Data from: Simultaneous quantification of β-carotene, anthocyanins, and total phenolics in sweetpotato with visible-near-infrared spectroscopy

These data were used for the manuscript “Simultaneous quantification of β-carotene, anthocyanins, and total phenolics in sweetpotato with visible-near-infrared spectroscopy” by Matthew C. Allan, Ragy M. Ibrahem, Christopher Parish, Suzanne D. Johanningsmeier, Kenneth V. Pecota, and G. Craig Yencho. They are β-carotene, total phenolics, total monomeric anthocyanins, and anthocyanidins (peonidin, cyanidin, and pelargonidin) contents along with visible-near-infrared spectra (Vis-NIRS) of 203 raw sweetpotato powders.<br><b>Materials and Methods</b>Freeze dried sweetpotato powders (n = 203) were generated from sweetpotatoes that were sliced, freeze dried, then ground into a powder. Sweetpotatoes were selected based on Vis-NIR spectra diversity and historical data of β-carotene and anthocyanin contents.<b>Visible - Near Infrared Spectroscopy</b>Spectra of sweetpotato powders were were collected using a FOSS XDS analyzer (FOSS Analytical, Hilleroed, DK) from 400 to 2500 nm in 2 nm increments.<b>Compositional analyses</b><b>β-Carotene</b>1 g of sweetpotato powder was weighed into a 15 mL polypropylene centrifuge tube, 7 mL of hexane with 0.01% w/v BHT (antioxidant) was added, vortexed to disperse, then mixed end-over-end at 40 rpm for 10 min. Tubes were then centrifuged at 6000 <i>g</i> for 5 min, supernatant decanted into 25 mL volumetric flask, and repeated for a total of 3 extractions. Flask was brought to volume, briefly mixed, an aliquot was passed through a 0.45 µm nylon syringe filter into a 2 mL amber vial, then the headspace of the vial was briefly flushed with nitrogen gas before capping. β-carotene was quantified using an external calibration curve and Shimadzu Prominence HPLC system (Kyoto, JP) with photo diode array detector at 450 nm. Carotenoids were separated isocratically with 36% methanol, 60% MBTE, and 4% water at 1 ml/min with a YMC (Kyoto, JP) C-30 carotenoid column (5µm, 4.6 x 250 mm) and guard column at 30°C. This method has a 98.9% extraction efficiency.<b>Phenolic and anthocyanin extraction and analyses</b>Phenolic compounds were extracted using hot acidified methanol. Two hundred and fifty milligrams of sweetpotato powder were weighed into 15 mL polypropylene centrifuge tubes, 10 mL of 0.12 M HCl methanol was added, then mixed for 10 min at 650 rpm and 65°C in a Thermomixer (Eppendorf, Hamburg, DE). These were centrifuged at 6500 <i>g </i>for 5 min, supernatant was decanted into a 50 mL volumetric flask, and the process repeated for a total of 4 extractions. This method has a 99.5% and 99.8% extraction efficiency for total anthocyanins and phenolics, respectively.<b>Total anthocyanins</b>Total monomeric anthocyanins in the methanolic extract were quantified using the pH differential method. Briefly, 200 µL aliquots of extract were mixed separately with 1800 µL of pH 1 0.025 M KCl and pH 4.5 0.4 M sodium acetate aqueous buffers. These were vortexed and absorbances at 520 and 700 nm were measured with a Cary 100 UV-Vis spectrophotometer (Agilent, Santa Clara, CA, USA). Extinction coefficient used was 26,900.<b>Total phenolics</b>Total phenolic compounds were quantified using the Folin-Ciocalteu total phenolic content assay. Briefly, 350 µL of phenolic extract, 350 µL FC phenol reagent, and 5 mL of water were combined, mixed, allowed to sit for 5 min, 1 mL of 20% sodium carbonate was added, mixed, then incubated for 2 h at 30°C. The 750 nm absorbance values were measured, and phenolics were calculated using an external chlorogenic acid calibration curve.<b>Anthocyanidin quantities</b>The anthocyanidins (anthocyanin aglycon) cyanidin, pelargonidin, and peonidin were quantified following acid hydrolysis. 1 mL of methanolic phenolic extract was pipetted into narrow mouthed (8mm) HPLC vials, 0.5 mL of 6 M HCl was added, vials were capped then mixed at 300 rpm and heated at 99°C in a thermomixer for 1 h. Anthocyanidins were separated using a YMC-Pack Pro C8 plus guard column at 35°C with the following gradient method at 1 mL/min: solvent A - 5% formic acid in water, solvent B - 5% formic acid in acetonitrile; linear gradient of 10% to 35% B from 0 to 8 min; followed by 5 min of 10% B. Cyanidin and peonidin were detected at 526 nm and pelargonidin at 513 nm and quantified using external standards. This was conducted on the same HPLC system as described above.<br>