ORIGINAL RESEARCH Microparticulation of mixtures of whey protein and inulin JOHN T TOBIN, 1,2 SINEAD M FITZSIMONS, 1 ALAN L KELLY, 2 PHILIP M KELLY, 1 MARK A E AUTY 1 andMARK A FENELON 1, * 1 Food Processing and Functionality Department, Moorepark Food Research Centre, Teagasc, Fermoy, Co. Cork, Ireland, and 2 Department of Food and Nutritional Sciences, University College Cork, Cork, Ireland *Author for correspondence. E-mail: mark.fenelon@teagasc.ie Ó 2009 Society of Dairy Technology This study investigated the effect of the presence of inulin, in the range 0 - 3.81 g/100g, on the physical and microstructural properties of microparticulated whey protein concentrates (MWPC) and powders. Substitution of lactose with inulin increased levels of whey protein denaturation during microparticula- tion. The increased denaturation levels were correlated with reductions in lactose and calcium content of the microparticulated solutions, which increased aggregate size and solution viscosity post-processing. In conclusion, it appears possible to successfully manufacture a low-calorie microparticulated whey protein based fat replacer using the dietary fibre inulin as the carbohydrate source. Keywords Microparticulation, Whey protein, Inulin, Lactose, Denaturation, Particle size. INTRODUCTION In developed countries, high intake of fat has led to an increasing prevalence of medical conditions such as obesity, coronary artery disease and certain types of cancer. Full or partial replacement of fat in food can offer the consumer organoleptic charac- teristics similar to those of its full-fat counterpart, while helping to maintain a healthier lifestyle (Miller and Rolls 1996). Fat replacers, substitutes, extenders and mimetics, are common terminolo- gies used to describe ingredients that lower the cal- orific value of high-fat foods. Fat mimetics in particular, have received much attention and can be derived from starch, fibre, proteins and gums (Jones 1996). An example of the use of proteins as fat replac- ers is the process of microparticulation, whereby protein aggregates ranging in size from 0.1 to 3 lm are created to impart a creamy perception in the mouth similar to that produced by fat globules (Singer and Dunn 1990). Microparticulated protein is a natural ingredient produced from whey protein concentrate (WPC, typically with 35 or 55% pro- tein) and thus compositionally similar to traditional WPC, ensuring that the same regulatory standards of identity apply. The principal proteins in whey are b-lactoglobulin (50% of total whey protein) and a-lactalbumin (20% of total whey protein) and, to a lesser extent, blood serum albumin, vari- ous immunoglobulins and other minor milk pro- teins. The process of producing microparticles involves heating and shearing the protein disper- sion for a pre-selected holding period conducive to formation of aggregates (Steventon et al. 1994). The unfolding, denaturation and aggregation of whey proteins during heating affects functional properties such as water immobilisation and heat-induced gel formation. Irreversible aggregate formation is primarily due to the ability of b-lacto- globulin to denature at temperatures above 70°C at neutral pH, while a-lactalbumin with its more ordered structure does not form aggregates. Hence, formation of microparticulates is dependent on the presence of b-lactoglobulin (Singh and Hevea 2003). In the microparticulation process itself, lac- tose and calcium content, as well as pH and heat- ing temperature have been shown to influence aggregate size and structure (Spiegel 1999; Spiegel and Huss 2002). A recently developed patented thermal process (LeanCremeÔ, APV, Silkeborg, Denmark), was used for the production of microparticulates from WPC containing low (i.e., 15.0 g/100g) solids content. Typically, concentrates with higher solids contents are required when using conventional scraped-surface heat exchangers, making the APV process a more efficient way of producing a microparticulated product. This study evaluated the addition of the dietary fibre inulin as a replacement for lactose and as a potential mechanism for a further reduction in solids content. Inulin is a nondigestible carbohydrate found in many plants, such as chicory and artichoke, as a storage carbohydrate (Roberfroid 1993). Inulin has a number of important attributes that make it a novel functional food ingredient including, its crystalline structure which gives it potential as a fat replacer, (Hennelly et al. 2006), its low calorific value (Molis et al. 1996; Roberfroid 1999), and its pre-biotic properties due to its resistance to digestion in the upper gastro-intestinal tract (Knudsen 1995). While there may be potential benefits to replac- ing the lactose in WPC with inulin in terms of 32 Vol 63, No 1 February 2010 International Journal of Dairy Technology doi: 10.1111/j.1471-0307.2009.00550.x