Commercial Skim Milk Research Articles

USANS and SANS investigations on the coagulation of commercial bovine milk: Microstructures induced by calf and fungal rennet

Coagulation of milk is a fundamental process in the manufacture of dairy products. Under the enzymatic action of rennet, casein micelles form aggregates resulting in a fractal gel network. There are few studies of microstructures using scattering techniques resulting from rennet coagulation in commercial milk in its native state. Here we employ ultra-small angle neutron scattering (USANS) and small angle neutron scattering (SANS) covering the scattering q-vector range of 5×10-5<q<2×10-2Å-1 and the fractal cylinder model to study fractal structures and sizes resulting from calf and fungal rennet-induced coagulation of commercial skim and whole milk. We report evidence of aggregation with fractal properties analogous to that of swollen, randomly-branched polymers. Calf rennet resulted in a larger fractal dimension in skim compared to whole milk. In milk coagulated by fungal M. miehei, the randomly-branched polymer-like structures had a slightly larger fractal dimension of 2.5 and the structural unit was smaller. These measurements provide an important foundation for continuing study of the structure of commercial cheese with scattering techniques.

The quality of skim milk curd produced using biduri (Calotropis gigantea) latex as rennet replacement

Physical and chemical quality of milk curd produced using various biduri latex as rennet placement were investigated in skim milk-clotting. The materials used in this study were rennet, commercial skim milk and biduri latex powder. Four types of formula namely P0: rennet 0.02% + CaCO3 0.01%; P1: biduri latex powder 0.015% + CaCO3 0.01%, P2: biduri latex powder 0.020% + CaCO3 0.01% and P3: biduri latex powder 0.025% + CaCO3 0.01% were applied to produce milk curd. As quality parameter, weight and yield (based on dry matter content in %) curd, dry matter (DM), water, protein (Kjeldahl method), and fat content were evaluated. Result showed that fat content, weight and yield of curd were higher in milk curd produced with biduri latex compared to control, however protein content was lower. As the conclusion, the use of biduri latex up to 0.025% able to replace rennet for milk curd production which shows better in physical quality.

Kinetics of available lysine in stored commercial skim milk powder at moderate temperatures

SummaryKinetics of lysine blockage, as an early step of the Maillard reaction, was investigated in commercial skim milk powder to understand the extent of the reaction, specifically after packages are opened and during the subsequent storage. Samples were stored at six conditions including three temperatures (30, 32.5 and 35 °C) and two relative humidities (43% and 52%) for 30 days, the period in which the product is recommended to be consumed after opening. The reaction rate was determined using a dye‐binding method. Based on our findings, decrease in available lysine follows first‐order reaction kinetics model. Small changes in temperature (2.5 °C) caused significant increase in the reaction rate constants. Relative humidity affected temperature dependency of the reaction, and activation energies were estimated to be 142.5–170.8 kJ mol−1. This study aims to increase the awareness of the significance of storage quality in relation to the nutritional status of the products.

Determination of lactadherin concentration in dairy by-products by ELISA: Effect of heat treatment and hydrolysis

Lactadherin is a peripheral glycoprotein of the milk fat globule membrane with several attributed biological activities. In this study, we developed an indirect competitive ELISA to determine lactadherin concentration by using a rabbit polyclonal antiserum. The ELISA was applied to quantify lactadherin in several dairy by-products. Of the products tested, raw and commercial buttermilk had the highest concentrations of lactadherin (6.79 and 5.27 mg/g of product, respectively), followed by commercial butter serum (4.86 mg/g), commercial skim milk (4.84 mg/g), and raw whey (1.20 mg/g). The concentration of immunoreactive lactadherin was also determined in dairy by-products after they were subjected to different technological treatments. Thus, raw products were heat treated at combinations of temperature and time typically used in the dairy industry, and commercial products were hydrolyzed using 3 proteolytic enzyme preparations. Heat treatments of whey and buttermilk resulted in a smaller decrease in lactadherin concentration than did hydrolysis as determined by ELISA and electrophoresis. At high temperatures for long durations, the loss of lactadherin was higher in whey than in buttermilk, with the maximal reduction of around 48% found after treating whey at 72°C for 60 min. Hydrolysis of commercial products with proteolytic enzymes resulted in a marked decrease of immunoreactivity within the first 5 min of treatment, which thereafter was constant throughout 4 h of hydrolysis. These results demonstrate that dairy by-products from milk fat processing are good natural sources of lactadherin, although technological processes have to be considered, because they have different effects on lactadherin content.

