Efficient biorefinery process for lactic acid production from date wastes with alleviating substrate inhibition effect u
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ORIGINAL ARTICLE
Efficient biorefinery process for lactic acid production from date wastes with alleviating substrate inhibition effect using thermo-alkaline repeated batch fermentation Mahmoud Ali Gaber 1 & Mohamed Ali Abdel-Rahman 1
&
Saad El-Din Hassan 1 & Mohamed Salah Azab 1
Received: 12 August 2020 / Revised: 8 September 2020 / Accepted: 25 September 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract In the current work, date wastes were used for lactic acid (LA) production under thermo-alkaline conditions to overcome some fermentation challenges. Amongst 27 bacterial isolates that produced LA from date juice, isolate D-218 exhibited better growth stability and LA production under various stressed conditions. This isolate was characterized as Bacillus coagulans D-218 using physiological and molecular identification methods. In batch fermentation mode, strain D-218 could not completely utilize 80 g/L of the total sugar and produced only 45.8 ± 2.8 g/L of LA at LA productivity of 0.214 g/L.h and high residual sugar (29.2 g/L) was unutilized in the fermentation media. Different repeated batch fermentations with different initial sugar concentrations and gradual increase in sugar concentrtions were conducted to maximize LA productivity. Starting with 60 g/L of total sugar, four runs of repeated batch fermentations were conducted that enhanced the LA productivity (70%) to 0.49 g/L.h. Another 9 runs were initiated with 40 g/L which further improved LA productivity that reached up to 0.77 g/L.h. Surprisingly, initiating fermentations with 20 g/L of total sugar successfully attained long-term fermentation (18 runs) with high LA yield and productivity without carbon loss of initiated startup sugar of date waste. In this process, strain D-218 could completely consume 80 g/L sugars with high LA production titer (72.9 ± 0.56 g/L), yield (0.92 g/g), and productivity (0.71 g/L.h). This study is the first to exploit date waste in a cost-effective system for high-titer lactic acid production under thermo-alkaline conditions (pH 9.0; 50 °C) and to report repeated batch fermentation for LA production from date wastes. Keywords Lactic acid production . Date wastes . Bacillus coagulans D-218 . Repeated batch fermentation . Thermoalkaline fermentation
Highlights • Bacillus coagulans D-218 is a promising candidate for lactic acid (LA) fermentation from date waste. • Substrate inhibition effect was alleviated using cell-adaptability in repeated batch mode. • Initial sugar concentration is rate-limiting for improved substrate utilization and long-term repeated batch process. • Strain D-218 produced 72.9 g/L of LA in repeated batch fermentation at 0.71 g/L.h Electronic supplementary material The online version of this article (https://doi.org/10.1007/s13399-020-01043-y) contains supplementary material, which is available to authorized users. * Mohamed Ali Abdel-Rahman [email protected]; [email protected] 1
Laboratory of Microbial Physiology; Botany and Microbiology Department, Faculty of Scienc
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