Recipient Organization
SOUTH CAROLINA STATE UNIVERSITY
(N/A)
ORANGEBURG,SC 29117
Performing Department
Engineering Technologies
Non Technical Summary
Sweet potato (Ipomoea batatas) is an extremely versatile and delicious vegetable that possesses high nutritional value and is ranked seventh in global food crop production. Sweet potato leaves and tuberous roots are high in protein, dietary fiber, micronutrients, vitamins as well as bioactive compounds such as carotenoids and polyphenols. The phytochemicals in sweet potato possess multifaceted actions, including antioxidant, antimutagenic, anticancer, antidiabetic, anti-inflammatory activities and to be a natural alternative to estrogen. Therefore, they are important for several health-promoting functions in humans. Different varieties of sweet potato are grown worldwide, and these are generally characterized the different flesh colors with varying phytochemical compositions. This proposal will investigate the quality characteristics of sweet potato leaves and tuberous roots in South Carolina farms and find out the effects of phytochemicals of sweet potato extract on foodborne pathogens. This project is aligned with the mission of South Carolina State University (SCSU) and one of 1890 research's focus areas, Food Safety and Health. There are two objectives for the proposed research project: 1) To determine the phenolic compounds and antioxidant activity in sweet potato leaves and tubers grown in South Carolina and 2) To investigate antimicrobial activity of phenolic compounds extract from sweet potato leaves and tubers grown in South Carolina on selected foodborne pathogens. Samples of sweet potato leaves and roots will be collected from local farmers in South Carolina, and the extension agent will coordinate with farmers. Phenolic compounds from sweet potato leaves and tuberous roots will be extracted, and individual phenolic compounds and antioxidant activity will be analyzed by High-Performance Liquid Chromatography and colorimetrically, respectively. A major goal of this proposal is to strengthen and expand the research capabilities of the University faculty and students at SCSU. Students involved in the project will develop research skills by engaging undergraduate students in intensive research on food safety and health, furthermore, preparing them for acceptance into graduate school. The project will improve the academic program and increase publicity through conference presentations and journal publications and prepare faculty members for external funding opportunities. Moreover, further building the capacity of a food safety laboratory at SCSU will place the university in a more competitive stance to submit grant applications for future funding from governmental agencies i.e., USDA. South Carolina State University is a historically black public land-grant University. The mission of SCSU is to prepare highly skilled, competent, and socially aware graduates to enable them to work and live productively in a dynamic global society as well as to improve the citizen's life and economic development of the state and nation. This project will help farmers and retailers in South Carolina with the quality characteristics of sweet potato. Their understanding of how phytochemicals are related to nutrition, cancer prevention and food safety in their sweet potato will have a positive impact on the quality of their products as well as consumer health. The 1890 Research & Extension Program at SCSU offers an important public service for rural and urban limited-resource families who need the latest research-based scientific knowledge, sustainable practices in agriculture, financial management, business development, parenting skills, health and nutrition, and computer skills. This project aligns with the mission of 1890 Research and Extension on awareness of diet, health, and nutrition of people living in South Carolina.
Animal Health Component
25%
Research Effort Categories
Basic
75%
Applied
25%
Developmental
0%
Goals / Objectives
The hypothesis is that the quality characteristics of sweet potato will vary among the varieties and farms tested in South Carolina. The goal of the study is to analyze the phytochemicals from varieties of sweet potato leaves and tuberous roots obtained from South Carolina farms. Moreover, the effectiveness of phenolic extracts isolated from sweet potato leaves and roots on reduction of foodborne pathogens will be tested.There are two objectives for the proposed research project: 1) To determine the phenolic compounds and antioxidant activity in sweet potato leaves and tubers grown in South Carolina and 2) To investigate antimicrobial activity of phenolic compounds extract from sweet potato leaves and tubers grown in South Carolina on selected foodborne pathogens.
