Total proteolysis in bovine raw bulk milk of Northern Sweden
Proteases are enzymes that catalyze protein breakdown. The major indigenous protease is plasmin, that together with proteases originating from somatic cells and bacteria, accounts for most of the proteolytic activity in bovine milk. In many dairy products, the key characteristics depends on the conc...
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| Formato: | H2 |
| Lenguaje: | Inglés sueco |
| Publicado: |
SLU/Department of Molecular Sciences
2020
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| Materias: |
| _version_ | 1855572732314386432 |
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| author | Toss Ekmyr, Elina |
| author_browse | Toss Ekmyr, Elina |
| author_facet | Toss Ekmyr, Elina |
| author_sort | Toss Ekmyr, Elina |
| collection | Epsilon Archive for Student Projects |
| description | Proteases are enzymes that catalyze protein breakdown. The major indigenous protease is plasmin, that together with proteases originating from somatic cells and bacteria, accounts for most of the proteolytic activity in bovine milk. In many dairy products, the key characteristics depends on the concentration and composition of the milk
proteins. It has been seen in other studies that environmental and production parameters can influence the level and activity of proteases. The objective of this study was
to measure the level of total proteolysis in raw bulk milk of Northern Sweden and
investigate if there are correlations between the total proteolysis and any of the parameters: plasmin, somatic cell counts, total bacteria number, milk pH, total milk
protein, breed, milking system, production system (tied or loose house), number of
animals or different seasons. The total proteolysis, that was measured as the level of
peptides in the milk samples, was significantly correlated to the milk protein content
(P<0.001) and the milk pH value (P<0.01) in a Pearson correlation. The same connection was seen when one variable at a time was compared in a regression; there
was a correlation between proteolysis and milk pH (P<0.05), as well as milk protein
content (P<0.001). In addition, there were significant differences between the breeds,
where Jersey cows had 25.7 % higher proteolytic activity compared to the other
breeds. There was also a difference between the housing systems, where milk from
tied cows had 10.6 % higher proteolysis, compared to milk from loose housed cows
(P=0.002). However, when all variables were included in a multivariable regression
model, no variable was significantly correlated to total proteolysis. Nevertheless,
some interesting trends were observed. The !-value was negative for all the breeds
(SRB, SLB, Mountain Breed and farms with both SRB and SLB), when they were
compared to the Jersey breed. Also, a trend towards a correlation between plasmin
and proteolysis, seen in the single regression, remained in the multivariable regression. The measurement of proteolysis was complemented with an SDS PAGE electrophoretic analysis of eight milk samples, in order to study the protein profile. The
images fortified the speculation on plasmin being the major protease responsible for
the proteolysis in this study, since !-CN (the major plasmin substrate) appeared to
be more extensively degraded in the samples with high proteolytic activity. Because
of the fact that the degree of explanation for the variance in total proteolysis was low
in the multivariable regression, even in the best model (R-sq. adj. 12.16 %), it was
concluded that there are probably other factors, e.g. individual differences – that was
not included in this study, that highly affect the proteolytic activity in bovine milk.
However, according to the results in this study, investigations with focus on genetical
differences might be an interesting perspective for future investigations. |
| format | H2 |
| id | RepoSLU16358 |
| institution | Swedish University of Agricultural Sciences |
| language | Inglés swe |
| publishDate | 2020 |
| publishDateSort | 2020 |
| publisher | SLU/Department of Molecular Sciences |
| publisherStr | SLU/Department of Molecular Sciences |
| record_format | eprints |
| spelling | RepoSLU163582021-01-06T02:01:49Z Total proteolysis in bovine raw bulk milk of Northern Sweden Total protolys i tankmjölk från gårdar i norra Sverige Toss Ekmyr, Elina total proteolysis plasmin SDS PAGE total bacteria count somatic cell counts Proteases are enzymes that catalyze protein breakdown. The major indigenous protease is plasmin, that together with proteases originating from somatic cells and bacteria, accounts for most of the proteolytic activity in bovine milk. In many dairy products, the key characteristics depends on the concentration and composition of the milk proteins. It has been seen in other studies that environmental and production parameters can influence the level and activity of proteases. The objective of this study was to measure the level of total proteolysis in raw bulk milk of Northern Sweden and investigate if there are correlations between the total proteolysis and any of the parameters: plasmin, somatic cell counts, total bacteria number, milk pH, total milk protein, breed, milking system, production system (tied or loose house), number of animals or different seasons. The total proteolysis, that was measured as the level of peptides in the milk samples, was significantly correlated to the milk protein content (P<0.001) and the milk pH value (P<0.01) in a Pearson correlation. The same connection was seen when one variable at a time was compared in a regression; there was a correlation between proteolysis and milk pH (P<0.05), as well as milk protein content (P<0.001). In addition, there were significant differences between the breeds, where Jersey cows had 25.7 % higher proteolytic activity compared to the other breeds. There was also a difference between the housing systems, where milk from tied cows had 10.6 % higher proteolysis, compared to milk from loose housed cows (P=0.002). However, when all variables were included in a multivariable regression model, no variable was significantly correlated to total proteolysis. Nevertheless, some interesting trends were observed. The !