Fatty acid profile differs between organic and conventionally produced cow milk independent of season or milking time.

Differing amounts of fresh forage and concentrates fed, and level of input contributes to the differences reported in fatty acid (FA) composition of organic and conventionally produced cow milk. In many previous studies designed to investigate this phenomenon, comparisons were made between grazed organic cows and housed conventional cows. In the present study, we have investigated differences between organic and conventional milk produced using year-round pasture grazing, as practiced in New Zealand. The FA composition was determined in milk sampled at morning and evening milking in both spring and autumn. Samples were taken from 45 cows from the Massey University organic herd and compared with 50 cows from the corresponding conventional herd grazed and managed similarly at the same location. Forty-three out of 51 analyzed FA were influenced by season, whereas 28 were different between production systems. In addition, one-half were also different due to time of milking. Levels of linoleic acid and α-linolenic acid were higher in organic milk, whereas conjugated linoleic acid (CLA) and vaccenic acid were higher in conventional milk. The first 3 FA (linoleic acid, α-linolenic acid, and CLA) were more abundant in milk harvested during autumn, and the CLA concentration was also significantly influenced by time of milking. Our results confirm reports that the FA profile is affected by season and time of milking, and we also showed an effect due to the production system, when both sets of cows were kept continuously on pasture, even after taking milking time and seasonal effect into account.

Invited review: organic and conventionally produced milk-an evaluation of factors influencing milk composition.

Consumer perception of organic cow milk is associated with the assumption that organic milk differs from conventionally produced milk. The value associated with this difference justifies the premium retail price for organic milk. It includes the perceptions that organic dairy farming is kinder to the environment, animals, and people; that organic milk products are produced without the use of antibiotics, added hormones, synthetic chemicals, and genetic modification; and that they may have potential benefits for human health. Controlled studies investigating whether differences exist between organic and conventionally produced milk have so far been largely equivocal due principally to the complexity of the research question and the number of factors that can influence milk composition. A main complication is that farming practices and their effects differ depending on country, region, year, and season between and within organic and conventional systems. Factors influencing milk composition (e.g., diet, breed, and stage of lactation) have been studied individually, whereas interactions between multiple factors have been largely ignored. Studies that fail to consider that factors other than the farming system (organic vs. conventional) could have caused or contributed to the reported differences in milk composition make it impossible to determine whether a system-related difference exists between organic and conventional milk. Milk fatty acid composition has been a central research area when comparing organic and conventional milk largely because the milk fatty acid profile responds rapidly and is very sensitive to changes in diet. Consequently, the effect of farming practices (high input vs. low input) rather than farming system (organic vs. conventional) determines milk fatty acid profile, and similar results are seen between low-input organic and low-input conventional milks. This confounds our ability to develop an analytical method to distinguish organic from conventionally produced milk and provide product verification. Lack of research on interactions between several influential factors and differences in trial complexity and consistency between studies (e.g., sampling period, sample size, reporting of experimental conditions) complicate data interpretation and prevent us from making unequivocal conclusions. The first part of this review provides a detailed summary of individual factors known to influence milk composition. The second part presents an overview of studies that have compared organic and conventional milk and discusses their findings within the framework of the various factors presented in part one.

Simultaneous separation and quantitation of the major bovine whey proteins including proteose peptone and caseinomacropeptide by reversed-phase high-performance liquid chromatography on polystyrene-divinylbenzene.

A precise, sensitive and reliable RP-HPLC method was developed to enable not only unequivocal determination of alpha-lactalbumin and beta-lactoglobulin in bovine whey samples, but also simultaneous measurement of proteose peptone, caseinomacropeptide, bovine serum albumin and immunoglobulin G. The optimised method on the Resource RPC column allowed separation of the proteins in 30 min and could be applied to the analysis of soluble proteins in a variety of commercial and laboratory whey products. Furthermore, some qualitative information on protein heterogeneity and quality could be derived from the RP-HPLC analyses with additional data available from on-line electrospray mass spectrometry. Within- and between-day repeatability over a wide range of concentrations was excellent (RSD< or =5%) for all proteins except immunoglobulin G and bovine serum albumin where RSD was 7-10%. Analysis of grouped data from whey protein concentrate and whey protein isolate samples gave a limit of detection of < or =0.3% powder mass and a limit of quantitation of < or =1.0% powder mass for all proteins except immunoglobulin G. Limits of detection and quantitation were 0.6% and 2.0%, respectively, for this protein. Quantitative data obtained by the RP-HPLC method compared very favourably with data obtained by alternative methods of whey protein analysis.

