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
