Effects of extraction conditions on improving the yield and quality of an anthocyanin-rich purple corn (Zea mays L.) color extract

Purple corn (Zea mays L.) is a rich and economic source of anthocyanin colorants and funtional ingredients. However, high levels of anthocyanin-rich waste are generated during processing, reducing the yields and increasing the costs of the final product. This waste has been associated with anthocyanin complexation with tannins and proteins. Our objective was to evalutate anthocyanin extraction methods to reduce purple corn waste. Different solvents (water, 0.01%-HCl-acified ethanol), temperatures (room temperature, 50, 75, and 100 degrees C), and times of exposure to the solvents were investigated. Acetone (70% acetone in water) extraction was used as control. Anthocyanins, total phenolics, tannis, and proteins in extracts were measured by the pH differential, Folin-Ciocalteu, protein precipitation, and BCA assay methods. Qualitative analyses were done by HPLC coupled to a PDA detector and SDS-PAGE analysis. Water at 50 degrees C achieved the highest yield of anthocyanins (0.94 +/- 0.03g per 100 g dry cornob) with relatively low tannins and proteins, comparable to the anthocyanin yield of anthocyanin yield obtained by 70% acetone (0.98 +/- 0.08 g per 100g dry cornob). Extending the extraction time for 20 to 60 min and using consecutive reextraction procedures reduced anthocyanin purity, increasing the yields of other phenolics. A neutral protease was applied to the extracts and effectively decomposed the major protein that was believed to contribute to the development of anthocyanin complexion and waste generation. Extraction time, consecutive reextraction procedures, and enzyme hydrolysis should be considered for highly yield of anthocyanins and waste reduction.