| The present study aimed at investigating the accumulation and regulation techniques of isothiocyanates (ITCs) in germinated broccoli sprouts (cultivar Lvlingxiang 80 day). Firstly, the hydrolysis condition of ITCs produced from glucosinolates in broccoli sprouts was optimized using response surface methodology. Secondly, the effects of spraying ZnSO4, K2SO4 and methionine on glucosinolates, sulforaphane, total phenolics and ascorbic acid contents and myrosinase activity of broccoli sprouts were investigated. After a suitable S-chemical was identified from the above three chemicals, a solution series of 0,2, 4,6 and 8 mmol/L was selected to determine its appropriate concentration for cultivation of broccoli sprouts with the most ITCs and sulforaphane contents. Thirdly, since it was found that spraying ZnSO4 would cause a stress situation to the growth of broccoli sprouts, exogenous Ca2+ was applied to relieve the stress of ZnSO4 and enchance ITCs and sulforaphane accumulation. The main results were listed as following:1. ITCs production was clearly enhanced by a suitable pH, addition of EDTA and ascorbic acid. The optimal enzymolysis conditions were adding EDTA 0.02 mmol and 0.16 mg ascorbic acid to 4 mL of the homogenized phosphate-citrate buffer solution (pH 4.00). At this optimal condition, a highest ITCs content of 698.98 mg/100g FW was observed.2. ITCs profiles were identified and seven kinds of individual ITCs were detected. Four kinds of individual ITCs including isobutyl isothiocyanate,4-isothiocyanato-l-butene, 1-isothiocyanato-3-methyl-butane and 1-isothiocyanato-butane are firstly reported in broccoli sprouts.3. ZnSO4 significantly raised glucosinolates, total phenolics and sulforaphane contents, and enhanced myrosinase activity. K2SO4 and methionine both significantly benefited total phenolics and ascorbic acid, while decreased glucosinolates, sulforaphane content and myrosinase activity. Spraying 4 mmol/L of ZnSO4 solution resulted in more glucosinolates, total phenolics and sulforaphane of sprouts than those treated with 0,2,6, and 8 mmol/L ZnSO4. Glucosinolates and sulforaphane contents as well as myrosinase activity all rose when increasing ZnSO4 concentration from 0 to 4 mmol/L while declined from 4 to 8 mmol/L.4. Exgenous Ca2+mitigated the stress condition of broccoli sprouts caused by ZnSO4 application. The MDA, ascorbic acid and total phenolics contents as well as the antioxidant activity were decreased. Ca2+enhanced the stress-resistant ability of broccoli sprouts seen as a better growth performance. Compared to that of ZnSO4 treatment, although Ca2+ addition decreased the total glucosinolates and ITCs contents of broccoli sprouts, the content of ghicoraphanin and sulforaphane was greatly promoted.5. Total glucosinolates and glucoraphanin contents of sprouts treated with ZnSO4 plus Ca2+were higher that that of the control. Hence, as their hydrolytic products, the content of ITCs and sulforaphane was also higher. Total glucosinolates and glucoraphanin contents decreased continuously with germination time, which could be effectively delayed by ZnSO4 plus Ca2+treatment. In addition, myrosinase activity was enhanced by ZnSO4 plus Ca2+treatment after the sprouts were germinated for 1 d.6. Total glucosinolates, glucoraphanin and myrosinase activity in the cotyledon of sprouts were significantly higher than that in the stem. Glucosinolates and glucoraphanin content in cotyledon was 7.30-9.31 and 5.39-9.02 folds of that of the stem, respectively. Consequently, ITCs and sulforaphane contents in the cotyledon were both higher than that of the stem. Compared to that of the water control, ZnSO4 plus Ca2+ treatment enhanced the contents of total glucosinolates, glucoraphanin, ITCs and myrosinase activity while decreased sulforaphane content. This might be due to a change of glucoraphanin hydrolysis direction to sulforaphane. |
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