Head Lettuce Research Articles

ABOUT FOOD VALUES AND REQUIREMENTS FOR THE QUALITY OF FRESH GREEN VEGETABLE CROPS - SALADS

The production of green crops, primarily salads, is one of the promising areas of greenhouse vegetable growing. The grounds for this are: year-round demand in the market for fresh greens, high profitability of production, the presence of a wide range of varieties and hybrids belonging to different varieties, an increased level of food culture of the population. The article describes the nutritional value of fresh vegetable greens - lettuce, describes the requirements for consumer characteristics, imposed by the enacted State Standard 33985-2016 “Lettuce. Endive curly, endive Eskariol fresh. Technical conditions”, features of packing, transportation and storage of lettuce are presented. It is established that the leaves of lettuce contain a significant amount of malic, citric and succinic acids, about 2% carbohydrates, 1.5% protein, 0.5% fiber. A large number of trace elements such as manganese, cobalt, copper, iodine and zinc, an excellent ratio in the salad of potassium and sodium. Pigments are represented, including carotene and xanthophyll (from 2.0 to 2.7 mg / 100 g), anthocyanins are present in the colored varieties of lettuce. According to the content of phenolic compounds (represented by cinnamic, caffeic, and chlorogenic acids), leaf varieties are distinguished - up to 192 mg / 100 g, rosette leaves of a head of lettuce - 113-127 mg / 100 g depending on the commercial grade, described unacceptable defects of vegetable greens, methods of laying and specific uniformity of lettuce in the packaging unit.

Environmental inactivation and irrigation-mediated regrowth of Escherichia coli O157:H7 on romaine lettuce when inoculated in a fecal slurry matrix.

Field trials were conducted in July–August and October 2012 to quantify the inactivation rate of Escherichia coli O157:H7 when mixed with fecal slurry and applied to romaine lettuce leaves. Lettuce was grown under commercial conditions in Salinas Valley, California. One-half milliliter of rabbit, chicken, or pig fecal slurry, containing an average of 4.05 × 107 CFU E. coli O157:H7 (C0), was inoculated onto the upper (adaxial) surface of a lower leaf on 288 heads of lettuce per trial immediately following a 2.5 h irrigation event. To estimate the bacterial inactivation rate as a function of time, fecal matrix, irrigation and seasonal climate effects, sets of lettuce heads (n = 28) were sampled each day over 10 days and the concentration of E. coli O157:H7 (Ct) determined. E. coli O157:H7 was detected on 100% of heads during the 10-day duration, with concentrations ranging from ≤340 MPN/head (∼5-log reduction) to >3.45 × 1012 MPN/head (∼5-log growth). Relative to C0, on day 10 (Ct = 12) we observed an overall 2.6-log and 3.2-log mean reduction of E. coli O157:H7 in July and October, respectively. However, we observed relative maximum concentrations due to bacterial growth on day 6 (maximum Ct = 8) apparently stimulated by foliar irrigation on day 5. From this maximum there was a mean 5.3-log and 5.1-log reduction by day 10 (Ct = 12) for the July and October trials, respectively. This study provides insight into the inactivation and growth kinetics of E. coli O157:H7 on romaine lettuce leaves under natural field conditions. This study provides evidence that harvesting within 24 h post irrigation has the potential to increase the concentration of E. coli O157:H7 contamination, if present on heads of romaine lettuce; foliar irrigation can temporarily stimulate substantial regrowth of E. coli O157:H7.

