Modifica Tion Of Soya Protein Isolate Films For Enhanced Functionalities Using The Maillard Reactions
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Date
2002-06
Authors
TEIK BENG, GOH
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Abstract
Soya Protein Isolate (SPI) films with or without reducing sugars were produced by
wet casting methods, followed by a curing treatment at 95°C for 24 h. Evidence of the
Maillard reaction was shown by changes in ph and absorbance values of film-forming
solutions and progressive decrease in the L-values of cured films with increasing reducing
sugar concentration. Physical, microstructure and barrier properties were also assessed by
estimating tensile strength, elongation at break, Scanning Electron Microscope (SEM)
microstructure and water vapour transmission rate. The antioxidative potential of the films
was assessed by extracting the "Ma.illard reaction products" (MRPs) using five different
types of solvent fractions followed by estimation of reducing power, radical scavenging,
metal cheIating and total phenolic compounds in a linoleic acid model system. The tensile
strength and water vapour transmission rates of films containing reducing sugars improved in
a concentration dependent manner. The SEM microstructure of SPI / reducing sugar films
showed improvement in homogenity with denser and less porous protein structure. The
antioxidative potentials of films containing reducing sugars were dependent on types of
solvent fractions used. Even though the butanol and ethanol fractions contained the highest
amount of phenolic compounds and showe.-4 the highest metal chelating ability, the highest
reducing power and radical scavenging ability were shown by methanol and ethanol
fractions. This would suggest that the anti oxidative potentials of MRPs extracted from films
containing reducing sugars were not solely attributed by the phenolic compounds.
Evaluation of Thiobarbituric Acid (TBA) values in linoleic acid systems showed the lowest
TBA values for methanol and ethanol fraction with the longest induction period of ca. 7
days. The applicability of the modified SPI films was investigated in a storage study (40°C,
30 days) performed using a high omega-3 fish oil covered with films containing reducing
sugars. During storage, the fish oil covered with reducing sugars (glucose) exhibited a
smaller increase in TBA values and a higher retention of docosa-hexaenoic (OHA) and
eicosa-pentaenoic (EPA) acids as compared to those uncovered or covered with sucrose. The
occurrence of anti oxidative compounds within SPI films containing reducing sugars was
evidenced. However, it is more likely that the additional protection provided by the Maillard
reaction is related to the enhanced film properties such as a reduction in oxygen gas
transmission rate and an increase in film density as a result of the formation of the "Maillard
Crosslinks". The occurrence of the so called "Maillard Cross-links" as evidenced by a lower
protein solubility in a disruptive solvents within the SPI films containing reducing sugars,
may partly contribute to the differences in mechanical, barrier and microstructure properties.
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Modifica Tion Of Soya Protein Isolate Films , For Enhanced Functionalities Using The Maillard Reactions