Antioxidant capacity of leafy vegetables as affected by high tunnel environment,fertilisation and growth stage

BACKGROUND: This study was conducted to evaluate the influences of protected environment, organic fertilisation and growth stage on the oxygen radical absorbance capacity (ORAC) values of leafy vegetables. RESULTS: In a first experiment, pac choi grown in high tunnels had significantly lower ORAC than field‐grown plants. Organic fertiliser markedly increased the antioxidant capacity of pac choi compared with conventional treatment, especially in the open field. However, both open field and organic production resulted in significantly lower yield and more severe leaf damage due to insect attack. In a second study, spinach showed the highest ORAC, followed by pac choi, red leaf lettuce and romaine lettuce. A significant decline in ORAC under high tunnel production was observed only in spinach. In contrast to the first trial, organic fertilisation did not cause an increase in antioxidant capacity of the leafy vegetables. The ORAC values of spinach from the open field and pac choi from high tunnels were significantly higher when harvested at the mature head stage than at the baby size stage. CONCLUSION: Further studies will help to elucidate effects of genotype, growth stage, and production environment on antioxidant capacities of vegetables and may lead to recommended practices to maximise antioxidant capacity of vegetable crops. Copyright © 2007 Society of Chemical Industry     

Comparison of phenolic acids in organically and conventionally grown pac choi (Brassica rapa L. chinensis)

BACKGROUND: Field and greenhouse studies were performed to investigate whether organic production methods influenced levels of phenolic acid compounds in pac choi (Brassica rapa L. chinensis cv. Mei Qing Choi) compared with conventional cultivation. RESULTS: In the field experiment, organic fertilisation (compost + fish emulsion) resulted in significantly higher phenolic concentrations compared with conventional fertilisation (NPK + CaNO₃) under both high tunnel and open field environments. Increased phenolics were accompanied by a significant reduction in plant fresh weight and dry weight, probably due to nitrogen deficiency. However, the elevated level of phenolics in organically grown pac choi could also have been due to confounding effects of nitrogen availability, insect attack and pesticide application. A follow‐up greenhouse experiment further demonstrated a significant increase in phenolic compounds and a reduction in yield with organic fertiliser (vermicompost + fish fertiliser) relative to conventional treatment (slow release inorganic fertiliser). Preventive insecticide application did not affect the phenolic levels in pac choi under either organic or conventional fertilisation. CONCLUSION: Given that higher phenolic content in pac choi was associated with low nitrogen availability and considerable yield reduction, research is needed to determine the extent to which phenolic compounds may differ in organic and conventional pac choi when nutrient levels are adjusted to produce comparable yields. Additional study is also warranted to determine the extent to which insect attack might contribute to elevated phenolic content in organic pac choi. Copyright © 2009 Society of Chemical Industry     

Consumer sensory analysis of organically and conventionally grown vegetables

ABSTRACT:  Consumers of organically grown fruits and vegetables often believe that these products taste better than conventional produce. However, comparison of produce from supermarket shelves does not permit adequate assessment of this consumer perception, given potentially confounding cultivar and environmental effects. We used replicated side-by-side plots to produce organic and conventional vegetables for consumer sensory studies. In one test, red loose leaf lettuce, spinach, arugula, and mustard greens, grown organically and conventionally, were evaluated for overall liking as well as for intensity of flavor and bitterness. Another consumer test was conducted comparing organically and conventionally grown tomatoes, cucumbers, and onions. Overall, organically and conventionally grown vegetables did not show significant differences in consumer liking or consumer-perceived sensory quality. The only exception was in tomatoes where the conventionally produced tomato was rated as having significantly stronger flavor than the organically produced tomato. However, overall liking was the same for both organic and conventional samples. As conventional tomatoes also were scored marginally significantly higher in ripeness and a positive correlation was found between ratings of flavor intensity and ripeness, the flavor difference observed could not be simply ascribed to the contrasting growing conditions. Consumer panelists in both tests considered organic produce to be healthier (72%) and more environmentally friendly (51%) than conventional produce, while 28% considered organic produce to have better taste. Covariance analysis indicated that consumer demographics affected sensory comparisons of organic and conventional lettuce and cucumbers. Future study is needed to substantiate the influence of segmentation of consumers on their preference for organic food.     

