Production and analysis of volatile flavor compounds in sweet fermented rice (Khao Mak)

¹ Department of Agricultural Engineering for Industry, Faculty of Industrial Technology and Management, King Mongkut's University of Technology North Bangkok Prachinburi Campus, Prachinburi, Thailand
² Department of Agro-Industrial, Food and Environmental Technology, Faculty of Applied Science, Food and Agro-Industry Research Center, King Mongkut’s University of Technology North Bangkok, Bangkok, Thailand
³ Department of Bioresource Technology, National Institute of Technology, Okinawa National College of Technology, Okinawa, Japan

^* Corresponding author: jittimon.w@fitm.kmutnb.ac.th

Abstract

Khao Mak is a sweet fermented rice-based dessert with a unique flavor profile commonly found throughout Thailand. The traditional starter culture (Look Pang) contains yeast, mold and herbs, which is used to ferment cooked glutinous rice. This research studied production of Khao Mak which resulted in volatile flavor compounds that were affected by rice varieties, including white glutinous rice (Kor Khor 6), Japanese rice (Hitomebore) and black glutinous rice (Kam Doi and Leum Phua). Total soluble solids (TSS) as degree Brix, pH, and alcohol concentrations were measured daily during the fermentation period. Volatile flavor compounds were separated and identified by gas chromatography mass spectrometry (GC-MS). At the end of the fermentation, samples had pH ranging from 3.91±0.16 to 4.30±0.09, total soluble solids of 32.65±1.65 to 44.02±1.72°Brix, and alcohol concentrations between 0.33±0.03 and 0.38±0.03% (v/v). The potent odors associated with Khao Mak were alcohol, wine-like, whiskey-like, solvent-like, sweet and fruity. The major volatile compounds, which have stimulant flavor in Khao Mak, included 1-propanal, 1-propanol-2-methyl, 1-butanal-3-methyl and acetic acid ethyl ester. Among all rice varieties tested, the white glutinous rice produced Khao Mak containing the highest TSS, alcohol concentrations followed by Hitomebore rice and black glutinous rice, respectively.