BACKGROUND: Taro (Colocasia esculenta cv. Daikichi) is believed to be one of the earliest cultivated tuber crops and it is a staple food in many parts of the world. The mother corm and side cormels (daughter and granddaughter tubers) form the major consumed parts; however, the former is rarely preferred. Taro is mainly cultivated using either unflooded or flooding cultivation, under dryland-rainfed and wetland-irrigated conditions, respectively. Although flooding cultivation has several advantages, such as lower risk of diseases, weeds, and insect pests, contributing to increased tuber yield, its effects on the quality characteristics of the tubers are largely unknown. In this study, the effects of controlled flooding cultivation on the quality of mother corm and side cormels were investigated. Their taste, color, physical properties, antioxidant activity, and starch, oxalic acid, nitrate ion, arabinogalactan (AG)/AG protein (AGP), γ-aminobutyric acid (GABA), and total polyphenol content was compared with those under unflooded cultivation. RESULTS: Flooding cultivation increased polyphenol levels and antioxidant activity and decreased oxalate, nitrate ion, GABA, and AG/AGP levels. Flooding cultivation also reduced the harshness and increased the hardness and stickiness of steamed mother corm paste, generally discarded under unflooded cultivation, thus rendering it suitable for consumption. CONCLUSION: Controlled flooding cultivation has economic advantages and the potential to improve the quality of cultivated taro.
Starch from the new sweetpotato cultivar Konamizuki (KM) was evaluated as a food material, and its basic properties were characterized. Change in elastic modulus during cold storage of KM starch gels and syneresis after freeze-thaw treatment were limited and indicated slow retrogradation properties. In addition, KM starch paste had higher and more stable storage modulus than other starches, suggesting desirable gel-forming properties. These KM gel properties reflected distinctive structural properties, including larger quantities of short unit chains with degree of polymerization 6-10 and amylose-like long chains of the amylopectin, as well as longer amyloses and longer amylose-like chains of the amylopectin compared with other starches. Finally, KM starch was used in the production of tapioca pearls and starchy noodles, and subsequent sensory analyses indicated highly desirable properties as a food material for starchy gel products.
We compared three sweet potato cultivars used mainly for starch and alcohol production, ('Shirosatsuma', 'Shiroyutaka' and 'Koganesengan') with another used for cooking ('Tosabeni') to study the feasibility of those three cultivars as an inexpensive diet material for the mass-production of adult sweet potato weevils to be sterilized for insect release. About 1,500 adult weevils (sex ratioԼ1:1) were reared on sweet potato storage roots for 2 wk to allow oviposition. Four roots (ca. 800 g) were set out at a time and were replaced with new ones at intervals of 3-4 d. The emergence time of new adults from the roots of Shiroyutaka tended to be a little earlier, and those of Koganesengan a little later than those of Tosabeni. The number of adult weevils available for sterile insect release was no more than 2.7% less when weevils were reared on Koganesengan than when reared on Tosabeni. There was no significant difference in the number of adult weevils produced per gram of sweet potato root between the three cultivars and Tosabeni. Importantly, the percentage of males among emerged adults (sex ratio) was significantly higher in the three cultivars than in Tosabeni. The weevils in a root of Shiroyutaka tended to reach the stage suitable for irradiation 1-2 d earlier than those in Tosabeni. Based on these results, it was concluded that the three cultivars 'Shirosatsuma, Shiroyutaka and Koganesengan' were suitable as diet materials for the mass-production of weevils.
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