Soon-Mi Shim

Metabolite profiling of doenjang, fermented soybean paste, during fermentation

BACKGROUND A fermented soybean paste known as doenjang is a traditional fermented food that is widely consumed in Korea. The quality of doenjang varies considerably by its basic ingredients, species of microflora, and fermentation process. The classification of predefined metabolites (e.g. amino acids, organic acids, sugars and sugar derivatives, and fatty acids) in doenjang samples according to fermentation was performed by using GC-FID and GC-MS data sets with the application of a multivariate statistical method. RESULTS The predominantly produced amino acids included alanine, valine, leucine, isoleucine, proline, glutamine, phenylalanine and lysine, showing remarkable increases in amounts during the later stages of fermentation. Carbonic acid, citric acid, lactic acid and pyrogultamic acid were identified as the major organic acids. Significant amounts of erythrose, xylitol, inositol and mannitol were detected during fermentation. Regarding fatty acids, relatively higher amounts of palmitic acid, stearic acid, oleic acid, linoleic acid and linolenic acid were found in the doenjang at each fermentation time point. Principal component analysis (PCA) successfully demonstrated changes in composition patterns as well as differences in non-volatile metabolites according to fermentation period. CONCLUSION A set of metabolites could be determined representing the quality of doenjang during fermentation, and which might also be correlated with taste ingredients, flavour, nutrition, and physiology activities that are claimed to be dependent on the quality control of commercial doenjang.

Metabolite Profiling of Cheonggukjang, a Fermented Soybean Paste, Inoculated with Various Bacillus Strains during Fermentation

Metabolite profiling of Cheonggukjang inoculated with different Bacillus strains including Bacillus amyloliqueciens CH86-1, Bacillus licheniformis 58, and Bacillus licheniformis 67 during fermentation, was performed using gas chromatography-time of flight-mass spectrometry after derivatization, combined with multivariate statistical analysis. A total of 20 amino acids, 10 sugars, five sugar alcohols, and seven organic acids were identified in three Cheonggukjang samples. With fermentation time, most of the amino acids showed increasing amounts. On the other hand, most of the sugars including sucrose, fructose, and glucose decreasing patterns, and the amounts of organic acids varied. In order to observe differences in metabolites with fermentation time and inoculated Bacillus strains, principal component analysis (PCA) and partial least squares discriminant analysis (PLS-DA) were carried out, respectively. On PCA plots, some sugars and organic acids including sucrose, fructose, glucose, mannose, succinic acid, and malonic acid, as well as most of the amino acids, contributed mainly to differentiation of the Cheonggukjang samples fermentation time. On the other hand, on PLS-DA, mannose, xylose, glutamic acid, and proline were mainly responsible for differentiating the Cheonggukjang among into various inoculated strains.

Profiling of fermentative metabolites in kimchi: Volatile and non-volatile organic acids

Gas chromatograph/mass spectrometry (GC/MS) analysis was carried out to determine both the volatile and nonvolatile organic acids in kimchi during 60 days of fermentation at 10°C. Principal component analysis (PCA) was applied to differentiate the pre-defined organic acids and lactic acid bacteria (LAB) during fermentation. Acetic acid was observed as dominant, which was vigorously produced until the middle of fermentation. Lactic acid was the major non-volatile organic acid in the kimchi and was produced throughout fermentation. In contrast, malic acid content decreased sharply at the initial stage of fermentation. Colony forming units of LAB in the kimchi, such as Leuconostoc, Lactobacilli, Pediococci, and Streptococci, were measured on selective media. Populations of Leuconostoc and Lactobacilli increased exponentially over 7 days of fermentation, indicating acetic acid and lactic acid were mainly produced by Leuconostoc and Lactobacilli. PCA demonstrated that acetic acid, propionic acid, lactic acid, butanoic acid, malic acid, Leuconostoc, and Lactobacilli were major components that differentiated the kimchi according to fermentation time.

Metabolites of amygdalin under simulated human digestive fluids

Abstract In the present study, degradation of amygdalin in the human digestive fluids and absorption of its metabolites by the human small intestine were evaluated by simulating a gastrointestinal digestion model combined with a human intestinal cell culture. Orally administered amygdalin was degraded into prunasin by digestive enzymes after passing through the salivary and gastrointestinal phases. Prunasin, the major metabolite of amygdalin in the digestive fluids, was incubated in a caco-2 cell culture system. Prunasin was degraded into the mandelonitrile by β-glucosidase and then hydroxylated across the small intestinal wall, producing hydroxymandelonitrile (149 Da). Results from this study suggest that risk assessment of amygdalin from food consumption can be done in a more accurate way by determining a pathway of amygdalin metabolism in the simulating human upper gastrointestinal tract.

Bioaccessibility of Total Sugars in Carbonated Beverages and Fermented Milks

Bioaccessibility of total sugars in foods significantly contributing to sugar intake of young children in Korea was estimated. Three phases of in vitro digestion model were performed for measuring the bioacessibility of total sugars from carbonated beverages and fermented milks in limited sampling. High Performance Liquid Chromatography (HPLC) analysis was carried out for determination of sugars. Total sugars in carbonated beverages ranged from 9.23 to 13.05 g/100 g, which is 1.1 times higher than that found in fermented milks, ranging from 8.13 to 12.86 g/100 g. Major sugars found in carbonated beverages were fructose and glucose, whereas most fermented milks mainly contained lactose and sucrose. Bioaccessibility of total sugars in carbonated beverages ranged from 54.6 to 69.4%, whereas in fermented milks were from 11.8 to 85.0%. This in vitro digestion model provides estimation of total sugars released from various food matrixes, which can be used to predict their bioavailability.