Effects of organic and conventional production systems on quality and nutritional parameters of processing tomatoes

BACKGROUND: The impact of organic and conventional production systems on quality and nutritional parameters of fruits and vegetables is still under discussion. The objective of this study is to determine whether the production system has a significant effect on the quality and nutritional content of one variety of processing tomatoes grown on a commercial scale by comparing three different growers for two production years. RESULTS: Conventional tomatoes appeared to be more mature at time of harvest as determined by visual inspection of color. Total and soluble solids were significantly higher and consistency was greater in organic tomatoes. Differences in nutrient content were not statistically significant between production systems. Glutamate, glutamine, and tyrosine levels were significantly higher in conventional tomatoes, as were total nitrogen and ammonium concentrations. CONCLUSION: Results from this study show that nutritional and quality parameters vary greatly by grower, production system, and year for the same tomato cultivar. Significantly higher average soluble solids content and consistency in organic tomatoes are especially important to the processing tomato industry. The apparent slower development of organic tomatoes may be responsible for many of the significant findings in this study and may explain some of the conflicting reports in previous literature. Copyright © 2008 Society of Chemical Industry     

Micronutrient contents in organic and conventional tomatoes (Solanum lycopersicum L.)

Organic food is associated by the general public with improved nutritional properties, and this has led to increasing demand for organic vegetables. The objective of this study was to investigate whether there were any differences in the micronutrient contents in organic and conventional tomatoes (Solanum lycopersicum L.). Two tomato cultivars ‘Lladó’ and ‘Antillas’ grown organically and conventionally were compared regarding their micronutrient in terms of K, Ca, Na, Mg, Fe, Zn, Mn, Cu, lycopene, ß‐carotene, ascorbic, malic and citric acids, and total phenolic compound content. Cultivar ‘Lladó’ had the highest concentration of the nutrient lycopene, ß‐carotene, Fe, Zn, Mn and Cu. Where cultivation method affected the concentration of ascorbic acid and Mn, only one cultivar was affected. For all nutrients examined, cultivar differences were greater than differences because of cultivation method. This study confirms that the most important variable in the micronutrient content of tomatoes is cultivar; organically grown tomato is no more nutritious than conventionally grown tomato when soil fertility is well managed.     

Phytochemical phenolics in organically grown vegetables

Fruit and vegetable intake is inversely correlated with risks for several chronic diseases in humans. Phytochemicals, and in particular, phenolic compounds, present in plant foods may be partly responsible for these health benefits through a variety of mechanisms. Since environmental factors play a role in a plant's production of secondary metabolites, it was hypothesized that an organic agricultural production system would increase phenolic levels. Cultivars of leaf lettuce, collards, and pac choi were grown either on organically certified plots or on adjacent conventional plots. Nine prominent phenolic agents were quantified by HPLC, including phenolic acids (e. g. caffeic acid and gallic acid) and aglycone or glycoside flavonoids (e. g. apigenin, kaempferol, luteolin, and quercetin). Statistically, we did not find significant higher levels of phenolic agents in lettuce and collard samples grown organically. The total phenolic content of organic pac choi samples as measured by the Folin-Ciocalteu assay, however, was significantly higher than conventional samples (p < 0.01), and seemed to be associated with a greater attack the plants in organic plots by flea beetles. These results indicated that although organic production method alone did not enhance biosynthesis of phytochemicals in lettuce and collards, the organic system provided an increased opportunity for insect attack, resulting in a higher level of total phenolic agents in pac choi.     

Qualitative and nutritional differences in processing tomatoes grown under commercial organic and conventional production systems

ABSTRACT:  Organically grown products experienced a doubling in percent penetration of organic sales into retail markets during the period from 1997 to 2003; however, there is still a debate over the perceived quality advantage of organically grown fruits and vegetables. In a study focusing on commercial production of processing tomatoes, samples were analyzed from 4 growers with matched organic and conventional fields. For the 4 growers studied, individual analysis of variance results indicated that tomato juice prepared from organically produced tomatoes on some farms was significantly higher in soluble solids (°Brix), higher in consistency, and titratable acidity, but lower in red color, ascorbic acid, and total phenolics content in the microwaved juice. Results were significantly different among specific growers, and this may be attributed to differences in soil type and soil nutrients, tomato cultivar, environmental conditions, or other production-related factors. Higher levels of soluble solids, titratable acidity, and consistency are desirable for the production of tomato paste, in that tomatoes with these attributes may be more flavorful and require less thermal treatment. This has the potential to result both in cost savings from less energy required in paste manufacture and potentially a higher quality product due to less thermal degradation of color, flavor, and nutrients. Future work may involve a larger number of commercial growers and correlation to controlled university research plots.     

Tomato pulp quality from transgenic fruits with reduced polygalacturonase (PG)

The physico-chemical and sensory properties of tomato pulps (i.e. diced tomatoes with 30% tomato juice as packing medium), prepared from transgenic tomato (Lycopersicon esculentum) fruits with reduced levels of polygalacturonase (PG) activity due to the expression of a PG antisense gene, were evaluated. The application of genetic modification yields products that have improved viscosity (40–60%), colour (30–40%) and many sensory attributes in comparison with their conventional counterparts.     

