Proportions of A1, A2, B and C β-casein protein variants in retail milk in the UK

The A1 variant protein of the β-casein family has been implicated in various disease states although much evidence is weak or contradictory. The primary objective was to measure, for the first time, the proportions of the key β-casein variant proteins in UK retail milk over the course of one year. In total, 55 samples of semi-skimmed milk were purchased from five supermarkets over the course of a year and the proportions of the A1, A2, B and C casein variant proteins were measured, using high resolution HPLC-MS. The results showed that β-casein in UK retail milk comprises approximately 0.58, 0.31, 0.07 and 0.03 A2, A1, B and C protein variants, respectively. The proportion of A2 is higher than some early studies would predict although the reasons for this and any implications for health are unclear

Fat composition of organic and conventional retail milk in northeast England

This study of UK retail milk identified highly significant variations in fat composition. The survey, conducted over 2 yr replicating summer and winter, sampled 22 brands, 10 of which indicated organic production systems. Results corroborate earlier farm-based findings considering fat composition of milk produced under conventional and organic management. Organic milk had higher concentrations of beneficial fatty acids (FA) than conventional milk, including total polyunsaturated fatty acids (PUFA; 39.4 vs. 31.8 g/kg of total FA), conjugated linoleic acid cis-9,trans-11 (CLA9; 7.4 v 5.6 g/kg of FA), and α-linolenic acid (α-LN; 6.9 vs. 4.4 g/kg of FA). As expected, purchase season had a strong effect on fat composition: compared with milk purchased in winter, summer milk had a lower concentration of saturated fatty acids (682 vs. 725 g/kg of FA) and higher concentrations of PUFA (37.6 vs. 32.8 g/kg of FA), CLA9 (8.1 vs. 4.7 g/kg of FA), and α-LN (6.5 vs. 4.6 g/kg of FA). Differences identified between sampling years were more surprising: compared with that in yr 2, milk purchased in year 1 had higher concentrations of PUFA (37.5 vs. 32.9 g/kg of FA), α-LN (6.0 vs. 5.1 g/kg of FA), and linoleic acid (19.9 vs. 17.5 g/kg of FA) and lower concentrations of C16:0 and C14:0 (332 vs. 357 and 110 vs. 118 g/kg of FA, respectively). Strong interactions were identified between management and season as well as between season and year of the study. As in the earlier farm studies, differences in fat composition between systems were greater for summer compared with winter milk. Large between-year differences may be due to changes in weather influencing milk composition through forage availability, quality, and intake. If climate change predictions materialize, both forage and dairy management may have to adapt to maintain current milk quality. Considerable variation existed in milk fat composition between brands.

Seasonal variation in the fatty acid composition of milk available at retail in the United Kingdom and implications for dietary intake

Milk and dairy products are major sources of fat in the human diet, but there are few detailed reports on the fatty acid composition of retail milk, trans fatty acids in particular, and how these change throughout the year. Semi-skimmed milk was collected monthly for one year from five supermarkets and analysed for fatty acid composition. Relative to winter, milk sold in the summer contained lower total saturated fatty acid (SFA; 67 vs 72 g/100 g fatty acids) and higher cis-monounsaturated fatty acid (MUFA; 23 vs 21 g/100 g fatty acids) and total trans fatty acid (6.5 vs 4.5 g/100 g fatty acids) concentrations. Concentrations of most trans-18:1 and -18:2 isomers also exhibited seasonal variation. Results were applied to national dietary intakes, and indicated that monthly variation in the fatty acid composition of milk available at retail has limited influence on total dietary fatty acid consumption by UK adults.

Variation in nutritionally relevant components in retail Jersey and Guernsey whole milk

This study investigates the quality of retail milk labelled as Jersey & Guernsey (JG) when compared with milk without breed specifications (NS) and repeatability of differences over seasons and years. 16 different brands of milk (4 Jersey & Guernsey, 12 non specified breed) were sampled over 2 years on 4 occasions. JG milk was associated with both favourable traits for human health, such as the higher total protein, total casein, α-casein, β-casein, κ-casein and α-tocopherol contents, and unfavourable traits, such as the higher concentrations of saturated fat, C12:0, C14:0 and lower concentrations of monounsaturated fatty acids. In summer, JG milk had a higher omega-3:omega-6 ratio than had NS milk. Also, the relative increase in omega-3 fatty acids and α-tocopherol, from winter to summer, was greater in JG milk. The latter characteristic could be of use in breeding schemes and farming systems producing niche dairy products. Seasonality had a more marked impact on the fatty acid composition of JG milk than had NS milk, while the opposite was found for protein composition. Potential implication for the findings in human health, producers, industry and consumers are considered.

