Retention of minerals, antioxidants, pigments, and glucosinolates by broccoli florets and green bean pods boiled in alkaline, neutral and acidic waters

Given the poor palatability and chewability of crude green bean pods ( Phaseolus vulgaris ) and broccoli florets ( Brassica oleracea var. italica Plenck) these vegetables are generally microwaved, steamed or water boiled. Hence, here, we evaluated the contents of minerals, antioxidants, phenolics, glucosinolates, pigments, colour, texture and flavour of water-boiling broccoli and green bean pods, with four mineral waters with variable composition and pH. Plant matrices were characterized by High Resolution Magic-Angle Spinning (HR-MAS) and plant extracts were analysed by pseudo-2D Diffusion-ordered nuclear magnetic resonance (NMR) spectroscopy. Mineral waters ranging from acidic to neutral and alkaline were used and the colour properties (lightness, greenness/yellowness, colour saturation and hue angles), minerals and bioactive contents retained by the vegetables were compared to microwaved and steamed material. Boiling bean pods for 5 min extracted more polyphenols and antioxidants, particularly with more acidic waters, than 5 min of microwaving or steaming. However, even if boiling broccoli with more acidic water could better preserve glucosinolates, the food material presented lower retention of pigments and poor palatability. Cooking with more alkaline water increased mineral retention and broccoli greenness, also leading to highest scores in “colour”, “texture”, and “flavour”. Hence, samples cooked in more alkaline water presented higher acceptability. • Carbohydrates and peptides stamp the HR-MAS NMR metabolite fingerprints of the vegetables. • Green bean pods boiled (5 min) with more acidic water (pH 5.7) retained more AC and TPC. • Glucosinolates are better retained when boiling broccoli florets with more acidic water. • Cooking broccoli with alkaline water (pH 9.5) promotes mineral retention and greenness. • Vegetables cooked in more alkaline water present better flavour and higher acceptability