Screening And Study Of Yeasts With Antioxidative Activity In Foods

Oxidation and antioxidation have become the leading edge and hot spot in recent years, so evaluating and screening natural resoures with antioxidant capacity have been the new trend in biology, medicine and food science.The yeast numbered Y11 with the highest antioxidant activity was screened out from 36 yeasts isolated from a variaty of foods via primary screening and further screening in this paper. Animals test was conducted to check its antioxidant activity in vivo. The isolate was indentified with molecular biology techniques. The simulated digestive tract experiment was researched, and the factors which can affect the antioxidant activity were explored.The primary screening was conducted by determinating the capability of 36 yeasts to scavenge DPPH radical and inhibit lipid peroxidation, including their intact cell and cell-free extracts, and 6 yeasts numbered Y7, Y11, Y25, Y32 and Y42 with comparatively high antioxidant activity were obtained. Then further screening was carried out including the capability to scavenge hydroxyl radical and superoxide anion radical, reducing activity, Fe2+ chelating capacity and major antioxidant enzymes. It was found that strain Yll showed excellent antioxidant activity. The capability to scavenge hydroxyl radical of intact cell and cell-free extract were 91.117% and 87.016% respectively, and the capability to scavenge superoxide radical were 90.656% and 22.787% respectively, and their reducing activity were 502.684μmol/L and 620.578μmol/L L-cystein equivalent respectively, and their capacity to chelate Fe2+ were 24.106% and 9.209% respectively, and the content of CAT and SOD in cell-free extracts were 6.996 U/mg protein and 21.310 U/mg protein.The antioxidant activity in vivo was studied by the means of intragastric administration. And the results showed strain Yll could improve the content of antioxidant enzymes and lower the content of MDA in the serum of the experimental mice markedly, which means strain Y11 can improve the antioxidant capacity of the experimental mice.The strain Y11 was identified as Aureobasidium pullulans with homology analysis of sequence in 26S rDNA D1/D2 and ITS region. The sequences in 26S rDNA D1/D2 and ITS region of strain Y11 have been submitted in GenBank, and the accession numbers were KC897668 and KC897669 respectively.The survival situation of strain Y11 in simulated digestive tract was also studied. The results showed the strain Y11 had good salt tolerance, and could grow in the media with 14%NaCl. It also had good tolerance against simulate gastric juice and simulate intestinal liquid. But its tolerance against simulate bile salt was bad, and its capability to scavenge DPPH which was determinate in the same time had no change although the viable cell decreased markedly.At the last, the factors which can affect the antioxidant activity were explored. The results showed the concentration of viable cells, heating, fermentation media and fermentation time would all affect the antioxidant activity. The antioxidant activity would increase when the concentration of viable cells increases, and heating could lower the antioxidant activity dramatically, and the antioxidant activity of strain Y11 would differ when the strain Yll was cultivated in different media, and the antioxidant activity of strain Y11 would change with fermentation time changing.