Studies on the characteristics of local strains of taro, eggplant, and rape native to Nara, with special reference to cooking properties of 'Ajimaimo', Yamato-Marunasu, and Yamato-Mana

These studies were conducted to clarify the diversity of the taste quality and texture of taro corms and eggplant fruits, and to clarify the suitability for cooking of local strains of taro (Colocasia esculenta (L.) Schott), eggplant (Solanum melongena L.) and rape (Brassica rapa L.) native to Nara. 1. Differences among taro cultivars in corm stickiness and firmness Investigations of the physical properties of boiled corm and a sensory evaluation were conducted with seven taro cultivars including 'Ajimaimo', a native strain in Nara. No correlation was found between the viscosity measured with a rotary viscometer and the texture to stickiness. A significant positive correlation was found between the tensile resistance of a disk-shaped plunger close-contacted to the cut surface of corm and the texture to stickiness. Therefore, the tensile resistance was considered an effective means to evaluate stickiness. Significant correlations were found between the moisture content of corms before boiling and the texture to stickiness or firmness. Actually, differences among cultivars in the moisture contents of corms were almost the same before and after boiling. Therefore, from the moisture contents of fresh corms, it might be possible to estimate the texture after boiling. In sensory evaluation, 'Ajimaimo' was evaluated as medium in both stickiness and firmness among cultivars. 2. Peeling method effects on boiled corm texture and physical properties Texture and physical properties of corms peeled in two ways and boiled were investigated. When corms were peeled by rubbing of sufficiently wrinkled aluminum foil, thin peels remained on the boiled corm surface. Comparerd with corms peeled using a knife, stickiness near the thin peel was felt strongly. 3. Differences among taro cultivars in suitability for cooking The effects of four processing methods on the taste quality and texture were investigated based on a sensory evaluation of seven cultivars including 'Ajimaimo'. Four processing methods were compared: steaming, steaming and seasoned with miso, boiling in seasoning, and cutting into 1.5 * 1.5 * 1.5 cm cubes and boiling in miso soup. The taste quality and texture to stickiness, firmness and mealiness were evaluated. Significant differences were found among cultivars in the taste quality of the two steamed dishes, but no significant difference was found in the taste quality of the two boiled dishes. Significant differences were found among cultivars in every texture parameter with all processing methods. Steamed corms were evaluated as delicious as mealy cultivars. Steamed corms with miso tended to be evaluated similarly. Boiled corms in miso soup tended to be evaluated as delicious as firm cultivars. Significant negative correlation was found between the textures to stickiness and firmness of steamed corms. 'Ajimaimo' was evaluated as more than moderately delicious among the seven cultivars in every cooking. 4. Differences among eggplant cultivars in the physical properties of fruit before and after cooking Investigations of the physical properties of fruit before and after cooking and a sensory evaluation after cooking were conducted with five eggplant cultivars including 'Yatakei', a native strain of Yamato-Marunasu in Nara. Yamato-Marunasu is a strain group selected from 'Kamonasu', a native strain in Kyoto. The moisture content and firmness were measured of flesh cubes of 2 * 2 * 2 cm before and after steaming or frying with salad oil. The fried flesh was then evaluated with respect to its taste quality and texture related to the oiliness. Results show that the total weight of flesh was increased by steaming and decreased by frying. The moisture content of flesh was highest in 'Mizunasu' and lowest in 'Kurowashi' before cooking. It was slightly increased in all cultivars, but no significant differences were found among five cultivars after the steaming. By contrast, a marked decrease and a significant difference in the moisture content of flesh were found in the five cultivars by frying. The moisture content of the fried flesh was higher in 'Yatakei' and 'Kurowashi', although they contained lower oil levels than the others. A significant negative relation between the moisture and oil contents of fried flesh was found. Before cooking, the flesh firmness was significantly different among the five cultivars: highest in 'Kurowashi' and lowest in 'Mizunasu'. It was markedly lower after cooking. It was highest in 'Yatakei' and lowest in 'Senryonigo' after steaming, but highest in 'Mizunasu' and lowest in 'Senryonigo' and 'Shoyaonaga' after frying. Sensory evaluation revealed a significant difference in the texture related to oiliness among cultivars, with higher levels of oiliness found in 'Shoyaonaga' and 'Mizunasu' than in 'Yatakei'. A strong relation was found between the texture related to oiliness and the moisture or oil content of the fried flesh. 5. Differences among eggplant cultivars in suitability for cooking To estimate the differences in the suitability of eggplant fruit for Japanese-style cooking, the effects of processing on the taste quality and texture were investigated based on a sensory evaluation of seven cultivars including 'Yatakei', treated as a high-grade ingredient in the market. Six processing methods were compared: salting, pickling in seasoning liquid, deep frying and soaking in seasoned soup stock, boiling with seasoning, steaming, and grilling over an open flame. Moisture contents of fruits before and after salting and the contents of chlorogenic acid and total polyphenols, affecting astringency, were also measured. Marked variations were found among the cultivars in terms of the taste quality for all processing methods except deep frying, the astringency of salted, steamed, and grilled fruits, the firmness of flesh and succulence with all processing methods, and the pericarp firmness of salted, pickled, boiled, and steamed fruits. Significant variations were also found for oiliness when deep fried, flavor permeability when boiled, and sweetness when grilled. Significant correlations were found between the taste quality score and texture parameters including astringency, firmness of flesh, succulence, and sweetness. Chlorogenic acid and total polyphenol contents of fresh flesh were positively associated with the astringency of salted, pickled, and deep fried fruits. 'Yatakei' was the most suitable for deep frying and grilling among the cultivars, as the taste quality score was the highest for firmness and sweetness. 6. Evaluation of taste characteristics of Yamato-Mana compared with Komatsuna To assess differences in taste characteristics between Yamato-Mana, a native rape strain group in Nara, and Komatsuna, the most popular rape cultivar group in Japan, the effects of processing methods on the taste quality were investigated based on a sensory evaluation. Seven processing methods were compared: steaming, boiling, salting for two periods, pickling in seasoning liquid for two periods, and boiling with seasoning. From comparison between 'Ymamatomana', a commercial purebred cultivar of Yamato-Mana, and 'Rakuten', a commercial hybrid cultivar of Komatsuna, no significant difference was found in the taste quality between two cultivars. In only three combinations of processing methods, sample parts and evaluation parameters, of all 70 combinations, significant differences were found between two cultivars. From comparison between two hybrid strains of Yamato-Mana and 'Rakuten', no significant difference was found between Ymamato-Mana strains and 'Rakuten'. Of all 126 combinations, only in 7 combinations of processing methods, sample parts and evaluation parameters, significant differences were found between Yamato-Mana and Komatsuna. In terms of taste quality, Yamato-Mana was equivalent to Komatsuna.