Dept. of Food Science and Human Nutrition, Univ. of Illinois at Urbana Champaign, Urbana, IL 61801, U.S.A.
J Food Sci. 2013 Sep;78(9):H1459-63. doi: 10.1111/1750-3841.12221. Epub 2013 Aug 5.
Frozen broccoli can provide a cheaper product, with a longer shelf life and less preparation time than fresh broccoli. We previously showed that several commercially available frozen broccoli products do not retain the ability to generate the cancer-preventative agent sulforaphane. We hypothesized that this was because the necessary hydrolyzing enzyme myrosinase was destroyed during blanching, as part of the processing that frozen broccoli undergoes. This study was carried out to determine a way to overcome loss of hydrolyzing activity. Industrial blanching usually aims to inactivate peroxidase, although lipoxygenase plays a greater role in product degradation during frozen storage of broccoli. Blanching at 86 °C or higher inactivated peroxidase, lipoxygenase, and myrosinase. Blanching at 76 °C inactivated 92% of lipoxygenase activity, whereas there was only an 18% loss in myrosinase-dependent sulforaphane formation. We considered that thawing frozen broccoli might disrupt membrane integrity, allowing myrosinase and glucoraphanin to come into contact. Thawing frozen broccoli for 9 h did not support sulforaphane formation unless an exogenous source of myrosinase was added. Thermal stability studies showed that broccoli root, as a source of myrosinase, was not more heat stable than broccoli floret. Daikon radish root supported some sulforaphane formation even when heated at 125 °C for 10 min, a time and temperature comparable to or greater than microwave cooking. Daikon radish (0.25%) added to frozen broccoli that was then allowed to thaw supported sulforaphane formation without any visual alteration to that of untreated broccoli.
冷冻西兰花可以提供更便宜的产品，与新鲜西兰花相比，它的保质期更长，准备时间更短。我们之前曾表明，几种市售的冷冻西兰花产品不保留生成预防癌症的萝卜硫素的能力。我们假设这是因为在冷冻西兰花加工过程中进行的烫漂过程中，必需的水解酶黑芥子酶被破坏。本研究旨在确定一种克服水解活性损失的方法。工业烫漂通常旨在使过氧化物酶失活，尽管在西兰花的冷冻储存过程中，脂肪氧合酶在产品降解中起着更大的作用。在 86°C 或更高的温度下烫漂会使过氧化物酶、脂肪氧合酶和黑芥子酶失活。在 76°C 烫漂会使 92%的脂肪氧合酶失活，而黑芥子酶依赖的萝卜硫素形成只有 18%的损失。我们认为解冻冷冻西兰花可能会破坏细胞膜的完整性，使黑芥子酶和葡萄糖苷酸前体接触。解冻冷冻西兰花 9 小时不会支持萝卜硫素的形成，除非添加外源黑芥子酶。热稳定性研究表明，作为黑芥子酶来源的西兰花根不如西兰花花头稳定。即使在 125°C 加热 10 分钟（与微波烹饪时间和温度相当或更高），白萝卜根也能支持一些萝卜硫素的形成。将 0.25%的白萝卜根添加到解冻的冷冻西兰花中，然后使其解冻，无需对未处理的西兰花进行任何肉眼可见的改变，就可以支持萝卜硫素的形成。
