| Goat milk has a high nutritional value and health care. But compared with cow milk, theprocessing characteristics are relatively poor and it can not be fully utilized in the productin process. Sohow to improve the thermal stability and coagulation properties of goat milk have become the presentmost intractable problems. This study was carried out selecting the best complex stability salts toimprove the liquid UHT goat milk heat stability on the basis of study that the effects of different heattemperature and salts on physical, chemical properties, protein structural chatacteristics, salts balanceand thermal stability of goat milk. In the terms of coagulation properties, selecting different evaluationmethods to evaluate the impact of different calcium, phosphates and pH value on rennet induced curdcharacteristics and determined the optimum condition to obtain better coagulation properties. What’smore, the ways of ultrasonic treatment to goat milk and milk power addition were considered and selectthe preffered approach by mathematical modeling. The study showed us that:(1) pH value and apparent viscosity presented small fluctuating growth but significantly. Alcoholstability reduced; compared to the cow milk, the centrifugal sediment of goat milk, sedimentation rate,turbiscan stability index and the rate of denatured whey protein increased significantly, and thedenaturizing rate of β-LG was greater than α-LA; the hydrophobic sites on the casein micelles surfaceincreased, but the hydrophobicity decreased; particle size of protein increased significantly; proteinsecondary structures had changes significantly. What’ more, the transformation trend of soluble calciumand solubled phosphorus to colloidal phase was obvious. These changes were sufficient to show thestability of goat milk reduced signicantly with temperature increasing.(2) The four stability salts of Sodium citrate(TSC), disodium hydrogen phosphate(DSHP), dodiumtripolyphosphate(STPP) and dodium pyrophosphate(TSP) made pH value and viscosity have differentincrease; the size of protein particle reduced more than twice; the denaturation rate of whey protein alsodecreased significantly; the sediment presented decrease first and then increase. The determination ofcomplex stability salts compounds by the four second-order factors simplex lattice mixture design wasTSC:DSHP:STPP:TSP=6:1:3:0. When the amount of salts was0.15%, the sediment, denaturation ofwhey protein and TSI value could reach minimum, which the stability of UHT goat milk was best.(3) The protein composition, content and calcium phosphate balance of sediment and supernatantof goat milk with heat treated changed significantly. The whey proteins, α-casein, calcium andphosphorus content in supernatant reduced and increased in sediment. While these changes could beregulated and protected after complex salts addition, which the whey protein, α-casein, calcium andphosphate levels increased significantly.(4) From dynamic rheological perspective, When calcium, phosphate and pH value were0.03~0.04%,0.01%,5.8~6.0, respectively, the G’max and CFRmax were more bigger, GT of goat milkcoagulation was smaller; From static textural perspective, the ideal gel of goat milk could be got whencalcium, phosphate and Ph value were0.05%,0.02%,5.8, respectively. And from the microscopic perspective, the tree factors were0.05%,0.05%,5.8that made the curd structure more compective. Theregression models of water holding capacity, hardness, GT, and elasticity were significant, and differentthree factors value could be got depending on the actual needs. When the calcium, phosphate, pH valuewere0.03%,0.05%,5.8, respectively, the WHC, hardness, elasticity were maximum.(5) US treatment could make the protein particle size reducing, distribution homogenous, rate ofwhey denaturation and soluble calcium and soluble phosphorus increasing, which might affect thecoagulation properties of goat milk. Appropriate US treatment time was10~15min, power was800w~1000w, addition of milk powder was3%~4%. The regression models of water capacity andhardness had a high feasibility, which were designed by orthogonal rotation experiment. The optimizedpower, time and amount of milk powder were650.32w,15min and3.33%, respectively, and the bestvalue of water holding capacity and hardness could be achieved24.01%and110.23N.（6） US treatment and milk power addition could also improve the goat milk acid gel. When thetime of US and milk power addition were10min and5%, the water holding capacity, gel strength andviscosity were much higher. But the simple addition of calcium would reduce the quality of goat milkyogurt.（7）Due to the poor colloidal stability,enzyme reaction or others factors, the pH value, degree ofhydrolysis and color of ultrahigh temperature goat milk decreased and the sediment increased withdifferent degrees. And the120℃goat milk’ stability would be better than137℃。... |
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