Baby Lettuce Research Articles

Life cycle assessment of a high-tech vertical decoupled aquaponic system for sustainable greenhouse production

IntroductionAquaponics provide multiple benefits due to the simultaneous yield of vegetables and fish, however they are characterized by increased greenhouse gas emissions owing to intensive production system. The most appropriate method for quantifying the environmental effects of these systems is Life Cycle Assessment with which the identification of hotspots and the suggestion of improved production plans can be achieved. The purpose of the present study was to evaluate the environmental impact of a pilot high-tech aquaponic system utilized for the simultaneous production of baby lettuce and rocket as well as rainbow trout, in indicators such as Global Warming Potential.Materials and methodsTo achieve this goal, data on inputs and outputs were collected from 12 case studies that were implemented, combining different fertilizer treatments, substrate choices, plant species cultivated and water source provision. Life Cycle Assessment was performed using SimaPro v.9.4.0.2 software.ResultsThe results showcase that the optimal case studies include the cultivation of baby lettuce and rocket in perlite substrate using wastewater from fish and partial use of synthetic fertilizers. Indicatively, Global Warming Potential of these cases was calculated at 21.18 and 40.59 kg CO2-eq/kg of vegetable respectively. The parameter with the greatest impact on most of the environmental indicators was electricity consumption for the operation of the oxygen supply pump for the fish tanks, while greenhouse infrastructure had the greatest impact in Abiotic Depletion and Human Toxicity impact categories. In an alternative production scenario tested where renewable energy sources were used, system impacts were reduced by up to 50% for Global Warming Potential and 86% for Eutrophication impact. The results of this study aspire to constitute a significant milestone in environmental impact assessments of aquaponic production systems and the adoption of more sustainable farming practices.

Greenhouse production of baby leaf vegetables using rainbow trout wastewater in a high-tech vertical decoupled aquaponic system

IntroductionAquaponics is an integrated food production system that links recirculating aquaculture with hydroponics, leading to higher water use efficiency than conventional food production systems while also saving on fertilizers. In the present study, baby lettuce and baby rocket plants cultivated hydroponically in a deep water culture system using wastewater from rainbow trout were evaluated as part of a vertical decoupled aquaponic system.Materials and methodsMore specifically, three different nutrient solutions were supplied: a) using fish wastewater only (designated as Fish); b) fish wastewater enriched with synthetic fertilizers (Mix); and c) a typical nutrient solution (Hoagland) as the control. Both lettuce and rocket plants were monitored in these nutrient solutions and in two different substrates, peat and perlite, as an organic and an inert substrate, respectively. The purpose of this study was to assess a vertical decoupled aquaponic system with regard to the resource use efficiency, such as water, land, and energy, while evaluating plant cultivation in the different treatments in terms of yield, growth, nitrate concentration on the leaf tissue, and foliar analysis. The photosynthetic rate and leaf color indices were also considered in the plant evaluation.ResultsThe Mix–Peat treatment was the most efficient growing combination in terms of land and water use efficiency, with approximately 7% better land use efficiency while using 38% less water and 10% less fertilizer than Hoagland–Peat. Moreover, lettuce plants had the highest yield in the Mix–Peat treatment, at 2,497 g m−2, which was approximately 6% higher than that of Hoagland–Peat while not being inferior in the quality measures. On the other hand, the yield of rocket was significantly higher in the Hoagland–Peat treatment, being 18% higher than that of Mix–Peat and 30% higher than that of Fish–Peat. Overall, the study confirmed that aquaponic systems could lead to higher water use efficiency and savings in fertilizers without undermining the yield and quality of lettuce, while the vertical arrangement developed within the scope of this study can increase the land useefficiency of the system.

