Prebiotic activity score and bioactive compounds in longan (Dimocarpus longan Lour.): influence of pectinase in enzyme-assisted extraction.

Abstract

The optimal extraction of bioactive compounds from longan fruit pulp using Pectinex® Ultra SP-L pectinase hydrolysis of the fruit homogenate was evaluated. The highest degree of hydrolysis (DH), as determined by the amount of reducing sugars released from the longan pulp, was obtained at a pectinase concentration of 2.5% (v/w) (257 polygalacturonase units/g fruit) for 4h. The level of bioactive compounds obtained from the pectinase-treated longan pulp increased with increasing DH to a maximum at the highest DH (21%) obtained, with an antioxidant activity of 0.083EC50 μg fresh mass (FM)/μg diphenyl-(2,4,6-trinitrophenyl)iminoazanium and 92.7μM Trolox equivalent/g FM, respectively. The total phenolic and flavonoid contents in the 21% DH extract were 196.0mg gallic acid equivalents/g FM and 19.6mg catechin equivalents/g FM, respectively. The 21% DH longan extract showed an enhanced (3.6- to 4.0-fold) inhibition of lipid peroxidation of oil compared to the untreated (0% DH) extract. In addition, the 21% DH longan extract had the highest soluble dietary fiber content, which was related to the decreased particle size of 345μM, and displayed enhanced prebiotic activity scores of 1.69 and 1.44 for Lactobacillus acidophilus La5 and Bifidabacterium lactis Bb12, respectively. Most of the 33 detected volatile compounds differed in their relative proportions after enzymic extraction (15 increased, 15 decreased with three showing no significant change) with the 0% and 21% DH hydrolysates exhibiting 25 and 22 different volatile compounds, respectively, with 11 and eight unique compounds between them, respectively.