Control of Red Discoloration of Fresh-Cut Sunchoke Tubers
Sunchokes (Helianthus tuberosus L.) are inulin-accumulating tubers native to North America that are edible raw or cooked, and have good potential as a fresh-cut product. Sunchokes perform well as fresh-cut slices except for the development of a reddish discoloration on the cut surface. Dip treatments with ethanol (5%) provided effective control of discoloration. Untreated or ethanol-treated sliced tubers (5% for 3 min) were stored in air at 0 and 5°C, with best quality of untreated slices (visual, color values) maintained at 0°C. Ethanol treatment retarded discoloration effectively at both temperatures. Ethanol treatment suppressed respiration, and reduced wound-induced phenylalanine ammonia-lyase (PAL) activity and phenolic concentrations. Controlled atmospheres of 3% O2 with 6 or 12% CO2 at 5°C were less effective than ethanol dips, although high-CO2 atmospheres also retarded PAL activity and increases in phenolics. Increased endogenous ethanol concentrations were developed by nitrogen-flushing of tubers at 10°C in closed containers, with accumulation of CO2. These precutting atmosphere treatments were only partially effective in controlling slice discoloration. Pre-processing hot-water dips (50°C for 6 min plus 1 or 3 days at 20°C) or tuber-warming treatments (20°C for 7 or 14 days) were also partially effective in controlling red discoloration of sliced tubers.