The application of ohmic heating for inulin extraction from the wet-milled and dry-milled powders of Jerusalem artichoke (Helianthus tuberosus L.) tuber

In this study, ohmic heating was applied for inulin extraction from the Jerusalem artichoke tuber (JAT). Raw materials for extraction were prepared by two different schemes comprising milling the blanched JAT slices and water mixture (wet milling) and grinding the dried JAT to be powder before mixing water (dry milling). Also, the inulin extracts were evaporated using a rotary evaporator and then spray-dried to be inulin powder. The main objectives were (1) to investigate the effects of applying ohmic heating on the extraction yield and quality of inulin extracts in comparison with conventional method and (2) to determine the suitable preparation method by comparing between wet and dry milling. The results indicated that the electrical conductivities of JAT solutions prepared from the wet-milled and dry-milled powders were 0.121-0.200 and 0.123-0.247 S/m respectively. The inulin extraction applying ohmic heating resulted in the significantly higher yield than conventional heating. Furthermore, the sample preparation using dry milling provided the higher extraction yield and inulin purity than that of wet milling. The scanning electron micrographs illustrated that in overall the dry-milled JAT samples were more porous and finer than the wet-mill samples. The inulin purity of the powder product obtained from the production with dry milling and ohmic method was about 57.29 g/100 g(dry mass) while its production yield was 17.59% which was rather low due to the loss of solids occurring in the blanching, extraction and spray drying processes.