Preparation of bioactive neoagaroligosaccharides through hydrolysis of Gracilaria lemaneiformis agar: A comparative study

•A high specific activity of β-agarase was used for Gracilaria lemaneiformis agar hydrolysis.•Hydrolysis of extracted G. lemaneiformis agar by acid and β-agarase was compared.•Structure and composition of the two hydrolysates was found to be very different.•Hydroxyl radical removing ability of agarolytic products was compared.•Anti-tyrosinase mechanism of the neoagaroligosaccharides was investigated.

Hydrolysis of Gracilaria lemaneiformis agar by β-agarase was compared with HCl hydrolysis. The results showed that optimum catalysis conditions for the β-agarase were pH 7.0 at 45 °C. Mass spectroscopy, thin-layer chromatography and GPC results showed that the polymerization degrees of the hydrolysis products by the β-agarase were mainly four, six and eight (more specific than the hydrolysate by HCl). The enzymatic degradation products of agar were distinctly different from those of HCl hydrolysis in the ratios among galactose and 3,6-anhydro-galactose and sulfate group contents. The NMR spectrometry proved that the products of β-agarase were neoagaroligosaccharides, which was not found in the agarolytic products by HCl. The neoagarotetraose inhibited tyrosinase activity competitively with the KI value of 16.0 mg/ml. Hydroxyl radical-scavenging ability of neoagaroligosaccharides was much greater than that of agar HCl hydrolysate. This work suggests that neoagaroligosaccharide products produced by our β-agarase could be more effective in function than products from acid hydrolysis.