It is well known that muscle is converted to meat as food during postmortem aging. Meat flavor as well as texture are improved during postmortem aging. The improvement of meat taste in flavor is involved in the increase in free amino acids and peptides in meats during postmortem aging. Especially, the increase in free amino acids is thought to contribute to the enhancement of brothy taste including umami, while the increase in peptides is responsible for giving mildness. The increase in peptides is caused by the action of cathepsins B and L, and calpains on muscle proteins, while the increase in free amino acids is caused by the action of aminopeptidases C, H and P on the peptides during postmortem aging.
The softening of Japanese radishes and the decomposition of pectin (0.5% pectin solution in 1/10 M phosphate buffer, pH 6.5) during the thermal process (100°C-110°C) under atmospheric and high pressures (100 MPa-400 MPa) were investigated. High pressure decreased the rates of softening for Japanese radishes and the decomposition of pectin during the thermal process. The activation volumes for the softening of Japanese radishes were 4.3 cm3/mol at 100°C and 3.1 cm3/mol at 110°C, and those for the decomposition of pectin were 10.4 cm3/mol (100°C) and 8.1 cm3/mol (110°C). Though the values indicated that the pressure lowered the pectin decomposition more than the softening of the radish, the ratios of the activation volume at 110°C to that at 100°C for both phenomena were nearly the same. These results suggested that the resistance to softening of the radish by pressure is closely related to the inhibition of the pectin decomposition in the radish by pressure.
The adsorption isotherms of some dipeptides composed of un-ionizable side chains were measured at 25°C in a single component system, and all of them obeyed the Langmuir equation. The parameters obtained at pH 7 could be roughly correlated with the hydrophobic and steric parameters of constituent amino acids. To find a method for predicting the amount of dipeptide adsorbed under various conditions, the applicability of the Polanyi adsorption potential theory was examined. The amount of dipeptide adsorbed could be roughly estimated from the adsorption isotherms of the amino acids, although the estimation lacked strictness in a physical sense.
Lactococcus lactis IO-1 isolated in our laboratory produces a peptide antibiotic, a natural nisin variant, nisin Z. Nisin Z was heat stable at acidic pH and showed a bactericidal mode of action against an indicator strain, Bacillus subtilis C1. The effect of proteolytic enzyme treatment on the activity and the antimicrobial spectrum were tested. These results indicated nearly the same characteristics as those of nisin A. In this study, it was found that two nisin variants (nisin Z and nisin A) were practically inactivated by proteinase K and actinase E. Interestingly, nisin-producing strains, L. lactis IO-1 and L. lactis NCDO 497 (a nisin A producer) were sensitive to a high concentration of nisin variants including their own products. The growth of a Gram-negative bacterium, Escherichia coli, was also inhibited by a high concentration of nisin, although nisin producers and Gram-negative bacteria are generally resistant to nisin variants.
The present study examines a method of improving the desalinization efficiency of the column-type desalinization process for soy sauce waste by feeding the water upward through the column. Four small-diameter perforated water-feeding pipes were inserted through the bottom of the desalinization column. Water was fed through these pipes into the pulverized soy sauce waste layer in the column producing a suspension. This allowed the salt in the soy sauce waste to be eluted into the water and ultimately discharged. The water was then fed again from the top of the column to wash out the remaining salt in the soy sauce waste. The proposed desalinization process addresses the problem of compressed soy sauce waste at the bottom of the column that affects the conventional column process and thus improves the stable desalinization efficiency not only for soy sauce waste produced from powdered raw materials but also for soy sauce waste produced up to five days. The efficiency of the proposed desalinization treatment is two and a half times higher than that of our previously reported process.
The influence of hop resins on the freeze-thawing resistance of Escherichia coli K-12 IFO3301 was investigated. When the freeze-thawing treatment of the strain was carried out in nutrient broth containing 0.01% of hop resins, a great decrease in the viable cell count was observed. Especially, the decrease in the count on the desoxycholate agar plate was remarkable, and no viable cells were found after 24-h freezing. Further, an extension of the lag phase was observed when the strain after freeze-thawing treatment was incubated in the nutrient broth. Namely, the freeze-thawing injury to the strain was greatly enhanced by the addition of the hop resins. It was thought that the effective utilization of hop resins for hygienic control of frozen foods is feasible.
The reduction of tetrazolium XTT with the Maillard reaction system containing various sugars or aldehydes and glycine was monitored and compared with the conventional indices of the Maillard reaction such as nitroblue tetrazolium (NBT) and dichlorophenolindophenol (DPI) reducibility, free hydroxymethylfurfural and browning. The change in XTT reducibility against the monosaccharide-glycine system showed a similar behavior as that of NBT and DPI reducibility, indicating that the Amadori product and reductones formed in the Maillard reaction may be involved in the reduction of XTT. In contrast, the XTT reducibility against the disaccharide-glycine system consisting of lactose, lactulose or cellobiose showed a different behavior from those indices. In the system, the reduction of XTT was caused by the substances which have a low reducibility of NBT. Such a property was recognized in some model systems, including the condensation reaction of D-glucosamine, that can form nitrogen-containing heterocyclic compounds such as pyrazinium and pyridinium. The condensation product of D-glucosamine rapidly lost the XTT reducibility with the addition of Cu2+. The phenomenon was also observed in the UHT-treated milk, and the decrease in the XTT reducibility during the storage was suggested to be due to the presence of Cu2+ in milk.
