pH Value Of Milk Research Articles

Exonic mutations of POU class 1 homeobox 1 are associated with milk pH in high-producing Holstein Friesian cows

Background and Aim: Milk physicochemical properties play essential role in the milk processing industry, which are moderately to highly affected by genetic factors. This study aimed to evaluate the association between single nucleotide polymorphisms in POU class 1 homeobox 1 (POU1F1) and the physicochemical properties of milk in high-producing Holstein Friesian (HF) cows. Materials and Methods: A total of 149 high-producing dairy cows from PT Ultra Peternakan Bandung Selatan was included in this study. The physicochemical properties of milk, including density, freezing point, pH, lactose, solid non-fat, protein, and ash content, were determined. Moreover, three polymorphisms within the exon regions of POU1F1 (c.195G>A, c.300G>T, and c.828G>A) were analyzed using polymerase chain reaction-restriction fragment length polymorphism. The association between these polymorphisms and the physicochemical properties of milk was determined using a mixed-effects model analysis, in which the lactation period was used as a covariate. Results: This study found that two polymorphisms, c.195G>A and c.828G>A, significantly affected the pH of fresh milk. Cows with both the GG genotypes c.195G>A and c.828G>A had lower milk pH values than those with the other genotypes. In addition, a non-significant effect of POU1F1 was observed on the other physicochemical properties of milk. Conclusion: Two POU1F1 polymorphisms determined the pH of fresh milk in the Indonesian HF population. These are potential marker candidates for milk pH that directly affect the development of dairy products in the milk processing industry. Keywords: exonic mutation, Holstein Friesian, milk pH, physicochemical properties, POU1F1.

The impact of Kakadu Plum (Terminalia ferdinandiana) fruit powder and its pectic oligosaccharides on the growth, survival and antimicrobial activity of probiotic bacteria in milk.

Prebiotics are essential for improving the growth and survival of probiotics in products, which leads to maintaining the balance of the gut microbiome for overall health. Therefore, the aim of this study was to develop a novel source of prebiotic from an Australian native fruit Terminalia ferdinandiana (Kakadu plum [KP]) and its pectic oligosaccharide (POS) extract by studying their prebiotic effect on growth, survival and milk acidification of six probiotic bacteria. Lactococcus lactis 537, Lactobacillus acidophilus ATCC 4356, Lactobacillus plantarum 299v, Lactobacillus rhamnosus GG, Lactobacillus reuteri ATCC 55730 and Lactobacillus casei ATCC 393 were cultured in skim milk containing 1% and 3% of KP, or 1% of POS derived from KP pectin or apple pectin. Based on the results, the stimulation effect of KP and KP POS on bacteria growth and acidification of milk was found to be species-dependent. A higher prebiotic potential was shown by 1% KP for most strains, while 3% KP significantly enhanced the antimicrobial activity of nisin-producing Lc. lactis 537 supernatant against Staphylococcus aureus. KP POS was more effective than KP in assisting probiotic survival during storage over 14 days at 4 °C and maintaining the pH value of milk of 6 or above during fermentation. Analysis of the monosaccharides and uronic acids of POS from KP revealed mostly glucose, fructose, galactose, arabinose and galacturonic acid. The KP and its POS could be classified as novel prebiotics which support improved growth, survival and antimicrobial activity of specific probiotic bacteria, and areas for future research are recommended.

