Pectin methylesterase catalyzed firming effects on low temperature blanched vegetables

The effect of low temperature blanching on firmness of eight vegetables was studied. Preheating vegetables at low temperatures prior to a conventional blanch resulted in firmer products. Temperature and time had significant effects on texture, with temperature the most influential. Under optimal conditions, firmness improvements in preheated vegetables as compared to blanched controls were: Bok choy-3.0 × (65 °C, 45 min); Chinese cabbage-1.8 × (55 °C, 45 min); cabbage-1.6 × (65 °C, 15 min); green bell peppers-1.36 × (70 °C, 15 min); sugar snap peas-1.7 × (65 °C, 30 min); carrots-2.1 × (60 °C, 15 min) and broccoli-2.9 × (60 °C, 15 min). Thermal stability and optimal temperature for pectin methylesterase in homogenates from these vegetables were also analyzed. The relationship between optimum preheating conditions for textural integrity and pectin methylesterase activity is discussed.