Project Methods
The experimental procedures used to determine phytochemicals, antioxidant and antibacterial activity of sweet potatoes leaves and tubers as follows:Chemicals and Reagents: Sodium carbonate, 2,2-diphenyl-1- picrylhydrazyl (DPPH), Trolox (6-hydroxy-2,5,7,8-tetramethyl chromane-2-carboxylic acid), formic acid, gallic acid, catechin, chlorogenic acid, caffeic acid, vanillin, p-coumaric acid, ferulic acid, m-coumaric acid, o-coumaric acid, rosmarinic acid, quercetin, and trans-cinnamic acid will be purchased from Sigma Inc. (St. Louis, MO., U.S.A.). All solvents employed for chromatography will be analytical HPLC grade: methanol, glacial acetic acid, acetonitrile, and ultrapure water.Sweet Potatoes samples collection: Samples of sweet potatoes leaves, and roots will be collected from farmers in Hampton, Williamsburg, Dorchester, and Charleston Counties in South Carolina during the Fall of each year. The extension agent will coordinate with farmers. The samples will be labeled, packaged in sterile polyethylene bags, transferred to the laboratory, and kept in a cool place (3-5°C) until analysis.Sample Preparation: For each sweet potato sample, leaves and roots were randomly taken, washed with tap water and blot dried. The root tubers will be diced into about 0.5cm cubes. About 100g of these cubes or leaves will be placed in paper bags, and frozen overnight at −20°C before freeze drying. Freeze-dried samples were ground using a warring laboratory electric blender into powder and stored at −20°C until analysis.Determination of Dry Matter Content: Moisture content of sweet potato will be determined by forced air oven drying at 105°C for 24 h. Dry matter content of the samples will be calculated from the initial and final weight of each sample.Extraction and analysis of phenolics: Extracts will be prepared from sweet potatoes powder following a method described by Padda and Picha (2008) (Scientia Horticulturae, 119 (1), 17-20), with some modifications. Briefly, 5 g of powdered sweet potatoes sample will be weighed into 15-mL centrifuge vials. Eight mL of 80% methanol:20% H2O (1% acetic acid) will be added, and the mixture will be shaken on an orbital shaker at room temperature for 24 h. The mixture will be centrifuged at 5000 rpm for 10 min and the resulting supernatant will be collected into a 25 mL volumetric flask. The extraction of the pellet will be repeated two more times, and the combined extracts will be filtered by using Whatman filter paper, ashless, grade 40 circles. The final volume will be adjusted to 25 mL with the extraction solvent. The combined filtrates will be concentrated by an evaporator (RapidVap N2 system, Labconco) and the final volume will be adjusted to 5 mL. A volume of 500 µL will be filtered, using a 0.20 µm PTFE syringe filter, before analysis for individual phenolic compounds by HPLC, and antioxidant activity by the DPPH assay. The remaining extract will be dried until constant weight will be obtained for antibacterial activity measurement.Determination of phenolic compounds by HPLC: The analyses will be performed on a high-performance liquid chromatograph LC-20AB (Shimadzu Scientific Instruments, Columbia, MD), equipped with two high-pressure pumps (LC-20AD), a diode array detector (SPD-M40), a column oven (CTO-20A) and an automatic sampler (SIL-20 AHT). Separations will be performed using a packed Shim-pack VP-ODS column (250 mm × 4.6 mmI.D., 5µm) connected to a Shim-pack GIS (G) C18 Guard column 5 um, (3.0 mm x 10mmI.D., 5µm). Samples will be eluted using two mobile phases: the first (A) will consist of water and acetonitrile (2%) and the second (B) will be comprised methanol, water, and acetonitrile in the proportions 70:28:2 v/v, respectively. Samples will be eluted under the following gradient: 0-25 min (0-40%B); 25 to 43 min (40-45%B); 43-50 min (45-80%B); 50-55 min (80-0%B); and 55-65 min (0%B). The absorbance will be measured at 280 nm at the flow rate 1 mL/min at a temperature of 35°C, and the injected volume will be 20 μL. The standards used for the chromatographic analysis will be gallic acid, catechin, chlorogenic acid, caffeic acid, vanillin, p-coumaric acid, ferulic acid, m-coumaric acid, o-coumaric acid, rosmarinic acid, quercetin, and trans-cinnamic acid.Total Antioxidant Capacity Assay (DPPH radical scavenging activity): The DPPH radical scavenging activity assay will be performed on the phenolic extracts, prepared as described above, following the procedure described by Teow et al. (2007) (Food Chemistry, 103 (3), 829-838). An aliquot (100 µL) of each sample will be pipetted into 3.9 mL of DPPH solution (0.08 M in 95% ethanol) to initiate the reaction. The reaction will be for 2 h at room temperature in the dark, and the absorbance of DPPH free radicals will be recorded at 515 nm against ethanol as a blank by spectrophotometer. Trolox (0, 100, 200, 300, 400, and 500 μM) will be used as a standard antioxidant compound and analysis will be performed in triplicate for each sample and each concentration of standard. The antioxidant activity will be reported in µmol of Trolox equivalents per gram dry weight (μmol TE/g DM).Microorganisms: Staphylococcus aureus (ATCC 25923), Bacillus cereus (ATCC 14579), Escherichia coli (ATCC 25922), and Salmonella enterica (ATCC 13076), will be used to assess the antimicrobial properties of the test samples. The organisms will be subcultured in blood agar culture medium and MacConkey's medium prior to use in experiments. These bacteria will be kept on sterile nutrient agar slant and plates at 4 °C.Assay for Antibacterial Activity: The antimicrobial activities of sweet potatoes extract will be determined by the modified agar well diffusion method as described by Esimore et al. (1998) (Journal of Pharmaceutical Research and Development, 3(2), 99-100). A volume of 20 μL bacterial suspensions with 0.5 McFarland in turbidity will be mixed with 20 mL agar media before solidified, and poured aseptically into a sterilized petri dish, and wait until solidified. A hole with a diameter of 6 to 8 mm will be punched aseptically with a sterile Cork-borer. The extract will be dissolved in an aqueous solution of 50% (V/V) dimethyl sulfoxide (DMSO) to obtain 5%, 10%, and 20% extract sample solutions, and standard antibacterial agent streptomycin (10µg/mL) will be used as the positive control. A volume of 50 µL of each solution and positive control will be added into well, and DMSO solution will be used as a negative control. A control plate will be also maintained in each case without any test materials. Plates will be incubated at 37ºC for 24 hours, and the test will be carried out in triplicate. The zone of inhibition (diameter) will be measured in a millimeter to determine the antibacterial effectiveness of the extracts. The mean and standard deviation of inhibition zones will be calculated.