Effect of αS1-casein genotype on phenolic compounds and antioxidant activity in goat milk yogurt fortified with Rhus coriaria leaf powder.

The aim of this work was to evaluate the phenolic compounds and antioxidant activity of goat milk yogurt characterized by different αS1-casein genotypes and fortified with Rhus coriaria leaf powder. The αS1-casein genotype was determined by isoelectric focusing, total phenol content was determined by the Folin-Ciocalteu method, phenolic compounds were identified and quantified by HPLC-UV analysis, and antioxidant activity was measured using 2,2'-azino-bis-3-ethylbenzothiazoline-6-sulfonic acid and ferric-reducing antioxidant power. The statistical analysis showed a significant effect of the studied factors. Comparing different genotypes it emerged that yogurt from goats with weak alleles at CSN1S1 loci (FF) showed the lowest phenolic compounds and therefore a lower antioxidant activity compared with yogurt from goats with strong alleles at CSN1S1 loci (AA, BB, AB). Rhus coriaria-fortified yogurt showed a significant increase in total phenolic compounds and antioxidant activity in comparison with plain yogurt. The FF-fortified yogurt presented the lowest total phenol content and antioxidant activity. This could be due to a greater capacity of proteins and peptides in this yogurt to form stable complexes with phenols. The different total phenol content detected in R. coriaria-fortified yogurt indicates that the αS1-casein genotype influenced the amount of added phenols that are bound to the caseins and, therefore, the part that remains free and that affects the biological capacity of the final product.