Foliar application of pig blood-derived protein hydrolysates improves antioxidant activities in lettuce by regulating phenolic biosynthesis without compromising yield production

•Foliar Ppb application significantly increased phenolic content and antioxidant activities in lettuce.•Foliar Ppb application upregulated the expressions of genes related in phenolic biosynthesis.•Enhanced antioxidant activities in Ppb-treated lettuce are mainly related to the increased flavonoid and anthocyanin contents.•No significant differences were found in the biomass production with the Ppb application. The application of natural biostimulants is proposed as an interesting approach to ensure sustainable yields and product quality in agricultural and horticultural crops. Here, the effects of foliar application of a protein hydrolysate derived from pig blood (Ppb) on biomass production, phenolic biosynthesis, and the correlation between phenolic profiles and antioxidant activities in lettuce were investigated. The Ppb application significantly enhanced the phenolic content and antioxidant properties in two genotypes of hydroponically cultivated lettuce by increasing the gene expression of enzymes (PAL, CHS, F3H, DFR, F35H, and UFGT) involved in phenolic biosynthesis. However, these changes occurred in a genotype-dependent manner. The results of HPLC and correlation analyses implied that the most contributory phenolic compositions to the increased antioxidant activities in Ppb-treated lettuce were flavonoids and anthocyanins. Meanwhile, no changes were observed in shoot and root fresh weights following Ppb application. These results clearly suggest that Ppb application is a useful strategy to improve antioxidant activities of lettuce by enhancing the biosynthesis of unique phenolic compounds without reducing plant yield. [Display omitted]