Enriching Eggs with Bioactive Compounds through the Inclusion of Grape Pomace in Laying Hens Diet: Effect on Internal and External Egg Quality Parameters

Abstract

(1) Background: Grapes and their associated by-products (such as grape pomace, GP) stand out for their polyphenol content, which makes them a source of bioactive compounds with antioxidant capacity. The aim of this research was to determine if the inclusion of 50 g/kg of GP in the diet of hens could enrich eggs with antioxidants and to study its effect on internal and external egg quality parameters. (2) Methods: A trial was conducted with two genetic lines of hens, which were fed either a control diet or a diet containing 50 g/kg of GP. Performance, internal and external egg quality, and egg yolk content of vitamins E and A and gallic acid were determined. (3) Results: In eggs laid by hens fed a GP diet, Haugh units and yolk color scores were enhanced, and eggshells became thinner, but without affecting the breaking strength. No dietary effect was observed on the vitamin contents of the yolk. A higher gallic acid content was observed in the yolks of eggs laid by hens fed the GP diet, suggesting that some dietary phenolic compounds could be transferred to the eggs. Hen genetics influenced egg weight, albumen Haugh units, shell thickness, and α- and γ-tocopherol concentration in yolks. (4) Conclusions: Dietary inclusion of GP improved the internal quality of eggs, enriching yolks with a phenolic compound but reducing shell thickness.

Keywords: antioxidants; egg quality; gallic acid; grape by-products; laying hen; polyphenols; poultry; vitamins.

Figure 1

Examples of shell-breaking force for eggs from ISA white laying hens fed control (a) and grape pomace (50 g/kg) (b) diets.

Figure 2

Effect of dietary inclusion of grape pomace (GP) on yolk gallic acid concentration (μg/g) in eggs of 31- to 34-week-old ISA white laying hens. Data are means of three replicates per treatment (a pool of four egg yolks per replicate). Figure shows mean ± standard deviation. SEM = 0.104, p = 0.074.

Figure 3

Extracted ion chromatogram (EIC) of gallic acid standard (a) and gallic acid content in egg yolk from hens fed a diet containing 50 g/kg of grape pomace (b) or a control diet (c).