Modified Coring Tool Designs Reduce Iceberg Lettuce Cross-Contamination

Contaminated coring tools may transfer bacteria to iceberg lettuce. The efficiency of coring tool design modifications in reducing bacterial transfer to lettuce heads was evaluated under simulated field operations. The standard coring tool consists of a stainless steel cylindrical tube welded to a tab that is inserted into a plastic handle. Design modifications included removal of the welded portion, incorporation of a shorter front straight bottom edge, or an angled bottom edge toward the front. In the first study, coring tools of four different designs were inoculated by dipping in a tryptic soy broth (TSB) suspension that contained 8.85 Log CFU/mL of Escherichia coli K-12 and then were used to core 100 lettuce heads, consecutively. Use of the standard tool resulted in 91% ± 9% positive lettuce heads. Removing the welded surface from the standard tool resulted in the highest reduction of E. coli transfer (44% ± 11.9% positive lettuce heads, P < 0.05), whereas incorporation of a short front straight edge with no welding resulted in 65.6% ± 5.6% of the cored lettuce heads being positive for E. coli. Removal of the welded surface resulted in a 40% decrease in E. coli contamination among the last 20 cored lettuce heads (81 to 100), which indicates that coring tool design modifications resulted in reduced cross-contamination. In the second study, the transfer of Salmonella to coring tools after their immersion in rinsing solutions was evaluated using imaging. The tools were dip inoculated for 2 min in water, water with lettuce extract, or TSB containing 7 Log CFU/mL bioluminescent Salmonella Newport; they were then imaged to observe spatial distribution of bacteria. There was greater retention and spatial distribution of Salmonella on the surface of tools immersed in water containing lettuce extract than in TSB and water. The results of the second study indicate that rinsing solutions that contain lettuce particulate and organic load could facilitate cross-contamination of Salmonella Newport to tool surfaces.

Growth promotion and productivity of lettuce using Trichoderma spp. commercial strains

ABSTRACT The aim of this study was to evaluate four strains of Trichoderma spp. (T. harzianum IBLF 006 WP, T. harzianum IBLF 006 SC, T. harzianum ESALQ 1306 and T. asperellum URM 5911) for seedling growth promotion in laboratory and head lettuce yield in field conditions. The experiment was carried out in a completely randomized design with four treatments (strains): IBLF 006 WP, IBLF 006 SC, ESALQ 1306 and URM 5911 and a non-inoculated (without Trichoderma) control. Each treatment consisted of 200 seeds, arranged in four replicates. Lettuce seeds cv. Astra were treated with 2 mL Trichoderma suspension (2.5 x 108 conidia mL-1 per each 100 g seeds) and submitted to growth assay in laboratory up to 7 days after sowing. For field experiment, we opened furrows, which were manually sprayed with 5 x 107 conidia mL-1. Afterwards, seedlings were transplanted (4 to 6 leaves of head lettuce cv. Mauren) and harvested 40 days later. Each treatment consisted of four replicates (1.2 x 1.2 m, 16 plants per plot) arranged in randomized blocks. In both experiments, a control without Trichoderma application was included, and we evaluated shoot length, root and total length, shoot, root and total fresh mass and shoot, root and total dry mass, shoot mass ratio, root mass ratio and shoot/root ratio. The germination (%) was evaluated by laboratory tests, whereas in field experiment, height, stem diameter, head diameter, number of leaves and yield were evaluated. The T. harzianum strain ESALQ 1306 provided the best head lettuce growth rate in laboratory test, which was confirmed in field experiment, in which the productivity (50.2 t ha-1) was superior when compared to the other strains (41.38 to 44.23 t ha-1) and the control (30.18 t ha-1).

Optimization of temperature and light, and cultivar selection for the production of high-quality head lettuce in a closed-type plant factory

Two separate experiments were conducted to identify suitable cultivars, to optimize light and temperature, and to understand the heading process in order to produce high-quality crisphead lettuce (Lactuca sativa L.) in a closed production environment. Three commercial crisphead lettuce cultivars (‘Adam’, ‘Manchu’, and ‘Sensation’) were grown on deep flow technique beds in a closed-type plant factory under three different fluorescent light intensities [150, 200, and 250 µmol m−2 s−1 photosynthetic photon flux (PPF)] and two temperature conditions. The plants were grown until 60 days after transplantation (DAT) under the high [22/18 °C (0–30 DAT) → 18/16 °C (30–60 DAT)] and low [18/16 °C (0–30 DAT) → 18/14 °C (30–60 DAT)] temperature conditions, with 50 ± 10% relative humidity and a 12-h day length. Growth parameters, including head formation rate and tip burn incidence, were measured in all experiments. All cultivars exhibited significantly higher growth rates in the 250 µmol m−2 s−1 light intensity compared to lower light intensities under both temperature conditions, and showed a cultivar-specific difference in the growth pattern at different light intensities. Our cultivation trials suggest that ‘Sensation’ is ideal for production in closed-type plant factory systems at 250 µmol m−2 s−1 PPF due to its stable head formation and superior head quality. Under the high temperature condition, head formation was only observed in two cultivars, ‘Sensation’ and ‘Adam’, while all cultivars showed head formation in the low temperature condition. The initiation of head formation began at the 8–10 true-leaf stage around 20 DAT, and then apparent head formation was observed around 30 DAT, followed by an increase of head density until harvest (60 DAT). Tip burn symptoms were observed throughout the experiment, with higher values in the high temperature condition. The results of our study suggest that good head formation can be achieved under high light intensities ( ≥ 200 µmol m−2 s−1 PPF) and low temperature [18/16 °C (0–30 DAT) → 18/14 °C (30–60 DAT)] in crisphead lettuce grown in a closed-type plant factory.