Development and Characterization of Carob Flour Based Functional Spread for Increasing Use as Nutritious Snack for Children

Carob flour enriched functional spread was developed and textural, sensory, colour, and some nutritional properties of the product were investigated. Spread samples were prepared with major ingredients for optimisation and minor ingredients for improving texture and aroma. Major ingredients were carob flour and hydrogenated palm oil (HPO) and minor ingredients were commercial skim milk powder, soya flour, lecithin, and hazelnut puree. The ratio of major ingredients was optimised using sensory scores and instrumental texture values to produce a carob spread that most closely resembles commercial chocolate spread (control), in both spreadability and overall acceptability. The amounts of minor ingredients (milk powder, 10%; soybean flour, 5%; lecithin, 1%; hazelnut puree, 4%) were kept in constant ratio (20%). Addition of hydrogenated palm oil (HPO) decreased the hardness and hardness work done (HWD) values in contrast to carob flour. Higher rates of carob flour were linked to lower lightness, greenness, and yellowness values. Spread was optimised at 38 g carob flour/100 g spread and 42 g hydrogenated palm oil/100 g spread level and the formulation tended to receive the highest sensory scores compared to other spreads and presented closer instrumental spreadability values to control samples. This indicates a strong market potential for optimised carob spreads.

Quality characteristics and plasmin activity of thermosonicated skim milk and cream

The shelf life of pasteurized milk is limited by heat-stable proteases, which cause gelation and bitter taste upon extended storage of milk. Ultra-high temperature processing inactivates proteases but detrimentally affects milk’s sensory quality. An adjunct to pasteurization is desired to extend milk’s shelf life while maintaining quality characteristics. In this study, the effects of combined heat and ultrasound (thermosonication) on total plasmin activity and various quality characteristics of skim milk and cream were studied. Thermosonication, at an average power of 115 W (152 µmp-p, where p-p=peak-to-peak amplitude) for 3 min, decreased the total plasmin activity (i.e., plasmin- and plasminogen-derived activity) by nearly 94% in fresh skim milk and cream. Enzyme activity in thermosonicated skim milk samples measured at the end of 30 d was 5- to 10-fold higher than on d 0, but remained stable in thermosonicated cream. Descriptive analysis of odor attributes was conducted for up to 4 wk with 8 trained panelists. No significant differences were observed between the intensities of offensive “eggy” and “rubbery” odor attributes of thermosonicated skim milk and pasteurized commercial skim milk and cream. In addition, lightness (L*) values and viscosity were not adversely affected by thermosonication. Thermosonication decreased the fat globule size in skim milk and cream, and the homogenizing effect increased with treatment time. Thermosonication at average powers of 104 W (133 µmp-p) and 115 W (152 µmp-p) for 1 and 3 min destroyed coliforms and over 99% of the total aerobic bacteria. The total aerobic bacteria counts of thermosonicated skim milk and cream samples were less than 20,000 cfu/mL on d 30. Because thermosonication did not induce off-aromas or viscosity changes but did inactivate microorganisms and protease enzymes, thermosonication may be an appropriate adjunct to pasteurization to extend milk shelf life.

