Effect of sulfur dioxide and lactic acid in steeping water on the extraction of anthocyanins and bioactives from purple corn pericarp

Background and objectives: Purple corn can be an economical source of anthocyanins, a natural alternate to synthetic FD&C Red 40 dye in foods. The effects of steeping purple corn pericarp in wet milling chemicals, namely sodium metabisulfite and lactic acid, and milling on the extraction of anthocyanins, polyphenols, flavonoids, and tannins were studied. Findings: Steeping water with 2,000 ppm SO₂ contained total monomeric anthocyanins (TA) equivalent of 20.5 ± 1.5 mg cyanidin-3-O-glucoside (C3G)/g pericarp, higher than using only water (7.1 ± 0.6 mg C3G/g pericarp). In the treatment with SO₂ and 5,000 ppm lactic acid, TA concentration was 22.9 ± 0.2 mg C3G/g pericarp. This was due to increased extraction of C3G and condensed forms of anthocyanins. Polyphenols and tannins were higher in SO₂ treatments while flavonoid concentration was not different. Chroma was positively correlated with anthocyanins (r = 0.999) and tannins (r = 0.994). Ball milled pericarp fractions yielded the highest amount of anthocyanins. Conclusions: Anthocyanin recovery from purple corn pericarp can be significantly increased using a milling step prior to SO₂-based extraction. Significance and novelty: A novel method for increasing anthocyanin yields from purple corn is proposed.