Vitamin contents and mutagenicity of the cooked rices keeping warm in various electric rice cookers : Differences by the cookers, various kinds of milled rices and enriched rices

[Author abstract]In order to achieve the purpose of this title, the vitamin B_1 and vitamin B_2 contents in cooked rices were determined by using the photofluorometry and the mutagenicity of these were assayed in Salmonella typhimurium TA 98 and TA 100 strains using the method of Ames et al. In the next report the mutagenicity of the cooked white rice warmed for 24 or 36 hrs are weak, using TA 98. However in this investigation the revertant colonies per 1.2 g of the cooked rice, warmed for 36 or 48 hrs was less than 71 in TA 100 and the dose-response curves of the mutagenicity were not obtained. Even these scorched rices had little mutagenic action in TA 100. Vitamin B_1 retentions of the cooked white rices, warmed for 12 hrs were 76～83% in a 1.5l cooker, 70% in a 2l cooker, and these retentions, warmed for 36 hrs were 42～72% in the 1.5l cooker, 49 % in the 2l cooker. On the B_1 contents of the warming cooked rices, these rices sampled from near the wall of the cooker were less than ones sampled from the center of the cooker. The B_1 retentions of brown rice, half-milled rice and undermilled rice, cooked and warmed for 12 hrs were 94%, 73～86% and 77% respectively. However, these B_1 contents were much higher than the cooked white rices, warmed for the same hrs. The B_1 retentions of the enriched rices using polyrice were 66～92% when these cooked rices warmed for 12 hrs, but the B_1 contents were 121～186μg%. Throughout all the experiments the B_2 contents in these rices during warming reduced little. From the facts described above, the results were as follows: the limiting time of warming of cooked rice was 12 hrs because of the loss of palatability and the retention of B_1. These B_1 contents were varied with the cooking and warming conditions and also different from the descriptions of these cookers. The B_2 contents did not reduce during warming in order to its thermostability. Judging from the bioassay for B_1,using common finches, the negative correlation between birds' ages and warming time of the cooked white rices was statistically significant at the level of 1% (N=45r=0.463). No bird did die by the addition of B_1・HCl solution to even the cooked rice, warmed for 36 hrs. No other harmful substance which kill even one bird was produced during warming, except the loss of B_1.[著者抄録]電子ジャー保温飯のビタミンB_1, B_2と変異原性の消長について,ジャーの器種,各種精白米及びポリライス強化白米などによる相異を検討して次の結果をえた.1.保温飯の変異原性は,TA100についてはDose-response curves はえられず,36時間では多くても疑陽性程度であった.2.1.5l容ジャーと2l容ジャーの比較では,前者が94～98℃で(夏季), 90℃で(冬季, Fig. 3)で保温し,後者が常に約74℃での低温保温で,これが変異原性に影響を与えたが,B_1の残存率にはむしろジャー内の含水量の影響の方が大きかった.また,B_2は耐熱性のため保温中ほとんど大きな減少はみられなかった.3.7分搗米,半搗米の保温飯はそれなりに多くのB_1を残存しており,精白度の低い方が保温後も多くのB_1を確保していた.4.玄米飯はその吸水率が悪い関係から2度炊飯を行った.2度目の炊飯にはさらに温湯を添加したため,含水率が多くB_1残存率が良好であったが通常のような1回炊飯では高温のためかB_1の破壊が多きかった.5.白麦米はそれなりの添加効果を示し,ポリライス強化白米飯はその目的どおり,多量のB_1を強化し保持しており,12 hrs保温後でも370μg%のB_1を含んでいた.6.電子ジャーの保温限度はその米の食味,ビタミンの損失などから考えて12hrsどまりであり,また,保温温度も低温における腐敗の進行からみて約74℃が望ましい.7.十姉妹による保温飯のみの給餌試験では,生存日数と保温時間とは負の相関があった(α=0.01).8.保温によりB_1を消失し,B_1欠乏によるへい死が観察されたがB_1を添加するとへい死は起らなかった.従って十姉妹をへい死せしめる有害物質は生成しなかった