Potassium iodate-induced proteolysis in ultra heat treated milk during storage: the role of β-lactoglobulin and plasmin

Grufferty, M B; Fox, Patrick F.

doi:10.1017/s0022029900033124

Cited by 35 publications

(21 citation statements)

References 23 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Thermal inactivation of plasmin in milk is thought to be due to thiol-disulphide interchange reactions with β-Lg [11]. Scollard et al [26] reported that HP treatment at 600 MPa did not inactivate plasmin in phosphate buffer, but inactivated >95% of plasmin in a phosphate buffer containing 5 mg·mL -1 β-Lg, which suggests that HP-induced inactivation of plasmin is also linked to β-Lg.…”

Section: Discussionmentioning

confidence: 99%

Plasmin activity and proteolysis in high pressure-treated bovine milk

Huppertz

Fox

Kelly

2004

Lait

Self Cite

View full text Add to dashboard Cite

-In this study, proteolysis resulting from the action of the indigenous milk proteinase, plasmin, in high pressure (HP)-treated raw skim bovine milk during storage was examined. Plasmin activity was reduced by treatment at pressures ≥400 MPa and decreased further throughout 28 d of storage at 5°C. In untreated milk or milk treated at 100 MPa plasmin activity increased during the first 3 d of storage at 37°C, indicating activation of plasminogen; considerably less activation occurred in milk treated at 200-600 MPa. However, considerable decreases in plasmin activity, probably due to autolysis, were apparent in all samples on storage at 37°C for >3 d. Proteolysis, as measured by increases in the level of pH 4.6-soluble N and decreases in the level of β-casein, was very limited on storage of milk at 5°C, with little difference between untreated and HP-treated samples. Proteolysis on storage of milk at 37°C was influenced only slightly by treatment of milk at a pressure ≤250 MPa and was reduced considerably in milk treated at 600 MPa for 30 min, but in milk treated at 300-400 MPa, proteolysis was more extensive than in untreated milk, possibly as a result of HP-induced disruption of casein micelles. Overall, HP can either induce or reduce proteolysis in milk, and may therefore have implications for products made from such milk.High pressure / milk / proteolysis / plasmin / casein micelle Résumé -Activité de la plasmine et protéolyse dans un lait de bovin traité par hautes pressions. Dans cette étude, nous nous sommes intéressés à la protéolyse résultant de l'activité d'une protéinase indigène du lait, la plasmine, au cours de l'incubation d'un lait de bovin frais écrémé et traité par hautes pressions. L'activité de la plasmine était réduite par un traitement à des pressions ≥400 MPa et diminuait progressivement au cours des 28 j de stockage à 5°C. Pour un lait non traité ou traité à 100 MPa, l'activité de la plasmine augmentait pendant les trois premiers jours d'incubation à 37°C, indiquant l'activation du plasminogène ; l'activation était bien moins importante pour un lait traité à des pressions comprises entre 200 et 600 MPa. Cependant, des diminutions considé-rables de l'activité de la plasmine, probablement due à une autolyse, étaient observées pour tous les échantillons incubés à 37 °C pour des durées de stockage >3 j. La protéolyse, mesurée par les augmentations du taux d'azote soluble à pH 4,6 et par les diminutions du taux de caséine β résiduelle, était très limitée pour un stockage du lait à 5°C, avec une petite différence entre les échantillons non traités et ceux traités aux hautes pressions. La protéolyse durant l'incubation du lait à 37°C était seulement légèrement influencée par le traitement du lait à des pressions ≤250 MPa et était considérablement réduite pour un lait traité à 600 MPa pour 30 min, mais pour un lait traité à 300-400 MPa, la protéolyse était plus importante que dans un lait non traité, cela étant probablement dû à la désintégration des micelles de caséine induite par les haut...

show abstract

Section: Discussionmentioning

confidence: 99%

Plasmin activity and proteolysis in high pressure-treated bovine milk

Huppertz

Fox

Kelly

2004

Lait

Self Cite

View full text Add to dashboard Cite

show abstract

“…The peak areas of separated peptides were determined by integration. The gradient described by [12] was used to measure β-lactoglobulin denaturation, using the same HPLC system.…”

Section: Methodsmentioning

confidence: 99%

“…Plasmin is relatively heat stable in simple buffer systems, but is greatly destabilised when heated in the presence of β-lactoglobulin, due to thiol-disulphide interchange reactions between the disulphide bonds within the enzyme structure and the exposed thiol group of denatured β-lactoglobulin [12,16]. This leads to greatly reduced plasmin activity in, for example, ultra-high temperature (UHT) milk [15].…”

Section: Introductionmentioning

confidence: 99%

Barostability of milk plasmin activity

Scollard

Beresford

Murphy

et al. 2000

Lait

View full text Add to dashboard Cite

-The influence of high pressure (HP) on the stability and activity of the milk alkaline proteinase plasmin was examined. Assays of enzyme activity following HP treatment of plasmin in phosphate buffer (pH 6.7) indicated that the enzyme was extremely pressure stable, retaining almost all activity even after treatment at 600 MPa for 20 min at 20 °C. Plasmin was also extremely stable when HP treated in buffer containing 25 mg . mL -1 sodium caseinate, and in cheese. However, HP treatment in buffer containing 5 mg . mL -1 β-lactoglobulin resulted in enzyme inactivation at pressures > 400 MPa, indicating that the presence of β-lactoglobulin greatly destabilises the enzyme under high pressure, which is analogous to the effect of this protein on the heat stability of plasmin. In separate experiments, hydrolysis of β-casein by plasmin at 20 °C for 30 min at various pressures (300-800 MPa) was studied. Parallel control incubations were performed at atmospheric pressure. Urea-PAGE analysis of digests showed that primary proteolysis of β-casein was decreased at P > 400 MPa. As judged from RP-HPLC analysis, production of 2%-TCA soluble peptides by plasmin appeared unaffected at P < 700 MPa, above which pressure the rates of peptide production decreased. Overall, plasmin is relatively pressure stable in most systems and can hydrolyse its preferred substrate (β-casein) at pressures up to 700 MPa, but is sensitive to destabilisation by denatured β-lactoglobulin. plasmin / high pressure / specificity / stability Résumé -Stabilité de la plasmine sous l'influence de hautes pressions. L'influence des hautes pressions sur la stabilité et l'activité de la plasmine bovine a été examinée. Les déterminations de l'activité enzymatique suivant le traitement à hautes pressions de la plasmine dans une solution tampon phosphate (pH 6,7) a indiqué que l'enzyme était très résistante à la pression, conservant presque toute son activité, même après un traitement a 600 MPa pendant 20 min à 20 °C. Lorsque la plasmine a été traitée dans une solution tampon contenant 25 mg . mL -1 de caséinate de sodium ou dans le fromage, elle s'est aussi avérée très stable. Cependant, le traitement à hautes pressions dans une Lait 80 (2000) 609-619 609

show abstract

“…The specificity of plasmin on a s1 -, a s2 -and b-CNs in solution has been determined (see ; it has little or no activity on k-CN, b-lactoglobulin (b-lg) or a-la (in fact, denatured b-lg is an inhibitor; Grufferty & Fox, 1986). In milk, the principal substrate for plasmin is b-CN, from which it produces g 1 -(b-CN f29-209), g 2 -(b-CN f106-209) and g 3 -(b-CN f108-209) CNs and proteose peptone (PP)5 (b-CN f1-105/107), PP8 slow (b-CN f29-105/107) and PP8 fast (b-CN f1-29).…”

Section: Plasminmentioning

confidence: 99%