Lupine Publishers| Agriculture Open Access Journal
Abstract
Keywords: Roselle; Hibiscus sabdariffa; Fertilizer; Phenols; Antioxidants and fruit yield
Introduction
Materials and Methods
Chemicals and reagents
ABTS (2,2'-azino-bis (3-ethylbenzothiazoline-6-sufonic acid), potassium persulfate were purchased from Sigma-Aldrich of St. Louis, MO, USA. Folin Ciocalteu's phenol reagent was purchased from MP Biomedicals of Solon, OH, USA. Water and methanol were purchased from Fisher Scientific of Fair Lawn, BJ, USA.Experiment and plant samples
A field experiment was conducted to evaluate the effects of the applied fertilizers at planting time on roselle plants of Senegal accession during the 2014 growing season at Southern University's research farm, Baton Rouge, Louisiana which has a subtropical climate (30.5240N and 91.1900W and elevation of 22m). The area has an average precipitation of 1700mm and the average annual temperature is 19.70C. The field has a silty clay loam soil with a pH of 7.1. The seeds of Senegal accession were planted in the 2x2 cell-pack trays in the greenhouse at the beginning of April, 2014. Seedlings were hand-transplanted into the field one month after germination. A completely randomized design with a total nine applications as treatments. These treatments were the control; 3, 6 and 9# (lb=454g)/30.48m. of organic fertilizer 4-2-2, respectively; 3, 6 and 9# (454g)/30.48m of organic fertilizer 8-5-5, respectively; and 3 and 6# (lb=454g)/30.48 m. of inorganic fertilizer 13-13-13, respectively. Each treatment consisted of 16 plants spaced at 6 feet (1.83m) between plants within a 3.5ft (1.07m) row. Between row spacing was 8 feet (2.44m.). Fertilizers were applied and incorporated on top of the raised bed. Seedlings were planted one day after fertilizer applications. Leaves were randomly collected in late July from branches at waist height from 10 plants of each treatment.Nutrient elemental analysis
Leaves in the brown paper bags were dried at 500C in the Precision Thelco Laboratory oven for 8 hours in the oven and then ground using Thomas-Wiley Model 4 grinder with a 30 mesh screen. The ground samples in the vials were subject to one-hour of drying before they were stored in the desiccator to prevent moisture contamination. Three individual 0.5g of composite ground leaf samples from each treatment were placed in 50mL Digi-tubes (SCP Sciences) and were digested using DEENA automatic digester. Each digested sample in the Digi tube was brought up to a total volume of 20mL with distilled water. The solution with digested sample was vacuum-filtered with a 1.0 micron Digi-filter. The filtrate was analyzed by SPECTRO ARCOS ICAP for Al, Bo, Ca, Cu, Fe, Mg, Mn, Mo, P, K, NA, S and Zn. Separately, 0.15g of dried leaf sample was used for determining the amount of carbon and nitrogen using LECO CN Analyzer.Sample preparation for total phenol and antioxidant activity determination
The method of sample preparation was adopted from Xu [3] and Zhen [2]. A 100mg of each dried and ground leaf sample was measured and placed in a volumetric flask. Twenty-five mL of 70% (v/v) methanol/water with 0.1% acetic solution was added into the flask. The sample extraction was then put in ultrasonic water bath for 10 minutes followed by shaking at room temperature for overnight. The extract of each sample was then filtered through 0.45um filter. The filtrate was used for the Folin-Ciocalteu and ABTS radical scavenging assays.Phenolic content determination (Folin-Ciocalteu assay)
The Folin-Ciocalteu assay with modifications [4] used by Zhen [2] was adopted for the determination of the total phenolic content of the leaves. 40ul of the prepared leaf extract was mixed with 900ul diluted Folin Ciocalteu's reagent followed by incubation at room temperature for 5 minutes. Then, 400ml of 15% sodium carbonate was added. The mixture was allowed to react at room temperature for 45 minutes. The UV absorption of the mixture solution at wavelength of 752nm was measured against a blank solution. The standard curve was measured based on the prepared gallic acid standard solution (0.38, 0.19, 0.095 and 0.475mg/ml). The result was transformed as mg/g of gallic acid. The results were calculated from the mean of three replicates.In vitro antioxidant activity (ABTS radical scavenging assay)
