Effect of Lactic Acid Bacteria Fermentation on Physicochemical Properties, Phenolic Compounds, Antioxidant Activity and Volatile Components of Hawthorn Juice

Six commercial lactic acid bacteria (LAB) including Lactobacillus plantarum 90 (Lp), L. casei 37 (Lc), L. paracasei 01 (Lpc), L. acidophilus 85 (La), Bifidobacterium lactis 80 (Bla) and L. helveticus 76 (Lh) were separately used to ferment hawthorn juice. The effect of lactic acid bacteria fermentation on physicochemical properties (pH, total soluble solids, and titratable acidity), phenolic compounds, antioxidant activity, color and volatile flavor components and sensory quality of hawthorn juice were investigated. The results showed that hawthorn juice regulated acidity to pH 4.70 was an excellent substrate for LAB. The growth of the six LAB strains in it was not obviously different. At the end of fermentation, the viable cell count was still higher than 8.5 (lg(CFU/mL)), and good fermentation performance was observed as manifested by lactic acid production exceeding 2.6 mg/mL. Bla and Lh fermentation significantly increased total phenols, but they had no significant influence on total flavonoids. In contrast, La, Lc and Lpc fermentation significantly reduced total flavonoids (P < 0.05), while they showed no significant effect on the total phenol content. In addition, the antioxidant activity of hawthorn juice was enhanced by fermentation with Lpc, Bla and Lh (P < 0.05), as evidence by the strong 2,2’-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radical cation-scavenging capacity (about 49.0%) and Fe³⁺ reducing antioxidant power (FRAP, about 25.0 mmol/L). Correlation analysis suggested that the antioxidant activity was negatively correlated with the contents of p-coumaric acid, chlorogenic acid, quercetin and epicatechin. Lactic acid fermentation greatly increased the number and amount of volatile components in hawthorn juice, resulting in the formation 17 new alcohols and 17 new esters and reducing the content of aldehydes. The sensory evaluation results showed that lactic acid bacteria fermentation improved the aroma, taste and flavor of hawthorn juice. The juice fermented by Bla had the best overall sensory quality, followed by Lh. Compared with any other lactic acid bacteria, Bla fermented juice had stronger antioxidant properties, was richer in aroma substances, and possessed good organoleptic quality, and thus could be worthy of further research and development.