DEVELOPMENT AND COMMERCIALIZATION OF PURPLE-FLESHED SWEETPOTATOES FOR THE NATURAL COLORANT MARKETS
Food Science Research
2013 Annual Report
1a.Objectives (from AD-416):
1. Rapid development and introduction of improved purple-fleshed sweetpotato (PFSP) varieties with higher pigment yield, better adaptation and disease resistance.
2. Develop near infrared spectroscopic (NIRS) method for high throughput screening and breeding of PFSP lines for increased anthocyanin content and varied cyanidin-peonidin ratios with specific color characteristics.
1b.Approach (from AD-416):
Advanced PFSP breeding lines from NCSU Sweetpotato Breeding Program will be evaluated for anthocyanin profiles and color characteristics. Anthocyanins will be extracted from freeze-dried samples using a Dionex ASE 200 accelerated solvent extractor. Total monomeric anthocyanin (TMA) content will be determined by pH-differential method. The extract will be acid hydrolyzed in a screw-cap vial at 100ºC for 1 hr for anthocyanin analysis. Anthocyanin and anthocyanidin compounds will be separated and identified by high pressure liquid chromatography (HPLC). Relationship between cyanidin-peonidin ratios and color values (L*, a*, b*) of the extracts will be assessed. Near-infrared (NIR) spectroscopy will be used to develop a more efficient and cost effective method for rapidly analyzing anthocyanin components. Samples will be scanned in the diffuse reflectance mode (400-2500nm) of NIR spectrometer. The mean NIR spectra of the analyzed samples will be modeled against the data generated by pH-differential and HPLC methods using partial least square regression, and the regression models will be validated by full cross-validation. Standard curves that relate the NIR spectra and quantitative measurements of anthocyanin components will be used for speeding up the breeding efforts in developing specific PFSP varieties that have exceptional agronomic and high anthocyanin traits for natural colorant markets.
This project is related to Objective 5 of this in-house project: Evaluate advanced sweetpotato genotypes intended for processing applications, postharvest handling systems, and processing technologies for their potential to increase levels of beneficial phytochemicals in concert with production of high quality food products. Polyphenols in freeze-dried powders from 105 purple-fleshed sweetpotato clones generated by the breeding program were extracted with acidified methanol using the pressurized liquid extraction method. Quantification of total phenolics, total monomeric anthocyanins and peonidin/cyanidin ratio was performed by spectrophotometric and high performance liquid chromatography methods as previously described. The anthocyanin and phenolic contents varied widely from < 1 mg to 650 mg/100 g powder and 71 mg to 3,145 mg/100 g powder, respectively, and the peonidin/cyanidin ratios ranged from 0.04 to 6.04. These wide variations suggested a feasibility of developing high-polyphenolic purple-fleshed sweetpotato varieties. Three promising clones with high anthocyanin yields and good field performance during the past several years have been identified. Near-infrared absorbance spectra, in the range from 400 to 2500 nm, were scanned for the 105 freeze-dried samples using a FOSS XDS Near Infrared Spectrometer and the ISI Scan program. Different near-infrared prediction models were evaluated using the partial least square regression analysis. Accuracy of the equations was assessed using the coefficient of determination (R^2). The precision of the equations was determined using the standard error of cross validation and the standard error of prediction. The residual predictive deviation, a ratio between the standard deviation of the calibration population and the standard error prediction, was also used to evaluate the calibration. Progress has been made in the development of different near-infrared predictive models for high throughput assessment of polyphenolic content in purple-fleshed sweetpotato clones.