Lack of Correspondence between Experimentally Determined Values of Vitamin E in Carrot (Daucus carota L.) and Those Reported in the USDA National Nutrient Database

Vitamin E compounds, known collectively as tocochromanols, are essential nutrients found in plant tissues. These compounds are present in fruits and vegetables at lower levels than in nuts and oils. However, since fruits and vegetables are frequently consumed in the diet, they represent important contributions to vitamin E intake. Knowledge of nutrient levels in fruits and vegetables is important in making dietary recommendations and in planning menus. The U.S. Department of Agriculture (USDA) National Nutrient Database (NNB) reports levels of vitamin E in carrot of 6.6 mg·g on a fresh weight basis and similar levels of vitamin E for food products containing carrots, such as baby food and carrot juice. We collected data on four tocochromanol compounds using reverse-phase high-performance liquid chromatography (HPLC) with fluorescence detection on both fresh carrots and on commercially available food products containing carrots. Our data revealed that levels of vitamin E in fresh carrot and food products containing carrot were in the range of 0.007–0.12 mg·g converted to a fresh weight basis. These levels were consistent with several published research studies for carrot, lower than several other published studies, and significantly lower than values reported in the NNB. Data from our studies show actual vitamin E values for this vegetable may be significantly lower than levels published in the NNB, but large discrepancies exist in the published reports for measurement of tocochromanol levels for this vegetable. Dietary guidance based on vitamin E values for carrot reported in the NNB could lead to inaccurate nutrient recommendations and should be clarified and standardized. Vitamin E is a group of eight lipid-soluble antioxidants (a-, b-, g-, and dtocopherols and tocotrienols, collectively known as tocochromanols) that are synthesized in the plastids of plants, algae, and some cyanobacteria (M ene-Saffran e and DellaPenna, 2010). Tocochromanols result from the condensation of homogentisate and phytyl pyrophosphate derived from the shikimate pathway and the nonmevalonate 1-deoxy-D-xylulose5-phosphate pathway, respectively (DellaPenna and Pogson, 2006). Vitamin E is an essential nutrient in the human diet, critical for membrane integrity and stability, and has a variety of health promoting properties (Hunter and Cahoon, 2007). Seeds, nuts, and oils are recognized as good sources of vitamin E and some orange and red vegetables and leafy greens have been noted to contain vitamin E.Murphy et al. (1990) found that vegetables were the second largest contributor, after fats and oils, to vitamin E intake in the adult U.S. diet, representing 15.1% of the total vitamin E contribution. Even though nuts and seeds are rich sources of vitamin E, they are consumed by fewer people and in smaller amounts than other vitamin E sources, and contribute 4-fold less to total vitamin E intake (Murphy et al., 1990). Carrots (Daucus carotaL. var. sativa), well known for high concentrations of provitamin A carotenoids, also contain vitamin E. Koch and Goldman (2005) and Luby et al. (2014) have reported several tocochromanols in carrot, including a-, band g-tocopherol and a, b-, and g-tocotrienol. Burns et al. (2003) and Koch and Goldman (2005) used reverse-phase HPLC equipped with an ultraviolet detector to quantify vitamin E levels in carrot roots. These studies reported values of 0.03–0.11 mg·g of totalaand btocopherol on a fresh weight basis. Luby et al. (2014) used more sensitive and specific fluorescence detection during HPLC analysis, which was capable of measuring additional tocotrienols and tocopherols. Luby et al. (2014) measured an average of 0.12 mg·g converted to a fresh weight basis of total tocochromanols in hybrid carrot roots. Ombodi et al. (2014), Metzger and Barnes (2009), and Nicolle et al. (2004) measured tocochromanols in carrot using various techniques. These three studies revealed levels of tocochromanols in carrot that were significantly higher than those reported by Burns et al. (2003), Koch and Goldman (2005), and Luby et al. (2014). The NNB contains values for vitamin E levels in fresh carrot and for some commercial food products that contain carrot. In this study, we evaluated tocochromanol levels in commercially available carrots and food products containing carrot to obtain a fuller picture of vitamin E levels in this vegetable, and compared our findings to published levels for vitamin E in carrot and to those in the NNB. Materials and Methods We purchased nine different commercially available food products containing carrots, including Just Veggies organic dehydrated carrots, Freshlike frozen sliced carrots, Clear Value whole canned sliced carrots, S&W canned julienne carrots, Whole Foods organic baby carrots, Copps fresh whole carrots, Whole Foods organic fresh whole carrots, Earth’s Best organic baby food with carrots, and Fresh Market organic carrot juice. All products were purchased inMadison, WI. For whole carrots, a sample of root 2 cm thick was removed from the top of the root, lyophilized, and ground into a powder. For commercial food products, a similar volume of material was lyophilized and ground. All samples were extracted and analyzed in duplicate. Samples were stored at –80 C until HPLC analysis. A modified protocol from Bligh and Dyer (1959) was used, based on the protocol of Maeda at al. (2008), where 50 mg of lyophilized carrot tissue or carrot food product was added to a 2-mLEppendorf tubewith 3 (3mm) glass beads, 400 mL of 2:1 methanol to chloroform (v/v) with 0.01% butylated hydroxytoluene (BHT), and tocol standard (rac-5,7 dimethyltocol; Matreya, Pleasant Gap, PA). Samples were shaken using aGenogrinder for 3 min at a setting of 500 strokes/ min. An additional 300 mL H20 and 125 mL chloroform were then added to the homogenates, which were further shaken for 30 s at the same settings. After phase separation by Received for publication 9 Mar. 2015. Accepted for publication 30 July 2015. We thank the Department of Botany, the College of Letters & Science, and the Graduate School of University of Wisconsin-Madison for providing start-up funds to Hiroshi Maeda. Corresponding author. E-mail: ilgoldma@wisc. edu. HORTSCIENCE VOL. 50(10) OCTOBER 2015 1595 MISCELLANEOUS