Total phenolic content and DPPH radical scavenging activity of lettuce (Lactuca sativa L.) grown in Colorado

Total phenolic content (TPC) and antioxidant capacity of lettuce were evaluated using the Folin-Ciocalteu method and DPPH assay, respectively, on 25 cultivars of lettuce, including leaf, romaine, crisphead, and butterhead types, cultivated over two harvest periods. Leaf lettuce possessed the highest TPC and highest DPPH scavenging ability, followed by romaine, butterhead and Batavia (crisphead subtype). Within a lettuce type, red pigmented lettuce cultivars had higher TPC and antioxidant capacity than did green cultivars grown under the same conditions. In addition, lettuce harvested in July possessed higher TPC and antioxidant capacity than did lettuce harvested in September, suggesting that environmental conditions could influence the phenolic content and antioxidant activity of lettuce. These results suggest that Colorado grown lettuce may serve as potential dietary sources of natural phenolic antioxidants.     

NITROGEN AND SULFUR EFFECTS ON LEAF LETTUCE QUALITY1

Nitrogen* sulfur fertilizer combinations and growing season effects on sensory quality/acceptability and color of hydroponically grown greenhouse lettuce cultivar, “Grand Rapids”, were studied. Lettuce samples were evaluated using an attribute rating scale for appearance, color, texture, flavor, bitterness and overall acceptability; actual leaf color was measured with a chromameter. Initially, 20 N*S treatment combinations were tested. Then based on specific sensory responses, eight N*S treatment combinations were selected forjurther study in the Winter and in the Spring. Univariate ANOVA showed that in both studies significant (P<0.05) color and texture differences were found. Generally, plants receiving the highest treatment level (240 mg/L) of nitrogen were greener (sensory) and darker and duller (chromameter) than the other samples. Spring samples receiving 30 and 60 mg/L N were perceived as having firmer texture. Between seasons, it was found that lettuce grown in the Spring was perceived as being greener and having a softer texture than lettuce grown in the Winter. Principal component (factor) analysis revealed three factors accounting for between 79 to 81% of the variance in the data. Factor loadings varied depending on the season grown.     

Glucosinolate Content and Sensory Evaluation of Baby Leaf Rapeseed from Annual and Biennial White‐ and Yellow‐Flowering Cultivars with Repeated Harvesting in Two Seasons

The chemical and sensory quality of field‐grown vegetables may be influenced by cultivar choice and agronomic factors but knowledge is lacking on the new rapeseed vegetables. White‐ and yellow‐flowering rapeseed cultivars were tested in two seasonally different field studies in Denmark at three different growing stages by early sowing the first year and late sowing the second year. Content of glucosinolates (GLSs) was analyzed, and the sensory quality of baby leaf samples was evaluated. The GLS content differed among cultivars across years in all growing stages, with biennial cultivars having the highest GLS content. In the second year, a higher content of all identified GLSs was found at two growing stages except for neoglucobrassicin and gluconasturtiin, compared to the first year. On the contrary, higher contents of all identified GLSs were found at a third stage in the first year except for progoitrin and 4‐methoxy glucobrassicin. Sensory evaluation of bitterness revealed differences among cultivars, higher intensities of bitterness in biennial cultivars, and a relationship between bitterness and content of bitter‐tasting and total GLSs. The effect of repeated harvesting on GLS content differed between the years and no general pattern was seen, except that the composition of individual GLSs was comparable for the biennial cultivars. We conclude that growing season and life cycle had a stronger influence on GLS content than stage at harvest. The link between bitter‐tasting GLSs and bitterness revealed that life cycle and seasonal effects affected the sensory profile of baby leaf rapeseed thereby making a healthier product due to high content of health‐beneficial GLSs.     

