The effect of dietary Chlorella vulgaris inclusion on goat's milk chemical composition, fatty acids profile and enzymes activities related to oxidation

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Microalgae, despite being more popular for biofuel production (Medipally et al., 2015), have gained significant attention as a source of biomolecules such as n‐3 polyunsaturated fatty acids (PUFA) (Lum et al., 2013; Yaakob et al., 2015). Thus, the inclusion of microalgae in ruminant's diets has been shown as an effective nutritional strategy to enrich cow's (Glover et al., 2012) and goat's (Kouřimská et al., 2014) milk with PUFA.
Microalgae contain also natural antioxidant compounds such as phenols, flavonoids, carotenoids and chlorophyll (Goiris et al., 2012; Lum et al., 2013; Yaakob et al., 2015) which enhance the antioxidant defence system. Indeed, an improvement in the antioxidant status of humans (Panahi et al., 2013), mice (Aliahmat et al., 2012) and fattening lambs (EL‐Sabagh et al., 2014) has been observed when their diets supplemented with microalgae. Among microalgae, Chlorella vulgaris is one of the most popular and its cultivation is easy and relatively cheap, while recently has been proven its high antioxidant capacity (Goiris et al., 2012).
In ruminants, several environmental, physiological and dietary factors can cause an imbalance between reactive oxygen species (ROS) production and neutralizing capacity of antioxidant mechanisms which lead to oxidative stress (Sies, 1991). The inclusion of feedstuffs in animal's diets rich in natural antioxidant compounds could protect them from possible oxidative stress and satisfy consumer concerns about safety. The oxidative stress is faced normally by the body with a wide range of antioxidant mechanisms that can be divided into enzymatic and non‐enzymatic (e.g. metabolites) (Ye et al., 2015). Several endogenous enzymes such as superoxide dismutase (SOD), glutathione reductase (GR), catalase (CAT) glutathione transferase (GST) and glutathione peroxidase (GSH‐Px) (Miller et al., 1993; Board and Menon, 2013), found both in blood and milk, represent the main components of the intracellular antioxidant defence mechanisms which regulate ROS accumulation within tissues (Celi, 2010; Sordillo, 2013). Further to that, the enzyme lactoperoxidase (LPO) in milk is related to the oxidation of lipids (O'Connor and O'Brien, 2006). To the best of our knowledge, there is no information available about the impact of microalgae to the antioxidant defence system of dairy ruminants. Research is also needed to define the effects of dietary supplementation with microalgae on the antioxidant status of milk.
Thus, the objective of this study was to investigate the effects of dietary inclusion of Chlorella vulgaris on the following: (i) milk yield, chemical composition and fatty acids profile, (ii) the activities of SOD, CAT, GR, GST and GSH‐Px in blood plasma and (iii) the activities of SOD, GR and LPO in goat's milk. Furthermore, the oxidative stress indicators for measuring total antioxidant and free radical scavenging activity [ferric reducing ability of plasma (FRAP) and 2, 2′‐azino‐bis (3‐ethylbenzothiazoline‐6‐sulphonic acid) (ABTS) assays] and oxidative stress biomarkers [malondialdehyde (MDA) and protein carbonyls (PC)] were also determined in blood plasma and milk of the animals.
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