Effect of milk type and processing on iodine concentration of organic and conventional winter milk at retail: implications for nutrition

Milk is the largest source of iodine in UK diets and an earlier study showed that organic summer milk had significantly lower iodine concentration than conventional milk. There are no comparable studies with winter milk or the effect of milk fat class or heat processing method. Two retail studies with winter milk are reported. Study 1 showed no effect of fat class but organic milk was 32.2% lower in iodine than conventional milk (404 vs. 595 μg/L; P < 0.001). Study 2 found no difference between conventional and Channel Island milk but organic milk contained 35.5% less iodine than conventional milk (474 vs. 306 μg/L; P < 0.001). UHT and branded organic milk also had lower iodine concentrations than conventional milk (331 μg/L; P < 0.001 and 268 μg/L: P < 0.0001 respectively). The results indicate that replacement of conventional milk by organic or UHT milk will increase the risk of sub-optimal iodine status especially for pregnant/lactating women.

Combined use of two genetic fingerprinting methods, pulsed-field gel electrophoresis and ribotyping, for characterization of Escherichia coli O157 isolates from food animals, retail meats, and cases of human disease

Two genetic fingerprinting techniques, pulsed-field gel electrophoresis (PFGE) and ribotyping, were used to characterize 207 Escherichia coli O157 isolates from food animals, foods of animal origin, and cases of human disease (206 of the isolates were from the United Kingdom). In addition, 164 of these isolates were also phage typed. The isolates were divided into two general groups: (i) unrelated isolates not known to be epidemiologically linked (n = 154) and originating from food animals, foods and the environment, or humans and (ii) epidemiologically related isolates (n = 53) comprised of four related groups (RGs) originating either from one farm plus the abattoir where cattle from that farm were slaughtered or from one of three different English abattoirs. PFGE was conducted with the restriction endonuclease XbaI. while for ribotyping, two restriction endonucleases (PstI and SphI) were combined to digest genomic DNAs simultaneously. The 207 E. coli O157 isolates produced 97 PFGE profiles and 51 ribotypes. The two genetic fingerprinting methods had similar powers to discriminate the 154 epidemiologically unrelated E. coli O157 isolates in the study (Simpson's index of diversity [D] = 0.98 and 0.94 for PFGE typing and ribotyping, respectively). There was no correlation between the source of an isolate (healthy meat or milk animals, retail meats, or cases of human infection) and either particular PFGE or ribotype profiles or clusters. Combination of the results of both genetic fingerprinting methods produced 146 types, significantly more than when either of the two methods was used individually. Consequently, the superior discriminatory performance of the PFGE-ribotyping combination was proven in two ways: (i) by demonstrating that the majority of the E. coli O157 isolates with unrelated histories were indeed distinguishable types and (ii) by identifying some clonal groups among two of the four RGs of E. coli O157 isolates (comprising PFGE types different by just one or two bands), the relatedness of which would have remained unconfirmed otherwise.

Selenium supplementation of lactating dairy cows: effects on milk production and total selenium content and speciation in blood, milk and cheese

