Japanese Journal of Farm Work Research

Recently, production of sweet potatoes has tended to decline, but expansion of use for Shochu (Japanese distilled spirits) and processed food is in progress. Under these circumstances, ‘Ayamurasaki’ a new cultivar with a high anthocyanin content has been released and is expected to be useful as confectionary and food material. Steaming or boiling is conducted in conventional processing of colored sweet potatoes for primary food materials, resulting in alphanizing of starch. We developed a new drying technique of sweet potatoes by fine cutting before drying to retain betanized starch and useful natural pigments.
1) We studied about the drying characteristics of fine cut sweet potato rhizomes and found a constant drying rate period. We also found out that the optimum air moisture ratio was 0.015 m³ /s·kg (water).
2) Retention of anthocyanin content was high(75 to 87% of before drying) when the drying air temperature was between 50 to 80°C, with the highest yield at 60°C, under an air flow rate of 0.015 m³ /s·kg (water).
3) Reducing the air temperature during drying was an effective method to retain anthocyanin content and betanized starch. Drying with an air temperature of 80°C until the cut raw sweet potatoes was heated, then gradually decreasing the temperature to end at 55°C showed a good performance.

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Bulk density and three phases distribution of soil were measured before and after tractor running to evaluate soil compaction phenomena on the Isahaya reclaimed soil. Mechanical properties of reclaimed soil were also evaluated by soil tests. Results obtained from the study were as follows : 1) Soil compaction caused by the tractor running markedly occurred near the soil surface, due to decrease of the gaseous phase in soil with increase of the solid and liquid phases. This trend was more eminent with increase in frequency of tractor passes. 2) Water in the trampled soil was not drained immediately after trampling, but was gradually drained around the soil resulting in decrease of the water content and increase of the bulk density. 3) From the compaction test in a laboratory, the reclaimed soil showed a maximum dry density of 1.07 g/cm³ when the water content was 51.0%. This condition coincided well with the optimum condition for machinery operations. 4) The undrained triaxial compression tests showed that though undisturbed soil had higher strength than disturbed soil, an unstable mechanical behavior such as softening occurred. One of the reasons may be that a soil structure has been developed in the undisturbed soil. From this point of view, more detailed evaluation of soil structure is indispensable for practical assessment of reclaimed soil on polders.

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