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Ca-D(-)-lactate production from orange baggase via enzymatic hydrolysis and fermentation

Baltacı, Saadet Fatma
The utilization of low-cost renewable carbohydrate sources for the production of lactic acid which is widely used organic acid in food and polymer industry is a recent strategy in bioeconomy. The objective of this work was to produce Ca-D(-) -lactate as a precursor for D(-)-polylactic acid through the bioconversion of orange bagasse (OB) by enzymatic hydrolysis and fermentation. The hydrolysis of OB carried with dried and fresh OB, and cellulolytic and pectinolytic enzymes at 55 C, 150 rpm and 4.8 pH to evaluate the effect of biomass and enzyme loading, pectinase, drying and recycling of hydrolysate. Optimal results; 12.1 g/L glucose and 19.3 g/L total sugar conversion, were obtained by the hydrolysis of 10 % (w/v) solid load with 0.5 (w/v) % of cellulase mixture and 0.5 % (v/v) pectinase loading for 24 hours. It was observed that pectinase addition had a significant increase on saccharification. Ca- D(-)-lactate was produced by Lactobacillus delbrueckii bulgaricus OZZ4 and Lactobacillus plantarum OZH8 at 38 C, 160 rpm with OB hydrolysate. The influence of growth media, filtration of FOB hydrolysate, inoculum size on batch fermentation and repetitive substrate addition for fed-batch fermentation was evaluated. It was found that by employing centrifugation followed by filtration the antimicrobial effect of D-limonene was eliminated. Around 0.95 g/g and 0.50 g/g lactic acid yield (YL/T) were attained by both of the strains as a result of batch and fed-batch fermentation conducted with 5 % (v/v) inoculum size in fermentation medium containing eMRS broth and DOB hydrolysate, respectively.