Date fruit pomace, a promising feedstock for L-lactic acid fermentation.

Abstract

Date fruit processing is a major food industry in the United Arab Emirates, with dates syrup as one of their key products. Date fruit pomace (DFP), a by-product from this industry, is currently being used as an under-valued ingredient, mainly in the animal feed industry. DFP is rich in sugars (35% on a dry basis) and can be regarded as a potential renewable resource to be used as a substrate for fermentation by microorganisms. This project aimed to valorize the DFP to produce L-lactic acid via fermentation using the bacteria, Lactobacillus casei. This study investigated the effect of supplementing the fermentation media with a nitrogen source and a salt mixture on lactic acid production. The fermentation parameters, such as DFP loading, inoculation load, and incubation time, were optimized. The optimum fermentation conditions were achieved when 20% DFP, 20 g/l yeast extract, and the salt mixture were inoculated with 10% bacteria and incubated for seven days. The lactic acid yield improved when the pH was maintained at 6.2 during incubation, and the enzyme Cellic CTec2 was used to release sugar from the pomace. At a controlled pH, a lactic acid concentration of 292 ± 1.2 g/kg DFP was achieved when 80 g DFP was inoculated with bacteria (3.9 × 1010 colony-forming units) and incubated for seven days. Upon hydrolysis with 40 FPU/g DFP Cellic CTec2, the sugar content increased to 482 g/kg DFP, and the lactic acid concentration increased to 457 ± 1.4 g/kg DFP. Using n-butanol, 78.9% pure l-lactic acid was extracted from the fermentation broth via phase partitioning.