Improvement of bioactive substances in soy-milk and soy-yogurt with kiwifruit juices (Actinidia deliciosa) and investigation of their antioxidant and antidiabetic potentials

Fruit-based food products enhance functional properties. This research is the first to examine fluctuations in biofunctional substances (isoflavone; CLA; GABA) and biological abilities (antioxidant; antidiabetic) in soy-milk (SM) and soy-yogurts (SY) using Lactobacillus strains with kiwifruit juice (0 → 5 → 10 %). Total isoflavones significantly decreased with 1231.9 → 539.3 (0 %), 1304.8 → 658.5 (5 %), and 1448.0 → 830.4 μg/g (10 %) between SMs and SYs supplemented with kiwifruit juice, while isoflavone-aglycones (genistein > daidzein > glycitein) increased considerably with 57.6 → 498.3, 64.4 → 611.5, and 78.7 → 771.3 μg/g. CLA increased, with the most abundant <i>cis</i>-9, <i>trans</i>-11 isomer (> 65 %) in SYs: nd → 1.8 (10 %) > nd → 1.0 (5 %) > nd → 0.8 mg/g (0 %). Moreover, SYs exhibited higher GABA contents than SMs in the following order: 0.7 → 1.6 (10 %) > 0.6 → 1.1 (5 %) > 0.7 → 0.9 mg/g (0 %). Antioxidant abilities were enhanced in SYs (500 μg/mL extracts) with increased kiwifruit juice, showing predominant activities at 10 % concentration: ABTS (65.5 → 93.5 %) > DPPH (49.9 → 86.9 %) > hydroxyl (35.6 → 70.4 %). Antidiabetic effects against enzyme inhibitions (α-glucosidase: 45.7 → 76.0 % > pancreatic lipase: 18.2 → 72.3 % > α-amylase: 8.6 → 65.7 %) exhibited similar patterns as antioxidant results. Thus, fermented SYs containing kiwifruit juice may be considered excellent sources of health benefits using soybeans.