Effect of pH value of milk and tomato paste on the quality and properties of Mozzarella cheese

Effect of pH value of milk and tomato paste on the quality and properties of Mozzarella cheese

Effect of Adding Propolis on Quality Standards of Raw Milk and Yoghurt

Food additives spread around the world may have potentially harmful effects; Propolis is considered a natural additive that meets the increasing demand for natural antioxidants and antimicrobials in place of synthetic preservatives. Different concentrations of water extract of Propolis (WEP) were assessed; the pH and microbiological quality of raw milk were evaluated, as well as the quality characteristics and bioactives in manufactured yoghurt. WEP 20% was the best concentration compared to WEP 5% and 10% and exhibited an acceptable pH value of milk for 48 hours. The addition of increased concentrations of WEP 20% (1, 2, and 3%) resulted in a significant decrease and gradual reduction of the total bacterial, coliform, yeast, and mold counts compared to the control group. Propolis-supplemented yoghurt had higher pH values than the control group. Yoghurt groups treated with 1% and 2% WEP achieved the highest scores and significantly different (P<0.05) with control and 3% WEP groups in sensory examination until the end of the storage period. Furthermore, the counts of yeast and mold progressively decreased with the addition of higher concentrations of WEP throughout the storage period as 2%, 3% WEP groups were significantly different (P<0.05) with control and 1% WEP groups. The total phenolic, flavonoid content and antioxidant activity of yoghurt treated with WEP were improved and significantly different (P<0.05) compared to the untreated group. In conclusion, the raw milk and yoghurt preserved with propolis improved the quality of milk and increased bioactivity and nutritional benefits of yoghurt by elevating its antioxidant capacity. As a consequence, the produced yoghurt in our study proved that it is an acceptable product with functional, probiotic potential and has health-promoting properties that might be commercialized.

PH-dependent sedimentation and protein interactions in ultra-high-temperature-treated sheep skim milk

Sheep milk is considered unstable to UHT processing, but the instability mechanism has not been investigated. This study assessed the effect of UHT treatment (140°C/5 s) and milk pH values from 6.6 to 7.0 on the physical properties of sheep skim milk (SSM), including heat coagulation time, particle size, sedimentation, ionic calcium level, and changes in protein composition. Significant amounts of sediment were found in UHT-treated SSM at the natural pH (∼6.6) and pH 7.0, whereas lower amounts of sediment were observed at pH values of 6.7 to 6.9. The proteins in the sediment were mainly κ-casein (CN)-depleted casein micelles with low levels of whey proteins regardless of the pH. Both the pH and the ionic calcium level of the SSM at all pH values decreased after UHT treatment. The dissociation levels of κ-, β-, and αS2-CN increased with increasing pH of the SSM before and after heating. The protein content, ionic calcium level, and dissociation level of κ-CN were higher in the SSM than values reported previously in cow skim milk. These differences may contribute to the high amounts of sediment in the UHT-treated SSM at natural pH (∼6.6). Significantly higher levels of κ-, β-, and αS2-CN were detected in the serum phase after heating the SSM at pH 7.0, suggesting that less κ-CN was attached to the casein micelles and that more internal structures of the casein micelles may have been exposed during heating. This could, in turn, have destabilized the casein micelles, resulting in the formation of protein aggregates and high amounts of sediment after UHT treatment of the SSM at pH 7.0.

Application of Calcium Citrate in the Manufacture of Acid Rennet Cheese Produced from High-Heat-Treated Goat's Milk from Spring and Autumn Season.

The stability of milk proteins is affected by changes in the pH value of milk, the heating temperature, and the addition of calcium compounds or chelating agents, which can cause alterations in calcium distribution. The purpose of this study was to determine the potential of the use of calcium citrate to manufacture fresh acid rennet cheese from high-temperature-pasteurized goat’s milk (90 °C, 15 s) from the spring and autumn season and the effect of the calcium dose used on the physicochemical and organoleptic properties of the cheese. Autumn milk was found to be a richer source of total solids, confirming the effect of the production season on milk quality. The applied doses of calcium did not cause the denaturation of goat milk proteins and allowed pasteurization to take place at 90 °C for 15 s. The addition of calcium citrate resulted in a significant increase in the pH value of milk and cheese compared to the control sample. Adding 15 and 20 mg of Ca 100 g−1 to milk as citrate had the most beneficial effect on increasing protein retention in cheese in both seasons, showing a rise from 1.33% to 2.40%. The production season significantly influenced the cheese yield. The control goat cheese from the autumn season showed a 6.85% higher yield compared to the spring cheese. An increase in cheese yield was also observed as the calcium dose of milk increased. The content of micro- and microelements in cheese was affected by the production season. The addition of calcium citrate to milk resulted in a significant increase in the calcium content of cheese—from 120.83 to 147.45 mg 100 g−1 in the spring season and from 130.66 to 151.21 mg 100 g−1 in the autumn season. Increasing the dose of calcium increased the hardness of cheese samples by 1.37 N in the spring and 0.90 N in the autumn. The organoleptic evaluation showed that adding calcium to milk did not significantly affect the organoleptic characteristics of goat cheese.

