Formation efficiency and color diversity of hydroxyphenyl-pyranoanthocyanins produced from purple corn cob anthocyanins and black sorghum bran 3-deoxyanthocyanins

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Pyranoanthocyanins are pigments formed by addition of a pyran ring to anthocyanins, exhibiting enhanced stability but typically low formation efficiency. This study investigated the effect of C-3 glycosylation on pyrano-derivative formation and color expression using a controlled comparison of anthocyanins from purple corn cob and 3-deoxyanthocyanins from black sorghum bran. These pigment-rich agri-food materials are promising sources of structurally similar precursor pigments that differ primarily in C-3 glycosylation and can form pyranoanthocyanins and pyrano-3-deoxyanthocyanins, respectively. Pyrano-derived pigments were formed using 4-vinylphenol at a 1:5 precursor pigment-to-cofactor molar ratio at 45 °C and pH 3.1 in the dark for up to 96 h. Formation kinetics were monitored by uHPLC-PDA, with MS/MS supported pigment identification, and CIELAB color parameters were derived from spectral measurements. After 96 h, pyranoanthocyanin yields (87.6%) were significantly higher than pyrano-3-deoxyanthocyanin yields (42.4%), with both approaching a practical plateau by ≈72 h. Pyrano-derived pigment formation showed class-specific color development. The ACN system exhibited stronger color changes and a hypsochromic shift (∆E* ab = 28.0, λ vis-max from 515 to 501 nm), with increased chroma and a hue shift toward orange-yellow tones (h ab from 25.8° to 51.6°). In contrast, the 3-deoxyanthocyanin system showed smaller color differences (∆E* ab = 11.3, h ab remained ≈63°) and a slight bathochromic shift (λ vis-max from 485 to 489 nm). Glycosylation may facilitate pigment-cofactor interactions through effects on pigment solubility and molecular collisions, contributing to greater pyranoanthocyanin formation. These results revealed distinct formation behavior and hue profiles among these pyrano-derivatives, broadening the natural pigment palette for industrial applications.