Control Methods and Evaluation of Bacterial Growth on Fresh and Cooled Stallion Semen

The penis and prepuce of the stallion have a high bacterial load on its surface, forming a natural microbial flora that contaminates the semen during ejaculation. Bacterial growth in semen may cause a decline on sperm quality, viability, and fertility and predisposes the occurrence of endometritis in inseminated mares. Thus, the aim of this study was to evaluate the effect of penile wash before semen collection, the addition of different commercial skim milk–based extenders containing antibiotics (BotuSemen and INRA96), and the removal of seminal plasma by filtration on the quality, viability, and bacterial proliferation on fresh and cooled stallion semen. Animals that were never submitted to penile wash before semen collection tended to have lower bacterial contamination in the ejaculate. Semen samples extended in BotuSemen showed superiority in total motility, progressive motility, average path velocity, and rapid sperm and lower bacterial contamination in relation to semen samples extended in INRA96 after 24 hours of cooling. No difference was found in these parameters between the storage temperatures (5°C and 15°C). Furthermore, the removal of seminal plasma by filtration reduced the bacterial load in semen after cooling. In conclusion, the penile wash before semen collection tended to reduce the bacterial growth in fresh semen. The use of a semen extender with appropriate antibiotics and removal of seminal plasma by filtration were effective in reducing the bacterial contamination and preserved the quality of cooled stallion semen.

Novel Convenient Method to Determine Wettability and Dispersibility of Dairy Powders.

This study was carried out to develop a simple, convenient, and reproducible testing device to determine wettability and dispersibility of dairy powders. The testing device consists of a sieve (150 μm) attached to a sample chamber, sensors mounted on a supporting body and a main control unit containing a display panel. The sensors detect the difference in electrical resistance between air and water. A timer is automatically triggered by the sensor when the bottom of sample-loaded chamber contacts water in the petri dish. Wettability and dispersibility of commercial skim milk powders (SMPs) produced at different heating strengths (low-, medium-, and high-heat SMP) are compared using the new testing device. Wettability of the SMPs were correlated with particle size and are found to increase in the order of medium-, low-, and high-heat SMP regardless of the amount of sample tested. Dispersibility of SMPs showed the same trend and high heat-SMP which has the smallest particle size resulted in the lowest dispersibility. Unlike existing methods, the new testing device can determine both wettability and dispersibility of powders and successfully detected differences among the samples.

Quantification of individual fatty acids in bovine milk by infrared spectroscopy and chemometrics: Understanding predictions of highly collinear reference variables

Predicting individual fatty acids (FA) in bovine milk from Fourier transform infrared (FT-IR) measurements is desirable. However, such predictions may rely on covariance structures among individual FA and total fat content. These covariance structures may change with factors such as breed and feed, among others. The aim of this study was to estimate how spectral variation associated with total fat content and breed contributes to predictions of individual FA. This study comprised 890 bovine milk samples from 2 breeds (455 Holstein and 435 Jersey). Holstein samples were collected from 20 Danish dairy herds from October to December 2009; Jersey samples were collected from 22 Danish dairy herds from February to April 2010. All samples were from conventional herds and taken while cows were housed. Moreover, in a spiking experiment, FA (C14:0, C16:0, and C18:1 cis-9) were added (spiked) to a background of commercial skim milk to determine whether signals specific to those individual FA could be obtained from the FT-IR measurements. This study demonstrated that variation associated with total fat content and breed was responsible for successful FT-IR–based predictions of FA in the raw milk samples. This was confirmed in the spiking experiment, which showed that signals specific to individual FA could not be identified in FT-IR measurements when several FA were present in the same mixture. Hence, predicted concentrations of individual FA in milk rely on covariance structures with total fat content rather than absorption bands directly associated with individual FA. If covariance structures between FA and total fat used to calibrate partial least squares (PLS) models are not conserved in future samples, these samples will show incorrect and biased FA predictions. This was demonstrated by using samples of one breed to calibrate and samples of the other breed to validate PLS models for individual FA. The 2 breeds had different covariance structures between individual FA and total fat content. The results showed that the validation samples yielded biased predictions. This may limit the usefulness of FT-IR–based predictions of individual FA in milk recording as indirect covariance structures in the calibration set must be valid for future samples. Otherwise, future samples will show incorrect predictions.

