Alpha‐lipoic acid: An inimitable feed supplement for poultry nutrition
Recently, alpha‐lipoic acid (1, 2‐dithiolane‐3‐pentanoic acid; ALA), an antioxidant is gaining widespread application in poultry diet to promote the growth of animals as well as enhance the quality of resulting poultry meat. It is an integral component of mitochondria that can regulate energy metabolism and its formula is shown in Figure 1 (Liu, 2008). It has been reported that α‐lipoic acid can scavenge free radicals, replenish endogenous antioxidants as well as act as a coenzyme in carbohydrate metabolism in the chicken birds (Packer, Kraemer, & Rimbach, 2001). Alpha‐lipoic acid is both fat and water soluble, and therefore, can easily be absorbed and transported across cell membranes resulting in optimal nutrient availability (Kofuji, Nakamura, Isobe, Murata, & Kawashima, 2008).
Poultry meat contains higher level of polyunsaturated fatty acids (PUFA) in relation to other meat; therefore, it is more susceptible towards oxidation. Lipid oxidation is among the vital causes for quality degradation apart from the microbial damage in poultry meat producing off odour compounds, rancid flavour as well as discolouration in meat and allied products ultimately yielding lower consumer acceptability. Lipid peroxidation rate in meat and its meat products is influenced by attributes such as fat level, distribution of fatty acids, antioxidants level, haeme pigment and iron contents. In this context, antioxidants added even in small amounts have the ability to retard oxidative process in substrates like lipids and proteins in meat thereby enhancing shelf stability and quality (Karre, Kelly, & Getty, 2013). The addition of antioxidants rich formulations in various fresh and cooked meat products have potential to reduce oxidation problems by hindering the free radical formation. Dietary supplementation of antioxidants into poultry feed has proven a convenient strategy to uniformly distribute them in inner and outer layers of phospholipid membranes (Sohaib, Anjum, Arshad, & Rahman, 2016).
To the best of our knowledge, ALA utilization as a poultry feed supplement started in 2001, however, several studies recently narrated the role of ALA for alleviating poultry stress as well as to enhance the oxidative stability of chicken meat and meat products. Alpha‐lipoic acid can exist in both oxidized as well as reduced form, however, its reduced form dihydrolipoic acid (DHLA) is a potent antioxidant and its dietary supplementation under normal glucose level facilitates mobilization of fatty acid as per β‐adrenergic response to isoproterenol (Moini, Packer, & Saris, 2002). Alpha‐lipoic acid is naturally occurring dithiol synthesized from octanoic acid in mitochondria and involved as cofactor using α‐keto acid dehydrogenases in mitochondrial reactions (Shay, Moreau, Smith, Smith, & Hagen, 2009). Alpha‐lipoic acid and DHLA quench reactive oxidative species as well as other radicals generated through the oxidation of different substrates mainly lipids & proteins in lipophilic and hydrophilic domains (Arshad, Anjum, Khan, & Shahid, 2013a; Arshad et al., 2013b).
Several studies explicated the protective role of ALA as feed supplement in poultry nutrition.