Forty-multiparous Holstein cows were used in a 16-wk continuous design study to determine the effects of either selenium (Se) source, selenized yeast (SY) (derived from a specific strain of Saccharomyces cerevisiae CNCM I-3060 Sel-Plex®) or sodium selenite (SS), or inclusion rate of SY on Se concentration and speciation in blood, milk and cheese. Cows received ad libitum a TMR with 1:1 forage:concentrate ratio on a dry matter (DM) basis. There were four diets (T1-T4) which differed only in either source or dose of Se additive. Estimated total dietary Se for T1 (no supplement), T2 (SS), T3 (SY) and T4 (SY) was 0.16, 0.30, 0.30 and 0.45 mg/kg DM, respectively. Blood and milk samples were taken at 28 day intervals and at each time point there were positive linear effects of SY on Se concentration in blood and milk. At day 112 blood and milk Se values for T1-T4 were 177, 208, 248, 279 ± 6.6 and 24, 38, 57, 72 ± 3.7 ng/g fresh material, respectively and indicate improved uptake and incorporation of Se from SY. While selenocysteine (SeCys) was the main selenised amino acid in blood its concentration was not markedly affected by treatment, but the proportion of total Se as selenomethionine (SeMet) increased with increasing inclusion rate of SY. In milk, there were no marked treatment effects on SeCys content, but Se source had a marked effect on the proportion of total Se as SeMet. At day 112 replacing SS (T2) with SY (T3) increased the SeMet concentration of milk from 36 to 111 ng Se/g and its concentration increased further to 157 ng Se/g as the inclusion rate of SY increased further (T4) to provide 0.45 mg Se/kg TMR. Neither Se source nor inclusion rate effected the keeping quality of milk. At day 112, milk from T1, T2, and T3 was made into a hard cheese and Se source had a marked effect on total Se and the proportion of total Se comprised as either SeMet or SeCys. Replacing SS (T2) with SY (T3) increased total Se, SeMet and SeCys content from 180 to 340 ng Se/g, 57 to 153 ng Se/g and 52 to 92 ng Se/g, respectively. Key words: dairy cow, milk and cheese, selenomethionine, selenocysteine, milk keeping quality

Selenium supplementation of lactating dairy cows: Effect on selenium concentration in blood, milk, urine and feces

The objectives were to determine effects of graded levels of selenized yeast derived from a specific strain of Saccharomyces cerevisiae (CNCM I-3060) on animal performance and in selenium concentrations in the blood, milk, feces, and urine of dairy cows compared with sodium selenite; and to provide preliminary data on the proportion of selenium as selenomethionine in the milk and blood. Twenty Holstein cows were used in a 5 × 5 Latin square design study in which all cows received the same total mixed rations, which varied only in source or concentration of dietary selenium. There were 5 experimental treatments. Total dietary selenium of treatment 1, which received no added selenium, was 0.15 mg/kg of dry matter, whereas values for treatments 2, 3, and 4, derived from selenized yeast, were 0.27, 0.33, and 0.40 mg/kg of dry matter, respectively. Treatment 5 contained 0.25 mg of selenium obtained from sodium selenite/kg of dry matter. There were no significant treatment effects on animal performance, and blood chemistry and hematology showed few treatment effects. Regression analysis noted significant positive linear effects of increasing dietary selenium derived from selenized yeast on selenium concentrations in the milk, blood, urine, and feces. In addition, milk selenium results indicated improved bioavailability of selenium from selenized yeast, compared with sodium selenite. Preliminary analyses showed that compared with sodium selenite, the use of selenized yeast increased the concentration of selenomethionine in the milk and blood. There was no indication of adverse effects on cow health associated with the use of selenized yeast.

The effect of calcium removal from milk on casein micelle stability and structure

The total calcium level of raw skimmed milk was reduced by 10, 19, 29, 40 and 51% using Duolite® ion-exchange resin. The products were examined for concentrations of ionic calcium, sodium and potassium and the pH, ethanol stability, micelle diameter and ζ-potential were also measured. Ionic calcium decreased with removal of calcium and pH increased. Calcium removal resulted in an increase in the ethanol stability from 88% to above 100%. Casein micelle diameter increased as calcium was removed. The ζ-potential of the skimmed bulk milk was -24.4 mV, gradually becoming more negative with calcium removal to -30.6 mV after 51% calcium removal. The milk became more translucent as calcium was removed. To investigate the reversibility of this process, calcium chloride was added back to the depleted samples to restore their original total calcium content. At 51% removal, restoration of the total calcium level resulted in formation of clots. At levels of 10 and 19% calcium removal, the ethanol stability remained above 100%, but at higher levels of calcium removal the alcohol stability was adversely affected when the calcium was added back. Adding back calcium resulted in partial restoration of the original casein micelle diameter.

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

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

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

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