| Broccoli (Brassica oleracea var. italica) is consumed popularly by human being as functional food due to its high nutritional and anticarcinogenic value, and it has been one of the most important vegetables in China for domestic market and export in recent years. Broccoli contains a high level of glucoraphanin, which is the most potent, naturally occurring, monofunctional phase 2 enzyme (such as quinone reductase) inducer identified thus far. In this study, the effect of different preharvest and postharvest factors, including broccoli cultivars, nitrogen fertilization, cooling and controlled atmosphere treatments on glucosinolate and quality of brocolli were investigated with an emphasis on anticancer glucoraphanin and quinone reductase (QR) activity. We also studied the effect of plant hormones (Jasmonate and Brassinosteroid) on content of glucosinolate, total phenolics and anthocyanin in broccoli sproutsThe results are as follows:1. The effect of five levels of nitrogen fertilization (0,100,200,300 and 400 kg N ha-1) on head size, shelf life, concentrations of ascorbic acid, glucoraphanin and QR activity of broccoli was investigated in two broccoli cultivars,'Youxiu'and'Lvling'. The results showed that both the average weight and diameter of main head were significantly increased with the increase of nitrogen fertilization in both cultivars. However, the ascorbic acid and glucoraphanin concentrations in broccoli floret and stem were decreased with the increase in nitrogen application and significant low levels of ascorbic acid were detected by nitrogen fertilization at range of 300-400 kg N ha-1. The nitrogen fertilization at 400 kg N ha-1 also significantly reduced the shelf life of broccoli as well as glucoraphanin concentration in broccoli floret and stem. The QR activity in broccoli floret and stem supplied with different nitrogen paralleled their glucoraphanin concentrations. In conclusion, moderate nitrogen fertilization rate (200-300 kg N ha-1) could significantly increase the head size and maintain the storage life, glucoraphanin concentration and QR activity.2. The effect of storage temperatures on shelf life, glucoraphanin concentrations and QR activity of broccoli was investigated. The results showed that the shelf life of stored broccoli is 34.7d,17.5d,9.0d,2.0d under 0℃,5℃,10℃,20℃conditions respectively, which indicated that storage at lower temperature is better for the quality maintenance of broccoli. The results also showed that both the glucoraphanin content and QR activity of broccoli florets increased during the initial 6 days of storage, and then decreased markedly at different temperatures of 0℃,5℃, and 10℃. Immediate cooling of broccoli florets at 0℃and 5℃could preserve the glucoraphanin content and QR activity for 12 days. Cooling delay treatment was recommended no more than 6 hours at 20℃, and therefore "cool as soon as possible" is the general recommendation for postharvest handling of broccoli.3.The effect of controlled atmosphere on shelf life, glucoraphanin concentrations and QR activity of broccoli was investigated. Controlled atmosphere (CA) treatments with elevated CO2 (21% O2+10% CO2, and 21% O2+20% CO2) and air treatment (21% O2) were found to increase the glucoraphanin content and the QR activity at first 5 days of storage at 5℃, while CA treatments with reduced O2 concentration (1% O2,1% O2+10% CO2) led to a steady decrease of glucoraphanin content and the QR activity during the 20 days of storage at 5℃. The highest content of glucoraphanin content and QR activity of broccoli florets was observed when stored under 21% O2+10% CO2 at 5℃. This condition was able to maintain the visual quality, glucoraphanin content and QR activity of the broccoli florets for 20 days.4. The effect of four levels of MeJA (0,0.01,0.1 and 1 mM MeJA) on quality, composition and content of glucosinolates in 7d broccoli sprouts was investigated. The results showed that MeJA treatment did not significantly affect antioxidant activity, concentrations of total phenolics and anthocyanin in broccoli sprouts. Significant increase in content of indole glucosinolates and total glucosinolates was observed 24 hours after 0.01 and 0.1 mM MeJA treatments. However, content of indole glucosinolates and total glucosinolates decreased 48 hours after treatments compared with the control. 5. The effect of of four levels of EBR (0,0.01,0.1 and 1μM EBR) on quality, composition and content of glucosinolates in 7d broccoli sprouts was investigated. The results showed that EBR treatments did not significantly affect antioxidant activity, concentrations of total phenolics and anthocyanin in broccoli sprouts within 24 hours after treatment. Significant increase in contents of glucoraphanin and total glucosinolates was observed under EBR treatments at moderate concentrations (0.01 and 0.1μM) from 24 to 48 hours after treatment, which helps to maintain good nutritional quality.
|
PDF Full Text Request