The analysis of the glass transition of foods by electrical methods and proton-NMR was reviewed and compared with that obtained by differential scanning calorimetry (DSC) . The glass transition temperature Tg for many foods are usually determined by DSC, which does not provide direct information on molecular mobility. The dielectric relaxation, i. e., the peak of the dielectric loss, ε”, was observed for some glassy foods and ascribed to the local motion of molecules. The relaxation time z and the activation energy Eact seemed suitable parameters to describe the enhancement effect of water on the mobility of molecules in the glassy state. However, when the ionic conductivity dominated the electrical properties, the ε” peak was masked. For analyzing such a system, the electric modulus, M* was an effective tool. The value of the activation energy obtained through M* formalism in the glassy state was larger than that in the rubbery state, probably due to a change in the free volume size due to glass transition. For NMR research, the mobility of maltose in the glassy and rubbery states has been examined. Free induction decay (FID) was measured with low-resolution NMR and was best fitted by a Gaussian lineshape multiplied by sinc function plus an exponential function. The T2 of mobile protons obtained from the FID spectra for maltose started to increase at a temperature lower than the midpoint Tg obtained by DSC. The dependency of secondary moment M2 on temperature for maltose showed typically one or two transition temperatures where the M2 decrease became steeper, reflecting motional changes in the immobile protons.
During food processing, adhesion of food itself and/or its components inevitably occurs on food contact surfaces of the equipment. Microbes can also adhere to the surface and survive if cleaning and disinfection are insufficient. These fouling deposits on the equipment surfaces make sources of cross-contamination and lower the quality and safety of food to be produced. An effective strategy for suppressing their adhesion is desired for reduction of the cross-contamination risk and for hygienic control of the surfaces. Thus the knowledge of adhesion behaviors and mechanisms of food components and microbes is basically important. Here, research results obtained recently on the adhesion behaviors of food proteins and bacteria to the surfaces of stainless steel and polypropylene are reviewed as the basic knowledge for hygienic control of food contact surfaces.
A concentration process is one of the most important technologies in vegetable and fruits processing, and greatly influences quality and cost of juice concentrate. In this research, it aimed to develop a new freeze-concentration technology to fit for concentration of many kinds of foods and small quantity production. The principle of the new freeze-concentration technology is to be progressive-freeze concentration. This system has characteristic that the formation, growth and separation of ice crystal can be done in the same ice manufacturing vessel. Therefore, this system is easy to operate. We have researched the best concentration condition, the best design of ice vessel and all equipment, and the automatic control system, and developed pilot scale freeze-concentration system. The examination of freeze-concentration of tomato juice was done with this system. The result was to be high density concentration about Brix40% possible, and the solute of 20-30% for juice concentrate in the separated ice was contained. And the quality of concentrate was very good taste and flavor.
Heat treatment is commonly used to inactivate microorganisms in liquid foods in order to improve food safety and extend shelf life. However, heat treatment to kill spores also causes thermal damage to the food, which can adversely affect the flavor and lead to loss of nutrients. We developed an apparatus to apply a high electric field AC (HEF-AC) that inactivates heat-resistant microbe spores in liquid food while preserving the freshness of raw food.
We have developed a novel technique for removing organic soilings from metal surfaces using hydroxy radicals (•OH) . In the cleaning system, a metal surface fouled with organic soilings is made to contact with an aqueous solution containing hydrogen peroxide and supporting electrolyte. A slightly negative potential is then applied into the metal. The •OHs, which are generated by the electrolysis of hydrogen peroxide (H2O2+e-> •OH+OH-) on the metal surface, effectively attack and subsequently remove the adsorbed organic soils. In this study, the removal behavior of model organic soilings (protein) during the H2O2-electrolysis cleaning using different types and concentrations of supporting electrolyte was investigated. The presence of ammonium compounds and potassium phosphate led to marked increase in the removal rate. The influences of the types of metal substrate and adsorbed material on the removal behavior were also investigated, which suggested that the adsorption state of organic soiling on a metal surface strongly affect the removal characteristics. Furthermore, the removal rates in the presence of various organic coexisting materials were investigated. It was found that the removal rate constant was only slightly lowered in many cases.
