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

Abstract

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.

Influence of transglutaminase treatment on properties of micellar casein and products made therefrom

“…The tan δ profile during acidification of pre-heated micellar casein/ WPI mixtures in SMUF had a maximum at pH 5.03 ± 0.04, which was similar to that in acid gels formed from heated skim milk [20]. The solubilisation of calcium phosphate has been suggested to partially loosen the bonds between the protein particles in the acid gel network resulting in the maximum in tan δ [22]. No such tan δ maximum was observed when incubated with Tgase.…”

“…However, the presence of active Tgase during the acidification step markedly increased the final gel strength compared to the situation where the Tgase was inactivated prior to acidification. Lorenzen et al [22] found markedly increased gel strength in yoghurt (made from whole milk preheated at 92°C for 5 min) containing active Tgase compared to yoghurt made from preheated skim milk that was incubated with Tgase but with the enzyme then inactivated. The current work suggested that the action of Tgase at neutral pH (intra-micellar cross-linking) affected the stability of micellar casein to increased acidity (see Fig.…”

Quality indices of the set-yoghurt prepared from bovine milk treated with horseradish peroxidase

“…Transglutaminase (TGase) can induce interaction through inter-and intra-molecular bonds in the protein molecules, resulting in formation of high molecular weight protein polymers and modification of the properties of the proteins and food products containing them (Nielsen et al 1995;Motoki and Seguro 1998). TGase had been applied in some dairy products including yoghurt (Faergemand and Qvist 1997;Lorenzen, et al 2002), but a need exists to study other enzyme systems capable of improving the quality of dairy products. Horseradish peroxidase (HRP, EC 1.11.1.7), a heme-containing enzyme from the tissue of edible horseradish (Yuan and Jiang 2003), can induce cross-linking of the proteins in the presence of H 2 O 2 and a low molecular weight hydrogen donor (e.g.…”

Quality attributes of the set-style skimmed yoghurt containing enzymatic cross-linked or thermal polymerized whey protein isolate

“…Cross-linking of milk proteins using a mixture containing horseradish peroxidase, glucose oxidase, and glucose can bring about higher hardness and adhesiveness to the yoghurt (Chang, Kong, & Zhao, 2014). The results from two past studies indicated that the yoghurt gels generated from the TGase-treated milk had significantly lower syneresis than the control yoghurt gels (Lorenzen et al, 2002;Şanlı et al, 2011). Cross-linking of milk proteins with three oxidases (Hiller & Lorenzen, 2011), or with the mixture containing horseradish peroxidase, glucose oxidase, and glucose (Chang et al, 2014) before yoghurt fermentation, has been proved to result in decreased whey drainage.…”

“…whey drainage). Traditional methods used to improve yoghurt texture and to decrease yoghurt syneresis include enrichment of dry matter (total solids) and/or protein contents, as well as the use of food hydrocolloids like gelatin (Lorenzen, Neve, Mautner, & Schlimme, 2002). In addition, yoghurt quality can also be improved at a molecular level via forming covalent bonds between or within milk proteins (Faergemand, Sørensen, Jørgensen, Budolfsen, & Qvist, 1999).…”