|dc.description.abstract||The use of natural antioxidants to improve the oxidative stability of food lipids has
received special attention because of the worldwide trend to avoid the use of synthetic
food additives. A wide range of natural sources has been shown to contain
antioxidant properties, these include plant extracts, herbs and spices, citrus fruits,
oilseeds and legumes. Some antioxidants have been found to be fonned during the
heat processing of foods, including the Maillard reaction products that are formed by
the reaction of amino acids, peptides and proteins with reducing carbohydrates.
A study was undertaken to investigate the antioxidant activity of Maillard
reaction products fonned during extrusion of soyabeans. A preliminary oxidation
study carried out to identify a suitable substrate revealed that sunflower oil stripped
of antioxidants was a suitable substrate with a low induction period of 15 minutes via
the Rancimat Method and 4.5 hours via the method of Ross and de Muelenaere.
Methyllinoleate was found to be sensitive to oxidation, but not readily available and
Storage test of antioxidant stripped sunflower oil under various headspace
conditions showed that the substrate stability was best at 4°C under nitrogen or
vacuum. Under such conditions the product could be stored for a period of 136 days.
Nitrogen was chosen as the most suitable for this exercise as it was not easy to
remove all residual air from the samples by vacuum. Furthermore with nitrogen
headspace residual 02 could be measured based on Ni02 ratio changes. Hexane
solvent was found to be able to remove all lipids from soyabeans.
Under the experimental conditions practised it was found that the induction
periods for extruded and unextruded soya flour hexane extracted lipids were very
similar. Addition of glucose or fructose to the extrusion mixture increased induction
period of hexane extracted lipids by 37.5% and 1.5% respectively as measured by the
Ross and de Muelenaere method and by 50% and 6.5% respectively as measured by
the Rancimat Method. Available lysine of glucose containing extrudate was reduced
by 69% while that of the fructose containing extrudate was reduced by 23%. Residual
glucose and fructose analysis of extrudates showed that 66% of glucose was utilized
in the formation of the Maillard reaction products while only 21% of fructose was
utilized during extrusion processing.
Comparison of induction periods of soya glucose and soya fructose extrudates
to induction period of TBHQ antioxidants (200ppm) in antioxidant stripped sunflower
oil gave antioxidant activity of 86ppm and 9ppm for soya glucose extrudates and soya
fructose extrudates respectively.
The observed antioxidant activity of Maillard reaction products could be
utilized with success in different types of processed foods without the need for
extensive testing as required for synthetic antioxidants but supplementation of lysine
may be required to maintain nutritional balance.||en