2018 ASHS Annual Conference

Fresh-cut, ready-to-eat, packaged lettuce has become increasingly popular in the USA; however, this product is highly perishable and browns quickly with a relatively short shelf-life. The selection of cultivars with improved quality and less cut-edge browning could help strengthen and expand the fresh-cut lettuce industry. The objective of this study was to characterize the quality and browning potential of 15 Romaine lettuce cultivars: Braveheart, Clemente, Green Forest, Green Towers, Heart’s Delight, King Henry, Lobjoits, Paris Island Cos, PI 4912242, RH11-1506, Siskiyou, SM13-R2, Sun Valley, Tall Guzmaine, and Triple Threat. Lettuce cultivars were selected, grown, and harvested by the United States Department of Agriculture (USDA) lettuce breeding program in Salinas, CA. Lettuce was shipped to the USDA Food Quality Laboratory in Beltsville, MD for processing, packaging, and shelf-life assessment. Romaine lettuce was trimmed, cut into 2.5 × 2.5 cm slices, washed for 30 seconds in a 100 mg L^-1 free chlorine solution adjusted to pH 6.5, centrifugally dried for 2 minutes at 666 rev min^-1, and packaged in polypropylene bags with a film oxygen transmission rate at 5°C of 16.6 pmol O₂ s^-1 m^-2 Pa^-1. Packaged lettuce (4 replicates) was stored at 5°C for up to 14 days. The cut lettuce pieces were analyzed for sensorial quality attributes (freshness, browning, overall quality, and off-odor), head-space gas composition (O₂, CO₂), and color. A new image analysis tool was developed to quantify the browning severity in cut lettuce pieces using high resolution images taken under controlled lighting and analyzed using a smart segmentation computer software (Image Pro Premier). Sensory results showed that Clemente had the lowest browning score (16.0±4.0) and highest overall quality score (75.2±9.1), while Triple Threat had the highest off-odor score (74.2±12.2) and lowest overall quality score (17.3±15.7) after 14 days of storage. Image analysis confirmed that Clemente had less extensive browning than Triple Threat, as demonstrated by the amount of lettuce leaf pixels that had a brown color after 14 days of storage (4.7±0.8% for Clemente, 15.1±3.0% for Triple Threat). Triple Threat also had the largest headspace CO₂ concentration compared to the other cultivars (12.4±0.9% CO₂ after 14 days), indicating that this variety had a higher respiration rate. These results and the image analysis tool developed in this research can be used in the selection and development of new Romaine lettuce cultivars with improved quality.