"The objective of the study was to determine the ascorbic acid, thiamin, riboflavin, and vitamin B6 content in a wide range of edible tissues of 'Beauregard' and 'LA 07-146' sweet potatoes, two important commercial cultivars in Louisiana," Barrera and Picha said. The scientists analyzed a variety of sweet potato tissue types (mature leaves, young leaves, young petioles, buds, vine sections, and root tissue) from a sweet potato plot at Louisiana State University in late October and again the following September. They conducted a third experiment to study water-soluble vitamin content among different sweet potato root tissues.
Analyses revealed differences in total ascorbic acid (AA) content among tissue types. Young leaves contained the highest AA content, followed by mature leaves and buds. Buds also contained significantly higher AA content than sweet potato roots, vines, and petiole tissues. "These results confirm previous studies that sweet potato foliar tissues are a good source of ascorbic acid, and that young leaves have the highest foliar AA content," the scientists noted. The experiments showed no presence of thiamin in foliar tissues, a finding the authors say differs from previous studies. "The lack of thiamin in our results might be explained by cultivar differences," they explained.
Results also showed that riboflavin content differed with sweet potato tissue type, but was consistently higher in the leaves; mature leaves contained higher amounts of riboflavin than young leaves and other plant tissues, including roots. "Leaf tissue also contained higher total vitamin B6 content compared with other tissues. Mature leaves contained 3.4 times higher vitamin B6 than roots, whereas mature petioles contained 2.3 times more than roots," the authors said. "Bud tissue and young leaves also contained higher B6 levels than roots, whereas the vine and young petiole tissue contents were lower than roots."
Barrera and Picha concluded that ascorbic acid, riboflavin, and vitamin B6 contents were higher in leaf tissue than in other tissue types. "Our results indicate that mature and young leaves of sweet potato could provide significant amounts of vitamin B6 to the human diet," they said. They noted that the vitamin B6 content in sweetpotato leaves compares well with fruits and vegetables such as broccoli, avocados, carrots, bananas, and cauliflower.