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

Abstract

The consumption of Brassica vegetables has been related to improved health benefits due to their phytochemical components, such as glucosinolates, that induce a variety of physiological functions. Glucosinolate levels can be affected when they are submitted to heat treatments before consumption. This paper investigates, by an HPLC-DAD method, the effect of three cooking treatments on the nutritional quality of turnip greens. Fresh turnip leaves were homogenized with sand and Milli-Q water and centrifuged. They remained there for 3 h for natural autolysis. Samples, fresh and processed, were extracted with dichloromethane; the organic extract had been evaporated to dryness, was dissolved in acetonitrile and injected into the chromatograph. Eight compounds were identified: allyl-isothiocyanate, erucin, sulforaphane, iberin, napin, goitrin, benzyl- isothiocyanate and phenethyl-isothiocyanate. Napin was the major compound in all samples followed by goitrin. The best treatment is steam cooking, followed by pressure-cooking, while the boiling treatment produced a 60% loss.