Binding of vitamin A by casein micelles in commercial skim milk

Recent studies have shown that reassembled micelles formed by caseinates and purified casein fractions (αs- and β-casein) bind to hydrophobic compounds, including curcumin, docosahexaenoic acid, and vitamin D. However, limited research has been done on the binding of hydrophobic compounds by unmodified casein micelles in skim milk. In the present study, we investigated the ability of casein micelles in commercial skim milk to associate with vitamin A (retinyl palmitate), a fat-soluble vitamin commonly used to fortify milk. Milk protein fractions from different commercially available skim milk samples subjected to different processing treatments, including pasteurized, ultrapasteurized, organic pasteurized, and organic ultrapasteurized milks, were separated by fast protein liquid chromatography. The fractions within each peak were combined and freeze-dried. Sodium dodecyl sulfate-PAGE with silver staining was used to identify the proteins present in each of the fractions. The skim milk samples and fractions were extracted for retinyl palmitate and quantified against a standard using normal phase-HPLC. Retinyl palmitate was found to associate with the fraction of skim milk containing caseins, whereas the other proteins (BSA, β-lactoglobulin, α-lactalbumin) did not show any binding. The retinyl palmitate content in the various samples ranged from 1.59 to 2.48µg of retinyl palmitate per mL of milk. The casein fractions contained between 14 and 40% of total retinyl palmitate in the various milks tested. The variation in the retention of vitamin A by caseins was probably explained by differences in the processing of different milk samples, including thermal treatment, the form of vitamin A emulsion used for fortification, and the point of fortification during processing. Unmodified casein micelles have a strong intrinsic affinity toward the binding of vitamin A used to fortify commercially available skim milks.

Effects of milk supplementation with skim milk powder, whey protein concentrate and sodium caseinate on acidification kinetics, rheological properties and structure of nonfat stirred yogurt

Abstract Milk supplementation with milk proteins in four different levels was used to investigate the effect on acidification and textural properties of yogurt. Commercial skim milk powder was diluted in distilled water, and the supplements were added to give different enriched-milk bases; these were heat treated at 90 °C for 5 min. These mixtures were incubated with the bacterial cultures for fermentation in a water bath, at 42 °C, until pH 4.50 was reached. Chemical changes during fermentation were followed by measuring the pH. Protein concentration measurements, microbial counts of Lactobacillus bulgaricus and Streptococcus thermophilus, and textural properties (G′, G″, yield stress and firmness) were determined after 24 h of storage at 4 °C. Yogurt made with milk supplemented with sodium caseinate resulted in significant properties changes, which were decrease in fermentation time, and increase in yield stress, storage modulus, and firmness, with increases in supplement level. Microstructure also differed from that of yogurt produced with milk supplemented with skim milk powder or sodium caseinate.

Inactivation of Calcium-Dependent Lactic Acid Bacteria Phages by Phosphates

The capacity of three phosphates to interrupt the lytic cycle of four specific autochthonal bacteriophages of lactic acid bacteria used as starters was assayed. The phosphates used (polyphosphates A and B and sodium tripolyphosphate–high solubility [TAS]) were selected on the basis of their capacity to sequester divalent cations, which are involved in the lytic cycle of certain bacteriophages. The assays were performed in culture media (deMan Rogosa Sharpe and Elliker broths) and reconstituted (10%, wt/vol) commercial skim milk to which phosphates had been added at concentrations of 0.1, 0.3, and 0.5% (wt/vol). Phosphate TAS was the most inhibitory one, since it was able to inhibit the lytic cycle of all bacteriophages studied, in both broths and milk. In broth, polyphosphates A and B inhibited the lytic cycle of only two bacteriophages at the maximal concentration used (0.5%), whereas in milk, they were not capable of maintaining the same inhibitory effect.

