Third Generation Lactic Acid Production by Lactobacillus pentosus from the Macroalgae Kappaphycus alvarezii Hydrolysates

Abstract

The evaluation of macroalgae as a new raw material for diverse bioprocesses is of great interest due to their fast growth rate and low environmental impact. Lactic acid has a high value in the bio-based industry and is mainly produced via fermentation. The anaerobic lactic acid fermentation of Kappaphycus alvarezii hydrolysates using the high-producing strain Lactobacillus pentosus was evaluated for detoxified and non-treated hydrolysates prepared from concentrated algal biomass and dilute acid solution mixtures. A novel hydrolysate detoxification procedure, combining activated charcoal and over-liming, for 5-hydroxymethylfurfural (HMF) removal was used. L. pentosus was found to successfully ferment detoxified and untreated hydrolysates produced in up to 30% and 20% w/v solutions, respectively. Significant production rates (1.88 g/L.h) and short lag phases were achieved in bioreactor fermentation operating at 37 °C and pH 6 with 150 rpm impeller velocity. A 0.94 g/g yield from fermentable sugars (galactose and glucose) was achieved, indicating that K. alvarezii could be used as a raw material for lactic acid production, within the context of Third Generation (3G) biorefinery.

The Macroalga Kappaphycus alvarezii as a Potential Raw Material for Fermentation Processes within the Biorefinery Concept: Challenges and Perspectives

“…When using higher biomass concentrations in more prolonged hydrolysis procedures, higher galactose concentrations can be obtained. As shown by Khambhaty et al [72] and Tabacof et al [24], more than 50 g/L of galactose can be reached in a mixture with about a 30% (w/v) biomass concentration. The hydrolysis conditions in these cases were 100-110 • C and 1% (v/v) sulfuric acid concentration, and the hydrolysis time was 45 to 60 min long.…”

“…Using similar conditions with an even higher biomass concentration of 50% (w/v) mix, Hargreaves et al [22] reached a galactose concentration of 82 g/L. The work carried out by Hargreaves et al [22] and Tabacof et al [24,73] showed that exposing K. alvarezii biomass to prolonged acid hydrolysis results in the formation of 1 g/L of HMF for every 4 g/L of galactose.…”

“…3.1.1. HMF Removal from K. alvarezii Hydrolysates Removal of HMF from K. alvarezii hydrolysates can be performed via activated charcoal filtration, where HMF is captured within the charcoal's pores [22,24,78]. Hargreaves et al [22] determined that fine powdered charcoal is preferable to charcoal granules, and that approximately 1 g/L of charcoal should be used for each 1 g/L of HMF removed from the hydrolysate.…”

“…Another reported method for HMF removal is that of overliming, which consists of the addition of calcium oxide (CaO) [25] or calcium hydroxide (Ca(OH) 2 ) [24,26,27]. A byproduct of HMF formation under acid-hydrothermal treatment are humins.…”

“…In some cases, HMF should be removed from fermentation media prior to the microorganism inoculation. The removal of HMF could be carried out using activated charcoal [22,24], and overliming processes [24][25][26][27]. Alternatively, HMF can be removed directly from the hydrolysates, applying reactive extraction via zeolites as catalysts or using absorption in an organic phase in slug flow reactors or stripping columns [28].…”