Monitoring of acid-induced coagulation of dromedary and cow's milk using different complementary analytical techniques

This study investigates the acid-induced coagulation of dromedary and cow's milk using rheological, light backscattering, and FT-MIR spectroscopy techniques. Throughout the acid-induced coagulation process, dromedary milk exhibited higher values of pH than cow's milk. Indeed, pH values of milk attained values of 3.94 and 3.84 at the end of the coagulation for dromedary and cow's milks, respectively. Rheology measurements showed that, throughout the acid-induced coagulation, dromedary milk significantly presented lower values of storage modulus (G′) and loss modulus (G″) than cow's milk. The type of milk significantly affects the curd firmness of acid milk gels. Indeed, the lowest curd firmness of dromedary (8.71 Pa) and cow's milk (11.37 Pa) was observed at pH = 3.8, and 3.94, respectively. The delta backscattering (ΔBS) showed a sigmoidal increase at the initial steps of acid-induced coagulation of dromedary milk.

EVALUATION OF THE USE OF MINERAL-PLUS ON PRODUCTION PERFORMANCE AND MILK QUALITY OF FRIESIAN HOLSTEIN CROSSBREED DAIRY COWS

Complementary feed or feed supplement is a feed ingredient that is added to animal feed to complement the nutritional content of feed in meeting the needs of livestock. Feed supplements are additional feed ingredients intended to add nutrients to animal feed, where the added nutrients are digested or help the digestive process. This study aims to evaluate the use of mineral-plus as a feed mixture for dairy cows on the appearance of milk production and quality. The used material with carried out on 30 lactating cows 1-3. 250 ml milk samples from the morning and evening milking of each cow were analyzed for milk quality analyzed with a Milk scan tool. The mineral added to the concentrate feed is 2% with the mineral composition in the form of a mixture of several macro, micro and herbal. The variables observed included feed consumption, milk production and quality (specific gravity, fat content, protein content, total solid content and pH value) of PFH dairy cows and the data were analyzed using descriptive statistical methods. The results showed that the average consumption of forage feed was 48.83 kg/head/day and concentrate was 13.42 kg/head/day. The average high milk production is 35.46 liters/head/day. The average quality of milk which includes fat content is 6.39%, SNF content is 8.13%, total solid is 14.48%, specific gravity is 1.0233, protein content is 4.57%, lactose content is 3.97 % and the pH value of milk is 6.48.This study shows that cow's milk production and quality is at a very high level above the average production of Friesian Holstein crossbreed cows.

Effect of Calcium Compound Type and Dosage on the Properties of Acid Rennet Goat's Milk Gels.

