Evaluation of Pre-treatments of Brewery’s Spent Grain for Growing Bacteria in the Production of Polyhydroxyalkanoates

Abstract

A suitable solution to solve the problems related to the conventional plastics is their replacement by biodegradable materials with similar properties such as polyhydroxyalkanoates (PHAs). PHAs can be produced by microorganisms using abundant low-cost substrates such as brewery’s spent grain (BSG). In this work, different pre-treatments were tested on BSG to improve the growth and production of biomass using three different strains highly recognized for their ability to produce PHA. A solid-state fermentation (SSF) was carried out to evaluate PHA production. An evaluation of biomass growth kinetics of the three selected bacteria was made after different hydrolytic pre-treatments of BSG. Results showed that bacteria did not grow in control BSG and the pre-treatments were necessary to release the principal substrate metabolised by bacteria. The best result was obtained with alkali pre-treatment although microwave pre-treatment showed good results too. The strains P. putida and C. necator showed productions of 1.95 and 1.45 mg biomass/g BSG and viable cell counts of 1.5 E+16 and 1.3 E+08 CFU/g BSG after 72 hours of SSF, respectively. On the other hand, Bacillus cereus was not able to grow in the pre-treated substrates. BSG is a promising substrate for bacterial growth and PHA production for its nutrient content.