Lipid oxidation and associated changes are major causes of quality deterioration of lipids and lipid-containing foods. Oxidative deterioration of lipids directly affects their flavor, color and nutritive value. In addition, free radicals formed during this process may also damage membranes, enzymes, vitamins and proteins that may be involved in the process of ageing. Thus, assessing the extent of oxidation in foods is necessary. This paper reviews the conventional methods as well as new procedures for determining oxidative stability of lipids. Criteria for selection of methods depend on a number of factors including the nature and history of sample, the type of information required, the time available for experimentation and test conditions.
A model was developed to predict the temperature and relative humidity of air and the temperature and moisture content of polished rice in deep-bed sorption. The model was based on one-dimensional heat and mass transfer equations with the appropriate boundary conditions and was solved using the finite difference method. Inlet temperature and inlet relative humidity were used as model inputs. For validation of the model, data were collected by ventilating the height of a 1 m polished rice column in a circular (0.14 m diameter) bin with moist air. Measured and predicted temperatures, relative humidity and grain moisture at different layers were in close agreement over a test period of 72 h. Thus the model and the parameter values used are applicable for predicting moisture content in deep-bed sorption.
Fouling of stainless steel surfaces from coffee drinks, oolong tea and apple juice was studied under various conditions by the continuous-flow stirred-tank method using SUS316L particles. Among the soft drinks tested, coffee drinks containing milk protein caused the highest amount of deposit. The amount of deposit formed from the coffee drink increased almost linearly with time and depended on temperature. Furthermore, it was suggested that tannin contained in the coffee drinks is largely responsible for the severe fouling of the stainless steel particles.
The desorption behavior of fouling deposits, which had been formed on stainless steel particles from coffee drinks, was studied using various detergents. The deposit from coffee drinks was difficult to remove from stainless steel particles by NaOH solution which is usually effective in removing deposits consisting of organic substances. Among the detergents tested, a chlorinated alkaline cleaner was the most effective in removing the deposit formed from coffee drinks. Both in the chlorinated alkaline cleaner and NaOH solution, the desorption rate of the deposit followed first-order kinetics. The desorption rate constant for cleaning with the chlorinated alkaline cleaner was about 50 times that with NaOH solution. The desorption rate constant depended not only on the cleaning conditions but also on the conditions under which the deposit formed. In the case of a model deposit formed from a solution containing β-lactoglobulin and tannic acid, the desorption occurred in two stages. This reaction was not described by simple first order kinetics.
Water sorption into ethylene-vinyl alcohol copolymer (EVOH) film largely affected the sorption behavior of flavors in aqueous solution. For EVOH-F (vinyl alcohol content; 68 mol%), the sorptions of flavors increased with temperature up to 20°C (10°C for EVOH-E; vinyl alcohol content; 56 mol%), and afterwards decreased. On the basis of the behavior of the water sorption and the corresponding glass transition temperature (Tg) changes in EVOH films, the signbell-type sorption behavior was considered to result from the flexibility change due to water sorption. Namely, the increase in sorption up to 20°C-storage for EVOH-F (10°C for EVOH-E) would be caused by the increasing free volume in EVOH films with decreasing Tg due to water sorption. On the other hand, at >20°C (EVOH-F)- and 10°C (EVOH-E)-storage, because the EVOH would behave as a rubbery polymer and have a roughly constant Tg, the sorption decreased with temperature.
We investigated the influence of three types of monoglycerides, glyceryl monostearate (monostearate), glyceryl monooleate (monooleate) and glyceryl monoelaidate (monoelaidate), on protein during dough preparation. The addition of monooleate and monoelaidate decreased the amount of protein in the ethanol soluble fraction (corresponding to gliadin) and increased the water soluble fraction. Monostearate did not produce these changes in the protein fractions. The quantities of monooleate and monoelaidate in the ethanol soluble fractions were larger than that of the monostearate. The surface hydrophobicity of the water soluble protein and the 0.01 N acetic acid soluble protein in the dough was determined using the magnesium of 1-anilino-8-naphthalenesulfonic acid. The doughs containing monooleate or monoelaidate showed a decrease in the hydrophobicity of the proteins. After the defatting operation with butanol to remove the monoglycerides, the surface hydrophobicity of these defatted proteins nearly increased to the level of protein which contained no added monoglyceride. It was indicated that the unsaturated monoglycerides, monooleate and monoelaidate were adsorbed into the protein during the dough mixing and lowered the surface hydrophobicity. It was considered that the presence of a double-bond component in the fatty acid may cause bonding to the dough protein.
