THE PHYSICO-CHEMICAL PROPERTIES OF LETTUCE (LACTUCA SATIVA 'GRAND RAPID') GROWN UNDER DIFFERENT PLANTING METHODS

A study was conducted to investigate the effect of different planting methods on the postharvest quality of lettuce (Lactuca sativa ‘Grand Rapid’). The lettuce plants were planted by using three different methods which were hydroponic, aquaponic and soil (conventional) planting. The growing period takes about 6 to 8 weeks before the lettuce can be harvested. The yield (weight/plant) and physico-chemical parameters of texture, colour, chlorophyll and carotenoid contents, moisture, ash and fibre contents of the lettuce samples were determined and analyses were done on the day of harvest. Sensory evaluation was also carried out for the acceptability of lettuce from different planting methods. The results showed that lettuce from hydroponic planting method had higher and better postharvest quality compared to that from soil and aquaponic planting methods. The crispness values of lettuce were also higher in hydroponic planting method. Lettuce from soil planting method had higher moisture and ash contents whilst lettuce from aquaponic was rich in fibre. However, there was no significant difference (p>0.05) among all the planting methods for color, chlorophyll and carotenoid contents. Sensory evaluation conducted showed that the hydroponic lettuce had good scores in all the attributes of appearance, taste, texture, odour and overall acceptability. No significant difference (p>0.05) was obtained between lettuce from soil and aquaponic planting methods for sensory evaluation. Therefore, hydroponic was found to be the best planting method to obtain higher yield and better quality lettuce. Lettuce grown under the aquaponic planting method also has the advantage of two commodities harvestable at the same time which are lettuce and fish.