MEASUREMENT OF FLOW ABILITY OF BUTTER BY CAPILLARY RHEOMETRY

Capillary rheometry was used to study and compare the rheological behavior of butters made from supercritically fractionated high melting triglyceride (HMT) and anhydrous milk fat (AMF) at different temperatures. Application of shear rates in the range of 17.37 to 346.93 _S⁻¹ showed a strong dependency of flow behavior on the capillary diameter, indicating slippage at the walls. Shear rates were corrected for wall-slippage using capillaries with different diameters but the same length, and for non-Newtonian behavior using the Rabinowitsch procedure. Shear stresses were corrected for entrance effect using capillaries of the same diameter but different lengths. Power law consistency indices (K), determined from loglog plots of corrected shear stresses versus shear rates, were found to have a negative correlation with temperature. Higher K values were observed for HMT butter depicting its more solid-like behavior due to greater concentration of high melting triglycerides. A slight increase in the K values was observed on storage probably due to rearrangement of fat crystals and formation of secondary bonds between them. Flow indices were found to be relatively insensitive to both time and temperature of storage. From the flow curves (apparent viscosity versus shear rates), master curves were generated using the time-temperature superposition principle.     

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.     

MEASUREMENT OF HEAT CAPACITY FOR BORAGE SEEDS BY DIFFERENTIAL SCANNING CALORIMETRY

Specific heat capacity of borage seeds was determined by differential scanning calorimetry (DSC) in the temperature range of 5 to 80C and moisture content range of 0.47 to 30.31 % wet basis. The specific heat ranged from 0.57 to 2.48 kJ/kgK. A multiple regression model with interaction terms correlated well the specific heat to temperature (T) and moisture content (M). It was found that the interaction terms T*M and T*M² were significant (α=0.01) and thus were included in the model, and the term M*T² was insignificant. Effect of measurement techniques with DSC were also investigated in this study to ensure that true specific heat values were obtained. Seal condition of the sample holders during DSC measurement had considerable effect on the specific heat of borage seeds. The difference between the specific heat of sealed and unsealed samples increased as seed moisture content increased, especially at higher temperatures. For the measurement of the specific heat of borage seeds by DSC in the above-mentioned temperature and moisture content ranges, an average of 5.75% deviation was found between the measurement with and without blank compensation.     

PREPARATION OF TOFU GEL BY HIGH-PRESSURE PROCESSING

The potential of high-pressure processing to produce high-quality foods that are microbiologically safe and with extended shelf life has received much attention in the food industry. Tofu is a nutritious and digestible food that is widely consumed in the world. Differential scanning calorimetry analysis indicated that high-pressure processing could denature soymilk protein completely. Soymilk mixed with glucono-delta-lactone, when processed at 500 MPa for 20 min, could form tofu gel with strength. These gels had smooth appearance, homogeneous texture, light-yellow color and less off-flavors. Scanning electron microscopy revealed it had a cross-linked network structure. This provided a novel method for the soymilk and tofu manufacturers to process soymilk for making tofu gels with new properties.

PRACTICAL APPLICATIONS

High-pressure processing is now getting an increasing interest in the food industry. It is a possible alternative to heat treatment. Soy proteins play an important role in food consumption worldwide. Tofu represents one of the major categories of soy foods. The objectives of this study were to investigate the novel method to make tofu with new properties by high-pressure processing. The results will help soymilk and tofu manufacturers to widen the method to make tofu gels.     

CAPILLARY EXTRUSION VISCOMETER FOR THE VISCOSITY MEASUREMENT OF FISH PROTEIN PASTE

To overcome various limitations of conventional viscometers in measuring salted or unsalted surimi paste, a capillary extrusion viscometer was developed. The viscosity of surimi paste was measured as a function of moisture content (MC) (75–80%), salt content (2–4%) and liquid egg white (LEW) content (2–4%). As moisture, salt and LEW contents increased, viscosity gradually decreased. The viscosity values, as affected by MCs, showed a highly negative relationship with fracture properties of surimi gel, especially shear stress from the torsion test, indicating that MC is linearly correlated to the strength of gels at fracture. This easy and quick viscosity measurement can effectively facilitate the production control of comminuted muscle foods, including surimi paste.

