Valorization of Tunisian secondary date varieties (Phoenix dactylifera L.) by hydrothermal treatments: New fiber concentrates with antioxidant properties

Abstract

a b s t r a c tTwo hydrothermal treatments were assayed on secondary date varieties from the Tunisian coastal oasis in order to obtain valuable solid extracts, rich in dietary fiber and antioxidants. The steam explosion treatment (SET) is based on high temperatures and pressures, with an explosive decompression. The steam treatment (ST), without rapid decompression, has lower pressures and temperatures, but longer treatments than SET. The recovery of the fiber concentrates (FCs) was very similar for the different assayed conditions. Only its granulometry showed differences, increasing the fraction with size lower than 4 mm in more intense treatments. Treatment conditions had higher influence than date variety in the FCs chemical composition. It was approximately 0.1e2% soluble sugar, 0.7e2% uronic acids, 4e8% phenols, 5e11% fat, 5e22% non-cellulosic sugars, 9e14% protein, 12e20% cellulose, and 44e71% lignin, depending on treatment conditions. They had also very high antiradical activity (230e580 mmols Trolox/ Kg FC). The use of ST reactor is highly recommended because it could be easily scaled up to the industry. The FC obtained by hydrothermal treatments from date fruits could be considered as a very interesting ingredient for healthier food, especially for bakery or dairy products due to its pleasant chocolate/coffee flavor.

Quality Characteristics and Antioxidant Properties of Muffins Enriched with Date Fruit (Phoenix Dactylifera L.) Fiber Concentrates

“…Fat content increased significantly with the addition of DFC‐165, partially caused by the higher content of fat of this fiber than DFC‐180, 6.8 and 6.0%, respectively (Mrabet et al . ). As a consequence, the energy value of both samples (DFC‐165 treatment, at 2.5 and 5% level) was significantly higher than the others.…”

“…These results could be related to an increase in the muffin water retention capacity due to the presence of DFC with moderate WHC, 8.50 and 6.01 mL water/g of DFC‐165 and DFC‐180, respectively (Mrabet et al . ), as is described for other fiber‐enriched baked products (Kim et al . ).…”

“…The WHC of DFC was relatively low, 6–8 mL water/g DFC (Mrabet et al . ), taking into account that native date dietary fiber had a WHC of around 15 mL/g (Mrabet et al . ).…”

“…DFCs were obtained after the steam treatment of secondary date varieties from Tunisia at different temperatures (165 and 180C, DFC‐165 and DFC‐180, respectively) (Mrabet et al . ). The wet treated material was freeze‐dried and ground to a fine powder (<0.5 mm).…”

“…A hydrothermal pretreatment at different conditions has been assayed for obtaining a date fiber concentrate (DFC) with antioxidant properties which could be easily incorporated into food formulation (Mrabet et al . ). Due to its pleasant chocolate/coffee flavor, it fits especially well with bakery or dairy products.…”