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| 2. |
- Rauh, Valentin M., et al.
(författare)
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Plasmin Activity in UHT Milk: Relationship between Proteolysis, Age Gelation, and Bitterness
- 2014
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Ingår i: Journal of Agricultural and Food Chemistry. - : American Chemical Society (ACS). - 0021-8561 .- 1520-5118. ; 62:28, s. 6852-6860
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Tidskriftsartikel (refereegranskat)abstract
- Plasmin, the major indigenous protease in milk, is linked to quality defects in dairy products. The specificity of plasmin on caseins has previously been studied using purified caseins and in the indigenous peptide profile of milk. We investigated the specificity and proteolytic pathway of plasmin in directly heated UHT milk (>150 degrees C for <0.2 s) during 14 weeks of storage at 20 degrees C in relation to age gelation and bitter peptides. Sixty-six peptides from alpha(s)- and beta-caseins could be attributed to plasmin activity during the storage period, of which 23 were potentially bitter. Plasmin exhibited the highest affinity for the hydrophilic regions in the caseins that most probably were exposed to the serum phase and the least affinity for hydrophobic or phosphorylated regions. The proteolytic pattern observed suggests that plasmin destabilizes the casein micelle by hydrolyzing casein casein and casein calcium phosphate interaction sites, which may subsequently cause age gelation in UHT milk
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| 3. |
- Rauh, Valentin M., et al.
(författare)
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Protein lactosylation in UHT milk during storage measured by Liquid Chromatography-Mass Spectrometry and quantification of furosine
- 2015
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Ingår i: International Journal of Dairy Technology. - : Wiley. - 1471-0307 .- 1364-727X. ; 68:4, s. 486-494
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Tidskriftsartikel (refereegranskat)abstract
- The initial stage of the Maillard reaction, protein lactosylation, occurs during heat treatment of milk and continues during subsequent storage. We compared the initial lactosylation as well as the rate of lactosylation of milk proteins during storage in UHT milk subjected to direct or indirect heat treatment using liquid chromatography (LC) coupled with electrospray injection mass spectrometry (ESI-MS). Furosine content was used as an overall marker to allow for a quantitative correlation of lactosylation measured by LC-ESI-MS in the UHT milks. Protein lactosylation increased during the storage period of 6months at 20 degrees C. Both the initial extent and the rate of lactosylation positively correlated with the number of lysine residues in the different proteins. An exponential or linear correlation with furosine concentration could be established for major and minor lactosylated proteins, respectively.
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| 4. |
- Poulsen, Nina A, et al.
(författare)
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Comparison of milk protein composition and rennet coagulation properties in native Swedish dairy cow breeds and high-yielding Swedish Red cows
- 2017
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Ingår i: Journal of Dairy Science. - : American Dairy Science Association. - 0022-0302. ; 100:11, s. 8722-8734
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Tidskriftsartikel (refereegranskat)abstract
- Recent studies have reported a very high frequency of noncoagulating milk in Swedish Red cows. The underlying factors are not fully understood. In this study, we explored rennet-induced coagulation properties and relative protein profiles in milk from native Swedish Mountain and Swedish Red Polled cows and compared them with a subset of noncoagulating (NC) and well-coagulating (WC) milk samples from modern Swedish Red cows. The native breeds displayed a very low prevalence of NC milk and superior milk coagulation properties compared with Swedish Red cows. The predominant variants in both native breeds were αS1-casein (αS1-CN) B, β-CN A2 and β-lactoglobulin (β-LG) B. For κ-CN, the B variant was predominant in the Swedish Mountain cows, whereas the A variant was the most frequent in the Swedish Red Polled. The native breeds displayed similar protein composition, but varied in content of αS1-CN with 9 phosphorylated serines (9P) form. Within the Swedish Mountain cows, we observed a strong inverse correlation between the relative concentration of κ-CN and micelle size and a positive correlation between ionic calcium and gel firmness. For comparison, we investigated a subset of 29 NC and 28 WC milk samples, representing the extremes with regard to coagulation properties based on an initial screening of 395 Swedish Red cows. In Swedish Red, NC milk properties were found to be related to higher frequencies of β-CN A2, κ-CN E and A variants, as well as β-LG B, and the predominant composite genotype of β- and κ-CN in the NC group was A2A2/AA. Generally, the A2A2/AA composite genotype was related to lower relative concentrations of κ-CN isoforms and higher relative concentrations of αS1-, αS2-, and β-CN. Compared with the group of WC milk samples, NC milk contained a higher fraction of αS2-CN and α-lactalbumin (α-LA) but a lower fraction of αS1-CN 9P. In conclusion, milk from native Swedish breeds has good characteristics for cheese milk, which could be exploited in niche dairy products. In milk from Swedish Mountain cows, levels of ionic calcium seemed to be more important for rennet-induced gel firmness than variation in the relative protein profile. In Swedish Red, lower protein content as well as higher fraction of αS2-CN and lower fraction of αS1-CN 9P were related to NC milk. Further, a decrease in the frequency of the composite β-κ-CN genotype A2A2/AA through selective breeding could have a positive effect on milk coagulation properties.
