Project Materials

EVALUATION OF ANTIOXIDANT POTENTIAL OF MONODORA MYRISTICA (AFRICAN NUTMEG)

ABSTRACT

This investigation assesses the antioxidant potential of Monodora myristica (African nutmeg). Monodora myristica extract was produced by solvent extraction using n-hexane and utilised as treatment on freshly prepared crude palm kernel oil and palm oil. Equal volume of oil samples were treated to different concentration of extract treatment (0.2ml,0.4ml, 0.6ml, 0.8ml, 1.0ml utilising syringe. These oil samples were equally divided into two groups SS and SR. Group SS was stored under the sun while group SR was stored in the room for three weeks. These treated oil samples were evaluated on weekly basis at two separate parameters: Acid value (AV) of free fatty acid and thiobarbituric acid (TBA) value, using conventional procedures. The main effect of extract was established using ANOVA. For the two varieties of oil, the acid value of free fatty acid increased significantly (P<0.05) as the period extends for group SS without extract whereas those for group SR showed no significant rise. But AV of oil samples treated with greater extract concentration reduced significantly (P<0.05) for both groups SS and SR. TBA value also followed the same trend of AV. Hence, monodora myristica extract provided lowering effect in the oxidative level of the oil types.

Chapter one

INTRODUCTION

Lipid oxidation is one of the key reasons that food deteriorate and is induced by the reaction of fat and oil with molecular oxygen, leading to off-flavours that are commonly dubbed rancidity(Basturk et al., 2007). Exposure to light, pro-oxidants and increased temperature will accelerate the process (Kubow, 2009).

Lipid oxidation and subsequent flavour degradation have severely limited the storage potential of most fat-containing foods (Ihekoronye and Ngoddy, 1985).

Rancidity encompasses a wide spectrum of biological activity whose effect is to “make things worse” and hence harm man’s economy. Free radicals and microorganisms are known to cause chemical changes that lead to oxidation and degradation of vegetable oils derived from plant seeds or fruit pulps (Basturk et al, 2007).

The chemical compositions of oils, such as percentages of unsaturation, have a significant impact on their keeping quality. Rancidity is related with an off-flavor and odour of the oil. There are two reasons of rancidity. One occurs when oil combines with oxygen, which is known as oxidative rancidity.

Another source of rancidity is the interaction of enzymes and moisture. Enzymes such as lipase liberate fatty acids from triglycerides, resulting in di and/or monoglycerides and free fatty acids. This liberation of fatty acids is known as hydrolysis, hence hydrolytic rancidity.

Fat oxidation is an important deteriorative reaction with significant commercial implications for product value. The first oxidation products to accumulate are hydroperoxides, which can then degrade to form lower-molecular-weight compounds such as alcohols, aldehydes, free fatty acids, and ketones, resulting in autoxidative rancidity.

The peroxide content of alimentary fats indicates their primary oxidation state and thus their tendency to go rancid. Unsaturated fatty acids, in fact, react with oxygen to form peroxides, which set off a chain reaction that results in volatile substances with the characteristic rancid smell.

High temperatures, as well as exposure to light and oxygen, have been shown to accelerate these reactions. The lower the peroxide and acid values, the better the quality and preservation of edible fats.