The consequences of implicit factors as cross-protective stresses on freeze-dried Bacillus subtilis SB-MYP-1 with soybean flour during storage

This study aimed to assess the effects of cross-protective stress conditions on the stability of freeze-dried Bacillus subtilis SB-MYP-1 cells with soybean flour (FDBSCs-SBF) during storage. We also sought to validate the control measurement prior to using Response Surface Methodology (RSM)-microbiological equations for predicting the shelf life of FDBSCs-SBF. During the storage of FDBSCs-SBF for 90 days at −25 °C, the viability, moisture content, and water activity were >107 CFU/g, 2.59 ± 1.21% (wet basis), and 0.30 ± 0.01, respectively. These values were all relative to the standard quality of the powdered starter culture. In the same manner, the functionality of FDBSCs-SBF, including the metabolic activity, cell membrane fluidity, and activity of three intracellular enzymes (glutamate dehydrogenase, GDH; 2-oxoglutarate aminotransferase, GOGAT; and glutamine synthetase, GS) remained. Among the equations, the actual reliability values of each RSM model were not significantly different from the predicted values (P > .05). Furthermore, the bias factor (Bf) and accuracy factor (Af) for each predictive model were also considered. These prototypes of RSM-microbiological models could be accurately used to guarantee the product stability of FDBSC-SBF stress targets and their shelf life during storage under various cross-protective conditions.