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Ji Gang Kim, Sun Tay Choi, and Chai Il Lim

Modified atmosphere (MA) packaging has been used to maintain quality of fresh-cut lettuce, but O2 depletion and excessive CO2 accumulation can be injurious. This study was conducted to evaluate the effect of delayed MA packaging using three different films on quality maintenance of fresh-cut iceberg lettuce. Iceberg lettuce leaves were sliced, washed, dried, and placed for 0, 5, 10, and 15 hours under air atmosphere at 5 °C. Samples were packaged with 2.9 and 16.6 pmol·kg·Pa·s, oxygen transmission rate (OTR) films and microperforated film (P-plus), and stored for 12 days at 5 °C. Results indicated that delayed packaging affected gas composition (O2 and CO2), fermentative volatile production, off-odor, color, and tissue electrolyte leakage. With 2.9 OTR film, longer delayed time maintained quality by inhibiting off-odor development and the accumulation of ethanol. However, delayed packaging was not effective in maintaining quality of samples packaged with 16.6 OTR film and P-plus film. Regardless of delayed time, all 16.6 OTR-packaged samples had severe discoloration after 7 days of storage. All delayed treatments packaged with P-plus film attained the desired O2 (3–5 kPa) and CO2 levels (10–12 kPa) from day 9 to the end of storage. A 15-hour delayed packaging into packages prepared from 2.9 OTR film and samples packaged with P-plus film maintained quality by inhibiting off-odor development. The results indicate that delayed packaging could be an alternative method when fresh-cut lettuce is packaged with low OTR films.

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M.A. Ritenour, M.J. Ahrens, and M.E. Saltveit

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.

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M.A. Ritenour, M.E. Saltveit, and M.J. Ahrens

Russet spotting (RS) is an important postharvest disorder in Iceberg lettuce (Lactuca sativa L.). Previous studies showed that RS is induced by exposure to ∼5 ppm (ul/l) ethylene at ∼5C for 3 days and is characterized by the appearance of 1 to 2 mm diam. oval, brown sunken spots along the midrib. Increases in phenylalanine ammonia-lyase (PAL) activity and phenolic content are highly correlated with RS development. Ethylene-induced PAL activity is much less at higher (12C) or lower (0C) temperatures. In this study isolated whole leaves were exposed to a log series of ethylene concentrations from 0.1 to 10 ppm at temperatures from 0.0C to 20C for up to 8 days. Tissue was transferred among these various treatments to investigate the kinetics of PAL induction, activity and deactivation, phenolic accumulation, and RS development. A subjective evaluation was then made of RS development using a 1 to 9 scoring system in which 1 was no RS, and then PAL activity and phenolic content were measured. Preliminary results indicate that ethylene-induced PAL activity was decreased more rapidly upon transfer to temperatures above 10C than to 0.0C. Accumulation of phenolic compounds and development of RS paralleled each other, and were positively related to PAL activity. Practical implications of these results will be discussed.

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Ryan J. Hayes, Karunakaran Maruthachalam, Gary E. Vallad, Steven J. Klosterman, Ivan Simko, Yaguang Luo, and Krishna V. Subbarao

The Agricultural Research Service, U.S. Department of Agriculture and the University of California, Davis, announce the release of two breeding lines of lettuce ( Lactuca sativa L.). Lines RH08-0472 and RH08-0475 are F 9 iceberg-type lettuce

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M. Murshidul Hoque, Husein Ajwa, Mona Othman, Richard Smith, and Michael Cahn

planting and iceberg lettuce was harvested 83 d after planting. A total of 30 plants was sampled from the center four seed rows by selecting every eighth marketable plant in a row. Whole-plant weight from a composite sample of 10 plants was determined

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Huangjun Lu, Alan L. Wright, and David Sui

lettuce production. Field experiments. Two separate sets of experiments, one for romaine and one for iceberg cultivars, were carried out using a randomized complete block design. Each set of the experiments with four replications in each experiment were

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Ryan J. Hayes, Bo Ming Wu, Barry M. Pryor, Periasamy Chitrampalam, and Krishna V. Subbarao

, 1960 ; Elia and Piglionica, 1964 ; Grube and Ryder, 2004 ; Madjid et al., 1983 ; Newton and Sequeira, 1972 ; Subbarao, 1998 ; Whipps et al., 2002 ). In the United States, romaine and iceberg-type lettuces are the most widely grown. However, many

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Timothy K. Hartz, P. R. Johnstone, E. Williams, and R.F. Smith

applicability to the California lettuce industry. Materials and Methods In 2004 and 2005, a total of 35 commercial fields of iceberg and 43 fields of romaine lettuce were sampled in the coastal production regions of central California. Fields were selected

Open access

Jesse J. Murray, Gulnoz Hisamutdinova, Germán V. Sandoya, Richard N. Raid, and Stephanie Slinski

fusarium wilt have been identified in cultivated lettuce, and research has shown that romaine cultivars tend to be more resistant than iceberg cultivars, particularly when exposed to warmer temperatures toward the beginning and end of the lettuce growing

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Lee F. Johnson, Michael Cahn, Frank Martin, Forrest Melton, Sharon Benzen, Barry Farrara, and Kirk Post

replicated trials. Relationships between applied water and crop yields were evaluated. Crops were grown using standard regional production, cultivation, and harvest practices. Materials and Methods Replicated field trials in iceberg lettuce ( Lactuca sativa