Since 1990's, utilization of hydrostatic pressure (HP) has been investigated as a new technique for food processing in Japan, and subsequently Europe and USA. We also started the study and especially chose the utilization of relatively low HP range (lower than 100MPa) in the view of practice. The pressure range, which can prevent microorganisms from growing, was between 40-70 MPa differently from spices of them. For instance, the growth of yeast, lactic acid bacteria and bacillus was inhibited at 40 MPa, 70 MPa, and 50 MPa, respectively. Then, we applied the growth inhibition of bacteria by HP to autolytic hydrolysis of unsalted fish. When the autolytic hydrolyses of anchovy, squid liver and the guts of sea cucumber were carried out under pressurization, each autolytic hydrolysis went well without decomposition. The total nitrogen, formol nitrogen and amino acids concentration of the extracts were relatively high, compared with the extracts produced by salting 20% NaCl (a traditional way) . An equipment for the purpose of carrying out the autolytic hydrolysis of fish under pressurization was also developed by a company in Hiroshima (TOYO KOATSU Co., Ltd) . The equipment could realize this way that we have proposed. We hope that the way of producing autolytic hydrolysate without addition of salt is applied to various marine materials from now on.
Adhesion behavior of Staphylococcus epideymidis from its suspension onto stainless steel (SUS304) surface was studied, focusing on the effects of such factors as initial cell concentration of suspension, suspending medium, and roughness of stainless steel surface. For all cell concentrations tested (102-104 CFU/ml), adhesion occurred at low levels within 0.5h of exposure to the cell suspension, and reached maximum levels in 3 h. The number of adherent cells per surface area was approximately proportional to the cell concentration of the suspension. Significantly higher adhesion was observed for cells suspended in peptone saline than those suspended in physiological saline. Significantly higher adhesion was also observed on roughly polished surface (Ra=1.37μm) than on smoother surfaces (Ra≤0.14μm) . Shear force application by whirlpool rinsing removed only 50-82% of the adherent cells. The presence of cells still remaining on the surface indicated that the adhesion of S. epideymidis cells was irreversible in part.
IGUSA (Juncos effuses var. decipiens), which is commonly used to make TATAMI and Japanese flooring mats, is disposed off as a waste material in large quantities that has became a serious problem in Japan. We investigated whether this IGUSA waste could be used as a substrate by Rhizopus strains for producing glucoamylase. R. cohnii produced 1034 U/ (g substrate) of glucoamylase activity from the growth medium containing the IGUSA waste. Supplementation of this growth medium with organic nitrogen sources inhibited protease production, but significantly increased (3-times or more) the glucoamylase production by R. cohnii. The most effective form of IGUSA waste was the rough powder form that retained the honeycomb structure of IGUSA. Use of the rough powder form in the growth medium increased the glucoamylase production to 9204 U/ (g substrate) . R. cohnii produced the similar amount of glucoamylase from all substrates (the IGUSA waste, Japanese flooring mat waste, and wheat bran) after 168 h growth. The specific activities of glucoamylase produced by R. cohnii from the IGUSA and Japanese flooring mat wastes were higher than that for the wheat bran. Thus, the method described here opens up new avenues for producing value-added products from the IGUSA waste.
Since heating by infrared radiation can heat directly liquid food, the surface of the food becomes a high temperature, and stainless steel plate which has contacted the food would be maintained a low temperature. As a result it seems to be able to reduce the adhesion of the fouling in the stainless steel plate, which was an important problem in the conventional heat exchanger. In this study we developed the continuous heating equipment using far-infrared radiation, and verified that this system is practically available to pasteurization. In this developed equipment, the liquid food flows down as a thin liquid film, because the penetration of radiation energy to the water is low and the heating of the liquid inside is difficult. Using this equipment, increased temperature of the sample was measured by changing the heating conditions such as supplied electricity to the heater and the liquid flow conditions such as flow rate. The result showed that the increased temperature rises, as liquid film thickness thins, and that the sample temperature could be heated to about 80°C. Using lactic acid bacteria and yeast, the pasteurization experiments were performed. As the result, the death of the bacterium and the yeast could be confirmed, and the effectiveness of this equipment could be verified.
We investigated the antimicrobial activity of several bacteriocins, which were produced by newly isolated lactic acid bacteria in koji extract medium supplemented with rice protein hydrolyzate (RPH), against strains of NBRC type culture and spoilage bacteria isolated from deteriorated sake. The partial sequences of the 16S rRNA gene of the spoilage bacteria isolated from sake showed a high similarity to those of Lactobacillus fructivorans, Lactobacillus hilgardii, and Lactobacillus paracasei, with 99.6-100% identity. Enterococcus durans C102901 (C102901), Lactococcus lactis subsp. lactis C101910 (C101910), and Lactococcus lactis subsp. lactis NBRC 12007 (NBRC 12007) grew well and produced bacteriocins with high activity in koji extract medium supplemented with RPH. When culture supernatants containing bacteriocins from C101910 and NBRC 12007 were added to the medium at a volume ratio of 10% (v/v), the growth of L. fructivorans NBRC 13954T was significantly inhibited and the viable cell concentration decreased below the detection limit (1.0×102 cells/ml) at 4 h. Further, by the addition of bacteriocin solutions from C102901, C101910, and NBRC 12007 to the medium at a volume ratio of 1% (v/v), the growth of L. hilgardii NBRC 15886T and H130 (closely related to L. hilgardii) isolated from putrid sake was bactericidally inhibited and the colony-forming units fell by more than three orders of magnitude within 4-12 h as compared with the initial cell concentration.
