Investigation of the color properties of anthocyanins with different copigmentation agents

Anthocyanins are natural colorants with bioactive properties, including antiviral and antimicrobial effects. However, their unstable structure makes them very sensitive to factors such as pH, oxygen, and temperature. This situation limits the use of anthocyanins in the food industry. Copigmentation, which is the focus of this study, is an important technique used to increase anthocyanin stability. Copigments are some substances that form stable complexes with anthocyanins and protect anthocyanins through molecular interactions. In this study, the effect of copigmentation of different anthocyanin structures (black carrot, sour cherry, pomegranate) with different types of copigments (phenolic acid, carbohydrate, protein) on the color properties and thermal stability of anthocyanins was investigated in detail. Firstly, anthocyanins from black carrot, sour cherry and pomegranate were purified and copigmented with gallic acid, maltodextrin and whey protein at molar ratios of 1:50 to 1:500. After copigmentation process, hyperchromic effect and bathochromic shift values were determined. Then, total monomeric anthocyanin amount, anthocyanin fragmentation criteria (color intensity, polymeric color and polymeric color ratio) and color values (L*, a*, b*, C*, h°) were analyzed. Color properties and anthocyanin stability were investigated at 90 °C for various time intervals (0, 30, 60, 120, 180 and 360 min.). Gallic acid provided a regular increase in ΔAmax(%) values as the molar ratio increased. In sour cherry, ΔAmax(%) value increased by 228% from 56.2 to 184.5, and in pomegranate, it increased by 603% from 45.9 to 323. Gallic acid initially increased the color intensity value in black carrot (5.44 → 7.43), sour cherry (1.35 → 3.75) and pomegranate (0.72 → 2.70) anthocyanins. Although copigmentation was effective, gallic acid showed a protective effect by reducing the thermal degradation of black carrot anthocyanins, while it accelerated the degradation of sour cherry and pomegranate anthocyanins. Maltodextrin did not show a good copigmentation effect as gallic acid and whey protein, but it showed a strong interaction especially with black carrot anthocyanins, providing 77% preservation of anthocyanins. Black carrot and maltodextrin copigmentation provided the highest fit with the inverse second-order model. Whey protein provided a significant increase in ΔAmax (%) values with increasing molar ratio, especially in pomegranate anthocyanins (531% increase, ΔAₘₐₓ: 114.6 → 725), while it did not show a significant change in black carrot and sour cherry anthocyanins. However, it changed the color intensity values from 5.44 to 5.88 in black carrot at the beginning, from 1.35 to 1.31 in sour cherry and from 0.72 to 1.68 in pomegranate anthocyanins. The color intensity values in sour cherry and pomegranate anthocyanins, which decreased in gallic acid and maltodextrin due to heating over time, increased with whey protein application. In this context, it is possible to say that thermal denaturation creates higher binding affinity for anthocyanins. The opposite situation in black carrot was explained by the di-acylation structure. In fact, black carrot anthocyanins exhibited a more stable behavior compared to sour cherry and pomegranate anthocyanins with their acylated structures. It was observed that whey protein provided superior thermal stability in all anthocyanin sources. The results showed that the copigmentation effect may vary depending on the different chemical structures and copigment type of anthocyanins, and especially acylated anthocyanins exhibited a more stable behavior compared to others. It is expected that the findings obtained will provide a scientific basis for studies to increase the stability of natural colorants to reduce the limitations in the use of anthocyanins in the food industry. Keywords: Anthocyanin interactions, color stability, phenolic anthocyanin interaction, carbohydrate anthocyanin interaction, protein anthocyanin interaction.