Microbial Contamination Reduction of Sorghum (Sorghum bicolor L.) Stalk Juice as Bioethanol Raw Material through Microfiltration Process
Abstract
Microbial contamination reduction for bioethanol raw material is commonly
achieved through heat sterilization process. However, heat sterilization process could contribute
up to 64.5% of the total energy requirement of bioethanol production; therefore microbial
contamination reduction process at lower temperature is preferable. This research studied the
implementation of microfiltration to reduce microbial contamination of sorghum stalk juice as
bioethanol raw material, in comparison to pasteurization. The raw sorghum (Sorghum bicolor
L.) stalk juice contains microbial contaminant load in the form of bacteria, yeast and
spore-forming mold. Effectiveness of microfiltration was observed by processing sorghum stalk
juice through micro filter with nominal pore size of 3.0 m, 1.0 m, and series of 3.0 m and 1.0
m. Pasteurization was conducted at 70o
C for 30 minutes in an autoclave. Total plate count
analysis showed that pasteurization reduced total microbial load to 99.93% while
microfiltration using pore size of 3.0 m, 1.0 m, series of 3.0 m and 1.0 m showed
non-significant difference with total microbial load reduction of 99.99% In 7 days of storage in
room temperature, juice treated by microfiltration using pore size 3.0 m maintained its total
microbial load of 1.12 ± 0.01x 106
CFU/ml, juice treated with microfiltration of pore size 1.0
m has 11.60 ± 0.74x 103
CFU/ml, series of filter gives 8.50 ± 0.64 x 103
CFU/ml, while
microbial load of pasteurized sorghum stalk juice increase to 1.06 ± 0.02 x 109
CFU/ml.
Suitability of process as pretreatment for bioethanol raw material was observed through
inoculation of Saccharomyces cerevisiae in the treated juice. Yeast growth in filtered media
gives Yx/s of 0.49 g biomass/ g substrate, higher than pasteurized media (0.44 g biomass/ g
substrate). It could be concluded that microfiltration using nominal pore size of 1.0 m is
sufficient to reduce microbial contamination for sorghum juice as bioethanol raw material.
