Impact of fortification with white willow ( <i>Salix alba</i> ) bark on the rheological properties, syneresis and colour of nonfat set‐type yoghurt

Background White willow ( Salix alba ) is a traditional medicinal plant known for its anti‐inflammatory and pain‐relieving properties, attributed to its high polyphenol content. Yoghurt can serve as an effective delivery carrier for bioactive compounds to develop health‐promoting foods due to its unique network structure. Aim This study aimed to investigate the impact of willow bark addition on the rheological properties, syneresis and colour of fortified nonfat yoghurt. Methods In this study, a nonfat set‐type yoghurt supplemented with different levels (0%, 2%, 5%, and 10%) of willow bark was prepared. Rheological properties of the samples were monitored in situ during fermentation and parameters including storage modulus (G′), loss tangent (tan δ), fracture strain (γ fracture ) and fracture stress (σ fracture ) were measured. In addition, syneresis (% w/w ) and colour values including lightness (L*), redness (a*) and yellowness (b*) of the final yoghurt were evaluated. Major Findings The results showed no significant differences in the final G′ between the control and samples containing 2% and 5% willow bark ( p &gt; 0.05), whereas 10% willow bark significantly reduced the final G′ ( p &lt; 0.05) after fermentation (at 42°C). When the nonfat set‐type yoghurts were cooled from 42°C to 4°C, G′ increased in a dose‐dependent manner with the addition of willow bark. Additionally, the level of syneresis increased in a dose‐dependent manner in all willow bark‐fortified yoghurt samples. Changes observed in the rheological properties and syneresis levels during and after gel formation could be associated with interactions between milk proteins and polyphenols from willow bark. Industrial Implications Overall, these results indicate that the fortification of skim yoghurt with low concentrations of willow bark (2% and 5%) has a relatively minimal impact on the rheological properties and appearance of the product, providing technical insights for functional yoghurt manufacturers.