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| 2. |
- Folkenberg, Ditte M., et al.
(author)
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Interactions between EPS-producing Streptococcus thermophilus strains in mixed yoghurt cultures
- 2006
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In: Journal of Dairy Research. - 0022-0299. ; 73:4, s. 385-393
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Journal article (peer-reviewed)abstract
- Mixed cultures of different EPS-producing Streptococcus thermophilus strains in combination with a Lactobacillus delbrueckii subsp. bulgaricus strain with negligible EPS-production were used for yoghurt production. The yoghurt texture was characterised with respect to sensory, rheological and microstructural properties and the EPS-concentrations were determined. The cultures resulted in yoghurts with highly different texture properties, and positive interactions between certain Streptococcus thermophilus strains were observed. The underlying properties of yoghurt texture are multidimensional, but a number of microstructural characteristics were apparent in the yoghurts with the highest mouth thickness, creaminess and viscosity. A strong protein network, not too dense and with medium size pores containing EPS, seems associated with these properties. The presence of capsular polysaccharides (CPS) also appeared to be beneficial as did a combination of FPS types, which were distributed differently in the protein network (in serum pores, respectively in association with protein). Obviously, a certain concentration of FPS must be present to provide for these effects on yoghurt texture, but other factors than concentration per se seem more important.
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| 6. |
- Madsen, Mikkel, et al.
(author)
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Unaided efficient transglutaminase cross-linking of whey proteins strongly impacts the formation and structure of protein alginate particles
- 2022
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In: Food Chemistry: Molecular Sciences. - : Elsevier BV. - 2666-5662. ; 5
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Journal article (peer-reviewed)abstract
- There is a dogma within whey protein modification, which dictates the necessity of pretreatment to enzymatic cross-linking of β-lactoglobulin (β-Lg). Here microbial transglutaminase (MTG) cross-linked whey proteins and β-Lg effectively in 50 mM NaHCO3, pH 8.5, without pretreatment. Cross-linked β-Lg spanned 18 to >240 kDa, where 6 of 9 glutamines reacted with 8 of 15 lysines. The initial isopeptide bond formation caused loss of β-Lg native structure with t1/2 = 3 h, while the polymerization occurred with t1/2 = 10 h. Further, cross-linking effects on protein carbohydrate interaction have been overlooked, leaving a gap in understanding of these complex food matrices. Complexation with alginate showed that β-Lg cross-linking decreased onset of particle formation, hydrodynamic diameter, stoichiometry (β-Lg/alginate) and dissociation constant. The complexation was favored at higher temperatures (40 °C), suggesting that hydrophobic interactions were important. Thus, β-Lg was cross-linked without pretreatment and the resulting polymers gave rise to altered complexation with alginate.
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| 7. |
- Rauh, Valentin M., et al.
(author)
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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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In: International Dairy Journal. - : Elsevier BV. - 0958-6946. ; 38:2, s. 199-207
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Journal article (peer-reviewed)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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| 8. |
- Rauh, Valentin M., et al.
(author)
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Plasmin Activity in UHT Milk: Relationship between Proteolysis, Age Gelation, and Bitterness
- 2014
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In: Journal of Agricultural and Food Chemistry. - : American Chemical Society (ACS). - 0021-8561 .- 1520-5118. ; 62:28, s. 6852-6860
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Journal article (peer-reviewed)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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| 9. |
- Rauh, Valentin M., et al.
(author)
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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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In: International Journal of Dairy Technology. - : Wiley. - 1471-0307 .- 1364-727X. ; 68:4, s. 486-494
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Journal article (peer-reviewed)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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| 10. |
- Rauh, Valentin M., et al.
(author)
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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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In: International Dairy Journal. - : Elsevier BV. - 0958-6946. ; 38:1, s. 74-80
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Journal article (peer-reviewed)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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