Evaluation of onion juices quality following heat-treatment and their application as a sugar substitute in Kimchi

This study was conducted to evaluate the quality of onion juices that had been heat-treated for different times as well as their use as a table sugar substitute in Kimchi. The onions were steamed at 100 ∘C for 30 min and boiled at 90 ∘C for 30, 60, and 120 min. The highest cycloalliin (0.76 mM), free-sugar (sucrose 1.66 g/L, glucose 8.62 g/L, and fructose 7.64 g/L), and malic acid (0.82 g/L) contents were observed in onion boiled at 90 ∘C for 120 min. The possibility of using heat-treated onion juices as an alternative to table sugar in Kimchi was evaluated by comparing the lactic acid bacteria count, pH, acidity, organic acid, and free-sugar in these juices with those in Kimchi prepared using table sugar (control). The total viable bacteria and lactic acid bacteria showed similar growth patterns as in the control. The average pH reduction and increase in titratable acidity (%) in all treated Kimchi samples during fermentation for 4 weeks were 1.18 ± 0.05 and 0.81 ± 0.06, respectively. Kimchi with onion juice heat-treated for 120 min (K120) had the most similar lactic acid and acetic acid contents to that in the control after fermentation for 4 weeks. The highest mannitol level after fermentation for 4 weeks was detected in K120, which showed better sensory qualities compared to the control.

Effects of the predominant bacteria from meju and doenjang on the production of volatile compounds during soybean fermentation

We inoculated five starter candidates, Enterococcus faecium, Tetragenococcus halophilus, Bacillus licheniformis, Staphylococcus saprophyticus, and Staphylococcus succinus, into sterilized soybeans to predict their effectiveness for flavor production in fermented soybean foods. All of the starter candidates exhibited sufficient growth and acid production on soybean cultures. Twenty-two volatile compounds, such as acids, alcohols, carbonyls, esters, furans, and pyrazines, were detected from the control and starter candidate-inoculated soybean cultures. Principal component analysis of these volatile compounds concluded that E. faecium and T. halophilus produced a similar profile of volatile compounds to soybeans with no dramatic differences in soybean flavor. B. licheniformis and S. succinus produced the crucial volatile compounds that distinguish the flavor profiles of soybean. During soybean fermentation, phenylmethanol and 2,3,5,6-tetramethylpyrazine were determined as odor notes specific to B. licheniformis and 3-methylbutyl acetate as an odor note specific to S. succinus.

Safety and technological characterization of coagulase-negative staphylococci isolates from traditional Korean fermented soybean foods for starter development

To select starters for the production of meju and doenjang, traditional Korean fermented soybean foods, we assessed the safety and technological properties of their predominant isolates, Staphylococcus saprophyticus, Staphylococcus succinus and Staphylococcus xylosus. Phenotypic antibiotic resistance, hemolysis and biofilm formation were strain-specific. None of the S. succinus isolates exhibited antibiotic resistance or hemolytic activities. Thirty-three selected strains, identified through safety assessments of 81 coagulase-negative staphylococci (CNS) isolates, produced cadaverine, putrescine, and tyramine, but not histamine in the laboratory setting. The production of these three biogenic amines may, however, be insignificant considering the high levels of tyramine produced by the control, Enterococcus faecalis. The 33 CNS strains could grow on tryptic soy agar containing 21% NaCl (w/v), exhibited acid producing activity at 15% NaCl, and expressed strain-specific protease and lipase activities. S. succinus 14BME1, the selected starter candidate, produced significant amounts of benzeneacetic acid, 2,3-butanediol, trimethylpyrazine, and tetramethylpyrazine through soybean fermentation.

Reduction of aflatoxins (B₁, B₂, G₁, and G₂) in soybean-based model systems

The effects of chemical, physical, and cooking treatments on the reduction of aflatoxin B1 (AFB1), B2, G1, and G2 in soybean matrix were investigated. A HPLC-FLD with a Kobra cell system was used for the quantitative analysis of aflatoxins (AFs). To decrease the level of AFs during the soaking process, the contaminated soybeans were submerged in organic acid solutions. The reduction rates of AFB1 in 1.0N citric acid, lactic acid, succinic acid, and tartaric acid for 18h were 94.1%, 92.7%, 62.0%, and 95.1%, respectively. In the case of pH and autoclave treatment, the level of AFB1 was significantly decreased during autoclaving process at pH 7.4, 9.0, and 11.1, compared with the non-autoclaved samples (p<0.05). In the case of physical treatment, the heating process at 100 and 150°C for 90min significantly decreased the level of AFB1 by 41.9% and 81.2%, respectively (p<0.05). The reduction rate of AFB1 after cooking was 97.9% for soybean milk and 33.6% for steamed soybeans.

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Furan (C₄H₄O) is a volatile compound formed mostly during the thermal processing of foods. The toxicity of furan has been well documented previously, and it was classified as “possible human carcinogen (Group 2B)” by the International Agency for Research on Cancer. Various pathways have been reported for the formation of furan, that is, thermal degradation and/or thermal rearrangement of carbohydrates in the presence of amino acids, thermal degradation of certain amino acids, including aspartic acid, threonine, α-alanine, serine, and cysteine, oxidation of ascorbic acid at higher temperatures, and oxidation of polyunsaturated fatty acids and carotenoids. Owing to the complexity of the formation mechanism, a vast number of studies have been published on monitoring furan in commercial food products and on the potential strategies for reducing furan. Thus, we present a comprehensive review on the current status of commercial food monitoring databases and the possible furan reduction methods. Additionally, we review analytical methods for furan detection and the toxicity of furan.