English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

Sweetpotato is considered a good source of ascorbic acid (vitamin C) and certain B vitamins. These water-soluble vitamins (WSV) play essential roles in sustaining human health. Besides the root, sweetpotato vegetative tissues are also edible and considered high in nutritional value. Despite the availability of general reference values for sweetpotato WSV content in the root and leaves, little is known about the distribution of these vitamins in specific sweetpotato root and vegetative tissues. The objective of this study was to determine the ascorbic acid (AA), thiamin (B1), riboflavin (B2), and vitamin B6 content in a range of foliar tissues including buds, vines, young petioles, young leaves, mature petioles, and mature leaves and root tissues including the skin, cortex, and pith tissue at the proximal, distal, and center regions of the root. Among foliar tissues of ‘Beauregard’ sweetpotatoes, the AA content was highest in young leaves (108 to 139 mg/100 g fresh weight) and lowest in mature petioles (7.2 to 13.9 mg). No thiamin was detected in foliar tissue, whereas mature leaves contained the highest riboflavin and vitamin B6 content (0.22 to 0.43 mg and 0.52 to 0.58 mg, respectively). In root tissues of ‘Beauregard’ and ‘LA 07-146’ sweetpotatoes, the AA content was lower in the skin (1.9 to 5.6 mg and 2.54 to 3.82 mg, respectively). The AA content in the cortex and pith tissue at the proximal, distal, and center of the root was generally similar. The thiamin content was variable among root tissues, whereas the skin contained the highest riboflavin content and the lowest vitamin B6 content across root tissues of both cultivars. The results of this study confirmed earlier reports suggesting that sweetpotato leaves can be a good source of multiple WSV in the human diet. Water-soluble vitamins, including AA and B vitamins, are essential compounds for adequate functioning of the human body. They play important roles as coenzymes in a wide variety of metabolic reactions that sustain life (Kawasaki and Egi, 2000; Nielsen, 2000; Padayatty et al., 2003; Ubbink, 2000). AA also has antioxidant properties that may protect the human body against reactive oxygen species (Padayatty et al., 2003). Sweetpotato is considered a good source of AA and a moderate source of certain B vitamins in human diets. Besides the root, other sweetpotato plant tissues including young leaves and petioles are edible and high in nutritional value (Johnson and Pace, 2010). Sweetpotato foliar tissues are predominantly consumed in African and Asian countries, functioning as a source of protein, essential amino acids, antioxidants, vitamins, minerals, and dietary fiber (Johnson and Pace, 2010). Sweetpotato foliar tissues have shown significantly higher contents of certain WSV compared with roots (Ishida et al., 2000). Despite the availability of general reference values for sweetpotato WSV content in root pith and leaves, little is known on the distribution of these vitamins in other sweetpotato root and foliar tissues. Limited research has been conducted on the WSV content of different sweetpotato root tissues. An earlier study reported no gradient in thiamin and riboflavin contents from proximal to distal ends of the root. However, thiamin was found more concentrated at 3 mm below the skin compared with the center pith area (Bradbury and Singh, 1986). It is unknown whether other sweetpotato root tissues differ in their WSV content. The objective of this study was to determine the ascorbic acid, thiamin, riboflavin, and vitamin B6 content in a wide range of edible tissues of ‘Beauregard’ and ‘LA 07-146’ sweetpotatoes, two important commercial cultivars in Louisiana. Materials and Methods Tissue origin and sampling procedure. Sweetpotato tissues were sampled on 28 Oct. 2012 from a ‘Beauregard’ sweetpotato plot at the Horticulture Hill Farm Teaching Facility at Louisiana State University, Baton Rouge, LA, and immediately processed for WSV analysis. Sweetpotato tissue types included mature leaves (the tenth fully expanded leaf from the apical meristem), mature petioles (from sampled mature leaves), young leaves (most recent fully expanded leaf from the apical meristem), young petioles (from sampled young leaves), buds (3 cm from the apical meristem), vine sections (15 cm from the apical meristem), and root tissue (central pith). All tissues were then frozen with liquid nitrogen and finely crushed with a mortar and pestle for WSV extraction and analysis. The experiment was repeated (second experiment) with tissue samples collected on 2 Sept. 2013 from a ‘Beauregard’ sweetpotato plot at the Louisiana State University (LSU) AgCenter Botanic Gardens, Baton Rouge, LA. For AA, thiamin, and riboflavin analysis, a total of six and five replicates (individual plants) were randomly sampled throughout the fields in the first experiment and second experiment, respectively. For vitamin B6, a total of four replicates was used in the first experiment. Vitamin B6 was not analyzed