Anthocyanin and glucosinolate occurrences in the roots of Chinese red radish (Raphanus sativus L.), and their stability to heat and pH

Roots of three unique Chinese radish cultivars were evaluated as potential sources for anthocyanin-type colourants or value-added products. These cultivars showed high variation in anthocyanins (63.77-160.74 mg/100 g FW). Seventeen pigments were tentatively identified by mass spectroscopy as pelargonidin-3-sophoroside-5-glucoside derivatives with multiple acylation of hydroxycinnamic acids. A bright colour (CIELab) of radish anthocyanins has been shown at a wide pH range, comparably stable at pH < 4.2. Those anthocyanins also showed a remarkable thermal stability, following a zero-order kinetics at pH 2.5 with half-lives of 14.5 or 8.7 h at 90 or 100 degrees C, respectively. Additionally, those cultivars varied in glucosinolate contents (59.69-163.91 mg/100 g FW), whereas their degradation was sensitive to pH and followed a first-order kinetics at pH 5.8 with half-lives of 11.44 or 7.05 h at 90 or 100 degrees C, respectively. However, the stable pH ranges for anthocyanins and glucosinolates were different: pH < 4.2 and pH > 3.6, respectively. In a radish juice model (pH 5.8/2.5), thermal degradation of anthocyanins or glucosinolates was associated closely with media pH values. In conclusion, cultivar selection, and thermal and pH conditions during processing or storage should be taken into account for quality, stability, and health benefits of radish derived natural colourants or nutraceutical products. (C) 2012 Elsevier Ltd. All rights reserved.