A Savory Odorant in Sweet Potato Shochu: 2-Methyl-3-(Methyldithio)-Furan

The purpose of this work is to determine the key odorants (KO) in shochu, a Japanese spirit made from sweet potato, barley, rice, soba, or sugarcane extract fermented with 20% rice koji. Each carbohydrate source produces a mild flavored spirit, but sweet potato produces shochu with a strong savory character.

The KOs released by sweet potato, barley, rice, and sugarcane shochus were determined using headspace solid-phase micro-extraction (HS-SPME), gas chromatography-olfactometry (GC-O) dilution analysis to determine aroma characteristics, gas chromatography-mass spectrometry (GC-MS), and authentic standards to determine identity.

The five top KOs found in sweet potato shochu were ethyl octanoate, ethyl cinnamate, 2-methyl-3-furanthiol, β-damascenone, 2-methyl-3-(methyldithio)-furan. The five top KOs in barley, rice, and sugarcane shochus were ethyl octanoate, ethyl hexanoate, isoamyl acetate, ethyl 2-methylbutanoate, and ethyl isobutyrate.

The unique savory aroma of sweet potato was found to have higher levels of ethyl cinnamate, 2-methyl-3-furanthiol, and 2-methyl-3-(methyldithio)-furan while the five top KOs in barley-, rice-, and sugarcane-derived shochus were esters common in most alcoholic fermentations.

There is growing evidence that a small number of odorants determine our perception of food aroma. The first challenge is to determine what these key odorants are and second to determine the rules used by the olfactory system to create odor images. This research identifies candidates for the unique aroma of sweet potato shochu.