Microbial Synthesis of Lactic Acid from Cotton Stalk for Polylactic Acid Production

Area of Science:

• Biotechnology
• Biorefining
• Sustainable Chemistry

Background:

• Agricultural waste, such as cotton stalk, presents an opportunity for sustainable bioprocessing.
• Lactic acid is a key precursor for polylactic acid (PLA), a biodegradable polymer with growing industrial demand.
• Current chemical synthesis of lactic acid produces a racemic mixture, unsuitable for many high-value applications.

Purpose of the Study:

• To investigate the use of cotton stalk as a low-cost substrate for microbial lactic acid production.
• To identify and characterize microbial strains capable of efficient lactic acid synthesis from lignocellulosic biomass.
• To optimize upstream process parameters for maximizing lactic acid yield.

Main Methods:

• Screening of Lactobacillus isolates from various sources for lactic acid production.
• Utilizing cellulose recovered from cotton stalk as a substrate for microbial fermentation.
• Optimization of fermentation parameters including inoculum size, substrate concentration, temperature, agitation, and production time.
• Synthesis of polylactic acid via direct polycondensation using various catalysts.

Main Results:

• A novel strain of Lactococcus cremoris isolated from kitchen waste demonstrated high lactic acid production (51.4 g/L).
• Optimal fermentation conditions were identified: 10% inoculum, 74.23 g/L reducing sugars, 37°C, 220 rpm, and 24h production age.
• Microbial synthesis yielded optically pure lactic acid, suitable for PLA production, unlike chemically synthesized racemic mixtures.
• Polylactic acid was successfully synthesized using catalysts like chitosan, YSZ, and Sb2O3.

Conclusions:

• Cotton stalk is a viable and cost-effective substrate for microbial lactic acid production.
• Microbial synthesis offers a route to optically pure lactic acid required for advanced PLA applications.
• This approach supports a low-carbon, circular bioeconomy by valorizing agricultural waste.