BACKGROUND: D-Lactic acid (DLA) has numerous industrial applications, including production of biodegradable polylactic acid, which is one of the most promising biodegradable polymers. Looking for alternative feedstocks is a high priority and recent focus has been on its biological synthesis and biotechnological valorization from food waste (FW) materials. In this study, a response surface methodology (RSM) approach and central composite design (CCD) were performed to hydrolyze FW, obtaining released reducing sugars (RRS) for DLA production using the lactogenic Escherichia coli strain JU15. RESULTS: After an optimized sulfuric acid-based pretreatment methodology using RSM and CCD, FW was utilized to obtain the maximum concentration of RRS, obtaining liquors containing glucose (85.59%), fructose (5.48%) and arabinose (8.92%) with an efficiency of ∼98% total sugar conversion from hydrolysis of FW. As the total sugar sources obtained titers of 26.85 ± 1.28 g L −1 (DNS) and DLA production was 22.66 ± 1.01g L −1 , the DLA yield was 0.99 g g −1 total sugar. While arabinose was discretely consumed, with a remaining concentration of 0.36 ± 0.02 g L −1 after culture, the production of DLA through bacterial fermentation of the FW hydrolysates by the JU15 strain showed total depletion of glucose and fructose, achieving a maximum DLA production of 22.66 g L −1 , with a maximum volumetric productivity of 0.73 g L −1 h −1 at 36 h. CONCLUSION: This study provides an experimental optimization of a pretreatment to obtain released reducing sugars to lactic acid production from food waste as feedstock using the lactogenic E. coli strain JU15.

Background A processing methodology of raw starch extraction from avocado seeds (ASs) and a sequential hydrolysis and fermentation bioprocess in just a few steps was successfully obtained for the bioethanol production by a single yeast Saccharomyces cerevisiae strain and this research was also to investigate the optimum conditions for the pretreatment of biomass and technical procedures for the production of bioethanol. It successfully resulted in high yields and productivity of all the experiments from the laboratory scale and the pilot plant. Ethanol yields from pretreated starch are comparable with those in commercial industries that use molasses and hydrolyzed starch as raw materials. Results Before the pilot-scale bioethanol production, studies of starch extraction and dilute sulfuric acid-based pretreatment was carefully conducted. The amount of starch extracted from dry and fresh avocado seed was 16.85 g ± 0.34 g and 29.79 ± 3.18 g of dry starch, representing a yield of ∼17 % and 30 %, respectively. After a dilute sulfuric acid pretreatment of starch, the released reducing sugars (RRS) were obtained and the hydrolysate slurries containing glucose (109.79 ± 1.14 g/L), xylose (0.99 ± 0.06 g/L), and arabinose (0.38 ± 0.01 g/L). The efficiency of total sugar conversion was 73.40 %, with a productivity of 9.26 g/L/h. The ethanol fermentation in a 125 mL flask fermenter showed that Saccharomyces cerevisiae (Fali, active dry yeast) produced the maximum ethanol concentration, pmax at 49.05 g/L (6.22% v/v) with a yield coefficient, Yp/s of 0.44 gEthanol/gGlucose, a productivity or production rate, rp at 2.01 g/L/h and an efficiency, Ef of 85.37%. The pilot scale experiments of the ethanol fermentation using the 40-L fermenter were also successfully achieved with essentially good results. The values of pmax, Yp/s, rp, and Ef of the 40-L scale were at 50.94 g/L (6.46% v/v), 0.45 gEthanol/gGlucose, 2.11 g/L/h, and 88.74%, respectively. Because of using raw starch, major by-products, i.e., acetic acid in the two scales were very low, in ranges of 0.88–2.45 g/L, and lactic acid was not produced, which are less than those values in the industries. Conclusion The sequential hydrolysis and fermentation process of two scales for ethanol production using the combination of hydrolysis by utilizing dilute sulfuric acid-based pretreatment and fermentation by a single yeast Saccharomyces cerevisiae strain is practicable and feasible for realistic and effective scale-up strategies of bioethanol production from the starch of avocado seeds.