The consumption of broccoli provides a large quantity of compounds with nutraceutical properties to the human diet. Broccoli has a high content of glucosinolates, compounds of the specialized metabolism with anticarcinogenic activity. In a previous work, we found that harvesting different time-points during the day affects the rate of senescence of broccoli heads during postharvest storage. In this work, we tested the same cultural practice to evaluate glucosinolate content and expression of genes involved in glucosinolate metabolism. Broccoli heads were harvested at 8:00, 13:00 and 18:00 hours and stored for 5 d at 20 °C in darkness. We found that content and composition of the glucosinolate pool was affected by the time of harvest. Levels of indolic glucosinolates decreased with the time of harvest on the day whereas indolic glucosinolate showed only a moderate decrease. The expression of genes associated to the biosynthesis of aliphatic glucosinolates was variable during the day. In relation to indolic glucosinolates, an increase in the expression of the transcription factor BolMYB51 was detected around 13:00 hours, which strongly correlated with the increase in expression of genes associated to their biosynthesis towards the end of the day.

During postharvest, the storage in darkness affected differently the metabolisms of indolic and aliphatic glucosinolates. The content of aliphatics decreased during the postharvest period, as well as the expression of the genes associated with their biosynthesis. In contrast, in the case of indolics, their content remained constant or varied slightly, while the expression of the associated biosynthetic genes decreased only slightly. Finally, the genes related to the degradation of glucosinolates appeared to be strongly regulated by light conditions, since their expression increased during the course of the day and decreased markedly during postharvest storage in darkness.

These results suggest that harvesting of broccolis close to noon would be convenient to maintain higher levels of glucosinolates during postharvest storage.

花椰菜的食用为人体饮食提供了大量具有营养保健性质的化合物。西兰花含有大量的芥子油苷，这是具有抗癌活性的专门代谢化合物。在以前的工作中，我们发现白天收获不同的时间点会影响西兰花头在收获后储存期间的衰老率。在这项工作中，我们测试了相同的文化实践，以评估芥子油苷含量和芥子油苷代谢相关基因的表达。在8：00、13：00和18:00时收获西兰花头，在黑暗中于20°C存放5 d。我们发现，芥子油苷库的含量和组成受收获时间的影响。吲哚芥子油苷的水平随一天的收获时间而下降，而吲哚芥子油苷的水平仅显示中等程度的下降。与脂族芥子油苷的生物合成相关的基因的表达在白天是可变的。关于吲哚芥子油苷，转录因子的表达增加在大约13:00时检测到BolMYB51，这与在一天结束时与其生物合成相关的基因表达的增加密切相关。

采后，在黑暗中的储存对吲哚和脂肪族芥子油苷的代谢有不同的影响。脂肪族的含量在收获后以及与其生物合成相关的基因的表达期间均下降。相反，就吲哚而言，它们的含量保持恒定或略有变化，而相关的生物合成基因的表达仅略有下降。最后，与芥子油苷降解相关的基因似乎受到光照条件的强烈调节，因为它们的表达在一天的过程中增加，而在黑暗中收获后的储存过程中表达明显减少。

这些结果表明，接近中午收获西兰花会在收获后的贮藏期间方便地维持较高水平的芥子油苷。