Structure modification of milk protein gels by enzymatic cross-linking: Dissertation

Research output: ThesisDissertationCollection of Articles

Abstract

Proteins are the structural building blocks of fermented dairy products such as yoghurt. The nature of the protein-protein interactions and the structure of the macromolecular matrices they form determine the textural and water holding properties of a gel. In this study, the potential of enzymatic protein cross-linking in modification of acid-induced milk protein gel structures was studied by using the oxidative enzymes laccase and tyrosinase as well as the acyltransferase transglutaminase (TG). The efficiency of different cross-linking enzymes with dissimilar reaction mechanisms in modification of milk proteins at various colloidal (in milk or in caseinate) or molecular (native, unfolded) states was investigated. Effects of enzymatically formed inter-molecular covalent bonds on the gel formation dynamics and the textural and water holding properties of acid-induced milk protein gels were elucidated. The results presented in this study have shown that enzymatic cross-linking, even with the non-conventional enzymes tyrosinase and laccase, alters the mechanical properties of acid-induced milk protein gels. However, the knowledge on the mode of action of these enzymes on proteins should be further elucidated in order to be able to exploit them as structure-engineering tools with maximum value. Comparison of tyrosinase and transglutaminase directly in milk, in which caseins are found as association colloids, showed that even rather similar extent of inter-molecular covalent linkages did not necessarily result in similar mechanical properties in final acid-induced gels. It was concluded that it is not solely the introduced covalent links but also the preceding impacts on colloidal interactions by physical means which determine the actual effect of cross-linking on the final product attributes. In this thesis, the potential of one oxidative enzyme, T. reesei tyrosinase (TrT), was demonstrated for the creation of intra-micellarly linked casein particles, similarly to TG. In the future, it will be necessary to determine the physicochemical properties of TrT-induced casein particles as compared to the TG-induced casein particles. Furthermore, in raw milk, TrT was the only enzyme able to increase the gel firmness. This makes TrT a potential enzyme for use in raw milk-based products such as cheese. Finally, elucidation of altered aggregation dynamics for cross-linked protein particles will help to determine the optimum production parameters in order to tailor protein gels for improved product characteristics.
Original languageEnglish
QualificationDoctor Degree
Awarding Institution
  • University of Helsinki
Supervisors/Advisors
  • Lantto, Raija, Supervisor
  • Partanen, Riitta, Supervisor, External person
  • Buchert, Johanna, Supervisor, External person
Award date23 Nov 2012
Place of PublicationEspoo
Publisher
Print ISBNs978-951-38-7950-1
Electronic ISBNs978-951-38-7951-8
Publication statusPublished - 2012
MoE publication typeG5 Doctoral dissertation (article)

Fingerprint

dairy protein
crosslinking
catechol oxidase
gels
protein-glutamine gamma-glutamyltransferase
enzymes
casein
laccase
acids
raw milk
proteins
mechanical properties
fermented dairy products
milk
acyltransferases
reaction mechanisms
milk proteins
colloids
protein-protein interactions
yogurt

Keywords

  • milk
  • protein
  • tyrosinase
  • laccase
  • transglutaminase
  • cross-linking
  • acid gel

Cite this

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title = "Structure modification of milk protein gels by enzymatic cross-linking: Dissertation",
abstract = "Proteins are the structural building blocks of fermented dairy products such as yoghurt. The nature of the protein-protein interactions and the structure of the macromolecular matrices they form determine the textural and water holding properties of a gel. In this study, the potential of enzymatic protein cross-linking in modification of acid-induced milk protein gel structures was studied by using the oxidative enzymes laccase and tyrosinase as well as the acyltransferase transglutaminase (TG). The efficiency of different cross-linking enzymes with dissimilar reaction mechanisms in modification of milk proteins at various colloidal (in milk or in caseinate) or molecular (native, unfolded) states was investigated. Effects of enzymatically formed inter-molecular covalent bonds on the gel formation dynamics and the textural and water holding properties of acid-induced milk protein gels were elucidated. The results presented in this study have shown that enzymatic cross-linking, even with the non-conventional enzymes tyrosinase and laccase, alters the mechanical properties of acid-induced milk protein gels. However, the knowledge on the mode of action of these enzymes on proteins should be further elucidated in order to be able to exploit them as structure-engineering tools with maximum value. Comparison of tyrosinase and transglutaminase directly in milk, in which caseins are found as association colloids, showed that even rather similar extent of inter-molecular covalent linkages did not necessarily result in similar mechanical properties in final acid-induced gels. It was concluded that it is not solely the introduced covalent links but also the preceding impacts on colloidal interactions by physical means which determine the actual effect of cross-linking on the final product attributes. In this thesis, the potential of one oxidative enzyme, T. reesei tyrosinase (TrT), was demonstrated for the creation of intra-micellarly linked casein particles, similarly to TG. In the future, it will be necessary to determine the physicochemical properties of TrT-induced casein particles as compared to the TG-induced casein particles. Furthermore, in raw milk, TrT was the only enzyme able to increase the gel firmness. This makes TrT a potential enzyme for use in raw milk-based products such as cheese. Finally, elucidation of altered aggregation dynamics for cross-linked protein particles will help to determine the optimum production parameters in order to tailor protein gels for improved product characteristics.",
keywords = "milk, protein, tyrosinase, laccase, transglutaminase, cross-linking, acid gel",
author = "Dilek Ercili-Cura",
note = "Project code: 78314",
year = "2012",
language = "English",
isbn = "978-951-38-7950-1",
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publisher = "VTT Technical Research Centre of Finland",
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address = "Finland",
school = "University of Helsinki",

}

Structure modification of milk protein gels by enzymatic cross-linking : Dissertation. / Ercili-Cura, Dilek.

