Physicochemical, rheological, textural, tribological, and sensory insights into the role of citrus fiber in quark cheese spreads with varying fat content

The objective of this study was to evaluate the effect of citrus fiber (1% wt/wt) on the physicochemical, rheological, textural, tribological, and sensory properties of quark cheese spreads with different fat content (10%, 15%, and 20% wt/wt). Physicochemical properties, including pH, DM, and water activity, were not affected by citrus fiber addition. Furthermore, rheological and textural analyses showed that citrus fiber increased samples' hardness and viscoelastic moduli, probably by reinforcing the protein-polysaccharide matrix, especially in low-fat variants. Tribological measurements indicated that higher fat improved lubrication, whereas fiber-containing quark cheese spread samples exhibited slightly higher coefficients of friction due to increased structural rigidity. Additionally, color analysis revealed minor shifts toward darker and more yellow tones when citrus fiber was used. Moreover, sensory evaluation confirmed that citrus fiber addition did not affect most of the tested organoleptic attributes, with slight improvement in flavor. The findings indicate that incorporating citrus fiber into quark cheese spreads can improve their functional properties, facilitate fat reduction, and promote the sustainable utilization of byproducts in dairy products.