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Dean A. Kopsell, David E. Kopsell and Joanne Curran-Celentano

Kale (Brassica oleracea L.) ranks highest among vegetable crops for lutein and beta-carotene carotenoids, which function as antioxidants in disease prevention. Nitrogen (N) rate and N form influence plant growth and alter pigment composition and accumulation. The objectives of these experiments were to investigate the effect of N rate and form on biomass and accumulation of plant pigments in the leaf tissues of kale. Three kale cultivars were grown using nutrient solution culture. In the first study, N treatment rates were 6, 13, 26, 52, and 105 mg·L–1, at a constant NH4-N:NO3-N ratio. Kale biomass increased linearly in response to increasing N rate. On a fresh weight basis, lutein and beta-carotene were not affected by N rate. However, carotenoids calculated on a dry weight basis increased linearly in response to increasing N rate. In a second study, kale was grown under: 100% NH4-N:0% NO3-N, 75% NH4-N:25% NO3-N, 50% NH4-N:50% NO3-N, 25% NH4-N:75% NO3-N, and 0% NH4-N:100% NO3-N, at a N rate of 105 mg·L–1. Linear increases in biomass were observed for each kale cultivar as percentage of NO3-N increased. Lutein concentrations increased 155%, 73%, and 39% for `Toscano', `Winterbor', and `Redbor' kale, respectively, as N form changed 0% NO3-N to 100% NO3-N. Concentration of leaf beta-carotene increased linearly in response to increasing NO3-N in each cultivar tested. Nitrogen management should be considered in crop production programs designed to increase the concentrations of nutritionally important carotenoids.

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Dean A. Kopsell, David E. Kopsell and Joanne Curran-Celentano

Sweet basil (Ocimum basilicum L.) is a popular culinary herbal crop grown for fresh or dry leaf, essential oil, and seed markets. Recently, basil was shown to rank highest among spices and herbal crops for xanthophyll carotenoids, which are associated with decreased risks of cancer and age-related eye diseases. The research goal for the current study was to characterize the concentrations of nutritionally important carotenoid pigments in popular varieties of basil. Eight cultivars of sweet basil (`Genovese', `Italian Large Leaf', `Nufar', `Red Rubin', `Osmin Purple', `Spicy Bush', `Cinnamon', and `Sweet Thai') were grown in both field and greenhouse environments and evaluated for plant pigments using HPLC methodology. Environmental and cultivar differences were observed for all of the pigments analyzed. `Sweet Thai' accumulated the highest concentrations of lutein, zeaxanthin, and β-carotene carotenoids in the field, while `Osmin Purple' accumulated the highest carotenoid concentrations in the greenhouse. Comparing the two environments, cultivar levels for carotenoid and chlorophyll pigments were higher in the field environment when expressed on both a fresh and dry weight basis. Exceptions were found only for the purple leaf basils (`Osmin Purple' and `Red Rubin'). Positive correlations existed between carotenoid and chlorophyll pigments in both environments. This study demonstrates sweet basil accumulates high levels of nutritionally important carotenoids in both field and greenhouse environments.

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William M. Randle, David E. Kopsell and Dean A. Kopsell

A major decision in producing onions with mild flavor on low sulfur soils is determining when to stop applying SO4 -2 to the crop. Sulfate (SO4 -2) is necessary for good early growth, but high levels of available SO4 -2 late in the season increase bulb pungency. The objective of this research was to determine how sequentially reducing the availability of SO4 -2 during onion growth and development would affect flavor intensity and quality of Granex-type onions. Starting 77 days before harvest, SO4 -2 concentrations were lowered from 1 mm to 0.05 mm on different blocks of onions in a greenhouse experiment at bi-weekly intervals. Total leaf and bulb S were measured at harvest to monitor S accumulation as SO4 -2 fertility was sequentially reduced. Bulbs were harvested and analyzed for flavor precursors and their biosynthetic intermediates, gross flavor intensity as measured by enzymatically developed pyruvic acid (EPY), and soluble solids content. As SO4 -2 fertility reductions were delayed during the experiment, total leaf and bulb S increased linearly. In addition, bulb EPY concentrations increased linearly as SO4 -2 reduction was delayed, indicating increases in overall flavor intensity. While the total concentration of flavor precursors did not significantly change in response to lowering SO4 -2 fertility during the experiment, the concentrations of MCSO to 1-PRENCSO did. MCSO concentration decreased and then increased in a quadratic manner. MCSO produces fresh onion and cabbage like flavors. 1-PRENCSO, on the other hand, increased linearly as the high SO4 -2 fertility level was extended through bulb maturation. Increasing concentrations of 1-PRENCSO causes onions to have significantly more heat and mouth burn when eaten. Reducing available SO4 -2 49 days prior to harvest coincided with a reduction in EPY and a change in the flavor biosynthetic pathway that appeared to be associated with the metabolic changes occurring with the onset of bulbing. Chemical names used: enzymatically developed pyruvic acid (EPY); methyl cysteine sulfoxide (MCSO); 1-propenyl cysteine sulfoxide (1-PRENCSO).

