The measurement and significance of ionic calcium in milk - A review

Physicochemical properties of micellar casein retentates generated at different microfiltration temperatures

Processing temperature has a significant influence on the composition and functionality of the resulting streams following microfiltration (MF) of skim milk. In this study, MF and diafiltration (DF) were performed at 4 or 50°C to produce β-casein (β-CN)-depleted and nondepleted (i.e., native casein profile) micellar casein isolate retentates, respectively. Microfiltration combined with extensive DF resulted in a 40% depletion of β-CN at 4°C, whereas no β-CN depletion occurred at 50°C. Microfiltration at 4°C led to higher transmission of calcium into permeates, with retentate generated at 4°C containing less total calcium compared with retentate generated at 50°C, based on the volume of retentate remaining. Higher heat stability at 120°C was measured for retentates generated at 4°C compared with those at 50°C, across all pH values measured. Retentates generated at 4°C also had significantly lower ionic calcium values at each pH compared with those generated at 50°C. Higher apparent viscosities at 4°C were measured for retentates generated at 4°C compared with retentates generated at 50°C, likely due to increased voluminosity of β-CN-depleted casein micelles. The results of this study provide new information on how changing the composition of MF retentate, by appropriate control of processing temperature and DF, can alter physicochemical properties of casein micelles, with potential implications for ingredient functionality.

Fermentation Practices Select for Thermostable Endolysins in Phages

Endolysins are produced by (bacterio)phages and play a crucial role in degrading the bacterial cell wall and the subsequent release of new phage progeny. These lytic enzymes exhibit a remarkable diversity, often occurring in a multimodular form that combines different catalytic and cell wall-binding domains, even in phages infecting the same species. Yet, our current understanding lacks insight into how environmental factors and ecological niches may have influenced the evolution of these enzymes. In this study, we focused on phages infecting Streptococcus thermophilus, as this bacterial species has a well-defined and narrow ecological niche, namely, dairy fermentation. Among the endolysins found in phages targeting this species, we observed limited diversity, with a singular structural type dominating in most of identified S. thermophilus phages. Within this prevailing endolysin type, we discovered a novel and highly conserved calcium-binding motif. This motif proved to be crucial for the stability and activity of the enzyme at elevated temperatures. Ultimately, we demonstrated its positive selection within the host's environmental conditions, particularly under the temperature profiles encountered in the production of yogurt, mozzarella, and hard cheeses that rely on S. thermophilus.

Influence of calcium concentration on the re-assembly of sodium caseinate into casein micelles and on their renneting behavior

Inducing the spontaneous aggregation from casein molecules (i.e. αs1, αs2, β, and κ-casein) into re-assembled casein micelles (RCMs) through the addition of salts as an alternative to native casein micelles, has garnered increasing attention in recent years. In this investigation, re-assembled casein micelles were generated by adding varying amounts of calcium, phosphate, and citrate ions to a sodium caseinate dispersion. The formed micelles were further characterized in terms of particle size, optical density, and partitioning of calcium ions and caseins. Besides, their small-angle X-ray scattering (SAXS) profiles and renneting properties were evaluated. The observations revealed that the particle size and optical density of RCMs increased with the continuous addition of salts, while the micellar yield improved and could exceed 85 %. Moreover, the quantity of individual casein molecules that contributed to the creation of micelles was in concordance with their level of phosphorylation (i.e. αs2-casein > αs1-casein > β-casein > κ-casein). Mineral analysis results and SAXS scattering profiles confirmed that the added calcium ions acted as cross-linkers and participated in the construction of calcium phosphate nanoclusters. The renneting ability of RCMs was primarily dependent upon the colloidal calcium content per gram of micellar casein.

