Application of graphite carbon black assisted-laser desorption ionization-mass spectrometry for soy sauce product discrimination.

In a previous study, we developed a novel analytical method to directly and simultaneously detect taste- and odor-active compounds using graphite carbon black (GCB)-assisted laser desorption ionization mass spectrometry (LDI-MS). In this study, we aimed to evaluate food quality using a variety of soy sauces using the method to discriminate each product. Graphite carbon black-laser desorption ionization-mass spectrometry allowed the provision of hundreds of MS peaks derived from soy sauces in both positive and negative modes without any tedious sample pretreatments. Principal component analysis using the obtained MS peaks clearly distinguished three soy sauce products based on the manufacturing countries (Japan, China, and India). Moreover, this method identified distinct MS peaks for discrimination, which significantly correlated with their quantitative amounts in the products. Thus, GCB-LDI-MS analysis was established as a simple and rapid technique for food analysis, illustrating the chemical patterns of food products.

Key compounds contributing to the fruity aroma characterization in Japanese raw soy sauce.

In order to clarify the aroma characteristics of raw soy sauce (RS), the application of gas chromatography-olfactometry analysis to the aroma concentrate from a RS revealed 76 aroma peaks, of which 25 peaks showed fruit-like aromas. Furthermore, the head space aromatic compounds of RS were analyzed with 32 peaks detected. Ethyl 2-methylpropanoate, ethyl butanoate, ethyl 2-methylbutanoate, ethyl 3-methylbutanoate, and ethyl 4-methylpentanoate were detected with higher flavor dilution factor (FD factor) than other aroma compounds by aroma extract dilution analysis. Quantitative analysis suggested that these compounds were common in all RS samples tested in this study, and were present at higher concentrations than their perception thresholds. The concentrations and the FD factors of these compounds were significantly decreased during the heating of the RS. Fruitiness is one of the key aroma characteristics of RS and the ethyl esters identified in this study are the key components contributing to this distinct aroma.

Contribution of 2-methyl-3-furanthiol to the cooked meat-like aroma of fermented soy sauce.

The cooked meat-like aroma compound, 2-methyl-3-furanthiol (2M3F), was detected in fermented soy sauce (FSS) by GC-olfactometry and GC-MS. 2M3F was present in FSS at a concentration considerably greater than the perception threshold, and the 2M3F concentration increased with heating temperature. Sensory analysis indicated that with the addition of only 0.2 µg/L of 2M3F to the soy sauce sample, the cooked meat-like aroma is significantly stronger than that of sample without the addition of 2M3F. Hence, 2M3F contributes to the cooked meat-like aroma of FSS, which constitutes the key aroma component of FSS. In addition, 2M3F was generated from the addition of ribose and cysteine in FSS by heating at 120 °C, but it was not detected in a phosphate buffer under the same condition. Furthermore, 2M3F was not detected in acid-hydrolyzed vegetable-protein-mixed soy sauce (ASS) and heated ASS. These results indicated that fermentation by micro-organisms facilitates the generation of 2M3F in FSS.

Metabolic profiling approach to explore compounds related to the umami intensity of soy sauce.

A metabolic profiling approach was employed to explore the compounds that affect the intensity of umami taste in soy sauce. Twenty-five kinds of soy sauces were analyzed using GC-MS and LC-MS, wherein measurement data for 427 compounds were obtained. The umami taste intensity of each soy sauce sample was also quantitated by sensory evaluation and a projection to latent structure (PLS) regression analysis was conducted using the compounds' measurements and umami taste intensity data. Variable importance for the projection (VIP) value obtained via PLS was used for the estimation of the relevance for umami taste intensity. N-(1-Deoxyfructos-1-yl)glutamic acid (Fru-Glu) had the highest VIP value, and addition of Fru-Glu to soy sauce increased umami taste intensity better than glutamic acid at the same concentration as confirmed by sensory evaluation. This study showed that the combination of metabolic profiling approach and sensory evaluation can be used effectively to determine compounds related to taste.

Analysis of the correlation between dipeptides and taste differences among soy sauces by using metabolomics-based component profiling.