Detection and Quantification of Pythium tracheiphilum in Soil by Multiplex Real-Time qPCR

In Canada, head lettuce (Lactuca sativa capitata) is extensively produced in the muck soils of southwestern Québec. However, yields are increasingly affected by various soilborne pathogens, including Pythium spp., which cause wilt and damping off. In a survey conducted in Québec muck soils in 2010 and 2011, Pythium tracheiphilum Matta was identified as the predominant Pythium sp. in the root of head lettuce showing Pythium stunt symptoms. Therefore, to improve risk assessment and help further understanding of disease epidemiology, a specific and sensitive real-time quantitative polymerase chain reaction (qPCR) assay based on TaqMan-minor groove binder (MGB) technology was developed for P. tracheiphilum. The PCR primers along with a TaqMan-MGB probe were designed from the ribosomal internal transcribed spacer 2 region. A 100-bp product was amplified by PCR from all P. tracheiphilum isolates tested while no PCR product was obtained from 38 other Pythium spp. or from a selection of additional lettuce pathogens tested. In addition to P. tracheiphilum, the assay was multiplexed with an internal control allowing for the individual validation of each PCR. In artificially infested soils, the sensitivity of the qPCR assay was established as 10 oospores/g of dry soil. P. tracheiphilum was not detected in soils in which lettuce has never been grown; however, inoculum ranged from 0 to more than 200,000 oospores/g of dry soil in commercial lettuce fields. Also, disease incidence was positively correlated with inoculum concentration (r = 0.764). The results suggest that inoculum concentration should be considered when making Pythium stunt management decisions. The developed qPCR assay will facilitate reliable detection and quantification of P. tracheiphilum from field soil.

A Conceptual Framework for Developing Recommendations for No-Harvest Buffers around In-Field Feces

None of the 39 lettuce heads >2 m from the feces had detectable levels of E. coli. Thirteen (39%) of the 33 heads <2 m from the feces had detectable levels of E. coli. Odds of harvesting E. coli-contaminated lettuce decrease with distance from feces. Analyses provide a framework for estimating no-harvest buffers around in-field feces. Risk assessments are needed to set appropriate buffer zones for different regions.

Rapid large-volume concentration for increased detection of Escherichia coli O157:H7 and Listeria monocytogenes in lettuce wash water generated at commercial facilities

In pilot-scale testing, dead-end ultrafiltration concentration (DEUF-C) sampling increased detection of pathogens in lettuce wash water. This study investigated DEUF-C performance when scaled up to commercial processing levels. Two sets of experiments were done to: 1) compare pathogen detection probability in lettuce wash water generated from commercial pilot-scale processing using DEUF-C versus standard grab sampling, and 2) evaluate DEUF-C to concentrate pathogens inoculated into commercially-generated flume and centrifuge lettuce wash water. In pilot-scale runs, one lettuce head inoculated to contain 2–8 × 104 CFU of Escherichia coli O157:H7 and 3–10 × 105 CFU of Listeria monocytogenes was processed along with 907 kg of uninoculated lettuce using sanitizer-free tap water. Two to four 40-L volumes of the wash water were concentrated to 400 mL by DEUF-C, and pathogen detection probability in these samples was compared to standard grab samples after 24 h–48 h of enrichment using qPCR. In the second set of trials, chlorine in flume and centrifuge water from a local commercial processing facility was neutralized with sodium thiosulfate (100 mg/L), spiked with both E. coli O157:H7 and L. monocytogenes at 102 CFU/mL, and processed by DEUF-C. Total filterable volume was determined for DEUF-C samples, and detection (qPCR) probabilities in unenriched DEUF-C and grab samples were determined. E. coli O157:H7 and L. monocytogenes were detected in 100% of the DEUF-C samples from pilot-scale water samples. Comparable grab samples yielded 6.7% detection for E. coli O157:H7, and 20 and 60% for 24 h- and 48 h-enriched L. monocytogenes samples, respectively. The total filterable volume in commercially-generated waters was significantly higher for flume than for centrifuge water. All unenriched DEUF-C samples yielded E. coli O157:H7 and L. monocytogenes compared to 11.1 and 22.2%, respectively, for the unenriched grab samples. These findings indicate DEUF-C can improve the probability of detecting E. coli and Listeria in commercial wash water. However, filtration of commercial lettuce wash water remains challenging, with more work needed to ensure DEUF-C is feasible for commercial use.

