Modeling ammonia accumulation and color changes of arugula leaves in relation to temperature, storage time and cultivar
Leonarda Mastrandea (Department of Science of Agriculture, Food and Environment, University of Foggia, Italy), Maria Luisa Amodio (Department of Science of Agriculture, Food and Environment, University of Foggia, Italy), and Marita Cantwell (Dept. Plant Sciences, UC Davis, Davis, CA 95616 USA)
Leafy greens produce ammonia as stressful conditions occur during postharvest handling. The objective of this study was to understand the relationship between ammonia accumulation and color variation of rocket or arugula leaves in relation to cultivar and storage temperature. Leaves of Five cultivars (Bellezia, Grazia, Letizia, Tricia, Wild Thing) were washed, centrifuged, placed in unsealed plastic bags, and stored at 0, 5 or 10 degrees C for 28, 20 and 12 days, respectively. Visual quality, color (hue angle) and ammonia accumulation were monitored periodically. Ammonia increased from 11-15 µg/g FW to 150-220 at 0 degrees C, 340-450 at 5 degrees C and to >590 µg/g FW at 10 degrees C at the end of storage-life. While there were some differences among cultivars, temperature played the major role in ammonia accumulation. Color varied due to leaf yellowing which increased with increasing temperature. Both Hue angle and ammonia changes were fitted with traditional (first and 0 order kinetics) and Weibullian models, with the latter explaining a higher percentage of the variance of experimental data. Moreover, considering that time was the common variable between the 2 kinetics, a new mathematical equation describing ammonia versus Hue for each cultivar/temperature of storage was obtained. In all cases a good correlation was obtained between ammonia and color change with more accurate results at 5 and 10 degrees C, since color at 0 degrees C was stable. These results demonstrate that ammonia may be a good indicator of senescence in Arugula since it correlated well to color change with storage temperature and storage time.