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| 5. |
- Rauh, Valentin M., et al.
(författare)
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Plasmin activity as a possible cause for age gelation in UHT milk produced by direct steam infusion
- 2014
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Ingår i: International Dairy Journal. - : Elsevier BV. - 0958-6946. ; 38:2, s. 199-207
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Tidskriftsartikel (refereegranskat)abstract
- The effect of enzymatic activity in direct steam infusion heat treated milk with ultra-short holding times (>150 degrees C for <0.2 s) on age gelation during storage was investigated. Preheating at either 72 or 95 degrees C for 180 s was performed. Milk pre-heated at 72 degrees C showed extensive proteolysis and exhibited bitter off flavour and contained <40% intact alpha(s)- and beta-caseins after 6 weeks storage at 20 degrees C. No proteolysis of kappa-casein was detected. Plasmin was identified as active protease and activation of plasminogen was observed as an increase in the rate of casein hydrolysis. Proteolysis in the stored samples correlated with a decrease in pH and with changes in colour. Gelation occurred after 10 weeks along with an increase in viscosity and extensive proteolysis of alpha(s)- and beta-caseins. In conclusion, plasmin activity was involved in age gelation and bitterness caused by proteolysis was the shelf-life limiting factor. (C) 2014 Elsevier Ltd. All rights reserved.
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| 6. |
- Rauh, Valentin M., et al.
(författare)
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The determination of plasmin and plasminogen-derived activity in turbid samples from various dairy products using an optimised spectrophotometric method
- 2014
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Ingår i: International Dairy Journal. - : Elsevier BV. - 0958-6946. ; 38:1, s. 74-80
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Tidskriftsartikel (refereegranskat)abstract
- A spectrophotometric assay for plasmin and plasminogen-derived activity in dairy products was optimised and extended to determine plasmin and plasminogen-derived activity in turbid samples of dairy products. The method was validated by assessing reproducibility, repeatability, level of detection and recovery of plasmin activity in different sample matrices. Plasmin activity in raw milk was not affected by skimming, but decreased by 30% in pasteurised and homogenised whole milk, leading to an underestimation of plasmin activity. The effects of dissociation of plasmin and caseins by epsilon-aminocaproic acid (EACA) plus NaCl on the plasmin activity were investigated. Comparison of pasteurised milk with a micellar casein solution showed that the dissociation of plasmin and caseins on adding EACA and NaCl decreases interference by caseins, but increases inhibition of plasmin with serum-based inhibitory components. The level of detection and repeatability of this method for plasmin activity analysis were improved compared with previous spectrophotometric assays. (C) 2014 Elsevier Ltd. All rights reserved.
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| 7. |
- Sheng, Bulei, et al.
(författare)
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Effects of genetic variants and sialylation on in vitro digestibility of purified κ-casein
- 2022
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Ingår i: Journal of Dairy Science. - : American Dairy Science Association. - 0022-0302. ; 105:4, s. 2803-2814
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Tidskriftsartikel (refereegranskat)abstract
- Milk with different κ-casein (CN) phenotypes has previously been found to influence its gastric digestion rate. Therefore, the aim of the present study is to disentangle contributions of genetic variation and its related sialylation on the in vitro digestion process of κ-CN. Accordingly, κ-CN was purified from milk representing homozygous cows with κ-CN phenotypes AA, BB, or EE and used as substrate molecules in model studies using the INFOGEST 2.0 in vitro static digestion model. Furthermore, the effect of removal of the terminal sialic acids present on the O-linked oligosaccharides of the purified κ-CN A, B, and E protein variants were studied by desialylation enzymatic assays. The κ-CN proteins were purified by reducing anion exchange chromatography with purities of variants A, B, and E of 93.0, 97.1, and 90.0%, respectively. Protein degradations of native and desialylated κ-CN isolates in gastric and intestinal phases were investigated by sodium dodecyl sulfate-PAGE, degree of hydrolysis (DH), and liquid chromatography electrospray ionization mass spectrometry. It was shown that after purification, the κ-CN molecules reassembled into multimer states, which then constituted the basis for the digestion studies. As assessed by DH, purified variants A and E were found to exhibit faster in vitro digestion rates in both gastric and intestinal phases compared with variant B. Desialylation increased both gastric and intestinal digestion rates for all variants, as measured by DH. In the gastric phase, desialylation promoted digestion of variant B at a rate comparable with native variants A and E, whereas in the intestinal phase, desialylation of variant B promoted better digestion than native A or E. Taken together, the results confirm that low glycosylation degree of purified κ-CN promotes faster in vitro digestion rates, and that desialylation of the O-linked oligosaccharides further promotes digestion. This finding could be applied to produce dairy products with enhanced digestibility.
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| 8. |
- Sheng, Bulei, et al.
