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Description
Anthocyanins are bioactive compounds that are present in various fruits and vegetables. They can enhance the visual appeal of food products, as they are responsible for their vibrant purple, blue and red hues. Anthocyanin-rich extracts obtained from plants can change colour in response to pH, temperature, light and oxygen variations. By changing their colour accordingly to the pH of the food product, anthocyanins have a potential to be used in active and intelligent food packaging as they can be incorporated in polymer/biopolymer films. In other words, when food deteriorates, it undergoes changes in pH and consequently, the colour of the film changes, providing information about the current state of food1-3. Furthermore, anthocyanins have raised a growing interest due to several factors: their antioxidant activity and antimicrobial properties, shifting from synthetic to natural dyes etc4.
In this research, a quantitative measurement of anthocyanin content is provided. Anthocyanins were obtained by solvent extraction from black rice, acai and purple cabbage using different concentrations of ethanol/water and citric acid. The absorbance of the extracted solution was determined using a spectrophotometer. The pH of the extracted solution was adjusted using 1M NaOH or 1M HCl for achieving basic or acidic state, respectively. The color spectrum was immediately measured at a pH range of 2–12 using a UV-Vis spectrophotometer at a wavelength range of 400–700 nm. The colour changes of the extracted solutions were also photographed and monitored using colorimeter5, 6.
References:
[1] Lei Zhao, Yaqi Liu, Liang Zhao, Yong Wang, Anthocyanin-based pH-sensitive smart packaging films for monitoring food freshness, Journal of Agriculture and Food Research 9, 2022
[2] Oana Emilia Constantin, Daniela Ionela Istrati, Extraction, Quantification and Characterization Techniques for Anthocyanin Compounds in Various Food Matrices—A Review, Horticulturae, 2022
[3] Suman Singh, K. K. G., Youn Suk Lee. Anthocyanin – A Natural Dye for Smart Food Packaging Systems. Journal of Packaging Science and Technology, 2018
[4] Swarup Roy, Jong-Whan Rhim, Anthocyanin food colorant and its application in pH-responsive color change indicator films, Food Science and Nutrition, 2020
[5] Jiaqi Tan, Y. H., Bo Han, Xiangmei Qi, Xu Cai, Shaoqin Ge, Hongkun Xue, Extraction and purification of anthocyanins - A review. Journal of Agriculture and Food Research 9, 2022
[6] Qingying Luo, A. H., Dur E Sameen, Saeed Ahmed, Jianwu Dai, Suqing Li, Wen Qin, Yaowen Liu, Recent advances in the fabrication of pH-sensitive indicators films and their application for food quality evaluation, Food Science and Nutrition, 2021
Keywords: anthocyanins, uv-vis spectroscopy
