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The effects of whey protein concentrates on physical and rheological properties of yogurt were studied. Five commercial whey protein concentrates (340 g kg−1 protein nominal) were used to fortify milk to 45 g protein kg−1. Fermentation was performed with two different starters (ropy and non-ropy). Resulting yogurts were compared with a control yogurt enriched with skim milk powder. The water-holding capacity of the yogurt fortified with skim milk powder was 500 g kg−1 and ranged from 600 to 638 g kg−1 when fortified with whey protein concentrates. Significant rheological differences have been noticed between the yogurts fortified with different whey protein concentrates, independent of the starter used. Three whey protein concentrates generated yogurts with a behavior similar to the control. The two others produced yogurt with lower firmness (15 g compared with 17 g), lower Brookfield viscosity (6 Pa s compared with 9 Pa s), lower yield stress (2 Pa compared with 4 Pa), lower complex viscosity (13 Pa s compared with 26 Pa s), and lower apparent viscosity (0.4 Pa s compared with 1 Pa s) than the control, respectively. The yogurts with the lowest firmness and viscosity were produced with concentrates which contained the highest amount of non-protein nitrogen fraction (160 g kg−1 versus 126 g kg−1 of the total nitrogen), and the highest amount of denaturation of the whey protein (262 versus 200 g kg−1 of the total nitrogen).


Dairy Science

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Published by Wiley-Blackwell. This is the pre-peer reviewed version of an article published in Journal of the Science of Food and Agriculture.

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