of fruit or veg- etable origin the products of wine industry are out- standing. Grape marc and wine lees are the basic by-products of wine making. Depending on the vari- ety, ripeness, vintage, and harvesting time, 100 kg of grapes produces 15–20 kg of grape marc.
The majority of grape marc goes to refuse; a small percentage is burned or used as compost. Unfortu- nately, it is also used for wine adulteration. Grape marc contains seeds that possess valuable substances such as oil, proteins, and tannins. Grape seed oil is the most valuable because of its health-protecting and cholesterol-lowering effects. This oil can be obtained by pressing or extraction. It has the main advantage of being pesticide free. Due to its valuable fatty acid content it can be used as a foodstuff, lubricant, and raw material for cosmetics as well. In the world’s vine-producing lands, the quantity of marc has been registered since 2001. In Hungary, after the EU ac- cession, like in other wine-producing countries, the by-products need be distilled or further utilized. EU requirements, for instance, are that grape marc be withdrawn from circulation within the framework of a controlled process, and then used for feed, organic manure, oil, distilled spirits, and tartaric acid produc- tion (Szenes, 1995).