title: [Effect of pH and fermentation time on yield and optical purity of lactic acid from kitchen wastes fermentation].
abstract: Batch experiments were carried out to analyze the effect of pH and fermentation time on the yield of total lactic acid and the distribution of L- and D-lactic acid among total lactic acid during the non-sterilized fermentation of kitchen wastes. The results show that the concentration of reduced sugar (calculated as organic carbon) is low, and its concentration was higher at neutral and alkali conditions (pH 6 - 8) than at acidic conditions (non-controlled pH and pH = 5). The maximum total lactic acid production rate and yield is 0.59 g x (L x h)(-1) and 0.62 g per gram VS at pH 7, respectively. The proportion of lactic acid (calculated as organic carbon) among the TOC reaches 78% and 89% at controlled pH 7 and 8, respectively. The L-lactic acid is the predominant isomer form at pH 8. Lactic acid concentration depends on pH, fermentation time and interaction from the response surface analysis. pH and fermentation time have a significant effect on the optical purity of lactic acid. At acidic conditions, the ratio of L-lactic acid to the total lactic acid increases with the fermentation time before 120 h, and the ratio reaches 0.9 at 120 h. At alkaline conditions, the ratio keeps at above 0.86 in the whole experimental fermentation time and reachs the maximum value (0.93) at 48 h. It decreases with fermentation time at pH 7. To obtain high lactic acid yield and optical purity simultaneously, it is suggested that pH should be contralled at 8.
authors.affiliation: State Key Laboratory of Pollution Control & Resource Reuse, Tongji University, Shanghai 200092, China. solidwaste@mail.tongji.edu.cn
authors.forename: Bo
authors.initials: B
authors.lastname: Zhang
authors.forename: Pin-Jing
authors.initials: PJ
authors.lastname: He
authors.forename: Li-Ming
authors.initials: LM
authors.lastname: Shao
mesh_terms: D005285:Fermentation; D006863:Hydrogen-Ion Concentration; D007536:Isomerism; D019344:Lactic Acid / Q000032:analysis* / Q000737:chemistry; D007778:Lactobacillus / Q000378:metabolism*; D012147:Restaurants; D012722:Sewage / Q000382:microbiology; D013997:Time Factors; D018505:Waste Management / Q000379:methods*; D014866:Waste Products / Q000032:analysis
chemical_list: D012722:Sewage; D014866:Waste Products; D019344:Lactic Acid