PRACTICAL APPLICATIONS

There had been a difficulty to measure the exact viscosity of comminuted muscle food pastes when conventional viscometers were used. This was due to the non-linearity between dilution rates and viscosity of muscle paste, or limited range of shear rate during viscosity measurement. New developed small capillary extrusion viscometer can measure a wide range of comminuted muscle paste viscosity. When using this capillary viscometer, flow behavior of non-Newtonian surimi paste and other comminuted muscle paste can be well defined.     

COMPARISON OF IN-LINE CONSISTENCY MEASUREMENT OF TOMATO CONCENTRATES USING ULTRASONICS AND CAPILLARY METHODS

This study focuses on the development of a noninvasive, in‐line rheometer using ultrasonics and its comparison with data from a traditional capillary viscometer. The ultrasonic based pointwise viscosity measurement technique combines a measurement of the velocity profile and the pressure drop to determine the shear rate and the shear stress distributions, respectively in a pipe. The experiments were carried out using tomato concentrates at 8.75%, 12.75%, and 17.10% total solids content. The flow system consisted of a 53.2 mm diameter acrylic tube, a positive displacement pump and two pressure transducers. Multiple shear viscosity‐shear rate data were recorded under actual pipeline conditions from a single combined measurement of the velocity profiles using ultrasonics and the pressure gradient, using the pressure transducers. The samples showed shear thinning behavior and a yield stress. Power law and Casson models were used to fit the data and both obtained R² values higher than 0.99. The yield stress was also directly determined from the velocity profiles. Shear viscosity versus shear rate data of the 12.75% total solids sample were obtained by capillary rheometry at four different flow rates. These showed very‐good agreement with those obtained using the velocity profile technique.     

ANALYSIS OF THE ELASTIC MODULUS OF AGAR GEL BY INDENTATION

This study used the approach taken by Bourne to obtain the compressive and shear components for an agar gel. But in addition, the low strain regime for the same experiments was used to evaluate the gel's elastic modulus using the theory of elasticity. Compression testing, using lubricated teflon platens and a travelling microscope, was used to independently measure the gel's elastic modulus (52 kNm⁻²) and Poisson's ratio (0.32). The compressive and shear coefficients compared favourably with analyses performed by other researchers, and indicated that shear dominated in the failure of the gel under the probe. Indentation measurements of reaction force (P) and deformation (h) were analysed with the theoretical relationship for frictionless flat cylinder indentation. A good linear fit (r²= 0.991) was obtained for P/h versus indenter radius, indicating the validity of the analysis. The value of the elastic modulus derived from indentation was 79 kNm⁻², an overestimate of 52%. The larger value suggests that additional factors to those considered in the theoretical model influence the indentation process, such as the presence of pores in the gel, frictional forces during indentation, and elastic mismatch between indenter and gel. Similarity in results for the elastic modulus determined from indentation compared to compression, indicates that a simple testing method can yield a more comprehensive evaluation of food textural quality.     

不同添加剂对鸡腿肉盐溶蛋白热诱导凝胶保水性的影响

以鸡腿肉为原料,研究不同添加剂对鸡肉盐溶蛋白热诱导凝胶保水性的影响.从鸡腿肉中提取盐溶蛋白,再向盐溶蛋白溶液中分别添加大豆分离蛋白(3%、5%、7%、9%、11%)、卡拉胶(0.1%、0.3%、0.5%、0.7%、0.9%)、花生蛋白(3%、5%、7%、9%、11%),再分别在40℃～90℃加热.形成热诱导凝胶,用离心法测定其凝胶的保水性.结果表明,当大豆分离蛋白、卡拉胶、花生蛋白单独分别添加浓度为7%、0.5%、7%,加热温度分别为80、70、80℃时,凝胶的保水性达到最佳.     

