Lactic Acid Production from Brewer’s Spent Grain Using Lactobacillus Plantarum
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Date
2018-06
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AAU
Abstract
Lactic acid is widely used in the food, cosmetic, pharmaceutical, and chemical industries and has
received increased attention for use as a monomer for the production of biodegradable poly (lactic
acid). It can be produced by either biotechnological fermentation or chemical synthesis, but the
former route has received considerable interest recently, due to environmental concerns and the
limited nature of petrochemical feedstocks. The objective of this study was to produce lactic acid
from Brewery Spent Grain by using lactobacillus plantarum. The production process was carried
out in four main stages, such as pretreatment, hydrolysis, fermentation and recovery of lactic acid.
Brewery spent grain was dried using oven at 80ºC temperature for 24 hr. Then for the hydrolysis,
Box Behnken Design (BBD) was applied to investigate the effect of temperature (115-130ºC),
reaction time (25-35min) and acid concentration (1.5-2M) using Design expert® 7 software. RSM
was applied to investigate the interaction effect of the hydrolysis process variables and to find the
optimum yield of lactic acid from BSG. After hydrolysis process, reducing sugar content of the
hydrolyzate was quantified using quantitative benedict reagent solution. Fermentation of the
hydrolyzate was performed using 150mL, Lactobacillus plantarum at 35ºC temperature, pH 5.0 –
5.5 and 200 rpm for 72hrs fermentation time for all samples. After fermentation recovery of lactic
acid and purification process was carried out by centrifuging all samples at 5000 rpm for 5 min
followed by filtration through 0.2μm paper filter. The concentration of lactic acid was determined
by titration of the sample using 4M of sodium hydroxide. Significance of the process variables
were analyzed using analysis of variance (ANOVA) and second order polynomial function was
fitted to the experimental results. Thus, the influence of all experimental variables, factors and
interaction effects on the response was investigated. Hydrolysis temperature, time, sulfuric acid
concentration and interaction between reaction temperature and sulfuric acid concentration have
significant effect on the yield of lactic acid. RSM optimization yielded the best yield of total
reducing sugar and the maximum yield of lactic acid were obtained at 129.75ºC, 32.39 min and
1.89M. Under these condition 53.07% and 26.71% per 150ml of hydrolysate of total reducing
sugar and lactic acid was obtained respectively.
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Keywords
Lactic Acid, Brewer’s Spent Grain, plantarum