Production of fermented lignocellulose by Phytase producing mushroom and application as fish feed Ingredient

Abstract

Phytase is an enzyme that breaks down phytates into phosphorus in an available form. This enzyme plays a vital role in animals, especially monogastric animals. It serves to improve phytate digestion along with phosphorus absorption, which is required for optimal growth performance. In this study, 5 mushroom species (Amauroderma rugosum, Ganoderma mastoporum, Marusmius sp., Pholiota adiposa and Piptoporellus triqueter) displayed positive phytase production by agar plate assay. Consequently, these five mushroom species were selected for determination of their potential ability to produce phytase under solid-state fermentation using five lignocellulosic residues (coffee parchment, oil palm empty fruit bunches, rice bran, sawdust, and water hyacinth) as substrates. It was found that the residues used had a significant impact on the phytase production of each selected mushroom strain. After one week of fermentation, the highest yield of phytase production (17.02 ± 0.92 units/gram dry substrate) was obtained in water hyacinth fermented with Ph. adiposa. Pholiota adiposa and water hyacinth were selected for further investigation. The investigation of nutrient factors (carbon and nitrogen sources) revealed that glucose (carbon source) at an average of 23.24 ± 0.37 U/gds and ammonium nitrate (nitrogen source) at an average of 24.48 ± 0.30 U/gds were the most effective for phytase production. The optimal conditions for phytase production were established statistically using the design of a Plackett–Burman (PB) to screen 10 factors. Two significant parameters, the amount of water hyacinth and the moisture content, were found to affect the production process of phytase. After the response surface methodology (RSM), the use of 2 g of water hyacinth and 10 ml of basal liquid medium produced the highest amount of phytase. Furthermore, the optimal temperature, pH value, and fermentation period were evaluated. The results indicated that the highest degree of phytase production at 53.66 ± 1.68 U/gds by increasing from 17.02 ± 0.92 U/gds (3.15-fold increase) was obtained in water hyacinth containing 85% moisture content by addition with a suitable basal liquid medium at a pH value of 6.5 after being incubated at 30 °C for 7 days. The crude phytase of Ph. adiposa fermented with water hyacinth was precipitated by ammonium sulfate and the precipitated extract was then used to determine enzyme characterizations. The precipitated extract displayed high activities after exposure to conditions of 42 °C and pH 5.0. Furthermore, 1mM and 5 mM Fe2+ enhanced phytase activity and precipitated extract displayed the best stability at a pH value of 8.0 and a temperature of 4 °C. The fermented water hyacinth by Ph. adiposa hyacinth under SSF product is being used to supplement fish diets and fed to Nile tilapia (Oreochromis niloticus) to evaluate growth performance and feed efficiency. After 6 weeks of the experiment, the results revealed no significant difference in growth performance and feed efficiency between fish given fish meal (control) and fish given fish 10% PFWH (Pholiota adiposa fermented water hyacinth) diet. However, fish fed with 10% PFWH had a greater feed intake, weight gain, and nutrient gain (nitrogen, calcium, and phosphorus) than fish fed with 10% WH (water hyacinth), 20% WH, and 20% PFWH. Additionally, serum from fish fed 10% PFWH had the highest phosphorus content at 9.61 ± 0.93 mg/dL after 4 h of feeding. This finding implies that 10% PFWH could be used as a dietary supplement for Nile tilapia because this fish has the highest ability to digest and absorb 10% PFWH diet. Keywords: lignocellulosic residues, fungal phytase, optimization, response surface methodology, solid-state fermentation