屬於十字花科之花椰菜，無論在動物或人體實驗都顯示防癌效果，其機轉是透過對肝臟解毒系統活化而加速致癌物之代謝。而造成此反映的是花椰菜中glucosinolate之裂解產物，是由myrosinase催化產生，所以一旦加熱，酵素活性則被抑制。本實驗欲探討加熱對花椰菜對解毒酵素活性之影響，實驗分三組，花椰菜（1）冷凍乾燥組（glucosinolate 已裂解），以2%重量混合成飼料，餵以小白鼠（4隻/組）7天，結果發現，在第（2）組小白鼠GST（phase II 酵素）活性顯著上升，顯示在植物裂解酵素不存在之狀況下，腸胃道之微生物仍可促進裂解反應，但由CYP1A（phase I 酵素）活性不顯著看來，根據定義：phase I 與II 酵素活性同時增加，稱之 bifunctional induction/inducer，單獨phase II 酵素活性增加，為monofunctional induction/inducer，我們假設：第（3）組小白鼠所攝取之加熱冷凍乾燥之花椰菜之monofunctional inducer 被裂解出及在腸胃道被吸收造成phase II 酵素活性上升，相反的，bifunctional inducer，如 I-3-C，直到腸道才被解出來而錯失在正常情形下在口腔裂解，在胃進行酸化而被活化之機會，而無法造成bifuctional induction，所以我們推測，經由加熱之花椰菜可去除可能致癌之bifunctional induction，而加強了花椰菜之健康效益。
Broccoli is a cruciferous vegetable with chemopreventive effects demonstrated in both animal and human studies. Chemoprevention activity is associated with inductions of drug-metabolizing enzymes that modulate carcinogen metabolism. Once the plant is damaged by chewing, conversion of breakdown products from parent glucosinolates (GS) in broccoli is triggered by myrosinase (EC 3.2.3.1), which can be inhibited by heating. The effects of heating broccoli on the inhibitory activities of myrosinase on drug-metabolizing enzyme activity was investigated in treatment groups with freeze-dried, heated freeze-dried or autolyzed freeze-dried broccoli powder in mice. Mice (4/group) were fed with a diet incorporated with these three broccoli preparation at 20% (w/w) for 7 days. Each group had its own pair-fed group. Significant inductions of glutathione S-transferase (GST, a Phase II drug-metabolizing enzyme) activities in heated freeze-dried groups were compared with inductions in their respective pair-fed groups. Results indicated that without plant myrosinase activity, intestinal microflora still hydrolyzed glucosinolates. Alteration of cytochrome P-450 1A (CYP1A, a Phase I drug-metabolizing enzyme) induction was not significant. Therefore, based on bifunctional induction promoting the activities of both Phase I and Phase II enzymes and on monofunctional induction enhancing Phase II alone, we hypothesize that in the case of heated broccoli powder, hydrolyzed monofunctional inducers produced by microflora and absorbed by the intestine cause Phase II enzyme inductions. In contrast, bifunctional inducers, such as indole-3-carbinol (13C), which have not been activated by acid condensation in the stomach, are not functional. Hence, heating may avoid hepatic bifunctional inductions that could bioactivate carcinogens and therefore increase the health benefits derived from eating broccoli.