Screening various food yeast strains revealed the growth capabililty of Candida utilis NBRC1086 on the medium of locust bean gum (LBG) . The composition of the LBG medium (pH 5.0) was 0.5% (w/v) LBG, 0.3% (w/v) (NH4) 2SO4, 0.02% (w/v) MgSO4⋅7H2O, 0.01% (w/v) Yeast extract, 0.15% (w/ v) NaH2PO4, 0.1% (w/v) KH2PO4. C. utilis has been cultivated for 24 hours, degraded by producing the β-mannosidase into the culture broth when transferred to shorten LBG (120 kDa) from LBG (300 kDa) . Each LBG could be separated by gel filtration chromatography. The homogeneity of shortened LBG was confirmed by paper chromatography and gel permeation chromatography (GPC) . The mannose / galactose ratio in the acid hydrolysate in shortened LBG was found to be 2.8: 1 using HPLC. The purified shortened LBG had a high level of cryoprotective activity (100%) at a concentration of 50μg⋅m1-1. Furthermore, the activity of the purified shortened LBG was higher than those of LBG, mannan and other sugars. This cryoprotective activity was specified for lactate dehydrogenase (LDH) and alcohol dehydrogenase (ADH) . The CP50 of purified shortened LBG was 8.3×10nM, which was almost one-fifth of the CP50 of BSA. The cryoprotective activity of shortened LBG against a freeze-labile enzyme, had the possibility of protecting protein component in food materials, e.g. eggs, meats etc. from freezing damage, then shortened LBG could provide for various frozen foods such as good appetite feelings. The shortened LBG is expected to be more effective as a cryprotectant than LBG for various frozen foods.
Effect of oxygen and temperature on the quality change of wakame leaf was studied. The color change of brown wakame leaf into brilliant light green upon boiling was the index of the quality. Raw leaf showed the maximum reflectance at 580 nm and the peak shifted to 560 nm upon boiling. Storage of wakame leaf with oxygen kept a high quality for 12 days showing a bright green color upon boiling like one before storage. Vacuum packed wakame readily lost the bright color. Respiration activity by wakame leaf during the storage with oxygen was proved by the consumption of oxygen and production of carbon dioxide. Storage at 0°C with oxygen gave a better result than those at 5 or 10°C in keeping the quality. These results demonstrated that the storage of wakame leaf with oxygen at low temperature to suppress the respiratory activity is effective in keeping its quality.
By-product of tofu contains useful ingredients as well as water but it begins to smell quickly. Then it becomes industrial waste, but if it is dried, powders suitable for food material are obtained. A new type drying equipment is proposed for that purpose. It is composed of air heater, drying drum, classifying chamber and cyclone separator. Ceramic balls about 5 mm diameter are contained in the drying drum and move about at high speed entrained in the hot air. Wet materials are added to the drum by rotary feeder, dispersed by the action of balls and conveyed by the gas stream. At steady operating condition, fuel flow rate, air flow rate, temperature and humidity are measured. Drying is done mainly in the drum and partly in the classification chamber according to the obtained temperature drop. The measured humidity agrees well with the predicted value from the mass balance of steam. The energy used for evaporation of water in the material was about 80% of the provided energy. This dryer has the ability of drying wet materials in short time, continuously and efficiently without burning the material. But its drying capacity is relatively small and enlargement is necessary for industrial use.
In the case of sterilizing foods by microwave heating, uneven heating is occurd inside heated foods. It is problem that unheated part occurs shortage of sterilization and overheated part occurs deterioration of foods. In this paper, uniform heating technique by arranging dielectric material is proposed, by applying previously-reported technique which using distilled water. By using the method, sterilizing food in arid condition become possible. And change of complex permittivity and thickness of material can control absorbed power distribution inside the food. We estimated this technique by focus on absorbed power inside the food and power loss inside dielectric material. As a result, uniform heating of food is achieved by arranging high-permittivity dielectric. But, high-permittivity dielectirc deteriorate heating efficiency because of increase of power loss inside dielectric material. There is trade-off between uniform heating and heating efficiency. It is considerd that an optimal value of dielectric constant and thickness is exist.
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