Introduction
Poultry products are susceptible to oxidative reaction, particularly lipid oxidation, a major threat to the quality of processed poultry product. Oxidative stress occurs due to imbalance of pre-oxidant and endogenous antioxidant mechanism that damage the cellular component. Heat stress associated with it affects the performance of birds, and involvement of avian viruses weakens the immune response because of reactive oxygen species (ROS) production.
Antioxidants prevent cell damage caused by free radicals, which are unstable molecule that body produces as a reaction to the environment and other stressors. These stressors increase the production of reactive oxygen species, which adversely affect growth performance, decrease immune response, lipid per oxidation and poor quality of meat.
Classification of Antioxidant
Antioxidant system provides three levels of protection in living cell as below.
- Free radical formation, protected by removing free radical precursor formation using antioxidant enzymes, SOD (superoxide dismutase), glutathione, GSH-Px (Glutathione peroxide) and metal binding proteins.
- This consist of vitamin E, ubiquinol, carotenoids, vitamin A, ascorbic acid, uric acid, etc. Hydroperoxide formed during the reaction with vitamin E and peroxyl radicals is removed because it disturbs cell membrane and its function. Selenium dependent GSH-Px turn hydroperoxide into non-reactive compound.
- This system eliminates and repair damaged molecule, and include lipases, protease and other enzymes; all forms of free radicals are oxidized by methionine residue of protein, constituting the mixture of R & S isomers of methionine sulphoxide.
Role of Antioxidant in Chicken Embryo Development
Chicken embryo tissue has a high proportion of polyunsaturated fatty acids, which requires a tissue-specific antioxidant defense. For example, in the brain, the amount of ascorbic acid is higher than Vitamin E, and effective recycling of vitamin E by ascorbic acid maintains successful antioxidant protection even at lower levels of Vitamin E. Besides, a highest selenium glutathione, peroxidase was observed more in the liver and kidney than the brain. The order of selenium (Se) concentration in the tissue of newly hatched chicks was liver>kidney>lungs>heart>brain>muscle, which makes the brain lipid composition and antioxidant concentration most vulnerable to lipid per oxidation. This situation may develop nutritional encephalomalacia at lower vitamin E or Se supplementation. Further, Vitamin E, Se, and carotenoids are transferred from the feed to egg yolk and further to embryonic tissue. An efficient carry over of Se and Vitamin E from the hen to progeny indicates an increase in the muscle selenium, liver GSH-Px activity, and vitamin E content at hatching.
Role of Antioxidant in Male Fertility
Avian spermatozoa characterized the by high proportion of polyunsaturated fatty acids are vulnerable tooxidative stress. Enzymatic and non-enzymatic antioxidant system in avian semen protect it against ROS and lipid peroxidation. Selenium, sourced from seleno protein of spermatozoa midpiece, which is a phospholipid hydroperoxide glutathione peroxidase- a form of selenium dependent GSH-Px, maintains the sperm quality. Antioxidant protection of mitochondria, a free radical located in the mid piece of spermatozoa is a crucial factor for sperm motility and fertilizing ability. Selenium deficiency in mitochondria causes sperm abnormality and decreased fertilizing ability, which becomes normal with the supplementation of organic selenium.
Prevention of Rancid Oxidation in Fat
Loss of hydrogen from the unsaturated fatty acid forms free radicals causing lipid per oxidation. Free radical gets converted into fatty acid peroxide free radical and finally into fatty acid hydroperoxide in the absence of Vitamin E or any effective antioxidant. This blocks per oxidation by supplying a hydrogen in free radical formation and reconverting it into original fatty acid. Antioxidant prevents losses of vitamin A and E, and pigmentor (oxy and keto carotenoids) in the mixed feed.
Role of Antioxidant Vitamin Supplementation during Heat Stress
Lack of sweat glandsin poultry birds and relatively high temperature leads to heat stress. This affects the acid base balance to alkaline balance in avian blood, with a drop in plasma and vitamin C levels in the adrenal cortex. Synthesis of antioxidant vitamins such as Vitamins A, E and C is reduced during heat stress and stimulate release of corticosterone and catecholamine, initiating the lipid per oxidation of cell membrane. Vitamin E reduces the negative effect of corticosterone, vitamin C is vital for various biosynthesis(collagen, 1,25 dihydroxy vitamin D and adrenaline) and regulation of diverse reaction(secretion of corticosterone, regulation of body temperature and activation of the immune system). Vitamin C enhances the activity of Vitamin E by reducing the tocopherol radical to their active form of Vitamin E.
Role of Antioxidant in Coccidiosis
Free radical oxidative species are produced during host cellular immune response invasion by Eimeria species. However, high concentrations of oxidative molecule leads to tissue damage and cytotoxicity, and partially contributing to the pathology of cell infection. Free radical oxidative species and nitric oxide promote vasodilation and hemorrhages in coccidian infection and are toxic to the parasite and host cells. Eimeria acervulina oocyst motivates increase in lipid peroxidation, oxidative damage and imbalance in antioxidant status. To alleviate oxidative stress, natural(e.g. Vitamin E, Se) and synthetic (e.g. butylated hydroxytoluene) antioxidant are used as feed supplement in poultry.
Phytobiotic Antioxidant
Phytobiotics are plant derived products added in feed for improved performance. These originate from the leaves, roots, tuber or fruit of herbs, spices and other plants that are available in solid dried, and ground forms or in extract (essential oil).
Antioxidant properties of phytobiotics are mainly related to their phenolic content.
- Green tea (camellia senensis), contains epigallocatechin-3 gallate (EGCG), epigallactocatechin (EGC), epicatechin-3 gallate (EGC), epicatechin and flavonoids, which inhibit oxidative enzymes. Whereas, a polyphenyl extract from green tea inhibits gram positive andgram-negative bacteria.
- Grape seeds are a rich source of proanthocyanidins (PAs) consisting procyanidin and esterified gallic acid, which inhibits the lipid oxidation of poultry during gastric digestion.
iii. Cinnamon is a spice with strong antimicrobial and antioxidant properties.
- Oregano leaves contain thymol and carvacrol, which when added to broiler diet reduces the number of oocysts in faeces.
- Turmeric containing curcumin, apolyphenolic, has antioxidant antiviral, antifungal, antihypertensive, anti-inflammatory and anti-carcinogenic activities. It stimulates the digestive system by promoting the intestinal lipase, maltase and sucrose activity, and secretion of pancreatic amylase, lipase, chymotrypsin and trypsin. Dietary supplementation of turmeric increases the production of egg and yolk weight, and yolk index.
- Saponins, sourced from Yucca schidigera, form pores in the cell membrane, and prevent the growth of protozoan parasites by interacting with cell membrane cholesterol content resulting in parasitic death.
vii. Tannins, a potent biological antioxidant used as feed additives, are polyphenolic compound found in the seed coat of many plants and grass cultivators. Tanninshave the antioxidant activity by free radical scavenging method, chelation of transition enzymes and inhibition of peroxidation enzymes.
Conclusion
Antioxidants in feed help to minimize lipid oxidation, improve the keeping quality of premix & feed, and minimizeoxidation in meat after slaughter. Oxidative degradation of lipids in products of natural origin damage biological membrane, enzymes and protein in meat that pose an immediate threat to human health. Feed additives from plants with their high content of natural antioxidant can improve the efficiency of growing poultry without compromising the product quality.
by Dr. Akash Gupta and Dr. Venket M. Shelke, Kemin Industries South Asia