The aim of this study was to determine the effect of adding calcium compounds to processed goat’s milk, and on the properties of acid rennet goat’s milk gels, which are a middle product obtained in the manufacture of acid rennet cheese. The properties of the gels directly affect the quality of acid rennet cheeses. The analysis of raw goat’s milk was carried out, then acid rennet gels were produced with the addition of six different calcium compounds (chloride, citrate, bisglycinate, gluconate, lactate, and carbonate). The dynamics of milk fermentation were performed by monitoring the pH value of milk during acidification. The pH, syneresis, color, and texture profile were determined in the formulated acid rennet gels. An organoleptic evaluation was also performed. The study demonstrated that, not only calcium chloride, but also calcium citrate, gluconate, lactate, bisglycinate, and calcium carbonate could be used in the production of goat’s milk acid rennet gels, or the middle product in the manufacture of acid rennet curd cheese from goat’s milk. Notably, the addition of citrate, bisglycinate, and calcium carbonate in doses of 20 mg Ca 100 g−1 most effectively reduced syneresis compared to the control sample by 4.76% (citrate), 7.85% (bisglycinate), and 10.28% (carbonate). The hardness of the control gels ranged from 2.35 N to 2.99 N. The addition of chloride, citrate, gluconate, lactate, and calcium carbonate to the milk improved the acid rennet gel’s hardness. The addition of 20 mg Ca 100 g−1 as gluconate increased the hardness the most (3.61 N). When increasing the calcium dosage in the form of all compounds, there was a tendency to increase the gel’s springiness. The addition of chloride, citrate, and bisglycinate to milk did not result in a darkening of the gel’s color. The addition of calcium compounds mostly reduced the intensity of goatish taste and odor. Calcium gluconate, in particular, reduced the goatish taste the most, a taste which is not always acceptable by the consumers.

The Effect of the Addition of Chokeberry Fiber on the Quality of Sheep's Milk Fermented by Lactobacillus rhamnosus and Lactobacillus acidophilus.

The global market for sheep's milk and its products is increasing due to higher demand for cheese and traditional dairy products, and as a novelty, sheep's milk is an ingredient in infant formulas and nutraceuticals. The aim of this study was to determine the properties of fermented sheep's milk, which combines probiotic benefits with increased dietary fiber content. The influence of the applied dose of chokeberry fiber on the growth of living cells of Lactobacillus acidophilus and Lactobacillus rhamnosus in fermented sheep's milk was also evaluated. Sheep milk with the addition of 0% (control sample), 1.5%, and 3.0% chokeberry fiber was fermented by two different probiotic monocultures L. acidophilus and L. rhamnosus. In the fermented milk, pH value, syneresis (%), color, and texture were determined. Furthermore, the microbiological analysis and an organoleptic evaluation were performed. With the increasing dose of chokeberry fiber, the pH value decreased already before the fermentation process. After fermentation, the milk's pH values with fiber were still lower than those in the control sample. Presumably, more acidic metabolites were produced by L. acidophilus, causing a more intense reduction of the pH value than L. rhamnosus both in control milk and in milk with the addition of fiber. The addition of chokeberry fiber affected the stimulation of the growth of both types of bacteria. In the milk sample without fiber addition, a more significant number of viable cells were counted for L. acidophilus by 0.5 log CFU g−1 more than the milk fermented with L. rhamnosus. Furthermore, in milk fermented by L. acidophilus with 1.5% chokeberry fiber (LA1), the number of viable bacterial cells was higher than that in milk fermented by L. rhamnosus with the same addition of fiber (LR1). However, in sample LA3, the number of viable bacterial cells was lower than that in sample LR3. Tested fermented sheep milk met the Recommendation of the International Dairy Federation's requirements regarding the number of live bacterial cells for dairy probiotics. The addition of chokeberry fiber increased syneresis in each fermented milk group, regardless of the bacteria used for fermentation. Moreover, the use of fiber caused a significant reduction in brightness L∗, an increase of red color, and a decrease of yellow color. Milk fermented with L. acidophilus was characterized by a harder gel, compared to their analogues fermented with L. rhamnosus. The addition of fiber intensified the sour taste and the taste of the additive in both types of fermented sheep milk.