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Dean A. Kopsell, David E. Kopsell and Joanne Curran-Celentano

Therapeutic compounds in herbal crops are gaining recent attention. Sweet basil (Ocimumbasilicum L.) is a popular culinary herbal crop grown for both fresh and dry leaf markets. Recently, basil (unidentified cultivar) was shown to rank highest among spices and herbal crops for xanthophylls carotenoids. This class of carotenoids is associated with decreased risks of certain cancer and age-related eye diseases. The research goal for the current study was to characterize the concentrations of nutritionally important carotenoid pigments among popular varieties of basil. Eight cultivars of sweet basil (`Genovese', `Italian Large Leaf', `Nufar', `Red Rubin', `Osmin Purple', `Spicy Bush', `Cinnamon', and `Sweet Thai') were grown in both field and greenhouse environments and evaluated for plant pigments using HPLC methodology. Environmental and cultivar differences were significant for all of the pigments analyzed. `Sweet Thai' accumulated the highest concentrations of lutein, zeaxanthin, and beta-carotene carotenoids, while `Italian Large Leaf' had the lowest concentrations. Comparing the two environments, cultivar means for carotenoid and chlorophyll pigments were higher in the field environment when expressed on both a fresh and dry weight basis. Exceptions were found only for the purple leaf basils (`Osmin Purple' and `Red Rubin'). Positive and highly significant correlations existed between carotenoid and chlorophyll pigments in both environments. This study demonstrates that sweet basil can accumulate high levels of nutritionally important carotenoids in both field and greenhouse environments.

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David E. Kopsell and William M. Randle

Pungency and bulb quality changes during storage were evaluated using onion (Allium cepa L.) cultivars representing different storage abilities, pungency, and soluble solids content. Bulbs were harvested from greenhouse-grown plants, cured, and stored for 3 or 6 months at 5 ± 3 °C, 80% ± 5% relative humidity (0.8 to 1.1 kPa vapor pressure deficit). Prior to storage, and after each month of storage, bulbs were evaluated for pungency by measuring enzymatically formed pyruvic acid (EPY), soluble solids content (SSC), percent loss in mass (%ML), and loss of dormancy. Pungency differed among cultivars prior to and during storage. Among short-day (SD) cultivars, EPY either decreased or increased linearly with increased storage duration. Among intermediate (ID)- and long-day (LD) cultivars, EPY decreased linearly or quadratically during storage. Short-day cultivar SSC increased, then decreased quadratically during storage, while ID and LD cultivar SSC decreased linearly over time. Percent loss in mass increased linearly during storage among all cultivars, although SD cultivars exhibited greater %ML than did ID or LD cultivars.

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David E. Kopsell and William M. Randle

Short-day (SD) and long-day (LD) cultivars of onion (Allium cepa L.) representing various storage and flavor characteristics were greenhouse-grown to maturity. Bulbs were harvested and cured, then stored at 4C and evaluated monthly for pyruvic acid concentration (EPY), soluble solids content (SCC), and weight loss (WL). The EPY of `Dehydrator #3' (SD) decreased linearly with storage while EPY of `Granex 33' (SD) increased linearly. The EPY of `Zenith' (LD) had a quadratic response, decreasing then increasing during storage, while EPY of `Sweet Sandwich' (LD) increased then decreased quadratically during storage. Cultivar SSC generally decreased, while WL increased during storage.

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Dean A. Kopsell, Carl E. Sams, T. Casey Barickman, Dennis E. Deyton and David E. Kopsell

Selenium (Se) is an essential mammalian micronutrient. Adult humans have a daily requirement of 55 to 70 μg/day Se depending on sex and pregnancy/lactation for females. In addition, recent studies have shown health benefits with dietary Se supplementation of 100 to 200 μg/day Se. However, daily intakes in humans greater than 900 μg Se will result in toxicity called selenosis. Although not essential in plant nutrition, some species can bioaccumulate Se. Brassica and Allium species became prime candidates for Se enrichment because of their ability to accumulate and tolerate high concentrations of Se in edible tissues; however, there is now concern that these species are too efficient at selenization and overconsumption of their selenized tissues could result in selenosis. Herbal crop species are consumed regularly in the diet for their culinary flavor attributes. Basil (Ocimum basilicum L.) and cilantro (Coridandrum sativum L.) are not classified as Se accumulators. Therefore, a study was undertaken to determine the potential to selenize basil and cilantro through foliar Se applications to consistently supplement diets with nutritionally beneficial levels of Se. Plants of each species were grown in both growth chamber and field environments and treated with foliar applications (5 mL per plant) of selenate-Se and selenite-Se at concentrations of 0, 2, 4, 8, 16, and 32 mg·L−1 Se. Crops received three separate foliar applications at ≈5-day intervals beginning 24 to 28 days after planting for the growth chamber plants and 50 days after planning for the field environment. Selenium accumulation in both basil and cilantro leaf tissues increased linearly under both selenate-Se (P ≤ 0.001) and selenite-Se (P ≤ 0.001) foliar treatments in growth chamber and field evaluations. Maximum Se leaf tissue concentrations for basil and cilantro ranged from 13 to 55 μg·g−1 Se dry weight. Selenization of basil and cilantro is possible through foliar Se applications, and Se fortification of herbal crops may provide alternative delivery systems in human diets.

