Firmness and Quality Changes in Broccoli Due to Dehydration and Hydration

A major quality concern for the marketing of broccoli is head or crown softening associated with water loss, which can occur at various points in the postharvest handling chain.  This research evaluated the influence of dehydration and hydration on head and stem firmness and other quality attributes. Broccoli heads (cv. Ironman) were harvested at 6 am and immediately placed in plastic bags inside coolers containing ice for transport to the lab. Based on previous experiments, five treatments were performed after trimming stems to 18cm: 1 – Control (as harvested); 2 –Short hydration (heads 30 min in 5C water); 3 – Long hydration (heads in water 2h (firmness and weight loss) or 4h (shelf-life and respiration); 4 – Dehydration (heads allowed to lose 2-3% fresh weight at 5C); 5 – Heads dehydrated 2-3% and then rehydrated for 30 min.  Product was placed in perforated plastic bags in boxes to simulate commercial storage.  Broccoli (12 heads per treatment) was evaluated before and after treatment and every 5d for 20d at 5C for weight loss and head and stem firmness (heads compressed 7.5mm with a 50 mm flat cylindrical probe; stems compressed 5mm on a three point bending rig).  Shelf-life (15 heads per treatment) was determined as the days to show incipient yellowing during storage at 5C (product in bags on trays) and respiration was determined daily on broccoli in flow-through chambers by analysis of net CO2 production. Hydration for 30 min or 2 h caused sharp and similar increases in fresh weight and head and stem firmness. Control broccoli lost 3% weight after 20d, while the 30min and 2h hydrated heads had corresponding fresh weights 0.8% and 2.5% higher than initial. For dehydrated and rehydrated broccoli, weight loss was similar to that of control heads. The changes in head firmness were similar to the trends in stem firmness for the 5 treatments. Head firmness of control broccoli decreased from 80 to 50N over 20d; firmness of dehydrated heads decreased to 50N and then was constant; head firmness of 30min and 2h hydration treatments reached 100N and then decreased to 80N after 20 days.  Hydrated heads had a shorter shelf-life than heads from control, dehydrated, or dehydrated and rehydrated treatments. Broccoli hydrated 4h had higher respiration rates than broccoli from any other treatment. Manipulation of the water status of broccoli has major consequences for head and stem firmness and other postharvest quality attributes.