Production, purification, and characterization of acid-active chitosanase from Lentzea sp. OUR-I1 using squid pen waste as low-cost nutrient source with simultaneous recovery of bioactive compounds from microbial fermentation

Abstract

Squid pen waste is a promising source of chitin and protein that can be converted to a vast array of industrially important products. This study used squid pen powder (SPP) as an inexpensive nutrient source and inducer for Lentzea sp. OUR-I1 to produce chitosanase (chitosanase OUR-I1). The highest chitosanase level was obtained from a medium containing 1.5% SPP, and 0.1% (NH4)2SO4 with initial pH 5.0 and incubation at 30 °C for 5 days. The enzyme possessed properties desirable in industrial application such as being acid active and acid tolerant (pH 3.0–5.5) with moderate thermal stability up to 60 °C. It was found that chitosanase OUR-I1 expressed an exceptional hydrolytic ability against native chitosan extracted from SPP and generated glucosamine (COS-DP1) and its dimer (COS-DP2) as main hydrolysis products which displayed great scavenging activities against DPPH and ABTS with EC50 values of 3.74 mg/mL and 9.82 mg/mL, respectively. Besides, protein hydrolysate of 5.7 mg/mL and reducing sugar of 0.18 mg/mL were generated from SPP during chitosanase production. Notably, the recovered fraction during purification step exhibited excellent antioxidant activities against DPPH (E50 = 0.99 mg/mL) and ABTS (E50 = 0.02 mg/mL). The findings showed the potential use of Lentzea sp. OUR-I1 as a candidate microbial tool for bioconversion of squid pen waste into chitosanase and hydrolysis products with high antioxidant activities. The present study has shown the cost-effective approach for chitosanase production with simultaneous recovery of industrially useful co-products.