Hygienic Production Practices and Microbial Quality of Cow Milk in Cheha District of Gurage Zone, Southern Ethiopia

The aim of the study was to assess hygienic production practices and to evaluate microbial quality of raw cows’ milk in Cheha district of Gurage Zone, Southern Ethiopia. The study was conducted by interviewing 180 smallholder milk producers from two agro-ecologies (highland and midland) and by collecting 40 milk samples from milk producers, small shops, cafes and consumers for microbial quality analysis. The result indicated that majority of the respondents (96.7%) did not have cow barn and milking area, 57.3% of them clean their barn once and more than once a week. Moreover, milking without hand washing, absence of udder washing, failure to use towel to clean the udder, and use of plastic pail as milking equipment were practiced by 33.9%, 52.2%, 74.4% and 95.6% of the respondents, respectively. Furthermore, higher number of respondents (69.4%) used river water without proper treatment as a major source of water for cleaning purpose and majority of them fail to regularly clean utensils with detergents. Concerning microbial quality, overall mean total bacterial counts (TBC), Coliform counts (CC) and pH values of milk from current finding were 5.675 ± 0.016, 4.414 ± 0.017 log10 cfu/ml, and 5.963 ± 0.081, respectively. In general, overall quality of milk produced as well as marketed in the study area was poor. These were justified from poor hygienic practices and high values of TBC and CC that were significantly higher than the acceptable limits set by Ethiopian Standards for unpasteurized milk. Therefore, adequate sanitary and control measures should be taken at all stages from production to consumer level to produce and supply wholesome milk.

Bacteriophage control of Salmonella Typhimurium in milk.

This study was designed to evaluate the effect of bacteriophage P22 on the inhibition of growth of Salmonella Typhimurium. The P22 belongs to Podoviridae family consisting of a hexagonal head and short tail. The inhibitory effect of phage in milk was noticeable at the early storage period, showing more than 3 log reduction at 4h and day 3. The pH values of milk treated with P22 were significantly decreased from 6.7 to 6.3 after 24h incubation at 37°C, while no significant changes in pH values were observed for the control and bacteriophage treatment throughout the storage at 4°C for 12days. The slight color changes were observed in the control and bacteriophage treatment throughout the storage at 4°C for 12days and 37°C for 24h. These results provide useful information for enhancing microbiological safety and quality of milk and designing effective bacteriophage-based control in food system.

IMPAKT OF THE NUMBER OF SOMATIC CELLS ON MILK QUALITY

One of the indicators of the hygienic quality of milk is the number of somatic cells, which is an internationally recognized parameter for the health condition of the udder. The increased number of somatic cells over 400.000/ml causes changes in the secretion and the chemical composition of the milk. In this research, based on the number of somatic cells, the milk is categorized in three categories. In milk from the first category the average number of somatic cells equals 444.780/ml, 825.560/ml in the second and 1,242.220/ml in the third category. In milk from the first category the average contents of milk fat, proteins, lactose, dry matter, casein and whey proteins are 4.206%, 3.268%, 4.723%, 12.127%, 2.910%, 0.8610% respectively. In the second category 4.106%, 3.192%, 4.349%, 11.647%, 2.665%, 0.9680%, and 3.989%, 3.139%, 3.964%, 11.092%, 2.386%, 1.1820% in milk from the third category. The pH value of milk in the first, second and third category is 6.627, 6.799 and 6.897 respectively. Between the three categories of milk, significant differences, at the level of (p<0.01), are determined in the number of somatic cells and average contents of milk components. A positive correlation in all three milk categories exists between somatic cells and the whey proteins, and a negative correlating dependency exists between the other chemical parameters and somatic cells.

