Distribution of D-amino acids in vinegars and involvement of lactic acid bacteria in the production of D-amino acids.

Levels of free D-amino acids were compared in 11 vinegars produced from different sources or through different manufacturing processes. To analyze the D- and L-amino acids, the enantiomers were initially converted into diastereomers using pre-column derivatization with o-phthaldialdehyde plus N-acethyl-L-cysteine or N-tert-butyloxycarbonyl-L-cysteine. This was followed by separation of the resultant fluorescent isoindol derivatives on an octadecylsilyl stationary phase using ultra-performance liquid chromatography. The analyses showed that the total D-amino acid level in lactic fermented tomato vinegar was very high. Furthermore, analysis of the amino acids in tomato juice samples collected after alcoholic, lactic and acetic fermentation during the production of lactic fermented tomato vinegar showed clearly that lactic fermentation is responsible for the D-amino acids production; marked increases in D-amino acids were seen during lactic fermentation, but not during alcoholic or acetic fermentation. This suggests lactic acid bacteria have a greater ability to produce D-amino acids than yeast or acetic acid bacteria.

Phenolic compounds responsible for the superoxide dismutase-like activity in high-Brix apple vinegar.

High-Brix apple vinegar (HBAV) with palatable drinking qualities has been developed using a greater amount of apple ingredients. In HBAV and in regular apple vinegar (RAV), constituents of 4 kinds of organic acids, 20 kinds of amino acids, 3 kinds of sugars, 4 kinds of minerals, and phenols were determined. These constituents, except for acetic acid, in HBAV are of higher abundance than in RAV. HBAV had a 7.1 times greater superoxide dismutase (SOD)-like activity compared with RAV. Those constituents, except for phenols, had very low SOD-like activity, and total phenol levels in HBAV were comparable to 181 mg of gallic acid equivalents/100 mL, which was 6.0 times more abundant than in RAV. Nine kinds of phenols including two kinds of hydroxycinnamates, two kinds of hydroxybenzoates, and five kinds of hydroxycinnamoyl quinates, originating from raw material were determined, but there were no ascorbic acid and flavonoids in HBAV. Chlorogenic acid, 4-p-coumaroylquinic acid, and caffeic acid were the three major phenols, and their content levels were 19.6, 13.5, and 0.76 mg in 100 mL of HBAV, respectively. Sum of contents of chlorogenic acid and the isomers was 24.0 mg/100 mL, and the percentage was 56.9% in the total identified phenols in HBAV. In RAV, only chlorogenic acid was determined as phenols, and the content was 3.1 mg/100 mL. SOD-like activities of the constituents of HBAV were obtained through high-accuracy assays using vinegar reconstitutions, and each contribution to the total SOD-like activity was found. As a result, 77.2% for all SOD-like activity of HBAV was reconstituted using the determined nine phenols and other constituents. Chlorogenic acids were the most effective, and the contribution to the total activity was 41.7%. The most abundant phenols, chlorogenic acids, were the most important contributors to the SOD-like activity. These SOD-active phenols originated from raw material and remained through the acetic acid fermentation processes. In the fermentation process of HBAV, the active constituents were well maintained, providing an advantage in the production of a phenol-rich product.

Saltiness and acidity: detection and recognition thresholds and their interaction near the threshold.

Interaction of saltiness and acidity at the threshold level was studied employing 35 to 40 young female panelists. As a 1st step, the detection and recognition thresholds of salt, rice vinegar, and rice black vinegar have been measured for each panelist. To investigate the above interaction, the thresholds have been again measured for each panelist of salt, but this time, vinegar at half the concentration of each panelist's detection threshold was added to the salt solution. Similar measurement has been performed for vinegars with salt at half the concentration of each panelist's detection threshold. The data analysis has been done in 2 ways, namely, (1) by using Student's t-test to detect the significant difference in average between the data with and without the added ingredient and (2) detecting significant deviations from zero in the individual shifts in 2 sensory tests among panelists who participated in the 2 measurements. In doing that, a conversion of the scale was necessary to correct the systematic skewness existing in the original data. As a result, both the detection and recognition thresholds of salt were decreased with the existence of the added vinegar ingredient (P < 0.001). This tendency was more pronounced with rice black vinegar than with rice vinegar. On the contrary, no significant changes in the threshold of both detection and recognition were observed when salt at the half concentration of the detection threshold was added to rice vinegar. The interaction therefore was found to be asymmetric.