Effects of Freezing and Frozen Storage Conditions on the Viability of Lactobacillus in Frozen Sourdough

Flour products fermented by traditional sourdough present better flavour, nutritional properties, and longer shelf life compared to that fermented by leavening agents.However, it is difficult to realize its commercial production due to the complex composition of traditional sourdough.Frozen technology was applied to preserve traditional sourdough, and effects of several freezing and frozen storage conditions on the viability of lactobacillus were investigated in order to maintain fermentative capability of microorganism in frozen sourdough.The results showed that five frozen storage factors had significant effects on the viability of lactobacillus.There was a linear relationship between frozen storage time and freeze-thaw cycles and the viability of lactobacillus.The survival rate and acid-producing capacity of lactobacillus significantly decreased with the prolongation of frozen storage time and the increase of freeze-thaw cycles.Effects of freezing rate, water addition amount, and GSH addition level on the viability of lactobacillus showed nonlinear.The optimal freezing and frozen storage conditions for maintaining the viability of lactobacillus in frozen sourdough were freezing rate 13.00 mm/h, water addition amount 45%, and GSH addition level 0.35%, which was optimized by response surface method.On the selected condition, the acid-producing capacity and survival rate of lactobacillus were 1.90 and 7.8×10⁶, respectively, which indicated lactobacillus having refermentation capability.The results of this research provide a new research approach for stable preservation of traditional sourdough and technical supports for the commercial production of sourdough.