Effects of genotype and transpiration rate on the uptake and accumulation of perchlorate (ClO4-) in lettuce

Although evidence of perchlorate accumulation in plants exists, there is a scarcity of information concerning the key factors and mechanisms involved. To ascertain whether genotypic variation in perchlorate accumulation occurs within lettuce, hydroponic plant uptake experiments were conducted with five types of lettuce (Lactuca sativa L.), which were grown to market size atthree perchlorate (ClO4-) concentrations (1, 5, or 10 microg/L). Perchlorate accumulated in the leafy tissues to varying amounts, ranging from 4 to 192 microg/kg fresh weight (FW), and the ranking of perchlorate accumulation was crisphead > butter head > romaine > red leaf > green leaf. The effect of transpiration rate on perchlorate accumulation was further examined using crisphead, butter head, and green leaf lettuce. By growing lettuce in controlled-environment chambers with two climatic regimes, "cloudy, humid, cool" (80% RH, 18/15 degrees C, 250 micromol/m2s photosynthetic photon flux density (PPFD)) and "sunny, dry, warm" (approximately 50% RH, 28/18 degrees C, 500 micromol/m2s PPFD), up to 2.7-fold differences in transpiration rates were achieved. Across all three genotypes, the plants that transpired more water accumulated more perchlorate on a whole-head basis; however, the effect of transpiration rate on perchlorate accumulation was not as great as expected. Despite 2.0-2.7-fold differences in transpiration rate, there were only 1.2-2.0-fold differences in perchlorate accumulation. In addition to whole-head analysis, plants were sectioned into inner, middle, and outer leaves and processed separately. Overall, the ranking of perchlorate accumulation was outer leaves > middle leaves > inner leaves. Transpiration rate has a clear effect on perchlorate accumulation in lettuce, but other factors are influential and deserve exploration.     

Application of Cudrania tricuspidata leaf extract as a washing agent to inactivate Listeria monocytogenes on fresh-cut romaine lettuce and kale

The present study aimed to examine the antimicrobial activity of silkworm thorn (Cudrania tricuspidata) leaf extract (CTLE) and its application as a washing agent for fresh-cut romaine lettuce and kale. The antimicrobial activities of CTLE at various concentrations against Listeria monocytogenes were determined using disc diffusion and viable cell count assays, and CTLE exhibited strong inactivation of L. monocytogenes. In particular, after the treatment with 0.4% CTLE, the protein content of L. monocytogenes cells was significantly (P < 0.05) decreased from 507.21 to 254.58 μg mL⁻¹, and damaged cells were observed by scanning electron microscopy. CTLE washing resulted in approximately 2-log reduction of microbial growth, similar to that of 0.01% NaOCl. In addition, CTLE washing did not affect the quality of romaine lettuce and kale. Therefore, these results suggest that CTLE is applicable as a new washing agent for inactivating L. monocytogenes on fresh-cut romaine lettuce and kale.     

Combined washing effect of noni extract and oregano essential oil on the decontamination of Listeria monocytogenes on romaine lettuce

Combined washing effect of noni extract (NE) and oregano essential oil (OE) on the decontamination of Listeria monocytogenes on romaine lettuce was examined. The fractional inhibitory concentration index (FICI) between NE and three different essential oils (cinnamon leaf, thyme and OE) was determined. Fractional inhibitory concentration index results indicated that OE only had an additive effect (FICI = 1). Noni extract/oregano essential oil combined washing resulted in the greatest reduction in viable cell numbers (3.42 log CFU g⁻¹) relative to non-washed samples. Furthermore, the combined washing was more effective than sodium hypochlorite washing in terms of reducing the microbial load (>1.44-log reduction). Washing treatment did not change the surface colour or total phenolic content in lettuce samples. These results suggest that NE/OE combined washing is applicable as a novel decontamination treatment to ensure the microbial safety of romaine lettuce without changing the quality.     