Optimization of vortex-assisted magnetic nanofluid based liquid phase microextraction for fast, green and reliable extraction of ibuprofen from real samples: Multivariate approach

In this research, the vortex-assisted magnetic nanofluid based liquid phase microextraction (VA-MNF-LPME) procedure was optimized using Box–Behnken Design (BBD) for the selective and reliable extraction of ibuprofen from aqueous solutions. Three MNFs were prepared and tested for the selective extraction of ibuprofen. Ultraviolet–visible spectrophotometry (UV–Vis) was used to determine the amount of ibuprofen and measurements were made at a wavelength of 238 nm. The effects of pH, MNF volume, vortex time, volume of back extraction solvent were optimized using BBD. Separation of the MNF phase containing the ibuprofen in aqueous solution was achieved using a neodymium magnet without the need for centrifugation step. Using optimized parameters (pH = 3.4, 690 μL of MNF, 100 s vortex and 230 μL of ethanol), the detection limit and working range of the V-MNF-LPME procedure were 0.6 ng mL−1 and 2–180 ng mL−1, respectively. Relative standard deviations and recovery (for 25 ng mL−1 of ibuprofen solution, N = 5) were 2.8% and 94.1%. Key validation parameters of the method were studied in detail and calculated under optimized conditions. The VA-MNF-LPME procedure was successfully applied to some drugs, baby lettuce and grape leaf samples in ten stages with a standard-addition approach, and quantitative recoveries were obtained (91.4–98.7%).

Response of hydroponic baby lettuce to UV-B radiation exposure during the growing period

Lettuce (Lactuca sativa L.) has a nutritional contribution comparable to other vegetables. It is produced in soil and hydroponics systems, outdoors or indoors, and in some cases, with the management of radiation. UV-B radiation exposure can influence the functional quality of vegetables and is becoming more frequent. Cultivars Kristine RZ and Versaï RZ were exposed to four radiation doses: UV-B0 (0 μW·cm-2), UV-B16 (16 μW·cm-2), UV -B33 (33 μW·cm-2) and UV-B58 (58 μW·cm-2), during 30 min for 10 days. Lettuce leaves were harvested twice. The leaf area of 'Versaï RZ' was not affected by radiation in the first harvest, while the high doses (33 and 58 µW·cm-2) reduced the leaf area of 'Kristine RZ' between 15-30 %, respectively. The radiation did not significantly impact the percentage of dry matter and the color parameters. However, functional compounds were affected. In general, the cv. Kristine RZ responded positively to the dose of 16 µW·cm-2 while 'Versaï RZ' to 58 µW·cm-2. An increase in the content of functional compounds was also observed in 'Versaï RZ' in the second harvest, and a reduction in the levels measured in 'Kristine RZ' indicated a different adaptation to UV-B radiation that must be studied individually.

Intermittence in irrigation management and nitrogen optimize yield and water use efficiency in baby lettuce

Aim of the study: To evaluate the influence of irrigation management strategies and nitrogen (N) on baby lettuce growth, yield, and water use efficiency in a protected environment. Area of study: Botucatu, SP, Brazil. Material and methods: The experiments were conducted in two consecutive cycles, and the treatments corresponded to the combination of irrigation management strategies with N doses. Irrigation strategies comprised 3 possibilities: continuous irrigation (Cont); intermittent irrigation with three irrigation pulses at one-hour intervals (Int1); and intermittent irrigation with irrigation depth split and applied at 7:00, 11:00, and 15:00 h (Int2). Two N doses were evaluated, 100 and 130 kg/ha of N, applied in daily fertigation according to the irrigation management strategies. Main results: Intermittent irrigation strategies (Int1 and Int2) promoted the highest vegetative growth, increased leaf water content, and increased total yield (49.55 and 55.30; 46.83 and 49.50 t/ha) and marketable yield (46.77 and 52.44; 45.11 and 47.17 t/ha) in the first and second cycles, respectively, in addition to optimizing water use efficiency. The N dose of 130 kg/ha increased the total yield (51.61 t/ha), marketable yield (48.98 t/ha), and water use efficiencies of total yield (53.60 kg/m³) and marketable yield (50.88 kg/m³) only in the first crop cycle. Research highlights: The use of intermittence in irrigation management proved to be more efficient in obtaining high yields and maximized the efficiency of use of water as a factor of production.