Comparison of physicochemical,microscopic and sensory characteristics of ecologically and conventionally grown crops of two cultivars of tomato (Lycopersicon esculentum Mill.)

BACKGROUND: Numerous studies have compared ecologically produced foods with conventionally produced competitors, with contradictory results. In this work we investigated the physicochemical, microscopic and sensory properties of two tomato cultivars (Lladó and Antillas), which were grown both ecologically and conventionally. RESULTS: The physicochemical variables size, weight, firmness, total acidity, pH, total solids content, lycopene content and CIELab a*, b*, a*/b*, C* and h* were all significantly influenced by cultivar, as were the sensory variables external colour, internal colour, external aroma intensity and flavour persistence. Compared with conventionally grown tomatoes, ecologically grown tomatoes had larger total solids contents and larger values of the CIELab colour parameters b*, C* and h*, but smaller sizes and weights and smaller values of the CIELab parameter ratio a*/b*; however, these physicochemical differences were insufficient for growing method to have a significant influence on any of the sensory attributes that were evaluated. Microscopy showed the influence of cultivar on lycopene content, but no other structural differences were observed between the two cultivars or between tomatoes grown by different methods. CONCLUSIONS: The statistically significant differences found in this study were mainly between cultivars rather than between tomatoes grown using different management practices. Copyright © 2009 Society of Chemical Industry     

Preharvest evaluation of coliforms, Escherichia coli, Salmonella, and Escherichia coli O157:H7 in organic and conventional produce grown by Minnesota farmers

Microbiological analyses of fresh fruits and vegetables produced by organic and conventional farmers in Minnesota were conducted to determine the coliform count and the prevalence of Escherichia coli, Salmonella, and E. coli O157:H7. A total of 476 and 129 produce samples were collected from 32 organic and 8 conventional farms, respectively. The samples included tomatoes, leafy greens, lettuce, green peppers, cabbage, cucumbers, broccoli, strawberries, apples, and seven other types of produce. The numbers of fruits and vegetables was influenced by their availability at participating farms and varied from 11 strawberry samples to 108 tomato samples. Among the organic farms, eight were certified by accredited agencies and the rest reported the use of organic practices. All organic farms used aged or composted animal manure as fertilizer. The average coliform counts in both organic and conventional produce were 2.9 log most probable number per g. The percentages of E. coli-positive samples in conventional and organic produce were 1.6 and 9.7%, respectively. However, the E. coli prevalence in certified organic produce was 4.3%, a level not statistically different from that in conventional samples. Organic lettuce had the largest prevalence of E. coli (22.4%) compared with other produce types. Organic samples from farms that used manure or compost aged less than 12 months had a prevalence of E. coli 19 times greater than that of farms that used older materials. Serotype O157:H7 was not detected in any produce samples, but Salmonella was isolated from one organic lettuce and one organic green pepper. These results provide the first microbiological assessment of organic fruits and vegetables at the farm level.     

Use of alginate or zein as edible coatings to delay postharvest ripening process and to maintain tomato (Solanum lycopersicon Mill) quality

BACKGROUND: Edible coatings could be effective tools for delaying the ripening process of fruits. Alginate or zein as edible coatings were assayed in tomato in order to maintain parameters related to quality during postharvest storage. RESULTS: Coated tomatoes showed lower respiration rate and ethylene production than control ones, with a twofold lower concentration of ethylene precursor. In addition, the evolution of parameters related to tomato quality losses, such as softening, colour evolution and weight loss, was significantly delayed (4–6 days on average) in coated tomatoes as compared to controls. Thereafter, sugars, organic acids (and especially ascorbic acid) and scores from sensory analysis remained at much higher levels at the end of storage in treated than in control tomatoes. CONCLUSIONS: Coatings based on alginate or zein could be effective tools for delaying the tomato‐ripening process during postharvest storage, and in turn maintaining tomato quality and its acceptability by consumers. Copyright © 2008 Society of Chemical Industry     

Comparison of mineral concentrations in commercially grown organic and conventional crops – Tomatoes (Lycopersicon esculentum) and lettuces (Lactuca sativa)

Trace element concentrations and stable nitrogen isotope data (δ¹⁵N‰) from tomatoes (Lycopersicon esculentum) and lettuces (Lactuca sativa) were subjected to multivariate analysis in an attempt to distinguish between conventional and organic cultivation. This approach improved the correct classification of tomato samples but appears to have had a limited effect on lettuces. Our findings support the growing body of evidence which suggests that systematic differences in the concentrations of certain elements such as manganese, calcium, copper, and zinc may occur between crops cultivated under organic and conventional regimes possibly due to the presence of elevated levels of arbuscular mycorrhizal fungi (AMF) in soils cultivated organically. We assert that such differences in elemental composition may be useful as ‘indicators of authenticity’. However, we recognise the limitation that this approach may be restricted to horticultural crops where there are significant differences in agricultural practice such as conventional-hydroponic versus soil-grown organic tomatoes.     