The establishment of a DNA fingerprinting database for 73 varieties of Lactuca sativa capitate L. using SSR molecular markers

Head lettuce originating near the Mediterranean coast was introduced to China in the fifth century. It is difficult to identify different varieties of head lettuce due to their close genetic relationships. Simple sequence repeats (SSR) technology is a practical method that has been widely used in variety identification, fingerprint construction and genetic diversity analysis. In this paper, 23 pairs of SSR primers were selected to identify and analyse 73 varieties of head lettuce. The results identified a total of 117 mutated alleles detected in 23 loci, with the number of each loci ranging from 2 to 11, with an average of 5.1 mutated alleles per locus. Additionally, 152 genotypes were detected in 23 loci, with an average of 6.6 genotypes per locus derived from a range of 2–13. The polymorphism information content ranged from 0.071 to 0.702, with an average of 0.499. The selected primer pairs could clearly reflect the genotypic diversity level of the 73 head lettuce varieties tested, and can be used in the detection and analysis of the head lettuce varieties. The results of our sequence analysis also showed that these 73 varieties of head lettuce could be effectively identified by a combination of 19 primer pairs even though the genetic similarity among the 73 varieties ranged from 0.647 to 0.991, with an average of 0.798. Based on a capillary electrophoresis platform, a DNA fingerprinting database of 73 head lettuce varieties was established.

Testing New Concepts for Crop Cultivation in Space: Effects of Rooting Volume and Nitrogen Availability.

Long term human missions to the Moon and Mars, rely on life support systems for food production and regeneration of resources. In the EU H2020 TIME SCALE-project, an advanced life support system concept was developed to facilitate plant research and technology demonstration under different gravity conditions. Ground experiments assessed irrigation systems and effects of rooting- and nutrient solution volume. The maximal allowed volume for existing International Space Station research facilities (3.4 L) was able to support cultivation of two lettuce heads for at least 24 days. A smaller rooting volume (0.6 L) increased root biomass after 24 days, but induced a 5% reduction in total biomass at day 35. Regulating effects of nitrate supply on plant water fluxes in light and dark were also investigated. At low concentrations of nitrate in the nutrient solution, both transpiration and stomatal conductance increased rapidly with increasing nitrate concentration. During day-time this increase levelled off at high concentrations, while during nigh-time there was a distinct decline at supra optimal concentrations. Plants supplied with nitrate concentrations as low as 1.25 mM did not show visible signs of nutrient stress or growth reduction. These findings hold promise for both reducing the environmental impact of terrestrial horticulture and avoiding nutrient stress in small scale closed cultivation systems for space.

Effect of Hot Calcium Chloride and Acetic Acid Solutions or Hot Water Treatments on Inhibition of Total Microbial Counts and Browning in Lettuce Stem Cut During Cold Storage

Heads of iceberg lettuce (Lactuca sativa L. cv. Iceberg) were harvested at the proper stage of maturity from Kaha Experimental Farm, Qalubia Governorate, Egypt, during two successive seasons in 2015 and 2016. Good heads were transported immediately to the laboratory of Handling of Vegetable Crops Department Horticulture Research Institute at Giza. Egypt. All leaves were removed and stems were cut by a sharp knife into round slices (1 cm thickness × 2.5 diameter) then dipped for 1 min in the following solutions, hot CaCl23% or 5% at 50oC, hot acetic acid 1% or 3% at 50oC, CaCl23% or 5% at 20oC, acetic acid 1% or 3% at 20oC, hot water at 50oC and distilled water (control) to study the effect of these treatments on inhibition butt discoloration and microbial count of the stem cut lettuce during storage at 2±1 °C and 95 % relative humidity (RH) for 10 days. Results indicated that all studied treatments reduced browning index, Polyphenol oxidase (PPO) activity, Phenylalanine ammonia-lyase (PAL) activity, had lower level of microbial load and maintaining total phenolic contents of the stem cut lettuce during cold storage comparing with untreated control. Stem cut lettuce dipped in hot Calcium Chloride 5% solution showed a positive effect on enzymes related to color maintenance. It reduced the activity of the browning related enzymes polyphenol oxidase (PPO) and Phenylalanine ammonia-lyase (PAL), maintained of total phenolic content, had the lowest total bacterial counts and inhibited browning on the cut surface of lettuce stem during storage at 2±1 °C and 95 % relative humidity for 10 days.

