Effect of Skim milk powder and sugars of terehalose and lactose in combination and single factor on the survival of Saccharomyces cerevisiae during freeze-drying

Background and Aim : Saccharomyces cerevisiae is commonly referred to as bread yeast. This yeast has been used in the bakery industry for many years. Since this yeast suffers from damage during the preparation of yeast and fermentation dough and its efficiency in fermentation and gas production is reduced, it is necessary to prepare stocks from this yeast for storage that provide the initial performance when entering the line Have production. In this study, the effect of carbohydrates (trehalose, lactose) and Skim milk powder on the survival of S. cerevisiae to protect against freezing was investigated using one-factor experiments. Vacuum freeze-drying was used for drying and long-term storage of the sample. Methods : The microorganism used in this study is Saccharomyces cerevisiae, which is environmentally isolated, purified, and finally used. The main ingredients used in this study include Skim milk powder ۱۲%, trehalose ۸%, and lactose ۸% All protective agents were dissolved in distilled water and prepared in different concentrations, and sterilized at ۱۰۵ ° C for ۱۵ minutes. YPD agar medium was obtained by combining YPD broth with ۲۰ g of agar and then sterilizing at ۱۲۱ ° C for ۱۵ minutes. Cells were cultured in a YPD agar medium and cell viability was determined. S. cerevisiae was inoculated with ۲% inoculation (v / v) in a ۲۵۰ ml flask containing ۵۰ ml of YPD broth and then incubated at ۳۰ ° C for ۴۸ h in a sugar incubator at ۱۵۰ rpm. After culturing, using a refrigerated ultracentrifuge, the product was centrifuged at ۱۰,۰۰۰ g ۱۰۰ g for ۱۰ minutes, then the supernatant was discarded and the wet biomass of S. cerevisiae was removed. The cells were then frozen at -۲۰ ° C for ۲۴ hours and then frozen by vacuum freeze-drying.Results : As a result, combining sugars with Skim milk powder has a better protective effect on the desired strain than Skim milk powder alone and without preservatives. Survival rates were ۳۳%, ۲۵%, and ۲.۳%, respectively, and the number of viable cells was ۳.۰۹۱ ×۱۰۷,۲.۳۸۳۳×۱۰۷,۰.۲۱۸×۱۰۷, respectively.Conclusion : The results showed that combined protective agents have a more effective protective effect than single-factor protectors.

کلیدواژه ها:

Saccharomyces cerevisiae ، freeze-drying ، protective agents ، sugars ، Skim milk powder