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David E. Kopsell, William M. Randle and Norman E. Schmidt

The tearing and burning sensations associated with raw onion consumption are caused by (Z,E)-propanethial S-oxide, the lachrymatory factor (LF). The LF is produced from the hydrolysis of S-1-propenyl-L-cysteine S-oxide (PREN), the dominant flavor compound in onions. Current methodology for LF quantification was optimized for Granex-type onions using a 2-min incubation time to allow for maximum formation. In this study, data were taken on PREN hydrolysis of `Dehydrator #3' and `Granex 33' at harvest and during storage and were compared to LF formation. `Dehydrator #3' PREN hydrolysis was 98% complete 5 s after cellular disruption at each sampling date. However, using the 2-min incubation procedure, only 10.25 μmol of LF was recovered from the hydrolysis of 30.11 μmol of PREN at harvest, thereby underestimating LF for this cultivar. Percent PREN hydrolysis for `Granex 33' was lower than `Dehydrator #3' during the enzymatic reaction at each sampling date, suggesting slower PREN hydrolysis activity. At harvest, 6.96 μmol of LF were recovered from 12.54 μmol of PREN hydrolyzed. After 2 storage months, however, micromol of LF were equal to micromol of PREN. LF quantification is currently being considered by the onion industry as a direct measurement of gross onion pungency. This data suggests that more optimization of LF quantification is needed before it can be applied to a broad range of cultivar types.

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David E. Kopsell, William M. Randle and Norman E. Schmidt

The lachrymatory factor [LF, (Z,E) propanethial S-oxide] is a direct product of 1-propenyl cysteine sulfoxide (1-PRENCSO) hydrolysis and dominates onion flavor when present in high concentrations. To evaluate LF as a potential means of assessing flavor quality, two onion cultivars were greenhouse-grown and the bulbs stored for 4 months at 3 ± 1 °C, 70% relative humidity. Onions were evaluated at monthly storage intervals for LF development in bulb macerates following a 120 seconds incubation time. When LF was compared to amounts of 1-PRENCSO hydrolysis, we found that LF was severely underestimated. The relationship of LF and 1-PRENCSO also varied between cultivars during storage. As `Granex 33' was stored for longer periods, the amount of LF measured at 120 seconds more closely reflected the amount of 1-PRENCSO hydrolyzed. LF from `Dehydrator #3', however, was consistently underestimated regardless of storage time. Therefore, a second experiment was conducted using individual bulbs of two onion cultivars in an attempt to determine the optimal incubation time for LF quantification. Maximum LF among bulbs was generally detected 5-10 seconds after tissue maceration for `Dehydrator' and after 15-30 seconds for `Sweet Vidalia'. The amount of LF quantified between 5 and 120 seconds decreased linearly for nine of ten bulbs of `Dehydrator', but this trend was less apparent for `Sweet Vidalia'. A uniform LF incubation time for individual bulbs, therefore, may not be possible for all cultivars. These data show a complex relationship among and within onion cultivars for 1-PRENCSO hydrolysis and the formation of LF in onion macerates.

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Dean A. Kopsell, David E. Kopsell, Mark G. Lefsrud, Joanne Curran-Celentano and Laura E. Dukach

Green leafy vegetables are important sources of dietary carotenoids, and members of Brassica oleracea L. var. acephala rank highest for reported levels of lutein and β-carotene. Twenty-three leafy B. oleracea cultigens were field grown under similar fertility over two separate years and evaluated for leaf lutein and β-carotene accumulation. Choice of B. oleracea cultigen and year significantly affected carotenoid levels. Lutein concentrations ranged from a high of 13.43 mg per 100 g fresh weight (FW) for B. oleracea var. acephala `Toscano' to a low of 4.84 mg/100 g FW for B. oleracea var. acephala 343-93G1. β-carotene accumulations ranged from a high of 10.00 mg/100 g FW for B. oleracea var. acephala `Toscano' to a low of 3.82 mg/100 g FW for B. oleracea var. acephala 30343-93G1. Carotenoid concentrations were significantly higher in year 2 than in year 1, but rank order among the cultigens for both lutein and ß-carotene did not change between the years. During each year, there were high correlations between leaf carotenoid and chlorophyll pigments. Under similar growing conditions, choice of B. oleracea cultigen will influence carotenoid accumulation, and this may affect the health benefits of consuming these leafy green vegetable crops.