Ricardo Peraça Toralles

Determinação das constantes cinéticas de degradação do ácido ascórbico em purê de pêssego: efeito da temperatura e concentração

Ascorbic acid (vitamin C) is extensively used in the food industry, not only for its nutritional value, but also for its many functional contributions to product quality. There have been many studies on the stability of ascorbic acid in different beverages, but no study was found on the reaction rate constants for ascorbic acid degradation in peach puree. In this work, the degradation of ascorbic acid in Jade peach puree was studied in anaerobic conditions and from 70-90 °C. The peach puree concentrations tested were 12, 22 and 32 °Brix. The kinetic analysis of the data suggests that the degradation was significantly represented by zero and first-order kinetic models. The rate of ascorbic acid degradation in peach puree was temperature dependent. The average activation energy was 45 kJ.mol-1 and independent of the concentration of soluble solids.

Thermal inactivation of polyphenoloxidase and peroxidase in jubileu clingstone peach and yeast isolated from its spoiled puree.

The thermal inactivation of yeast isolated from spoiled Jubileu peach puree and that of polyphenoloxidase (PPO) and peroxidase (POD) in cv. Jubileu, which is widely cultivated in southern Rio Grande do Sul state, Brazil, were studied. PPO and POD were extracted using the protein powder method and submitted to partial purification by precipitation followed by dialysis. The enzymatic activity was determined measuring the increase in absorbance at 420 nm for PPO and 470 nm for POD. The yeast used in this investigation was isolated from spoiled Jubileu peach puree at 22 °Brix, with total initial microbial count of 22 × 102 UFCmL - 1. Stock cultures were maintained on potato dextrose agar (PDA) slants at 4 °C and pH 5 for later use for microbial growth. In all cases, kinetic analysis of the results suggests that the thermal inactivation was well described by a first-order kinetic model, and the temperature dependence was significantly represented by the Arrhenius law. Both enzymes were affected by heat denaturation, and PPO was more thermostable. PPO was also more thermosTable than the yeast isolated from peach puree. The D60-values were 1.53 and 1.87 min for PPO and yeast isolated from spoiled Jubileu peach puree, respectively.

EXTRAÇÃO E CARACTERIZAÇÃO PARCIAL DE INVERTASE DE LEVEDURA DE PURÊ E RESÍDUO DE PÊSSEGO

A frutohidrolase frutofuranosidase (EC 3.2.2.26), tambem chamada invertase ou sacarase, catalisa a hidrolise de sacarose, produzindo uma mistura equimolar de glicose e frutose, denominada acucar invertido. Este produto tem alto poder edulcorante e cristalizacao lenta, causando um melhoramento na textura e no sabor dos alimentos. Para tal finalidade, a invertase foi extraida da levedura do pure e do residuo de pessego c.v. Jubileu, que e amplamente cultivada no sul do Rio Grande do Sul, Brasil. A invertase de levedura comercial de pao foi utilizada como testemunha. Os extratos enzimaticos foram obtidos usando o metodo de extracao com bicarbonato de sodio. As condicoes de reacao otimas foram estudadas utilizando sacarose como substrato, a 40 mM para a invertase de pao e a 220 mM para a invertase de pure de pessego. A glicose formada foi determinada por colorimetria utilizando DNS e as proteinas pelo metodo de Biureto. O pH ideal foi na faixa de 5 - 6 para ambas as enzimas. As temperaturas otimas foram na faixa de 40 - 50°C para invertase de levedura de pao e na faixa de 20 - 30°C para invertase de levedura de pure de pessego. Ambas as enzimas foram afetadas pela desnaturacao de calor, sendo a invertase de pao mais termoestavel. Definidas as condicoes otimas de hidrolise da sacarose, estudou-se o efeito da concentracao do substrato na atividade das invertases, bem como para determinar seus parâmetros cineticos. Ambas as enzimas apresentaram comportamento Michaeliano. Os parâmetros cineticos foram calculados por regressao nao linear, sendo que os valores de K m foram 20 mM e 180 mM para a invertase de levedura de pao e para invertase de levedura de pure de pessego, respectivamente . Para ambas, o grafico da velocidade de hidrolise em funcao da concentracao de sacarose foi confirmado pela linearidade da Lineweaver-Burk. Finalmente, observou-se uma equivalencia entre as atividades das invertases isoladas de pure de pessego e de seu residuo a

Extracción optimizada y purificación parcial de invertasa aislada de S. Cerevisiae en puré de durazno