Trophic Transfer and Transformation of CeO2 Nanoparticles along a Terrestrial Food Chain: Influence of Exposure Routes.

The trophic transfer and transformation of CeO2 nanoparticles (NPs) through a simulated terrestrial food chain were investigated using a radiotracer technique and X-ray absorption near edge structure (XANES). Radioactive 141CeO2 NPs were applied to head lettuce ( Lactuca sativa), treated via root exposure in its potting soil (5.5 or 11 mg/plant) for 30 days or foliar exposure (7.2 mg/plant, with half of the leaves treated and the other half not) for 7 days. Subsequently, two groups of land snails ( Achatina fulica) were exposed to 141Ce via either a direct (i.e., feeding on the lettuce leaves with 141Ce-contaminated surfaces) or an indirect/trophic (i.e., feeding on the lettuce leaves with systemically distributed 141Ce) route. To evaluate the influence of exposure routes, the Ce contents of the lettuce, snail tissues, and feces were determined by radioactivity measurements. The results show that both assimilation efficiencies (AEs) and food ingestion rates of Ce are greater for the trophic (indirect) exposure. The low AEs indicate that the CeO2 NPs ingested by snails were mostly excreted subsequently, and those that remained in the body were mainly concentrated in the digestive gland. XANES analysis shows that >85% of Ce was reduced to Ce(III) in the digestive gland under direct exposure, whereas Ce in the rest of the food chain (including feces) was largely in its original oxidized (IV) state. This study suggests that CeO2 NPs present in the environment may be taken up by producers and transferred to consumers along food chains and trophic transfer may affect food safety.

Physicochemical characterization and sensory evaluation of lettuce cultivated in three growing systems

ABSTRACT There exists a growing demand and promising market for new lettuce varieties in Brazil. Cv. Brunella is an innovative lettuce variety which mixes crisp lettuce and head lettuce characteristics besides being adapted to the Brazilian growing conditions. The physicochemical and sensory quality of this lettuce, cultivated under different growing systems, was evaluated. The conventional planting and the hydroponic systems were carried out in the experimental area of the Universidade Federal de São Carlos, São Paulo State, Brazil and the organic system was done by certified organic producer in the municipality of Cordeirópolis. After harvesting, leaf area, leaf size, unit leaf area, fresh mass, mass loss, turgor pressure, instrumental color, pH, total titratable acidity (TTA), total soluble solids (TSS), total phenolic compounds (TPC), and sensory characterization were evaluated. We verified that the growing system influenced on physicochemical traits producing lettuces of different sizes, weights and stability. For pH, TSS and TPC, difference among the three growing systems was not observed. For TTA, the hydroponic sample showed higher acidity. About sensory evaluation, the testers noticed difference for green color, thickness, size and leaf crispness, grass aroma and bitter taste. The samples cultivated in conventional and hydroponic systems showed greater preference and purchase intention.

Shelf life of iceberg lettuce affected by hydro cooling and temperature of storage

Pre cooling is applied to remove the field heat of harvested horticultural produces. The goal of this work was to determine the cooling curve and the effects of hydro cooling on quality and shelf life of iceberg lettuce ‘Lucy Brown’ stored at 5°C and 22°C. Through shelf life, it was determined the changes on accumulated fresh weight loss, leaf relative water content and total chlorophyll, total soluble sugars, reducing and non-reducing sugars, and starch. The field heat from iceberg lettuce heads was removed within the first 10 min when submerged into cooled water at 4°C. Hydro cooled lettuce heads accumulated water over the leaf surfaces resulting in higher rate of fresh weight loss during storage when compared to control. Lettuce stored at 5°C kept higher relative water content in the leaves throughout the shelf life. Hydro cooling treatment delayed the wilting of the external leaves in three and two days when stored at 5 and 22°C, respectively. Hydro cooling did not influence the decrease on total soluble sugars, reducing sugars, non-reducing sugars and starch throughout shelf life, but affected the leaf chlorophyll content. Independent of the temperature in which the ‘Lucy Brown’ iceberg lettuce will be stored, hydro cooling is recommended to prolong quality and shelf life.