Gastric aggregation of micellar casein powders induced by high hydrostatic pressure: Effect of serum Ca2+ level

Micellar casein (MC) has a unique gastric colloidal behavior in response to Ca2+ cross-linking, and its aggregation properties are closely related to pepsin and gastric acid. In this study, MC with different levels of colloidal calcium phosphate (CCP) was obtained by high hydrostatic pressure (HHP) at different pressures, followed by spray drying to obtain the powders. Different amounts of calcium chloride (exogenous Ca2+) were added to MC powders prior to in vitro simulated digestion to investigate the effect of exogenous serum Ca2+ levels on the aggregation behavior and the structure change of curds generated in gastric tract. The results revealed that HHP induced the emergence of more Ca2+-binding sites, thus Ca2+ was more likely to bind to MC matrix with low CCP levels. Meanwhile, high serum Ca2+ level provided more opportunities to form aggregates. The Highest pressure (500 MPa) with the highest Ca2+ level (5 mM) caused the lowest solubility aggregates, which were only 30% at the end of gastric digestion (120 min), half of the control sample (0 MPa with 0.15 mM Ca2+). The results of wide-angle X-ray scattering / small-angle X-ray scattering suggested that both pepsin and gastric acid-induced aggregation via Ca2+ as a bridge. For pepsin, Ca2+ cross-linked between para-κ-casein; For gastric acid, Ca2+ recombined phosphorylation sites and caused cross-linking of casein subunits.

Influence of Calcium-Sequestering Salts on Heat-Induced Changes in Blends of Skimmed Buffalo and Bovine Milk

Heat-induced interactions of calcium and protein in milk lead to undesirable changes in the milk, such as protein coagulation, which can be minimized through the addition of calcium-sequestering salts prior to heat treatment. Thus, the present study investigated the influence of 5 mM added trisodium citrate (TSC) or disodium hydrogen phosphate (DSHP) on the heat-induced (85 °C and 95 °C for 5 min) changes in physical, chemical, and structural properties of buffalo and bovine skim milk mixtures (0:100, 25:75, 50:50, 75:25, and 100:0). Significant changes in pH and calcium activity as a result of TSC or DSHP addition subsequently resulted in higher particle size and viscosity as well as non-sedimentable protein level. These changes are mostly observed during heat treatment at 95 °C and increased proportionally to the concentration of buffalo skim milk in the milk mixture. Significant changes were affected by TSC addition in the 75:25 buffalo:bovine milk blend and buffalo skim milk, but for other milk samples, TSC addition effected comparable changes with DSHP addition. Overall, the addition of TSC or DSHP before heat treatment of buffalo:bovine milk blends caused changes in milk properties that could reduce susceptibility of milk to coagulation.

Characteristics of Red Deer (Cervus elaphus) Milk: Lactational Changes in Composition and Processing Impacts on Structural and Gelation Properties

In an increasingly diversified global market, milk of minor dairy species has gained interest as a novel and premium source of nutrition. Relative to the major dairy species, much is lacking in our understanding of red deer (Cervus elaphus) milk. In this study, we characterized the compositions (macronutrients, minerals, fatty acids, and proteins) of red deer milk and their variations throughout lactation. We also investigated the structures, physical properties, and gelation (acid- and rennet-induced) properties of deer milk and how they are impacted by typical processing treatments (e.g., homogenization and pasteurization). We identified unique features in the composition of deer milk, including being richer in protein, fat, calcium, zinc, iodine, branched-chain fatty acids, and α-linolenic acid than other ruminant milks. Different deer milk components displayed diverse variation patterns over the lactation cycle, many of which were different from those demonstrated in other ruminant species. Other physicochemical features of deer milk were identified, such as its markedly larger fat globules. Processing treatments were demonstrated to alter the structural and gelation properties of deer milk. Most of the gelation properties of deer milk resembled that of bovine milk more than ovine and caprine milks. This study furthers our understanding of red deer milk and will aid in its processing and applications in novel products.

Acid and rennet gelation properties of sheep, goat, and cow milks: Effects of processing and seasonal variation

