Many studies on the conjugates of proteins and saccharides (neoglycoproteins) have been carried out over the past 20 years to improve the function of proteins. However, most have been carried out by attachment or elimination of low-molecular weight molecules for single purposes. The structure-function relationship of the conjugates has not been well understood, and little is known about the improvement of proteins by conjugation with polysaccharides. We sought to achieve functional improvements in food proteins in multiple aspects by conjugation with charged polysaccharides. We chose bovine β-lactoglobulin (β-LG) as the target protein for improvement of the function and attached carboxymethyl dextrans (CMDs) of different molecular weight (10, 40, 70 and 162 kDa) covalently. After conjugation and purification, we explored the structure of the β-LG-CMD conjugates to prove that we could prepare conjugates while maintaining the native-like structure of protein molecule. By conjugation with CMDs, enhancement of thermal stability, improvement in the emulsifying properties and reduction of immunogenicity of β-LG could be achieved. Increases in the CMD content and net charge were viewed as the major factors in the improved emulsifying properties. Conjugation with high saccharide content using polysaccharides of higher molecular weight is believed to be effective in reduced immunogenicity of β-LG.
Modified atmosphere conditions which would prolong the storage life of ‘Rong-Rien’ rambutan (Nephilium lappaceum) was investigated. Rambutans were packed in 0.04 mm low-density polyethylene (LDPE) bags with 0, 1, 2 or 3 ventilation holes and stored at 12°C. Bags both with and without ventilation holes reduced the weight loss and extended the storage life of the fruit. Rambutan stored in a normal atmosphere had a storage life of only 8 days, while the fruits stored in the bags with and without ventilation holes retained a good appearance for 12 and 16 days, respectively. Respiration and ethylene production were significantly suppressed in rambutans that were stored in LDPE bags without ventilation hole, and electrolyte leakage from the peel tissue of the fruit was also reduced. Ascorbic acid content in control fruits decreased sharply while the fruits stored in LDPE bags maintained their original level for 10 days before decreasing. Gas composition inside the bag without ventilation holes had 7% oxygen and 14% carbon dioxide at the end of storage, while internal gas composition of the perforated bags was almost the same as normal air.
The quantitative correlation between rheological properties and characteristic values of structure for steamed abalone meat was studied. Abalone Haliotis discus was steamed in a food steamer for 1 h, 2 h, or 3 h, then cut up and separated it into cross- and vertical sections. Changes and characteristic values were enumerated by image processing and analysis techniques. Rheological properties were determined by stress-relaxation experiments; in raw abalone meat, those properties were mainly correlated with the characteristic values of collagen fibrils. For steamed meat, there was clearly a negative correlation between two of the characteristic structural values: the distance between myofibrils (Dm) and the void area between myofibrils (Am), and rheological properties. This negative correlation between structural and rheological characteristic values (elastic moduli, relaxation time, and viscosity) has been expressed by logarithmic expressions. The results suggested that rheological properties are quantitatively influenced by the characteristic values of structure.
Freshly fractionated β-lactoglobulin AB (β-Lg) from Cheddar whey was dispersed at pH 3.5, 7, and 9 buffers containing 20 mM EDTA, and circulated at 25°C through a closed loop containing a 200 nm pore size membrane, to remove traces of dust and large aggregates, and an water jacketed cuvette placed within a Dynamic Light Scattering (DLS) device for real-time data acquisition. Filtered samples were step-wise heated from 25°C to 90°C with continuous data acquisition to study dynamic changes in mean aggregate diameter (MAD). Data were analyzed by cumulant method for apparent MAD and CONTIN for size distribution. Initial MAD (IMAD) of about 200 nm, reflecting the pore size of the filter used, was observed for all experiments prior to heating. Mid-range aggregate, Agg3 (100–599 nm), was ubiquitous in all distributions and Agg1 (monomer-dimer) was only seen at pH 7 and 25°C. Increased temperatures gave rise to larger aggregates (>micron) (Agg4 and 5) with concomitant disappearance of Agg3. The greatest increase in MAD was at pH 3.5 and the lowest was at pH 9. Pre-gelation (<70°C) kinetic rates were 4.29, 1.53, and −0.11×10−4 s−1 for pH 3.5, 7.0, and 9.0, respectively, giving MADs that were 3.5, 2.2 and 0.8 fold compared to IMAD. Above 70°C (apparent gelation range), relative aggregate enlargement was greatest at pH 3.5 being 55, 21, and 4.2 fold of IMAD, respectively, for pH 3.5, 7, and 9 at 90°C. An apparent gel formed at pH 3.5 and a turbid gel/coagulum formed at pH 7 and none at pH 9. It is conceivable that increased association at pre-gelation temperatures is required for gelation. A mechanism has been postulated.
