We found that the change with time of milk curd strength during the process of lactic acid fermentation and the change with time of freezing rate during the freezing process of food material can be monitored by measuring ultrasonic velocity. While the ultrasonic velocities of fruits and vegetables depend on not the “hardness” but the gas volume fractions of their tissues, the propagation velocities of impact vibration have strong correlations with their elastic properties. We have developed a measurement system for volume/density of food material by using phenomena of Helmholtz acoustic resonance. We found that the Helmholtz resonant frequency for food material having a pore structure is lower than that of non-porous food material having the same volume. Based on the theoretical consideration on the relations between the physical properties of porous food and the reduction of resonant frequency, we have also developed a measurement system for evaluating beer foam characteristics and bread texture. In another study we have found that the frequency of crack vibrations generated during chewing deep-fried foods has a close correlation with the results of sensory evaluation of their crispness.

Tomato juice is a popular beverage and a convenient cooking ingredient. Especially, straight pressed tomato juice (not from concentrate) maintains fresh flavor, showing different characteristics from the juice from concentrate. We studied changes in the profile of volatile compounds in straight pressed tomato juice upon heating. We heated two types of commercial packaged straight pressed tomato juices at 95 – 100°C for 0 – 5 h and extracted volatile compounds in each sample by headspace-solid phase microextraction. A total of 176 and 187 compound peaks were detected, of which 81 and 86 compounds were identified or tentatively identified by GC/MS analysis, respectively. Principal component analysis (PCA) indicated that the samples could be divided into six groups based on heating time; the volatile profiles changed in a time-dependent manner. Furthermore, seven chemicals were identified as heat markers using partial least squares (PLS) regression, namely 2-pentylfuran, phenylacetaldehyde, hexanal, furfural, cyclohexanone, β-damascenone, and 1,4-dimethylbenzene. A prediction model based on only these seven marker profiles for heating period, also showed good linear regression (R²＞0.987). Gas chromatography-mass spectrometry/olfactometry (GC-MS/O) analysis and quantification of these volatiles suggested that phenylacetaldehyde, hexanal, β-damascenone and 2-pentylfuran influence the flavor characteristics of tomato juice.

The effect of near-infrared (NIR) irradiation before storage on the quality of fresh-cut lettuce was investigated in this study. It was shown that the NIR irradiation was effective in suppressing the number of viable bacteria and weight loss during the storage of cut lettuce, statistically. However, it was also shown that the browning ratio increased slightly under the stronger NIR irradiation conditions of the 30 s and 60 s, which could deteriorate the appearance quality. This was thought to be the result of increase in the Phenylalanine Ammonia Lyase (PAL) activity and total polyphenol content. Meanwhile, no increase in browning ratio was observed at 10 s, and there was no difference in PAL activity and total polyphenol content from the control. In the range of irradiation conditions set in this study, thus, the 10 s NIR irradiation was expected to be effective in suppressing the number of general viable bacteria and mass, without affecting polyphenol synthesis.

Recent studies in lactic acid bacteria (LAB) biofilm formation have reported that the functional properties of LAB are associated with biofilm formation. In this study, Pediococcus acidilactici and Lactobacillus plantarum showed the ability to form a biofilm on a solid surface under static conditions. The morphology of LAB on MRS-CR agar showed that both P. acidilactici and L. plantarum could produce exopolysaccharide (EPS) on the cell surface which mainly contributed to forming the biofilm of single and co-culture strains on solid surfaces. Under the flow condition, cell motility played an important role in supporting the cell to overcome the repulsive force to reach and interact with the surface. As a result, the L. plantarum and co-culture cells with higher motility caused a noticeably thicker biofilm on the glass surface compared to the P. acidilactici strain. Moreover, the antagonistic activity assay showed that co-culture biofilm formation improved the antagonistic effects of LAB against Pseudomonas aeruginosa and Salmonella typhimurium compared to those in planktonic culture. It suggested that co-culture biofilm could be an effective model to apply useful LAB as potential probiotics and to control pathogen in food chain, especially under the flow condition.