The establishment of callus and cell suspension cultures of Hylocereus costaricensis for the production of betalain pigments with antioxidant potential

Abstract

Hylocereus costaricensis, commonly known as red-purple dragon fruit or pitaya, is a climbing vine cactus that is currently widely grown as a fruit crop and has gained popularity as a potential source of both natural colourants and antioxidants contributed by betalain compounds. Betalains comprised of red-purple betacyanins and yellow betaxanthins. This study aimed to establish callus and cell suspension cultures of H. costaricensis from in vitro germinated seedlings and to evaluate their betalain content and antioxidant profiles. Epicotyl and cotyledon segments of 60-day-old axenic seedlings were examined for their callus induction potential on half-strength Murashige and Skoog (MS) medium supplemented with various concentrations of naphthaleneacetic acid (NAA) and Thidiazuron (TDZ) under different illumination (16-h photoperiod and darkness). Different combinations of picloram and 2,4-dichlorophenoxyacetic acid (2,4-D) were subsequently tested for the induction of friable callus. The betalains, total phenolic content, total flavonoid content and antioxidant activity DFRSA in cell suspension cultures were quantified using spectrophotometric analysis. Generally, cotyledon explants cultured under 16-h photoperiod was optimum for callus induction. Compact callus with roots was formed on medium supplemented with NAA while granular callus was formed in TDZ supplemented medium. Among the 36 treatments tested, supplementation of 10 μM picloram induced friable callus with average fresh mass of 0.817 g (10.2-fold as compared to the control treatment). Picloram at 10 μM concentration was also found to be effective for callus proliferation and initiation of cell suspension culture. Yellow and red callus were produced and proliferated on the same medium through repetitive clonal selection. The higher concentration of sucrose was more effective for cell mass accumulation while lower sucrose concentration stimulated the accumulation of betalain compounds and antioxidants in the cell suspension cultures of H. costaricensis. This study indicates that callus and cell suspension culture could be used as an efficient system for sustainable production of betalain compounds which can contribute to functional food colouring and pharmaceutical industries.