Antifreeze Activity of gamma-Polyglutamic Acid and Its Impact on Freezing Resistance of Yeast and Frozen Sweet Dough

摘要

This study investigated the antifreeze activity (AF) of gamma-polyglutamic acid (gamma-PGA), freezing resistance of yeast cells and sweet dough, and the mechanism influenced by gamma-PGA. Properties studied included AF of gamma-PGA, water-holding capacity of flour, survival ratio and oxidation resistance capability of yeast cells, ice melting enthalpy (DH), and fermentation and breadmaking properties of sweet dough. The AF of gamma-PGA was 8.03 g of unfrozen water/g of sample, indicating good AF. gamma-PGA was tested on yeast cells and sweet dough stored frozen for 0, 1, 2, 4, and 8 weeks at four levels (0, 0.5, 1, and 3%). Survival ratio of yeast cells with gamma-PGA was significantly higher than the corresponding control. A possible mechanism might be related to the modulation of oxidation resistance capability of yeast cells by gamma-PGA. A decrease in glutathione release from frozen yeast cells and an increase in water-holding capacity of wheat dough were observed with the addition of gamma-PGA. In the presence of gamma-PGA, DH, ice melting temperature, and proofing time of frozen sweet dough decreased significantly, and fermentation parameters improved, compared with the corresponding control sample. Specific volume of bread made from frozen sweet dough with 0.5, 1, and 3% gamma-PGA increased by 6.3, 8.9, and 3.3%, respectively, after 8 weeks of frozen storage. gamma-PGA enhanced the freezing resistance of yeast cells and sweet dough effectively, and the effect on specific volume of bread was not linear, with 1% showing better results.