Heat treatment is commonly used to inactivate microorganisms in liquid foods in order to improve food safety and extend shelf-life. However, using heat treatment to kill heat-resistant microbial spores also thermally damages the food, which can adversely affect the flavor and lead to loss of nutrients. We have developed an apparatus for applying high electric field alternating current (HEF-AC), which inactivates not only vegetative cells but also spores in liquid foods while preserving the freshness of raw fruit. In this study, HEF-AC was applied to inactivate Alicyclobacillus acidoterrestris spores in fresh juice. As a result, A. acidoterrestris spore numbers were reduced by four logarithmic orders of magnitude. The purpose of this study was to clarify qualitative changes in treated juice, and an ultra-high-temperature (UHT) treatment was employed for comparison purposes. Quality parameters of orange juice treated with HEF-AC maintained higher values compared to UHT treatment; meanwhile, the two treatments showed an equal inactivation effect. Notably, lemon juice treated with HEF-AC has been commercially available since 2014 from POKKA SAPPORO Food & Beverage Ltd.

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Secondary metabolites produced in food plants influence their quality attributes, such as palatability and functions in health maintenance. Therefore, the control of secondary metabolite contents and composition is important for a number of processes, such as breeding, preservation, distribution, and cooking. Here, we investigated the main secondary metabolites involved in the palatability of savory foods, such as ginger, sweet basil, and tomato. In particular, analysis using gas or liquid chromatography-mass spectrometry (GC or LC-MS) facilitated the structural elucidation of key compounds and enabled the prediction of their biosynthesis. This article reviewed our studies: (1) identification and quantification of pigment compounds in ginger rhizome, (2) biosynthesis of geranial, a key compound of ginger flavor, (3) biosynthetic control of terpene volatiles in different cultivars of sweet basil, and (4) prediction of chemical changes in secondary metabolites by comprehensive analysis using LC-MS.

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Previous studies have demonstrated a number of physiological functions for shiitake mushroom (Lentinula edodes), among which the antioxidant activity has been evaluated primarily using conventional chemical techniques. To date, there have been no reports on the anti-oxidative stress effect or on the antioxidant enzyme induction activity of shiitake/shiitake artifact. Therefore, in this study, we evaluated the anti-oxidative stress effect of shiitake grown in Miyazaki Prefecture and shiitake artifact from luminescence values obtained using a HepG2-ARE luciferase reporter assay system. The results showed that shiitake exhibited an anti-oxidative stress effect and, based on western blot analysis, was able to induce the expression of the antioxidant enzyme HO-1. Moreover, the anti-oxidative stress effect was found to be retained in dried shiitake. It is possible that the anti-oxidative stress effect of shiitake might be increased via heat processing or lactic acid fermentation.

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We recently focused on the gelatin/transglutaminase (TGase) cross-linking reaction, and successfully prepared powdered fish oil (PFO) by mixing fish oil with water, emulsifiers, gelatin, and TGase, with subsequent freeze-drying and pulverization of the mixture. Since the cross-linking reaction is considered key in the preparation of PFO, we investigated its role by preparing PFO with and without TGase. As a result, both PFOs contained high amounts of lipids (about 73% by dry weight). PFO prepared with TGase showed good oxidation stability and slow-release property in vitro compared to PFO prepared without TGase. Microscopic observation revealed almost no changes in shape and oil distribution during preservation of both powers. Atomic force microscopy revealed that the cross-linking reaction increased the molecular density of the gelatin surface. This might be related to differences in the properties (i.e., oxidation stability and slow-release property) of the powders. Hence, the production of high quality PFO by using the cross-linking technique is possible.

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We investigated the effects of drying methods and pre-treatment conditions on the functional component contents and antioxidant activities in egoma (Perilla frutescens (L.) Bitt. var. frutescens) leaves. It was found that the contents of α-linolenic and rosmarinic acids in the leaves were higher after treatment by vacuum-microwave drying than after hot-air drying; α-linolenic acid in particular retained the same level of contents after vacuum-microwave drying and after freeze drying. Vacuum-microwave drying conditions were found to be superior at high power and short drying time for the retention of functional components. An evaluation of the blanching conditions used during pre-treatment found that there was no change in α-linolenic acid contents during boiling treatment, while the rosmarinic acid contents decreased with increasing boiling time. On the other hand, the contents of both components did not change during steam-treatment. Steaming as a pre-treatment therefore prevented the loss of rosmarinic acid before freezing and thawing. The DPPH radical scavenging activities of the samples decreased less under vacuum-microwave drying. The activities of all drying treatments after steaming, freezing, and thawing were significantly higher than with no treatment other than freeze drying. For the retention of functional components and color, vacuum-microwave drying was found to be superior to the traditional method of hot-air drying, suggesting that drying the samples after pre-treatment by steaming may produce dried products with high antioxidant activities.

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The rheological properties of a soybean protein emulsion prepared using soybean protein isolate (SPI), soybean oil, vinegar and water were investigated. The effects of altering the amount of added vinegar as well as the preparation order were examined. The results showed that when vinegar was added after the emulsification process, partly dehydrated SPI can produce a stable emulsion in which a smooth texture is maintained. Non-dehydrated SPI, however, did not produce a similar emulsion from the same process. In order to determine the optimal mixing ratios of SPI, soybean oil, vinegar and water, Scheffé’s simplex lattice design was adapted, and the properties of emulsions with ten ingredient ratios were examined. The emulsions with high stability were within the range of the following mixing ratio:partly dehydrated SPI, 4-16.7%;soybean oil, 36-55 %;vinegar, 5%;and water, 36-45.5%. This emulsion showed pseudoplastic flow. In cake and mayonnaise-like emulsions, when sugar was added after making the emulsion, depending upon the amount of sugar added, the emulsion made using the ingredient ratio above had low stability and Newtonian flow. However, when sugar was added during emulsification and vinegar added thereafter, favorable stability was achieved. Overall, altering the ingredient order was found to influence the physiological texture of the final emulsions and/or foods.

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The purpose of this study was to investigate the effect of extrusion cooking on the digestion and absorption of dietary lipids. Cornstarch with and without soybean oil (EXO and EXS, respectively) was extruded and then fed to rats for 21 days. The amount of fecal triacylglycerol in the EXO group was greater than that in the EXS and non-extruded diet groups. In addition, hepatic mRNA expression of PPARα in the rats fed EXS or EXO was significantly lower than the control group. Significant differences, however, were not observed in other parameters such as serum lipids and body weight.

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