Gelation is an important functional property of milk that enables the manufacture of various dairy products. This study investigated the acid (with glucono-δ-lactone) and rennet gelation properties of differently processed sheep, goat, and cow milks using small-amplitude oscillatory rheological tests. The impacts of ruminant species, milk processing (homogenization and heat treatments), seasonality, and their interactions were studied. Acid gelation properties were improved (higher gelation pH, shorter gelation time, and higher storage modulus (G') by intense heat treatment (95°C for 5 min) to comparable extents for sheep and cow milks, both better than those for goat milk. Goat milk produced weak acid gels with low G' (<100 Pa) despite improvements induced by heat treatments. Seasonality had a marked impact on the acid gelation properties of sheep milk. The acid gels of late-season sheep milk had a lower gelation pH, no maximum in tan δ following gel formation, and 70% lower G' values than those from other seasons. We propose the potential key role of a critical acid gelation pH that induces structural rearrangements in determining the viscoelastic properties of the final gels. For rennet-induced gelation, compared with cow milk, the processing treatments of the goat and sheep milks had much smaller impacts on their gelation properties. Intense heat treatment (95°C for 5 min) prolonged the rennet gelation time of homogenized cow milk by 8.6 min (74% increase) and reduced the G' of the rennet gels by 81 Pa (85% decrease). For sheep and goat milks, the same treatment altered the rennet gelation time by only less than 3 min and the G' of the rennet gels by less than 14 Pa. This difference may have been caused by the different physicochemical properties of the milks, such as differences in their colloidal stability, proportion of serum-phase caseins, and ionic calcium concentration. The seasonal variations in the gelation properties (both acid and rennet induced) of goat milk could be explained by the minor variation in its protein and fat contents. This study provides new perspectives and understandings of milk gelation by demonstrating the interactive effects among ruminant species, processing, and seasonality.

Seasonal Variations in the Composition and Physicochemical Characteristics of Sheep and Goat Milks

There has been growing consumer interest in sheep and goat milk products as alternatives to cow milk products. The physicochemical characteristics of milk vary not only between ruminant species, but also during different seasons; they determine the nutritional quality and processing properties of the milk. In this study, we characterized sheep and goat milks from New Zealand over the seasons for their composition (macronutrients, macro- and micro-minerals, fatty acids, and proteins) and physicochemical properties (e.g., ionic calcium, fat globule size, casein micelle size, viscosity, and melting behavior of milk fat). Heat-induced (95 °C for 5 min) protein interactions and changes in the physical properties of the milks were also investigated. The compositional and structural features of sheep and goat milks were identified and compared with those reported for cow milk. Seasonal variations in the milk characteristics were more pronounced for sheep milk than goat milk and were probably affected by the production systems. Sheep milk, particularly in the late season, had the largest heat-induced increases in casein micelle size and viscosity, probably arising from the greater casein–whey protein and casein–casein interactions during heat treatment. This study provides comprehensive information on the properties of sheep and goat milks and highlights the interaction effects between species, season, and processing.

Uncertainty of measurement of ionic calcium in milk measured by ISE: a Monte-Carlo insight

Practically almost all technological processes that affect the milk influence the content of ionic calcium present in it. The most popular method to determine ionic calcium is direct potentiometry using ion-selective electrodes (ISEs). This study proposes an approach to evaluate the measurement uncertainty for the determination of ionic calcium by the ISE method based on JCGM 100 - evaluation of measurement data - guide to the expression of uncertainty in measurement (GUM) with the simulation of the total uncertainty by the Monte Carlo method. The uncertainty of reading and uncertainty of regression coefficients were chosen as the starting input values. Other sources of uncertainty, such as the preparation of calibrators and the incomplete description of the measurand, do not make a significant contribution to the total uncertainty. The type of distribution that describes the results in the best way is the log-normal one. However, deviations from normality are small enough to make the possible use of the coverage factor k = 2. It is established that in realistic operating conditions the expanded uncertainty is about 20% (k = 2) and increases sharply simultaneously with increasing uncertainty of reading.

Impact of physicochemical changes in milk ultrafiltration permeate concentrated by reverse osmosis on calcium phosphate precipitation

This study aimed to characterize and compare the mechanisms of calcium phosphate precipitation in skimmed milk ultrafiltration permeate (MP) and MP preconcentrated by reverse osmosis (ROMP).

