Title:
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Characterisation of glucono-δ-lactone induced soy protein isolate gelation and its application in soy cheese
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The purpose of this project was to conduct an investigation into the development of a
soy cheese with acceptable texture. The effects of heat treatment, different oils/fat and
reducing and non-reducing sugars on the soy protein isolate (SPI) and SPI curd were
studied. The physico-chemical, biochemical and textural properties of three types of
soy cheese were compared: (1) glucono-8-lactone (GDL) induced, (2) bacterially
fermented and (3) GDL-induced and fermented. The results indicate that the fermentedGDL-
cheese had the most acceptable texture.
Heat treatment of SPI at neutral pH caused it to denature partially and increased the
storage modulus and hardness of subsequently GDL-induced gels. Subsequent heat
treatment of the acidic gels further significantly enhanced the storage modulus and gel
hardness.
The SPI emulsion containing palm stearin showed higher emulsifying stability,
emulsifying activity, protein adsorption and denaturation degree than the emulsions
containing sunflower and soy oil at neutral pH. The acidified emulsion gel containing
palm stearin was significantly harder than the control (without fat), whereas emulsion
gels containing sunflower and soy oil were softer than the control.
Glucose, lactose and sucrose increased the onset denaturation temperature of SPI,
resulting in decreased gel hardness and stiffness at acidic pH. At neutral pH, both
reducing and non-reducing sugars increased the emulsifying activity of SPI emulsions
and decreased the emulsifying stability and protein adsorption at oil/water interface.
The Maillard reaction took place between SPI and glucose and lactose, resulting in
increased gelation of SPI and decreased emulsifying activity at neutral pH.
Chemical analysis indicated that disulfide bonds were involved in maintaining the
structure ofthe gels. Furthermore, evidence was found of other types of covalent bonds
besides disulfide bonds in acidic gels formed by glycated SPI.
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