From grape pomace to stable food colorants: a simplified and sustainable approach to pyranoanthocyanin production and application in yogurt

BACKGROUND: Replacement of synthetic colorants with stable natural alternatives remains a major challenge for the food industry. While pyranoanthocyanins (PACNs) offer superior stability compared to their anthocyanin (ACN) precursors, their scarce natural occurrence and slow formation kinetics restrict their industrial applicability. This study aims to develop a sustainable valorization strategy for grape pomace by utilizing a reactive vinyl cofactor for the transformation of ACN-rich crude extracts into high-value PACNs, and to evaluate their application in a real food system. RESULTS: PACN formation was achieved in 72 h at 25 °C using a 1:5 ACN-to-cofactor molar ratio, reaching ca 40% yield. By utilizing bioproduced 4-vinylcatechol (4-VC) as cofactor, the process bypassed the extended reaction times and high cofactor requirements associated with PACN synthesis. Notably, the direct derivatization of crude grape pomace extract outperformed the semi-purified extract, eliminating purification steps commonly required. Furthermore, the use of biotransformation broth as the source of 4-VC yielded results comparable to those of the purified cofactor, further streamlining the process. The resulting PACNs exhibited superior chromatic stability across a wide pH range and higher antioxidant capacity than native ACNs. When incorporated into yogurt, they maintained stable coloration for 14 days without affecting the viability of lactic acid bacteria. CONCLUSION: This study demonstrates a streamlined and promising approach for producing stable PACNs directly from agro-industrial byproducts. By integrating efficient transformation under mild conditions with validation in a real food matrix, this strategy overcomes kinetic limitations and supports the development of clean-label colorants from sustainable sources. © 2026 Society of Chemical Industry.