On-Chip Purification of Tetracyclines Based on Copper Ions Interaction

Antibiotics are widely used to both prevent and treat bacterial diseases as well as promote animal growth. This massive use leads to the presence of residual antibiotics in food with severe consequences for human health. Limitations and regulations on the tolerated amount of antibiotics in food have been introduced and analytical methods have been developed. The bioanalytical methods usually employed to detect antibiotic residues, however, are time-consuming, expensive and laboratory-based. Novel methods with improved rapidity, portability and cost that are easy-to-use and sustainable are therefore highly desirable. In the attempt to fulfill this need, a microfluidic system was set up herein for the purification and pre-concentration of tetracyclines from raw milk selected as the case-study. The system includes a polymeric microfluidic chip containing magnetic beads loaded with copper to exploit the preferential interaction of tetracycline with divalent ions. The microfluidic system was demonstrated to efficiently pre-concentrate tetracycline, oxytetracycline and chlortetracycline with similar performances and efficiently purify tetracycline from raw milk without any pre-treatment. The simplified method described in this paper could be easily integrated in a compact and portable device for the in-field detection of tetracyclines, with the economic advantage of preventing food wastes and guaranteeing food safety.

Calcium: A comprehensive review on quantification, interaction with milk proteins and implications for processing of dairy products

Calcium (Ca) is a key micronutrient of high relevance for human nutrition that also influences the texture and taste of dairy products and their processability. In bovine milk, Ca is presented in several speciation forms, such as complexed with other milk components or free as ionic calcium while being distributed between colloidal and serum phases of milk. Partitioning of Ca between these phases is highly dynamic and influenced by factors, such as temperature, ionic strength, pH, and milk composition. Processing steps used during the manufacture of dairy products, such as preconditioning, concentration, acidification, salting, cooling, and heating, all contribute to modify Ca speciation and partition, thereby influencing product functionality, product yield, and fouling of equipment. This review aims to provide a comprehensive understanding of the influence of Ca partition on dairy products properties to support the development of kinetics models to reduce product losses and develop added-value products with improved functionality. To achieve this objective, approaches to separate milk phases, analytical approaches to determine Ca partition and speciation, the role of Ca on protein-protein interactions, and their influence on processing of dairy products are discussed.

Molecular Understanding of Fouling Induction and Removal: Effect of the Interface Temperature on Milk Deposits

Molecular details concerning the induction phase of milk fouling on stainless steel at an elevated temperature range were established to better understand the effect of temperature on surface fouling during pasteurization. The liquid-solid interface that replicates an industrial heat exchanger (≤75°C), including four stages (preheating, heating, holding, and cooling), was investigated using both a quartz crystal microbalance (QCM-D) and a customized flow cell. We found that the milk fouling induction process is rate-limited by the synergistic effects of bulk reactions, mass transfer, and surface reactions, all of which are controlled by both liquid and surface temperatures. Surface milk foulant becomes more rigid and compact as it builds up. The presence of protein aggregates in the bulk fluid leads to a fast formation of surface deposit with a reduced Young's modulus. Foulant adhesion and cohesion strength was enhanced as both interfacial temperature and processing time increased, while removal force increased with an increasing deposit thickness. During cleaning, caustic swelling and removal showed semilinear correlations with surface temperature (T_S), where higher T_S reduced swelling and enhanced removal. Our findings evidence that adsorption kinetics, characteristics of the foulant, and the subsequent removal mechanism are greatly dependent on the temperature profile, of which the surface temperature is the most critical one.

Effect of protein concentrate mixtures and dietary addition of exogenous phytase on major milk minerals and proteins, including casein phosphorylation

Variations in major milk minerals, proteins, and their posttranslational modifications are largely under genetic influence, whereas the effect of nongenetic factors is less studied. Through a controlled feeding experiment (incomplete balanced Latin square design), the effect of concentrate mixtures, based on fava beans, rapeseed meal, or soybean meal as main P and protein sources, on milk composition was examined under typical Danish management conditions. Concentrations of P, Ca, and Mg, together with proteomics for relative quantification of major milk proteins and their isoforms, were analyzed in milk samples from 24 cows sampled in 4 periods. Each cow was fed 1 of the 3 diets in each period with or without addition of exogenous phytase. Cows were blocked by lactation stage into early and mid-lactation (23.3 ± 6.7 and 176 ± 15 d in milk, respectively, at the beginning of the experiment, mean ± standard deviation). Significant effects of feed concentrate mixture were observed for milk protein concentration, milk urea nitrogen, citrate, and the percentage of mixed and preformed fatty acids as well as mineral composition, and their distributions within micellar or serum phases. Furthermore, relative contents of α_S1-casein (CN) 9P form and unglycosylated κ-CN and thereby phosphorylation degree of α_S1-CN (PD) and the glycosylation degree of κ-CN were found to be significantly affected by these diets. To our knowledge, we are the first to document that feed concentrate mixture can affect the relative concentrations of α_S1-CN phosphorylation isoforms in milk, and the results suggested an effect on α_S1-CN 9P and PD, but not on α_S1-CN 8P. Furthermore, although only significant for α_S1-CN 8P, we found a lower relative concentration of α_S1-CN 8P and higher α_S1-CN 9P (and thus higher PD) in milk from cows in mid compared with early lactation. Also, protein concentration and concentration of Mg in skim milk and serum as well as relative concentration of α-lactalbumin were found to be significantly affected by lactation stage. Addition of dietary exogenous phytase only had a minor effect on milk composition or functionality with significant effect detected for α-lactalbumin and micellar Mg concentration.

