Altered physicochemical properties of dairy based systems through high pressure processing

Devi, A 2013, Altered physicochemical properties of dairy based systems through high pressure processing, Doctor of Philosophy (PhD), Applied Sciences, RMIT University.


Document type: Thesis
Collection: Theses

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Title Altered physicochemical properties of dairy based systems through high pressure processing
Author(s) Devi, A
Year 2013
Abstract The potential of high pressure processing (HPP) to alter the physical and chemical properties of milk proteins with and without the presence of gelatin was investigated. Viscosity increase was observed in mixtures of skim milk (15 or 20%, w/w) and gelatin (0.6% w/w) following HPP (300 MPa, 15 min, room temperature) due to the formation of milk protein aggregates and gelatin associations, whereas HPP at 600 MPa resulted in a decline in viscosity attributed to disruption of polymeric interactions. Direct association between milk protein and gelatin in the pressure treated mixtures was weak as confirmed by reduced viscosity at the vicinity of gelatin melting point and a possible formation of intermolecular hydrogen bonds. Results were further refined by focusing on whey protein isolate (WPI, 5−20% w/w) in the presence of gelatin (5% w/w). The values of storage modulus (G’) in high pressure treated (600 MPa, 15 min, 5 or 30 °C) mixed gels were below those for the thermally (at 80 °C) treated counterparts. When WPI-gelatin solutions (30 °C) were subjected to HPP, they yielded higher G’ than the HPP treated WPI-gelatin cold-set gels (5 °C). The former system allowed WPI to self associate in the polymeric matrix, as compared to the latter. Both pressurised systems displayed gelatin continuity in the binary mixture, which was the opposite of that in thermally induced gels. HPP, combined with thermal processing, can induce chemical reactions different from conventional thermal processing. The effect of high pressure thermal processing (HPTP), in the range of 100−140 °C and 0.1−600 MPa up to 60 min, on the colour change and the proteolysis of reconstituted skim milk (10% w/w) was investigated. Both reactions accelerated with increasing temperature and pressure. Kinetics of an apparent reduction in free amino acids implied an accelerated sugar conjugation with milk proteins/peptides with increasing temperature at constant pressure whereas increasing pressure at constant temperature decelerated the conjugation. Gas chromatography, carried out on skim milk subjected to HPTP, identified forty five volatile compounds; their concentrations changed upon temperature and/or pressure variations following distinct trends. Principal component analysis resulted in the separation of skim milk treated under the influence of high pressure (200–600 MPa, 100–130 °C, up to 60 min) from skim milk heated at ambient pressure. Heated skim milk was characterised by high amounts of furfural and pyrazine whereas skim milk undergone HPTP was characterised by high amounts of nonanal, 2-furanmethanol and 2-pentanone. In summary, HPP can manipulate the structure and molecular interactions of biopolymers leading to a unique rheological profile. The technique can also influence chemical reactions occurring to a different extent than those induced by conventional heat treatment. The nutritional and health aspects of the resultant peptides merit further investigation in relation to bioactivity. Similarly, further studies are required to entirely comprehend the molecular mechanism behind the generation of volatile Maillard-compounds under the influence of high pressure. The present work alongside recommended future research is expected to further the development of HPP in milk and dairy-based food products.
Degree Doctor of Philosophy (PhD)
Institution RMIT University
School, Department or Centre Applied Sciences
Keyword(s) high pressure processing
milk
gelatin
rheology
proteolysis
maillard reaction
volatile
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