(författare)
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Influence of genetic variants and sialylation of purified κ-casein on peptide release during in vitro digestion
- 2023
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Ingår i: Food Chemistry Advances. - 2772-753X. ; 3
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Tidskriftsartikel (refereegranskat)abstract
- In the present study, digestion pattern of purified bovine κ-casein (κ-CN) variants A, B, E as well as desialylated variant B, using INFOGEST 2.0 in vitro gastrointestinal digestion were investigated using peptidomics. Peptide profiles of the digests were identified and quantified using ion abundancies by liquid chromatography electrospray quadropole time of flight mass spectrometry (LC-ESI/Q-TOF MS/MS). Results showed that the κ-CN variants A and E had comparable digestion patterns at most digestion time points. In the in vitro gastric and in the initial intestinal phases fewer peptides and with lower total abundances were identified for variant B compared to variants A and E, indicating a slower digestion rate for κ-CN B. By desialylation, the digestion rate of desialylated variant B in both gastric and initial intestinal phases increased compared to the natural sialylated counterpart. Bioinformatics search revealed nine potential bioactive peptides released from all three variants A, B and E by the in vitro intestinal digestion, with four additional potential bioactive peptides being released after desialylation of κ-CN B.
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| 9. |
- Sheng, Bulei, et al.
(författare)
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Phosphorylation and glycosylation isoforms of bovine κ-casein variant E in homozygous Swedish Red cow milk by liquid chromatography-electrospray ionization mass spectrometry
- 2022
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Ingår i: Journal of Dairy Science. - : American Dairy Science Association. - 0022-0302. ; 105:3, s. 1959-1965
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Tidskriftsartikel (refereegranskat)abstract
- Variations in the phosphorylation and glycosylation patterns of the common κ-casein (CN) variants A and B have been explored, whereas studies on variant E heterogeneity are scarce. This study reports for the first time the detailed phosphorylation and glycosylation pattern of the κ-CN variant E in comparison with variants A and B. Individual cow milk samples representing κ-CN genotype EE (n = 12) were obtained from Swedish Red cows, and the natural posttranslational modifications of its κ-CN were identified and quantified by liquid chromatography-electrospray mass spectrometry. In total, 12 unique isoform masses of κ-CN variant E were identified. In comparison, AA and BB milk consisted of 14 and 17 unique isoform masses, respectively. The most abundant κ-CN E isoform detected in the EE milk was the monophosphorylated, unglycosylated [1P 0G, ∼70%; where P indicates phosphorylation from single to triple phosphorylation (1–3P), and G indicates glycosylation from single to triple glycosylation (1–3G)] form, followed by diphosphorylated, unglycosylated (2P 0G, ∼12%) form, resembling known patterns from variants A and B. However, a clear distinction was the presence of the rare triphosphorylated, nonglycosylated (3P 0G, ∼0.05%) κ-CN isoform in the EE milk. All isoforms detected in variant E were phosphorylated, giving a phosphorylation degree of 100%. This is comparable with the phosphorylation degree of variants A and B, being also almost 100%, though with very small amounts of nonphosphorylated, glycosylated isoforms detected. The glycosylation degree of variant E was found to be around 17%, a bit higher than observed for variant B (around 14%), and higher than variant A (around 7%). Among glycosylation, the glycan e was the most common type identified for all 3 variants, followed by c/d (straight and branched chain trisaccharides, respectively), and b. In contrast to κ-CN variants A and B, no glycan of type a was found in variant E. Taken together, this study shows that the posttranslational modification pattern of variant E resembles that of known variants to a large extent, but with subtle differences.
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| 10. |
- Sundekilde, Ulrik K, et al.
(författare)
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Association between the bovine milk metabolome and rennet-induced coagulation properties of milk.
- 2014
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Ingår i: Journal of Dairy Science. - : American Dairy Science Association. - 1525-3198 .- 0022-0302. ; 97:10, s. 6076-6084
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Tidskriftsartikel (refereegranskat)abstract
- The milk metabolomes of 407 individual Swedish Red dairy cows were analyzed by nuclear magnetic resonance spectroscopy as part of the Danish-Swedish Milk Genomics Initiative. By relating these metabolite profiles to total milk protein concentration and rheological measurements of rennet-induced milk coagulation together using multivariate data analysis techniques, we were able to identify several different associations of the milk metabolome to technological properties of milk. Several novel correlations of milk metabolites to protein content and rennet-induced coagulation properties were demonstrated. Metabolites associated with the prediction of total protein content included choline, N-acetyl hexosamines, creatinine, glycerophosphocholine, glutamate, glucose 1-phosphate, galactose 1-phosphate, and orotate. In addition, levels of lactate, acetate, glutamate, creatinine, choline, carnitine, galactose 1-phosphate, and glycerophosphocholine were significantly different when comparing noncoagulating and well-coagulating milks. These findings suggest that the mentioned metabolites are associated with milk protein content and rennet-induced coagulation properties and may act as quality markers for cheese milk.
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