Influence of sodium citrate on the heat stability of buffalo milk and its concentrate

The influence of added sodium citrate (0.05%, 0.10% and 0.15%) on the heat stability (at 130°C) of buffalo milk and its 2:1 concentrate was determined. It was observed that added citrate caused a decrease in the heat stability of buffalo milk and its concentrate which was statistically significant and progressive as the concentration of citrate was increased. The decrease in the heat stability of buffalo milk and its concentrate due to the addition of citrate may be attributed to an increase in pH to a level of minimum stability. However, with an optimum adjustment in the pH, sodium citrate may be used for the stabilization of buffalo milk and its concentrate. It was also observed that, in all samples of buffalo milk, the normal pH was on the alkaline side of the pH of maximum heat stability.     

INFLUENCE OF HOMOGENIZATION ON THE HEAT STABILITY AND SALT BALANCE OF BUFFALO MILK AND ITS 1:2 CONCENTRATE

The influence of homogenization (two stage) on heat stability (determined as heat coagulation time at 130°) as well as the salt balance of buffalo milk and its 1:2 concentrate was determined. Homogenization had no significant influence on the heat stability and salt balance (molar ratio of Ca + Mg to P + Cit. in the dissolved phase) of fluid milk. However, during concentration both the heat coagulation time and salt balance of homogenized milk were affected significantly. Homogenization caused a significant decrease in the dissolved phosphate but had no significant effect on calcium and magnesium and this resulted in a significant increase in the molar ratio of Ca + Mg/P + Cit. This disruption in the salt equilibrium caused the destabilization of homogenized concentrated milk.     

Influence of stabilizers on the salt balance and pH of buffalo milk and its concentrate

The influence of three different concentrations (0.05%, 0.10% and 0.15%) of two stabilizers, disodium phosphate and trisodium citrate on the salt balance (concentration and molar ratios of salt constituents in the dissolved phase) and pH of buffalo milk and its 2:1 concentrate was determined. The disodium phosphate caused a significant shift in all the salt constituents (calcium, magnesium, phosphate and citrate) from the dissolved to the colloidal phase while the trisodium citrate produced a significant shift from the colloidal to the dissolved phase. Further, the phosphate caused a uniform decrease in the molar ratios of Ca/P and (Ca+Mg)/(P+Cit.) in the dessolved phase, while the citrate produced only a small and non-significant effect. Both salts caused a significant increase in pH which was progressive with increase in the concentration of added salts. Therefore, the primary effect of stabilizers in stabilizing or destabilizing the milk is a consequence of their influence on the pH and not on the mineral equilibrium of milk.     

Heat stability and calcium bioavailability of calcium-fortified milk

The objective of the study was to fortify calcium in cow milk in order to prepare calcium-enriched heat-stable milk for individuals who may not ingest enough calcium to meet minimum daily requirements. Therefore, cow milk was fortified with calcium at the rate of 50 mg/100 ml using three salts of calcium, viz. calcium chloride, calcium lactate and calcium gluconate. Upon addition of calcium salts, there was a marked drop in the pH and heat stability. However, restoration of pH to the original value with the addition of disodium phosphate stabilized the fortified milk and enhanced its heat stability over unfortified milk. The maximum in heat stability (HCT) of calcium-fortified cow milk samples remained slightly higher than that of unfortified milk. Metabolic study on mice revealed that calcium bioavailability of cow milk fortified with calcium lactate and calcium gluconate and stabilized with disodium phosphate was slightly higher than unfortified cow milk. Fortification of cow milk with calcium and restoration of its pH resulted in a calcium to phosphorus ratio still greater than one, which is considered ideal for retention of calcium in the body.     

Influence of added lyophilized butter serum on the heat stability of unconcentrated and concentrated bovine milk

The influence of added lyophilized butter serum on the heat stability of milk was investigated. The addition of lyophilized serum from salted butter to unconcentrated skimmed milk (SM) reduced the heat coagulation time (HCT) at, and increased the pH of, the maximum in the pH–HCT profile and caused disappearance of the minimum. NaCl had similar effects on the heat stability of SM as lyophilized salted butter serum, whereas lyophilized serum from unsalted butter had little effect. The addition of lyophilized salted butter serum to concentrated skimmed milk (CSM) also shifted the pH of maximum heat stability to a higher value and, at certain concentrations, increased the maximum HCT; similar effects were obtained on addition of NaCl, but lyophilized serum from unsalted butter had little effect. These results suggest that the effects of lyophilized serum from salted butter on the heat stability of SM or CSM are due primarily to the presence of a high level of NaCl in this serum.     

