Fortification of goat yogurt with roasted date seeds ( Phoenix dactylifera L.) powder: impact on nutritional, technological, phenolic profile, antioxidant and sensory properties

Date seeds (DS) are one of the major waste of date processing plants and have vital therapeutic properties. It represents an inexhaustible source of dietary fiber and bioactive compounds. Roasting could be an essential process in ensuring that this date by-product is used. Due to functional properties of roasted date seeds and the high consumption rate of yogurt, the fortification of these products is a novel track for the revalorization of date by-products and the development of a functional and bioactive yogurt, which is of practical industrial importance. The effects of roasted DS supplementation (1, 2 and 3%) in goat and cow yogurt formulation were assessed in order to develop a new functional yogurt. The analysis of the basic nutritional composition revealed that the roasted DS powder was rich in soluble fiber (42.29 ± 3.41 g.100 g −1 ) and characterized by excellent techno-functional properties (especially water-holding and swelling capacities). In terms of mineral content, roasted DS powder contained high levels Ca (354.0 ± 6.0 mg 100 g −1 DW), Mg (63.1 ± 0.6 mg 100 g −1 DW) and Fe (17.2 ± 1.4 mg 100 g −1 DW). Phenolic compounds detected in roasted DS included epicatechin, catechin ( + ) and quinic acid as dominant ones among 19 types. Thanks to its good DPPH•-radical scavenging activity (IC 50 = 0.04 mg ml −1 ) and its dark color (L* = 53.29 ± 0.07), roasted DS powder served as natural and anti-oxidant agent in formulated yogurt. The 3% DS-fortified yogurts (goat and cow) presented the lowest moisture (81.23 ± 1.95 and 79.38 ± 1.02 g 100 g −1 for goat and cow yogurt, respectively) and the highest in protein content (3.76 ± 0.16 and 2.92 ± 0.81 g 100 g −1 for goat and cow yogurt, respectively). Interestingly, fortified goat and cow yogurts with 3% of roasted DS recovered 58.5%, and 96.11% of recommended dietary allowances in Mg and Fe, respectively. Rising levels of roasted DS powder into goat and cow yogurts increased viscosity, water holding capacity and antioxidant capacity, and decreased syneresis. LC-ESI-MS-analysis, revealed the presence of new phenolic compounds in fortified yogurts and the disappearance of some other despite their existence in roasted DS. Sensory evaluation showed that yogurts fortification with roasted DS powder weakened greatly the goaty flavor.