Investigations into the Post-Harvest Physiology of Asparagus

Abstract

Various aspects of the post-harvest physiology of asparagus (Asparagus officinalis cv. Limbras 10) were investigated with particular emphasis placed on the problem of tip breakdown in spears and the short shelf-life of spears after cool storage. It was hoped that studies would reveal post-harvest techniques that would increase the shelf-life of spears after storage and thereby enable the sea-freight of spears to Japan and the USA. The effect of humidity conditions on the development of tip breakdown and the shelf-life of spears stored at different temperatures for up to four weeks, was tested experimentally. It was found that storage at 2.5° C and 95% relative humidity resulted in more visually appealing spears which exhibited less weight loss and had a longer shelf-life than spears stored at the other storage temperatures at high and low humidity. The shelf-life of such spears was not however, extended enough to make the sea freight of spears to overseas markets feasible. Spears stored at 5° C and 85% relative humidity exhibited less tip softening than other stored spears however, the shelf-life of such spears was not extended enough to warrant storage under these conditions. The effects of post-harvest applications of the ethylene inhibitor AVG on storage life, respiration and ethylene production were studied although only weight loss was found to be significantly affected by the AVG. Ethylene production in spears was noted to occur before the respiratory decline suggesting that ethylene synthesis is one of the first metabolic indicators of senecence. Spears were hydrocooled in various concentrations of calcium chloride and the effect of the calcium upon shelf-life and the severity of tip breakdown was noted. The organic acid and calcium content of spears was also investigated. All calcium data appeared to support the chelation hypothesis proposed by French et al. (unpub.).Calcium was found to effectively reduce tip softening and weight loss and shelf-life was prolonged by up to one day, although this was not long enough for sea freight of spears to Japan and the USA to be feasible. Ultrastructural studies revealed that storage at low temperatures partially inhibited the onset of cell deterioration. Once spears were placed into shelf-life however, the deteriorative processes began to progress. After four weeks storage and three days shelf-life, most of the cellular contents in the outer cortical cells of spear tips had degraded, although cell walls remained intact. Further studies on the effect of temperature and AVG on shelf-life and the incidence of tip breakdown are required for more conclusive results. It would also be beneficial if the organic acid studies were repeated and ultrastructural changes of calcium hydrocooled spears were investigated.