Quantification of glutamine in proteins and peptides using enzymatic hydrolysis and reverse-phase high-performance liquid chromatography.

An enzymatic method for hydrolyzing bovine milk proteins was developed. Purified milk proteins (alpha-lactalbumin, beta-lactoglobulin, and beta-casein) were hydrolyzed in 0.1 M Hepes buffer (pH 7.5) containing pronase E, aminopeptidase M, and prolidase at 37 degrees C for 20 h. Free glutamine and other amino acids were derivatized with phenylisothiocyanate and separated using a C18 Pico-Tag column. Amino acids were eluted from the column with an aqueous sodium acetate-acetonitrile gradient with detection at 254 nm. Glutamine recoveries from hydrolyzed alpha-lactalbumin, beta-lactoglobulin, and beta-casein were 78 +/- 4, 98 +/- 3, and 101 +/- 3% of the theoretical values, respectively. The recoveries of most amino acids were comparable with those obtained using acid hydrolysis, except for the recoveries of proline and acidic amino acids. These peptide bonds appeared to be resistant to enzymatic hydrolysis and also to inhibit the hydrolysis of adjacent amino acids. Free glutamine was found to be very stable (97% recovery) under the enzymatic hydrolysis conditions.

Identification, characterisation and cDNA cloning of two caseins from the common brushtail possum (Trichosurus vulpecula)1.

Two major caseins have been isolated from the milk of the common brushtailed possum (Trichosurus vulpecula). These have been identified as alpha- and beta-casein on the basis of the similarity of their N-terminal sequences to those of the caseins of another marsupial (Macropus eugenii). Both proteins appear to exist in multiple forms. Possum alpha-casein is glycosylated mainly in the form of sialic acid residues and was shown by electrospray mass spectrometry to have multiply phosphorylated forms of three families with molecular masses 22700 and 23200 Da that may represent genetic variants. Two-dimensional electrophoresis showed that beta-casein exists as a complex of five or six proteins of identical N-terminal sequence but differing pI. Electrospray mass spectrometry indicated that the beta-caseins also are multiply phosphorylated with masses between 32300 and 32600 Da. A subfamily with mass values 1530 greater was also detected. The patterns were not affected by stage of lactation and quantitative analysis of two-dimensional gels of whole milk shows that alpha- and beta-caseins are present at a constant ratio throughout lactation. cDNA clones for the possum alpha- and beta-caseins have been isolated from an early lactation mammary cDNA library and sequenced.

Application of capillary electrophoresis in the identification of phenotypes containing the beta-lactoglobulin C variant.

A method for the separation of the beta-LG variants A, B, and C was developed using free zone capillary electrophoresis. A separation buffer consisting of 50 mM 2-(N-morpholino)ethane sulfonic acid (pH 8.0) and polyoxyethylene (20)-sorbitan monolaurate was used for the separation. Milk samples from 424 Jersey cows were phenotyped using this method, and the gene frequencies for beta-LG A, B, and C were .41, .53, and .06, respectively. These frequencies were different from those found in studies of Jersey populations in other countries, where the beta-LG B allele had a significantly higher frequency, and the beta-LG A allele a significantly lower frequency, than those of this present study. The frequency of the beta-LG C allele was intermediate to those of other studies. The concentration of beta-LG in the milk was different among the beta-LG phenotypes and was, from greatest to least: AA, AB, AC, BB, and BC.

Use of capillary zone electrophoresis in an investigation of peptide uptake by dairy starter bacteria.