羊奶酪蛋白热稳定性的研究

以莎能和关中羊奶为原料,通过从羊奶中提取酪蛋白,分别在不同的pH、温度以及添加不同浓度的Ca^2＋、柠檬酸钠、三聚磷酸钠、干酪素的条件下测定酪蛋白的热凝固时间（HCT）,研究其对羊奶酪蛋白热稳定性的影响。结果表明,pH在6．8时酪蛋白的热稳定性最好,高温会降低酪蛋白的热稳定性,钙离子可以降低羊奶酪蛋白的热稳定性,适量的柠檬酸钠或三聚磷酸钠可以有效提高羊奶酪蛋白的热稳定性,干酪素对酪蛋白稳定性影响不明显。     

Effect of whey protein concentrate,pH and salt on colloidal stability of acid dairy drink (Doogh)

Serum separation of Doogh, an Iranian yoghurt drink, is a major problem. In this study, the effects of whey protein concentrate (WPC) addition, pH of the product and dissolved salt (sodium chloride) in milk on the colloidal stability of Doogh were investigated. By increasing the amount of WPC (from 0.5 to 3%) and salt in milk (from 0 to 1.6%), the serum separation decreased. Increasing pH values of sample (from 3.5 to 4.5), WPC (from 0.5 to 4%) and salt concentration in milk (from 0 to 2%) also increased the samples’ viscosity. All samples showed Newtonian behaviour except samples at pH 4.5, containing 4% WPC and 2% dissolved salt in milk.     

Bioavailability of calcium and physicochemical properties of calcium-fortified buffalo milk

Buffalo milk was fortified with calcium at the rate of 50 mg calcium/100 ml milk using calcium chloride, calcium lactate and calcium gluconate, and the resulting decrease in pH was restored to its original value by adding disodium phosphate. The maximum heat stability of calcium-fortified buffalo milk remained slightly lower than that of unfortified milk. Calcium gluconate-fortified milk had the highest heat stability, bioavailability of calcium, partitioning of calcium in the dissolved state and viscosity, and the least curd tension compared to other fortified milk, without any adverse impact on sensory properties. The bioavailability of calcium and heat stability was lowest in the case of buffalo milk fortified with calcium chloride.     

Effect of starches on the heat stability of milk

Starches from different botanical sources have been added (0.5–1.5% w/w) to skim milk and pregelatinized by heating at 70°C for 30 min. the heat coagulation time (HCT) of the milk-starch mixtures was then evaluated at 140°C. the addition of native starches to milk had a destabilizing effect. Increasing the concentration of added starch caused a decrease in HCT's. the reduction in the heat stability of milk proteins was not related to the amylose/amylopectin composition or to the granular structure of the starches. Modification of the molecular properties of the starch components by acid hydrolysis or cross-linking resulted in an enhancement of the heat stability of the mixtures.     

Impact of source and level of calcium fortification on the heat stability of reconstituted skim milk powder

Calcium enrichment of food and dairy products has gained interest with the increased awareness about the importance of higher calcium intake. Calcium plays many important roles in the human body. Dairy products are an excellent source of dietary calcium, which can be further fortified with calcium salts to achieve higher calcium intake per serving. However, the addition of calcium salts can destabilize food systems unless conditions are carefully controlled. The effect of calcium fortification on the heat stability of reconstituted skim milk was evaluated, using reconstituted skim milks with 2 protein levels: 1.75 and 3.5% (wt/wt) prepared using low and high heat powders. Calcium carbonate, phosphate, lactate, and citrate were used for fortification at 0.15, 0.18, and 0.24% (wt/wt). Each sample was analyzed for solubility, heat stability, and pH. The addition of phosphate and lactate salts lowered the pH of milk, citrate did not have any major effect, and carbonate for the 1.75% protein samples increased the pH. In general, changes in solubility and heat stability were associated with changes in pH. Calcium addition decreased the solubility and heat stability. However, interestingly, the presence of carbonate salt greatly increased the heat stability for 1.75% protein samples. This is due to the neutralizing effect of calcium carbonate when it goes into solution. The results suggested that the heat stability of milk can be affected by the type of calcium salt used. This may be applied to the development of milk-based calcium enriched beverages.     