The oxidation process of a polyunsaturated acylglycerol mixed with a saturated or unsaturated acylglycerol was measured at 65°C and ca. 0% relative humidity. When two polyunsaturated acylglycerols were mixed, their oxidation processes were expressed by the kinetic model in which one acylglycerol acts as a diluent for another acylglycerol, and the oxidation product of the acylglycerol participates in the oxidation of another acylglycerol. However, the oxidation process of 1-monolinolein mixed with a saturated or monounsaturated acylglycerol was not expressed by the model but obeyed the kinetics of an autocatalytic type. The rate constant in the mixed system was greater than the constant which was predicted under the assumption that the saturated or monounsaturated acylglycerol merely acted as a diluent.
The difference in interposition ratio of pink muscle fiber among various fish species was studied to learn its influence in dorsal ordinary muscle on the post-mortem change of K-value. A remarkable mosaic pattern was exhibited in the interpositioned white and pink muscle fibers in many of the species. The relative number and area percentages of these fibers to all muscle fiber types differed greatly among fish species, and distributed from 12.9% to 56.53% in a number, and from 2.22% to 53.68% in an area. The relationship between the area and numerical percentages had significantly high positive correlation. Size of the pink muscle fiber was somewhat smaller than that of white muscle fiber.
Causes of the differences in degree of disintegration after cooking in three potato cultivars with the same starch content, Kita-akari, May Queen, and Hokkaikogane were sought by studying, properties of isolated starches, degree of cell separation in EDTA treatment, and amounts of calcium and galacturonic acid on tubers. The isolated starch of Hokkaikogane had the highest swelling power value and the highest phosphorus content, although this cultivar had the lowest degree of disintegration after cooking of the three cultivars. The degree of cell separation with EDTA, on the other hand, was higher in Kita-akari and lower in Hokkaikogane under conditions without starch swelling. Hokkaikogane had the highest calcium content in the NaCl-insoluble fraction, followed by May Queen and Kita-akari. Furthermore, Hokkaikogane had the highest content of galacturonic acid. These results suggest that factors related to the cohesion of the cells, such as the amounts of calcium and galacturonic acid, are more related to the degree of disintegration after cooking than the properties of the isolated starches in these cultivars.
Application of the flow cytometry (FCM) technique for rapid determination of the total number of microbial cells grown on yellow-fin horse mackerel was described. An ultrasonic treatment was used to remove the cells on seafood samples of yellow-fin horse, Japanese common squid, short-neck, and common octopus. Almost of cells were removed from the samples in 9 min by the treatments. Since seafood products might contain various non-microbial debris particles in addition to microbial cells, propidium iodide was used to discriminate the two groups. A fluorescence histogram distinguished the cells from the particles. The FCM method allowed determination of the number of microbial cells adhering to fish during the preservation period. Cell numbers determined by FCM well paralleled that measured by the raditional colony counting method in the range of 105–109 cells/g. One FCM assay could be completed within 60 s and the total assay time including preparation of the microbial cells was within 30 min.
Sensory test of the grassy odor with 2, 3, 5 and 7-day-old seedlings of alfalfa showed that 2-day-old seedlings are the grassiest. To identify the substance responsible for the grassy odor, the composition of fatty acid and the characteristics of lipoxygenase were investigated. The results showed that more than 50% of total fatty acid is linoleic acid; lipoxygenase has a high specificity to linoleic acid and produces mainly 13-Z, E-HPOD from linoleic acid. Because 13-Z, E-HPOD is converted to n-hexanal which has a grassy odor, the content of n-hexanal in the seedlings after germination was measured. It was found that it did not change remarkably throughout the tested growth period. Most of the n-hexanal was adsorbed weakly to insoluble materials with hydrophobic interaction. However, when the seedlings were homogenized, soluble n-hexanal increased rapidly and the increase was greatest in 2-day-old seedlings. Among three enzymes involved in the formation of n-hexanal, only the change in lipoxygenase activity correlated with that in the increase of n-hexanal.
Heat-induced gels were prepared from glycinins of various soybean cultivars at protein concentrations of 18 to 20%. Textural properties of the gels measured by a compression-decompression test were evaluated by the three-dimensional representation of the gels through factor analysis of the instrumental data and calculation of factor scores for each gel. Differences in gel texture were clearly observed among the soybean cultivars,with Shirotsurunoko gel being the most fracturable and Yamabe-A3 gel the most unfracturable. The most elastic was the gel from Hill and Matsuura gel exhibited the lowest elasticity. The existence of A4 polypeptide also contributed to the textural features of the gels. The gels of A4-containing cultivars were more unfracturable and less elastic compared to those of A4-lacking cultivars. Physical properties of the gels, gel network structure, and polypeptide composition of the glycinin were related each other to some extent. The compressibility which corresponded to the textural attribute of fracturability was related to regularity and/or pore size of network structure of the gels. The acidic polypeptide of A4 seemed to be responsible for whether the gel network was aggregate or strand type, thereby relating to the physical properties of compressibility and resiliency of the gels. The results obtained here suggest that polypeptide composition of the glycinin affects the properties of gel networks and thereby contributes to different physical and textural properties of the gels.
