Effects of cooling treatments and physical damage on tip rot and postharvest quality of asparagus spears

The effects of postharvest cooling rates and physical damage to tips, on the incidence of tip rot and other quality attributes of asparagus spears (Asparagus officinalis L. 'New Zealand Beacon Syn 2'), harvested early and late in the season, were investigated. The half cooling times were 1 1 / 2 min, l 1 / 2 h, and 5 3 / 4 h for hydrocooled, forced-air cooled, and passively cooled spears, respectively. Apical tissue cooled more rapidly than middle and basal zone tissues. Incidence of tip rot, and visible quality and toughness of asparagus spears, was not affected by the method of cooling, or delays after harvest of up to 12 h at ambient temperatures before hydrocooling. However, overall spear quality was marginally higher, and weight loss significantly less, in hydrocooled spears than in forced-air or passively cooled spears. It is recommended that spears are hydrocooled or forced-air cooled within 4-12 h of harvest. In this study, the incidence of tip rot was not linked to the time of harvest within a season. Incidence of tip rot increased with increasing severity of non-visible impact damage to spear tips. Impact on apical tissues after drops from 0, 50, 100, and 150 mm resulted in 0, 34, 36, and 64% tip rot, respectively, after 5 days at 20°C and 93-95% relative humidity (RH). Washing spears after impact increased the incidence of tip rot. Although adverse physiological stress may be a factor involved in the expression of tip rot, results indicate that physical damage may be a major contributing factor, exploited by micro-organisms present on the asparagus spears and in packhouse wash water, leading to spoilage.