Extraction of ibuprofen from baby lettuces by natural deep eutectic systems

Vegetable crops can adsorb hazardous pollutants from water and soils. The occurrence of pharmaceuticals in the environment is considered a problematic matter with unknown long-term effects. Thus, the objective of this work was to develop, for the first time, a rapid, sensitive, and ecological methodology based on Natural Deep Eutectic Systems (NADES) to extract ibuprofen in baby lettuce samples. The proposed strategy involves a sustainable sample preparation step, leading to an efficient and selective analytical methodology suitable for high-throughput analysis (<3 samples min). NADES were designed and physicochemically characterized. The effect of experimental variables on extraction selectivity and efficiency: NADES composition, sample/solvent ratio, and extraction time and temperature were studied and optimized, resulting in 0.1 g of dry sample, 1 mL of choline chloride:glycerol 1:5, and 10 min of extraction at 80 °C. The limits of detection and quantification were 2.74 and 8.31 ng g−1 (dry weight), respectively; with a linear range of 8.31–4000 ng g−1 dw. The recovery % and RSD % were 98.1–99.6% and < 2.97%, respectively. The methodology and the sample preparation show excellent green performance using the greenness calculator, obtaining scores of 0.68 and 0.83. Finally, the ibuprofen uptake study revealed that baby lettuces adsorb ibuprofen at high concentration levels.

Risk assessment for uptake and accumulation of pharmaceuticals by baby leaf lettuce irrigated with reclaimed water under commercial agricultural activities

The use of reclaimed water to irrigate agricultural crops has increased in recent years as a consequence of water shortage constituting a potential risk for human health. The main objective of this study was to evaluate the impact on the soil-plant system and determining the accumulation of carbamazepine (CBZ), diclofenac (DCF), ketoprofen (KTP) and naproxen (NPX) in the edible part of lettuce under commonly used agricultural practices in commercial production. For this purpose, red oak baby lettuce (Lactuca sativa L.) was irrigated with reclaimed water fortified with different concentrations of pharmaceuticals. The study was carried out in two different scenarios: soil and tray. The tray experiments were conducted with substrate and took place at three different seasons of the year. Lettuce tissue sampled from these experiments were analysed 3 times during the lettuce growing cycle (first, second and third harvest). The practices of first harvest regrowth were also evaluated. For all experiments, CBZ showed the highest accumulation in lettuce leaves of the pharmaceuticals tested, showing a correlation between irrigation exposure time and pharmaceutical uptake. Unexpectedly, DCF was the compound with the highest uptake levels after regrowth practices. Results suggested that pharmaceuticals uptake could be directly associated with the irrigation method and possible accumulation in soil and substrates, while concentration of pharmaceuticals in substrates were 10 times higher. Based on the concentration values detected in lettuce leaves, the risk assessment suggests that no compounds imply any risk to human health, except CBZ for those on vegetarian diets in the tray scenario. Although commercial agricultural practices are usually not considered with regards to risk reduction, in this experiment we demonstrated that climatic conditions are a key factor in pharmaceuticals uptake and different agricultural practices (soil cropping and drip irrigation) can limit the presence of pharmaceutical compounds in crops.

In-door germination and seedling growth of green and red lettuce under LED-light spectrum and subsequent effect on baby leaf lettuce

