Feasibility of Leum Pua glutinous rice substrate for sugar syrup and vinegar production by raw starch degrading enzyme hydrolysis

Raw starch degrading enzyme (RSDE) from Laceyella sacchari LP175 was applied for hydrolysis of Leum Pua glutinous rice powder (200 g/L) and compared with other brown and black rice varieties in 250 mL Erlenmeyer flasks at 50 degrees C for 12 h. Results showed that Leum Pua glutinous rice gave the highest liberated sugar syrup and anthocyanin contents at 11 degrees Brix and 82.27 mg/L, respectively. Leum Pua glutinous rice powder (250 g/L) was up-scaled for hydrolysis in 5.0 L glass jar by simultaneous liquefaction and saccharification at 50 degrees C for 12 h and obtained liberated sugar syrup at 13 degrees Brix. Sugars were fermented by two mixed strains of Saccharomyces cerevisiae for 10 d without shaking at room temperature. During fermentation, total soluble solids decreased from 22 to 10 degrees Brix while alcohol content increased to 15% (w/v). Leum Pua glutinous rice wine was subjected to acetic acid surface culture fermentation (SCF) with Acetobacter aceti TISTR 354 at room temperature. After 6 d of fermentation, acidity of Leum Pua glutinous rice vinegar increased to 5.7%. Antioxidant activity and vinegar concentration were determined during acetic acid fermentation for 6 d. Results suggested the feasibility of producing Thai rice vinegar using cold hydrolysis with raw starch degrading enzyme without the heating process. (C) All Rights Reserved