Effect of cyclodextrins and co-pigmentation on the thermal stability of the anthocyanin extract of Saffron petal in the model drink

Anthocyanins are one of the most important of food colorants, which are found in many fruits, flowers, and vegetables, and have been used as natural pigments in commercial foods and beverage products due to their desirable colors and potential nutritional benefits. Saffron (Crocus sativus) is the most expensive spice of the world and an average 86.4% of wet weight or 96.4% of dry weight of saffron flowers is related to petals. Saffron petals usually do not have a commercial value but contain large amounts of anthocyanins, flavonoids and glycosides. Thus, these petals can be a good source of natural dyes applicable in pharmaceuticals, confectionery, and soft drinks. However, anthocyanins are readily unstable compounds with exposure to oxygen, pH, temperature, enzyme, light, as well as surrounding components, which reduces food color and quality. Losses of anthocyanins occur during juice processing and storage, and methods are needed to prevent these losses. Up to now, various methods including the encapsulation and the co-pigmentation have been tried to intensify the stability of anthocyanins. The co-pigmentation based on the molecular interactions, has been shown to be an efficient way to stabilize anthocyanins. The addition of organic acids, flavonoids, alkaloids, polysaccharides, proteins, etc. as a co-pigment, can improve the stability, and change the bioactivity of anthocyanins. Encapsulation of anthocyanins by alpha and beta cyclodextrins is a potential treatment that could d anthocyanin losses. Anthocyanins can form inclusion complexes with cyclodextrin molecules, which may protect anthocyanins from hydration and polymerization reactions. Therefore, saffron petal is a potential resource of anthocyanin in Iran. Low thermal stability of the anthocyanins caused a tendency to the synthetic colorants. Therefore, the main goal of this research was to investigate the effect of cyclodextrins and co-pigmentation on the anthocyanin extract of saffron petal during heat treatment. 

Anthocyanin extract of saffron petal was extracted by 50% acidic ethanol solution at ambient temperature. Acidified extract was concentrated by a rotary evaporator at 40˚C up to 9 percent concentration of solid materials. Different concentrations of alpha and beta cyclodextrin (10, 25, 50, 75 and 100 mole alpha or beta cyclodextrin to one mole anthocyanin) and also, different co-pigments such as gallic acid (at two molar ratio of 50:1 and 100:1of galic acid/anthocyanin), ferulic acid (at two molar ratio of 50:1 and 100:1of ferulic acid/anthocyanin), quercetin (at two molar ratio of 2.5:1 and 5:1 of quercetin/anthocyanin) and rutin (at two molar ratio of 10:1 and 25:1 of rutin/anthocyanin) were used to study the thermal stability of anthocyanin. Furthermore, the hydroalcoholic extract of rosehip was prepared and concentrated thereby, the rosehip extract (at two molar ratio of 50:1 and 100:1gallic acid equivalent/anthocyanin) was used as a co-pigment. Total anthocyanin content was measured using differential pH method and reported based on mg of cyanidin 3-glucoside per 100 ml the model drink. a* value was measured by Hunter Lab. Model drink (20 mM acid citric buffer in pH of 3) containing 0.01 % CaCl2 and anthocyanin extract was prepared. Prepared model drinks were heated at 90 °C during 0, 15, 30, 45, 60, 90 and 120 min and then, were cooled up to room temperature. Half time of anthocyanin was calculated and the mentioned treatments were investigated to evaluate the stability of the different compounds. 

The results indicated that alpha cyclodextrin at molar ratio of 50:1 (alpha cyclodextrin to anthocyanin) hadn’t any significant effect on the anthocyanin stability but beta cyclodextrin at molar ratio of 50:1 increased the colorant stability, which can be due to the smaller cavity of alpha cyclodextrin rather than beta cyclodextrin that lead to the lower interaction between alpha cyclodextrin and anthocyanin. Although, phenolic co-pigments hadn’t any significant effect on the anthocyanin stability of the model drink but the rosehip extract at two molar ratios of 50:1 and 100: 1 increased the anthocyanin retention. Total phenolic content of rosehip extract was 14.56 g gallic acid equivalent per liter of the extract and total flavonoid content was 365 mg quercetin equivalent per liter of the extract. According to the studies and our results about total phenol and flavonoid content, the increased retention of the anthocyanin can be related to the variety of the phenolic and flavonoid compounds of the rosehip extract. Therefore, beta cyclodextrin as a trapping agent and rosehip extract as a co-pigment, can increase the anthocyanin stability of the saffron petal during heat treatment.