ABSTRACT The effect of temperature in protein denaturation and Maillard reaction in whole and skim milk with hydrolyzed lactose was evaluated. Hydrolyzed milk was thermally treated at 100, 110, 120 and 130 °C over a period of 1 hour and glucose concentration, browning degree and protein denaturation were measured. The browning degree in whole milk varied from 14.42 (100 °C) to 42.63 (130 °C) and 20.21 (100 °C) to 38.03 (130 °C) in skim milk. Glucose concentration in whole milk (47% - w/v) and skim milk (41% - w/v) after heat treatment (130 °C) showed a significant reduction in relation to the control (25 °C). The temperature effect in protein denaturation in whole and skim milk in relation to the control (25 °C) was 100%. Thermally treated milk with hydrolyzed lactose promoted protein denaturation with increasing browning characteristic of the Maillard reaction, thus affecting the nutritional quality.

RESUMEN Se evaluó el efecto de la temperatura sobre la desnaturalización de proteínas y la reacción de Maillard en leche entera y descremada con lactosa hidrolizada. Las leches hidrolizadas se trataron térmicamente a 100, 110, 120 y 130 °C durante un período de 1 hora y se midió la concentración de glucosa, el grado de pardeamiento y la desnaturalización de proteínas. El grado de dorado en la leche entera varió de 14.4 (100 °C) a 42.6 (130 °C). Para la leche descremada fue de 20.2 (100 °C) a 38.0 (130 °C). La concentración de glucosa en leche entera (47% p/v) y en leche descremada (41% p/v) después del tratamiento térmico (130 °C) mostró una reducción significativa en relación con el control (25 °C). El efecto de la temperatura en la desnaturalización de proteínas en leche entera y descremada en relación con el control (25 °C) fue del 100%. La leche tratada térmicamente con lactosa hidrolizada promovió la desnaturalización de proteínas con un aumento del pardeamiento característico de la reacción de Maillard, lo que afectó la calidad nutricional.

Resumo O presente trabalho teve como objetivo estudar a melhor composição do meio de fermentação para máxima produção de lactase por Saccharomyces fragilis IZ 275 usando diferentes fontes de carbono incluindo o soro de queijo em pó reconstituído. Primeiramente, um delineamento fatorial 24 foi aplicado para verificar dentre as variáveis estudadas as que apresentavam efeito significativo. Logo após, foi aplicado um delineamento de máxima inclinação ascendente e máxima inclinação descendente para obter a máxima atividade. Para otimizar o meio de fermentação, foi então, realizado um delineamento Composto Central Rotacional (DCCR) 24. Foi observado que o soro de queijo, um subproduto da indústria de lacticínios, e altamente poluidor para o meio ambiente, pode ser empregado como excelente meio de fermentação por leveduras, dentro do conceito de bioeconomia com valor agregado. O emprego da metodologia é uma ferramenta eficiente para otimizar o processo de produção da β-galactosidase. No meio de fermentação otimizado, a máxima produção de β-galactosidase (54,68 U/mL) por S. fragilis IZ 275 é obtida com 14 g/L sacarose, 17,7 g/L soro de queijo em pó reconstituído, 5,14 g/L extrato de levedura e 8,85 g/L peptona.

Abstract This study sought to create a better fermentation medium to maximize lactase production by Saccharomyces fragilis IZ 275 using different carbon sources, including reconstituted powdered cheese whey. A factorial design 24 was applied to evaluate the significant effects of variables which compose the fermentation medium. Then, a steepest descent-ascent design was applied to obtain the maximum activity. A Rotational Central Composite Design (RCCD) 24 was made to optimize the fermentation medium. We verified that the cheese whey, a by-product of the dairy industry, can be employed as an excellent fermentation medium by yeast, within the bioeconomy concept and used by the dairy industry as product with additional value. The employed methodology is an efficient tool in the optimization process for β-galactosidase production. In the optimized fermentation medium, the maximum production of β-galactosidase (54.68 U/mL) by S. fragilis IZ 275 is obtained with 14 g/L sucrose, 17.7 g/L reconstituted powdered cheese whey, 5.14 g/L yeast extract and 8.85 g/L peptone.

Abstract The commercial enzyme (E.C. = 3.2.1.23) from Kluyveromyces lactis (liquid) and Aspergillus oryzae(lyophilized) was investigated for its hydrolysis potential in lactose substrate, UHT milk, and skimmed milk at different concentrations (0.7; 1.0 and 1.5%), pH values (5.0; 6.0; 6.5 and 7.0), and temperature (30; 35; 40 and 55 ºC). High hydrolysis rates were observed for the enzyme from K. lactis at pH 7.0 and 40 ºC, and from A. oryzae at pH 5.0 and 55 ºC. The enzyme from K. lactis showed significantly higher hydrolysis rates when compared to A. oryzae. The effect of temperature and β-galactosidase concentration on the lactose hydrolysis in UHT milk was higher than in skimmed milk, for all temperatures tested. With respect to the thermal stability, a decrease in hydrolysis rate was observed at pH 6.0 at 35 ºC for K. lactisenzyme, and at pH 6.0 at 55 ºC for the enzyme from A. oryzae. This study investigate the hydrolysis of β-galactosidase in UHT and skimmed milk. The knowledge about the characteristics of the β-galactosidase fromK. lactis and A. oryzae enables to use it most efficiently to control the enzyme concentration, temperature, and pH in many industrial processes and product formulations.