Evaluation of physical and chemical properties and total phenolic content in baker’s yeast obtained from grape juice

Abstract

Baker`s yeast is mainly produced from molasses in various parts of the world, and other sources, including grape juice. In this study, the grape juice was chosen. This study aimed to produce a biomass from dry baker`s yeast. Its physical and chemical properties was evaluated. The biomass from baker’s yeast S. cerevisiae was equal to 41.50±0.01 g/L. The following fermentation conditions, i.e. temperature (30.1oC), pH (4.75), sugar concentration (158.36 g/L), ratio of carbon to nitrogen (11.9), and initial concentration of yeasts (2.5 g/L) were used. The fermentation was carried out for a period 12 h. Grape juice was subjected to four different heat treatments as follows: pasteurized grape juice at (65, 70, and 75oC) for 10 min, and sterilized grape juice in the autoclave at 121oC for 20 min. The effect of each treatment was determined on inhibition of the enzyme polyphenol oxidase present in grape juice. The total phenolic content was determined in the yeast. Heat treatments gave the best phenolic content in the resulting yeast. The heat treatments of the juice succeeded in reducing the activity of the enzyme polyphenol oxidase and autoclave heat treatment gave the best phenolic content in the yeast.