Yogurt made from milk heated at different pH values

Milk for yogurt manufacture is subjected to high heat treatment to denature whey proteins. Low milk pH values (≤6.5) at heating result in most denatured whey proteins becoming associated with casein micelles, whereas high milk pH values (≥7.0) at heating result in the formation of mostly soluble (nonmicellar) denatured whey protein complexes. There are conflicting reports on the relative importance of soluble and casein-bound whey protein aggregates on the properties of acid gels. Prior studies investigating the effect of pH of milk at heating used model gels in which milk was acidified by glucono-δ-lactone; in this study, we prepared yogurt gels using commercial starter cultures. Model acid gels can have very different texture and physical properties from those made by fermentation with starter cultures. In this study, we investigated the effects of different pH values of milk at heating on the rheological, light backscatter, and microstructural properties of yogurt gels. Reconstituted skim milk was adjusted to pH values 6.2, 6.7, and 7.2 and heated at 85°C for 30 min. A portion of the heated milk samples was readjusted back to pH 6.7 after heating. Milks were inoculated with 3% (wt/wt) yogurt starter culture and incubated at 40°C until pH 4.6. Gel formation was monitored using dynamic oscillatory rheology, and parameters measured included the storage modulus (G′) and loss tangent (LT) values. Light-backscattering properties, such as the backscatter ratio (R) and the first derivative of light backscatter ratio (R′), were also monitored during fermentation. Fluorescence microscopy was used to observe gel microstructure. The G′ values at pH 4.6 were highest in gels made from milk heated at pH 6.7 and lowest in milk heated at pH 6.2, with or without pH adjustment after heating. The G′ values at pH 4.6 were lower in samples after adjustment back to pH 6.7 after heating. No maximum in the LT parameter was observed during gelation for yogurts made from milk heated at pH 6.2; a maximum in LT was observed at pH ~4.8 for samples heated at pH 6.7 or 7.2, with or without pH adjustment after heating. Higher R-values were observed with an increase in pH of heating, with or without pH adjustment after heating. The sample heated at pH 6.2 had only one major peak in its R′ profile during acidification, whereas samples heated at pH 6.7 and 7.2 had 2 large peaks. The lack of a maximum in LT parameter and the presence of a single peak in the R′ profile for the samples heated at pH 6.2 were likely due to the partial solubilization of insoluble calcium phosphate when milk was acidified to this lower pH value. No clear differences were observed in the microstructures of gels between the different treatments. This study indicates that heating milk at the natural pH (~6.7) created an optimum balance of casein-bound and soluble denatured whey proteins, which resulted in yogurt with the highest gel stiffness.

Effect of insoluble calcium concentration on endogenous syneresis rate in rennet-coagulated bovine milk

The rennet coagulation of milk has been extensively studied. Mathematical modeling of the gelation process has been performed, mainly for the purpose of predicting the gel point. Rheological profiles of rennet gels during aging (long reaction times) have indicated that the gel stiffness (modulus) attains a maximum and thereafter decreases. We wanted to model this type of behavior and used the Carlson model, which includes terms for the proteolysis of κ-casein hairs (creating active sites) and the crosslinking of these activated sites. To account for the observed decrease in the gel modulus with time, we modified the Carlson model by adding an exponential decay term, which we ascribe to endogenous syneresis. We believe that this decay (i.e., syneresis rate) would likely be influenced by the mobility of bonds within casein micelles (in gels as indicated by the rheological loss tangent parameter). To modify the internal structural bonding of casein micelles, reconstituted skim milk was acidified to pH values 6.4, 6.0, 5.8, 5.6, and 5.4, or EDTA was added to milk at concentrations of 0, 2, 4, and 6mM, and the final pH values of EDTA-treated samples were subsequently adjusted to pH 6.0. These treatments were then used to prepare rennet gel samples that were monitored by dynamic low amplitude oscillatory rheometry. When the modified Carlson model was fitted to the actual experimental storage modulus values of each sample, it fitted the data reasonably well (especially the pH trial data). As the pH values of milk decreased, the modulus values at infinite reaction time (G′∞) increased; however, G′∞ decreased with an increase in the EDTA concentration. In the pH trial, the rate constants for the proteolysis of κ-casein hairs and the crosslinking of these activated sites exhibited a maximum at pH 5.6 and 6.0, respectively. The rate constant for endogenous syneresis increased at pH values <6.0. The rate constant for endogenous syneresis was significantly positively correlated (r≥0.96) with the loss tangent values of gels (indicating greater mobility), probably due to the loss of insoluble calcium phosphate crosslinking within micelles, which was significantly negatively correlated (r≥0.81) with the rate constant for endogenous syneresis. In the EDTA trial, with an increase in the EDTA concentration no maximum was observed in the rate constants related to proteolysis of κ-casein hairs or crosslinking of these activated sites. The rate constant for endogenous syneresis decreased at higher EDTA levels. The different rheological/modeling behavior in the EDTA trials was likely due to the very significant inhibition of rennet gelation induced by the use of EDTA, which also resulted in extremely long reaction times. Our modified Carlson model fit our experimental pH trial data very well, which indicates that the rennet gel system has the potential to synerese from the start; indeed this ability is an innate property of the casein micelle. Endogenous syneresis was enhanced by the loss of insoluble calcium phosphate crosslinking within casein micelles as this increased bond mobility within rennet gels.