Comparison of the Microbiological Quality of Environmentally Friendly and Conventionally Grown Vegetables Sold at Retail Markets in Korea

Fresh produce is usually eaten raw without cooking or heating, which may increase the probability of foodborne infection. The microbiological quality of 11 types of fresh, raw vegetables (romaine lettuce, sesame leaves, crown daisy, garlic chives, iceberg lettuce, cabbage, broccoli, leek, chili pepper, capsicum, and zucchini) purchased at retail markets in Iksan, Korea as affected by cultivation method (environmentally friendly vegetables [organic, pesticide‐free, and low‐pesticide vegetables] and conventionally grown vegetables) and harvest season was determined. Escherichia coli O157:H7 and Salmonella were not detected in all samples of vegetables tested. Aerobic mesophiles (>6 log cfu/g) were detected in environmentally friendly romaine lettuce and crown daisy and environmentally friendly and conventionally grown garlic chives, which also contained coliforms (>3 log cfu/g). Sesame leaf and crown daisy (regardless of cultivation method), as well as conventionally grown romaine lettuce and leek, contained >1 log cfu/g of E. coli. The overall microbiological quality of environmentally friendly and conventionally grown vegetables was not significantly different (P > 0.05). However, there were seasonal effects on populations of coliforms and generic E. coli on vegetables. The greatest numbers of microorganisms were isolated from environmentally friendly or conventionally grown vegetables purchased in winter. The vegetables, regardless of cultivation method or season, should be subjected to appropriate antimicrobial treatment to enhance their microbial safety.     

Characterisation of polyphenols and antioxidant properties of five lettuce varieties and escarole

Salad vegetables could be relevant as dietary sources of natural antioxidants. A better knowledge of their composition can be useful for understanding their potential bioavailability and biological activities. The antioxidant compounds, polyphenols and vitamin C, have been determined in five varieties of lettuce (iceberg, romaine, continental, red oak leaf, lollo rosso) and one variety of escarole (frissé). The polyphenol study by HPLC-DAD-MS/MS ESI allowed the identification of two compounds previously not reported in lettuce; quercetin and luteolin rhamnosyl-hexosides. Qualitative and quantitative differences were observed between the polyphenol profiles. Caffeic acid derivatives were the main phenolics in green varieties, while flavonols were detected in higher quantities in red varieties and escarole, and anthocyanins were only present in red-leafed varieties. The highest total phenolic content was observed in red-leafed varieties while the highest level of vitamin C was detected in the continental variety. The red varieties showed the highest antioxidant activity by all the methods assayed.     

Effects of Olive Maturation and Stoning on Quality Indices and Antioxidant Content of Extra Virgin Oils (cv. Coratina) during Storage

ABSTRACT: Quality indices, antioxidant compounds, and antioxidant activities of extra-virgin oils from Coratina olives were evaluated during a 12-mo storage. Whole and stoned olives, picked at 2 different maturation index (MI), were submitted to malaxation for 45 min and extracted by a 3-phase continuous system. A 90-min malaxation trial was also performed for the stoned olives. The following parameters were monitored: free acidity, peroxide value, K₂₃₂ and K₂₇₀ indices, sensory profile, total phenolic content (TPC), phenolic profiles, tocopherol compounds, and antioxidant activity (AA). The highest TPC, AA, and sensory score were found for the oils obtained by olives picked at low MI and by stoned olives. After 12 mo, all the oils were still included into the “extra-virgin” category, and those deriving from whole olives picked at the lowest MI showed the best sensory characteristics due to high fruity and well-balanced pungent and bitter tastes. Practical Application: This study could represent a helpful tool for oil-makers to improve the marketing of extra-virgin olive oils produced from cultivars with very high phenolic contents, such as Coratina, generally not adequately appreciated by consumers because of their excessive bitterness and pungent taste. These oils, when extracted from whole olives, are generally consumed after a certain period of time (at least 6 mo) during which a decrease in the phenolic content occurs. The results of the present work demonstrate that oils extracted from olives picked at low maturation index can be marketed immediately after production if subjected to stoning and malaxed for a short time. This procedure allows to adjust the phenolic content and to obtain a high flavor and a well-balanced taste.     

