Date Fruits and Their Products for Almond Beverage Fortification: Assessment of Beverages and Resulting Residues

The shift towards plant-based beverages, particularly almond drinks, has increased the need to develop innovative products using fruits and herbal extracts to improve their nutritional and sensory properties. In this study, date palm fruits, Deglet Nour variety (tamr stage) and Besser Helou variety (khalal stage), and two Deglet Nour-derived products (date powder and syrup) were evaluated as fortifying ingredients in almond drinks. The antioxidant and nutritional properties of the recovered solid residues were also evaluated.

The beverage-making process involved grinding blanched almonds into flour (w=12 %), mixing with date products (w=20 %), water extraction, filtration, and pasteurisation. Proximate composition, physicochemical properties, phenolic profiles (liquid chromatography-high resolution electrospray ionization mass spectrometry), and antioxidant activity of the raw ingredients, beverages, and recovered residues were analysed using 2,2-diphenyl-1-picrylhydrazyl (DPPH) and Fe(III) reducing antioxidant power (FRAP) assays. In addition, physical stability, rheological behaviour, and sensory attributes of the beverages were evaluated using descriptive analysis and acceptability tests.

The addition of date-based ingredients to almonds significantly reduced the extraction yields of beverages, with the reduction being least significant in syrup, moderate in Deglet Nour and Besser Helou varieties, and most significant in date powder. Combining almonds with any form of dates significantly increased carbohydrate and ash mass fraction, energy value and antioxidant activity of beverages, as confirmed by both FRAP and DPPH assays. Phenolics previously present in almonds and dates were found to multiply, while new ones appeared in both drinks and residues, such as caffeic acid. A distinctive rheological profile was observed in beverages fortified with Deglet Nour, date syrup and date powder, characterised by shear thickening at low shear rates and a transition to shear thinning at higher shear rates. Sensory evaluations of enriched drinks revealed that dates provided new colour shades, increased sweetness and mouthfeel viscosity, and improved almond taste perception. Date powder-based drinks received the highest overall acceptability rating, while syrup-based drinks received the lowest. Combining date ingredients with almonds reduced the fat and protein mass fraction of residues while increasing carbohydrate mass fraction. Quinic acid and quercetin were the prevalent phenolic acids and flavonoids in almond residue, while caffeic acid and luteolin were the primary compounds in date-based residues.

This study presents the first comprehensive evaluation of the nutritional, rheological, antioxidant and sensory properties of almond beverages fortified with date-based ingredients. The nutritional and antioxidant properties of the raw ingredients and the produced residues were also assessed. The results suggest that additional phenolics may be generated in fortified almond drinks during processing and show that the resulting date residue is as relevant as potent dietary supplements.