Effects of different calcium salts on properties of milk related to heat stability

Insoluble calcium salts were added to milk to increase total calcium by 30 mM, without changing properties influencing heat stability, such as pH and ionic calcium. There were no major signs of instability associated with coagulation, sediment formation or fouling when subjected to ultra high temperature (UHT) and in‐container sterilisation. The buffering capacity was also unaltered. On the other hand, addition of soluble calcium salts reduced pH, increased ionic calcium and caused coagulation to occur. Calcium chloride showed the largest destabilising effect, followed by calcium lactate and calcium gluconate. Milk became unstable to UHT processing at lower calcium additions compared to in‐container sterilisation.     

Naturally occurring variations in milk pH and ionic calcium and their effects on some properties and processing characteristics of milk

Considerable variations were found for ionic calcium and pH in milk from individual cows. Milk with lower pH tended to have a higher Ca²⁺ concentration, although the relationship was weak. Milk samples with a higher Ca²⁺ concentration and lower pH produced less sediment during in‐container sterilisation, which was contrary to expectations. Rennet coagulation time was lower for milk with a higher Ca²⁺ concentration, but curd firmness was not related to Ca²⁺ concentration. There was a poor correlation between the pH reduction caused by acid addition and that resulting from increasing temperature. Sediment formation was related to pH change at high temperature.     

Effects of stabiliser addition and in-container sterilisation on selected properties of milk related to casein micelle stability

Different stabilising salts and calcium chloride were added to raw milk to evaluate changes in pH, ionic calcium, ethanol stability, casein micelle size and zeta potential. These milk samples were then sterilised at 121 °C for 15 min and stored for 6 months to determine how these properties changed. Addition of tri-sodium citrate (TSC) and di-sodium hydrogen phosphate (DSHP) to milk reduced ionic calcium, increased pH and increased ethanol stability in a concentration-dependent fashion. There was relatively little change in casein micelle size and a slight decrease in zeta potential. Sodium hexametaphosphate (SHMP) also reduced ionic calcium considerably, but its effect on pH was less noticeable. In contrast, sodium dihydrogen phosphate (SDHP) reduced pH but had little effect on ionic calcium. In-container sterilisation of these samples reduced pH, increased ethanol stability and increased casein micelle size, but had variable effects on ionic calcium; for DSHP and SDHP, ionic calcium decreased after sterilisation but, for SHMP, it remained little changed or increased. Milk containing 3.2 mM SHMP and more than 4.5 mM CaCl₂ coagulated upon sterilisation. All other samples were stable but there were differences in browning, which increased in intensity as milk pH increased. Heat-induced sediment was not directly related to ionic calcium concentration, so reducing ionic calcium was not the only consideration in terms of improving heat stability. After 6 months of storage, the most acceptable product, in appearance, was that containing SDHP, as this minimised browning during sterilisation and further development of browning during storage.     

Comparison of heat stability of cow's milk subjected to ultra‐high temperature and in‐container sterilisation

Cow's milk of different fat contents with or without stabilising salts was sterilised by in‐container and UHT sterilisation. Heat stability decreased with increasing fat content following both UHT and in‐container sterilisation. Adding small amounts of stabilising salts (6.4 mM) increased heat stability in UHT‐treated milk, while excessive addition (12.8 mM) decreased heat stability. In contrast, increasing stabilising salts from 6.4 to 12.8 mM caused a decrease in heat stability after in‐container sterilisation. Increasing in‐container sterilisation time from 10 to 30 min caused a decrease in heat stability arising from an increase in particle size. This study confirmed discrepancies in heat stability for two sterilisation procedures.     

Effects of milk pH alteration on casein micelle size and gelation properties of milk

The effects of changes in pH above and below the natural pH of milk (ca 6.6) on the casein micelle size and the gelation properties of the pH adjusted and restored samples were investigated. The size of casein micelles increased at pH 7.0 and 7.5, then started to decrease above pH 8.5. It is postulated that at pH below 8.5 the casein micelles swell, while elevated pH causes their dissociation. Conversely, the size of casein micelles decreased on acidification to pH 5.5 and increased when the pH dropped below 5.5, due to the shrinkage of casein micelles at lower pH before their aggregation at pH below 5.5. In response to neutralising treated milk back to normal milk pH of 6.6, it was found that the casein micelle size of treated milk with a narrow range of pH change between 6.0 and 7.0 was reversible, while beyond this range the structure of casein micelles became irreversible. The restoration of casein micelle size was followed by the restoration of some parameters such as soluble calcium, ethanol stability, and milk whiteness. Acid-induced gelation did not change the elastic modulus, while rennet-induced gelation was affected by initial milk pH. In reference to the size of reversible range elastic modulus (G’) of acid or rennet gels made from restored milk, the sizes were similar to control milk after 6 h of gelation.     

