Effect of postharvest treatments on Amaranthus betacyanin degradation evaluated by visible/near-infrared spectroscopy

A visible/near-infrared spectrophotometric method was developed for betacyanin and moisture content in Amaranthus samples. A standard error of prediction (SEP) of 0.25 mg/g for betacyanins (r(2) = 0.97) and 2.18% for moisture (r(2) = 0.99) was obtained on the validation sample set. Effect of 5 postharvest treatments on betacyanin degradation was assessed. Freeze-drying and -18 degreesC frozen storage gave over 97% pigment retention, compared to natural air (52.8%), solar drying (63.5%), air oven drying (61.9 to 83.1%), and 14 degreesC storage (78.3%). Air-drying gave the lowest degradation rate and longest half-life among the solar and oven-drying treatments for 8 h. Dried samples showed good pigment stability with 28.6 mo half-life at 25 degreesC.