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Acid hydrolysis of dried fodder's yeast Candida utilis was studied by a central composite design taking into account three independent variables: temperature (105–165C), processing time (30–70 min) and HCl concentration (7.5–17.5%). Response variables were: color, dry matter solubilization and amino nitrogen. Temperature was the most significant variable followed by acid concentration and processing time. Response surfaces were generated from fitted polynomials. Higher temperatures to prevent amino nitrogen degradation were not investigated. As different effects were found for color development and amino nitrogen, a combined function was tested which yields the behavior of all responses simultaneously. The best conditions were: 150C, 15% HCl and 40 min. After neutralization with 6N NaOH and centrifugation, the raw sauce was supplemented with 12% NaCl, 0.1% monosodium glutamate, 2% vinegar and 0.1% sodium benzoate and evaluated by sensory analysis for eight distinct attributes. Imitation sauce from yeast was at least as good as commercial hydrolyzed soybean sauce.

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The kinetics of thermal denaturation of yeast proteins in intact cells of Saccharomyces cerevisiae instant dry yeast and Kluyveromyces fragilis L-1930 have been studied through differential scanning calorimetry. Maximum deflection-peak temperatures (TP) were greater for S. cerevisiae (66.65°C) than for K. fragilis (63.21 °C). Kinetic parameters showed that the former was slightly more resistant to thermal protein denaturation and exhibited a higher activation energy (Ea) of 63.80 kcal/mol compared to 42.92 kcal/mol of K. fragilis. Reaction rate constants (Kd) demonstrated that the shelf-life of yeast proteins at temperatures above 60°C, in whole cells was very limited.

A yeast autolysis modified process consisting of a previous homogenization step at~52 MPa (N = 2) with pH adjustment at 9.5 is developed. The process carried out in 16 h reached a total biomass solubilization around 85%. Autolysis course was not affected by yeast concentration in the studied range (60-140 mg/mL). Initial NaCl concentration of 1% led to a reduced content of this salt in final extract of about 7%, under optimum conditions, in good agreement with current requirements of the food industry. The high levels of biomass solubilization in this process allowed a yield increase of extract from 0.13 kg per liter of yeast suspension (150 mg/mL) in untreated cells to 0.15 kg/L in homogenized cells.Se ha desarrollado una modificación del proceso de autolisis de levadura consistente en un paso de homogenización previa a 52-53 MPa (N = 2) con el ajuste de pH a 9.5. El proceso se completó en 15 horas con una solubilización de la biomasa de 85%. La concentración de levadura no afectó a la autolisis en el intervalo estudiado desde 60 hasta 140 mg/mL. Una concentración inicial de NaCl 1% condujo a un contenido de sal en el extracto del 7%, en condiciones óptimas, en concordancia con los requerimientos actuales de la industria alimenticia. La elevada solubilización de la biomasa permitió auemntar el rendimiento de extracto desde 0.13 kg/L de suspensión de levadura (150 mg/mL) en las células no tratadas hasta 0,15 kg/L en las células homogenizadas.

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