Abstract
The prebiotic potential of longan juice obtained by a commercial Viscozyme L for conversion of constituent sucrose to fructo-oligosaccharide was investigated. The physicochemical properties and carbohydrate composition of the longan juice was evaluated before and after enzymatic treatment. The stimulation effects of the treated longan juice on probiotic bacteria growth were also studied in vitro. The results showed that total soluble solids, yield and clarity of longan juice were all significantly improved after enzyme treatment. The water-soluble polysaccharide content, including pectin, was significantly increased. Compared with the natural longan pulp, the enzyme treated juice showed a significant decrease in sucrose content. Substantial fructo-oligosaccharides including 1-kestose and nystose were synthesized after enzyme treatment. The molecular weight distribution and the monosaccharide composition of the water-soluble polysaccharide were significantly changed by enzyme treatment. The treated longan juice and its ethanol-soluble sugar fraction promoted the growth of Streptococus thermophiles, Lactobacillus acidophilus and Lactobacillus delbrueckii, showing a good potential of the treated longan juice for producing functional foods and nutraceuticals.
Highlights
Longan (Dimocarpus longan Lour.) is an important economic fruit in southern China [1]
Longan pulp was treated by Viscozyme L during juice production, and the results showed that enzyme treatment improved the processing characteristics of longan juice including yield, clarity and total soluble solids, and changed its carbohydrate compositions
The acceleration effect of water-soluble polysaccharide (WSP) from enzyme treated longan juice (104.48 and 103.53%) was not as remarkable as its untreated longan juice counterpart (122.14%). These results show that components produced during enzyme treatment of longan juice could improve the growth of L. acidophilus, and that these effective components are most possibly the FOS in the ESS fraction produced during enzyme treatment
Summary
Longan (Dimocarpus longan Lour.) is an important economic fruit in southern China [1]. It has been reported that longan is rich in phenolic compounds and polysaccharides, which have excellent radical-scavenging activities, potent immune-modulatory, great antitumor effects and regulating intestinal flora effects [2,3,4]. It is preferred for its desirable flavor and for its nutritional value [5,6]. Enzymes are commonly added during maceration, prior to the pressing of fruits to obtain satisfactory juice yield [8]. Physicochemical properties such as viscosity and the carbohydrate composition of juice are impacted [11]
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