Isolasi bakteri asam laktat dan selulolitik serta aplikasinya untuk meningkatkan kualitas tepung jagung

Abstract

Corn has the potential to be converted into flour, but the hard endosperm causing coarse particle size, corn flour also do not have a long shelf life and induce the production of mycotoxin. To overcome these problems, the milling of corn grain can be done by steeping it in the water. Steeping process caused spontaneous growth of microbes, such as lactic acid and cellulolytic bacteria. Lactic acid bacteria in the steeping process produce antimicrobial and antifungal compounds that are able to control the growth of pathogenic bacteria, spoilage bacteria, and fungi. The use of lactic acid and cellulolytic bacteria in the steeping process can soften the horny endosperm, so it can improve the corn grits to grind into fine flours. Based on the role of both microbes, the consortium of bacteria inoculated as starter in the steeping process of corn grits. It was expected that the introduction of starter would shorten the steeping time, improve the fine flour yield, and suppress the growth of undesired microbes. This study aimed to obtain isolates of indigenous lactic acid and cellulolytic bacteria from corn steeping process, and to apply them as a starter in the steeping process of corn grits to increase the quality of corn flour. The experiment conducted into three steps: analysis of microbial population dynamics in spontaneous fermentation of corn grits during steeping process, isolation and selection of lactic acid and cellulolytic bacteria, and the use of starter in the steeping process of corn grits. Population dynamics of microbes during spontaneous fermentation is the basic rule for the formulation of appropriate starter culture. The fermentation during steeping process conducted for 0, 12, 24, 36, and 48 hours. The amount of lactid acid bacteria increased until 48 h of steeping and the population of cellulolytic, amylolytic, and yeast increased until 36 hours. In this study, only lactic acid and cellulolytic bacteria were isolated and used as a starter. Amylolytic bacteria and yeast were not used to prevent the damage of starch, and yeasts are generally found at the end of fermentation. Seven LAB isolates and 10 cellulolytic bacteria isolates were obtained from the 48 hours of spontaneous fermentation, and 10 cellulolytic bacteria isolates from 12 hours of fermentation. Isolate E2213BAL (BAL) was lactic acid bacteria selected as the highest optical density at logarithmic phase, while isolate B2121SLT (BST) was cellulolytic bacteria with the highest enzyme activity. The use of starter in the fermentation of corn was done by steeping the corn grits in sterile distilled water containing bacterial starter. Both microbes were inoculated into steeping water according to the composition starter: control without starter (A), 106 CFU/ml of BAL:106 CFU/ml of BST (B), 106 CFU/ml of BAL:2X106 CFU/ml of BST (C) , 2X106 CFU/ml of BAL:106 CFU/ml of BST (D). During the fermentation, the number of lactic acid, cellulolytic, amylolytic bacteria, and yeast growths from inoculated fermentation (B, C, D) were higher compared to spontaneous fermentation (A). 7 During the fermentation, the pH of steep water decreased as the increasing of total acidity. Treatment D with 36 hour steeping time produced the highest total acidity which dominated by lactic acid. Lactic acid was expected to be absorbed into the flour, which can play role to inhibit pathogenic microbes and improve the palatibility of corn flour. The starter in the fermentation process could reduce the fiber content, high yield of fine flour and increase the protein content. The acid also caused some diruption of starch granules, and supressed the microbes of 1 month flour. The starter with the composition 2X106 CFU/ml of BAL:106 CFU/ml of BST (D) was able to shorten the steeping time. This could be seen in the steeping of 12 hours and 24 hours of treatment D was able to produce smaller crude fiber content of flour pass 80 mesh (0.53-0.56%) than spontaneous treatment (0.60-0.74%). Treatment D with 24-48 hours of steeping could reduce the <60 mesh of flour particle size and increase the 80-100 mesh of flour particle size, higher yield (36.20-38.37%) than spontaneous treatment (35.98-37.00%). The use of starter in the fermentation process could also maintain the flour protein content up to 48 hours of steeping, the lowest decreasing of flour protein was produced by treatment D. Treatment with the composition 2X106 CFU/ml of BAL:106 CFU/ml of BST (D) could decrease the total microbes in flour that has been stored for one month, the highest decline in the total microbes were produced by treatment D (5.44 log CFU/ml on medium plate count agar, 3.70 log CFU/ml on medium potato dextrose agar). It shows that treatment D (2X106 CFU/ml BAL:106 CFU/ml BST) with 36 hour steeping produced the best quality of corn flour.