Innovative synbiotic fat-free yogurts enriched with bioactive extracts of the red macroalgae Laurencia caspica: formulation optimization, probiotic viability, and critical quality characteristics

In this study, we investigated the effect of the bioactive extract of the Caspian Sea red macroalgae, Laurencia caspica on the critical quality characteristic of the synbiotic fat-free yogurt. Microwave-assisted extraction (MAE) process was initially used to obtain ethanolic bioactive extracts from L. caspica . At 50 μg/mL of L. caspica extract, the highest DPPH·scavenging capacity (87.3%), the antiproliferative rate on the growth of A549 (61.3%) and HepG2 (53.9%) cells, and antibacterial activity against Escherichia coli PTCC 1763 (16.1 mm) and Bacillus cereus PTCC 1015 (10.7 mm) were detected. After solvent evaporation, the extract (40–50 μg/mL) was added to yogurt-making skim milk containing oligofructose-enriched inulin (OFEI, 2–4%) and then inoculated with the single probiotic culture of Lactobacillus acidophilus La-5 (10 7 –10 9 CFU/g). The formulation and quality attributes of healthy yogurts were optimized based on the second-order polynomial models (R 2 > 0.98) using response surface methodology (RSM). The 10 7 CFU/mL-inoculated yogurt containing 4.0% OFEI and 50 μg/mL of L. caspica extract had the optimal pH (4.49), the maximum firmness (0.183 N) and viscosity (7.71 Pa.s), and the minimum syneresis rate (29.0%) with the superior sensory characteristics and the probiotic viability rate compared to the control. The consumption of this functional non-fat dairy product containing Caspian Sea red macroalgae extract may cause health promotion and immune system improvement.