The temperature dependence of the gelation process for various rennet-casein micelle systems was investigated by analysis of gelation curves obtained from viscoelastic measurements under the conditions of a fixed weight ratio of rennet to casein micelle. The gelation rate for the casein micelle suspension decreased abruptly with decreasing temperature and the maximum modulus shows a maximum at 20 to 40°C. On the other hand, the gelation rate for reconstituted skim milk passed through a maximum between 30 and 40°C, and the maximum modulus decreases with increasing temperature. The gelation rate for reconstituted skim milk is much slower than that for the casein micelle solution at the corresponding temperature. These results were explained by assuming that the presence of lactose and β-lactoglobulin caused the reduction in the gelation rate for rennet-casein micelle systems.
The influences of standard sodium alginate and that extracted from “Mekabu” (sporophyll of Undaria pinnatifida) both at 3% (w/w) in diet on body weight gain, digestive organs and cecal contents were compared in rats fed test diets for 5 weeks. The latter preparation had a higher viscosity than the standard sodium alginate. Relative tissue weight of the stomach and colon did not vary among the dietary treatments. The relative weight of the small-intestinal and cecal tissues of rats fed sodium alginate extracted from “Mekabu” was heavier than that of rats fed the control diet. The weight of the cecal lumen contents was heavier in rats fed sodium alginate diets than the control diet. The total dry matter weight of the cecal contents did not vary among the dietary groups. The free and bound water content of the cecal contents was higher in both sodium alginate groups than in the control groups. Increased water content was mainly responsible for the increase in the cecal contents of sodium alginate groups. Most of the sodium alginate effects did not vary between the extracted and standard sodium alginates. However, the effects of extracted sodium alginate on tissue weight and water content of the cecal contents were larger than those of standard sodium alginate. The difference in viscosity between the preparations might be responsible for this difference.
Changes in saltiness evaluated by sensory analysis, 23Na nuclear magnetic resonance (NMR) signal and water activity (aw) of miso during fermentation were investigated. The line width (full width at half maximum intensity) of the 23Na NMR signal of the miso extract increased with fermentation time, while the aw and the saltiness decreased with fermentation time. The saltiness correlated with the line width (p<0.001) and the aw (p<0.001). The line width was not much affected by NaCl concentration, but it increased on addition of glucose, casamino acid, ethanol and lactic acid. The line width of 23Na NMR and the aw of the miso model solution consisting of sodium chloride and these substances were not much changed during storage over 100 days. This suggests that the increase in the line width and the decreases in the aw and the saltiness of miso during fermentation were caused by the increase in water-soluble substances such as glutamic acid.
Erythritol in various natural cheeses was quantitatively determined using high-performance liquid chromatography (HPLC). The peak detected at the position of erythritol by HPLC was identified by gas chromatography-mass spectrometry (GC-MS). Erythritol was detected in cheese samples ripened with fungi and contents ranged from 0.01-2.96 mg/g, and surface-ripened cheeses with white fungi especially contained more erythritol compared to blue-vein cheeses with blue fungi inside. No erythritol was found in cheese samples ripened with bacteria and without ripeness. In the case of surface-ripened cheeses, much more amounts (1.99-6.86 mg/g) of erythritol was found in their surface part compared to the inner part (0-0.33 mg/g). These results seem to suggest that erythritol is being produced by conventional microorganisms, Penicillium sp., used in ripeness.
