Identifying traits to improve postharvest processability in baby leaf salad

The 'processability' of baby salad leaves may be defined as the ability to withstand the postharvest washing and packing processes that are involved in the production of ready-to-eat bagged salads. The inability of baby salad leaves (species including Lactuca sativa L. and Spinacia oleracea L.) to withstand processing results in a reduction in crop shelf-life. Leaves from geographically diverse locations displayed strikingly different processability scores from visual inspection. We have shown that these 'good' and 'poor' quality leaves may be differentiated from assessments of the biophysical properties of the cell wall (% plasticity) and epidermal cell size. Artificial manipulation of processability in the glasshouse through the application of a mechanical stress or a high salt stress produced L. sativa cv. Ravita (a leaf type 'lollo rosso' lettuce) leaves covering a range of processability. Mechanical stress, applied as a daily dose of 100 paper strokes, increased lettuce leaf shelf-life by 33% and was associated with reduced % plasticity and smaller leaf epidermal cells. These traits are thus proposed to be of key importance in the description of processability, with the plant cell wall and plant cell wall gene expression implicated. The potential for future manipulation of these traits for the pre-packed salad market is considered. (C) 2003 Elsevier B.V. All rights reserved.