Influence of added calcium chloride on the heat stability of unconcentrated and concentrated bovine milk

The influence of added calcium chloride (1–10 mmol/L) on the heat-induced coagulation of skim bovine milk was examined. Unconcentrated milk displayed a pH-heat coagulation time (HCT) profile with a maximum at pH 6.6 and minimum at pH 7.0. Adding calcium chloride to unconcentrated milk progressively reduced the HCT at the maximum, increased the pH at which the maximum occurred and reduced the HCT at pH > 7.0. For concentrated milk, the shape of the pH-HCT profile, that is, a maximum at pH 6.6, was not altered by added calcium chloride, but HCT was reduced progressively with increasing concentration of calcium chloride. Preheating (90°C for 10 min) shifted the maximum in the pH-HCT profile of unconcentrated milk to a more acidic pH, and addition of 5 mmol/L calcium chloride to preheated milk induced changes in heat stability similar to those noted for unheated milk. Addition of calcium chloride to milk prior to preheating strongly reduced the stability of milk against heat-induced coagulation. These data suggest that calcium has a strong destabilizing effect on the stability of milk systems against heat-induced coagulation.     

浓缩与冻结方式对牛乳品质的影响

通过膜分离将鲜牛乳浓缩成不同总固形物含量的乳样(11. 83%、14. 94%、17. 61%、23. 01%),采用4种冻结方式(冰箱冻结、冷库冻结、螺旋冻结、平板冻结)对乳样进行冻结处理。测定乳样的色度、p H值、酸度、粒度、乙醇稳定性和热稳定性,并结合共聚焦显微镜和十二烷基硫酸钠-聚丙烯酰胺凝胶电泳进行对比分析。结果表明,随着总固形物含量的升高,牛乳的p H值、酸度、乙醇稳定性和热稳定性降低,总色差值、平均粒径增大。经冻结处理后乳样中β-乳球蛋白含量均降低。在4种冻结方式中,平板冻结速率最快,乳样的乙醇稳定性和热稳定性均最高;冰箱冻结的乳样平均粒径和乳脂肪球粒径均最大。综上,推荐将鲜牛乳浓缩至总固形物含量为23. 01%,然后采用平板冻结的工艺,可以更好地维持冻结乳样的品质。     

Stability of buffalo casein micelles.

Buffalo skim-milk is less heat stable than cow skim-milk. Interchanging ultracentrifugal whey (UCW) and milk diffusate with micellar casein caused significant changes in the heat stability of buffalo casein micelles (BCM) and cow casein micelles (CCM). Buffalo UCW dramatically destabilized CCM, whereas buffalo diffusate with CCM exhibited the highest heat stability. Cow kappa-casein stabilizes alphas-casein against precipitation by Ca better than buffalo kappa-casein. About 90% of alphas-casein could be stabilized by kappa:alphas ratios of 0.20 and 0.231 for cow and buffalo, respectively. Sialic acid release from micellar kappa-casein by rennet was higher than from acid kappa-casein in both buffalo and cow caseins, the release being slower in buffalo. The released macropeptide from buffalo kappa-casein was smaller than that from cow kappa-casein as revealed by Sephadex gel filtration. Sub-units of BCM have less sialic acid (1.57 mg/g) than whole micelles (2.70 mg/g). On rennet action, 47% of bound sialic acid was released from sub-units as against 85% from whole micelles. The sub-micelles are less heat stable than whole micelles. Among ions tested, added Ca reduced heat stability more dramatically in whole micelles, whereas added phosphate improved the stability of micelles and, more strikingly, of sub-micelles. Citrate also improved the heat stability of sub-micelles but not of whole micelles.     

