Standardization of starter culture for rice wine (tapuy) processing

Bubod, a local name of traditional starter culture for rice wine (tapuy) processing, is produced mainly from the northern part of Luzon. Previous studies revealed that it contains both beneficial and harmful microorganisms due to lack of quality control and technical know-how of the producers. Its use has resulted in inconsistent quality of products. This study was focused on the improvement and standardization of starter culture for rice wine processing. The study revealed presence of Rhizopus oryzae, Mucor piriformis and Mucor racemosus, for molds; Saccharomycopsis fibuligera and three Saccharomyces cerevisiae, for yeast; and Lactobacillus plantarum, for lactic acid bacteria (LAB) in bubod from Ifugao, Benguet, and Baguio City. Screening of isolates for saccharifying power and alcohol production showed that the highest reducing sugar (RS) converted from rice starch was observed in R. oryzae (29.20%) fallowed by M. racemosus (25.20%), M. piriformis (15.71%) and S. fibuligera (6.76%). On the other hand, the highest alcohol producing yeast was S. bayanus, which also belonged to S. cerevisiae. In another study, highest saccharification and liquefaction of binuburan was established using mixed cultures of identified molds. Different forms of dried starter cultures (bubod, freeze-dried mixed cultures, and oven-dried mixed cultures) were prepared. Preliminary studies showed that freeze-dried and bubod inoculated with mixed cultures had long shelf-life and high activity for rice wine processing. The conditions for bubod preparation was established, such as heating of ground rice at 60 deg C, 24h; 2 slants of each mold suspensions per 500g ground rice to produce viable cell counts of 10sup6-10sup7 CFU/ml; drying at room temperature then at 37 degC until moisture content of 11.0-13.0% was attained; and storage of properly packed bubod at 4-8 deg C. The developed starter cultures were utilized in the production of rice wine (Multiparallel and traditional methods) using a low-amylose type rice variety (NSIC Rc 160) at the rate of 1.0% based on the weight of cooked rice. Microbial and chemical analyses of the fermenting mash and final products using the multiparallel method of fermentation showed that in general, yeast counts of fermenting mash was sustained at 10sup9-10sup10 CFU/ml until the 3rd addition of binuburan and water regardless of the form of starter culture used. This is due to continues addition of hydrolyzed rice starch to maintain yeast viability. Counts continuously decreased thereafter as fermentation progressed. Likewise, counts of acid-producing bacteria gradually increased to 10sup4-10sup5 CFU/ml during the first 3 days of fermentation. Prolonged fermentation revealed remarkable decrease in counts and were almost inhibited after 14d fermentation due to high alcohol content of the fermenting mash. Chemical analysis of rice wine revealed higher alcohol content for freeze dried A. oryzae starter (11.0%) compared to other two treatments (9.0%). The pH and TSS of wine were also found higher for the former samples compared to the latter with values of 4.10 and 3.80, and 7.30 deg Brix and 5.30-5.60 deg Brix, respectively. Using the multi-parallel fermentation, percentage recovery was 139.50% and 276.13% in A. oryzae-inoculated setup while samples added with freeze-dried and bubod obtained 162.00%-162.50% and 330.00%-330.32%, based on the weight of cooked rice and raw rice, respectively. Traditional method of fermentation, however recovered very low amount of wine thus the use of glutinous rice variety is recommended to increase wine recovery. Sensory evaluation of wine from multi-parallel fermentation revealed that wine from bubod had significantly the most intense yellow color and highest score for overall acceptability, typical wine flavor and smoothness but not differing from the other treatments. Wine samples from A. oryzae had the highest score for clarity and aroma, while wine from freeze-dried mixed starter had the most intense alcoholic taste, most bitter and astringent taste and had the least typical wine flavor, smoothness, and highest off-odor, therefore it was the least acceptable among the three wine samples which suggests that there is a need to further refine the quality of the wine produced from laboratory-prepared starter cultures.