Survival of Escherichia coli O157:H7 during the Manufacture and Storage of Fruit Yogurt

The objectives of the study were to assess the behavior of Escherichia coli O157:H7 during the manufacture of fruit yogurt at different fermentation and storage temperatures. Reconstituted milk was fermented at 37, 40 or 45C; the resultant product was stored at 4, 10 or 15C for 7 days. Samples of milk and yogurt were analyzed. E. coli O157:H7 and lactic acid bacteria (LAB) counts; pH of samples was recorded. During fermentation, E. coli O157:H7 grew in the presence or absence of LAB regardless of temperature. E. coli O157:H7 increased in presence of thermophilic LAB more than 2.75 log cfu/mL. The growth of LAB in all samples showed the same trend. The pH values of milk containing E. coli O157:H7 and LAB decreased gradually to reach 4.6 ± 0.1 at the end of fermentation period. During cooling, there was neither growth nor death of E. coli O157:H7 at 4 and 10C, while a slight increase at 15C. All the experiments showed significant differences in the population of E. coli O157:H7 in the presence or absence of LAB. During storage, E. coli O157:H7 number declined for all experiments and approached undetectable levels at the end of storage. The sensitivity of E. coli O157:H7 to acidity and lowered temperature was noticed during storage. Practical Applications Escherichia coli O157:H7 has emerged as a major foodborne pathogen and has been implicated in several outbreaks involving milk and dairy products. The results of the present study indicate that E. coli cannot tolerate the acidity and storage temperature. Applying quality control systems in the processing line will ensure that the E.coli will not survive in the commercially prepared fruit yogurt.

Acid gelation of colloidal calcium phosphate-depleted preheated milk

This study aimed at understanding the role of colloidal calcium phosphate (CCP) in acid gelation of milk. Milks were depleted in Calcium (Ca) by dialysis against milk permeate containing a cation-exchange resin. Dialysed milks were then heated (90 °C-10 min) and acid-gelled at 42 °C with a yoghurt culture. Minerals, total and soluble protein contents, pH and optical density were measured in unheated and heated dialysed milk, together with diameters and ζ-potentials of particles. Dialysis of milk led to a dissociation of 45% total Ca and 30% total phosphorus, to an increase in sodium content and pH of milk, to lower turbidity and ξ-potential, but did not change the casein particle size. Soluble Ca and casein-bound Ca were removed from milk, CCP being removed increasingly, while Ca removed from the phosphoserine residues increased very little during the dialysis experiments. Maximal dissociation of αs1- and αs2-casein was 20%, while that of β- and κ-casein was 35–40% of total at the end of dialysis, and it increased after heating, especially for κ-casein. The pH value at which the milk sample begins to gel increased for low mineral depletion rates but decreased for higher depletion levels. This was due to the increase in the pH value of milk and in the κ-casein dissociation. The elastic modulus decreased in samples at the lowest depletion and then levelled off, which suggested that the phosphoserine-bound Ca played a critical role in the formation of acid gels.

