Enhanced production and identification of antioxidants in in vitro cultures of the cacti Mammillaria candida and Turbinicarpus laui.

Cacti are an important source of metabolites but present limitations for their commercial exploitation, like slow growth and a decrease of wild populations. An alternative to obtain their biocompounds without affecting the natural environment are the in vitro culture techniques. We established in vitro cultures from Mammillaria candida Scheidweiler and Turbinicarpus laui Glass and Foster and used different stresses to increase metabolites and antioxidant activity. The cultures were exposed to 1.25% polyethylene glycol to induce a moderate drought stress, 50 g L^-1 sucrose to generate an osmotic stress, chitosan (1.25 to 5 mg mL^-1) to simulate a biotic attack, or to UV light. Chitosan was the best elicitor improving 1.5 times the concentration of phenolics, 9 to 10 times the content of flavonoids and betalains, and 16% the antioxidant activity in M. candida suspensions. In T. laui suspensions, this elicitor duplicates the flavonoids content and antioxidant activity. The antioxidant levels in elicited suspensions increased 5 to 10 times in relation to plant tubercles. Eleven compounds were identified in M. candida suspensions being digalloyl rhamnoside and epicatequin gallate the most abundant; in the T. laui suspensions, 16 compounds were detected and the most abundant were 17-decarboxi neobetanin and derivatives of luteolin. Thus, cacti in vitro culture is an efficient system to obtain high level of metabolites of biological interest.