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Vuvu D. Manseka and James R. Hicks

Butternut squash was harvested at two stages of maturity in 1994 and was cured for 10 days at 26°C and 80% or 95% relative humidity (RH) before storage in air at 12°C and 65% or 80% RH for 144 days. Fresh weight was assessed right after harvest along with carotene (milligram per 100 grams fresh weight), carbohydrates (milligrams per gram dry weight) and internal color (L, a, b). Percent weight loss and all quality components were assessed immediately after curing and every 48 days thereafter. Weight loss increased with days in storage and was substantially minimized by a humidified environment down to 6%. The 95% curing treatment reduced weight loss to levels below the upper threshold for consumer acceptance (<15%) after 144 days. Maturity at harvest did not affect weight loss during storage, but rather the percent dry weight. Beta-carotene increased by >100% during storage. A positive correlation was established between weight loss and beta-carotene and also between the a value and beta-carotene. Curing at 95% RH obviously reduced beta-carotene content to less than one-third of its corresponding amount in noncured fruit. Sucrose increased as glucose and fructose and starch decreased during storage in cured and noncured fruit. Starch was found to decrease by 26% after 144 days in storage. The lowest levels of starch were found early during storage in fruit cured at 95% RH, but the difference between treatments disappeared by the end of storage.

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J.O. Kuti

Flavonoid content and antioxidant activity in peel and pulp samples of four different cactus pear fruit varieties were investigated. Major cactus fruit flavonoids were quercetin, kaempferol, and isorhamnetin. Greater amount of quercetin was found in the pulp compared with the peel samples in all varieties examined. Both kaempferol and isorhamnetin were found in at least three of the varieties (Opuntia ficus-indica; O. lindheimeri; O. streptacantha) exclusively in the peel samples. Generally, pulp tissue samples of all the cactus fruit varieties contained greater ascorbic acid, glutathione, alpha-tocopherol and beta-carotene and antioxidant activities than the peel tissue samples. Total flavonoids correlated well with antioxidant activity (r 2 = 0.89). Ascorbic acid had the highest antioxidant activity, followed by glutathione, beta-carotene, and alpha-tocopherol on equimolar basis.

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J.A. Kirkpatrick, J.B. Murphy, and T.E. Morelock

Interest in the health benefits of vegetables prompted an investigation of the levels of carotenoids in commercial varieties and UA breeding lines of spinach. Plant carotenoids perform a critical function as antioxidants, providing protection against a variety of reactive oxygen species generated primarily during photosynthesis. When ingested by humans, these compounds maintain their antioxidant activities and are receiving considerable attention in relation to multiple health benefits, including cancer prevention. While the best-known and most-studied carotenoid is beta-carotene, other carotenoids are now receiving attention due to their higher antioxidant activity compared to beta-carotene. Most dark-green leafy vegetables, such as spinach and kale, are relatively high in carotenoids, especially lutein. In this study, significant differences in average content of both lutein and beta-carotene were found between genetic lines of spinach. Some lines exhibited considerable variation between plants, while others were highly uniform. There was a very high correlation (r 2 = 0.96) between lutein content and betacarotene content. The significant difference between spinach lines suggests that improvement of general carotenoid antioxidants and lutein could be obtained through a breeding program.

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Mark G. Lefsrud and Dean A. Kopsell

Plant growing systems have consistently utilized the standard Earth day as the radiation cycle for plant growth. However, the radiation cycle can easily be controlled by using automated systems to regulate the exact amount of time plants are exposed to irradiation (and darkness). This experiment investigated the influence of different radiation cycles on plant growth, chlorophyll and carotenoid pigment accumulation in kale (Brassica oleracea L. var. acephala D.C). Kale plants were grown in growth chambers in nutrient solution culture under radiation cycle treatments of 2, 12, 24, and 48 h, with 50% irradiance and 50% darkness during each time period. Total irradiation throughout the experiment was the same for each treatment. Radiation cycle treatments significantly affected kale fresh mass, dry mass, chlorophyll a and b, lutein, and beta-carotene. Maximum fresh mass occurred under the 2-h radiation cycle treatment. The maximum dry mass occurred under the 12-h radiation cycle treatment, which coincided with the maximum accumulation of lutein, beta-carotene, and chlorophyll a, expressed on a fresh mass basis. The minimum fresh mass occurred during the 24 h radiation cycle treatment, which coincided with the largest chlorophyll b accumulation. Increased levels of chlorophyll, lutein and beta-carotene were not required to achieve maximum fresh mass production. Environmental manipulation of carotenoid production in kale is possible. Increases in carotenoid concentrations would be expected to increase their nutritional contribution to the diet.

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Kanta Kobira, Khalid Ibrahim, Elizabeth Jefferey, and John Juvik

Considerable epidemiological evidence exists on the association between consumption of antioxidant-rich vegetables and incidence of chronic diseases, including cancer and cardiovascular disease. Broccoli (Brassica oleracea L. sp. italica) florets are relatively abundant sources of antioxidants, and potentially amenable to genetic manipulation to enhance this vegetable's health-promoting properties. This investigation focuses on the identification of chromosomal segments in the nuclear genome of broccoli associated with antioxidant carotenoid and tocopherol variability. A broccoli F2:3 population consisting of 163 families derived from a cross between two parents (VI-158 and BNC) and previously mapped with 62 polymorphic SSR and SRAP marker loci was evaluated for carotenoid and tocopherol concentration in floret tissue over two growing seasons. Significant differences were observed among F2:3 family means for concentrations of lutein (10-fold difference between the lowest and highest family), beta-carotene 17-fold), alpha-tocopherol (8-fold) and gamma-tocopherol (6-fold). On a concentration basis, beta-carotene, lutein, alpha-tocopherol, and gamma-tocopherol were the most abundant antioxidant forms in broccoli. Heritability estimates of primary phytochemicals ranged from 0.35 to 0.38, 0.40, and 0.44 for beta-carotene, alpha-tocopherol, gamma-tocopherol, and lutein, respectively. Composite interval mapping (CIM) identified two quantitative trait loci (QTL) associated with carotenoid variability on two linkage groups and five QTL associated with tocopherol variability on four linkage groups. The QTL identified in this study have potential for use in marker-assisted crop improvement programs to develop elite germplasm designed to promote health among the consuming public.