Disruption of Tight Junction Integrity, and Induced Mammary Involution in Lactating Goats by Saponins

Four multiparous pregnant Nubian goats at late lactation were subjected to injection of a saponin preparation from Gypsophila roots. Saponin solution was injected into one single gland of each goat after milking 8 times. At day 2 in treatment, milk yield began to be affected, and dropped down dramatically from day 3 till dry off at day 8. The pH value of milk was increased in udder halves treated with the saponin solution after 2 days, whereas the control halves exhibited semi-plateau manner all over the experiment. Sodium concentration increased and potassium concentration decreased after 2 d in treatment. Calcium concentration in the treated udder declined after 8 d and the values of these ions were roundabout the plasma concentrations indicating that milk secreted from the treated udder halves with saponins was mostly composed of interstitial fluid.

Effect of pH on the Gelation Properties of Skim Milk Gels Made From Plant Coagulants and Chymosin

The effect of three milk pH values, 6.0, 6.3 and 6.7, on gelation properties was monitored by small amplitude oscillatory rheology as well as a large deformation (yield) test for gels induced by the plant coagulants, Cynara cardunculus L. and Cynara humilis L., and chymosin. Gel microstructure was studied using confocal scanning laser microscopy. For each coagulant, a decrease in pH of milk resulted in a decrease in gelation time (tg), and an increase in the rate of increase in storage modulus (G′). At pH 6.0 and 6.3, plant coagulant-induced gels reached a maximum value in G′ (G′max) followed by a decrease in G′ values during the rest of the experiment, reflecting higher proteolytic activity of plant coagulants towards caseins as determined by SDS-PAGE. Gels produced at pH 6.0 and 6.3, exhibited a minimum in loss tangent (tan δ) followed by slight increase in tan δ during gel aging, that may have been associated with faster rearrangements of the gel network structure. In gels aged for ∼6h, the values for G′, tan δ at low frequency (0.006Hz) and yield stress were higher for chymosin than for plant-induced gels. For gels with the same pH value, no major differences were observed in microstructure between coagulants. Gels made at low pH values (6.3 and 6.0) appeared to have a denser or more interconnected structure than gels made at pH 6.7. Our results suggest that, at a low pH, the type of coagulant used in gelation is likely to have a considerably impact on gel/cheese structure.

Excretion of aminopyrine and its metabolites into cows' milk

The mechanism by which aminopyrine and its two most common metabolites, 4-aminoantipyrine and N-acetyl-4-aminoantipyrine, pass into cows' milk from the systemic circulation was studied. Healthy lactating dairy cows were infused via the jugular vein with appropriate loading doses followed by a continuous intravenous infusion for a 6-hour period. Blood and milk samples were taken simultaneously at hourly intervals, milk pH values were determined, and drug concentrations were measured. Protein binding was determined in milk and plasma using equilibrium dialysis techniques. Theoretical milk-to-plasma ratios for passive diffusion were calculated on the basis of the pH-pK a partition concept. Experimentally obtained milk-to-plasma ultrafiltrate ratios agreed with theoretical ratios for passive diffusion when aminopyrine and N-acetyl-4-aminoantipyrine were infused. Experimental milk-to-plasma ratios obtained for 4-aminoantipyrine were consistently lower than theoretically calculated ratios. Average experimental ratios of 1.10, 0.50, and 1.00 were obtained for antipyrine, 4-aminoantipyrine, and N-acetyl-4-aminoantipyrine, respectively, with a corresponding average theoretical ratio for passive diffusion of 1.00 in all cases. Changing milk pH did not affect the amount of these compounds that was cleared into the milk. The appearance of aminopyrine and N-acetyl-4-aminoantipyrine in milk can be explained by diffusion concepts. 4-Aminoantipyrine gains access to milk by a process which cannot be explained by simple passive diffusion.