Tipburn of romaine lettuce is a serious quality defect, which causes significant economic loss to lettuce growers in the Salinas Valley of California. This defect is particularly problematic for the producers of fresh-cut salad mixes because the
Timothy K. Hartz, Paul R. Johnstone, Richard F. Smith, and Michael D. Cahn
Catherine E. Belisle, Steven A. Sargent, Jeffrey K. Brecht, Germán V. Sandoya, and Charles A. Sims
, and loss of crispness in fresh-cut Romaine lettuce ( Manolopoulou et al., 2010 ). For subjective ratings, numerical or descriptive thresholds are set, typically using hedonic scales with ratings from 1 (extremely poor quality) to 9 (excellent quality
Qingquan Chu, Jiangang Liu, Khaled Bali, Kelly R. Thorp, Richard Smith, and Guangyao (Sam) Wang
in the last 2 to 3 years, little research has been conducted on the performance of these automated thinners. Plant spacing affects lettuce yield and quality significantly ( Maboko and Du Plooy, 2009 ; Ririe, 1972 ). In both iceberg and romaine
Rahmatallah Gheshm and Rebecca Nelson Brown
Romaine lettuce ( Lactuca sativa ) is one of the most important fresh market vegetable crops in the United States. The annual lettuce consumption in 2017 was 24.5 lb per person, of which 45% (11 lb per person) were romaine and leaf lettuce. Ninety
T. Casey Barickman, Thomas E. Horgan, Jennifer R. Wheeler, and Carl E. Sams
income. Romaine type lettuce is the main lettuce grown by small to medium producers. Depending on plant spacing, the average yields of romaine lettuce can be around 30,000 kg·ha −1 ( Mossler and Dunn, 2005 ). Romaine type lettuce is a preferred leafy
the effect of water quality and the product-to-water ratio on the quality and microbial growth of packaged sliced Romaine lettuce. Materials and Methods Plant material. Romaine lettuce ( Lactuca sativa L.) was purchased from a produce
Thomas L. Thompson and Thomas A. Doerge
Two field experiments were conducted with subsurface trickle-irrigated romaine lettuce (Lactuca sativa L. cv. Parris Island Cos) during the 1990–92 winter growing seasons in southern Arizona. The objectives were to determine 1) yield and quality response to varying combinations of soil water tension (SWT) and N fertilizer, 2) seasonal patterns of N uptake, and 3) unutilized fertilizer N. During 1990–91, N rates were 35, 120, and 205 kg·ha–1. During 1991–92, the experiment was factorial with N levels from 50 to 300 kg·ha–1 and target SWT levels of 7.0 and 4.0 kPa. Unutilized fertilizer N was the difference between fertilized and nonfertilized plots in total N inputs not harvested in the crop. When excessive irrigation was not applied (SWT between 6.5 and 7.4 kPa), 95% of the maximum crop yield and yield quality (head length and fresh mass) response occurred at N rates of 156 to 193 kg·ha–1, with unutilized fertilizer N <60 kg·ha–1. Excessive irrigation (4.6 kPa) resulted in lower yields and yield quality and higher unutilized fertilizer N. Romaine accumulated >74% of its total N uptake in the 38 days before harvest. Unutilized fertilizer N increased sharply when adequate N and water rates were exceeded. These results suggest that a target SWT of no wetter than 6.5 kPa is appropriate for subsurface trickle-irrigated romaine lettuce.
Robert J. Dufault, Brian Ward, and Richard L. Hassell
The objective of this study was to determine the best combination of planting dates (PDs) and cultivars on yield and quality for long-term production of romaine lettuce. `Green Forest' (GF), `Apache' (AP), `Darkland' (DK), `Green Tower' (GT), `Ideal Cos' (IC), and `Tall Guzmaine' (TG) were successfully grown to harvest maturity on 19 PDs from September 1998 to April 2001. Lettuce planted in September and April PDs (pooled over cultivars and year), required as little as 47 and 49 days, respectively, to reach harvest (all cultivars harvested on the same day). Lettuce planted in October, November, February, and March PDs (pooled over cultivars and year), required on average 64, 66, 75, and 67 days to reach harvest, respectively, but in the coldest PDs of December and January, 90 and 98 days, respectively, were needed to reach maturity. Of the eight PDs evaluated, marketable numbers/plot (pooled over cultivars and years) were greatest in the September PD, followed by April (–8% decrease from September PD) > March (–13%) > October (–17%) > November (–21%) > December = January = February (about –30%) and heads weighed the most in September > January = February (–7% decrease from September PD) > March = April (–14%) > October (–21%) > December (–25%) > November (–31%). Cull heads/plot (pooled over cultivars and years) were greatest in April > December (–5% decrease from April PD) > January = February (–16%) > November (–27%) > October (–34%) > March (–44%) > September (–49%). Two out of three November PDs were lost to freezing damage and this PD should be avoided. Significant bolting occurred primarily in the September and October PDs (in 1 of 3 years) with negligible bolting in the November, December, and January PDs, but bolting recurred again in the February, March and April PDs. Marketable numbers/plot (pooled over all PDs and years) were greatest for GF > GT (–7% decrease from GF) > AP (–8%) > IC (–9%) > DK (–11%) > TG (–21%). The interaction effect of cultivar × PD indicated that GF yielded the most marketable heads in 6 out of 8 PDs. The best performing cultivars by PD (pooled over years) were September and February = GF and IC; October = TG; November = AP; December, January, March, and April = GF.
Kevin I. Segall and Martin G. Scanlon
The first goal of this study was to determine the packaging film O2 permeability required to maintain a steady-state O2 concentration of 3% in modified-atmosphere packaging (MAP) of minimally processed romaine lettuce (Lactuca sativa L.). The second goal of the study was to determine the extent to which MAP could preserve lettuce quality and consequently extend product shelf life. Oxygen consumption rates of commercially prepared lettuce samples were determined in a closed system for each of three atmospheres (3% O2 combined with either 6%, 10%, or 14% CO2). Enzymatic, quadratic, and linear mathematical models were compared to determine which best described the respiratory data. The linear model was the most suitable and was used to predict the O2 consumption rate of the minimally processed romaine lettuce under the desired package headspace gas concentrations. The predicted O2 consumption rate was used to calculate the necessary O2 permeability for the packaging film. Packages (21.6 × 25.4 cm) were constructed from a polypropylene-polyethylene-laminate film with the appropriate O2 permeability. Packaged samples were stored under three modified atmospheres (MAs) (3% O2 combined with either 6%, 10%, or 14% CO2) for 20 days, and headspace gas concentrations, lettuce appearance, and color were evaluated every other day. Growth of pectinolytic and lactic acid bacteria was also studied. The O2 consumption rate of the lettuce decreased with increasing CO2 levels. The O2 levels in the MA packages equilibrated at 7% to 11%. Compared to a control atmosphere of air, MAP delayed the development of tissue discoloration. Preliminary results indicated no effect of MAP on microbial growth. Of the three CO2 levels, 10% was slightly more effective than 6% and 14%. Critical choice of packaging permeabilities combined with MAP maintained the quality of minimally processed romaine lettuce and thereby increased shelf life by about 50%.
Ji Gang Kim, Yaguang Luo, Robert A. Saftner, and Kenneth C. Gross
of fresh-cut lettuce. Use of a company name or product by the USDA does not imply approval or recommendation of the product to the exclusion of others that also may be suitable.