Effect of enzymatic cross‐linking of milk proteins on functional properties of set‐style yoghurt

This paper presents research on the effect of enzymatic cross‐linking of milk proteins on the properties of yoghurt. Whole milk was incubated with transglutaminase (TG) prior to fermentation (2 h, 40°C, E/S ratio 1/2000). Enzyme action was stopped by heating (1 min, 80°C). Skim‐milk was treated by simultaneous use of TG and thermophilic yoghurt starter culture without inactivation of the enzyme. A TG treatment of milk prior to fermentation led to prolonged fermentation, while the concomitant use of TG and culture had no influence on fermentation time. Post acidification of yoghurt during storage was lower for products from enzyme‐treated milk. This applies both for products cross‐linked prior to fermentation with enzyme inactivation, and for simultaneous use of culture and TG without inactivation of the enzyme. Scanning electron microscopic studies revealed that a TG treatment of milk led to reduced mesh sizes of the protein network, and a more regular distribution of the proteins in the yoghurt gel. As a result, yoghurt products from enzyme‐treated milk showed increased gel strength and less syneresis, especially when the enzyme was not inactivated. Sensory studies revealed that odour and consistency properties of products from TG‐treated milk were assessed as less ‘yoghurt specific’. On the other hand, products from enzyme‐treated milk were described as being more creamy, indicating that a TG treatment may simulate fat in fermented milk products.