A Mathematical Model for Pathogen Cross-Contamination Dynamics during the Postharvest Processing of Leafy Greens.

We developed a probabilistic mathematical model for the postharvest processing of leafy greens focusing on Escherichia coli O157:H7 contamination of fresh-cut romaine lettuce as the case study. Our model can (i) support the investigation of cross-contamination scenarios, and (ii) evaluate and compare different risk mitigation options. We used an agent-based modeling framework to predict the pathogen prevalence and levels in bags of fresh-cut lettuce and quantify spread of E. coli O157:H7 from contaminated lettuce to surface areas of processing equipment. Using an unbalanced factorial design, we were able to propagate combinations of random values assigned to model inputs through different processing steps and ranked statistically significant inputs with respect to their impacts on selected model outputs. Results indicated that whether contamination originated on incoming lettuce heads or on the surface areas of processing equipment, pathogen prevalence among bags of fresh-cut lettuce and batches was most significantly impacted by the level of free chlorine in the flume tank and frequency of replacing the wash water inside the tank. Pathogen levels in bags of fresh-cut lettuce were most significantly influenced by the initial levels of contamination on incoming lettuce heads or surface areas of processing equipment. The influence of surface contamination on pathogen prevalence or levels in fresh-cut bags depended on the location of that surface relative to the flume tank. This study demonstrates that developing a flexible yet mathematically rigorous modeling tool, a "virtual laboratory," can provide valuable insights into the effectiveness of individual and combined risk mitigation options.

Series of Norovirus Outbreaks Caused by Consumption of Green Coral Lettuce, Denmark, April 2016.

Introduction: In early April 2016, an unusual high number of point-source outbreaks of gastrointestinal disease were reported to occur in Denmark.Methods: Outbreaks were individually investigated. Two analytical studies were performed. Patient stool samples collected and analysed; positive stool samples were sequenced over the polymerase and/or capsid gene areas. Implicated lettuce heads were collected and analysed for the presence of norovirus. Foods were traced-back and traced-forward and international alert systems applied.Results: A total of 23 linked point-source outbreaks occurred over the course of one week. Fresh green coral lettuce (Lollo Bionda lettuce) had been consumed in all settings. In a cohort study including 234 participants a dish containing green lettuce was associated with illness. Norovirus of Genogroup I (GI) was detected in samples from 28 patients comprising eight of the outbreaks. Sequencing showed GI.P2-GI.2. GI norovirus was detected in one of 20 examined lettuce heads. All lettuce consumed was supplied by the same packer who in turn had bought the lettuce from a wholesaler in France. The two lots of lettuce came from two different growers in different parts of France.Discussion: Green coral lettuce produced in France was found to have caused a large series of linked norovirus outbreaks in Denmark as established by a number of lines of evidence. A similar incidence occurred in 2010. Fresh lettuce increasingly appear to be a risk food for norovirus infections.

СОЧЕТАННЫЕ ТЕХНОЛОГИИ КОНСЕРВИРОВАНИЯ ПИЩЕВЫХ ПРОДУКТОВ С ИСПОЛЬЗОВАНИЕМ БИОЛОГИЧЕСКИХ БАРЬЕРОВ

In this work, we investigate a combined effect of bioprotective cultures and inert gas packaging on the preservation of semi-finished vegetable products under the conditions of standard refrigerated storage. For the preparation of semi-finished vegetable products, fruits of red and yellow bell pep-per, zucchini and eggplant, as well as celery stalks and Iceberg lettuce heads were used. These products were packaged using a flat multilayer film PA/adhesive/PE and a combined film material PET/A1/PE (Lyon company, Russia), along with food gas mixtures Biogon ®NC20 and Biogon ®NC40 (Linde Gas, Russia). Microbial single-strain preparations produced by Chr. Hansen (Den-mark) were used as biobarrier cultures. Technological recommendations for treating semi-finished vegetable products by a suspension of bioprotective cultures, which are resistant to the inert gas media of Biogon ® NC40, are presented. The products were packaged in a gas-barrier film using a mixture of Biogon ® NC40. The as-packaged semi-finished products were stored in a refrigeration chamber at a temperature not exceeding 4 ± 2 °C. The effect of the modified gas media of Biogon ® NC40 and Biogon ® NC20 on the viability of Lactobacillus sakei, Pediococcus acidilactici surva-tus, Lactobacillus and Leuconostoc carnosum cultures was studied. A mixture of Biogon NC40 and Lactobacillus sakei is found to be optimal for preserving the quality of semi-finished pepper, egg-plant and zucchini. Iceberg lettuce is best preserved using Leuconostoc carnosum. The proposed method for the bio-preservation of semi-finished vegetable products has been introduced into production in the Russian company 'Velikoross' (St.-Petersburg).

