Effect of Date Palm (Phoenix dactilyfera L.) Juice Concentration with Mixed Culture on Product Quality and Antioxidant Activity of Synbiotic Yoghurt

The development of functional fermented foods with improved nutritional and antioxidant properties has attracted increasing interest in food science. This study examined the effect of adding date palm juice at different concentrations with a mixed culture on product quality and antioxidant activity of synbiotic date yogurt. The date palm juice concentrations used were 0%, 10%, 15%, and 20% (v/v). The fermentation process was carried out for 8 hours at 37°C with a mixed starter culture consisting of two yogurt starter bacteria and three probiotic strains. Then, chemical quality testing was carried out in the form of pH values using a pH meter and total titratable acidity (TTA) with acid-base titration, microbiological quality (total LAB) using the Total Plate Count (TPC) method, organoleptic testing using the hedonic test, and antioxidant activity testing using the DPPH (2,2-diphenyl-1-picrylhydrazyl) method expressed as IC50. Test data were analyzed using SPSS software to determine the effect of date palm juice concentration on test results. Synbiotic date yogurt has met the yogurt quality requirements in the form of pH, TTA, and total LAB according to SNI 2981:2009 at date palm juice concentrations of 0% to 20% (v/v). Increasing the concentration of date juice in synbiotic date yogurt affects the pH value, TTA value, total LAB and IC50 value as the results of antioxidant activity testing. The 20% Ajwa date juice treatment produced the best overall results, with a pH of 3.87, a TTA of 0.9394%, a total LAB count of 3.61 × 10⁸ CFU/mL, and the strongest antioxidant activity (IC₅₀ = 60.785 ppm). The results of this study indicate that Ajwa date juice can be utilized as a functional ingredient in the development of synbiotic yogurt with good quality and antioxidant activity.