Optimization of the Two-step Fermentation Process for Xuehua Pear Ferment
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Abstract:
Fermentation experiments were performed on Xuehua pears using the Plackett–Burman experimental design to optimize the two-step fermentation process for the preparation of Xuehua pear ferment. Four out of six factors indicating yeast fermentation were identified as significant; the solid-to-liquid ratio, fermentation temperature, inoculum size, and fermentation time. On this basis, the Box–Behnken design was used to optimize the yeast fermentation conditions based on total phenolic content and protease activity, and a single-factor design was used to optimize the conditions for Lactobacillus plantarum fermentation based on superoxide dismutase (SOD) activity and titratable acidity. The final timing for L. plantarum inoculation was determined based on the total phenolic content, protease activity, SOD activity, titratable acidity, pH, and soluble solids content (SSC). The results suggest that the optimal parameters for the two-step fermentation of Xuehua pears by yeast and L. plantarum are an initial broth pH of 4.5, solid-to-liquid ratio of 1:1, sugar content of 13%, yeast inoculum size of 0.14% for the first fermentation step, fermentation period and temperature of 24 hours and 26 ℃ for the first fermentation step, a L. plantarum inoculum size of 1.50% for the second fermentation step, and a fermentation period and temperature of 36 hours and 39 ℃ for the second fermentation step. Xuehua pear ferment obtained under these conditions shows an appropriate level of sourness and sweetness, uniform color, and an aroma unique to fermented pears, whilst being clear and free of impurities. The physicochemical indices of the obtained ferment are a total phenolic content of 32.32 μg/mL, protease activity of 45.15 U/mL, SOD activity of 1 140 U/mL, titratable acidity of 4.43 g/L, pH value of 3.49, and SSC of 11.3 Brix%, which are in line with the requirements of edible liquid plant-based ferments. The results obtained can be used as a theoretical reference for the comprehensive development of Xuehua pear ferments.