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.     

Bovine milk composition parameters affecting the ethanol stability

The objective of the present work was to identify the compositional parameters of raw milk that affected ethanol stability at natural pH when natural milk conditions were not modified. Heat stability, measured as coagulation time (CT), was included in the analysis to verify relation to alcohol test. Statistical models were proposed for alcohol and heat (CT) stabilities. Milk samples of good hygienic quality from dairy farms were classified in two groups according to their alcohol stability. Unstable samples to ethanol (72%, v/v) presented lower values of pH, somatic cells count, casein and non-fat-solids relative to ethanol stable samples (ethanol at 78%, v/v or more); whereas freezing point, chloride, sodium and potassium concentrations were higher in the unstable group. Logistic regression and multiple regression were applied to modelling alcohol and heat stability behaviour respectively. Chloride, potassium, ionic calcium and somatic cell count were included in the alcohol regression model, whereas calcium, phosphorous, urea, pH and ionic calcium were part of CT model. Ionic calcium was the only measured variable that contributed to both models; however coagulation time was noted to be more sensitive to ionic calcium than alcohol. The relation between ionic strength and casein was found to contribute to the alcohol model but not to the CT model. However, the interaction calcium plus magnesium plus phosphorous and casein contributed only to CT model.     

Physicochemical characterisation of calcium phosphates prepared from milk ultrafiltrates: Effect of the mineral composition

This study deals with the precipitation of calcium phosphate in permeates removed from milks at different pH (6.7, 5.2 and 4.6). An overall high yield of precipitation of calcium and phosphate (70–80%, respectively) was obtained for all precipitates with Ca/P molar ratios close to 1.5. The suspended milk‐derived calcium phosphate (MDCP) precipitates had 8–14 μm size and ?14 to ?28 mV zeta potential. The dried MDCP precipitates were identified as amorphous calcium phosphate (ACP), stable over 18 months of storage at room temperature.     

Composition and calcium status of acid whey from pasteurized,UHT‐treated and in‐bottle sterilized milks

Whey extracts were obtained from pasteurized, UHT‐treated and in‐bottle sterilized milks. After acidic precipitation of casein the concentration of protein, NPN, lactose, lipid, calcium, magnesium and potassium was determined. Among the parameters examined, protein content was significantly reduced in the whey extracts from UHT‐treated and in‐bottle sterilized milks compared with that from pasteurized milk, while lactose content was increased. Calcium extracted in whey was at least 80% of total calcium of the milk. The total calcium to protein ratio of whey was increased as a function of the thermal treatment of milk, while ionic calcium was about 50% of total calcium in all whey extracts. In vitro protein digestibility was found to be significantly lower in whey from UHT‐treated and in‐bottle sterilized milks than in that from pasteurized milk. Parallel estimation of the percentage of ionic calcium and of the solubility of proteins in the pH range 2–10 indicated that calcium was not involved in the pH‐dependent solubility of proteins extracted in the whey, the extent of solubility being essentially a function of the thermal treatment of milk. The results suggest that calcium was not responsible for the formation of soluble protein macroaggregates with impaired digestibility that are present in whey from milk subjected to heat treatment of increasing intensity.     

Preparation of lactose‐free milk by using salt‐fractionated almond (Amygdalus communis) β‐galactosidase

β‐galactosidase was isolated from almond (Amygdalus communis) extract by ammonium sulfate precipitation. Almond proteins precipitated by using ammonium sulfate and then dialysed exhibited 5.3‐fold purification of β‐galactosidase, and the yield of enzyme preparation was 96.5%. The partially purified β‐galactosidase exhibited pH and temperature optima at pH 5.5 and 50 °C, respectively. The enzyme was significantly stable against heat, pH, calcium and magnesium ions and D ‐galactose. The almond β‐galactosidase preparation exhibited over 89% activity even after 2 months storage at 4 °C. Hydrolysis of lactose in milk and whey was performed in a stirred batch process by using this enzyme preparation. These observations indicated that the hydrolysis of lactose increased continuously with time. The enzyme could hydrolyse 94% of lactose in buffer solution and whey whereas 90% of lactose hydrolysis was achieved in milk. The main aim of the present study was to prepare lactose‐free milk, which must be free from contamination, and the process should be inexpensive. Copyright © 2007 Society of Chemical Industry     

Measurement of ionic calcium, pH, and soluble divalent cations in milk at high temperature

