Sub-critical water extraction of reducing sugars and phenolic compounds from date palm fruit

Recently, natural fruit sugar products are highly preferred by consumers due to growing consciousness of the various health risks and diseases related to commercial refined sugar. Date palm ( Phoenix dactylifera ) fruit is an excellent source for natural reducing sugars, but the tough skin, gummy consistency, and rigid cell walls limit the sugar extraction from the fruit using conventional techniques. To overcome these limitations, this work evaluates a novel sub-critical water extraction (SCWE) technique to recover the reducing sugars and other nutrients from the date fruits. Microwave-pretreated fruit pulp (MW-FP) was subjected to batch SCWE by varying the critical operating parameters such as pressure ( P ) (10–30 bar), temperature ( T ) (100–130 bar °C), extraction time ( t ) (5–15 min), and solvent-feed ratio ( L / S ) (5–15 mL/g). Experimental results based on the Box-Behnken factorial design showed that the temperature and pressure highly influenced the sugar and phenolics recovery. Maximum yield of 69.67 g/100 g MW-FP was obtained at P = 37.5 bar, T = 130 °C, L / S = 11 mL/g, and t = 11 min. Also, a high recovery efficiency of 81% was observed for the reducing sugars at this condition. Phenolics assay and ABTS-radical-scavenging test showed that the extract possessed total phenolics of 1.26 g/100 g MW-FP and 92% antioxidant activity. Overall extract yield and reducing sugar recovery by the SCWE were 1.6 and 2.1 folds higher respectively, than the conventional hot water extraction. Thus, the SCWE technique assures to be a clean and efficient technology for the date fruit sugar recovery. Graphical abstract