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 12%, trehalose 8%, and lactose 8% All
protective agents were dissolved in distilled water and prepared in different concentrations, and sterilized at 105 ° C for 15 minutes. YPD agar medium was obtained by combining YPD broth with 20 g of agar and then sterilizing at 121 ° C for 15 minutes. Cells were cultured in a YPD agar medium and cell viability was determined. S. cerevisiae was inoculated with 2% inoculation (v / v) in a 250 ml flask containing 50 ml of YPD broth and then incubated at 30 ° C for 48 h in a sugar incubator at 150 rpm. After culturing, using a refrigerated ultracentrifuge, the product was centrifuged at 10,000 g 100 g for 10 minutes, then the supernatant was discarded and the wet biomass of S. cerevisiae was removed. The cells were then frozen at -20 ° C for 24 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 33%, 25%, and 2.3%, respectively, and the number of viable cells was 3.091 ×107,2.3833×107,0.218×107, respectively.Conclusion : The results showed that combined
protective agents have a more effective protective effect than single-factor protectors.