Optimizing Date Fruit (Phoenix dactylifera L.) Juice Extraction: the Influence of Temperature on Quality and Physicochemical Properties

Abstract
Date juice from Phoenix dactylifera L. offers nutritional and functional benefits, and thus is attracting increasing interest in food industries. However, processing parameters—particularly extraction temperature—significantly influence juice quality. This study evaluates how different extraction temperatures (25°C, 50°C, 75°C, and 90°C) affect the physicochemical, rheological, and thermal properties of Barhi date juice.

Dates (Tamer stage) were homogenized with deionized water (1:3 w/v) and extracted at the specified temperatures. The total phenolic content (TPC), color, browning index, pH, and rheological and thermal behavior were analyzed. TPC was assessed via the Folin–Ciocalteu method; color and browning were measured using Hunter Lab values, and HMF was evaluated through GC-FID. Rheological behavior was tested with a hybrid rheometer, and thermal properties were analyzed via DSC.

Higher extraction temperatures decreased L* values, resulting in darker juice due to Maillard reactions, although no HMF was detected. TPC increased with temperature, enhancing antioxidant potential. Rheologically, juices exhibited non-Newtonian, shear-thinning behavior. Viscosity was highest at 50°C and 75°C, likely due to polysaccharide and Maillard compound release. Dynamic analysis revealed viscoelastic behavior, with elastic dominance (G′ > G″) at lower temperatures and a transition to viscous behavior (G″ > G′) at higher strains, especially at 90°C. DSC profiles showed endothermic transitions between 105°C and 183°C, linked to sugar degradation.

Conclusion
Moderate extraction temperatures (50°C–75°C) optimized juice quality by enhancing phenolic content and maintaining desirable rheological and thermal properties while minimizing browning. These findings offer insights for the date processing industry to produce high-quality, antioxidant-rich juice. Further work should explore sensory attributes and alternative technologies.