Extraction of purple corn (Zea mays L.) cob pigments and phenolic compounds using food-friendly solvents

Abstract

Purple corn cob (PCC) is an economic anthocyanin-rich source that could serve as food colorant. Pigment extraction from PCC using mild solvent can be difficult because PCC have hard texture and complex matrix. Due to toxicity concerns, most acidified aqueous organic solvents that produce high anthocyanin recovery from PCC are not desirable for food applications. In this study a consumer-friendly solvent (aqueous ethanol) was used at different ethanol ratios (0–100%) to determine PCC anthocyanin recovery as compared to methanol and 70% (v/v) aqueous acetone. Different acidity levels (0–2% 6 N HCl, v/v) were also investigated to see if the PCC pigment extraction yield could be improved by adjusting solvent acidity.The PCC extract obtained by water-ethanol ratio around 1:1 (40%–60% ethanol) achieved highest yield of monomeric anthocyanins (>13.5 mg/g FW) with low polymeric color, comparable to 70% acetone (14.3 mg/g FW). The amount of PCC monomeric anthocyanin and phenolics recovery extracted with different water-ethanol combination could be predicted using quadratic models (R2 = 0.94 and 0.95). The solvent acidity seemed to impacted water PCC extraction but not much in 70% acetone extraction. This study provides valuable reference information to extract pigments from PCC for potential food application, as synthetic red dye alternatives.