Watercress is a highly perishable crop and this thesis is a study of post-harvest changes in watercress which will aid an understanding of deterioration processes during storage and transport, and of conditions which affect senescence. The effects of three different daylengths (8, 12 and 16 h), corresponding to winter, spring and summer conditions, on growth, yield and shelf-life of plants were studied. The commercial distribution chains of watercress were studied over a five month period to determine the post-harvest conditions to which it is exposed and to measure both physiological and sensory changes occurring. Comparisons were made between long and short haul distribution chains, refrigerated and unrefrigerated transport, and two types of prepacks. The results of these commercial distribution chain studies led to the development of a sensory profile for watercress. This type of assessment proved of value in determining changes in quality which could not be detected by the physiological methods used. Aroma was found to be a reliable indicator of watercress freshness and volatiles were collected and compounds identified for use as odour reference samples. Volatiles emitted from the plant material were collected using headspace apparatus and a number of compounds not previously reported in watercress were identified. Their detection is accounted for by the use of nondestructive methods of collection, resulting in minimum glucosinolate degradation. Few isothiocyanates or thiocyanates were collected from fresh material, but as the plant deteriorated the amounts of sulphur compounds in samples increased as glucosinolate degradation occurred. Changes in the production of watercress volatiles under different storage conditions were monitored using a dual headspace apparatus. Storage in the dark at 10°C in a current of air kept the watercress fresh and crisp apart from yellowing of leaves, which was prevented by cytokinin treatment. A preliminary examination was made of watercress microflora for the presence of microorganisms which might be responsible for the large quantities of acetic acid found in the samples of volatiles. The epicuticular wax was analysed to determine whether it retains aroma components liberated from within the plant, or whether it contributes to the aroma itself. The wax surface was examined using scanning electron microscopy and found to be an amorphous layer without any structures capable of retaining flavour compounds.
|Date of Award||1980|