in the second experiment. A third experiment was conducted to study WSV content among different sweetpotato root tissues. Sweetpotato root material was collected from the LSU AgCenter Sweetpotato Research Station in Chase, LA. Roots from cultivars Beauregard and LA 07-146 were harvested on 24 Aug. 2012, cured at 29 C for 6 d, and stored at 14 C and 85% relative humidity for 5 months before sampling for WSV analyses. Tissues sampled included skins, cortex, pith at the proximal end, pith at the distal end, and pith at the central region of the root (Fig. 1). Skin samples were collected by gently rubbing the sweetpotato root surface with a knife. The cortex tissue was sampled by careful tissue excision with a knife from roots that the skin had previously been removed. To sample pith tissue, the root was peeled (skin and cortex tissue were removed), and a root piece from the indicated pith locations was obtained with a knife. The pith pieces were then finely chopped into smaller pieces. All root tissues were then frozen with liquid nitrogen and finely crushed with a mortar and pestle. A replicate in each tissue type was representative of an individual root. A total of six roots/ replications were sampled for all tissues. Vitamin extraction and analysis procedures. All vitamin extraction procedures were conducted using amber vials to prevent photo-degradation of the WSV analytes. The total AA extraction methodology was adapted from Chebrolu et al. (2012). Depending on tissue type, 1 g of sweetpotato skins or 3 g of other tissues were placed in an amber vial, and 9 mL of 3% (w/v) meta-phosphoric acid was added. The tissue was homogenized at 3000 rpm for 30 s with a 1-cm diameter VirtiShear homogenizer (The Virtis Co., Gardiner, NY), and then the content was transferred to a 15-mL test tube. The sample was centrifuged at 12,857 · g for 10 min. Approximately 3 mL of the supernatant was carefully filtered through a Phenex 25 mm, 0.45-mm nylon membrane syringe filter, (Phenomenex Inc., Torrance, CA). Then, 0.5 mL of the filtered sample was transferred to an amber 8 · 40 mm (1 mL) high-performance liquid chromatography Received for publication 16 June 2014. Accepted for publication 24 Sept. 2014. To whom reprint requests should be addressed; e-mail wilmer_barrera@yahoo.com. 1470 HORTSCIENCE VOL. 49(11) NOVEMBER 2014 (HPLC) vial and then mixed with 0.5 mL of 5 mmol/L of tris(2carboxyethyl)phosphine hydrochloride. The sample was manually agitated for 15 s and then allowed to remain at room temperature (21 C) for 30 min for complete reduction of dehydroascorbic acid to AA. The sample was then analyzed for total AA content by injecting 5 mL of the sample in an HPLC system (Waters Corp., Milford, MA) consisting of a Model W600 pump, a 717 Plus autosampler, and a 2487 ultraviolet detector. The separation was achieved with a reverse phase C18 GraceSmart column (150 mm · 4.6 mm, 3-mm particle size) from Grace Davison Discovery Sciences Corp (Deerfield, IL). An isocratic mobile phase was used consisting of 25 mM monobasic sodium phosphate with the pH lowered to 2.5 with 17% (w/v) orthophosphoric acid. The flow rate of the mobile phase was 1 mL·min and the run time was 10 min. The AA signal was detected at 254 nm. The software used for HPLC programming and data collection was Waters Empower 3. A representative chromatogram for the separation AA from a sweetpotato root pith tissue sample is presented in Figure 2. For thiamin and riboflavin extraction and analysis, sampled tissues were initially frozen with liquid nitrogen and finely crushed with a mortar and pestle. For sweetpotato skins, 1 g of tissue was placed in a 25-mL erlenmeyer flask and 10 mL of 0.1 M HCl was added. For all other foliar or root tissues, 5 g was transferred into a 250-mL erlenmeyer flask and 50 mL of 0.1 M HCl was added. The mixture was autoclaved for 30 min at 121 C. It was allowed to cool and the pH was adjusted to 4.5 ± 0.1 with 2 M sodium acetate. In each individual sample, 100 mg of taka-diastase was added followed by gentle manual stirring for 10 s. All samples were then put in an incubator (Innova 4000 Incubator shaker; New Brunswick Scientific Co, Inc., Enfield, CT) at 37 C with agitation speed of 60 rpm for 12 h. The volume was then brought to 25 mL (sweetpotato skins) or 100 mL (all other sweetpotato tissues) with distilled water and filtered through Whatman #4 paper (GE Healthcare Co., Buckinghamshire, U.K.). Three hundred microliters of 0.03 M potassium ferricyanide was added to 5 mL of sample extract followed by 15 s of vigorous manual stirring. The sample extract was placed in the dark for 10 min to reduce thiamin to thiochrome. To prevent degradation of analytical column performance, the pH of the sample was then adjusted to 7.0 with a 17% orthophosphoric acid solution followed by filtration through a Phenex 0.45-mm nylon membrane syringe filter (Phenomenex Inc.) and injected in the HPLC system for simultaneous determina

Ascorbic Acid, Thiamin, Riboflavin, and Vitamin B6 Contents Vary between Sweetpotato Tissue Types