Satomi Tsutsuura’s research while affiliated with Niigata University and other places

2,5-Dimethylpyrazine (2,5-DMP) and 2,3,5-trimethylpyrazine (T3MP) are flavor compounds in natto. Threonine seems to relate to the formation of these pyrazines by Bacillus subtilis var. natto (Bacillus natto), although the mechanism is unclear. When B. natto was cultured in minimal medium supplemented with L-threonine, L-glutamic acid, or L-serine, both 2,5-DMP and T3MP were formed only in the culture supplemented with L-threonine. Next, B. natto was cultured in the medium supplemented with ¹³C4, ¹⁵N-labeled L-threonine. ¹³C and ¹⁵N were incorporated into 2,5-DMP, T3MP, and aminoacetone during culture, suggesting that these compounds are formed from ¹³C4, ¹⁵N-labeled L-threonine through threonine metabolism by B. natto. When B. natto was cultured on steamed soybean, the amounts of threonine and aminoacetone increased, followed by the formation of 2,5-DMP and T3MP. These results show that 2,5-DMP and T3MP in natto are mainly formed through threonine metabolism by B. natto instead of Strecker degradation.

Aquaponics is a sustainable food production system that combines aquaculture and hydroponics. However, limited studies focused on the nutritional and functional properties of aquaponic produce. Thus, this study aimed to explore the nutritional and functional components of four leaf lettuce lines with different colors cultivated in a commercial aquaponic farm in four seasons from summer 2022 to spring 2023. The leaf lettuce lines grown in aquaponics had high levels of micronutrients such as vitamin C, vitamin K, and folic acid, with the levels of vitamin K and folic acid meeting Japan's health claim criteria. The lettuce lines, especially red leaf lettuce, were also rich in bioactive compounds such as nitrate ions, which are linked to blood pressure regulation, and antioxidants such as anthocyanins and chlorogenic acid. These findings suggest that leaf lettuce grown in aquaponics has potential use as a high-value functional food.

High-pressure treatment was utilized in this study to produce high-quality, reduced-sodium pork gels with desirable texture and sensory properties, addressing the challenge of maintaining quality in low-sodium meat products to meet health-conscious consumer demands. High-pressure treatment applied within the range of 150–200 MPa significantly reduced cooking loss while maintaining moisture content and provided an ideal network structure for reduced-sodium pork gels. High-pressure treatment at up to 100–200 MPa, in combination with added sodium chloride and sodium polyphosphate, was evaluated for its effects on gel texture, with results indicating that high-pressure treatment significantly improved breaking stress (increased by 10.01% under 150 MPa and 14.66% under 200 MPa), modulus of elasticity (increased by 14.77% under 150 MPa and 24.17% under 200 MPa), and hardness (increased by 11.12% under 150 MPa and 11.45% under 200 MPa). Rheological characteristic measurements revealed that gel strength was highest at 150 MPa (G′ = 443,000 Pa; G″ = 66,300 Pa and tanδ = 0.15), which showed higher G′ and G″ values and similar tanδ compared to the 0.1 MPa, 2% NaCl + 0.5% SPP condition (G′ = 334,000 Pa; G″ = 49,200 Pa; tanδ = 0.148). Protein analysis by sodium dodecyl sulfate–polyacrylamide gel electrophoresis showed a reduction in the α-actinin band with increased pressure, which suggested protein interactions were enhanced. Differential scanning calorimetry analysis indicated that protein denaturation occurred more readily at higher pressures (0.071 J/g at 0.1 MPa, 0.057 J/g at 150 MPa, and 0.039 J/g at 200 MPa). These findings underscore the value of treatment under high pressure at 150 MPa developing reduced-sodium meat products with desirable texture and flavor characteristics.

Infectious and foodborne diseases pose significant global threats, with devastating consequences in low- and middle-income countries. Ozone, derived from atmospheric oxygen, exerts antimicrobial effects against various microorganisms, and degrades fungal toxins, which were initially recognized in the healthcare and food industries. However, highly concentrated ozone gas can be detrimental to human health. In addition, ozonated water is unstable and has a short half-life. Therefore, ultrafine-bubble technology is expected to overcome these issues. Ultrafine bubbles, which are nanoscale entitles that exist in water for considerable durations, have previously demonstrated bactericidal effects against various bacterial species, including antibiotic-resistant strains. This present study investigated the effects of ozone ultrafine bubble water (OUFBW) on various bacterial toxins. This study revealed that OUFBW treatment abolished the toxicity of pneumolysin, a pneumococcal pore-forming toxin, and leukotoxin, a toxin that causes leukocyte injury. Silver staining confirmed the degradation of pneumolysin, leukotoxin, and staphylococcal enterotoxin A, which are potent gastrointestinal toxins, following OUFB treatment. In addition, OUFBW treatment significantly inhibited NF-κB activation by Pam3CSK4, a synthetic triacylated lipopeptide that activates Toll-like receptor 2. Additionally, OUFBW exerted bactericidal activity against Staphylococcus aureus, including an antibiotic-resistant strain, without displaying significant toxicity toward human neutrophils or erythrocytes. These results suggest that OUFBW not only sterilizes bacteria but also degrades bacterial toxins.

This study aimed to clarify the effects of deep-sea pressure storage on the quality of whale meat, especially microbiological safety and physical properties, to examine the effectiveness of deep-sea storage for long-term aging of whale meat. Microbiological safety, physical properties, color and appearance, water content, water activity, and pH of whale meat were examined after storage in the deep sea at depths of 2200–6000 m (22–60 MPa) for 4 months. During storage under high pressure at a depth of >4000 m (40 MPa), the growth of aerobic bacteria was inhibited in whale meat. The toughness of whale meat stored in deep sea at a depth of >4000 m became significantly tender than that before deep-sea storage. Long-term storage of whale meat under high pressure and low-temperature conditions in the deep sea at a depth of >4000 m was clarified to improve the microbiological safety and tenderness of whale meat.

Raw and/or insufficient heat-cooked chicken meats are the major vehicles of human campylobacteriosis in Japan. These often cause human foodborne salmonellosis as well. Hence, the establishment of effective treatments for reduction of these pathogens from chicken meats in combination with heat processing is an important issue for food safety. In this study, the effects of high hydrostatic pressure (HHP) treatment prior to heat cooking for reduction of foodborne pathogens in cooked chicken meat was examined. Raw yakitori (Japanese chicken brochette) samples which were treated with HHP at 500 MPa for 10 min showed negative results of Campylobacter and Salmonella by detection methods after cooking at 200̊C for 5 min. On the other hand, HHP treatments with 300 MPa and 400 MPa for 10 min were not sufficient for inactivation of these pathogens under condition used in this study. Color and hardness of the HHP-treated yakitori samples were almost comparable to the samples without HHP treatment after cooking. These results suggest the effectiveness of HHP treatment prior to heat cooking to reduce the foodborne cases caused by insufficient cooked meats.

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