# Application of Natural Antioxidants from Fruits Waste for Improving Egg Quality Characteristics
## 5 Mechanisms of Antioxidants in Laying Hens
### Influence of Genetics on Antioxidant Metabolism
[132] reported that when 1%, 2%, and 3% sea buckthorn was tested, only the 2% and 3% groups resulted in significantly higher egg production (77.38% and 79.76%) compared with a control (70.24%). The egg weight was significantly higher only in the 3% group (61.10 g) compared with a control (58.85 g), with no effect on feed intake. All three groups had higher egg yolk weight when compared to a control and the same groups were reported to have significantly lower cholesterol content in eggs (255.59 mg/egg in 1%; 243.91 mg/egg in 2%; and 232.18 mg/egg in 3%) compared to a control (282.85 mg/egg). The use of 3% sea buckthorn waste was also reported [37] to be very effective in increasing the total polyphenols' content and antioxidant capacity in eggs enriched in polyunsaturated fatty acids. From these studies, it can be concludedthat a maximum of 3% in laying hens' diets is the adequate amount in maintaining the production performances, improving eggs' quality. A more exotic fruit waste, resulting from mango, was recently tested in laying hens' diets by [PERSON] et al. [133]. The four treatments included 3.5%, 7%, 14%, and 28% mango peel. No significant differences were noted for the majority of production parameters, except for FCR, which was very high in the 28% group (3.09 kg feed/kg egg) compared with a control (2.36 kg feed/kg egg). The same group registered the lowest eggshell thickness; however, it registered the highest egg yolk color. The authors recommended that up to 7% can be used safely, without negatively affecting production performances. To the contrary, [PERSON] et al. [134] tested more than 50% mango waste as a maize replacement in laying hens and obtained improved feed consumption and body weight and larger egg weight. The authors recommended that mango waste is a great substitute for maize to reduce a dependency on cereals while promoting the valorization of fruits' waste. The effects of dietary banana waste (3%, 6%, 9%), with or without 1000 mg multienzyme, significantly increased egg production, especially the 3% diet, while the 9% diet decreased egg weight and egg production. All diets increased egg yolk yellowish while decreasing the redness parameter. The 9% diet significantly improved the health status and biochemical parameters compared with a control, as shown by [PERSON] et al. [135]. Further research is required to better understand the adequate levels of banana peel effects in laying hens' diet. The effects of some berries' (raspberry, black currant, black chokeberry, and blueberry) dried pomace were also evaluated in laying hens' nutrition. The 3% use of raspberry, black currant, and black chokeberry had significant effects on yolk coloration, but the most noticeable was the black currant group. Using 3% raspberry reduced egg weight and shell density when compared with a control. The use of raspberry and black chokeberry had a positive impact on the immune system of the laying hens, as confirmed by the changes in the white blood cell smear and the higher spleen percentage [136]. Also, fermented blueberries included at 0.25%, 0.50%, and 1.0% during the late laying period improved egg quality and nutritional values by increasing the albumen height, Haugh unit, and eggshell thickness, which may be partly mediated by up-regulating expressions of genes related to yolk precursor synthesis (_ESR2_ and _VTG II_). Additionally, fermented blueberries improved the antioxidant capacity in the ovary of laying hens by increasing CAT and GSH-PX activities [137]. The authors recommended for fermented blueberries that the optimal level should not be over 0.76% inclusion. Another lesser studied fruit waste with an important nutritional content is the waste of the papaya fruit. [PERSON] et al. [138] showed that low levels (5 g/kg, 10 g/kg, or 15 g/kg) of papaya waste supplementation improved egg production (84.36 to 85.76%) compared to a control (81.69%) and egg mass (49.84 to51.94) versus a control (46.67) and significantly decreased FCR (1.99 to 1.96) compared to a control (2.03).