The spectrum and intensity of light play a significant role in the primary and secondary metabolism of plants. Low intensity can make the photosynthetic process less efficient, while inadequate spectrum can impair plant growth and quality. This study investigates the effect of different LED light spectra at low intensity on germination and growth of lettuce (Lactuca sativa L.) seedlings under a temperature-controlled chamber and the subsequent impact on mature plants grown in a greenhouse under natural light. The purpose was to reach a commercial plant seedling using a low amount of energy to achieve the yield potential in a shorter period. The experiment was carried out in three trials. In trial 1, the effect of different LED light wavelengths [100% blue (B); 100% red (R); mixed light 1 (52% blue, 27% green and 21% red) (BGR1), and mixed light 2 (29% blue, 53% green and 17% red and 1% far red) (BGR2)] at low intensity (55 μmol m–2 s–1 and 12 h light photoperiod) and darkness (control) on germination of two lettuce cultivars [‘Levistro’ (green) and ‘Carmolí’ (red)] was evaluated in a controlled temperature chamber (20±1.2°C). In trial 2, the effect of the same light conditions of the first experiment on agronomic characteristics and pigment contents of lettuce seedlings compared to the natural light (control: 451±66 μmol m–2 s–1) were evaluated. In trial 3, the seedlings developed under different LED light wavelengths were transplanted to evaluate the subsequent effect on the growth of baby lettuce cultivated hydroponically in the greenhouse under natural light. The results of this study show that red wavelength reduced germination percentage, while lights with a higher blue component (B and BGR1) accelerated germination and increased the number of germinated seeds in ‘Levistro’. Red also delayed germination and decreased the number of germinated seeds in ‘Carmolí’ compared to darkness. Seedlings of ‘Levistro’ had a higher fresh weight (FW) than ‘Carmolí’. In addition, FW increased under BGR2 and R, which coincided with the highest number of leaves and leaf length. Nevertheless, fresh weight was higher under BGR2 and B after transplanting, coinciding with the highest number of leaves. A higher blue component of the light (B and BGR1) increased the dry matter percentage (DMP) of seedlings, but there was no significant difference after transplanting. Chlorophyll (CHL) a and b content increased under BGR2; however, the highest CHL a/b ratio was observed under BGR1 in ‘Levistro’ and B in ‘Carmolí’, but it was higher after transplanting when seedlings were grown under B. The anthocyanin (ANT) content of ‘Carmolí’ seedlings was promoted by a higher blue component of the light (B and BGR1) but significantly increased under natural light (control) at the highest intensity. This work shows that varying the spectrum at low intensity can positively modify the growth and biochemical characteristics of lettuce seedlings, although the effect depends on the cultivar. This modification improves the performance of plants during greenhouse growth after transplanting, especially seedlings grown under B and BGR2. Highlights - Blue light enhanced germination and increased the number of germinated seeds of green lettuce. - High blue component lights improved the morphology, dry matter percentage, and chlorophyll a/b ratio of lettuce seedlings. - Blue and full-spectrum lights applied to lettuce seedlings affect fresh weight after transplanting. - The anthocyanin content of seedlings was stimulated by blue light at 55 μmol m–2 s–1, but even more so by PAR of natural light at 451 μmol m–2 s–1.

The effect of lime oil emulsion on seed germination, antimicrobial and antioxidant properties of hydroponic baby green oak lettuce for the assurance of safety from farm to fork

AbstractThis study aimed to investigate the effect of soaking lettuce seeds in a lime oil emulsion at 0 (control), 10, 20, 30, 40, and 50 μl/ml before growing them in a hydroponic plantation. After harvesting baby lettuce at Day 21, all lettuce was kept inside the refrigerator (4 ± 2°C) for the next 7 days. The microbiological quality and the antioxidant properties of lettuce were also investigated. The results revealed that while lime oil emulsion at 10 μl/ml had no effect on seed germination, it delayed the growth of black spot molds and reduced the incidence and severity of black spot fungal disease in baby lettuce by around 87.5%. The morphology of Alternaria sp. and Cercospora sp. shows ruptured conidia and shriveled and damaged mycelium, with a decrease in fungal infection in baby lettuce. In addition, α‐terpineol (~53%) was identified from treated baby lettuce after 21 days that was able to inhibit growth of molds. Regarding the microbial eating quality of baby lettuce, mesophiles (~3.0 log10 CFU/g), psychrophiles (~3.6 log10 CFU/g), total coliforms (~1.3 log10 CFU/g), total yeast and mold (~2.0 log10 CFU/g) and lactic acid bacteria (~3.7 log10 CFU/g) were significantly reduced in the treated lettuce. The antioxidant capacity in the treated lettuce was higher than the control and maintained stability without affecting its leafy green color and chlorophyll content. This finding is critical for horticulture, particularly in hydroponic vegetable farming. It can be applied in food safety from farm to fork.

