Sugars move through stalks to be deposited in kernels in sweet corn (Zea mays L.). Concentrations of sugars in stalks change as plants pass through developmental stages. To follow such changes, carbon-13 nuclear magnetic resonance spectroscopy (C-nmr), a technology that can measure concentrations of sugars in tissues, was compared with analysis by high-performance liquid chromatography (HPLC). A shrunken-2 hybrid (cv. Illini Gold), was monitored from mid-whorl to fresh-market maturity (R3). Internodes near the base of the stalk, just below the ear, and between an ear and the tassel were sampled at each developmental stage. Chemical shifts in C-nmr spectra were measured in parts per million hertz (ppm) down-field relative to tetramethyl silane. Through silk emergence (R1) C-nmr spectra were similar regardless of internode, having line positions between 60 and 105 ppm. Unique lines for glucose, fructose, and sucrose were at 96, 98, and 104 ppm, respectively, and mole fractions were similar to those determined by HPLC. The highest concentrations were recorded at R1 for sucrose (26.1 mg·mL-1), from tasseling (VT) through R3 for fructose (avg. 30.4 mg·mL-1), and from VT to R1 for glucose (avg. 32 mg·mL-1). Carbon-13 nuclear magnetic resonance spectroscopy can be used, with minimal sample handling, to monitor sugar concentrations in sweet corn.
V.M. Russo, J. Williamson, K. Roberts, J.R. Wright, and N. Maness
Mustafa Ozgen, Faith J. Wyzgoski, Artemio Z. Tulio Jr, Aparna Gazula, A. Raymond Miller, Joseph C. Scheerens, R. Neil Reese, and Shawn R. Wright
Black raspberries (Rubus occidentalis L.) are rich in phytonutrients that have demonstrated chemoprotective properties against certain degenerative diseases. To estimate variability in phytonutritional quality among sources of black raspberry, 19 samples representing four common midwestern cultivars obtained from eight production sites were assayed for their antioxidant capacity [2,2-diphenyl-1-picrylhydrazyl (DPPH) and ferric reducing ability of plasma (FRAP) methods], total phenolic content (TP), total monomeric anthocyanin levels (TMA), and levels of cyanidin 3-rutinoside. The antioxidant potential among samples averaged 2.92 ± 0.29 and 4.62 ± 0.88 mmol TE·100 g−1 fresh weight by the DPPH and FRAP methods, respectively; TP, TMA, and cyanidin 3-rutinoside means averaged 449 ± 62, 336 ± 109, and 244 ± 84 mg·100 g−1 fresh weight, respectively. Levels of FRAP, TP, TMA, and cyanidin 3-rutinoside were strongly correlated (r = +0.85 to +0.96). Mean antioxidant capacities and phenolic constituent levels were similar among ‘Bristol’, ‘Jewel’, and ‘MacBlack’ samples; values for a single sample of ‘Haut’ were lower but comparable to levels found in individual samples of the other three cultivars. Black raspberry production site differences were statistically significant for FRAP, TMA, cyanidin 3-rutinoside, and titratable acidity (TA) levels. Inverse relationships (r = –0.65 to –0.74) among black raspberry samples for FRAP, TMA, or cyanidin 3-rutinoside levels versus levels of TA suggested that site differences may be partially attributable to fruit ripeness at harvest. Relationships among these parameters versus regional differences in soil temperatures were also significant but weak. Regardless of its environmental or physiological drivers, point-source variation in fruit phytonutrient contents may be a relevant concern in health-related studies or clinical applications. Moreover, it may impact the nutritional benefits to the consumer and affect the quality advantages associated with direct-marketed black raspberries.