L-Ascorbic acid (AsA) plays an important role in the rheological properties of bread dough. Protein was extracted from the wheat flour or dough using sodium dodecyl sulfate buffer with sonication, and was separated by size-exclusion high-performance liquid chromatography into 5 fractions on the basis of molecular weight. When the dough was prepared from flour by mixing with water, the relative area of fractions 1 and 2 (molecular weights were more than 130,000) increased, while that of fractions 3 and 4 (molecular weights were 20,000-130,000) decreased. Furthermore, the relative area of fractions 1 and 2 extracted from AsA added dough, and from the dough with the superoxide anion radical (O2-) generation system increased. Thus, it was suggested that the O2- produced during the autoxidation of AsA affect the polymerization of flour protein in dough.
Two new phenolic compounds, 1-O-(2,6-dimethoxy-4-hydroxyphenyl)-β-D-glucopyranoside, named leonuriside A and β-(3,4-dihydroxyphenyl)-ethyl-O-α-L-arabinopyranosyl-(1→2)-α-L-rhamnopyranosyl)-(1→3)-D-glucopyra-noside, named leonuriside B were isolated from Leonurii Herba (dried whole part of Leonurus japonicus) along with four known flavonol glycosides, rutin, isoqeurcitrin, tiliroside and isorhamnetin 3-O-rutinoside, and a known iridoid glycoside, leonuride. Their structures were elucidated on the basis of physical and spectroscopic data. Subsequent anti-oxidative assay of these compounds using the ferric thiocyanate method revealed that they, except for leonuride, have stronger anti-oxidative activities than that of α-tocopherol. Moreover, the four flavonol glycosides and leonuriside A were identified as stronger antioxidants than 3-tert.-butyl-4-hydroxyanisole.
The pressure resistance of microbes (14 genera) was investigated at pressures ranging from 300 MPa to 500 MPa at 20°C for 20 min using a compact pressure vessel. Acinetobacter sp., Pseudomonas fluorescens and Vibrio parahaemolyticus, all of which are gram negative bacteria, and Saccharomyces cerevisiae were dead at 300 MPa, although gram positive bacteria were all alive at that pressure. At 400 MPa, Salmonella Typhimurium, Morganella morganii, Leuconostoc mesenteroides, and Candida parapsilosis were dead. At 500 MPa, Escherichia coli and Lactobacillus plantarum were dead. However, Staphylococcus aureus, Enterococcus faecalis, Corynebacterium sp., and Neosartorya hiratsukae (ascospores) survived even at 500 MPa, and the organisms except for N. hiratsukae were all gram positive bacteria.
A method was proposed to determine the optimum packaging conditions for modified atmosphere packaging (MAP) of selected fresh vegetables. Each vegetable has an optimum gas composition for maintaining quality. When vegetables are packaged in a polymeric film, the in-package environment is expected to be maintained in this optimally selected composition. Broccoli and spinach respiration rates were measured in chambers in which the optimum gas composition was maintained. Optimum packaging conditions are a combination of surface area and gas permeability in which oxygen and carbon dioxide diffusing into the package are equal to the respiration rate. In this case, the inside and outside gases are equilibrated and the in-package gas composition is apparently maintained. The optimum gas conditions were calculated based on the respiration rate, and broccoli and spinach were stored under these conditions. Experimental results were in good agreement with the predicted optimum gas composition.
A nonfermented bread-like food, quick bread, was prepared using microwave heating in the leavening process and yogurt as the acidifying agent. The use of microwave heating effectively shortened the time of breadmaking, reduced the amount of sodium bicarbonate necessary as the leavening agent and increased the specific volume of the loaf. Yogurt used as the acidifying agent improved the loaf properties such as crust color and odor. The crumb grain of the bread-like food was more homogeneous in the loaf prepared by simultaneously heating three doughs than by heating a single dough. The highest evaluations in a sensory test were obtained for the loaf prepared using microwave heating with the addition of sodium bicarbonate and yogurt. Firming during brief storage was slower in the loaf containing these additives.
We have identified two triterpene carboxylic acids of oleanolic acid and ursolic acid isolated from the leaves of loquat (Eriobotrya) by NMR spectroscopy. We have investigated the effects of oleanolic acid and ursolic acid on the growth of lymphoid leukemia Molt 4B cells and obtained results in which both compounds inhibited the proliferation of Molt 4B cells. In an in vitro experiment, ursolic acid inhibited ornithine decarboxylase (ODC) activity by 25.9% and 39.7% at the concentrations of 1 mM and 2 mM, respectively, while oleanolic acid inhibited ODC activity to a lesser extent than did ursolic acid. Both compounds slightly suppressed S-adenosylmethionine decarboxylase (AdoMetDC) activity. Polyamine contents were decreased in these compound-treated cells. These findings demonstrate that growth suppression of human Iymphoid Molt 4B cells by ursolic acid and oleanolic acid may result from the depletion of polyamines caused by the inhibition of ODC and AdoMetDC activities.