Brassinolide Soaking Reduced Nitrite Content and Extended Color Change and Storage Time of Toona sinensis Bud during Low Temperature and Near Freezing-Point Temperature Storage

Low temperatures are often used to preserve fruits and vegetables. However, low-temperature storage also causes problems, such as chilling injury, nitrite accumulation, and browning aggravation in plants. This study investigated the effects of brassinolide (BR,1.0 mg L(−1)) solution soaking, storage temperatures (−2 ± 0.5 °C, 4 ± 0.5 °C, and 20 ± 1 °C), and their combinations on nitrite content, color change, and quality of stored Toona sinensis bud. The results showed that low temperature (LT, 4 ± 0.5 °C) and near freezing-point temperature (NFPT, −2 ± 0.5 °C) storage effectively inhibited the decay of T. sinensis bud compared to room temperature (20 ± 1 °C, the control). The combined treatments of BR with LT or NFPT reduced nitrite content and maintained the color and the contents of vitamin C, carotenoids, saponins, β-sitosterol, polyphenol, anthocyanin, flavonoids, and alkaloids in T. sinensis bud. BR soaking delayed the occurrence of chilling injury during NFPT storage. Meanwhile, BR soaking enhanced the DPPH radical scavenging activity, ABTS activity, and FRAP content by increasing SOD and POD activity and the contents of proline, soluble, and glutathione, thus decreasing MDA and hydrogen peroxide content and the rate of superoxide radical production in T. sinensis bud during NFPT storage. This study provides a valuable strategy for postharvest T. sinensis bud in LT and NFPT storage. BR soaking extended the shelf life during LT storage and maintained a better appearance and nutritional quality during NFPT storage.