The Effect of Nitrogen Fertilizer and Water Supply Levels on the Growth, Antioxidant Compounds, and Organic Acids of Baby Lettuce

Applications of solutions with various organic acids have been widely demonstrated as effective disinfectants on lettuce. However, agronomic techniques of improving the concentration of internal organic acids in lettuce are not well investigated. Hereon, changes in growth, antioxidants, and organic acids of baby lettuce (Lactuca sativa L. var. longifolia) resulting from different levels of nitrogen fertilizer (0.10, 0.14, 0.18, or 0.22 g/5 kg soil) and water supply (300, 600, or 900 mL) were investigated. The pot experiment was conducted under a net house at North-West University (Mafikeng Campus), South Africa. Data on growth parameters (number of leaves and leaf area) and chlorophyll concentration were sampled weekly until leaf organic acids (citric, malic, and tartaric), total antioxidant compounds (TAO), as well as dry matter content, were measured at harvest. Reducing the amount of water supplied to baby lettuce significantly (p &lt; 0.05) increased the chlorophyll concentration, leaf area, TAO, citric acid, and malic acid. The number of leaves and the leaf tartaric acid concentrations were increased by increasing the treatment levels. It was conclusive that decreasing water supply increases the organic acids regardless of the nitrogen level.

Exploitation of Liquid Digestate as the Sole Nutrient Source for Floating Hydroponic Cultivation of Baby Lettuce (Lactuca sativa) in Greenhouses

Sustainable agriculture relies on replacing fossil-based mineral fertilizers, which are highly cost-energetic to produce, and demand extensive use of scarce natural resources. Today, agronomic practices within the concept of circular economy are emerging and, as such, the exploitation of digestate as a biofertilizer and soil amender is extensively investigated. This study aimed at evaluating the agronomic potential of liquid digestate as the sole nutrient source for hydroponic cultivation of baby lettuce in greenhouses. Growth rate, physiological responses, concentration of secondary metabolites, and nutrient uptake were compared between baby leaf lettuce grown in digestate in concentrations of 5, 10, and 20% diluted in water (either with or without pH adjustment) and in Hoagland solution (control). Results showed that the production yield was negatively correlated with the concentration of the added digestate. Nevertheless, the antioxidant capacity was significantly enhanced in 5 and 10% liquid digestate treatments compared to the control. Additionally, the nutrient composition in the baby leaf lettuce and the reduction in nutrient concentrations in the growth media demonstrated efficient mineral uptake by the plants. Thus, the application of liquid digestate as a fertilizer in hydroponic systems is a promising practice to recover residual resources, leading to the transition towards more sustainable greenhouse production.

Configuration by Osmotic Eustress Agents of the Morphometric Characteristics and the Polyphenolic Content of Differently Pigmented Baby Lettuce Varieties in Two Successive Harvests

Salinity eustress is one of the pre-harvest factors that can be used to improve the phytochemical profile and the quality attributes of horticultural species, and most of the studies are carried out using NaCl. In this work, we compared the effect of three mildly saline iso-osmotic nutrient solutions (NS) differing in the cation employed (either K, Na, or Ca) in baby lettuce cultivated in a floating system. Specifically, we analyzed the impact on key morphological traits and polyphenol composition in leaves in a completely randomized design experiment with the following experimental factors and levels: two differently pigmented lettuce varieties (green and full red), three NSs (20 mM KCl, 20 mM NaCl, 13.3 mM CaCl2, each with a final ionic concentration of 40 mM), and two successive harvests. The lettuce response to mild salinity was multifaceted and with a marked role for the cultivar factor and its interactions, as also indicated by multivariate analysis. The morphological response of baby lettuce to the saline solutions was predominantly affected by the osmolarity, and ion-specific alleviating or detrimental effects were not observed. The phytochemical analysis revealed significant interactions among all tested factors, with ion-specific differences over some of the detected phenolics. This is consistent with the high sensitivity of this class of bioactive compounds to environmental factors. This work indicated that certain combinations of the experimental factors tested can be exploited to improve the biochemical profile and possibly the nutraceutical quality of baby lettuce in a floating system.