Dialysis and ultrafiltration were investigated as methods for measuring pH and ionic calcium and partitioning of divalent cations of milk at high temperatures. It was found that ionic calcium, pH, and total soluble divalent cations decreased as temperature increased between 20 and 80°C in both dialysates and ultrafiltration permeates. Between 90 and 110°C, ionic calcium and pH in dialysates continued to decrease as temperature increased, and the relationship between ionic calcium and temperature was linear. The permeabilities of hydrogen and calcium ions through the dialysis tubing were not changed after the tubing was sterilized for 1 h at 120°C. There were no significant differences in pH and ionic calcium between dialysates from raw milk and those from a range of heat-treated milks. The effects of calcium chloride addition on pH and ionic calcium were measured in milk at 20°C and in dialysates collected at 110°C. Heat coagulation at 110°C occurred with addition of calcium chloride at 5.4 mM, where pH and ionic calcium of the dialysate were 6.00 and 0.43 mM, respectively. Corresponding values at 20°C were pH 6.66 and 2.10 mM.     

Measurement of ionic calcium in milk

There are many reports in the literature regarding the effects of ionic calcium on reactions related to casein micelle stability, such as heat stability, ethanol stability and susceptibility to gelation, sediment formation and fouling. However, experimental evidence supporting these assertions is much less readily available.
This paper evaluates three selective ion electrode systems for measuring ionic calcium directly in milk as well as looking at the effects on pH reduction and addition of calcium chloride.
The best electrode system was the Ciba Corning 634 system, which was designed for blood but has been modified for milk. This was found to be reproducible and stable when calibrated daily and allowed direct measurements to be taken on milk in 70 s. This has been found to perform well now for 3 years. The other systems were not so useful, as they took longer to stabilize, but may be useful for higher ionic calcium concentrations, which are found in acidified milk products.
Reducing the pH increased ionic calcium and reduced ethanol stability. Calcium chloride addition reduced pH, increased ionic calcium and reduced the ethanol stability. Readjusting the pH to its value before calcium addition reduced the ionic calcium, but not back to its original value. Milks from individual cows showed wide variations in their ionic calcium concentrations.
This establishes the methodology for a more detailed investigation on measurement of ionic calcium in milks from individual cows and from bulk milks, to allow a better understanding of its role in casein micelle stability.     

Estimation of Calcium Status in Selected Food Systems

Ionic and total dialyzable calcium in nonfat dry milk, soy protein isolate, and a 50:50 mixture of the two were estimated in dialysates before and after in vitro digestion by HCl/pepsin and pancreatin/bile. Heat pasteurization did not affect % ionic or % total dialyzable calcium, before or after digestion, for the three food systems. Digestion increased % ionic dialyzable calcium for non-fat dry milk and the mixture, and increased % total dialyzable calcium for all three food systems. After digestion, % total dialyzable calcium did not differ between the milk and the mixture. Soy protein did not bind substantial amounts of calcium from the milk.     

Heat‐induced coagulation of whole milk by high levels of calcium chloride

This study investigated the interaction of calcium ions and milk proteins during heat‐induced coagulation of milk. Addition of 20–200 mM calcium chloride to milk caused coagulation on heating to 70 °C. Preheating milk at 90 °C for 10 min or ultra‐high temperature treatment at 140 °C for 6 s increased the sensitivity of milk proteins to coagulation. The former treatment was more effective than the latter in coagulating proteins. A maximum of 98% of the protein in milk preheated at 90 °C for 10 min was coagulated by 50 mM added calcium chloride at 70 °C with holding for 5 min.     

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.     

Production of quarg by ultrafiltration

The increased protein concentration in UF concentrate caused some problems in achieving the desired pH for quarg making when yogurt and mixed lactic cultures were used. Yogurt culture could ferment concentrated milk to a lower pH than the mixed culture. With the increasing concentration during UF, levels of total ash, calcium and phosphorus in the concentrate increased, but these increases were much lower at pH 4.6. Quarg obtained from UF concentrated sour milk was rated close to conventional quarg and had no bitter taste. A high heat treatment of milk before lactic fermentation and subsequent UF concentration resulted in a quarg with a smoother texture. Diafiltration of UF concentrated milk did not result in significant elimination of excessive calcium. The quality of the quarg was also poor with respect to taste, body and texture. Thus diafiltration would be of little use in quarg making.     

