Rheological, texture, structural, and functional properties of Greek-style yogurt fortified with cheese whey-spent coffee ground powder

The present study evaluated the feasibility of the fortification of Greekstyle yogurt with a newly developed ingredient consisting of cheese whey-spend coffee ground (CW-SCG) powder. The yogurts were analyzed using a battery of tests, including whey production, water holding capacity, firmness, rheological properties, protein content, available lysine, and antioxidant activity. The milk base was fortified to 15% dry matter with different skim milk powder to CW-SCG ratios (100/0, 75/25, 25/75, and 0/100 wt./wt.). The addition of CW-SCG up to 75% did not significantly change the acidification curve when comparing with the control sample (P \u3e 0.05), reaching the target pH 4.7 after 270–300 min. The available lysine decreased with the addition of CW-SCG, yielding values of 78.55 ± 1.56, 28.89 ± 2.45, 23.61 ± 4.42, 20.03 ± 2.71 mg per 100 g for 0-, 25-, 75-, and 100-CW-SCG, respectively. The highest value of whey production was obtained in those samples fortified with 100-CW-SCG (6.33 ± 0.35%), followed by 75- and 25-CW-SCG (5.17 ± 0.99 and 3.01 ± 0.81%, respectively). The antioxidant capacity increased proportionally to the added CW-SCG powder, yielding values of 68.41 ± 2.78, 80.71 ± 2.54, 100.51 ± 3.44, and 120.21 ± 3.18 μmol TEs per 100 g for 0-, 25-, 75-, and 100-CW-SCG, respectively. Fortification of the yogurt with CWSCG decreased the water holding capacity by 13 to 25%, depending on the level of fortification. Similarly, the addition of CW-SCG significantly decreased the hardness of the yogurts from 76.57 ± 1.18 to 30.27 ± 1.73 N s (P \u3c 0.05). Additionally, fortified yogurts with CW-SCG yielded a product with less shear-thinning behavior as compared with control. The scanning electron images of the fortified yogurts revealed the incorporation of spent coffee ground particles within the protein network. Polyphenol-Protein associations may explain the texture and rheological behavior of the yogurts. The fortification of the yogurt up to 25% of CW-SCG yielded comparable properties than the control. The industrial development of fortification of yogurt with small amounts of CW-SCG will require further studies to evaluate consumer acceptance and storage stabilit