Study on the compositional factors involved in the variable sensitivity of caprine milk to high-temperature processing

The heat sensitivity of individual caprine milk displayed considerable variation from one sample to another. Compared to heat-unstable milk samples, heat-stable milk samples were characterised by a higher pH, a lower soluble calcium concentration, a higher phosphorus concentration, and a higher whey protein content. The heat stability of caprine milk showed a marked pH dependence, but different patterns of heat stability vs. pH were observed between heat-stable and heat-unstable samples. Heat-stable milk samples had a maximum heat stability at pH 6.8, i.e. close to their natural pH, while heat-unstable milk samples had a maximum heat stability at pH 7–7.1, i.e. higher than their natural pH. The dependence on pH is discussed with respect to both the milk salt balance and the interaction of whey protein with casein.     

Effect of Transglutaminase on Physicochemical Properties of Set-style Yogurt

In this study, the effect of some ingredients such as skimmed milk powder, whey, sodium caseinate, calcium caseinate, whey protein concentrate (35, 60 kg/100 kg dry solids), whole milk powder, condensed milk and transglutaminase (TGase) on the properties of set-style yogurt was investigated. These protein and dry matter sources (2%) and TGase (1 U/g milk protein) were added into pasteurized milk and incubated prior to fermentation for 2 h at 40°C. After fermentation, enzyme action was stopped by heating for 1 min at 80°C. The control groups were conducted with addition of these materials into milk without TGase. All of the milk samples were inoculated with yogurt cultures at 45°C, until the pH was dropped to 4.4. Syneresis, gel-strength, acetaldehyde amounts, and the degree of TGase reaction were determined. As a result, yogurt products made from enzyme-treated milk showed increased gel strength and less syneresis. SDS-PAGE results showed that the enzyme TGase produced crosslink formation between different protein fractions of milk. In addition, it was also determined that TGase application caused a decrease in acetaldehyde amounts.     

Short communication: Effect of pH on the heat stability of reconstituted reduced calcium milk protein concentrate dispersions

This study aimed to investigate the heat stability of dispersions from reconstituted reduced-calcium milk protein concentrate (RCMPC) with 80% protein or more. The tested RCMPC powders were produced from skim milk subjected to CO₂ treatment before and during the process of ultrafiltration. The CO₂ injection was controlled to obtain 0 (control, no CO₂ injection), 20, 30, and 40% reduction in calcium levels in the RCMPC powders. The RCMPC powders were reconstituted to 10% (wt/wt) protein in deionized water. These dispersions were tested for heat stability in a rocking oil bath at 140°C at unadjusted, 6.5, 6.7, 6.9, and 7.1 pH. Calcium ion activity (CIA) and ionic strength measurements were carried out using a Ca ion-selective electrode and conductivity meter. Unadjusted pH of the dispersions varied from 6.8 in control to 5.96 in 40% RCMPC dispersions. The CIA of unadjusted dispersions ranged from 1.31 mM in control to 2.83 mM in 40% RCMPC. Heat stability, expressed as heat coagulation time (HCT) of unadjusted dispersions decreased as the level of Ca removal in powders increased (from 13.81 min in control to 0.46 min in 40% RCMPC) and was negatively correlated with the CIA of the dispersions. For control RCMPC dispersions, the minimum and maximum heat stability were observed at dispersion pH of 6.5 and 6.9, respectively, followed by a decrease at pH 7.1 (CIA was the lowest). Dispersions from 40% RCMPC and pH 7.1 had the maximum HCT of 30.94 min among all RCMPC dispersions at all pH values. From this study, it can be concluded that improved heat stability in high protein formulation beverages subjected to UHT processing could be achieved through calcium reduction in milk protein concentrates using CO₂ injection.     

Effect of beta-lactoglobulin and precipitation of calcium phosphate on the thermal coagulation of milk

The effect of beta-lactoglobulin and heat-induced precipitation of calcium phosphate on the pH dependence and mechanism of thermal coagulation of milk throughout the pH range 6.3-7.3 was studied using serum protein-free milk and sodium caseinate as models for micellar and non-micellar milk protein systems respectively. It appears that the specific effect of beta-lactoglobulin at the pH of maximum stability may be related to its ability to chelate calcium. The effect of beta-lactoglobulin at the pH of minimum stability does not appear to be directly related to heat-induced dissociation of K-casein or micellar integrity but may be due to its ability to sensitize casein micelles to heat-induced precipitation of calcium phosphate, by increasing micellar hydrophobicity. The extent of heat-induced precipitation of calcium phosphate, as a function of pH, is an inverse reflection of the pH dependence of heat stability. Micellar integrity appears to play a critical role in the heat stability of milk but for reasons not previously appreciated.     