Characterisation and variation of antioxidant micronutrients in lettuce (Lactuca sativa folium)

The main phenolic compound in six studied lettuce cultivars (five green and one red) was identified as dicaffeoyl tartaric acid. Quantitative but not qualitative differences were found in the phenolic profiles among green cultivars. The red oak leaf cultivar contained twofold more dicaffeoyl tartaric acid and 10‐fold more chlorogenic acid than the green cultivars. Total phenolics ranged from 8.4 to 12.9 mg g^?1 dry weight in green varieties and reached 27.8 mg g^?1 dry weight in red oak leaf. Carotenoids and vitamins E and C were also quantified. Lutein was the main carotenoid found in all cultivars, together with another xanthophyll. The period of harvesting had only a marginal influence on total phenolic levels, whereas carotenoid and vitamin E levels were higher at the second period of harvesting. Vitamin C levels ranged between 6.1 and 9.9 mg per 100 g fresh weight. We investigated the total antioxidant power in lettuce. Total phenolics accounted for more than 60% of the total antioxidant capacity. Dicaffeoyl tartaric acid accounted for 55%. Copyright © 2004 Society of Chemical Industry     

Effect of cultivars and irrigation waters on persistence of indicator bacteria on lettuce grown in high tunnel

Effect of irrigation with groundwater (GW), primary-treated wastewater (PTWW), secondary-treated wastewater (STWW), and roof-collected rainwater (RCR) on the microbial quality of lettuce cultivars “Annapolis,” “Celinet,” and “Coastline” grown in high tunnel was investigated. Lettuce plants were spray irrigated with irrigation waters once a week for 2 weeks and analyzed for indicator and pathogenic bacteria. PTWW irrigation resulted in the highest Escherichia coli recovery on the lettuce plants (4.7 log MPN/g) as compared to irrigation with other three waters on 0 day postirrigation (dpi). Lettuce cultivars affected the bacterial die-off rate, where E. coli populations reduced the most by 1.5 log MPN/g on “Annapolis” lettuce on 2 dpi. The STWW and RCR irrigation did not significantly influence indicator bacterial populations on lettuce as compared to GW irrigation. The STWW and RCR containing low populations of indicator bacteria may be suitable for lettuce irrigation in Mid-Atlantic area without affecting its microbial quality.     

Influence of sorghum grain type on wort physico‐chemical and sensory quality in a whole‐grain and commercial enzyme mashing process

To determine the most suitable types of sorghum for whole‐grain adjunct in lager beer brewing, 14 cultivars of five different types: white tan‐plant, white non‐tan‐plant, red non‐tannin, white tannin (type II) and red tannin (type III) were evaluated. The effects of grain type on wort physico‐chemical and sensory quality with raw grain and malt plus commercial enzyme mashing were assessed. Tannin content correlated significantly and negatively with wort extract and fermentable sugars (p < 0.001) and free amino nitrogen (FAN; p < 0.1). This is attributable to inactivation of the exogenous enzymes by the tannins during the mashing process. However, the type II tannin sorghums had wort quality attributes closer to the non‐tannin sorghum types, probably owing to their relatively low tannin content (≤1%). Malting gave a great improvement in wort extract, fermentable sugars and FAN, but substantially influenced wort sensory properties in terms of higher sourness, bitterness and astringency, as well as the expected more malty flavour. Worts from raw red non‐tannin sorghums were similar to those of white tan‐plant sorghums in both physico‐chemical and sensory quality. Thus, red non‐tannin sorghums, in view of their better agronomic quality, have considerable potential as a whole‐grain adjunct in lager beer brewing. Copyright © 2013 The Institute of Brewing & Distilling     

Provitamin A and Ascorbic Acid Content of Fresh Pepper Cultivars (Capsicum annuum) and Processed Jalapeños