After treatment with 200 ppm hypochlorite solution, ume fruit (Japanese apricot, Prunus mume Sieb. et Zucc.) was soaked in 3% NaCl with hardeners, Ca(OH)2 and ashed seaweeds, prepared from wakame and kelp. The fruit was stored at a pressure of 1.2×103 Pa. After six months storage, we analyzed the pectic substances and divalent cations (Ca and Mg). We also measured hardness, and yeasts and lactic acid bacteria were examined. Furthermore, the tissue structure was observed with a scanning electron microscope, and we investigated the relationships among hardness, pectic substances, and tissue structure. The following results were obtained: (1) Number of yeast was less than 102/g, and lactic acid bacteria were not detected. (2) Though ume fruit stored in 3% NaCl solution obviously softened, the fruit with 0.2% Ca(OH)2, 1.0% ashed wakame or 1.0% ashed kelp showed adequate hardness as material for hardened brined ume fruit. (3) Ca contents in alcohol insoluble substances (AIS) prepared from ume fruits with Ca(OH)2 or ashed seaweeds exhibited an increase with amounts of additives. But, Ca in ashed seaweeds seemed to bind easier to some substance in AIS, such as pectic substances, than Ca in Ca(OH)2. (4) Since an increase in water soluble pectin (WSP) and 0.4% hexametaphosphate soluble pectin (HXSP) in ume fruit without hardener is accompanied with a decrease in the amounts of 0.05 N HCl soluble pectin (HSP), it was presumed that there is some effective relationship between HSP and WSP or HXSP. When the hardener was added, the changes in HSP, WSP and HXSP were inhibited. Furthermore, ashed seaweeds seemed to promote the change in HSP to 0.05 N NaOH soluble pectin (SSP). (5) Using a scanning electron microscope, small rectangular cells were clearly observed in the sarcocarp of fresh ume fruit. But, cells of stored ume fruit without hardener had been transformed to unclear flat shapes. Those of the fruit with Ca(OH)2 or ashed seaweeds were observed as rectangular cells similar to that of the fresh fruit. The changes in cell shapes of the fruit without hardener were understood to be caused by the transformation of HSP to WSP and HXSP. Such changes of pectic substances, especially from HSP to WSP seemed to cause a decrease in hardness. The fruit with Ca(OH)2 or ashed seaweeds in which firm rectangular cells were observed, had a lower ratio of WSP and higher ratio of HSP and SSP. The cell shapes might originate from the strengthening of the tissue structure due to intra- and intermolecular crosslinking between the pectic substances and Ca in the hardeners.
In order to improve the odor of foods containing volatile sulfur compounds, we screened 198 molds and yeasts, and found 14 molds that provided an 80% decrease in 1,000 ppm didecyl sulfide in MY medium after 4 days of culture shaking at 25°C. Of the 14 molds, 13 of which were molds of the Aspergillus niger group, Asp. awamori var. kawachii No. 91 most effectively decreased the amount of didecyl sulfide. This mold oxidized dibutyl sulfide into dibutyl sulfoxide and dibutyl sulfone. The optimum pH for conversion of dibutyl sulfide was approximately pH 6.5, and the optimum temperature was approximately 30°C. If used to treat food, it could weaken the pungent odor of onion and garlic.
A genetic algorithm (GA) was applied to optimizing sets of aroma components in black teas for calculating multiple linear regression (MLR) models to predict sensory scores. Selections of components were performed so as to maximize the coefficients of determination (R2) based on three and four components. True optimum combinations of components seemed to be found by GA because almost the same components were repeatedly selected by optimization starting from randomized conditions. Comparing R2s calculated from stepwise MLR and GA-MLR, the predictability of GA-MLR was generally superior over those from stepwise MLR. Although GA-MLR requires a much longer time than that for stepwise MLR, the time is much shorter than those required for all possible regression methods. (E)-2-hexenal, (Z)-3-hexen-1-ol, linalool and α-cedrene tended to be selected by GA-MLR while 1-penten-3-ol, linalool oxide (trans furanoid), (E,E)-2,4-heptadienal, α-cedrene were selected by stepwise MLR.