SDS-PAGE Analysis of Soluble Proteins in Reconstituted Milk Exposed to Different Heat Treatments

This paper deals with the investigation of the impact of the heat treatment of reconstituted skim milk conducted at different temperatures, and the adding of demineralized whey on the protein solubility, soluble protein composition and interactions involved between proteins in a chemical complex. Commercial skim milk has been reconstituted and heat treated at 75°C, 85°C and 90°C for 20 minutes. Demineralized whey has been added in concentrations of 0.5%, 1.0 and 2.0%. The soluble protein composition has been determined by the polyacrilamide gel electrophoresis (SDS-PAGE) and by the densitometric analysis. Due to the different changes occurred during treatments at different temperatures, proteins of heat-treated samples containing added demineralized whey have had significantly different solubility. At lower temperatures (75°C and 85°C) the adding of demineralized whey decreased the protein solubility by 5.28%-26.41%, while the addition of demineralized whey performed at 90°C increased the soluble protein content by 5.61%- 28.89%. Heat treatments, as well as the addition of demineralized whey, have induced high molecular weight complex formation. β-Lg, α-La and κ-casein are involved in high molecular weight complexes. The disulfide interactions between denatured molecules of these proteins are mostly responsible for the formation of coaggregates. The level of their interactions and the soluble protein composition are determined by the degree of temperature.

Effect of milk fractions on survival of equine spermatozoa

Milk-based semen diluents are known to be practical and effective in protecting equine spermatozoa during storage. Due to complex composition of milk, the components which are beneficial or harmful to spermatozoa are unknown. To address these unknowns the effect of various milk fractions on motility of stallion spermatozoa was evaluated. The fractions tested were native phosphocaseinate (NPPC), β-casein, whey protein concentrate (WPC), α-lactalbumin, β-lactoglobulin, microfiltrate, and ultrafiltrate. The standard reference diluents were INRA 82, commercial skim milk, and Hank's salts solution supplemented with Hepes, glucose, lactose (HGLL) supplemented with BSA. After 48 and 96 h storage at 4 or 15 °C some milk fractions (ultrafiltrate, microfiltrate, and α-lactalbumin fraction) decreased spermatozoal survival. Others (β-lactoglobulin (BL) and native phosphocaseinate) were protective. Native phosphocaseinate (NPPC) at milk concentration afforted better protection than did the standard reference diluents. The optimal concentration of β-lactoglobulin afforted significantly better protection than did BSA. The protection afforded by native phophocaseinate was not synergistic with β-lactoglobulin. This implies a similar mechanism of protective action of these two components. Semen diluted in HGLL supplemented with NPPC (HGLL-NPPC) or in INRA 82 and stored 24 h at 15 °C or 4 °C, respectively, produced no difference of spermatozoal motility. However, fertility of semen stored in HGLL-NPPC (60%) was higher (p < 0.05) than that stored in INRA 82 (36%).

Electroacoustic determination of size and zeta potential of casein micelles in skim milk

SummaryMeasurements of the zeta potential and particle size of casein micelles in skim milk suspensions at natural and lower pH have been made using the technique of electroacoustics. This technique requires no dilution or change of environment of the casein micelles. The zeta potential obtained at natural pH for a commercial skim milk suspension was −18 mV; it became less negative with decreasing pH. The median particle size observed at natural pH for a commercial skim milk suspension was 0·2 εm, in good agreement with previously reported values. The particle size increased as the pH was decreased.

Influence of Intake of Skim Milk from Cows Immunized with Intestinal Bacterial Antigens on Onset of Renal Disease in (NZB × NZW)F1 Mice Fed Ad Libitum or Restricted in Energy Intake

