Structure-function relationships of pectic polysaccharides from broccoli by-products with in vitro B lymphocyte stimulatory activity.

To study structure-function relationships of pectic polysaccharides with their immunostimulatory activity, broccoli by-products were used. Pectic polysaccharides composed by 64 mol% uronic acids, 18 mol% Ara, and 10 mol% Gal, obtained by hot water extraction, activated B lymphocytes in vitro (25-250 µg/mL). To disclose active structural features, combinations of ethanol and chromatographic fractionation and modification of the polysaccharides were performed. Polysaccharides insoluble in 80 % ethanol (Et80) showed higher immunostimulatory activity than the pristine mixture, which was independent of molecular weight range (12-400 kDa) and removal of terminal or short Ara side chains. Chemical sulfation did not promote B lymphocyte activation. However, the action of pectin methylesterase and endo-polygalacturonase on hot water extracted polysaccharides produced an acidic fraction with a high immunostimulatory activity. The de-esterified homogalacturonan region seem to be an important core to confer pectic polysaccharides immunostimulatory activity. Therefore, agri-food by-products are a source of pectic polysaccharide functional food ingredients.

Blanching impact on pigments, glucosinolates, and phenolics of dehydrated broccoli by-products.

Because of high water content, the valorisation of broccoli by-products requires dehydration that can preserve bioactive compounds. Blanching pre-treatment has been reported to improve the drying rate of broccoli. As a thermal treatment, it promotes also enzyme inactivation. Therefore, in this study, the impact of pre-dehydration blanching step, freeze-drying, air-drying at 40 °C, and microwave hydrodiffusion and gravity (MHG) dehydration on the levels of pigments, glucosinolates, and phenolics, was evaluated by UHPLC-DAD-ESI/MSn. When compared to freeze-drying, a technique known to preserve compounds, a pre-blanching step increased the extractability of both pigments and phenolics, while air-drying only retained 49% of the pigments and 70% of phenolics, both without affecting glucosinolates. However, when air-drying was preceded by blanching, less than 50% of compounds were retained. On the other hand, MHG dehydration increased the phenolics extractability by 26%, particularly that of kaempferol derivatives while also retaining the amount of the glucosinolate glucoraphanin, when compared to freeze-drying. Nevertheless, only 23% of indole glucosinolates were recovered and pigments were severely reduced, with lutein accounting only for 32% and only chlorophyll b was observed in trace amounts after MHG dehydration. Therefore, to valorise broccoli by-products as ingredients, different drying technologies may be used when targeting different composition richness: freeze-drying is suitable for pigments and glucosinolates, air-drying is suitable for glucosinolates, while MHG promotes the extractability of phenolic compounds.