The extraction was performed using an autolysis process where enzymes degrade cell structures and release the cytoplasmic contents to the extracellular medium. The autolysis process was carried out in shake flasks with different agitation speeds (50 350 rpm) and the concentration of sodium bicarbonate (50 -350 mM NaHCO3) at 40 ° C for 24 hours, using a central composite design adapted for two variables and five levels and response surface methodology (RSM) and canonical analysis to define the optimal conditions of extraction of invertase S. cerevisiae from peach puree (ISc). In great condition extraction, we studied the effect of the liofilization and purified in the invertase activity using colorimetric method of 3,5-dinitrosalicílico (DNS) at 490 nm to monitor their activity. One unit (U) defined as 1 mg glicose.min-1. Protein concentrations were determined by Lowry and invertase comercial yeast (ICY). The influence of concentration NaHCO3 and stirring speed to extract the enzyme invertase showed linear effect, quadratic and interactive. The polynomial model of second order could explain the extraction phenomenon of invertase with R2 of 0.80, with significantly dependent on both variables activity. The maximum extraction was observed in the experimental center point (200 mM NaHCO3 and 200 rpm) with an activity of 14.7 U.mg-1. The stationary point is a point of maximum extraction, differing by at least 10% of the experimental center point. Based on these characteristics, the optimal conditions for extraction of S. cerevisiae invertase from peach puree (ISc) are 200 mM NaHCO3 as autolysis agent, 200 rpm orbital shaking at 40oC for 24 hours and freeze-dried using biomass. Ethanol is more effective than acetone for recovery of specific activity.

ATIVIDADE DE ß-GLUCOSIDASES EM EXTRATO ENZIMÁTICO OBTIDO DE AMÊNDOAS DE PÊSSEGO

The presence of cyanogenic glycoside amygdalin and prunasin, and of s-glucosidases which hydrolyze these molecules, causes potential toxicity in peach kernel by the possible hydrogen cyanide release, disabling the use of the kernel and their sub-products as foods. Until now, no data are available in the literature on the conditions of the enzymes hydrolysis present in this material. This study aimed to measure the amygdalin content, and the optimal conditions of pH, temperature and substrate concentration of s-glucosidases crude extract for the enzymatic activity. The results showed the presence of the glycoside in peach almond in levels similar to those found for other almond kernels. Regarding the activity of s-glucosidase, the enzyme showed Km and Vmax of 2.7 mmol L-1 of amygdalin and 0.1407 mmol of glicose.min-1.mg-1 of protein respectively, values ??that indicate lower affinity for amygdalin substrate than purified enzymes that catalyze the same reaction. The optimum pH of the enzyme was 7.0, but between 5.0, 6.0 and 8.0 high activity still occurs. The enzyme showed stability at the temperatures employed in this study, with maximum activity at 60 ° C. Thus, the use of these changes is not sufficient for enzyme inactivation and safe use of peach kernels.

OTIMIZAÇÃO DE PROCESSAMENTO DE COBERTURA DE FRAMBOESA (Rubus idaeus) PELA ADIÇÃO DE AMIDO DE MILHO MODIFICADO E ÁCIDOS CÍTRICO E TARTÁRICO

O objetivo deste trabalho foi otimizar um processo para a elaboracao de cobertura de framboesa pela adicao de amido de milho modificado e dos acidos citrico e tartarico. Foi realizado um delineamento composto central 23 , onde as variaveis dependentes estudadas foram cor, brilho, consistencia e sabor, perfazendo um total de 20 ensaios. Foram tambem determinadas algumas caracteristicas fisicas e quimicas da cobertura. Os atributos sensoriais foram avaliados por 2400 consumidores em potencial durante a 15a Fenadoce (Feira Nacional do Doce) na cidade de Pelotas/RS. As diferentes combinacoes dos acidos influenciaram nos resultados das caracteristicas fisicas e quimicas das formulacoes testadas. Todas as formulacoes apresentaram excelente aceitacao por parte dos consumidores, que apreciaram a cor e o brilho atrativos e o sabor agridoce que contrastou com o flan de baunilha, utilizado como veiculo. O delineamento realizado estabeleceu que a melhor combinacao entre as variaveis independentes testadas seria acido citrico 0,3 a 0,5% e amido de milho modificado 4%; que garantiria as caracteristicas sensoriais desejadas e de qualidade do produto, viabilizando a sua comercializacao.