DEPENDENCE OF THERMAL PROPERTIES AS WELL AS NETWORK MICROSTRUCTURE AND RHEOLOGY ON PROTEIN CONCENTRATION FOR OVALBUMIN AND VICILIN

Critical protein concentration (CPC) values for network formation for ovalbumin (5.5%, w/w) and vicilin (8%, w/w) were determined based on the appearance of a well crosslinked network using light microscopy, in conjunction with a significant decrease in the dynamic rheological parameter, tan δ= G"/G'. Increasing protein concentration resulted in increased G' (storage modulus) and G" (loss modulus) for both proteins. These relationships were described by power law equations. Ovalbumin networks had a lower CPC and tan δ value at protein concentrations above the CPC than did vicilin networks. This was related to a greater increase in the G' and G" moduli during the initial stages of cooling.     

MICROSTRUCTURE AND PHYSICAL PROPERTIES OF QUARG CHEESE AS AFFECTED BY DIFFERENT HEAT TREATMENTS

The effects of different heat treatments on the rheological properties, microstructure and yield of production of quarg cheese were investigated. Three levels of time–temperature combination were used: 72C–16 s, 82C–5 min, 90C–5 min. Rheological properties were studied by means of frequency sweep experiment with the measurement of elastic modulus ( G' ). Microstructures of samples were observed by scanning electron microscopy (SEM). Maximum and minimum G' and cheese yield were obtained at 90 and 72C, respectively ( P <  0.05). Yield at 82 and 90C was higher than 72C but difference between heat treatment at 82 and 90C was not significant ( P <  0.05). G' values at 82 and 90C were higher than that at 72C. The difference between 82 and 90C was initially low; subsequently increase in frequency made G' at 90C higher than 82C. SEM micrographs of samples at 82 and 90C were closely similar and no differences were observed between them. Micrographs showed the regular microstructure with branched clusters and numerous small pores at 82 and 90C, whereas micrographs of heat treatment at 72C had larger protein aggregates and fewer but larger pores. This study showed that heat treatments at 82 and 90C were more suitable for quarg cheese making than that at 72C.

PRACTICAL APPLICATIONS

Quarg cheese is one of the most popular acid-coagulated cheeses. This study shows that heat treatment at 82C–5 min is preferred for quarg production compared with other heat treatments. Contribution of denatured whey proteins in gel network led to higher cheese-making yield as well as high nutrition value. Heat treatment at 82C is also suggested in economic and energy consumption aspect.     

RHEOLOGY AND THERMAL PROPERTIES OF SYRUPY COMPOSITES OF SACCHARIDES AND MILKFAT

Viscous syrups with between 20 and 34% moisture were made from homogenized slurries of sugars, nonfat dry milk, anhydrous butteroil and emulsifiers. Homogenized mixtures were condensed under vacuum at 45C for 35 min, to form ordered structures with a syrup-like consistency. Complex viscosity determined through dynamic spectrometry increased with increasing fat content. At low frequency, high fructose corn syrup and maltose-based syrups showed more solid-like behavior (G" > G") while the sucrose-based syrup was more liquid (G" > G'). Thermal analyses showed all composites to have a uniform melting range (95–140C), whereas the original components melted in the range 20–200C. The rheological and thermal properties suggest that these syrups could be useful confectionery ingredients.     

EFFECT OF pH AND CATIONS ON THE THERMALLY INDUCED GELATION OF OVALBUMIN

The gelation of ovalbumin in the presence of salts containing Ca⁺² and Mg⁺² at various pH values was investigated. Characteristics of the gels produced were evaluated using penetration measurements on an Ottawa Texture Measuring System as well as dynamic rheology on a Bohlin VOR rheometer. Gel properties were related to cation binding (equilibrium dialysis) and to changes in protein structure (differential scanning calorimetry). Cation binding generally increased with increasing salt concentration, and Mg⁺² bound to a greater extent than Ca⁺² at the higher levels studied. The impact of this binding on gel structure was dependent on pH and the technique used to evaluate structure. At pH 5 proteins tended to coagulate regardless of the type or amount of salt. At pH 7, the highest rigidity values from penetration measurements were obtained at salt levels of 0.005 M. At pH 9, the salt concentration for maximum rigidity varied with the salt, while the storage moduli (G') from dynamic rheology were highest at the highest salt concentration used. Based on rigidity data, the inclusion of 0.005 M MgSo₄ would give a product with the greatest rigidity over a wide pH range.     