Espoo : VTT Technical Research Centre of Finland, 2012. 132 p.

Research output: ThesisDissertationCollection of Articles

TY - THES

T1 - Structure modification of milk protein gels by enzymatic cross-linking

T2 - Dissertation

AU - Ercili-Cura, Dilek

N1 - Project code: 78314

PY - 2012

Y1 - 2012

N2 - Proteins are the structural building blocks of fermented dairy products such as yoghurt. The nature of the protein-protein interactions and the structure of the macromolecular matrices they form determine the textural and water holding properties of a gel. In this study, the potential of enzymatic protein cross-linking in modification of acid-induced milk protein gel structures was studied by using the oxidative enzymes laccase and tyrosinase as well as the acyltransferase transglutaminase (TG). The efficiency of different cross-linking enzymes with dissimilar reaction mechanisms in modification of milk proteins at various colloidal (in milk or in caseinate) or molecular (native, unfolded) states was investigated. Effects of enzymatically formed inter-molecular covalent bonds on the gel formation dynamics and the textural and water holding properties of acid-induced milk protein gels were elucidated. The results presented in this study have shown that enzymatic cross-linking, even with the non-conventional enzymes tyrosinase and laccase, alters the mechanical properties of acid-induced milk protein gels. However, the knowledge on the mode of action of these enzymes on proteins should be further elucidated in order to be able to exploit them as structure-engineering tools with maximum value. Comparison of tyrosinase and transglutaminase directly in milk, in which caseins are found as association colloids, showed that even rather similar extent of inter-molecular covalent linkages did not necessarily result in similar mechanical properties in final acid-induced gels. It was concluded that it is not solely the introduced covalent links but also the preceding impacts on colloidal interactions by physical means which determine the actual effect of cross-linking on the final product attributes. In this thesis, the potential of one oxidative enzyme, T. reesei tyrosinase (TrT), was demonstrated for the creation of intra-micellarly linked casein particles, similarly to TG. In the future, it will be necessary to determine the physicochemical properties of TrT-induced casein particles as compared to the TG-induced casein particles. Furthermore, in raw milk, TrT was the only enzyme able to increase the gel firmness. This makes TrT a potential enzyme for use in raw milk-based products such as cheese. Finally, elucidation of altered aggregation dynamics for cross-linked protein particles will help to determine the optimum production parameters in order to tailor protein gels for improved product characteristics.

AB - Proteins are the structural building blocks of fermented dairy products such as yoghurt. The nature of the protein-protein interactions and the structure of the macromolecular matrices they form determine the textural and water holding properties of a gel. In this study, the potential of enzymatic protein cross-linking in modification of acid-induced milk protein gel structures was studied by using the oxidative enzymes laccase and tyrosinase as well as the acyltransferase transglutaminase (TG). The efficiency of different cross-linking enzymes with dissimilar reaction mechanisms in modification of milk proteins at various colloidal (in milk or in caseinate) or molecular (native, unfolded) states was investigated. Effects of enzymatically formed inter-molecular covalent bonds on the gel formation dynamics and the textural and water holding properties of acid-induced milk protein gels were elucidated. The results presented in this study have shown that enzymatic cross-linking, even with the non-conventional enzymes tyrosinase and laccase, alters the mechanical properties of acid-induced milk protein gels. However, the knowledge on the mode of action of these enzymes on proteins should be further elucidated in order to be able to exploit them as structure-engineering tools with maximum value. Comparison of tyrosinase and transglutaminase directly in milk, in which caseins are found as association colloids, showed that even rather similar extent of inter-molecular covalent linkages did not necessarily result in similar mechanical properties in final acid-induced gels. It was concluded that it is not solely the introduced covalent links but also the preceding impacts on colloidal interactions by physical means which determine the actual effect of cross-linking on the final product attributes. In this thesis, the potential of one oxidative enzyme, T. reesei tyrosinase (TrT), was demonstrated for the creation of intra-micellarly linked casein particles, similarly to TG. In the future, it will be necessary to determine the physicochemical properties of TrT-induced casein particles as compared to the TG-induced casein particles. Furthermore, in raw milk, TrT was the only enzyme able to increase the gel firmness. This makes TrT a potential enzyme for use in raw milk-based products such as cheese. Finally, elucidation of altered aggregation dynamics for cross-linked protein particles will help to determine the optimum production parameters in order to tailor protein gels for improved product characteristics.

KW - milk

KW - protein

KW - tyrosinase

KW - laccase

KW - transglutaminase

KW - cross-linking

KW - acid gel

M3 - Dissertation

SN - 978-951-38-7950-1

T3 - VTT Science

PB - VTT Technical Research Centre of Finland

CY - Espoo

ER -

Ercili-Cura D. Structure modification of milk protein gels by enzymatic cross-linking: Dissertation. Espoo: VTT Technical Research Centre of Finland, 2012. 132 p.