The author has conducted engineering research on thermal food processing (TFP) using various heating methods to intend optimal operations. In this paper the following four themes related to TFP were reviewed. (1) Heat and moisture transfer and shrinkage deformation: Theoretical analysis of heat and moisture transfer, which are the most basic phenomena in TFP, was reviewed, and the strain-stress analysis was introduced to reveal the mechanism of shrinkage deformation and crack formation of foods during drying or roasting processes. (2) Heat transfer with convection: When convection occurs in a container or a vessel, the heat transfer rate becomes much larger than that of heat-conductive food, and it is necessary to consider the natural convection in the fundamental equations. A method to predict the temperature history of liquid food using its apparent viscosity was developed. In addition, an analysis of natural convection in a pan heated by induction heating (IH) and gas range using Computational Fluid Dynamics was outlined. (3) TFP with internal heat generation: During microwave heating, radio-frequency heating, and ohmic heating, foods can be heated faster than conventional heating methods because of the internal heating, but uneven heating is a crucial problem. A computational method was introduced for predicting the temperature distributions in food by coupling an analysis of the electromagnetic field and the heat transfer. (4) Chemical reaction accompanying heating: Various chemical reactions occur with heating, which affects the quality of foods. Kinetic analysis of protein denaturation and color change due to Maillard reaction during fish grilling was outlined.
Several research aiming at systematic understanding, prediction and control of ice recrystallization in frozen foods were reviewed. The change of ice crystal shape under recrystallization was numerically estimated by using the concept of fractal. The recrystallization rate constants of various sugar solutions showed good correlation to the properties of water in freeze-concentrated matrix; diffusion coefficient, spin-spin relaxation time T2, and dielectric relaxation time. This suggested that these are useful for predicting recrystallization of ice crystals in frozen foods. The recrystallization of ice crystals in sucrose solution were greatly suppressed if its freeze-concentrated matrixes were in glassy state. The ability of antifreeze protein (AFP) type I to suppress ice recrystallization was numerical estimated and it was confirmed that ATP type I suppressed the ice recrystallization significantly at 1μg/mL. Searching for AFP from marine products in Tohoku region, the northeastern portion of Honshu, the largest island of Japan, was conducted. Among 21 species sold in local fisheries market, it was shown that 2 species, pacific cod (Gadus microcephalus) and marbled sole (Pseudopleuronectes yokohamae) had AFP. As for the AFP from pacific cod, seasonal change of AFP activity in the extract and effect of heating on AFP activity were also clarified.
Emulsion hydrogel that incorporates oil droplets are commonly used as food models due to easy manipulation of their mechanical characteristics and compositions. A novel in vitro gastric model called the “human gastric digestion simulator (GDS)” equipped with peristalsis enables the simulation and direct observation of the disintegration of food particles induced by peristalsis. The objective of this study was investigating the gastric digestion behavior of emulsion hydrogels with variable mechanical characteristics using the GDS. Four types of emulsion hydrogels containing soybean oil droplets were prepared, namely agar (AG), agar and native-type gellan gum (AG-NGG), deacetylated gellan gum (DGG), and deacetylated gellan gum and native-type gellan gum (DGG-NGG). During peristalsis in a GDS digestion experiment, DGG and DGG-NGG emulsion hydrogel shrank without releasing oil droplets, whereas AG and AG-NGG emulsion hydrogel disintegrated, releasing oil droplets. The disintegration and oil release rates for the AG-NGG emulsion hydrogel were lower than those for the AG hydrogel, where a linear relationship was observed between these two rates. The fracture stress and strain differed between these two hydrogels. The results indicate that lipid release from gels in the human stomach can be controlled by adjusting the gelling agent without changing the lipid amount.
Gochujang is a typical fermented food of Korea, and similar as Japanese Miso in manufacturing process. Recent favorite of consumers is preservative additive-free gochujang, and this sometimes has brought swelling incidents. The previous studies reported that salt tolerant yeast or lactic acid bacteria caused the incidents. This study sought out acid and salt tolerant and gas-generating microorganisms from an incident product of gochujang through some kinds of microbiological tests, whereas they could not reveal any salt tolerant yeast nor lactic acid bacteria. DNA sequence data of 16S rRNA gene concluded acid and salt tolerant and gas-generating microorganisms isolated should be two species of Bacillus or their relatives: one was Bacillus amyloliquefaciens and another was B. licheniformis. The former generated ca.70％ more gas than the later in intentional contamination of fresh gochujang. This could infer that the gas-generating Bacillus strains, B. amyloliquefaciens and/or B. licheniformis relatives might be the causative microorganisms of swelling incident of gochujang.
The residual waste solution obtained during the recovery of functional components from Isada krill was treated under subcritical water conditions. Properties of the treated solution, such as solid, protein, and carbohydrate contents, were measured. The characteristic smell of the solution was evaluated. The smell intensity increased with a rise in the treatment temperature by gasification of the soluble components. In particular, the treatment at 160–180℃ strengthened the shrimp-like fragrant smell and retained the unpleasant fishy and rotten smell at lower level. The treated solution, therefore, may serve as a promising seasoning ingredient. The gas chromatography mass spectrometry analysis of the smell revealed the formation of pyridine- and pyrazine-related compounds after the treatment that contributed to the improvement in shrimp-like flavor.
In recent years, dried nori with a high protein content has been commercialized as tasty produce. Although free amino acids have been examined as taste components of dried nori, the components constituting the taste of dried nori and their roles have not been identified. Therefore, we carried out a sensory evaluations to identify the taste-active components of dried nori and determine their roles in taste. The main extractive free amino acids of dried nori were Ala, Glu, and Asp. In addition to these components, Tau was also abundant. These four components accounted for 85% of the free amino acids. The main ATP-related compound was IMP. Together, these five compounds were identified as taste-active components. The role of each taste-active component of dried nori was as follows: Ala imparts sweetness, saltiness, umami, and richness; Glu imparts saltiness, umami, and richness; Asp imparts saltiness, umami, and richness; Tau imparts sourness; and IMP imparts umami and richness.
We first found that arabinofuranosyl-vitexin (AFV) belonging to flavonoid-C-glycoside is highly contained in Basella alba leaves, therefore a simple method was developed for preparing an AFV fraction and evaluating AFV as functional food materials. A fraction containing a high AFV concentration (purity, 62.4％) could be prepared from the leaves by extraction with 80％ ethanol and then adsorption on Diaion HP 20 column. Because Basella alba is traditionally used as a food that suppresses nerve enlargement or promotes sleeping, the effects of AFV (purity, 94％), isolated from the fraction using silica gel column chromatography, was assessed by the thiopental anesthesia test system. After AFV (100 mg /kg) was orally administered to mice, sedative and hypnotic effects were observed, indicating that similar to γ-aminobutyric acid (GABA), AFV contained in Basella alba has nerve-stabilizing effects and is useful as functional food materials.