The effect of ultrafiltration on the acid gelation properties of protein-standardised skim milk systems

In this study, we investigated the impact of ultrafiltration (UF) on the acid gelation of milk using two protein-standardised milk systems, consisting of either skim milk and retentate (SR) or permeate and retentate (PR), over different seasons in New Zealand. The composition and the physicochemical properties of the two systems before heating were comparable, whereas the levels of heat-induced α-lactalbumin denaturation and the association of the casein micelles with α-lactalbumin were significantly lower in PR than in SR. PR displayed superior acid gelation properties compared with SR, which was most pronounced in the late season. The structural modifications of the whey proteins and casein micelles that were induced by UF and the re-equilibration of calcium in the milk mixtures may have affected the acid gelation properties of the milk by influencing the denaturation and micelle association of the whey proteins. The results suggest that UF has the potential as a tool for tuning the acid gelation properties of milk.

INVESTIGATION OF SAFETY AND QUALITY PARAMETERS OF GRANULATED FILLERS

Within the conducted studies there were highlighted urgent questions of introducing the management system of quality and safety of food products. Quality and safety parameters that determine the notion of food product quality have been established by analyzing the normative and legislative base. There were studied quality parameters of granulated fillers that are structured systems of the ball-like form with diameter (3…7)·10-3 m and are characterized with a plastic, a bit crumbling consistence. Granules may be used as fillers for milk and sour-milk products, cheeses, ice-cream, dessert products, confectionary ones, beverages, salads, culinary floury products. The organoleptic quality evaluation of the products was realized by the descriptive (qualitative) method and by the profile analysis one (quantitative). Each organoleptic parameter (consistence, taste, smell and so on) is presented as a totality of components (descriptors), evaluated by quality, intensity and manifestation order. A characteristic of organoleptic parameters with intensity scales of separate signs is presented as profile diagrams. The complex organoleptic index that is 4.89…4.95 points has been determined. Basic physical-chemical properties of the new products were studied. It has been determined, that the content of main nutritive substances in the composition of fillers is: proteins 3.4…7.2 %, lipids – 2.5…6.5 %, total carbohydrates 7.8…13.2 %, mineral substances 0.25…1.12 %, that allow to pose fillers as products with the high food value. Safety parameters of the granulated fillers were studied – microbiological and toxicological ones, and also the content of mycotoxins and antibiotics. It has been proved, that the new products fully correspond to established norms by these parameters. The study of microbiological indices of the new products has proved the content of viable lactate bacteria in the fillers in amount 3·108…1·107 CFU in 1 g of a product and the absence of the pathogenic and conventionally pathogenic microflora. The expert evaluation of safety of the granulated fillers as to the content of food supplements in their composition allows to make a conclusion about the correspondence of the developed products to international legislative requirements. It has been proved, that the storage term of new products is 90 days at temperature 1…6 °С and relative air humidity no more 75 %.

Changes in fatty acids composition, antioxidant potential and induction period of UHT-treated tea whitener, milk and dairy drink

Background

In developing and developed countries, several versions of safe and shelf-stable Ultra High Temperature, UHT-treated products are manufactured. Terminologies and formulations of UHT-treated tea whitener, milk and dairy drink considerably vary. Comprehensive studies have been performed on UHT-treated milk; however, fatty acids compositional changes and oxidation status of UHT-treated tea whitener and dairy drink at different storage intervals have not been reported in literature.

