SOLUBILITY AND EMULSIFYING PROPERTIES OF KAPPA CASEIN AND ITS CASEINOMACROPEPTIDE

Kappa-casein A was treated with chymosin in order to isolate the caseino-macropeptide corresponding to the C-terminal 106–169 residues of K-casein. Whole casein, K-casein and the caseinomacropeptide (CMP) were studied for their water solubility and emulsifying activity. The CMP was soluble over the range of pH from 1 to 10, with a "minimum" solubility (88%) in the range of pH 1–5 and a "maximum" solubility (98%) in the range of pH 5–10. For whole casein and K-casein, at pH values above 5.5, the emulsifying activity increased when pH increased and the maximum value was obtained for very alkaline solutions; for pH values below 4.5, the increase in emulsifying activity was much more pronounced at pH 2.5; below pH 2.5, emulsifying activity decreased. For CMP, the increase in emulsifying activity was much more pronounced in the acidic range than in the alkaline range. After 24 h storage and heating of the emulsion, a large pH-dependant decrease of emulsifying activity (22–60%) was observed for CMP for pH values below 4.0; under the same conditions, the emulsifying activity of whole casein and K-casein showed a 5–19% and a 1–21% decrease, respectively. For pH values above 6.0, a 22–59% decrease was observed for CMP as compared to a 1–12% and a 4–17% decrease with whole casein and K-casein, respectively.     

ENZYMATICALLY AND CHEMICALLY MODIFIED ZEIN FOR IMPROVEMENT OF FUNCTIONAL PROPERTIES

Limited specific hydrolysis of zein by trypsin was used to produce 1.42%, 1.70%, and 1.87% hydrolysates (percentage of peptide bonds cleaved), containing three to four polypeptides (by Fast Protein Liquid Chromatography (FPLC)) ranging in size from ～16,000 to 3,500 daltons. The mixtures of polypeptides had substantially increased solubilities at pH below 11, including at the isoelectric point of zein (pH 6–7). In general, the emulsifying activity index was less for the hydrolysates than for native zein; the emulsion stability was higher for the 1.70% hydrolysate than was the emulsion of native zein only at pH above 8. At lower pHs, the stability of the emulsions was similar for all samples. The foamability (% overrun) of the hydrolysates was higher than for native zein; the foam stability was higher for the 1.87% hydrolysate than for the other hydrolysates. Phosphorylation and deamidation of the hydrolysates markedly increased the water solubility in the pH range from 4 to 10. Chemical modification of the native zein improved the solubility at pH 2 to 9 after phosphorylation and pH 6 to 11 after deamidation as compared to the native protein. In general, the emulsifying activity index, as well as its stability, was less for the phosphorylated and deamidated hydrolysates than for native zein but the emulsifying activity index of deamidated native zein was higher at pH 7 to 11. Foaming activity and stability of chemically modified hydrolysates were similar to the 1.87% hydrolysate.     

脱色血蛋白乳化特性研究

比较了猪脱色血蛋白粉（FP）、猪血细胞蛋白粉（CP）、酶解法脱色血蛋白粉（EP）和大豆分离蛋白粉（PI）的乳化特性,并着重研究了乳化时间、蛋白浓度、油的比例、pH值、乳化温度对FP蛋白乳化性的影响.     

DESTRUCTION OF POTATO PEEL TRYPSIN INHIBITOR BY PEELING AND EXTRUSION COOKING

Potato peels, a by-product of potato processing, can serve as a source of concentrated dietary fiber, but potato trypsin inhibitors (TI) in peels could reduce nutritional quality. Peels prepared by two methods (abrasion or steam) were extruded at 110C or 150C with feed moistures of either 30% or 35%. Prior to extrusion, abrasion and steam peels contained 45.57 and 8.06 TIU/g, respectively. Extrusion reduced TI activity by 75–85% in abrasion peels, but no reductions were observed for steam peels. TI may not pose a nutritional problem for steam peels with or without extrusion. Abrasion peels should be extruded, or processed by another thermal method, prior to use in foods.     

