Tempura is a dish of battered and deep-fried foods, and wheat flour is typically used; however, barley, buckwheat, and Job’s tears have an antioxidant capacity. This study investigated whether replacing wheat flour with flours from these three crops in tempura affects the antioxidant capacity and deterioration of frying oil. Radical scavenging activity and polyphenol content of tempura were measured by chemiluminescence-based assay and the Folin–Denis method, respectively. The peroxide value, p-anisidin value, acid value, and polar compound of the oil used in frying were measured as indexes of oil deterioration post-frying due to oxidation. Although the frying oil of barley showed higher p-anisidin value than that of wheat, the oil samples’ deterioration level measured in this study was low. The antioxidant capacity and polyphenol content in the three flours samples were higher than those in wheat sample, with buckwheat producing the greatest values, followed by Job’s tears, and then barley. Thus, deep-fried products prepared using the three flours demonstrated superior antioxidant capacity owing to the abundance of antioxidant components. Therefore, tempura can be enjoyed in a healthier manner by using batter prepared using those flours, and substituting wheat flour with the three flours can increase the antioxidant capacity of deep-fried products.

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Tempura coating that is fried with wheat flour batter should have crispy texture; however, the gluten present in wheat prevents the development of a favorable texture. Thus, we prepared tempura using barley flour, buckwheat flour, or Job's tears flour, which do not form gluten structure. Their quality and palatability were compared to that of normal rice and waxy rice, which are gluten-free grains, in addition to wheat flour. We focused on the changes over time of texture which was an issue with tempura. We hypothesized that the changes in the texture involved moisture absorption from the ingredients, and aimed to reveal the difference in the changes over time by using grain flours. Changes in crispiness and moisture content were different based on the grain flour. Wheat, normal rice, and buckwheat tempura coating absorbed moisture from ingredients and lose crispiness over time. Waxy rice and barley tempura absorbed ingredients moisture only in the tempura coating near ingredients, and there was no change in the crispiness of that surface. Alternatively, Job's tears tempura coating did not change crispiness and moisture content even after 30 min of frying. Therefore, it would be beneficial to use appropriate tempura coating material based on the occasion.