Optimization of Fermentation Condition and Characterization for Lactic Acid Production from Khat (“Catha edulis”) Waste by Using Immobilized Lactobacillus Plantarum

Abstract

Huge amounts of petroleum-based plastic wastes are generated annually possessing serious environmental problems that must be addressed. Poly lactic acid, which is an eco-friendly bioplastic product that can be used as an alternative to fossil-based plastics has gotten the attention of many researchers. Accordingly, owing to its great potential as a building block for the synthesis of poly lactic acid, the demand for lactic acid has grown substantially in recent years. Lactic acid production from lignocellulosic biomass is becoming more popular as a way to solve the problem associated with first-generation biomass. In the present study, the optimum fermentation conditions for maximum lactic acid production from khat waste biomass by using immobilized lactobacillus plantarum was investigated. Characterization of the khat waste like proximate analysis, chemical composition analysis, Fourier Transform Infrared Spectroscopy, and some physio-chemical properties of the product was done. The chemical composition analysis result revealed that khat waste has cellulose (43.7  0.71%), hemicellulose (17.42  0.85%), and lignin (30.63  0.93%). The investigated physio-chemical properties (density, kinematic viscosity, odor, reactivity, and miscibility) and functional groups of the product were in good agreement with the standard one. The effect of cell immobilization on the yield of lactic acid has been investigated and the yield obtained from immobilized lactobacillus plantarum cell is 24.7% higher than the free cells’. The effects of three process parameters (incubation temperature, incubation time, and pH) on the yield of lactic acid were investigated. Response surface methodology with a central composite design was used for the optimization of lactic acid yield and process parameters. Based on the analysis, the optimum fermentation conditions were found to be incubation temperature of 42.3 oC, incubation time of 40.0 hrs, and pH of 6.18. Under these conditions, the maximum lactic acid yield obtained was 23.05 g/L. The experimental yield of lactic acid (22.98  0.10 g/L) is in smooth agreement with the predicted one (23.05 g/L), showing the suitability of the quadratic model used. The exponential growth of lactobacillus plantarum cell was observed from the kinetic model of microbial growth study under optimum conditions. The applicability of the produced product for poly lactic acid synthesis was investigated. Generally, the findings of the study suggest that utilization of khat waste as a potential carbohydrate source and immobilization of lactobacillus plantarum cells for lactic acid production is worthful