-value was negative for all the breeds (SRB, SLB, Mountain Breed and farms with both SRB and SLB), when they were compared to the Jersey breed. Also, a trend towards a correlation between plasmin and proteolysis, seen in the single regression, remained in the multivariable regression. The measurement of proteolysis was complemented with an SDS PAGE electrophoretic analysis of eight milk samples, in order to study the protein profile. The images fortified the speculation on plasmin being the major protease responsible for the proteolysis in this study, since !-CN (the major plasmin substrate) appeared to be more extensively degraded in the samples with high proteolytic activity. Because of the fact that the degree of explanation for the variance in total proteolysis was low in the multivariable regression, even in the best model (R-sq. adj. 12.16 %), it was concluded that there are probably other factors, e.g. individual differences – that was not included in this study, that highly affect the proteolytic activity in bovine milk. However, according to the results in this study, investigations with focus on genetical differences might be an interesting perspective for future investigations. Proteaser är enzymer som katalyserar nedbrytning av proteiner. I mjölk är den protolytiska aktiviteten huvudsakligen orsakad av plasmin, vilket överförs från blodet, och proteaser som utsöndras från somatiska celler och bakterier. Många av de karaktäristiska kvalitetsegenskaper som önskas i mejeriprodukter påverkas av koncentrationen och sammansättningen av mjölkproteinerna. Tidigare studier har visat att såväl koncentrationen som aktiviteten av de olika proteaserna påverkas av miljö- och produktionsfaktorer. Syftet med den här studien var att mäta den totala protolysen i tankmjölk från gårdar i norra Sverige, och undersöka om det finns statistiska samband mellan nivån av protolys och faktorerna: plasmin, somatiska celltal, totalt bakterieantal, mjölkens pH-värde, mjölkens totala proteininnehåll, olika raser, mjölksystem, stallsystem (uppbundet eller lösdrift), antal djur eller olika säsonger. Den totala protolysen, skattad som mängden peptider i mjölkproverna, var signifikant korrelerad med både det totala proteininnehållet (P<0.001) och pH-värdet (P<0.01) i mjölken, när detta undersöktes i en Pearson korrelation. Detta samband sågs även när de olika variablerna jämfördes i enkla regressioner; både proteinhalten och mjölkens pHvärde var positivt korrelerade till mängden protolys (P<0.001 respektive P<0.05). Skillnader i medelvärden jämfördes för grupperade data. Detta visade på signifikanta skillnader mellan raserna från de medverkande gårdarna, där Jerseykor hade 25.7 % högre protolytisk aktivitet jämfört med de andra raserna. Det var även 10.6 % högre total protolys i mjölk från gårdar med uppbundna kor, jämfört med kor i lösdriftssystem (P=0.002). När alla variabler inkluderades i en multivariabel regressionsmodell var däremot ingen faktor signifikant korrelerad med nivån av protolys. Dock fick samtliga raser (SRB, SLB, Fjällkor och gårdar med en blandning av SRB och SLB) ett negativt !-värde vid jämförelse med Jerseykorna. Resultatet visade även på en trend mot signifikant positiv korrelation mellan plasmin och total protolys; denna trend syntes både vid enkel regressionsjämförelse och bestod i den multivariabla modellen. I detta arbete genomfördes även en elektroforetisk analys (SDS PAGE). Proteinprofilen i de analyserade proverna styrkte antagandet att plasmin var det mest aktiva enzymet i mjölkproverna då !-kasein, det främsta substratet för plasmin, bedömdes vara lägre i de prover där en hög protolys uppmätts. Med tanke på att förklaringsgraden över variationen av den totala protolysen var relativt låg (R-sq. Adj. 12.16 %), drogs slutsatsen att den totala protolysen antagligen påverkas i stor utsträckning av andra faktorer än de som inkluderades i denna undersökning. Enligt resultatet i detta arbete, kan ett intressant utgångsläge för vidare studier vara fokus på genetiska skillnader. SLU/Department of Molecular Sciences 2020 H2 eng swe https://stud.epsilon.slu.se/16358/ |
| spellingShingle | total proteolysis plasmin SDS PAGE total bacteria count somatic cell counts Toss Ekmyr, Elina Total proteolysis in bovine raw bulk milk of Northern Sweden |
| title | Total proteolysis in bovine raw bulk milk
of Northern Sweden |
| title_full | Total proteolysis in bovine raw bulk milk
of Northern Sweden |
| title_fullStr | Total proteolysis in bovine raw bulk milk
of Northern Sweden |
| title_full_unstemmed | Total proteolysis in bovine raw bulk milk
of Northern Sweden |
| title_short | Total proteolysis in bovine raw bulk milk
of Northern Sweden |
| title_sort | total proteolysis in bovine raw bulk milk
of northern sweden |
| topic | total proteolysis plasmin SDS PAGE total bacteria count somatic cell counts |