超高压杀菌处理对牛乳感官和理化特性的影响

以原乳为参照,研究了超高压杀菌处理对牛乳感官和理化特性的影响,并且与巴氏杀菌乳和UHT杀菌乳进行了比较。结果表明,超高压杀菌处理虽然降低了牛乳的白度和浊度,改变了牛乳的感官特性,但是增加了牛乳中游离态钙的含量,降低了乳清蛋白的变性程度,最大限度的保留了牛乳的营养价值。而巴氏杀菌和UHT杀菌处理增加了牛乳的白度和浊度,同样改变了牛乳的感官特性,但是降低了牛乳中游离态钙的含量,使乳清蛋白的变性程度增加,导致牛乳的营养价值降低。     

Stability of casein micelle subjected to reversible CO2 acidification: Impact of holding time and chilled storage

Casein micelle stability and reactivity were assessed on milk subjected to reversible acidification by carbonation. Pressurised CO₂ was injected at 4 °C, leading to controlled acidification from 6.63±0.02 to a target pH (5.5 or 5.2). After holding the pressurised milk under these conditions for 15 or 60 min, the pressure was released and the milk pH returned to its initial value under stirring and vacuum degassing. Upon CO₂ treatment, calcium and protein partition, zeta potential and size of casein micelles were restored directly after neutralisation. The rheological properties of the gel obtained by acid coagulation of CO₂-treated milk did not change as a result of carbonation. Micelle hydration increased after neutralisation and during storage. Milk buffering capacity in the pH range of 4.5–5.5 decreased after neutralisation of milk acidified by carbonation, but increased during chilled storage of this milk. Holding time of carbonated milk at low pH was found to have no impact on the physicochemical characteristics of casein micelles and the rheological properties of the gel obtained by acid coagulation of this milk.     

Factors affecting the clotting properties of sheep milk

A Formagraph was used to test the effects of some of the exogenous factors that can affect the processing properties of milk (pH, soluble calcium, rennet concentration, coagulation temperature), and two of the endogenous factors (protein and fat concentration), on the comparative clotting properties of sheep and cows' milk, namely renneting time (r), rate of firming (k20) and curd consistency (A30). A lower pH decreased r and k20 and increased A30 in both sheep and cows' milk. The addition of calcium chloride did not affect the clotting properties of sheep milk, but in cows' milk it decreased r and k20 and increased A30. Increasing the concentration of rennet decreased r and k20 and increased A30 for both sheep and cows' milk. Increasing the coagulation temperature from 30 to 38 °C decreased r for both sheep and cows' milk, but it decreased k20 and increased A30 only in cows' milk. Increasing the protein concentration decreased r in both sheep and cows' milk; it did not affect k20 of sheep milk, but it decreased that of cows' milk and increased A30 in both milks. Increasing the fat concentration had little effect on r and k20 in either sheep cows' milk, but it decreased A30 in both milks. In general, sheep milk had faster renneting times and rates of firming and greater curd consistency than cows' milk, and its clotting properties tended to be less affected by changes in the clotting conditions. © 2002 Society of Chemical Industry     

High pressure versus heat treatments for pasteurisation and sterilisation of model emulsions

Heat treatments can have considerable influence on the droplet size distribution of oil-in-water emulsions. In the present study, high-pressure (HP) pasteurisation and sterilisation were evaluated as alternatives for heat preservation of emulsions. HP conditions used were 600 MPa, 5 min, room temperature and 800 MPa, 5 min, 80 °C initial temperature, 115 °C maximum temperature for HP pasteurisation and HP sterilisation respectively. The effects on droplet size of these conditions were compared to heat treatments for whey protein isolate (WPI) and soy protein isolate (SPI) emulsions at two pH values and two ionic strengths. For WPI, also the effect of protein in the bulk phase was evaluated.Both HP and heat pasteurisation treatments resulted in similar or slightly decreased average droplet sizes compared to the untreated samples. For neutral SPI emulsions, heat sterilisation increased the average droplet size from 1.6 μm to 43.7 μm, while HP sterilisation resulted only in a small increase towards an average droplet size of 2.1 μm. The neutral WPI emulsions, except those with a high ionic strength, gave similar results with respect to the droplet size, showing that for neutral pH WPI or SPI emulsions HP sterilisation is preferable above heat sterilisation. Concerning the low pH WPI emulsions, the droplet sizes were unaffected after both heat and HP sterilisation.Industrial relevanceHeat pasteurisation and sterilisation are effective treatments to preserve food products that are based on emulsions with respect to microbial safety. However, heat treatments can negatively affect emulsion stability. Currently, in addition to high pressure at room temperature, high-pressure treatments at elevated temperature received a great deal of interest to achieve sterilised products. This study evaluated the effects of both heat and high-pressure pasteurisation and sterilisation on droplet size of whey protein isolate and soy protein isolate emulsions. It was shown that for pasteurisation treatments, both heat and high pressure have minor effects on the droplet size of the emulsion. However, for sterilisation purposes high-pressure treatment is preferable for emulsion at neutral pH. High-pressure sterilisation can therefore be interesting alternatives to heat treatments to preserve emulsion stability.