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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Estudo das intera??es polifenol-prote?na e das rea??es de escurecimento n?o-enzim?tico para o processamento de caju?na

Damasceno, Leandro Fernandes 15 June 2007 (has links)
Made available in DSpace on 2014-12-17T15:01:12Z (GMT). No. of bitstreams: 1 LeandroFD.pdf: 1531484 bytes, checksum: 8c328385e5fe3dc7294b86f55a82c108 (MD5) Previous issue date: 2007-06-15 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / The cashew, a fruit from Brazilian Northeast is used to produce juice due to its flavor and vitamin C richness. However, its acceptance is limited due to its astringency. Caju?na is a derivate product appreciated by its characteristic flavor, freshness and lack of astringency, due to tannin removal. Caju?na is a light yellow beverage made from clarified cashew juice and sterilized after bottling. It differs from the integral and concentrated juice by the clarification and thermal treatment steps. Many problems such as haze and excessive browning could appear if these steps are not controlled. The objective of this work was divided into two stages with the aim to supply process information in order to obtain a good quality product with uniform characteristics (sensory and nutritional). Polyphenol-protein interaction was studied at the clarification step, which is an empirical process, to provide values on the amount of clarifying solution (gelatin) that must be added to achieve a complete juice clarification. Clarification essays were performed with juice dilutions of 1:2 and 1:10 and the effect of metabissulfite and tannic acid addition was evaluated. It was not possible to establish a clarification point. Metabissulfite did not influenced the clarification process however tannic acid addition displaced the clarification point, showing the difficulty visual monitoring of the process. Thermal treatment of clarified juice was studied at 88, 100, 111 e 121 ?C. To evaluate the non-enzymatic browning, vitamin C, 5-hidroximetilfurfural (5-HMF) and sugar variation were correlated with color parameters (reflectance spectra, color difference and CIELAB). Kinetic models were obtained for reflectance spectra, ascorbic acid and 5-HMF. It was observed that 5-HMF introduction followed a first order kinetic rate at the beginning of the thermal treatment and a zero order kinetic at later process stages. An inverse correlation was observed between absorbance at 420 nm and ascorbic acid degradation, which indicates that ascorbic acid might be the principal factor on caju?na non-enzymatic browning. Constant sugar concentration showed that this parameter did not contribute directly to the nonenzymatic browning. Optimization techniques showed showed that to obtain a high vitamin C and a low 5-HMF content, the process must be done at 120 ?C. With the water-bath thermal treatment, the 90 ?C temperature promoted a lower ascorbic acid degradation at the expense of a higher 5-HMF level / O caju, frut?fera origin?ria do Nordeste brasileiro ? utilizado para produ??o de suco devido ao seu sabor e ser rico em vitamina C. Entretanto, sua aceita??o ? limitada devido a sua adstring?ncia. Um produto bastante apreciado pelo seu sabor caracter?stico, refrescante e n?o adstringente, devido ? remo??o dos taninos, ? a caju?na. A caju?na ? uma bebida elaborada a partir do suco de caju clarificado e esterilizada no interior de garrafas, apresentando uma colora??o amarelo-?mbar. Ela diferencia-se dos sucos de caju integral e concentrado por meio das etapas de clarifica??o e tratamento t?rmico. Uma s?rie de problemas como turva??o e escurecimento excessivo do produto, pode aparecer se estas etapas n?o forem bem controladas. O objetivo deste trabalho foi dividido em duas etapas, mas com o mesmo prop?sito de fornecer subs?dios que possibilitem o controle do processo de maneira a se obter um produto de qualidade, com caracter?sticas mais uniformes (em termos sensoriais e nutricionais). Na clarifica??o, por se tratar de um processo emp?rico, buscou-se o entendimento das intera??es polifenol-prote?na para fornecer valores adequados de solu??o de clarificante (gelatina) necess?ria para promover a clarifica??o completa do suco. Realizaramse ensaios de clarifica??o com suco de caju dilu?do nas propor??es 1:2 e 1:10 e avaliou-se a influ?ncia da adi??o de metabissulfito e ?cido t?nico ao suco. Pelas t?cnicas utilizadas n?o foi poss?vel determinar um ponto de clarifica??o completa do suco de caju. O metabissulfito n?o influenciou o processo de clarifica??o enquanto que adi??o de ?cido t?nico deslocou o ponto de clarifica??o, mostrando a dificuldade da observa??o deste ponto pelo operador. O efeito do tratamento t?rmico no suco clarificado foi estudado nas temperaturas de 88, 100, 111 e 121 ?C. Para avaliar o escurecimento n?o-enzim?tico, a varia??o de vitamina C, 5- hidroximetilfurfural (5-HMF) e a??cares foram correlacionados com par?metros colorim?tricos (espectro de reflect?ncia, diferen?a de cor e CIELAB). Modelos cin?ticos foram obtidos para a mudan?a no espectro de reflect?ncia, ?cido asc?rbico e 5-HMF. A forma??o de 5-HMF seguiu dois mecanismos cin?ticos: taxa cin?tica de primeira ordem no come?o do tratamento t?rmico e taxa cin?tica de ordem zero em um per?odo mais avan?ado do processo. Observou-se correla??o inversa da absorb?ncia a 420 nm e a perda de ?cido asc?rbico, o que indica que o ?cido asc?rbico pode ser o fator principal que causa o escurecimento da caju?na. A concentra??o constante dos a??cares mostrou que eles n?o influenciaram diretamente o escurecimento n?o-enzim?tico. T?cnicas de otimiza??o mostraram que para se obter uma caju?na com concentra??o elevada de vitamina C e baixo teor de 5-HMF, o tratamento t?rmico deve ser realizado a 120 ?C. No caso da utiliza??o de banho-maria para o tratamento t?rmico, a temperatura de 90 ?C promove uma menor degrada??o de ?cido asc?rbico ? custa de um ?ndice de 5-HMF mais elevado

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