Encapsulation of extract from roasted Kabkab date (Phoenix dactylifera L.) seed using freeze-drying

The present study aimed to investigate the physicochemical characteristics of the encapsulated roasted date-seed (180°C, 20 min) extract. Date-seed (Phoenix dactylifera L. cv Kabkab) extract was obtained using a combination of ultrasound- (25 ± 5 ºC, 15min.) and microwave- (2.30min.) assisted extraction. Phenolic-compounds of the extract were identified by HPLC. The encapsulation process was done by the freeze-drying method. Soy-protein concentrate and maltodextrin were used as wall materials (M(100): Pure Maltodextrin; S(100): Pure Soy-protein; MS(75:25): Maltodextrin: Soy-protein (75:25%); MS (50:50): Maltodextrin: Soy-protein (50:50%); MS (25:75): Maltodextrin: Soy-protein (25:75%)). Gallic-acid (536.87 mg 100 g-1dEx) and catechin (214.79 mg 100 g-1dEx) were the major phenolic and flavonoid compounds of the extract. The type of wall material had no significant effect on the moisture content and water-activity. The microparticle's bulk-density was varied from 0.232-0.178 g cm-3. The difference between M(100) and S(100) was significant. The microparticles showed a heterogeneous and irregular structure with flake- and sheet-shaped morphology. Several cracks were visible on the M(100) surface. The best encapsulation-efficiency was achieved for microparticles using a combination of maltodextrin and soy-protein (especially, MS(50.50)). While 68.88% of free-extract polyphenols were destroyed after 35 days at 35 °C, the encapsulation process caused retaining 61.79% (M(100)) to 76.69% (MS(50.50)). Overall, due to the appropriate solubility, low moisture, water-activity and the ability to preserve phenolic compounds of date-seed extract, encapsulation in maltodextrin-soy-protein (MS(50.50)) wall materials could be proposed as an efficient and cost-effective bioactive compound to preserve different food products and improve their nutritional value.