Methods

UHT-treated tea whitener, milk and dairy drink samples (450 each) of the same manufacturing date were purchased from the market and stored at ambient temperature (25-30 °C) for 90 days. At the time of collection, all the samples were only one week old. Samples of UHT-treated tea whitener, milk and dairy drink were regarded as treatments and every treatment was replicated five times. Chemical composition, fatty acid profile, 2, 2-Diphenyl-1-picrylhydrazyle (DPPH) radical scavenging activity, total antioxidant activity, reducing power, antioxidant activity in linoleic acid system and induction period were determined at 0, 45 and 90 days of storage.

Results

Fat content in freshly collected samples of UHT treated-tea whitener, milk and dairy drink were 6 and 3.5%. UHT treated milk had highest total antioxidant capacity, antioxidant activity in linoleic acid and 2, 2-Diphenyl-1-picrylhydrazyle (DPPH) free radical scavenging activity followed by UHT tea whitener and dairy drink. In freshly collected samples of UHT-treated milk, concentrations vitamin A and E were 0.46 μg/100 g and 0.63 mg/100 g, respectively. UHT-treated tea whitener had the lowest concentrations of vitamin A and E. With the progression of storage period, amount of vitamin A and E decreased. In freshly collected samples, amount of short, medium and unsaturated fatty acids in UHT-treated milk were 10.54, 59.71 and 27.44%, respectively. After 45 days of storage of UHT-treated milk, the loss of short, medium and unsaturated fatty acid was 7%, 7.1 and 5.8%, respectively. After 90 days of storage of UHT-treated milk, the loss of short, medium and unsaturated fatty acid was 8.53, 13.51 and 11.88%, accordingly. After 45 days of storage of UHT-treated tea whitener, the loss of medium and unsaturated fatty acid was 1.6 and 0.99%, respectively. After 90 days of storage, the loss of medium and unsaturated fatty acids were 8.2 and 6.6%, respectively. The induction period of fresh UHT-treated tea whitener, milk and dairy drink was 15.67, .74 and 7.27 h. Strong correlations were recorded between induction period and peroxide value of UHT-treated products.

Conclusion

This investigation disclosed that UHT-treated tea whitener had 6% fat content with no short-chain fatty acids. Antioxidant capacity of UHT-treated milk was higher than dairy drink and tea whitener. Due to the presence of partially hydrogenated fat, oxidative stability of UHT-treated tea whitener was better than UHT-treated milk and dairy drink. Vitamin A and E was not found in UHT-treated tea whitener. For the anticipation of oxidative stability of UHT-treated milk, dairy drink and tea whitener, induction period/ Rancimat method can be used.

Seasonal variations in composition, properties, and heat-induced changes in bovine milk in a seasonal calving system

We determined seasonal variations in the composition and characteristics of bovine milk, as well as heat-induced changes in the physicochemical properties of the milk, in a typical seasonal-calving New Zealand herd over 2 full milking seasons. Fat, protein, and lactose contents varied consistently during the year in patterns similar to those of the lactation cycle. Seasonality also had significant effects on milk calcium, ionic calcium, fat globule size, buffering capacity, and ethanol stability, but not on casein micelle size. The ratio of casein to total protein did not vary significantly over the season, but late-season milk had the highest content of glycosylated κ-casein (G-κ-CN) and the lowest content of α-lactalbumin in both years. We observed significant between-year effects on protein, total calcium, ionic calcium, pH, and casein:total protein ratio, which might have resulted from different somatic cell counts in the 2 years. Compared with heating at 90°C for 6 min, UHT treatment (140°C for 5 s) induced greater dissociation of κ-casein, a similar extent of whey protein denaturation, a lower extent of whey protein-casein micelle association, and a larger increase in casein micelle size. Indeed, UHT treatment might have triggered significant dissociation of G-κ-CN, resulting in aggregation among the casein micelles and increased apparent mean casein micelle diameter. Seasonality had significant effects on the partitioning of G-κ-CN between the micelle and the serum phase, the extent of whey protein-casein micelle association under both heating conditions, and the casein micelle size of the UHT milk.