Autoimmune disease-prone (NZB x NZW)F1 (B/W) female mice are a model of human lupus erythematosus. Immune milk, obtained from cows immunized with various intestinal bacterial antigens, was given to B/W mice as a component of diets beginning at 8 wk of age. Diets were fed ad libitum or restricted to 60% of ad libitum energy intake. Controls were fed commercial skim milk. In B/W mice fed ad libitum, the titers of anti-single-stranded DNA antibodies were significantly lower in immune milk-fed mice at 4 and 6 mo of age. Onset of proteinuria was delayed and life span was significantly prolonged by immune milk feeding. Surface phenotypes of the T cells and levels of the responsiveness of lymphocytes to mitogens were not changed by immune milk feeding. The B/W mice restricted to 60% of ad libitum energy intake, which preserved immune responsiveness, had not developed proteinuria by 14 mo of age, irrespective of immune milk feeding or control milk feeding. However, at 10 mo of age, the level of plasma antibodies against intestinal bacteria was significantly higher in energy-restricted mice fed control milk than in those fed immune milk or in mice fed ad libitum.

Classification of Commercial Skim Milk Powders According to Heat Treatment Using Factorial Discriminant Analysis of Near-Infrared Reflectance Spectra

Near-infrared reflectance (NIR) spectroscopy is well established as a rapid and nondestructive analytical technique in many agro-food industries. Most published applications have been concerned with the use of NIR for quantitative analyses of technologically important chemical constituents such as water and protein in grain, alcohol in wine, oil in mayonnaise, etc., although successes have been reported with the prediction of less precisely defined but nonetheless functionally important sample attributes (e.g., wheat hardness). A number of mathematical techniques have been used to develop accurate and stable prediction equations, among which may be mentioned stepwise multiple linear regression, principal component regression, partial least-squares regression, and derivative quotient mathematics.

Chemical and nutritional changes of milk powder proteins under various water activities.

Milk powders (commercial skim milk and modified milk powders) were stored at 30°C and 40°C for one month under various water activities (Aw), 0.23~0.82. After storage under Aw 0.57 and 0.80, they turned a dark brown color, and the contents of methionine and lysine had significantly decreased: methionine had been oxidized to methionine sulfoxide and lysine had changed to an unavailable form. The contents of arginine, tyrosine and tryptophan had also decreased, as had the contents of leucine and histidine in the skim milk powder. The tryptic digestibility of the milk powders had markedly decreased, and both the chymotryptic and peptic digestibilities of the skim milk powder had also decreased. The samples lost the property of being clotted by chymosin treatment.No significant change was observed with casein under these conditions, nor with milk powders under dry conditions and Aw 0.23.

Co‐processing Soy Proteins and Milk Proteins with Commercial Ultrafiltration Membranes

ABSTRACTUltrafiltration (UF) membranes were used to co‐process soy protein extract and skim milk seeking to produce soy‐milk food ingredients with protein efficiency ratios (PERs) of 2.5 or higher. Extracts from two commercial soy flours and ground soybeans were blended with commercial skim milk before and after ultrafiltration. Protein blends of 67% soy‐33% milk, 50% soy‐50% milk and 33% soy‐67% milk were processed. Soy‐milk products possessed high nitrogen solubility and light color. Lysine contents of soy‐milk products ranged from 7.34–6.82%. PERs ranged from 2.36 for 33% soy‐67% milk to 1.47 for UF soy isolate without milk. Soy and milk proteins exhibited some synergistic effects, but none of the soy‐milk PERs reached the 2.5 level.

A COMPARISON OF SOME CHEMICAL PROPERTIES OF YOGURTS MADE FROM CONTROL AND LACTASE‐TREATED MILKS

ABSTRACTCertain properties of yogurts made from regular commercial skim milk and from milk which had been treated with lactase enzyme so that 70‐75% of the lactose was hydrolyzed to glucose and galactose were evaluated. Initially faster rates of acid production in lactase‐hydrolyzed milks (LH) during fermentation resulted in somewhat shortened processing times, although a decrease in the rate of acid production occurred earlier during fermentation in the LH milk so that final product pH was similar for both the control and LH yogurts. Control yogurts contained 5.0% lactose and 0.2% galactose while LH yogurts contained 1.6% glucose, 1.5% lactose and 2.1% galactose. Appreciably more lactic acid was produced in LH yogurts and this effect has been related to fermentation by the starter culture organisms of a greater proportion of the available sugar as glucose.