Changes in low molecular weight carbohydrates in kale during development and acclimation to cold temperatures determined by chromatographic techniques coupled to mass spectrometry.

Kale (Brassica oleracea) is a cool-season vegetable widely employed in the elaboration of diverse products such as tea and smoothies in USA or in the Northern German cuisine in wintertime. Besides, kale is gaining attention due to the diverse health benefits reported in the literature for its consumption, e.g. antigenotoxic and anticarcinogenic effect, protection of cardiovascular system and gastrointestinal tract. Low molecular weight carbohydrates (LMWC) are compounds directly related with kale flavour and nutritional quality. Despite different studies focusing on the chemical composition of kale, few information on LMWC is available. Thus, in this work a multianalytical approach was conducted in order to perform a comprehensive study of kale LMWC; their evolution during plant development and acclimation to cool temperatures was also evaluated. Gas chromatography coupled to mass spectrometry allowed the identification of 13 LMWC, being myo-inositol, galactinol, maltose and melibiose described for the first time in kale. Eight major LMWC were quantified in three different commercial kale cultivars using hydrophilic interaction liquid chromatography coupled to mass spectrometry to monitor possible differences in their content during plant development and as consequence of plant acclimation to cold temperatures. Overall, for all types of kales under study, the content of maltose and sucrose decreased during the plant development while the concentration of fructose, melibiose, maltose, raffinose and galactinol was increased in all kale types exposed to low temperatures. These results underline the importance of controlling the temperature during kale cultivation in order to obtain products with a high nutritional value.