Onion (Allium cepa L.) bulbs are most sensitive to base plate impacts

Although onion bulbs have one of the highest storage potentials under ambient conditions of any vegetable, physical impacts to bulbs during mechanical postharvest handling can reduce this capacity. This presents a significant challenge in production systems that rely on mechanised harvesting and handling operations to remain economically competitive. In this study, the respiration rate of onions sampled immediately after travelling over a commercial packing and grading line was elevated compared with pre-graded samples. Elevated respiration rate was linked to a higher rate of weight loss and reduced storage potential. Controlled impacts applied to individual bulbs also increased the rate of bulb respiration and internal sprout growth. Bulbs were more sensitive to impacts to the base plate than to impacts to the equator or neck. Environmental scanning electron microscopy revealed intra-cellular disruption within the scales where bulbs were impacted on the equator. No physical damage could be distinguished in bulbs impacted on the base plate. Minimising postharvest respiration rate of mature bulbs is recommended for long-term storage. Furthermore, it is recommended that the design of handling equipment consider both impact magnitude and position.