Effect of Reduced Nitrogen and Supplemented Amino Acids Nutrient Solution on the Nutritional Quality of Baby Green and Red Lettuce Grown in a Floating System

Excessive nitrogen fertilization results in nitrate accumulation in leafy vegetables. Reducing the dose of mineral nitrogen or using alternate fertilizers lowers the nitrate accumulation; however, a critical minimum level of mineral nitrogen is necessary to maintain yield and nutritional quality. The aim of this study was to evaluate the effect of two levels of mineral nitrogen (100% and 50%) and three levels of an amino acid solution (0, 0.3, and 0.9%) in the nutrient solution of two baby lettuce cultivars (green and red) grown in a floating system. Nitrogen reduction did not affect yield (12.9–13.4 and 11.0–11.3 g/plant, respectively) but reduced nitrate accumulation (by 43 and 19%, respectively) in both green and red lettuce, while enhancing phenolic content (by 28%) and antioxidant capacity (by 69%) in green lettuce and soluble solid (by 7%) and total chlorophyll content (by 9%) in red lettuce. Although nitrate accumulation was prevented (&lt; 355 mg/kg FW) and most nutritional components increased in both lettuce types by amino acids supplementation, plant growth was negatively affected, especially in red lettuce, in both concentrations of amino acids (reduction by 9 and 35% in 0.3 and 0.9%, respectively). In both lettuce types, proline content increased by 0.9% amino acids supplementation (by 45%), implying a probable induction of a stress condition. Mineral nutrients were slightly affected by nitrogen reduction, which was probably perceived as an abiotic stress.

Mixing fresh-cut baby green and red leaf lettuce from soilless cultivation preserves phytochemical content and safety

The objective of this study was to evaluate the impact of different mixtures of two fresh-cut baby lettuce (Lactuca sativa L. var. crispa cv. Lollo Bionda [LB] and cv. Lollo Rossa [LR]) cultivars on lettuce phytochemical composition during postharvest. Lettuces were grown in a soilless culture system with continuous flotation (FL) in a greenhouse, mixed at harvest and packaged in polypropylene bags and stored at 4 °C for 9 days (d9). Mixes were made of 100, 75, 50, 25 and 0% of LB, respectively. The results showed that the phytochemicals were preserved during storage. In specific, 25LB had the highest pigment content on d1, while 50LB and 25LB had the highest inherent quality on d1.FL led to a reduced microbial contamination, thus, limiting its growth during storage. The results have revealed that high quality and microbiologically safe baby leaf vegetables (BLV), can be obtained by means of FL. The adopting a mix of lettuce cultivars could represent a positive postharvest practice to preserve the phytochemicals of BLV throughout their shelf life.

Effect of Vegetal- and Seaweed Extract-Based Biostimulants on Agronomical and Leaf Quality Traits of Plastic Tunnel-Grown Baby Lettuce under Four Regimes of Nitrogen Fertilization

Nitrogen (N) fertilizers play a crucial role in agriculture, representing a powerful tool for farmers for increasing yields throughout the seasons under both optimal and suboptimal conditions. At the same time, their synthetic/chemical nature could have several influences on ecosystems and human health. For this reason, there is an urgent need to find new and more sustainable means of production to increase plant productivity and optimize nitrogen use. An experiment was conducted in a plastic tunnel to assess the response of baby lettuce crop to the foliar application of three plant biostimulants (PBs): Legume-derived protein hydrolysate (LDPH) ‘Trainer®’, tropical plant extract (TPE) ‘Auxym®’ and seaweed extract (SwE) from Ecklonia maxima ‘Kelpak®’ under different N rates of 0, 10, 20 and 30 kg N·ha−1. The responses of baby lettuce plants were assessed in terms of yield, growth parameters and physicochemical composition of the leaves. The fresh yield of baby lettuce in both biostimulant-treated and untreated plants was positively affected by increasing N rates from 0 to 20 kg N·ha−1, reaching a plateau thereafter indicating luxury N conditions at 30 kg N·ha−1. However, high N fertilizer application (20 and especially 30 kg N·ha−1) resulted in undesirable decreases in antioxidant activities and total ascorbic acid (TAA). Under non-fertilized regimens, foliar PBs application boost growth and yield of baby lettuce in comparison to non-treated plants. Foliar spray with LDPH and especially SwE elicited significant increases in marketable fresh yield (averaging 14%, 6% and 7% at 10, 20 and 30 kg N·ha−1, respectively) compared to TPE and untreated plants. Improved agronomical performance of baby lettuce under optimal (10 kg N ha−1) and especially suboptimal N regimens (0 kg N ha−1) was associated with increasing photochemical efficiency and a better activity of photosystem II (higher Soil Plant Analysis Development-SPAD index and chlorophyllous pigments biosynthesis). The application of LDPH enhanced antioxidant capacity and TAA in baby lettuce leaf and did not increased nitrate content as recorded in SwE and TPE treatments. Overall, plant biostimulants may be considered as a sustainable tool of production to increase leafy vegetable productivity in low fertility soils.

