Identification of romaine lettuce (Lactuca sativa var. longifolia) Cultivars with reduced browning discoloration for fresh-cut processing

Discoloration (browning) represents a major challenge that limits the quality and shelf life of fresh-cut lettuce. In this study, we aimed to find romaine lettuce (Lactuca sativa var. longifolia) accessions with low browning potential. Midribs of 14 accessions (11 cultivars, two breeding lines, and a single plant introduction) were shredded and packaged in perforated bags for five days. Images of processed samples were captured daily and analyzed with computer vision technology to quantify browning intensity via L*a*b* color values and browning index (BI). Enzymatic activity [phenylalanine lyase (PAL), peroxidase (POD), and polyphenol oxidase (PPO)] and total phenolic content (TPC) were measured daily. After five days in storage, the accessions in the Tall Guzmaine and Parris Island Cos pedigree groups exhibited the greatest and least browning, respectively. In addition, while the PAL, POD, and TPC increased substantially over time, the PPO of twelve accessions fluctuated with only minor increases. For all accessions, the temporal increase of PAL, POD, and TPC showed significant, positive correlation to browning progression. Comparing between accessions, those that had greater amounts of accumulated PAL and smaller amounts of POD tended to have a greater amount of browning after five days of storage, despite relatively low correlation coefficients. However, the accumulation of TPC and PPO was not correlated to browning severity after five days of storage. This systematic study provides lettuce growers and breeders with guidance for selecting accessions with limited browning, and it supplies researchers in plant physiology and genetics with more information on the roles of enzymes in the lettuce browning process.