Production and optimization of lactic acid using <i>Chlorella vulgaris</i> as a source of fermentable sugar

Abstract

The use of plant waste product for maximum sustainability has led to the search for bio based raw material such as Chlorella vulgaris which can make a tremendous contribution on the ecological and economical production of different organic acids like lactic acid. This study aimed to evaluate the enzymatic and or acidic hydrolysis of Chlorella vulgaris cell wall Intercellular starch as a source of fermentable sugar for lactic acid production. Lactic acid was produced through acid hydrolysis, enzyme hydrolysis and a combination of acid and enzyme hydrolysis of four different substrates. Each of the substrate was inoculated with a lactic acid bacterium (Lactobacillus plantarum) and a fungus (Rhizopus oryzae) while acid/enzyme hydrolysis was inoculated with mixed culture of the organism within a retention period of tendays.  Results showed that the physico-chemical properties of C. vulgaris had a total carbohydrate of 17.4% and a reducing sugar of 24.0µg/ml. According to treatment, C. vulgaris had the highest reducing sugars (6.4 ± 0.2) and (4.4 ± 0.3) with Lactobacillus Enzyme Hydrolysis (LEH) and Rhizopus Enzyme Hydrolysis (REH) treatments, respectively indicating that C. vulgaris was the most hydrolyzed sample. Results of the optimization of various responses showed that using Corn Steep Liquor (CSL), REH day 2 treatment for fermentation at 370C for 48h were best combinations that yielded the optimal of Y1=0.249, Y2= 5.461 and Y3=33.704, respectively with a desirability of 0.619. The results indicated Chlorella vulgaris produced the highest lactic acid of about 20% signifying that its biomass contains high source of carbohydrate accessible for lactic acid production.