Cooking methods of Brassica rapa affect the preservation of glucosinolates, phenolics and vitamin C

Abstract

18Cooking Brassica vegetables as a domestic processing method has a great 19 impact on health-promoting bioactive compounds: glucosinolates (GLS), flavonoids, 20 hydroxycinnamic acids, and vitamin C. In Galicia (NorthWestern Spain), one of the 21 most consumed horticultural crops is Brassica rapa, by using the leaves (turnip greens) 22 and the young sprouting shoots (turnip tops) in different culinary preparations. In order 23to determine the effect of cooking, on turnip greens and turnip tops, bioactive GLS, 24 flavonoids, hydroxycinnamic acids and vitamin C were analysed and simultaneously 25 determined. The level of retention of each individual compound after cooking 26 procedures was evaluated in the edible organs, and we also in the cooking water, in 27 order to compare their composition to a fresh uncooked control. Steaming, conventional 28 boiling, and high-pressure cooking, traditional processing methods of this kind of 29 vegetables, were the three domestic processing methods used in this work. Results 30 showed that total GLS and phenolics were significantly affected by the cooking 31 procedure and the loss rate varied among individual compounds. Steaming was the 32 method that better preserved GLS and phenolic compounds. Conventional boiling and 33 high-pressure cooking methods presented similar rate of losses of total GLS content 34 (64%) and total phenolic content (more than 70%). Degradation among glucosinolate 35 classes, aliphatic or indolic, was similar. The total flavonoids lost in turnip greens were 36 64% and 67% for conventional boiling and high-pressure, respectively. The main losses 37 were caused by leaching into the cooking water. The concentration of vitamin C 38 suffered a drastic loss in the process of sample handling and after cooking. Despite the 39 fact that any cooking procedure affected negatively the nutritional composition of the 40 turnip greens and tops, our results showed high retentions of individual compounds in 41 steaming, and the lowest retentions were obtained in the traditional high-pressure 42 ACCEPTED MANUSCRIPT 3 cooking. High retention of health-promoting compounds in the cooking water should be 43 considered for increasing the intake of properties of Brassica rapa. 44

Modification of glucosinolates in turnip greens (Brassica rapa subsp. rapa L.) subjected to culinary heat processes

“…Compared with fresh samples, all cooking methods were found to cause significant reduction in anthocyanin and total glucosinolates contents (Jones et al 2010;Francisco et al 2010;Korus et al 2014;Xu et al 2014). Heat treatments in Brassica affect the glucosinolate and the isothiocyanates.…”

“…It is known that cooking induces significant changes in chemical composition, influencing the concentration and bioavailability of bioactive compounds (Gao-Feng, Bo, Jing, & Qiao-mei, 2009;Francisco, Velasco, Moreno, García-Viguera, & Cartea, 2010;Jones, Frisina, Winkler, & Tomkins, 2010;Clariana, Valverde, Wijngaard, Mullen, & Marcos, 2011;Tanongkankit, Chiewchan, & Devahastin, 2011;Hanschen, Bauer, Mewis, Keil, Schreiner, Rohn, & Kroh, 2012;Korus, Słupski, Gebczynski, & Banas, 2014;Xu, Zheng, Yang, Cao, Shao, & Wang, 2014). Glucosinolates and their hydrolysis products are primarily lost from Brassica vegetables by leaking into the cooking water, but the rate and extent of loss depend on the type of treatment used, the cooking time and/or the amount of water used (Song & Thornalley, 2007).…”

Effect of NaCl treatments on glucosinolate metabolism in broccoli sprouts

“…Temperature (van Eylen et al, 2008), growth conditions such as nitrogen and sulfur assimilation (Pérez-Balibrea et al, 2010), selenium application (Nyberg, 1991), water deficiency (Schreiner et al, 2009), and phenological stage (Velasco et al, 2007) can all make an impact on the content of glucosinolates in plants. In addition, cooking methods may also affect the content of glucosinolates in Brassica rapa (Francisco et al, 2010). The influence of salt stress on the primary metabolism such as photosynthesis and metabolism of antioxidants in mustard (Brassica juncea L.) has been well documented (Khan et al, 2009).…”

Influence of Freezing Steps on Color Attributes, Phytochemical Contents and Antioxidant Capacity of Green Beans

“…Phenolic compounds in vegetables are presented in both soluble forms and combined with cell-wall complexes. Thus, increased surface area of tissues in contact with steam blanching and cooling water, high blanching temperature and lengthy freezing time are all likely to have resulted disruption of cell walls and breakdown of phenolic compounds (Francisco et al, 2010). Ahmed and Ali (2013) reported that steam-blanched, steamboiled and microwaved cauliflower had significantly losses in phenolics content by 16.6, 17.53 and 18.30%, respectively. Regarding the total flavonoids content, results showed that, it was significantly decreased from 394.89 mg 100 g -1 (on dry weight basis) to 354.24 and 300.20 mg 100 g -1 , DW after blanching and freezing treatments, respectively ( Table 2).…”