Stabilisation of anthocyanins and anthocyanin-metal chelates with hydrocolloids for their application as red and blue food colourants

Colour is one of the most important attributes for food, indicating its freshness and quality, thus strongly swaying the consumer’s purchase decision. Anthocyanins are responsible for the red to blue hues of many fruits and flower petals, and are preferably applied as natural colourants in acidic food products. However, they are sensitive to heat, light and oxygen, and decompose or polymerise to colourless or brown products during processing and storage of food. Therefore, much effort has been dedicated to improve pigment stability. Supportive effects of macromolecules on anthocyanin stability have been suggested for decades; nevertheless, experiments addressing this issue have been mostly inadequate. With the purpose to better understand anthocyanin–pectin interactions and their influencing factors, the 1 st project of the present thesis aimed at a systematic evaluation of the stabilising interactions between different anthocyanins, varying in the number of hydroxyl groups in the B-ring, and pectins of different types and sources at a food relevant pH value of 3.0. While stabilisation of strawberry pigments was limited and independent of the pectin type and source, black currant pigment stability was significantly enhanced by pectins. These results corroborate the hypothesis that pigment stabilisation is predominantly based on hydrogen bonds, and only to some extent on electrostatic interactions. The hydrogen bonds are formed with the functional groups of the homogalacturonan backbone of pectins, thus confirming the stabilising role of the pectin type in the following order: amidated > low methyl esterified > high methyl esterified. Depending on the number of hydroxyl groups in the anthocyanin B-ring and the pectin structure, one, two, or even three hydrogen bonds may be formed, leading to a successively increasing stabilisation. Furthermore, for stabilisation of black currant anthocyanins the particularities of each pectin source played an important role. These results demonstrate that specific strategies considering the individual pigment source have to be developed to achieve optimal pigment