Alcoholic fermentation of raw cassava starch by Rhizopus koji without cooking

Abstract

Using only wheat bran koji from the Rhizopus strain, raw cassava starch and cassava pellets converted reasonably well to alcohol (ethanol) without cooking at 35 degrees C and pH 4.5-5.0. When the initial broth contained 30 g raw cassava starch, 10 g Rhizopus sp. koji, and 100 mL tap water, 12.1 g of alcohol was recovered by final distillation from fermented broth. In this case, 12.1 g alcohol corresponds to an 85.5% conversion rate based on the theoretical values of the starch content. When the initial broth contained 40 g cassava starch, 14.1 g of alcohol was recovered, where 14.1 g corresponds to a 74.5% conversion rate. The alcoholic fermentation process described in the present work is considered more effective and reasonable than the process using raw starch without cooking reported until now, since the new process makes it unnecessary to add yeast cells and glucoamylase preparation.

Selection of raw-starch digestive glucoamylase-producing Rhizopus strain.

“…Based on Fujio et al (2), the Rhizopus strains and A. niger reference strain were pre-cultured in potato dextrose agar (PDA) slopes for 10 days. One milliliter of spore of each strain was inoculated into the medium consisting of 20 g wheat bran, 2 g corn starch (Wako Pure Chemical Industries, Ltd., Tokyo, Japan) and 20 ml tap water, pre-sterilized at 121°C for 15 mm in cotton plugged 500 ml Erlenmeyer flasks.…”

“…The former can digest both soluble and insoluble raw starch particles but the latter can digest only soluble starch. The raw starch digestive activity (GARS) could be beneficial in the viewpoint of energy saving, because the saccharification of starch can be carried out without gelatinization by cooking (2). This special enzyme characteristic was utilized for possible industrial applications such as the production of ethanol from uncooked starch (6).…”

Recent Advances in Microbial Raw Starch Degrading Enzymes

“…To date, RSDE have been tried in production of ethanol [27,44,[113][114][115][116][117][118][119][120][121], organic acids [122], amino acids [123], cyclodextrin [124], and SCP [125]. Among them, the application in ethanol production was the most developed technology.…”

Production of l-lactic acid by Rhizopus species

“…Rhizopus oyzae 2710 and R. oyzue 28627 produced the highest concentrations of ethanol (25 and 16 g/l, respectively) ( Table 1). Fujio et al (1984) demonstrated that certain Rhizopus strains could also produce ethanol from raw cassava starch.…”