Carbon dioxide (CO₂) is a safe and inexpensive gas that is used as a food additive. In this study, microbial control by pressurized CO₂ was examined. Pre-solubilization of CO₂ at 1MPa at 4°Cmarkedly decreased the heat tolerance of vegetative bacterial cells through acidification of intracellular pH. Further, a 5- to 6-log reduction in vegetative bacterial cells was observed after incubation at around 60°Cfor 1 min. The inactivation effect of pressurized CO₂ on bacterial spores was increased in the presence of monoglycerol monocaprate (MC10; 0.05% w/v). The pressurized CO₂ accelerated MC10 adhesion to the spores as well as the release of dipicolinic acid from the spores, considerably decreasing physiological germination and/or heat resistance. When pressurized CO₂ was applied during the fermentation of sardine fish sauce, the salt concentration required for the inhibition of undesirable microorganism growth was reduced from 20% to 10%. In addition, the reduction of salt in fish sauce improved its nutritional and sensory qualities compared to that produced by the conventional method. These findings support the practical application of CO₂ for microbial control in foods and contribute to the development of improved food processing methods.

Cultured ayu (Plecoglossus altivelis) are screened out at different growing stages of seed production; these larvae are typically underutilized. In this study, the chemical composition and antioxidant activities of the edible parts of these screened ayu (average body weight: 0.65-63.5g) were analyzed. Juvenile cultured ayu with an average body weight of 0.65g were totally edible (100%). On the other hand, for ayu weighing 7.59-63.5g, edible parts accounted for 27.4-28.1% (w/w) of body weight. The ratio of n-3 fatty acids to total fatty acid, amounts of total free amino acids and several minerals (Na, Ca, P and Zn), and antioxidant activities were all highest in juveniles and decreased significantly as the growing stage became later. Considering the possibility of easier storage and longer shelf life, four rice cracker samples blended with the edible parts of cultured ayu were produced for sensory evaluation. The results showed that producing rice crackers containing ayu muscle, juvenile fish and potato starch was an efficient way to utilize cultured ayu that had been screened out at different growing stages of seed production.

Based on the production method for “funa-narezushi,” which has a long fermentation period, we established technology to manufacture “ayu-narezushi” made from ayu (Plecoglossus altivelis altivelis). The pH of raw ayu is 6.15. After 10 months of fermentation, the pH in the muscle portion of narezushi drops to between 4.20 and 4.70, and to between 4.00 and 4.65 in nare-meshi. The predominant microorganisms in ayu-narezushi were Lactobacillus sp. (2.57±0.2×10⁴－1.13±0.46×10⁹ cfu/g), mold or yeast (2.95±0.07×10⁴－2.0±0.0×10⁸ cfu/g), and Bacillus sp. (2.83±0.74×10³－2.26±0.23×10⁴ cfu/g). Based on microflora analysis using a next-generation sequencer, the predominant bacteria in fermented ayu-hon-narezushi belonged to the genera Lactobacillus, Tetragenococcus and Staphylococcus. After 10 months of fermentation, the free amino acid content in nare-ayu-zushi increased seven-fold from that in raw ayu, and 10- to 15-fold in nare-meshi from that in meshi. In particular, the glutamic acid and hydrophobic amino acid content increased in both the fish and the rice. We isolated Lactobacillus buchneri, L. parabuchneri and L. plantarum which produce γ-aminobutyric acid (GABA) from glutamic acid during fermentation. It is thought that these microorganisms also produce GABA in nare-zushi.

This study examined changes in hydrophilic oxygen radical absorbance capacity (H-ORAC) of fruits from one line and four cultivars of strawberry (Fragaria × ananassa Duch.) harvested thorough January to April. The H-ORAC of strawberry fruits changed significantly (p<0.01) over the course of harvest time, showing a tendency to increase from winter to spring. Total anthocyanin content and total polyphenol content in strawberry fruits were both highly correlated to H-ORAC (r＝0.83 and 0.97, respectively). Total soluble solids and titratable acidity were not significantly correlated with H-ORAC (p<0.01). Compared to the other four cultivars, strawberry line “Kurume 66” exhibited potent H-ORAC with higher anthocyanin and polyphenol contents.