The evaluation of nitrogen effect on lettuce quality by means of descriptive sensory profiling

Butterhead, romaine and oak leaf lettuces were grown at 0, 80 and 160 kg ha(-1) nitrogen on fall and spring cycles. After harvest, the heads were stored for either: 4 days at room temperature; 7 days at 4 C; or 7 days at 4 C + 4 days at room temperature. Two nine-point descriptive scales were developed for sensory analysis of intact and cut heads, including characters such as size, colour, firmness, turgor and visual defects. The heads were evaluated at harvest and after storage, by a panel of 9 people trained in the basic use of the scales. A significant effect of nitrogen was detected on most individual traits. The first principal component extracted from the descriptive profile set was an indicator of overall quality, whereas the second was positively correlated to head size and defects. Both components showed a curvilinear response to nitrogen, with an increase from 0 to 80 kg ha 1, but no further increase at the highest nitrogen rate. The results indicate that nitrogen-induced quality variation of lettuce can be perceived and quantitatively assessed by means of descriptive sensory profiling. There was no response of main external quality traits beyond an application of 80 kg/ha N, which was lower than that usually employed by growers, corresponding to the reccommendations of the local advisory services.