고온기 결구상추의 포장재와 포장방법 적용에 따른 선도 비교

Effects of different packaging methods for maintaining the shelf life and postharvest quality of iceberg lettuce (Lactuca sativa L.) were studied after harvesting in summer season. Lettuce heads were packaged in plastic crate with or without different films such as (A) Individual lettuce head sealed packaging with linear low density polyethylene (LLDPE) film; (B) Packaging lettuce head in plastic crate and wrapped with LLDPE film; (C): Individual lettuce head sealed packaging with perforated high density polyethylene (HDPE) film; (D) Packaging lettuce head in plastic crate and wrapped with perforated HDPE; and (E) Packaging lettuce head in plastic crate without any film (control), and stored at 2°C for 35 days. Several quality parameters such as fresh weight loss, SPAD (soil & plant analyzer development) meter value, respiration rate, moisture content and appearance of lettuce were investigated. The lettuce wrapped with individually- sealed LLDPE film showed the lowest weight loss and the highest SPAD value rendering the best appearance index among the treataments throughout the three-week storage period at 2oC. Extending the freshness of iceberg lettuce during low temperature storage will definitely increase the salability potential in the domestic market even during summer season.

Effects of Weed-Free Periods on Organic Romaine Lettuce Production

ABSTRACTWeed management in Romaine lettuce (Lactuca sativa L. var. longifolia) is an economic challenge for organic farmers. This study evaluated the effect of weed-free durations on crop yield and quality, weed densities and biomass, and weeding time in two growing seasons. Treatments included weedy entire-season; weed-free for 7 days after transplanting (DAT), 14 DAT, 21 DAT, 28 DAT, 35 DAT, 42 DAT; and weed-free entire season (49 DAT). Weeds were removed by hand-hoes and the time taken to weed each plot was recorded. Weed densities were recorded prior to each weeding and weed biomass was recorded at crop harvest. Total and marketable lettuce heads were recorded and crop quality was estimated. Weed interference up to 21 DAT resulted in approximately 45% total and 58% marketable yield loss. Weed control beyond this period did not result in significant (p < 0.05) increases in crop yield and quality. However, weed densities at the end of the season were 4- to 15-fold and weed biomass approximately 18-fold greater in plots kept weed-free only for 21 DAT compared with plots kept weed-free season-long. This suggested that weed seed-return may be a concern if late-season weeding is not conducted. To minimize weed seed-return, the plots would have to be kept weed-free for about 35 DAT. However, labor costs must be taken into consideration because the time required to hand-hoe was approximately 87 hr ha−1 person−1 greater in plots kept weed-free for 35 DAT compared with plots kept weed-free for 21 DAT.

EFFECT OF BIO-EXTRACTS ON GROWTH AND QUALITY OF LETTUCES

The aim of this work was to determine the effects of bio-extracts on growth and quality of lettuces. The experimental design was RCBD (Randomized Complete Block Design) with 3 treatments and 4 replications include chemical fertilizer (16-16-16), bio-extract of fish meal and bio-extract of soybean meal. This experiment was conducted at The Division of Crop Production, Faculty of Agricultural Technology, Rajamangala University of Technology Thanyaburi. The result of this study showed that the vegetative yield of butter head and red oak lettuces treated with bio-extract of fish meal and soybean meal was similar to chemical fertilizer. There was no statistically difference on the vegetative yield of red coral and green oak lettuces. Both of bio-extract of fish meal and soybean meal could increase the color of leaves in red oak and green oak lettuces than chemical fertilizer. Bio-extract of fish meal could increase the color of leaves in red coral and butter head lettuces than bio-extract of soybean meal and chemical fertilizer respectively.