Development and evaluation of an enriched natural antioxidant preparation obtained from aqueous spinach (Spinacia oleracea) extracts by an adsorption procedure

Spinach (Spinacia oleracea) leaves contain antioxidant flavonoids, in particular spinacetin and patuletin. An adsorption procedure for the recovery of these flavonoids from a crude spinach extract was developed and evaluated. Four different resin and charcoal adsorbents, chosen for their high affinity for polyphenolic compounds, were tested in an open batch system. All proved to be very efficient in adsorbing polyphenols. However, while a major portion of the flavonoids could be desorbed from the resin matrices under the experimental conditions imposed by an industrial context, most of these compounds stayed irreversibly bound to the charcoal matrices. The use of a polymeric resin matrix, to purify a spinach crude extract, allowed the removal of almost 80% of the initial extract dry mass, while keeping the flavonoid content nearly constant. Using the nitro blue tetrazolium (NBT) and the DPPH tests to evaluate the antioxidant character of these preparations, it was determined that the spinach flavonoids, as well as the crude aqueous or resin-purified extracts, exhibit high antioxidant activities. Moreover, the antioxidant efficiency of the spinach polyphenol extracts was significantly increased by the elimination of a major part of non-phenolic components.