THE MEASUREMENT OF EMULSIFYING CAPACITY BY ELECTRICAL RESISTANCE

SUMMARY— A method was developed to objectively measure the emulsifying capacity (ECJ of meat and fish protein extracts by electrical resistance. The method of Swift et al. (1967) was modified to deliver oil at a constinuous rate at the point of blender agitation, thus forming an emulsion for testing the validity of the electrical resistance method. This modification reduced the variance of the end-point determination within samples. The precision of end-point determinations by electrical resistance was equivalent to the modified visual method, and had the advantages of being objective, having a finite end-point and providing a continuous record of the emulsion during formation and collapse. The EC of fresh muscle slurry extracts from fish were higher than those from beef and pork. However, the EC of fresh muscle supernatant extracts ranked from highest to lowest are beef, fish and pork, respectively. In all cases, the EC of supernatant and fresh muscle extracts was higher than the slurry and frozen muscle extracts, respectively.     

STRUCTURE AND SOLUBILITY OF COLLAGEN AND GLYCOSAMINOGLYCANS IN TWO BOVINE MUSCLES WITH DIFFERENT TEXTURAL PROPERTIES

Meat samples were collected from two bovine muscles , psoas major and semitendinosus, exhibiting different textural properties as measured by Warner Bratzler Shear Force. The structure and composition of the intramuscular connective tissue was compared by transmission electron microscopy, fibril diameter measurements, statistical analysis, collagen and glycosaminoglycan solubility studies in acetic acid and acetic acid added pepsin. The mean fibril diameter was significantly larger in the tougher muscle and the fibrils were tightly bundled into fibers. The tender muscle exhibited mainly randomly oriented fibrils with more space in between. The biochemical study confirmed the microscopy, showing a higher hexuronic acid/hydroxyproline ratio in the tender muscle, mainly in pepsin digested samples. The content of hydroxyproline after defatting in acetone was 30% higher in ST. No major differences were seen in the proportion of acid labile or stable cross-links in the collagen of the tough and tender muscle.     

变性淀粉及谷朊粉对面团特性的影响研究

研究淀粉及变性淀粉、谷朊粉对面团特性的影响。结果显示：在面粉中，按4％的比例添加马铃薯变性淀粉，对面团的稳定时间、弱化度及抗张强度等均有显著的影响（P〈0．01）；添加6％木薯变性淀粉，面团抗张力增加26、6％；添加3％的谷朊粉，面团形成时间及稳定时间均有较大增加。木薯原淀粉及其变性淀粉等对面团的特性影响不大。     

TRYPSIN INHIBITORS OF WINGED BEAN TUBERS (PSOPHOCARPUS TETRAGONOLOBUS): PURIFICATION AND PROPERTIES

Two trypsin inhibitors (WBT-TI-I and WBT-TI-II) which differ in their physicochemical properties have been isolated from winged bean tubers, using affinity chromatography and ion-exchange chromatography. WBT-TI-I inhibits trypsin, has a molecular weight of 45,000 (± 1000) and has two subunits of M_r 22,000 as determined by gel filtration, ultracentrifugation and SDS-PAGE studies. WBT-TI-II inhibits trypsin in addition to chymotrypsin and pepsin, and has a molecular weight of 24,000 (± 1000) as estimated by gel-filtration, ultracentrifugation and SDS-PAGE. Although WBT-TI-I and WBT-TI-II were homogeneous by gel filtration, ultracentrifugation and SDS-PAGE, they were electrophoretically heterogeneous on PAGE at pH 8.3. Since WBT-TI-II, when purified by immunoaffinity chromatography, did not show heterogeneity by PAGE at pH 8.3, it was concluded that heterogeneity arose from modification of the native inhibitor on trypsin affinity column. WBT-TI-I and WBT-TI-II are immunologically different. The antibodies of WBT-TI-II cross react with winged bean seed extract.     

DETERMINATION OF COLLAGEN SOLUBILITY AND CONCENTRATION IN MEAT BY NEAR INFRARED SPECTROSCOPY

This paper examines the feasibility of measuring collagen properties by near infrared spectroscopy (NIRS) in ovine Semimembranosus and Biceps femoris muscles. Because collagen concentration within a muscle was rather narrow, the R for collagen concentration was never more than 0.55. By contrast, R for solubility was better, especially for Semimembranosus, always exceeding 0.80. No one scanning method — fiberoptic probe or the in-built transport module — was superior, either in reflectance or transmittance modes. The equations developed were tested for predictive power by cross-validation procedures within muscles and between muscles. In the latter case, Biceps femoris data were used in a Semimembranosus equation and vice versa. The equations worked in any combination. However, there were indications that the correlations were sensitive to the state of the meat, whole tissue or homogenized, although the wavelength range 910 to 950 nm did not vary with sample state.