Abstract
The present study aims to examine the process for L-lactic acid production from low-grade cassava chips (LGC) using a two-step fermentation approach (TSF) and simultaneous saccharification and fermentation (SSF) by proficient, newly isolated Lactobacillus rhamnosus strain SCJ9. The optimized medium composition revealed by response surface methodology for TSF was 166 g/L LGC hydrolysate and 20 g/L yeast extract (YE), while other medium components were fixed (g/L) as follows: tween80 (2.0), (NH4)2HPO4 (2.0), CH3COONa∙3H2O (6.0), (NH4)2HC6H5O7 (2.0), MgSO4∙7H2O (0.5), and MnSO4∙H2O (0.3). Based on the optimization conditions, the maximum experimental L-lactic acid of 134.6 g/L was achieved at 60 h fermentation time with a production efficiency of 89.73%, 0.95 g/g yield and 2.24 g/L/h productivity. In contrast, L-lactic acid production by SSF under optimized concentrations of thermostable-α-amylase (AA) and glucoamylase (GA) gave maximum L-lactic acid of 125.79 g/L at only 36 h fermentation time which calculated to the production efficiency, yield and productivity of 83.86%, 0.93 g/g and 3.49 g/L/h, respectively. The L-lactic acid production obtained from SSF was significantly improved when compared to TSF based on lower enzyme loading usage, shorter hydrolysis time and increase in production efficiency and productivity. Furthermore, there were no significant differences in the production by SSF between experiments conducted in laboratory bottle and 10-L fermenter. The results indicated the success of up-scaling for L-lactic acid production by SSF which could be developed for a further pilot-scale production of L-lactic acid.
Highlights
Lactic acid is a natural organic acid with multifunctional in different ranges of application such as beverages, flavorings and food preservatives, animal feed, drugs, and leather and textileProcesses 2020, 8, 1143; doi:10.3390/pr8091143 www.mdpi.com/journal/processesProcesses 2020, 8, 1143 industries [1,2]
Among ten lactic acid producing bacteria isolated from the fresh sugarcane juice, the proficient ten lacticbacterial acid producing bacteria isolated owing from the sugarcane juice, the proficient lactic Among acid producing isolate SCJ9 was selected to fresh the fastest and biggest yellow clear lactic acid producing bacterial isolate
SCJ9 was selected owing to the fastest and biggest yellow clear zone formed on MRS agar containing 125 ppm of bromocresol purple after cultivation at 37 °C for
Summary
Lactic acid is a natural organic acid with multifunctional in different ranges of application such as beverages, flavorings and food preservatives, animal feed, drugs, and leather and textileProcesses 2020, 8, 1143; doi:10.3390/pr8091143 www.mdpi.com/journal/processesProcesses 2020, 8, 1143 industries [1,2]. The most recent and attractive applications of lactic acid are found in the manufacturing of biodegradable agro-based products as well as poly-lactic acid (PLA), which is more environment eco-friendly products and alternatives to petroleum-based plastics [3,4,5]. Since optically pure Dand L-lactic acid is the precursor in PLA production, the demand for both forms of lactic acid is increasing continuously. L-lactic acid constitutes 92 to 99% of total lactic acid in various commercial PLA polymers. A high percentage of optically pure L-lactic acid provides a good-quality PLA polymer with high crystallinity and melting point [6]. Lactic acid can be commercially produced either by chemically synthesis or microbial fermentation systems. Since the chemically synthesis from petroleum substrates produces a racemic mixture of the two isomeric forms, the optically pure D- or
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