Integrated investigation on application of infrared rays to food processing was dissertated from the view points of infrared radiation and spectroscopy. Drying and pasteurization of the food models were dealt in the most effective application of infrared radiation. The infrared drying characteristics of the food models were studied by focusing on the factors influencing their characteristics, and the importance of the diffusive infrared spectroscopic characteristics was emphasized for the quantitative evaluation of the effects of infrared drying. Moreover, infrared pasteurization of bacteria was more effective than the conventional thermal heating methods, and it was suggested that the infrared pasteurization effect was due to the absorption of infrared radiation energy by the sample in a very thin domain near the surface and to the bulk temperature. Then the infrared spectroscopy was studied for the qualitative and quantitative analysis of foods. In addition, the developed infrared spectroscopic methods were applied to get a good grasp of the sugar metabolic kinetics of suspension cells, the monitoring of the enzyme reaction associating with ionic dissociative metabolites, and the food tasting. Consequently, these studies represented an important step in the developments of the effective thermal operations and the on-line monitoring for food processing.
For more than three decades, membrane technology has drawn keen attention and has been applied to various fields in food industry in Japan. The Research Association of Membrane Technology for Food Industry (MRA), which was established by the Japanese Ministry of Agriculture, Forestry and Fishery in 1982, continued the activity to accelerate the spread of membrane technology for 6 years. In 1989, Membrane Research Circle of Food (MRC) was established by the researchers and technologists in industry-government-academia. Watanabe, one of the present authors, who worked for Ministry of Agriculture, Forestry and Fishery at that time, participated in the activity as an executive committee member of MRA and as a chairperson of MRC, respectively. In 1996, one year after Watanabe moved to Niigata University as a professor of food engineering, Food Engineering Division in Food Research Laboratory in Niigata Prefecture was established. In 1997, when MRC 10th Autumn Workshop was held in Niigata, Membrane Application Research Circle (MARC) for food industry in Niigata was established. The research to apply membrane technology to food industry in Niigata started with collaboration among local companies just after Watanabe's coming to Niigata University. The establishment of MARC accelerated the widespread of knowledge of membrane technology. The research projects in the authors' laboratory and companies were: 1.Establishment of clarification and recycle system for rice washing drainage from packed rice cake manufacturing plant, 2.Establishment of concentration and recycle system for pickles seasoning drainage, 3.Development of squeeze and clarification technology of soy-sauce fermented broth by micro-fiber cloth for direct membrane filtration, 4.Gamma-Amino butyric acid production using clarification with membrane, 5.Sterilized and clarified raw soy-sauce production by ceramic MF membrane Under present circumstances, the research subjects of No.4 and No.5 came successfully into practical use.
The application of far-infrared heating or microwave heating has been used in many food processings such as drying, cooking, and thawing. In the far-infrared heating, since excessive heating causes the degradation of food, it is very important to know how the temperature distribution is formed in the food during heating. To investigate the heat transfer process, a mathematical model was developed and was used to examine the effect of heating condition on the temperature distribution of food. Microwave heating has a tendency to heat foods unevenly, causing problems with both sensory and microbiological quality. This uneven heating is caused by various factors; the shape or size of food affects the microwave power distribution in the food, electric field intensity in a microwave oven is non-uniform, dielectric properties of food vary with temperature, and dielectric properties of some foods are non-uniform. To investigate the effects of these factors on temperature distribution, a mathematical model was developed by using Lambert' s law. It was confirmed that the mathematical model is useful in predicting the temperature distributions of food during microwave heating.
Oleic, linoleic and linolenic acids were oxidized at 40°C in darkness. The near infrared reflection spectra applied to them were measured in appropriate intervals. At the same time, the peroxide values of fatty acids were measured by a titration method. As a result, a regression equation to presume the peroxide value by using the second derivative values of the spectra was obtained. This regression equation was applicable to the three kinds of fatty acids. The rate constant at each stage of the oxidation (initiation, chain reaction, polymerization, and decomposition period) was obtained by using the kinetic equation of autoxidation of fatty acid. The rate constants of the initiation period of the three fatty acids were almost the same, regardless of the kind of the fatty acid. Those of the chain reaction periods were also the same. However, the rate constants of the polymerization and the decomposition periods increased in relation to the number of double bonds present in the three fatty acids.