Influence of mild saline stress and growing season on yield and leaf quality of baby lettuce grown in floating system

Consumer demand has been increasing and many vegetable farmers have oriented their production plans towards baby leaf vegetables such as lettuce. The management of the nutrient solution as well as the growing conditions could significantly affect the yield and quality of leafy vegetable crops. The aim of the present work was to determine the effects of increasing the level of salinity in the nutrient solution (1, 10 or 20 mM NaCl) during two consecutive growing seasons (spring and autumn) on the yield and quality of Lactuca sativa L. var. acephala grown in floating raft culture. Increased salinity in the nutrient solution decreased marketable yield and dry biomass with more detrimental effect during the warm season. The percentage of yield reduction in comparison to the non-saline control was 7 and 20% in the spring season and 4 and 13% in the autumn growing season at 10 and 20 mM NaCl, respectively. Plants grown in the spring season exhibited higher yield and dry biomass but lower leaf quality than those grown in the autumn season. When averaged over salinity level the lipophylic antioxidant activity, total ascorbic acid, phenols and nitrate contents were significantly increased by 7.1, 20.1, 19.4 and 24.4%, respectively, in plants grown in spring as compared to autumn growing season. The floating system could be considered an efficient and low-cost tool to improve quality aspects through proper management of the salt concentration in the nutrient solution with an acceptable yield reduction.

Suitability of chlorine dioxide as a tertiary treatment for municipal wastewater and use of reclaimed water for overhead irrigation of baby lettuce

Reclaimed wastewater used for agricultural irrigation should meet specific microbiological standards in order to prevent microbial contamination of the irrigated produce. The objective of this study was to evaluate the suitability of chlorine dioxide (ClO2) for the disinfection of secondary-treated municipal wastewater and its subsequent use for overhead irrigation in greenhouse production of baby lettuce. The impact of reclaimed water tertiary-treated with ClO2 on E. coli concentration, the presence of pathogenic bacteria, and the occurrence of chlorates as disinfection by-products was evaluated in water and in baby lettuce. E. coli was quantified using both conventional plating methods and a quantitative real time PCR (qPCR) method with propidium monoazide (PMA) pre-treatment to differentiate between viable and non-viable bacteria. Population density of cultivable E. coli was significantly lower (p < 0.05) in reclaimed water, tertiary-treated using ClO2 (ClO2W), when compared with secondary-treated municipal wastewater (SW). However, no significant differences in viable but non-cultivable (VBNC) E. coli loads were observed between treatments when quantifying using the PMA-qPCR method. These results could indicate that ClO2 treatment of water did not kill the bacteria but it induced bacteria to enter a VBNC state. The proportion of samples positive for the presence of pathogenic bacteria was lower in ClO2W (1/8) compared with SW (7/8). Significantly lower E. coli counts (p < 0.05) were detected in plants irrigated with ClO2W compared with those irrigated with SW. Relationship between higher E. coli counts and the presence of pathogens was observed when lettuce samples were analyzed by PMA-qPCR (Mann-Whitney U Test, p < 0.05). Baby lettuce irrigated with ClO2W showed a significantly higher concentration of chlorates than lettuce irrigated with SW. The quantification of viable bacteria using molecular methods suggests that the efficacy of ClO2 could be overestimated when conventional plating quantification methods are used. Additionally, the accumulation of chlorates in the tissue should be considered as it represents an adverse effect of this disinfection treatment.

