Influence of emulsion composition

Several studies have been published on the behaviour of whey protein concentrate or whey protein isolate either alone or in combination with lactose and/or sodium caseinate (Faldt & Bergenstahl, 1996; Keogh & O’Kennedy, 1999, Landstrom et al., 2000; Millqvist-Fureby et al., 2001; Vega & Roos, 2006). The main disadvantage of using whey proteins for emulsification is their susceptibility to heat denaturation and aggregation (Damodaran & Anand, 1997; Vega & Roos, 2006). Faldt and Bergenstahl (1996) studied the encapsulation ability of whey proteins by measuring the amount of oil present at surface of the powder particle after spray drying. They found that 45-60% of the surface of the powder made with whey proteins was covered with oil which was relatively higher compared to investigation made using NaCas (Landstrom et al., 2000; Vega & Roos, 2006). The level of fat in the emulsion also impacted the total free fat and surface fat. Higher levels of fat in the emulsion resulted in higher levels of surface fat (Keogh & O’Kennedy, 1999; Vega & Roos, 2006).

The use of whey protein in combination with NaCas has been shown to increase the stability of emulsions during drying. No significant change in the droplet diameter was noticed before and after drying (Sliwinski et al., 2003). Only in emulsion with more than 70% of whey protein, a shift in the particle size towards larger ranges post spray drying was observed. Sliwinski et al. (2003) also observed the displacement of

had majority of the surface, covered with NaCas before spray drying. The authors attributed this shift in the composition of the oil droplet surface to heat denaturation and aggregation as the amount of β-lactoglobulin increased the most as compared to

α-lactalbumin (Sliwinski et al., 2003).

The impact of spray drying on whey protein denaturation and aggregation has not received much attention. However, heating of whey proteins before emulsion formation has been studied by Millqvist-Fureby et al. (2001) under a wide range of conditions. The authors showed that heat treatment of whey proteins before emulsification and drying caused a shift in the droplet diameter towards the larger size range but they did not compare the unheated samples before and after drying. Other studies using whey proteins have shown large surface oil coverage, suggesting that denaturation and aggregation might be less important in whey protein stabilized emulsion powders (Faldt & Bergenstahl, 1996; Vega & Roos, 2006).

Due to the lack of heat sensitivity of caseinates, most studies have shown a lower fat surface coverage in powdered emulsions made using NaCas as compared with whey protein products (Rosenberg & Young, 1993; Young et al., 1993 a, b; Vega & Roos, 2006). When used as an encapsulant on its own, NaCas stabilized emulsions showed a decrease in the microencapsulation efficiency and protein load with an increase in the oil-to-protein ratio. Microencapsulation efficiency has been defined as the ratio of extractable oil measured using a solvent extraction method to the total oil content as measured using the Rose-Gottlieb method (Hogan et al., 2001). The association between surface protein concentration of the emulsion and the surface oil coverage or microencapsulation efficiency has been made rarely in literature (Vega & Roos, 2006). Hogan et al. (2001) also suggested that oil-to-protein ratio was not the only

factor driving microencapsulation efficiency but also the concentration of the filler material played a role. However, the role of matrix forming material in combination with proteins has not been addressed widely. Also, the comparison of different protein materials (monomeric vs. aggregated) has not been made (Vega & Roos, 2006).

2.9.1.2 Carbohydrates

Lactose is exclusively found in milk and is widely used as a matrix forming material in spray dried products. In addition, it widely used in the pharmaceutical industry as an excipient in tablet manufacture. Lactose used in some products goes through a pre-crystallisation stage to avoid caking problems during drying and further storage (Schuck & Dolivet, 2002). However, this is not common for dairy products. Rapid evaporation of water from dairy products means that lactose remains in an amorphous form in finished powders (Vega & Roos, 2006). This lactose in a glassy state is thought to be the main encapsulant of milk fat in dairy-like emulsions (Buma, 1971; Vega & Roos, 2006). Being amorphous, lactose is only stable below its glass transition temperature (Miao & Roos, 2004). Exceeding this, crystallisation of lactose and related processes may impact food quality (Roos & Karel, 1991; Vega et al., 2005). The presence of lactose in spray-dried formulation also has implications during drying, such as stickiness and fouling of the dryer cones (Schuck et al., 2005; Vega & Roos, 2006). Therefore, attention must be paid to choosing the right dryer conditions when using lactose as a bulk ingredient in powdered emulsion formulations (Vega & Roos, 2006). Also, it is critical to have the correct post drying conditions to maintain stability of powders containing lactose as prevention of caking and lumping will depend on the relationship between humidity and

Maltodextrin is a hydrolysis product of starch with a dextrose equivalent of less than 20 (Chronakis, 1998). With a broad range of molecular weight distribution of oligosaccharides, maltodextrins are highly soluble in water with low viscosity. This is the reason for their widespread commercial use as co-encapsulants (McNamee et al 1998; Hogan et al., 2001; Vega & Roos, 2006). Dollo et al. (2003) reported excellent stability during spray drying when a mixture of maltodextrin and NaCas was used to stabilize fractionated coconut oil. No noticeable change was seen in emulsion particle size before and after drying and reconstitution (Vega & Roos, 2006). With increased dextrose equivalent (DE) of maltodextrin in formulation, a significant increase in microencapsulation efficiency was observed. This was attributed to the presence of lower molecular weight carbohydrates, which created a less porous matrix which was less impervious to extraction solvents (Vega & Roos, 2006).