On a food heating process, a heat transmission system has been used widely. But, this system involves some intrinsic problems such as overheating, defective sterilization and scorching. Recently, the Joule heating system has been received keen attentions as a sophisticated heating system because of non-scorching, accurate heating and cleanness. However, there are few reports concerning with internal temperature distribution of food materials, especially on Joule heating system. We developed the visualizing method to observe and record the internal temperature distribution as a picture in food materials. The heat sensitive (color changeable) liquid crystal was adapted as a thermo indicator. The visualized results were compared with the data which simulated by a finite element method (FEM) . The visualized results were accurately coincided with the FEM simulations. We demonstrated that heat should be generated uniformly in Joule heating process, if food material was homogenous.
The deterioration of palm oil during deep frying was mainly examined at 180°C by measuring the acid value (AV) of the oil to which water was continuously fed at a constant rate. The addition of water simulated importing water from the material being fried. In most cases, the AV rapidly increased after an induction period, reached a plateau, and then gradually decreased in most cases. The addition rate of water significantly affected the change in the AV. The changes in the AV were also exmined for the mixtures of the constituent fatty acids of palm oil with or without glycerol. Based on these experimental results, a kinetic model was proposed for describing the change in the AV during deep frying. The rate constants of the model were evaluated at various feed rates of water. The rate constant for the degradation of the AV-positive compound scarcely depended on the feed rate of water, but the rate constants for the hydrolysis and reverse-hydrolysis of the ester bond were mostly affected by the feed rate. The changes in the AV were also measured at 160 to 200°C at a constant feed rate of water. The AV continued to increase at 160°C, while the AV increased, reached a plateau and then gradually decreased at 180 and 200°C during the late stage of the test period.
Food texture described using Japanese onomatopoeic words was correlated with the physical properties and also with the acceptability. Sensory evaluation using the 11 onomatopoeic words; “pare-pari”, “shari-shari”, “hoku-hoku”, “kori-kori”, “toro-toro”, “gunya-gunya”, “karat”, “pasa-pasa”, “saku-saku”, “kotteri” and “fuwa-fuwa”, was carried out on the 11 kinds of foods representing different textures; cookie, jelly, bread, marshmallow, raw radish, pickled radish, raw abalone, fried chicken, steamed sweet potato, sesame tofu and stewed pork. A laboratory panel of 11 members described the food texture as well as the difficulty of chew and swallow and the acceptability of the texture. A mechanical compression test was conducted using a universal testing machine. The detected load was converted to true stress in accordance with the contact area between the sample and the plate measured by a multipoint sheet sensor. The evaluated intensities of food texture were correlated to the true stresses at different compression strains, and also to the difficulty of chew and swallow and the acceptability. The stress at 70% strain correlated positively with the intensity of “kori-kori” which concerned significantly to the difficulty of chew. The stresses at 10% and 30% strains correlated positively to the intensity of “saku-saku”, “shari-shari” and “pari-pari” affecting the acceptability significantly.
Although it is widely accepted as a useful tool for analyzing water migration in food bodies, Fick's law of diffusion is applicable to a single-phase system which is homogeneous in terms of that a flat water content profile is reached at equilibrium when the system is isolated. However, some starchy food often turns into a multiphase system when it is cooked, even though the system is of single phase before it is cooked. In order to make Fick's law of diffusion applicable to such a multiphase system, Relative Water Content Model is proposed in this paper. In this model, relative water content is used as the substitute to water content in Fick's law of diffusion. Relative water content is defined as existing water content divided by the standard water content. The standard water content becomes effective when it is set in such a region of water content where water activity can be approximated as a linear function of water content.
The retention behaviors of caffeine and vanillin in columns packed with thermostable octadecyl silica gels and zirconium particles with an extremely stable thin layer of cross-linked polybutadiene were observed using water at various temperatures or methanol mixed with water at 30°C as the eluent. For both columns, the retention times of the solutes at a specific flow rate became shorter at higher temperatures when water was used as the eluent. The effect of the temperature on the retention behaviors of the solutes were examined for the latter column in the temperature range of 70°C to 210°C. It was shown that the retention behaviors could be more effectively controlled by changing the temperature when using water as the eluent than by changing the methanol content in its mixture with water at 30°C.
Linoleic acid was heated in the presence or absence of water in the temperature range of 200 to 260°C using a pressure-resistant batch reactor to examine the possibility of its conversion to conjugated isomers. The conversion occurred at very low yields, and the major products were the c9, t11 and t10, c12 conjugated linoleic acids. The t10, c12 isomer seemed to be produced more than the c9, t11, and the ratio of the isomers did not depend on both the temperature and the ratio of linoleic acid to water. When a dilute potassium hydroxide was used as the aqueous solution, the yield of the conjugated isomers was lower than that of the isomers in the mixture of linoleic acid with distilled water.
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