A capillary zone electrophoresis (CZE) method to separate the peptide series val-glyn, where n is 1 to 4, has been evaluated and compared to separation by reversed-phase high-performance liquid chromatography (RP-HPLC). The method was able to quantitate peptides present a very low concentrations (down to 0.05 mM) with high reproducibility and accuracy and was capable of separating peptides differing in size by only a single glycine residue. It could also separate the peptides val-gly and leu-gly which differed in only a single side-chain methylene group. The method was fast, required small sample volumes, and proved to be superior to RP-HPLC. The suitability of the CZE method to analyze peptide uptake by dairy starter bacteria is discussed.

Separation of beta-lactoglobulin A, B and C variants of bovine whey using capillary zone electrophoresis.

beta-Lactoglobulin is a whey protein that affects milk composition and product functionality and which can be present in up to eight genetic variant forms. A free zone capillary electrophoresis method has been developed to separate and identify the beta-lactoglobulin A, B and C variants. Three buffer systems [borate, 2-(N-morpholino)-ethanesulphonic acid (MES) and bis(2-hydroxyethyl)imino-tris(hydroxymethyl)methane (Bistris)] were examined over a range of pH values and with the addition of the separation buffer modifiers Tween 20 and/or ethanolamine. The most successful combination of these was 50 mM MES at pH 8.0 with the addition of 0.1% Tween 20 which clearly resolved the three variants from both each other and from the other whey proteins even though the MES buffer was acting well outside its pKa range (pH 5.3-7.3). The retention times and identification of the individual variants were verified by spiking with commercially purified beta-lactoglobulin A and B proteins and a beta-lactoglobulin AC whey. The method was then used to phenotype beta-lactoglobulin in a sample population of New Zealand Jersey cows.

Comparison of capillary electrophoresis with traditional methods to analyse bovine whey proteins.

The separation of the four major whey proteins by sodium dodecyl sulphate (SDS)-capillary gel electrophoresis (CGE) is described. Whilst commercially purified whey proteins could be analysed using the recommended protocol, the more complex nature of an acid whey and a reconstituted whey protein concentrate (WPC) powder necessitated considerable refinement of the CGE sample buffer. Individual whey proteins in the acid whey and WPC samples were then also separated and quantitated using capillary zone electrophoresis, polyacrylamide gel electrophoresis (PAGE) and HPLC methods and the results were compared. The values obtained for alpha-lactalbumin (alpha-Lac) and beta-lactoglobulin (beta-Lg) were consistent throughout the various methods, although size-exclusion HPLC, SDS-PAGE and SDS-CGE could not separate the two beta-Lg variants or the glycosylated form of alpha-Lac from the beta-Lg. There was considerable variation in the values for the bovine serum albumin and immunoglobulin determined by the different methods and it was concluded that none of the methods could satisfactorily quantitate all four whey proteins.

Desorption of Trichoderma reesei cellulase from cellulose by a range of desorbents.

The desorption of Trichoderma reesei cellulase from Avicel by a wide range of desorbents was measured. Emphasis was placed on desorption at alkaline pH. A maximum desorption of 65-68% Avicelase activity was achieved by contact with NaOH, pH 10.0, at 40 degrees C for 5 min in the presence of 0.005% Triton X-100 or Tween 80. The design of a suitable desorption process using these conditions is discussed. Glycerol was also effective as a desorbent either alone or in combination with alkali and detergent. However, relatively high concentrations of glycerol were needed and the maximum desorption achieved, 68%, was not significantly greater than that with only alkali and detergent.

Disturbance of lysosomal glycogen metabolism by liposomal anti-alpha-glucosidase and some anti-inflammatory drugs.

The size-distribution of liver glycogen was shown to be distinctly affected by the anti-inflammatory drugs salicylate and indomethacin. By measurement of the incorporation of radioactive glucose into glycogen, salicylate was shown to have a depressing effect on overall liver glycogen metabolism. These effects appear to arise from the stabilizing of the lysosome by the drugs. The incorporation, via liposomes, of purified anti-1,4-alpha-glucosidase activity and in the content of high-molecular-weight glycogen. These changes are increased by prolonged liposomal antibody treatment and suggest that a possible feedback control mechanism operates in the incorporation of glycogen into lysosomes. These experiments may be useful as a model of glycogen turnover and its failure in glycogenosis type II (Pompe's disease).