Secondary metabolite production in callus cultures of Vitis vinifera: influence of genotype and sucrose concentration in the medium on antioxidant activity

The aim of the study was to optimize the culture medium by varying sucrose concentrations for callus growth and efficient secondary metabolite production. After callus induction from Vitis vinifera cvs Syrah and Chardonnay petiole explants, callus cultures were established with non-embryogenic callus and subcultured on semi-solidified medium of B5 basal salts with 0.1 mg L⁻¹ NAA, 0.2 mg L⁻¹ kinetin and 250 mg L⁻¹ casein hydrolysate at a range of sucrose concentrations (20, 30, 40, 50, and 60 g L⁻¹) for 30 days. The differential effects of sucrose concentrations on callus growth index and total anthocyanins (TA), total phenolics (TP) and total flavonoids (TF) contents of callus tissue were measured. Also, dependent upon secondary metabolite accumulation, the antioxidant potential of ethanolic callus extracts were investigated using 2,2-diphenyl-1-picrylhydrazyl (DPPH), ferric ion reducing antioxidant power and molybdenum ion reducing antioxidant power assays. Medium enriched with 30 g L⁻¹ sucrose gave the maximum callus growth, while higher concentrations (50 and 60 g L⁻¹) inhibited the callus growth of both cultivars. However, these higher concentrations increased the accumulation of TA, TP and TF in the tissue. The highest total anthocyanin (23.2 mg malvidin-3-glucoside kg⁻¹ FW) and flavonoids (1,629 mg CE kg⁻¹ FW) were produced in Syrah callus at all sucrose concentrations and the highest total phenolic (9284 mg GAE kg⁻¹ FW) was produced in Chardonnay callus. The antioxidant potential of the callus extract was highly correlated with secondary metabolite accumulation. These results suggest that sucrose modulates callus growth and secondary metabolite synthesis, consequently, the antioxidant activity of two grape cultivars.