Low dose irradiation of plum peel anthocyanins: Impact on stability and antioxidant activity

Consumer demand for both natural food colorants and non-thermal methods of preservation has increased overwhelmingly during the last few decades. Preventing loss of appeal and color through non-thermal methods without compromising on quality will provide an alternative to conventional thermal methods. In the present study, irradiation of plum peel anthocyanins after extraction and purification was done in a range of 0.1 - 1.0 kGy. Results revealed that degradation was significantly (p ≤ 0.05) dependent on both time and dose of irradiation. The percentage degradation observed in the first 3 h of treatment was 9.0 – 21.0±1.2%. The maximum anthocyanin degradation recorded during 8 h of irradiation was 45.3%. Anthocyanin degradation was apparently less at 0.1 – 0.5 kGy compared to 0.6 – 1.0 kGy. The retention of anthocyanins was up to the extent of 88.8 – 62.3% in samples irradiated at 0.1 – 0.5 kGy. Comparison of the individual anthocyanin indicated that diglucoside anthocyanins were stable towards irradiation than monoglucoside anthocyanins. For monoglucoside anthocyanins, a 50% decrease was observed as the irradiation treatment exceeded 0.6 kGy. A close comparison of the data revealed that at irradiation dose of 1.0 kGy, the decrease in L* and a* values was almost four and three times higher than that observed in samples irradiated at 0.5 kGy and below; while an increase in b* value was almost double. In spite of marginal degradation in color, low dose irradiation (up to 0.5 kGy) significantly (p ≤ 0.05) increased the antioxidant activity of the plum peel anthocyanins.