Alpha and beta carotene, provitamin A activity, dehydroascorbic acid, L-ascorbic acid and total ascorbic acid content of “jalapeño,”“bell,” long green/red “chile,”“serrano” and “yellow wax” peppers (Cupsicum annuum L.) at green and red stages of maturity were determined by HPLC. Effects of thermal processing on vitamin A and C retention in “jalapeno” peppers was also determined. Provitamin A activity ranged from 27.3 to 501.9 Retinol Equivalents (RE/100g). Ascorbic acid concentration ranged from 76.1 to 243.1 (mg/100g). Provitamin A activity and ascorbic acid content increased with maturity in all cultivars. Thermal processing of “jalapeño” cultivars resulted in a 25% decrease of total provitamin A activity and a 75% decrease in total ascrobic acid.     

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.     

A study of variation in the tendency for postharvest discoloration in a lettuce (Lactuca sativa) diversity set

Lettuce as a component of processed salad packs often suffers from pinking or browning discoloration on leaf surfaces within a few days after harvest limiting product shelf life. A lettuce diversity set representing the primary gene pool was used to investigate phenotypic variation for postharvest discoloration. Discoloration of minimally processed lettuce was assessed using material harvested from a replicated field trial. Significant variation for pinking and browning was recorded (P < 0.001). Rates of discoloration were specific to lettuce type, however potential for pinking or browning within a type varied. Interestingly, accessions were significantly more susceptible to browning (P < 0.05) early postharvest (day 1) but significantly more susceptible to pinking (P < 0.05) during later stages (days 6, 9 and 13). The results indicate that there is a genetic basis for this phenotypic variation and this natural allelic variation could be exploited through breeding to develop discoloration resistant cultivars, consequently minimising pre‐ and postharvest treatments and reducing food wastage.     

Suspending lettuce type influences recoverability and radiation sensitivity of Escherichia coli O157:H7

An outbreak strain of Escherichia coli O157:H7 was inoculated onto closely related but structurally distinct types of lettuce (Lactuca sativa): Boston (butterhead lettuce), iceberg (crisphead lettuce), and green leaf and red leaf (colored variants of looseleaf lettuce). The E. coli O157:H7 was inoculated either onto the surface of cut leaf pieces or into a homogenized leaf suspension. Samples were gamma irradiated, and the radiation sensitivity of the inoculated bacteria was expressed as a D-value (the amount of ionizing radiation necessary to reduce the bacterial population by 90% [kGy]). The recovery of bacteria from nonirradiated leaf pieces was also measured. When inoculated onto the leaf surface, E. coli O157:H7 had significantly stronger radiation sensitivity on red leaf lettuce (D = 0.119 +/- 0.004 [standard error]) and green leaf lettuce (D = 0.123 +/- 0.003) than on iceberg lettuce (D = 0.136 +/- 0.004) or Boston lettuce (D = 0.140 +/- 0.003). When E. coli O157:H7 was inoculated into a homogenized leaf suspension, its sensitivity was significantly stronger on iceberg lettuce (D = 0.092 +/- 0.002) than on green leaf lettuce (D = 0.326 +/- 0.012), Boston lettuce (D = 0.331 +/- 0.009), or red leaf lettuce (D = 0.339 +/- 0.010), with a threefold difference. Significantly fewer bacteria were recovered from the surface of iceberg lettuce than from the surfaces of the other types of lettuce examined. Following radiation doses of up to 0.5 kGy, the texture (maximum shear strength) of lettuce leaves was measured along the midrib and along the leaf edge for each type of lettuce. There was no meaningful change in texture for any type of lettuce for either leaf section examined at any dose up to 0.5 kGy. These data show (i) that relatively subtle differences between lettuce types can significantly influence the radiation sensitivity of associated pathogenic bacteria and (ii) that doses of up to 0.5 kGy do not soften lettuce leaves.