A partir dos resultados apresentados pode-se concluir que:
Thermoascus aurantiacus ATCC 204492produz a maioria das enzimas do complexo celulolítico e hemicelulolítico. Apresentou bom crescimento em farelo de trigo, destacando a predominância na produção de endo-β-1,4-xilanase perante as demais enzimas. Os ensaios de estabilidade térmica confirmaram a estabilidade da xilanase em temperaturas elevadas.
A hemicelulose foi extraída com alto rendimento com peróxido alcalino e apresentou alta solubilidade, coloração clara e baixo teor de lignina. De acordo com sua composição química pode ser classificada como L-arabino-(4-O-metil-D-glucurono)-D-xilana. As propriedades desse polissacarídeo foram adequadas para emprego em ensaios de hidrólise enzimática, diferente da hemicelulose extraída com hidróxido de sódio, a qual apresentou baixa solubilidade.
A hidrólise da hemicelulose extraída do bagaço de cana-de-açúcar com enzimas de T.
aurantiacus e T. reesei resultou em maior conversão em XOs do que as enzimas de A. niger.
O uso de xilanases comerciais na hidrólise da hemicelulose não superou o desempenho das enzimas de T. aurantiacus na produção de XOs, provavelmente pela presença de várias enzimas acessórias além da xilanase no extrato de T. aurantiacus. A xilanase de T.
lanuginosus mostrou-se uma excelente enzima para a obtenção de xilobiose, uma vez que não
produziu xilose.
A xilanase de T. aurantiacus hidrolisou de modo semelhante as hemiceluloses de bagaço de cana-de-açúcar, bétula e semente de aveia. As diferenças estruturais como ramificações e presença de lignina não interferiram na ação dessa enzima. Em todos os casos houve formação apenas de xilo-oligossacarídeos lineares.
A hidrólise da hemicelulose com as enzimas de T. aurantiacus e T. reesei apresentou algumas diferenças. T. aurantiacus produziu XOs principalmente em tempos longos de reação (acima 48 h) e T. reesei produziu XOs em tempos mais curtos (6 a 24 h), sendo que o aumento do tempo favoreceu a produção de xilose. Os resultados mostram diferenças entre as xilanases, evidenciando diferenças nas propriedades bioquímicas e atividade específica, o que
consequentemente causam diferenças na eficiência e extensão da hidrólise.
A auto-hidrólise do bagaço de cana-de-açúcar gerou predominantemente xilose e uma baixa quantidade de XOs. Entre os XOs formados destacou-se a xilobiose, como na hidrólise enzimática, porém houve formação de furfural.
A produção de XOs pela auto-hidrólise do bagaço foi 5,8 vezes menor que na hidrólise enzimática da hemicelulose e desta forma etapas de concentração e purificação seriam necessárias para a obtenção de um produto final com as características desejadas. Por outro lado, o tempo de reação foi curto e a moagem foi a única operação realizada no bagaço antes do tratamento térmico.
Os melhores resultados de produção de XOs pelas enzimas de T. aurantiacus foram diferentes das enzimas de T. reesei. Deve ser levado em consideração o custo de cada etapa, enquanto a reação com enzimas de T. aurantiacus produz 41,6 % de XOs em 96 h, a reação com enzimas de T. reesei produz 20 % em 6 h. Entretanto, com T. reesei deve ser empregado mais substrato e enzima. Considerando o custo de extração de hemicelulose e de produção de enzima, T. aurantiacus seria mais indicado para esse processo.
Enfim, a produção de XOs se torna possível através de uma etapa de extração da hemicelulose e outra etapa de hidrólise enzimática. A primeira etapa deve ocorrer em meio alcalino com peróxido de hidrogênio, por gerar um polissacarídeo solúvel e passível de hidrólise enzimática. Na segunda etapa, destaca-se a ação das enzimas de T. aurantiacus, pela maior conversão da hemicelulose em XOs e também pela alta produção de xilanase no cultivo em meio sólido, fatores que contribuem para viabilidade econômica.
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