HPLC enantioseparation of chiral monoterpenes was studied using amylose (AD-H), cellulose (OD-H) and β-cyclodextrin (CD-Ph), phenyl carbamate derivatives as chiral stationary phases (CSPs). The contributions of various functional groups of the chiral monoterpenes in capacity factor (k), separation factor (α) and resolution factor (Rs) were investigated. AD-H column clearly showed the chiral recognition in 7 chemicals from a total of 9 analytes and especially for linalool, while the CD-Ph column could achieve efficient enantioseparation on carvone. The enantioseparation mechanism between the analytes and the CSPs is discussed. Chiral HPLC system coupled with ORD detector could be applied to isolate and directly determine the configuration of (3S)-(+)-linalool, which is not commercially available. Moreover, 100% enantiomeric excess of the isolated (3S)-(+)-linalool was observed from the SPME-GCMS result. Additionally, enantioseparation of (3S)-(+)-linalool by preparative HPLC system offered a 500-fold higher sample loading capacity than that of GC.
The effects of ginsenosides and extracts containing melanoidins, which are components of red ginseng, on TNF-α production by rat peritoneal macrophages were examined. The ginsenosides by themselves had no effect on TNF-α production, whereas water extract containing melanoidins, which are Maillard reaction products, stimulated TNF-α production by rat peritoneal macrophages. The total ginsenoside fraction and ginsenoside Rc increased TNF-α production with LPS, as did stimulation by ginsenosides with the water extract. These results suggest that for a healthy immune response it might be better to consume red ginseng itself, which contains a mixture of ginsenosides, polysaccharides and Maillard reaction products, rather than ingesting pure ginseng alone. Red ginseng as an immuno-modulator may be effective in defending against infections or tumors.
Lipases produced extracellularly by bacteria and fungi are being widely used in the food industry for flavour development. During tea processing, the possibility of enhancing the flavour of tea by the exogenous addition of lipase has not been reported. It was therefore considered worthwhile to amend tea leaves with microbial lipases and observe the changes in the flavour profile of the finished product. Among a few fungal lipases screened, the enzyme secreted by Rhizomucor miehei increased the formation of desired flavour compounds. Hence, studies were initiated to achieve enhanced production of this industrially useful enzyme. Under solid-state fermentation R.M. miehei produces an extracellular lipase in copious amounts on a simple solid substrate within 96 h, which is active at lower temperatures and at near-neutral pH. These attributes make this enzyme suitable for use during the manufacturing of tea, where reactions are carried out at temperatures of 15 to 20°C and pH range of 5 to 7. In the present study, exogenous addition of lipase resulted in an increase in flavour volatiles, which contribute to the aroma of tea.
The recovery of Escherichia coli IFO3301 injured by glycine (Gly) and/or ethanol (Et) was investigated. After treatment with 0.39 M Gly (Gly0.39) and 3 M Et (Et3), cells recovered in VSHINSKY broth (V-broth) but were unable to grow in glycerol. Further, the recovery was delayed in the presence of 0.75 M Gly and 1 M Et (Et1). In Et1-injured cells, ammonium lactate was required to restore respiratory activity. The organic ingredients of V-broth rescued the respiratory activity of the injured cells in the presence of puromycin, chloramphenicol and sodium azide. Treatment with Et at 3 M stopped the respiratory activity completely in V-broth. The β-Galactosidase (β-Gal) activity of the cells decreased slightly after treatment with 0.26 M Gly or Et1. Not only 2 M Et (Et2) combined with Gly0.26 but also Et2 alone inhibited the β-Gal activity strongly. This indicated that Et inhibited the β-Gal induction more than Gly. The results suggested that Et plays a role in the prevention of protein synthesis and respiratory electron transport to inhibit bacterial growth.
Protease hydrolyses of an Okara protein yielded antioxidative activity against the peroxidation of linoleic acid in an aqueous system at pH 7.0. Four antioxidative peptides were isolated from the hydrolysate prepared with Protease N by size exclusion chromatography and reversed-phase HPLC. The peptides were composed of two and three amino acid residues, including aromatic amino acid at the C terminal end. Their amino acid sequences were determined to be Ala-Tyr, Gly-Tyr-Tyr, Ala-Asp-Phe, and Ser-Asp-Phe, respectively. The antioxidative activity of Gly-Tyr-Tyr is nearly equal to that of carnosine.