Cultivar choice provides options for local production of organic and conventionally produced tomatoes with higher quality and antioxidant content

BACKGROUND: Tomatoes (Solanum lycopersicum L.) are widely consumed and well known for their health benefits, many of which have been associated with the high levels of antioxidants present in tomatoes. With a growing interest in local and organic foods, it would be helpful to determine whether farmers could naturally improve the quality and antioxidant content of tomatoes for sale in local markets. This study evaluated antioxidant properties, quality attributes, and yield for 10 tomato cultivars grown for 2 years using certified organic and conventional practices. RESULTS: Cultivar and year effects impacted (P < 0.05) all tests conducted, while growing method influenced (P < 0.05) yield, soluble solids content, ascorbic acid, and antioxidant radical scavenging capacity. Even when accounting for year‐to‐year variability, cultivars in the highest groups had 1.35‐ to 1.67‐fold higher antioxidant levels than cultivars in the lowest groups. ‘New Girl’, ‘Jet Star’, ‘Fantastic’, and ‘First Lady’ were always in the highest groups, while ‘Roma’ and ‘Early Girl’ consistently had the lowest antioxidant content. CONCLUSION: Compared to production practices and environmental effects of years that are generally beyond the control of small‐scale producers, choice of cultivar provides the simplest and most effective means of increasing antioxidant properties. Knowledge of tomato cultivars with naturally higher antioxidant levels could assist smaller‐scale producers to grow fruit that may provide a competitive advantage and the opportunity to capitalize on the increasing popularity of locally grown, high‐quality fresh produce. Copyright © 2010 Society of Chemical Industry     

Free and bound phenolic compounds in leaves of pak choi (Brassica campestris L. ssp. chinensis var. communis) and Chinese leaf mustard (Brassica juncea Coss)

Eleven pak choi cultivars and two leaf mustard cultivars grown under field conditions in China were investigated for the free polyphenol content in their outer and inner leaves, as well as in their leaf blades and leaf stalks. In most cases, there were no significant differences between the hydroxycinnamic acid derivative and flavonoid derivative contents in the outer and inner leaves for the 13 cultivars. However, the contents of blades and stalks differed: hydroxycinnamic acids and flavonoids were present in greater amounts in the leaf blade than in the leaf stalk. Trace or small amounts of flavonoids were detected in the pak choi and leaf mustard stalks. Additionally, the bound phenolic contents of two pak choi cultivars and two leaf mustard cultivars were investigated. The concentrations of cell wall-bound phenolic compounds were higher in the leaf blade than in the leaf stalk under field conditions in China. These compounds represent only a minor portion of the total phenolic contents (flavonoids and hydroxycinnamic acids) in leaf stalks (0.81–1.18%) and leaf blades (0.05–0.08%) from fresh plant material. The storage of plant samples from four Chinese cabbage cultivars resulted, in most cases, in an increase of phenolic content, within six days, at 4 °C and 20 °C. The increase might have been triggered by post-harvest plant stresses, which stimulate the biosynthesis of polyphenols.     

Nitrogen form affects yield and taste of tomatoes

Different nitrogen forms in organic or mineral fertilizers affect yield, quality and taste of tomatoes. Tomato plants were grown in a greenhouse for 10 weeks and fertilized with two different organic fertilizers (manure or grass and clover mulch) or with three different mineral nutrient solutions (NO₃^?:NH₄⁺) ratios 4:1 or 1:4). In an attempt to mimic the nutrient supply of the organic production systems, mineral fertilizers with ammonium as the dominating N‐source were combined with two chloride levels. Total nitrogen supply was 650 mg N plant^?1 week^?1 in all treatments. There was no difference in the yield of red tomatoes between the treatments (mean 1.95 kg FW plant^?1). However, the yield of green tomatoes at the final harvest was significantly higher in the mineral nutrient treatments (mean 1.37 kg FW plant^?1) compared with the organic treatments (mean 0.88 kg FW plant^?1). Plant biomass was higher for the mineral nutrient treatments (mean 1.05 kg FW plant^?1) compared with the organic treatments (0.89 kg and 0.72 kg FW plant^?1 in the manure and the grass and clover mulch treatments, respectively). Significantly higher scores were achieved for sweetness, acidity, flavour and acceptance for the tomatoes grown with the organic or the ammonium‐dominated treatments compared with the tomatoes grown with the nitrate dominated nutrient solution. It is suggested that ammonium is an equivalent nitrogen source for tomato plants compared with nitrate and that, when tomato plants are supplied with reduced nitrogen forms such as ammonium or organic nitrogen, an improved tomato fruit taste can be observed. Copyright © 2005 Society of Chemical Industry