利用毛细管电泳法测定乳品中乳铁蛋白含量

将样品经样品缓冲液处理,毛细管柱选择为直径50 μm,有效长度400 mm的涂层中性毛细管柱;柱温为40℃;缓冲溶液为柠檬酸缓冲液(pH为3.0±0.2);工作电压为21 kV;检测波长为214nm;进样时间为5s,进行检测.结果乳铁蛋白平均回收率为75%～91%;相对标准偏差(RSD)为1.1%～2.8%;最低检出限位0.003mg/mL.该方法简便,准确,灵敏度高,能快速检测乳品中乳铁蛋白含量.     

INVESTIGATION OF FISH OIL QUALITY BY DIRECT CAPILLARY GAS CHROMATOGRAPHY

A simple, rapid method to separate and identify volatile compounds from oils extracted from farm raised catfish and Gulf of Mexico menhaden is described. Major volatile compounds that can be used as markers to assess for quality were the following: pentane, heptane, pentanal, hexanal, pentylfuran, heptadienals, nonanal, decanal, and decadienals. The method was also used to assess the quality of a commercial sample of fish oil sold as a source of omega-3 fatty acids. The method can be used to investigate off-flavors caused by handling, processing, or storage.     

HEAT STABILITY OF STAPHYLOCOAGULASE MEASURED BY A CAPILLARY TUBE METHOD

Staphylocoagulase is highly heat resistant. Inactivation profiles of crude staphylocoagulase at 80, 100 and 121°C showed that total inactivation occurred after heating for 5 h,2 h and 30 min, respectively. Heat treated coagulase has the ability to reactivate when placed at 25°C for 24 hrs similar to previous observations on staphylococcal enterotoxins B and C. Staphylocoagulase could be recovered from beef broth and chicken broth before or after heating at 80°C for 5 min. Coagulase activities were measured by a quantitative capillary tube method.     

ANALYSIS OF SURIMI GEL PROPERTIES BY COMPRESSION AND PENETRATION TESTS

Gel properties of surimi of different quality were analyzed using compression and penetration tests. Parameters used to vary the surimi quality were species, freshness, freeze-abuse and added ingredients. Compressive force at failure was more discriminative than penetration force. The result of a failure response analysis suggests that the compression test is useful in assessing the cohesive property, while the penetration test is better for assessing density and compactness. Good correlations between compression and penetration force values were seen in surimi gels prepared from the same species with and without ingredients, while poor correlations were observed in the surimi which either underwent freeze-abuse or was prepared from different species.     

THE ANALYSIS OF NON-VOLATILE CONSTITUENTS OF WINE BY GLASS CAPILLARY GAS CHROMATOGRAPHY*

A considerable amount of quantitative and qualitative information on the non-volatile constituents of wine (acids, sugars, and polyols) can be readily obtained, from small sample volumes without prefractionation, by glass capillary gas chromatography of their trimethylsilyl derivatives. A continuous check on the correct functioning of the method, and in particular on the inertness of the glass capillary and injector, is obtained by the use of two internal standards, whose trimethylsilyl derivatives vary considerably in stability. Any variation in the ratio of the peak areas of the latter derivatives indicates incorrect sample preparation or possible adsorptive/catalytic activity of the GC system. As a general method, the technique may be applied to other alcoholic beverages.     

聚丙烯酰胺凝胶电泳研究硫酸铵盐析分离猪血清IgG

通过聚丙烯酰胺凝胶电泳对硫酸铵盐析分离猪血清G型免疫球蛋白进行了研究，结果显示pH值7．4时，猪血清IgG主要沉淀区间为硫酸铵饱和度25-40％，10倍稀释猪血清IgG最佳硫酸铵沉淀参数为：pH值7．4，硫酸铵饱和度37％，此时IgG得率为80．5％，纯度为72．9％。沉淀的血清蛋白中还含有约12％白蛋白和9％其它γ-球蛋白。沉淀时IgG活性保持不变。