Production of dried sweet potato leaves and stems with high polyphenol content using airflow drying and steam blanching.

摘要

The main aim of this study was to produce dried leaves and stems of sweet potato for use in functional animal feed. Although these plant components are rich in polyphenols, enzymatic activity during airflow drying results in degradation of the polyphenolic content. In a previous study, steam blanching prior to drying was shown to be effective for retaining polyphenols in sweet potato leaves in laboratory-scale experiments. In the present study, the effect of steam blanching on polyphenol content was evaluated on a practical scale. This article describes the difference in the polyphenol reductions between the material dried after blanching and that without any blanching. Two hundred kilograms of material (sweet potato leaves and stems) was blanched with a steamer for 6 min and then dried with an airflow oven dryer at 100.0 degrees C until the moisture content reached 11.1% d.b. (10.0% w.b.). For the material treated with blanching, the polyphenol content after drying was 72.5% of that of the raw material. In contrast, no more than 28.7% of the initial polyphenol content remained in the material after drying it without blanching. Therefore, it was confirmed that steam blanching was effective for polyphenol retention on a practical scale. Pulverized leaves and stems were produced from the dried material for use in supplemental animal feed. Furthermore, the consideration of energy consumption in the production process is described. The total energy for processing 200.0 kg of material was 3882.5 MJ, and the energy consumption in the drying process accounted for 78.3% of the total energy.