We investigated the effects of α-casein (α-CN) and sodium caprate (NaC_{10 : 0}) on the formation of mixed gels with ovalbumin (OVA) using rheological measurement, ultrasound spectroscopy, flourier transform-infrared (FT-IR) analysis and scanning electron microscopy (SEM) observation. Although α-CN shows quite heat-stable rheological properties during the heating process, the mixture formed a soft gel with or without NaC_{10 : 0}. In the presence of NaC_{10 : 0}, the mixture shows a clear sol-gel transition, which is different from those in the absence of NaC_{10 : 0}. The ultrasonic gradient velocity between α-CN/OVA+NaC_{10 : 0} and OVA+NaC_{10 : 0} mixed systems indicated that the effects of α-CN addition began at around 46°C for the formation of a unique gel from the mixed protein system. FT-IR analysis indicated a decrease of 3₁₀-helices, α-helices, and β-sheets by the addition of NaC_{10 : 0}, and α-CN/OVA+NaC_{10 : 0} showed a characteristic spectrum which is different from that of the OVA+NaC_{10 : 0} system. The results imply that the mixed protein system containing milk casein is an interesting material for creating processed foods with novel texture and appearance.

View full abstract

A taste sensor system has been used to grade the astringency and umami of green tea infused with hot water. The objectives of this study were to evaluate the capability of the taste sensor system for evaluating the taste of green teas infused with water of various temperatures, including ice brewing, and brewing durations. Sensory evaluation indicated that the concentration of gallate-type catechins was a better indicator than the total catechin concentration for evaluating the astringency of green tea infusions. The estimated intensity of astringency by the taste sensor system showed a high positive correlation with gallate-type catechin concentrations in green tea infusions prepared with different water temperatures or infusion durations. Also, the estimated umami intensity in the same green tea infusion samples by the taste sensor system showed a high positive correlation with the total amino acid concentration. Amino acids are the main contributors to umami. Regarding mainly high-grade teas, we propose that a taste sensor system is suitable for determining the best combination of time and temperature for brewing green tea and for evaluating the quality of green tea brewed with low-temperature water.

View full abstract

Changes in physicochemical properties and sensory characteristics of indirect (plate type, PLT) and direct (injection type, INJ) ultra-high- temperature (UHT) pasteurized milk during storage at 10°C were examined. The physicochemical analyses of whey protein denaturation, rennetability (RNT), furosine, and lactulose, which are indicators of heating degree in milk, showed that INJ milk pasteurized at 150°C for 2.4s was less affected by heating than PLT milk pasteurized at 140°C for 2s. RNTs of both milks decreased with storage time, however, the change of INJ milk was smaller than that of PLT milk. The dissolved oxygen (DO) content of both milks decreased slightly with storage time, however, the DO content of INJ milk was much smaller than that of PLT milk during storage. Principal component analysis of sensory attribute scores by an analytical panel showed that both milks increased thickness with storage time, and INJ milk was fresher and thicker than PLT milk. In an evaluation of palatability, the sensory score of INJ milk hardly changed with storage time, whereas, that of PLT milk decreased. In conclusion, it was suggested that the direct heating method (INJ) is more suitable than the indirect heating method (PLT) for the manufacture of UHT long life milk of stable quality during 10°C storage.

View full abstract

For studies on the physiological functions of proteoglycan (PG) in salmon nasal cartilage for humans, it is important to clarify the qualitative and quantitative differences in PG contained in nasal cartilage among different types of salmon and among the locations of cartilage in the salmon head. In this study, as an alternative source of PG, we selected ‘Kaikyo salmon’ head cartilage. ‘Kaikyo salmon’ is rainbow trout that is farmed in the Tsugaru channel. We divided the head cartilage into 4 regions (those collected from the region around the brain, frontal head, upper region of the jaw, and tip of the nose and around the eyes), and investigated the PG content and molecular weight distribution of each cartilage. Among the 4 regions, the cartilage contents of the region around the brain and nasal tip and around the eye accounted for 33 and 32% of the total cartilage content, respectively, and were greater than those of the frontal head (20%) and upper region of the jaw (15%). However, the uronic acid content per g cartilage wet weight (representing the PG content) was 17.6-21.8mg and the protein content was 15.9-18.9mg in the 4 regions, showing no marked differences among them. In addition, no difference was noted in the molecular weight distribution of PG contained in the hot water extracts of cartilage among the regions, and 20-30% of the total PG was distributed in the high molecular weight region (5000000 or higher), similar to the distribution of a hot water extract of salmon nasal cartilage. These findings suggest that cartilage in the Kaikyo salmon head can be used as a substitute for the nasal cartilage of wild salmon. The raw materials for PG can be stably supplied using farmed fish, and the use of the head, a previously unused resource, may significantly contribute to the revitalization of the local industry.

View full abstract