Destabilisation and stabilisation of anthocyanins in purple-fleshed sweet potatoes: A review

As a category of natural colourants, anthocyanins are abundant in purple-fleshed sweet potato (PFSP). Recently, anthocyanins from PFSP are proven to have multiple bioactivities, but they are liable to undergo discolouration and degradation upon thermal treatment, light exposure, oxidation, etc. Thus, the destabilisation/stabilisation of PFSP anthocyanins has received extensive attention from both academic and industrial views. This work aims to present an updated overview of the occurrence, destabilisation, and stabilisation of anthocyanins in purple-fleshed sweet potato varieties. In total, forty-two anthocyanin monomers are found in PFSP, and they belong to the glycosylated and acylated derivatives of cyanidin, peonidin, pelargonidin, and delphinidin, with the first two predominating. Notably, PFSP anthocyanins were susceptible to destabilisation (degradation/discolouration) when exposed to acid/alkaline, heat, light, oxygen, ascorbic acid, sulfite, metal ions, and enzymes. Herein, the destabilising mechanism, the loss in food processing and the structure-stability relationship of PFSP anthocyanins were deeply discussed. More importantly, it was of high industrial significance that PFSP anthocyanins could be stabilised or protected by intramolecular or intermolecular copigmentation, encapsulation, and certain protective agents. Intramolecular copigmentation often occurred in acylated anthocyanin molecules, while phenolic acids, metal ions, polysaccharides, and proteins could serve as copigments in intermolecular copigmentation. When embedded in polysaccharide-based microcapsules and hydrogels, trapped in β-cyclodextrin cavities, and loaded in surfactant micelles, PFSP anthocyanins demonstrated enhanced stability. In addition, the replacement of ascorbic acid with its derivatives and the applications of antioxidants and enzyme inhibitors favoured the stabilisation of PFSP anthocyanins.