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CHARACTERISATION OF A COMMERCIAL SOY ISOLATE BY PHYSICAL TECHNIQUES
Author(s) -
CHRONAKIS IOANNIS S.,
KASAPIS STEFAN,
RICHARDSON ROBERT K.,
DOXASTAKIS GEORGIOS
Publication year - 1995
Publication title -
journal of texture studies
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.593
H-Index - 54
eISSN - 1745-4603
pISSN - 0022-4901
DOI - 10.1111/j.1745-4603.1995.tb00978.x
Subject(s) - globular protein , soy protein , breakage , denaturation (fissile materials) , materials science , urea , native state , aqueous solution , chemical engineering , thermodynamics , chemistry , crystallography , composite material , organic chemistry , food science , nuclear chemistry , physics , engineering
The mechanical features of a partially denatured commercial soy isolate (PP 500E) have been explored for comparison with data available on the gelation characteristics of native globular proteins and to improve the understanding of its textural properties as a structuring ingredient in the production of low fat products. The soy sample was reconstituted at 30C and networks were developed either during cooling to 5C or on heating to 90C (complete denaturation of the protein) followed by cooling to 5C. Throughout the course of experimentation, dynamic oscillatory (time, temperature, frequency and strain sweeps) and creep testing (in aqueous or urea solutions) measurements were recorded. Reduction in the thermal energy of the system causes a monotonic increase in storage modulus (G′) whereas the temperature rise results in equilibrium G′ values well below the elastic response observed at 30C. The absence of a positive thermal transition, observed in the gelation of native globular proteins, indicates a different mechanism for structure formation in commercial soy isolates. Application of the cascade treatment to the concentration dependence of the storage modulus argues that the heated and cooled networks possess a higher degree of bond permanency than their cooled‐only counterparts. Mechanical spectra in combination with the pattern of network breakage at high deformations suggests that disulphide bonds participate in the network formed by totally denatured soy protein (heated and cooled samples). Inclusion of urea in the aqueous preparations destabilises the predominantly physical forces of attraction in the unheated gels. By contrast, the heated and cooled samples achieve an equilibrium deformation whose storage modulus can be employed in the constitutive equation of rubber elasticity theory. On that basis the number of disulphide bridges per molecule was found to vary between 2.0 and 2.03. This result is consistent with the “string of beads” model proposed for the three‐dimensional structure of globular protein gels, where a dendric network is built by the occasional cross‐linking of corpuscular strands.