Multifunctional-separation-mode ion chromatography method for determining major metabolites during multiple parallel fermentation of rice wine.

Facile and effective analysis methods are desirable for elucidating the behaviours of metabolites during fermentation reactions. Herein, a multifunctional-separation-mode ion chromatography (MFS-IC) method was developed for the simultaneous monitoring of major metabolites during multiple parallel fermentation, including those related to central carbon metabolism (saccharification, glycolysis, alcoholic fermentation, and the tricarboxylic acid (TCA) cycle). The use of two types of sulfo-modified size-exclusion columns and phthalic acid as the eluent allowed the separation of oligosaccharides (disaccharides, trisaccharides, and tetrasaccharides), glucose, pyruvate, and major organic acids during the TCA cycle (cis-aconitate, citrate, iso-citrate, malate, fumarate, and succinate but not α-ketoglutarate) from other non-target analytes. The MFS-IC method was successfully applied to monitoring the major metabolites in the rice wine brewing process. This approach can contribute to an improved understanding of metabolite behaviour during fermentation without requiring the use of expensive advanced instrumentation methods such as liquid chromatography-mass spectrometry and gas chromatography-mass spectrometry.

Reduction of the alcohol-stimulative taste of Japanese pot-distilled spirits.

The Japanese traditional pot-distilled spirit shochu has various tastes that are produced by variations in the manufacturing processes. In this study, an alcohol-stimulative taste was organoleptically evaluated using shochu samples, and the chemical components and proton nuclear magnetic resonance (1H NMR) spectra were measured. In some shochu samples, the alcohol-stimulative taste was weaker than that of the standard 15% (v/v) EtOH-H2O mixture, and the water-ethanol hydrogen-bonding structure was stronger compared to a water-ethanol solution. However, some shochu samples filtered with ion-exchange resin had a strong alcohol-stimulative taste comparable to that of the standard 15% (v/v) EtOH-H2O mixture, and the hydrogen-bonding structure was found to be similar to that of the water-ethanol solution. We also investigated the effect of MgCl2 on reducing the alcohol-stimulative taste, and it was observed most strongly with in shochu samples filtered with ion-exchange resin. The change in chemical shift values of the 1H NMR spectra was also the largest in ion-exchange resin filtered shochu samples. The sensory reduction in the alcohol-stimulative taste could be enhanced by the strengthening of the water-ethanol hydrogen-bonding structure. Shochu samples contained many components in larger quantities compared to vodkas. It was found that MgCl2 could reduce the alcohol-stimulative taste of shochu samples. Some salts, such as MgCl2, can be introduced into spirits through the water used to dilute the ethanol content before bottling the products. Our results indicated that some components, such as MgCl2, present in water used can reduce the alcohol-stimulative taste of different spirits produced worldwide.

Effects of solutes on the alcohol-stimulative taste of vodkas.

Quantitative analyses of chemical components and sensory tests were carried out on vodka samples to test for stimulative taste of ethanol. Proton nuclear magnetic resonance (1H NMR) spectra of the vodkas were measured with 600 MHz NMR. The effects of salts on the alcohol-stimulative taste were investigated for 15% (v/v) EtOH-H2O solution. 1H NMR spectroscopy results showed that a magnesium salt could reduce the stimulative taste of ethanol organoleptically and, at the same time, strengthen the hydrogen-bonding structure of water-ethanol, although the effect of the magnesium could not be clarified quantitatively in the products of vodka. It was also suggested that a change in the water-ethanol hydrogen-bonding structure could lead to a reduction in the stimulative taste of ethanol in vodka.

Hydrogen bonding of water-ethanol in alcoholic beverages.

An alcoholic beverage is a type of water-ethanol solution with flavor and taste. The properties of the hydrogen bonding of water-ethanol in alcoholic beverages have not been clarified sufficiently. We investigated factors that could affect the hydrogen-bonding structure of water-ethanol on the basis of proton nuclear magnetic resonance (1H NMR) chemical shifts of the OH of water-ethanol and Raman OH stretching spectra. Not only acids (H+ and HA: undissociated acids) but also bases (OH- and A-: conjugate-base anions from weak acids) strengthened the hydrogen-bonding structure of water-ethanol. It was also demonstrated that the hydrogen bonding is strengthened by chemical components in alcoholic beverages (whiskey, Japanese sake, shochu). It can be suggested that hydrogen-bonding donors as well as acceptors in alcohol beverages, which exist as the initial components or are gained later on, should cause the tight association between water and ethanol molecules.

Hydrogen bonding in alcoholic beverages (distilled spirits) and water-ethanol mixtures.

The hydrogen-bonding properties of water-ethanol of alcoholic beverages and water-ethanol mixtures of the corresponding ethanol contents were examined on the basis of OH proton NMR chemical shifts and the Raman OH stretching spectra of water and ethanol. Japanese shochu, an unaged distilled spirit of 25% (v/v) alcoholic content made from various grains, was provided for the samples; it is a high-purity spirit as it contains only small amounts of dissolved components, like typical vodka, gin, and white rum. The hydrogen-bonding structure in shochu containing some acids was found to be different from that of the water-ethanol mixture with corresponding ethanol content. It was concluded that, by the presence of small amounts of organic acids, the water-ethanol hydrogen-bonding structure was strengthened, at the same time, the proton exchange between water and ethanol molecules was promoted in shochu, compared with the water-ethanol mixture. The NMR chemical shifts of fruit cocktail drinks suggested that the hydrogen bonding of water-ethanol in the solution was developed by organic acids and (poly)phenols from fruit juices.

Proton nuclear magnetic resonance and Raman spectroscopic studies of Japanese sake, an alcoholic beverage.

The hydrogen-bonding property of water--ethanol in Japanese sake, a kind of brewage, was examined on the basis of both (1)H NMR chemical shifts of the OH of water--ethanol and the Raman OH stretching spectra. In 20% (v/v) EtOH-H(2)O solution, amino acids as well as organic acids caused low-field chemical shifts, i.e., the development of a hydrogen-bonding structure. Additional functional groups, apart from the essential amino- and carboxyl groups, in amino acids caused differences in their effects. The low-field chemical shifts caused by solutes were demonstrated under constant pH conditions maintained by sodium hydrogen citrate. Using both the measurement of (1)H NMR chemical shifts and Raman OH stretching spectra, the strength of the hydrogen bond of water--ethanol in Japanese sake products was found to be correlated with the total concentration of organic acids and amino acids. Glucose or saccharides should not have a strengthening effect on the hydrogen bond of water--ethanol. The effects of the main inorganic ions and amines were also discussed. It was concluded that chemical components originating from the starting material, rice, or products produced by microorganisms during the ethanol fermentation affect the hydrogen-bonding structure in Japanese sake.

Solute effects on the interaction between water and ethanol in aged whiskey.

The hydrogen-bonding structure of water-ethanol in whiskey was examined on the basis of (1)H NMR chemical shifts of the OH of water and ethanol. Phenolic acids and aldehydes (gallic, vanillic, and syringic acids; vanillin and syringaldehyde) exhibited their structure-making effects regardless of the presence or absence of 0.1 or 0.2 mol dm(-3) acetic acid. The OH-proton chemical shifts were measured for 32 malt whiskey samples of a distillery, aged for 0-23 years in five different types of casks. The OH-proton chemical shift values of the whiskies shifted toward the lower field in proportion to their contents of total phenols. It can be concluded that the strength of the hydrogen bonding in aged whiskies is directly predominated by acidic and phenolic components gained in oak wood casks and not dependent on just the aging time.