During the past years, there is much attention has been given to the oxidative stress in the body, which defined as a condition of increased oxidant creation in living cells characterized by the production of free radicals that cause many cellular oxidative damage (Sies, 1986). Several studies have been demonstrated a correlation between this condition and a wide range of diseases such as; cancer, diabetes and atherosclerosis (Harrison et al., 2003; Sander et al., 2004; Johansen et al., 2005). Also several studies suggested that dietary supplementation with antioxidants can prevent the oxidative damage effects of these free radicals (Halliwell, 1996; Engelhart et al., 2002). Conjugated linoleic acids (CLAs) are fatty acids which is currently the focus of greatly interest due to its several attributed beneficial effects. These include anti-carcinogenic (Park et al., 2007), anti-diabetic (Eyjolfson et al., 2004) and anti-atherogenic effects (Kritchevsky et al., 2004), although the mechanisms which responsible for these beneficial effects of CLA are still unclear (Yu, 2001; Leung et al., 2000). Therefore, it is critical to clarify whether CLAs can act as free radical scavenger.
Cis-9, trans-11 and trans-10, cis-12 are the more active CLA isomers and they have been found predominantly in meat and dairy products from ruminant animals. The cis-9, trans-11 CLA is produced primarily in the mammary gland from desaturation of vaccenic acid (trans-11 C18:1) via ∆9-desaturase enzyme. In addition, it's produced as an intermediate throughout the incomplete biohydrogenation of dietary linoleic acid to stearic acid in the rumen while trans-10, cis-12 CLA in cow milk fat arises directly from ruminal production and can not be produced endogenously (AbuGhazaleh et al., 2007).
A number of factors have been shown to influence the levels of CLAs and other FA composition in cow milk fat, including exogenous factors such as feed allowance (Bargo et al., 2006), oil supplementation (AbuGhazaleh et al., 2003) and seasonal variation (Nudda et al.,2005), meanwhile endogenous factors like breed, lactation period, and parity (Dhiman et al., 2005). The exogenous factors have been extensively investigated the effectiveness on FA profile. In contrast, the endogenous factors have received little attentions.
General organization and objectives of the study
The present study was organized into two parts, the first part was focused on determine the breed effect of CLA and other FA contents in cow milk fat and the second part was focused on evaluating the free radical scavenging activities of selected and commercially available CLA isomers against the stable 2, 2-diphenyl-1-picryhydrazyl radical (DPPH) in ethanol.
This thesis includes five chapters. Chapter I present the general description for the work carried out in the thesis. Chapter II covers literature review that summarizes in general the present knowledge on fatty acids and lipids, and in particular conjugated linoleic acids. More highlight has been given for chemical structure, biosynthesis and health benefits of CLA. In addition, general description about oxidative stress, oxidants and antioxidants relate the current knowledge on CLA as antioxidant is included in this chapter. Chapter III describes materials and methods used and detailed outcomes of the study on CLA concentrations and other FA composition in milk fat of Mafriwal and Jersey cow cows. The study on the free radical scavenging activity effects of CLA against the stable 2, 2-diphenyl-1-picryhydrazyl radical (DPPH) in ethanol is described in Chapter IV. Finally, chapter V provides general conclusions and recommendations for future research which concludes results of the two parts and provides directional comments for future research.
It was hypothesized that the CLA level in milk fat of Mafriwal cows could be different compared to Jersey cows fed with the same diet, and CLA isomers could have antioxidant effects as free radical scavenger. Therefore, the objectives of this study were:
1. To determine the levels of CLA and other FA contents in milk fat of Mafriwal and Jersey cows with an identical dietary intake.
2. To determine the free radical scavenging properties of trans-10, cis-12 and cis-9, trans-11 as single or mixed CLA isomers at two selected ratios, 1:6 and 1:13 (trans-10, cis-12/ cis-9, trans-11), against the stable 2, 2-diphenyl-1-picryhydrazyl radical (DPPH).