Abstract:
Background: Honey contains various bioactive compounds, including polyphenols, and its functional properties are influenced by the botanical origin of nectar. Sweet potato (Ipomoea batatas (L.) Lam.) generally exhibits poor flowering ability under open-field conditions in Japan. Our research group has developed and maintained sweet potato breeding lines specifically selected for their ability to flower under open-field conditions and their potential suitability as nectar sources for apiculture. These lines may provide a novel nectar source for honey production. We recently succeeded in producing honey from the flowers of these breeding lines To the best of our knowledge, this is the first instance of honey production from sweet potato flowers in the world. However, the nutritional properties of this sweet potato honey—such as its polyphenol content and antioxidant activity—had not previously been evaluated. Therefore, this study aimed to evaluate the antioxidant capacity of sweet potato flower honey using multiple assays and to compare its antioxidant properties with those of commercially available Japanese honeys.
Materials and Methods: Honey samples were collected in October 2025 from flowers of open-field flowering sweet potato breeding lines cultivated at the experimental field of Ishikawa Prefectural University, Japan. For comparison, seven commercially available Japanese honeys, including thistle, horse chestnut, apple, linden, mandarin orange, clover, and acacia honeys (Nishizawa Apiary Co., Ltd., Miyazaki, Japan). Antioxidant capacity was evaluated using three complementary assays: the DPPH radical scavenging assay, ferric reducing antioxidant power (FRAP) assay, and ABTS radical cation scavenging assay. Total polyphenol content (TPC) was determined using the Folin–Ciocalteu method. Color intensity was evaluated by absorbance at 450 nm (ABS450), and relationships among ABS450, TPC, and antioxidant capacity were examined.
Results: Honey derived from sweet potato flowers exhibited high antioxidant capacity compared with the commercially available Japanese honeys. DPPH radical scavenging activity and FRAP values were 28.8 and 125.3 μmol Trolox equivalents/100 g honey, respectively, and were significantly higher than those of the commercial honeys except thistle honey. In the ABTS assay, sweet potato flower honey showed an antioxidant capacity of 97.0 μmol Trolox equivalents/100 g honey, which was significantly higher than those of the other commercial honeys except thistle honey. Sweet potato flower honey also showed the highest total polyphenol content among all honey samples examined (64.5 mg gallic acid equivalents/100 g honey), significantly exceeding those of all commercial honeys. A strong positive correlation was observed between DPPH radical scavenging activity and TPC (r = 0.96, p < 0.05). Significant relationships were also observed among ABS450, TPC, and antioxidant capacity.
Conclusion: Honey derived from sweet potato flowers exhibited high antioxidant capacity across multiple antioxidant assays. The findings of this study are expected to help demonstrate that honey derived from sweet potato flowers may contribute to various health benefits. Further studies will focus on evaluating its broader functional properties and exploring its potential as a novel honey and region-specific functional food material.
Keywords: sweet potato, honey, antioxidant activity, polyphenols, functional foods