Stability of anthocyanin extracts from chokeberry, grape, hibiscus, and purple sweet potato in ω-3-fatty acid rich oil-in-water emulsions.

The food industry is actively investigating the stability of natural red pigments to replace artificial food colorants from all food applications in the near future. In this study, the stability of coloring extracts from chokeberry, grape, hibiscus, and purple sweet potato was investigated in ω-3 fatty acid-rich flaxseed oil-in-water emulsion during storage. The red color of the oil-in-water emulsions faded within 4 days, indicating that the anthocyanin extracts were susceptible to lipid oxidation reactions of the ω-3 fatty acids. The color stability varied between all used extract sources: The chokeberry (degradation constant k = 19.6 h-1) and grape (k = 15.2 h-1) extracts showed similar degradation kinetics, whereas purple sweet potato extract (k = 10.7 h-1) degraded significantly slower, and hibiscus extract (k = 110.2 h-1) significantly faster. The differences can be explained by the different anthocyanins contained in the plant extract, especially by the proportion of acylated anthocyanins.

Effect of chlorogenic acid on spectral properties and stability of acylated and non-acylated cyanidin-3-O-glycosides.

Spectral characteristics and heat stability (90°C, 5h) of six isolated, structurally related cyanidin-3-O-glycosides from black carrot were investigated in aqueous solutions (pH 3.6 and 4.6) supplemented with chlorogenic acid (molar anthocyanin:co-pigment ratios 1:62.5-1:250). Chlorogenic acid supplementation generally increased absorbance of non-acylated anthocyanins by up to 97.9 and 122.9% at pH 3.6 and 4.6, respectively, being mainly attributed to the formation of intermolecular anthocyanin:co-pigment complexes. The effect significantly decreased when the chain length of the 3-O-linked non-acylated anthocyanins was increased from mono- to di- to triglycosyl moieties, possibly due to steric interferences of bound sugars and co-pigments. Intermolecular co-pigmentation was investigated for the first time for feruloylated and sinapoylated cyanidin-3-O-triglycosides. They exhibited weaker effects (10.8-16.0%) at pH 4.6, and no spectral response was observed at pH 3.6. Chlorogenic acid addition evoked weak enhancement of thermal pigment stability at pH 3.6, while it was highly detrimental for all anthocyanins at pH 4.6.