Drinking yoghurts with berry polyphenols added before and after fermentation

Health-promoting berry polyphenols (PPs) can be added in the form of berry fruit juice, or an extract from berry materials (which has a much higher PP concentration), to yoghurt products either pre- or post-fermentation to add flavour and antioxidant functionality. This study compared the effects of adding purified PP (cyanidin 3-o-β-glucopyranoside chloride, Cyanidin) or a blackcurrant PP extract (BPE) before or after fermentation on the chemical, rheological and microbiological properties of drinking yoghurts formulated with low or high methoxyl (LM or HM) pectin. The control yoghurt (in the absence of added PPs) and PP-enhanced yoghurts were subjected to total extractable PP content (TEPC) analysis, PP profiling by High Performance Liquid Chromatography (HPLC), rheological examinations, and microbiological testing for the survival and growth of starter cultures. Results show that adding BPE before fermentation led to the presence of small phenolic molecules (e.g. phenolic acids) in the yoghurts and a TEPC that was 3.5–3.9 times greater than BPE added after fermentation. Fermentation influenced the PP profiles of yoghurt. BPE and Cyanidin added before fermentation affected differently the colony number and appearance of starter cultures Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus, as well as the elastic property and viscosity of the resultant yoghurts. Addition of pectins modified the rheological properties of the yoghurts, with the HM pectin yoghurts having a stronger gel structure than the LM pectin yoghurts. The effects of added PPs on the starter cultures were diverse, depending on yoghurt formulation (e.g. type of pectin stabiliser), starter culture type, PP type, and approach for PP addition. Such effects can be tailored to maximise the TEPC and desirable PPs as metabolites of initially incorporated PPs, offering both the probiotic effects of starter cultures and the proven health benefits of blackcurrant PPs. We conclude that the pre- and post-fermentation approaches for adding PPs to drinking yoghurts are both feasible, but present different product processing challenges and functionality advantages.