Effect of microfluidization of heat-treated milk on rheology and sensory properties of reduced fat yoghurt Chr. Ian E. Ciron a, b , Vivian L. Gee a , Alan L. Kelly b , Mark A.E. Auty a, * a Food Chemistry and Technology Department, Teagasc Food Research Centre, Moorepark, Fermoy, Co. Cork, Ireland b Department of Food and Nutritional Sciences, University College Cork, Ireland article info Article history: Received 19 November 2010 Accepted 17 February 2011 Keywords: Reduced-fat yoghurt Homogenization Microfluidization Rheology Sensory analysis Principal component analysis abstract The effects of microfluidization at 150 MPa (MFz) and conventional homogenization at 20/5 MPa (CH) of heat-treated milk on the rheology and sensory properties of non- (0.1%) and low- (1.5%) fat stirred yoghurts were compared. Homogenization conditions clearly affected the sensory properties of reduced- fat yoghurts, but the effect was highly dependent on fat content. MFz of heat-treated milk yielded products with very different sensory profiles from the conventional yoghurts. For non-fat yoghurts, MFz of heat-treated milk enhanced the perception of buttermilk and soft cheese flavours, and natural yoghurt aroma and flavour, but also increased the intensity of undesirable mouthfeel characteristics such as chalkiness, mouth-dryness and astringency. For low-fat yoghurts, MFz significantly improved creaminess and desirable texture characteristics such as smoothness, cohesiveness, thickness, and oral and spoon viscosity. These differences in sensory profiles, especially textural properties, were partially related to rheological properties, particularly flow behaviour. MFz of heat-treated milk resulted in non- and low-fat yoghurts with higher yield stress, more pronounced hysteresis effect and higher viscosity than those of CH yoghurts of similar fat contents. These findings suggest that microfluidization may have applications for production of high-quality yoghurt with reduced-fat content. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction In the dairy industry, consistent production of yoghurt with desirable texture is achieved by heat treatment and homogeniza- tion of the milk base, increasing the milk solids/protein content, and use of commercial starter cultures. The addition of stabilizers, such as gelatine, modified starches and polysaccharides is also a common practice in the manufacture of yoghurt. Milk-derived ingredients (Janhoj, Petersen, Frost, & Ipsen, 2006; Johansen, Laugesen, Janhoj, Ipsen, & Frost, 2008) and exopolysaccharide- producing bacterial cultures (Folkenberg, Dejmek, Skriver, Guldager, & Ipsen, 2006) have been investigated to assess their potential for manufacture of reduced-fat yoghurts (i.e., at least 25% less fat than the full-fat counterpart) with desirable texture prop- erties. Milk proteins have been modified to serve as protein-based fat replacers by mimicking the functionality of fat in structure formation and imparting attractive sensory properties to yoghurt (Seydim, Sarikus, & Okur, 2005). Recent studies have examined a range of new technologies, including high-pressure processing (Penna, Gurram, & Barbosa-Canovas, 2006), thermosonication (Riener, Noci, Cronin, Morgan, & Lyng, 2009), high-pressure homogenization (Lanciotti, Vannini, Pittia, & Guerzoni, 2004; Serra, Trujillo, Quevedo, Guamis, & Ferragut, 2007) and microfluidization (Ciron, Gee, Kelly, & Auty, 2010), to determine their potential as alternative processes for producing good quality reduced-fat yoghurts. Few studies have investigated the potential of microfluidization to improve the texture and stability of yoghurt. Partial replacement of milk solids with microfluidized starch was shown to enhance viscosity and reduce syneresis in yoghurt (Augustin, Sanguansri, & Htoon, 2008). Cobos, Horne, and Muir (1995) studied the impact of using microfluidization as a homogenization technique on the rheological properties of acid gels. Recently, microfluidization was utilized for production of stirred yoghurts and shown to affect the texture, water retention and physical properties of the resultant yoghurt. High-pressure homogenization using a MicrofluidizerÔ reduced the particle size in heat-treated non- and low-fat milk samples to sizes smaller than those normally occurring in milk processed in a conventional valve homogenizer, and resulted in yoghurts with different gel particle size and microstructure (Ciron et al., 2010). Such differences in particle size and structure would be expected to influence rheological behaviour, which could in turn * Corresponding author. Tel.: þ353 25 42442; fax: þ353 25 42340. E-mail address: mark.auty@teagasc.ie (M.A.E. Auty). Contents lists available at ScienceDirect Food Hydrocolloids journal homepage: www.elsevier.com/locate/foodhyd 0268-005X/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.foodhyd.2011.02.012 Food Hydrocolloids 25 (2011) 1470e1476