羊初乳热稳定性研究初探

本文以不同泌乳期的羊初乳为原料,研究了不同泌乳期的初乳的热稳定性,以及酸度,添加物磷酸盐、柠檬酸盐、蔗糖、钙离子、卡拉胶等对初乳热稳定性的影响。结果表明:初乳的热稳定性随泌乳期和pH值的增大而增大;磷酸盐、柠檬酸盐、蔗糖均对初乳的热稳定性有改善作用;而钙离子、卡拉胶使初乳的热稳定性下降。在80℃下初乳热稳定性改善最适条件为:pH6.9,柠檬酸0.02mol/L,磷酸盐0.2mol/L,蔗糖30%。     

Heat stability of reconstituted, protein-standardized skim milk powders

We determined the effects of standardization material, protein content, and pH on the heat stability of reconstituted milk made from low-heat (LH) and medium-heat (MH) nonfat dry milk (NDM). Low-heat and MH NDM were standardized downward from 35.5% to 34, 32, and 30% protein by adding either edible lactose powder (ELP) or permeate powder (PP) from skim milk ultrafiltration. These powders were called standardized skim milk powders (SSMP). The LH and MH NDM and SSMP were reconstituted to 9% total solids. Furthermore, subsamples of reconstituted NDM and SSMP samples were set aside to measure heat stability at native (unadjusted) pH, and the rest were adjusted to pH 6.3 to 7.0. Heat stability is defined as heat coagulation time at 140°C of the reconstituted LH or MH NDM and SSMP samples. The entire experiment was replicated 3 times at unadjusted pH values and 2 times at adjusted pH values. At an unadjusted pH, powder type, standardization material, and protein content influenced the heat stability of the samples. Heat stability for reconstituted LH NDM and SSMP was higher than reconstituted MH NDM and SSMP. Generally, decreased heat stability was observed in reconstituted LH or MH SSMP as protein content was decreased by standardization. However, adding ELP to MH SSMP did not significantly change its heat stability. When pH was adjusted to values between 6.3 and 7.0, powder type, standardization material, and pH had a significant effect on heat stability, whereas protein content did not. Maximum heat stability was noted at pH 6.7 for both reconstituted LH NDM and SSMP samples, and at pH 6.6 for both reconstituted MH NDM and SSMP samples. Furthermore, for samples with adjusted pH, higher heat stability was observed for reconstituted LH SSMP containing PP compared with reconstituted milk from LH SSMP containing ELP. However, no statistical difference was observed in the heat stability of reconstituted milk from MH NDM and MH SSMP samples. We conclude that powder type (LH or MH) and effect of standardization material (ELP or PP) can help explain differences in heat stability. The difference in the heat stability of powder type may be associated with the difference in the pH of maximum heat stability and compositional differences in the standardization material (ELP or PP).     

Effects of sodium bicarbonate with three ratios of hay crop silage to concentrate for dairy cows

Three ruminally cannulated Holstein cows were fed total mixed diets of hay crop silage and concentrate (30:70, 50:50, 70:30, 100:0) to evaluate effects of sodium bicarbonate supplements equivalent to 0, .4, and .7% of total ration dry matter (0, 68, and 114 g/d). Yields of milk, fat-corrected milk, fat, protein, and solids-not-fat, percentages of milk protein and solids-not-fat, and efficiency of production of fat-corrected milk declined with decreasing concentrate proportion. Buffer supplementation reduced milk fat percentage and milk yield was greater with 68 g/d sodium bicarbonate than with 114 g/d. Digestibilities of dry matter, organic matter, gross energy, cell solubles, and crude protein declined with decreasing proportion of concentrate while cellulose digestibility increased linearly. The proportion of dietary nitrogen transferred to milk decreased linearly with decreasing proportion of concentrate and sodium bicarbonate increased this transfer with the 70% concentrate diet. Sodium bicarbonate increased ruminal pH and acetate proportion while decreasing ammonia concentration. Acetate:propionate ratio was decreased by sodium bicarbonate addition to the 70% concentrate diet. High concentrate diets with hay crop silage may require higher amounts of buffers to influence production.