Irrigating Lettuce with Wastewater Effluent: Does Disinfection with Chlorine Dioxide Inactivate Viruses?

Reclaimed water obtained from urban wastewater is currently being used as irrigation water in water-scarce regions in Spain. However, wastewater can contain enteric viruses that water reclamation treatment cannot remove or inactivate completely. In the present study, greenhouse-grown baby lettuce ( L.) was irrigated with secondary treatment effluent from a wastewater treatment plant untreated and treated using chlorine dioxide (ClO). The effect of ClO treatment on the physicochemical characteristics and the presence of enteric viruses in irrigation water and lettuce was assessed. The presence of human noroviruses genogroups I and II (NoV GI and NoV GII), and human astroviruses (HAstV), was analyzed by real-time polymerase chain reaction (RT-qPCR). Additionally, to check for the loss of infectivity induced by the disinfection treatment, positive samples were re-analyzed after pretreatment with the intercalating dye PMAxx before RNA extraction and RT-qPCR. There were no significant differences in the proportion of positive samples and the concentration of enteric viruses between treated and untreated reclaimed water without PMAxx pretreatment ( > 0.05). A significantly lower concentration of NoV GI was detected in ClO-treated water when samples were pretreated with PMAxx ( < 0.05), indicating that inactivation was due to the disinfection treatment. Laboratory-scale validation tests indicated the suitability of PMAxx-RT-qPCR for discrimination between potentially infectious and ClO-damaged viruses. Although the applied ClO treatment was not able to significantly reduce the enteric virus load of the secondary effluent from the wastewater treatment plant, none of the lettuce samples analyzed ( = 36) was positive for the presence of NoV or HAstV.

Disinfection by-products in baby lettuce irrigated with electrolysed water.

Irrigation water disinfection reduces the microbial load but it might lead to the formation and accumulation of disinfection by-products (DBPs) in the crop. If DBPs are present in the irrigation water, they can accumulate in the crop, particularly after the regrowth, and be affected by the postharvest handling such as washing and storage. To evaluate the potential accumulation of DBPs, baby lettuce was grown using irrigation water treated with electrolysed water (EW) in a commercial greenhouse over three consecutive harvests and regrowths. The impact of postharvest practices such as washing and storage on DBP content was also assessed. Use of EW caused the accumulation of chlorates in irrigation water (0.02-0.14 mg L-1 ), and in the fresh produce (0.05-0.10 mg kg-1 ). On the other hand, the disinfection treatment had minor impact regarding the presence of trihalomethanes (THMs) in water (0.3-8.7 μg L-1 max), and in baby lettuce (0.3-2.9 μg kg-1 max). Disinfection of irrigation water with EW caused the accumulation of chlorates in the crop reaching levels higher than the current maximum residual limit established in the EU legislation for leafy greens. © 2017 Society of Chemical Industry.

Loop-Mediated Isothermal Amplification-Lateral-Flow Dipstick (LAMP-LFD) to detect Toxoplasma gondii oocyst in ready-to-eat salad

The apicomplexan parasite Toxoplasma gondii is the causative agent of toxoplasmosis, a foodborne zoonosis with a global distribution and estimated to cause up to 20% of the total foodborne disease burden in Europe. Association between T. gondii infection and the consumption of unwashed raw fruits and vegetables contaminated with oocysts has been reported and the increasing habit to eat pre-washed ready-to-eat salads poses a new potential risk for consumers. It is therefore important to trace the occurrence of potential contamination with this parasite to guarantee the safety of ready-to-eat vegetables. Detection of T. gondii in vegetables by molecular techniques has been achieved but low sensitivity (PCR) or expensive equipments (qPCR) limit routine applicability. Here, we describe the development and validation of a sensitive and robust method relying on a LAMP assay, targeting the 529 bp locus, to detect T. gondii oocysts down to 25 oocysts/50 g in ready-to-eat baby lettuce. The LAMP has been also adapted for a faster visualization of the result by a lateral flow dipstick chromatographic detection method.