The procedure of the decolonization of the ABTS radical cation [5] used by Zhen [2] was adopted for the determination of antioxidant activity. 38.4 mg of ABTS and 6.6 mg of potassium per sulfate were co-dissolved in 10ml of water and stored for 16 hours in the dark environment to form stable radical action (ABTS+). The stored radical solution was then diluted using ethanol to a concentration with UV absorption of 0.70+/-0.20 at734nm. 900ul of the diluted ABTS radical working solution was mixed with 10ul of the leaf extract followed by 20 minutes of reaction at room temperature. The decolonization of the mixed solution indicates that antioxidant compounds in the extract quenched ABTS radical actions. There was a quantitative relationship between the reduction absorbance at 734nm and the concentration antioxidants present in the sample [2]. The standard curve was built up by plotting the concentrations of Trolox against the percentage of inhibition. The value of antioxidant capacity of the sample was calculated as Trolox equivalent antioxidant capacity. The final result was expressed as the % of antioxidant per dry weight basing on the calculation from the mean of three replicates.Results and Discussion
Figure 1: Effects of the type and rate of fertilizer applied at planting time on fresh roselle fruit yield in kg/plant. Note: # is
denoted as lb. (454 g) of fertilizer applied per 100 feet (30.48 m) row.
Figure 2: Effects of the type and rate of fertilizer applied at planting time on total polyphenol and antioxidant contents of
roselle leaves in % of sample dry weight. Note: # is denoted as lb. (454 g) of fertilizer applied per 100 feet (30.48 m) row.
Figure 3 shows the effects of the type and rate of fertilizer applied
at planting time on (A) macro-nutrients and (B) micro-nutrients of
roselle leaves. The results when the effects were compared to that
of the Control treatment, showed that (a) 3# of organic fertilizer
4-2-2 and 3#, 6# and 9# of organic fertilizer significantly (P<0.05)
increased N content of the leaves, (b) all fertilizer treatments had
no significant effect on P content of the leaves, (c) 9# of organic
fertilizer 4-2-2 significantly (P<0.05) increased K content of the
leaves, (d) all fertilizer treatments had no significant effect on Ca
content of the leaves, (e) 9# of organic fertilizer 4-2-2 , 6# and
9# of organic fertilizer 8-5-5 significantly (P<0.05) increased Mg
content of the leaves, (f) 3#, 6# and 9# of organic fertilizer and 6#
of inorganic fertilizer 13-13-13 significantly (P<0.05) increased S
content of the leaves, (g) all fertilizer treatments had no significant
effect on Cu and Fe contents of the leaves, (h) 3# and 6# of organic
fertilizer significantly (P<0.05) increased B content of the leaves,
(i) 3# and 9# of organic fertilizer 4-2-2, 9# of organic fertilizer
8-5-5 and 3# and 6# of inorganic fertilizer 13-13-13 significantly
increased Mn content of the leaves and (j) 9# of organic fertilizer
4-2-2, 3#, 6# and 9# of organic fertilizer 8-5-5 and 6# of inorganic
fertilizer significantly increased Zn content of the leaves. The results
of this study showed inconsistent in nutrient elemental contents of
plants in response to fertilizer treatments. In general, N, P, K, Ca, Mg,
S, B, Mn, and Zn were significantly increased by selective fertilizer
types and rates while Cu and Fe were not significantly affected by
the fertilizer applications.
Figure 3: Effects of the type and rate of fertilizer applied
at planting time on (A) macro-nutrients and (B) micro-nutrients of
roselle leaves. Note: # is denoted as lb. (454 g) of fertilizer applied
per 100 feet (30.48 m) row. Macro-nutrients are expressed in
% of dry weight while micro-nutrients are expressed in PPM in dry
weight.
Conclusion
https://lupinepublishers.com/agriculture-journal/fulltext/fertilizer-effects-on-nutrient-elements-total-polyphenols-and-anti-oxidant-contents-of-roselle-hibiscus-sabdariffa-leaves.ID.000142.php
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https://lupinepublishers.com/agriculture-journal/abstracts/fertilizer-effects-on-nutrient-elements-total-polyphenols-and-anti-oxidant-contents-of-roselle-hibiscus-sabdariffa-leaves.ID.000142.php
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