Antioxidant and Prebiotic Activity of Enzymatically Hydrolyzed Lychee Fruit Pulp

Naraporn Fasawang¹ and Pranee Anprung²*

¹Program in Biotechnology, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand
²Department of Food Technology, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand

Article history:
Received August 27, 2013
Accepted April 29, 2014

Key words:
pectinase, lychee pulp, antioxidation, prebiotics

Summary:
The optimal extraction of bioactive compounds from lychee fruits using commercial Pectinex^® Ultra SP-L pectinase hydrolysis of the fruit pulp homogenate was evaluated. The  lychee fruit pulp was treated with the pectinase at volume per mass ratios between 0.5 and 2.5 % for 0.5–5 h. The degree of hydrolysis (DH), monitored as the level of released reducing sugar, increased with the increase of enzyme volume per mass ratio and time up to 2 % and 4 h, respectively, to give a maximum DH of 19 %. The antioxidant activity in lychee pulp hydrolysates increased with increasing DH, with the highest DH of 19 % displaying an EC50 of 0.25 g of fresh mass (FM) per g of diphenyl-(2,4,6-trinitrophenyl)- iminoazanium and 53.17 M of Trolox equivalents per g of FM. The lychee hydrolysate with the DH of 19 % had the highest level of total phenolic acids (165.8 mg of gallic acid equivalents per 100 g of FM) and flavonoids (70.8 mg of catechin equivalents per 100 g of FM), and the highest prebiotic activity score of 1.68 and 0.82 of Bifidobacterium lactis Bb12 and Lactobacillus acidophilus La5, respectively. In accordance with the level of phenolic acids and flavonoids, the lychee hydrolysate with the DH of 19 % revealed a reasonably good level (72–77 %) of lipid peroxidation inhibition in soya bean, lard and olive oil. The lychee hydrolysate with the DH of 19 % increased the number of detected volatile compounds to 37, with 11 new compounds that were not found in the lychee hydrolysate with the DH of 0 %. Moreover, the particle size and insoluble fibre level were reduced with a concomitant increase in the soluble fibre level.

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