INFLUENCE OF CULTIVAR AND STEEP REGIME ON SOME PROTEIN RELATED PROPERTIES OF SORGHUM MALTS

Cold water extract (CWE), cold water soluble protein (CWS-protein), CWS-protein modification and free alpha amino nitrogen (FAN) were determined for three improved Nigerian sorghum cultivars malted under four different steep conditions. The levels of these variables in the sorghum malts differed significantly when malted under identical steep regimes. This indicates that soluble protein accumulation and modification in these grains are cultivar dependent. Grains exposed to a combination of air rest cycles and final warm steeping gave highest values of cold water solubles, CWS-protein modification and FAN. Amylolytic activity was enhanced over the rate of proteolysis when grains were steeped under regimes incorporating final warm steep. Cultivar SK 5912 with highest soluble protein solubilisation activity showed lowest FAN accumulation under all steep regimes suggesting roles for factors other than proteolysis in FAN accumulation.     

热处理对牛奶蛋白纤维纱性能的影响

研究了热处理对牛奶蛋白纤维纱性能的影响,包括热收缩、白度和黄度、断裂强度和断裂仲长率、失重率.通过对实验结果的分析可以发现,当温度低于150℃时,牛奶蛋白纤维纱的性能变化较小;当温度高于150℃时,牛奶蛋白纤维纱的性能变化显著,说明牛奶蛋白纤维纱在后整理加工中热处理温度应该低于150℃,以减少对牛奶蛋白纱性能的影响.     

羟丙基和磷酸酯化对不同玉米杂交种淀粉糊化特性的影响

采用了实验室方法提取了高直链、糯性和普通玉米杂交种的淀粉，并分别进行了羟丙基化和磷酸酯化反应。采用快速粘度分析仪（RVA）和差示扫描量热仪（DSC）分别分析了淀粉的糊化和热力学性质。结果表明：羟丙基化和磷酸酯化反应都不同程度地降低了所有淀粉的热焓值和糊化温度，缩短了出峰时间，增加了峰值粘度。二者相比，羟丙基化更显著地降低了原淀粉的糊化温度和热焓值，缩短了出峰时间；而磷酸酯化则更明显地提高了原淀粉的峰值粘度和终粘度．     

THE THERMAL PROPERTIES OF POTATOES AND CARROTS AS AFFECTED BY THERMAL PROCESSING1

The effects of processing on the thermal properties of white potatoes and carrots were studied. The test samples were blanched, boiled, cooked and canned. Whole potato tubers were baked to study the effects of starch gelatinization. The thermal conductivity (k) and density (ρ) were measured and the specific heat (c_p) and thermal diffusivity (α) were calculated. Results showed that in general, α initially decreased and then increased during processing. Test samples were found to have a gain in α when their moisture content increased by more than 9%. The α of potatoes decreased after canning and increased after boiling. In carrots, a similar trend was also observed but to a lesser degree. The k of potatoes was unaffected after blanching or cooking. In all the processing baking study showed that gelatinization significantly decreased the k of potatoes.     

EFFECTS OF CURING ON MORPHOLOGICAL AND THERMAL PROPERTIES OF SALMON-NOSE CARTILAGE AS A VINEGARED DISH IN JAPAN

ABSTRACT Sliced salmon-nose cartilage was cured in 4% acetic acid up to 168h. Using optical microscopy, we observed the reddish-purple color produced by staining with toluisine-blue turned lighter during curing. This meant that the mucopoly-saccharide level of cartilage matrix decreased, causing the structure of the cartilage to become porous. In addition, using scanning electron microscopy, loosenings of collagen fibers was observed after 72 h of curing, thus making the structure of the cartilage fragile. DSC thermograms showed that the denaturation temperature of the native collagen fibers was lowered and an additional peak appeared during curing. These findings lead us to suggest that the collagen in salmon-nose cartilage changes qualitatively during curing.     

WHEY PROTEIN DENATURATION OF UHT PROCESSED MILK AND ITS EFFECT ON RHEOLOGY OF YOGURT

The denaturation of whey proteins in whole milk during processing by the indirect UHT and vat systems was determined. Whey protein denaturation plateaued at about 88% following a UHT heat treatment of 149°C for 10 s. However, it reached about 88% with a vat heat treatment of 82°C for 5 min and reached 95 to nearly 100% after 10 to 15 min. Vat processing under pasteurizing conditions at 63°C for 30 min resulted in less than 10% denaturation. The yogurts prepared from the vat processed milk had considerably higher structural firmness than those prepared from the UHT milk, as confirmed by the lower value of curd firmness and the higher shear stress of these yogurts. It was also found that the structural or curd firmness of yogurts prepared from UHT milk was highest when the milk was processed for 3.3 s process holding time and was lower when the milk was processed for longer or shorter process holding times. The results suggest that the vat process at 63°C or 82°C brings about a specific change in the whey protein which leads to formation of a firm structure. This change apparently does not occur during the brief UHT treatment.