Consumer acceptance of synbiotics, which are synergistic combinations of probiotics and their prebiotic substrates, continues to expand in the functional food category. This research aimed at evaluating the effect of antibacterial manuka honey on the probiotic growth and sensory characteristics of potentially synbiotic yogurts manufactured with Lactobacillus reuteri DPC16. Probiotic viable count in yogurts with 5% w/v Manuka honey (Blend, UMF^TM 18⁺, AMF^TM 15⁺ and AMF^TM 20⁺) was evaluated by the spread plate method over the refrigerated storage period of three weeks. A panel of 102 consumers preferred the yogurt made with invert syrup over the manuka honey variants, and the unsweetened control was least liked overall. Invert syrup yogurt was also the most effective in promoting the growth of the probiotic lactobacilli. However, the honey-sweetened yogurts had a more favourable fermentation metabolite profile, especially the lactic and propionic acids, as estimated by nuclear magnetic resonance (NMR) analyses. The probiotic counts in AMF^TM 15⁺ manuka honey yogurt (7 log cfu/mL) were significantly higher than the other honey yogurt types (Manuka Blend and UMF^TM 18⁺) and above the recommended threshold levels. The combination thus can be developed as a synbiotic functional food by further improving the sensory and physicochemical properties such as texture, apparent viscosity and water holding capacity.

Manuka honey is known for its strong antibacterial effect against pathogens but can promote probiotic growth in certain conditions. In a two-factor ANOVA study, AMF^TM Manuka honey (Active Manuka Factor: 05⁺, 10⁺, 15⁺ and 20⁺) was utilised as a substrate for probiotic Limosilactobacillus reuteri DPC16 in an anaerobic batch fermenter for 36 h. The biomass growth in MRS broth was noticeably higher with AMF Manuka honey than invert syrup and control samples without any additional sweetener source. The pH value was significantly lowered below 4.0 only in the AMF samples with the formation of lactic acid as the major metabolite. Other beneficial short-chain fatty acids (SCFA), such as acetic, succinic, and propionic acids, produced during the fermentation, along with the honey saccharides, were quantified by two-dimensional (2-D) nuclear magnetic resonance (NMR) spectroscopy. A significantly (p < 0.05) high biomass in AMF 20⁺ sample after 36 h, can partly be attributed to the high total sugar and oligosaccharide content in the honey. Importantly, however, no statistically significant difference was observed in the recorded major fermentation outcomes for the different AMF levels. The results, nevertheless, indicate the potential prebiotic efficacy of Manuka honey as a fermentation substrate for the lactobacilli probiotic strain.