POST HARVEST KEEPING QUALITY OF LETTUCE (LACTUCA-SATIVA L VAR CAPITATA L) - MEASUREMENT AND ANALYSIS OF CLIMATIC FACTORS AND TRANSPIRATION

Numerous factors that affect both internal and external quality in hor ticultural produce and their marketing capability must be taken into c onsideration in order to minimize losses in quality of harvested produ ce. The relationship between climatic effects and plant responses (CO2 and H2O gas exchange) is established using mass and heat transfer mec hanisms that take the influence of air temperature, relative humidity, air velocity, atmospheric pressure, atmospheric composition, and radi ation into account. The experimental equipment for the simulation inve stigations includes a system of cuvettes with six measuring and one re ference cuvette for the simultaneous investigation of six lettuces, in tegrated CO2 and H2O gas analysers combined with a multiplexer system for switching gas channels, and a computer-aided datalogging system wi th test-related sensors. The effect of climatic conditions on H2O gas exchange can be determined using the relationship between the transpir ation rate on the one hand and the active area of transpiration and th e characteristic shape factors on the other hand, while taking the var ying appearance of lettuce into consideration. An average total resist ance in the water vapour pathway of individual lettuce which takes the overlapping of leaves into account can be ascertained according to it s morphological structure and to the defined active area of transpirat ion. Regarding the mass transfer of water vapour it is therefore possi ble to record the influence of simultaneously acting climatic paramete rs on harvested lettuce while incorporating phenotypical variation. Al so a new quality scoring of lettuce is introduced.