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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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Andrew Schofield* and Gopinadhan Paliyath

The accumulation of carotenoids such as lycopene and beta-carotene greatly influences the quality of ripe tomato (Lycopersicon esculentum) fruit because cellular levels of these compounds determine the intensity of red color. As well, lycopene has anti-cancer properties and beta-carotene is a Vitamin A precursor. Recent work has demonstrated phytochrome regulation of the carotenoid pathway but the mechanism is not completely understood. This work investigates phytochrome regulation of 1-deoxy-D-xylulose 5-phosphate synthase (DXS) and phytoene synthase (PSY), two key enzymes of carotenogenesis. A simple procedure for the assay of PSY from crude pericarp extracts was developed and mRNA levels of DXS and PSY1 genes were measured by relative RT-PCR. Discs from mature green tomatoes were ripened in total darkness, or in darkness interrupted by brief daily treatments of red light, or red light followed by far red light. After ten days of incubation, lycopene levels of red light-treated discs had reached ≈12 mg/100 g fresh weight; nearly a 50% increase over discs ripened in total darkness. This increase was not observed in discs treated with red light followed by far red light, demonstrating the red/far red reversibility (and thus phytochrome control) of carotenoid accumulation. Similar patterns of phytochrome control are observed for PSY activity but not for DXS and PSY1 transcript levels, suggesting the mechanism of control may be at the level of post-translational modification of PSY. Potential applications of this regulation of carotenoid accumulation will be discussed.

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Carl M. Jones and James R. Myers

Continued and mounting evidence of the health benefits provided by carotenoid and anthocyanin pigments has increased public interest in dietary sources of these important phytonutrients. Tomatoes (Lycopersicon esculentum) are the primary dietary contributor of lycopene and an important source of beta-carotene. A collection of tomatoes containing the genes hp-1, dg, ogc, Ip, B and Af that are known to affect carotenoid and anthocyanin levels have been analyzed using HPLC. Levels of lycopene, beta-carotene, phytoene, and phytofluene have been determined in these accessions. Accession LA 3005, containing the dg gene, had the highest lycopene levels of the accessions analyzed (14 mg/100 g fresh wt.). A rapid HPLC method for quantitation of carotenoid levels from tomato fruit has been developed. “Heirloom” black and purple tomatoes have also been included in the accessions analyzed and have carotenoid levels comparable to cultivated red tomatoes. Anthocyanin presence has been confirmed only in the accessions LA 1996 (Af) and in some fruit of segregating plants from LA 3668 (Abg). Total monomeric anthocyanin content of LA 1996 as measured by the pH differential method is estimated to be 5.6 mg/100 g in the outer pericarp tissues and 18.6 mg/100 g in the skin tissue.

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Murshidul Hoque*, Husein Ajwa, and Beiquan Mou

Lettuce (Lactuca sativa L.) is an essential salad crop in the American diet. Nitrogen (N), phosphorus (P), and potassium (K) are required for successful lettuce production and can influence lettuce quality. The objective of the study was to evaluate changes in nutritional composition of romaine (`Green Tower') and iceberg (`Sharp Shooter') lettuce in responses to N, P and K fertilization during fall production in Salinas, Calif. Sixteen treatment combinations of fertilizer were selected to provide a range of treatments. N was applied at 0, 112, 225, and 338 kg·ha-1 as ammonium nitrate; P was applied at 0, 112, and 225 kg/ha as super phosphate; and K was applied at 0 and 112 kg·ha-1 as muriate of potash. Nutritional content of fresh tissue of two types of lettuce was analyzed using high performance liquid chromatography (HPLC). Among the parameters analyzed were lutein, beta-carotene, chlorophyll a, and chlorophyll b. Yield was increased with increasing N fertilizer level, but was not affected by P or K application rates. The best post harvest quality, however, was at moderate P application rate. Increasing the N and P rates gradually increased glucose content in lettuce but decreased the shelf life. Significant differences between the two types of lettuce were found in chlorophyll, lutein and beta-carotene content. No significant correlations were found between soil fertilizer application levels and nutritional content of lettuce. However, the ratio of chlorophyll a and b were greater with the increase of fertilizer rate. Nutritional composition including vitamin C will be presented.

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Michael Cavalier, Armen Kachatryan, Evodokia Menelaou, Jack Losso, and Don LaBonte

Fresh leaves of six sweetpotato [Ipomoea batatas (L.) Lam.] genotypes, `Beauregard', `Bienville', L 99-35, L 00-8, L 01-145, and L 01-29 were characterized for lutein. Lutein is a carotenoid capable of delaying blindness-related macular degeneration. The content of lutein in sweetpotato ranged from 0.38 to 0.58 mg·g-1 fresh weight. Beta-carotene separated from lutein on HPLC chromatograms, and, when spiked in pure lutein extract, did not interfere with lutein separation. Stems were also characterized and found not to contain lutein. Our results showed that sweetpotato leaves are an excellent source of dietary lutein and surpass levels found in leafy crucifers. Leaves of sweetpotato and a related species are used as human food in some countries and could be a source of extracted lutein for commercial purposes.