Characterizing the relationships between the components and taste differences among soy sauces can help evaluate and improve the quality of soy sauces. Although previous studies have reported that certain taste-active dipeptides, the relationships between taste differences and dipeptides of soy sauces are unknown. Therefore, our objective in this study was to investigate the correlations between the dipeptides and the taste differences among soy sauces. To analyze the dipeptides, we constructed an analytical method using liquid chromatography/tandem mass spectrometry (LC/MS/MS) in multiple reaction monitoring mode. Based on this method, we detected 237 dipeptides, the largest number ever detected in soy sauce research. Next, orthogonal projections to latent structures regressions were performed. The data matrix of components, including dipeptides and other low-molecular-weight hydrophilic components obtained from gas chromatography/mass spectrometry (GC/MS), served as explanatory variables (366 in total), whereas a sensory data matrix obtained using quantitative descriptive analysis served as the response variable. The accuracy of models for the sweetness and saltiness differences constructed using the LC/MS/MS and GC/MS data matrix were higher than did models constructed using only the GC/MS data matrix. As a result of investigation of the correlation between the dipeptides and taste differences among soy sauces by using variable importance in the projection (VIP) score, many dipeptides showed the high correlation with taste differences. Specifically, Ile-Gln, Pro-Lys, Ile-Glu, Thr-Phe, and Leu-Gln showed the high VIP score on sweet differences. This study is the first report that reveals the correlations between the dipeptides and taste differences among soy sauces.

Suppression of umami aftertaste by polysaccharides in soy sauce.

Umami is one of 5 basic tastes that make foods savory and palatable. The umami aftertaste is a long-lasting taste sensation that is important for Japanese broth (dashi) utilized for various Japanese foods. Soy sauce is usually added when making dashi-based dishes; however, different soy sauces produce distinct effects on the umami aftertaste. In this study, we attempted to identify the substances that cause the suppression of the umami aftertaste in soy sauce by combining sensory analysis, size fractionation, chemical analysis, and enzymatic treatment. The suppressive substance was revealed to be polysaccharides with molecular weights between 44900 and 49700. The results of acid hydrolysis and enzymatic treatment suggested that the polysaccharides were cellulose. These results indicate that a type of water-soluble cellulose derived from soybean, wheat, or microorganisms has a suppressive effect on the umami aftertaste of soy sauce. Future studies should focus on developing a strategy that regulates the amount of these polysaccharides generated during soy sauce production, to maintain or enhance the umami aftertaste.

Metabolite profiling of soy sauce using gas chromatography with time-of-flight mass spectrometry and analysis of correlation with quantitative descriptive analysis.

Soy sauces, produced from different ingredients and brewing processes, have variations in components and quality. Therefore, it is extremely important to comprehend the relationship between components and the sensory attributes of soy sauces. The current study sought to perform metabolite profiling in order to devise a method of assessing the attributes of soy sauces. Quantitative descriptive analysis (QDA) data for 24 soy sauce samples were obtained from well selected sensory panelists. Metabolite profiles primarily concerning low-molecular-weight hydrophilic components were based on gas chromatography with time-of-flightmass spectrometry (GC/TOFMS). QDA data for soy sauces were accurately predicted by projection to latent structure (PLS), with metabolite profiles serving as explanatory variables and QDA data set serving as a response variable. Moreover, analysis of correlation between matrices of metabolite profiles and QDA data indicated contributing compounds that were highly correlated with QDA data. Especially, it was indicated that sugars are important components of the tastes of soy sauces. This new approach which combines metabolite profiling with QDA is applicable to analysis of sensory attributes of food as a result of the complex interaction between its components. This approach is effective to search important compounds that contribute to the attributes.

Tissue distribution of antihypertensive dipeptide, Val-Tyr, after its single oral administration to spontaneously hypertensive rats.

The distribution of an antihypertensive dipeptide, Val-Tyr (VY), in the tissues of spontaneously hypertensive rats (SHR) was investigated in this study. A single oral administration of VY (10 mg/kg) to 18-week-old SHR resulted in a prolonged reduction of systolic blood pressure (SBP) up to 9 h (SBP0h 198.0+/-3.6 mmHg; SBP9h 154.6+/-3.5 mmHg). As a result of VY determination, a roughly 10-fold higher increment of plasma VY level was observed at 1 h than that at 0 h, whereas thereafter the level declined rapidly. In tissues, VY was widely accumulated in the kidney, lung, heart, mesenteric artery and abdominal aorta with the area under the curve over 9 h of more than 40 pmol h/g tissue; of these a higher VY level was observed in the kidney and lung. In addition, a mean resident time (MRT) for each tissue (>5 h except for liver) revealed that VY preferably accumulated in the tissues rather than in the plasma (MRT 3.8 h). Significant reductions of tissue angiotensin I-converting enzyme activity and angiotensin II level were found in the abdominal aorta as well as in the kidney, suggesting that these organs could be a target site associated with the antihypertensive action of VY.