Application of ultrasonic pretreatment on fermentation of jujube juice by Lactobacillus plantarum: investigation on physicochemical and volatile aroma components

This research was initiated to investigate the impact of ultrasonic pretreatment (USP) of jujube juice prior to its fermentation with Lactobacillus plantarum CICC 20,022 (L. plantarum), including physicochemical and flavor attributes, jujube juice with non-USP was used as control. The results showed that there was no significant difference in L. plantarum morphology between USP and non-USP. When the power was 280 W, the number of viable bacteria was maximum (9.38 Lg CFU/mL), and the total sugar consumption increased by 55.3%. The intracellular β-glucosidase activity was increased by 70.85%, 57.79%, 55.54% and 48.05% in the USP 280 W, 420 W, 560 W and 700 W compared with non-USP, respectively. The activity of H+ -ATPase reached its peak at USP 280 W and decreased as power increased. In addition, USP 280 W improved the flavor of fermented jujube juice by promoting the metabolism of phenolic acids such as gallic acid, p-hydroxybenzoic acid and ferulic acid and organic acids such as lactic acid, malic acid and citric acid. The color of the fermented jujube juice was relatively well maintained at USP 280 W, but the stability of the fermented jujube juice was better at USP 700 W. Additionally, the contents of esters, aldehydes and ketones of sample increased significantly (p < 0.05) under USP 280 W, the main volatile aroma compounds were identified as beta-damascenone and ethyl caprylate. In conclusion, pretreating jujube juice with 280 W ultrasonic wave before fermentation could improve the nutritional value and flavor of fermented jujube juice.