Effects of ascorbic acid applied by two hydrocooling methods on physical, chemical and sensory attributes of green leaf lettuce stored at 5°C

Quality and shelf life of lettuce are limited by detrimental problems such as textural changes and browning during post harvest stages. The effects of ascorbic acid applied by two hydrocooling methods on chemical, physical and sensory properties of Waldmann's dark green leaf lettuce were evaluated. Lettuce heads were immersed (in 1% ascorbic acid or tap water) or sprayed (in 1% ascorbic acid or tap water) or left untreated (control). Treatment solutions for immersion or spraying were applied at 5°C for 2 min. After treatment application, lettuce heads were packaged and stored at 5°C for up to 21 days. Analytical assays conducted included total ascorbate content, total phenolic content, antioxidant capacity, instrumental color and texture measurements, relative water content and consumer sensory evaluation. All analytical assays were completed at 5 time intervals: before treatment application, and on days 1, 7, 14 and 21 of storage time. Consumer sensory evaluation panels were conducted at 3 storage time intervals: on days l, 7 and 14 of storage time. Lettuce sensory attributes evaluated included appearance, color intensity, flavor, texture, bitterness, tartness and overall acceptability. Data analyses for all variables were performed using 2-way ANOVAs. Differences between means were determined using Least Significant Differences (P < 0.05). Hydrocooling of leaf lettuce by immersion or spraying using 1% ascorbic acid solution increased total ascorbate content for up to 7 days, with an increase of more than 300% in total ascorbate content on day 1 compared to its initial value before treatments. Ascorbic acid immersed lettuce maintained its relative water content throughout the 21 days of storage, and its texture (instrumental measurement) was firmer than all other treatments on days 14 and 21. Sensory results showed that the lettuce hydrocooled by spraying with 1% ascorbic acid increased in firmness and became less bitter over the storage time, while hydrocooling by immersion using 1% ascorbic acid negatively affected lettuce appearance and resulted in a darker color over storage time. Further experimentation with the application of ascorbic acid during hydrocooling is needed to fully assess its usefulness in maintaining the quality of leaf lettuce during storage.