Effects of Temperature on Ethylene-induced Phenylalanine Ammonia Lyase Activity and Russet Spotting in Harvested Iceberg Lettuce

Abstract

<jats:p>Experiments were conducted to study the effect of temperature on the ethylene inducibility of phenylalanine ammonia lyase (PAL, EC 4.3.1.5) activity and the development of russet spotting (RS) in Iceberg lettuce (Lactucu sutiva L.). Tissue exposed to ethylene and held at 15 or 20C showed earlier hut lower peaks in PAL activity than tissue held at 5C. Accumulation of total soluble phenolic compounds, and the development of RS paralleled increases in PAL activity after a short lag period. Lettuce tissue transferred from 5 to 15C after 1 to 3 days showed later hut higher peaks in PAL activity than tissue continuously held at 15C. Transferring ethylene-exposed tissue to 0C before RS symptoms developed greatly limited further rise in PAL activity and RS development. Discontinuing ethylene exposure after 4 days resulted in a rapid decrease in PAL activity. Lettuce tissue exposed to ethylene for 4 days and then transferred from 5 to 0C after the development of moderate RS symptoms showed no difference in RS after 8 days compared to tissue stored continuously at 5C.</jats:p>

Phenylalanine ammonia lyase activity in minimally processed Romaine lettuce

“…opez-G! alvez et al (1996b) and Ritenour, Ahrens, and Saltveit (1995). This could be attributed to the inherent differences among the lettuce varieties assayed, differences in the content of phenolic compounds (Saltveit, 2000) and differences among the experimental designs.…”

“…In the studies just mentioned, model systems were used where the effect of wounding and exogenous ethylene over PAL activity were analysed separately. In these studies, lettuce pieces including leaf and midrib were placed in jars where the effect of wounding over the enzymatic activity was assayed excluding ethylene from the surrounding environment and the enzymatic induction caused by ethylene was assayed in tissue up to 2.5 cm away from the site of wounding (Ritenour et al, 1995). In the present work, minimally processed lettuce were placed in polypropylene trays and covered with a PVC film in which ethylene was allowed to accumulate to simulate normal commercialization procedures.…”

“…1) but did not produce a noticeable peak during the storage period analysed. Ritenour et al (1995) working with whole Iceberg lettuce leaves found that the peak of ethylene-induced PAL activity depends on the storage temperature. In general, when the temperature was higher the PAL activity peaked earlier but this also created a smaller peak.…”

Modified atmosphere (MA) prevents browning of fresh-cut romaine lettuce through multi-target effects related to phenolic metabolism

“…On the contrary, PAL activity correlates negatively with the visual quality and positively with the leaf edge browning (Lopez-Galvez et al, 1996a). Most of the reports that correlate PAL activity with the increase in some phenolic compounds such as chlorogenic acid and isochlorogenic acid have been related to russet spotting on ethylene-treated lettuce midribs (Hyodo et al, 1978;Ke and Saltveit, 1989a;Ritenour et al, 1995;Tomás-Barberán et al, 1997b) or to brown stain in excised lettuce midrib when exposed to CO 2 (Ke and Saltveit, 1989b;Mateos et al, 1993). In the case of cut edge browning, also known as senescence browning, differences in browning development have not been attributed to differences in enzymatic activities, in the quantity of phenolic substrates (Cantos et al, 2001), and/or in endogenous ascorbic acid (AA) content (Heimdal et al, 1995).…”

Impact of Shelf Life on Content of Primary and Secondary Metabolites in Apple (Malus domestica Borkh.)

“…The increase in total phenols during storage could be a result of ethylene activity. This hormone stimulates the activity of phenylalanine ammonia lyase, the key enzyme in biosynthesis of phenolic compounds, with the consequent accumulation of phenolic constituents (Ritenour and others 1995). At ambient temperatures, ethylene production is higher, thus stimulating the biosynthetic pathway of phenolic compounds (Napolitano and others 2004).…”