Effect of Sweeteners on the Microstructure of Yogurt.

Abstract

The objective was to determine the effect of a peptide sweetener, Aspartame, compared to a carbohydrate sweetener, sucrose, on the microstructure of yogurt. Microstructure was determined by transmission and scanning electron microscopy. Without the sweeteners, casein micelles, that make up the yogurt matrix, were observed in single longitudinal polymers. When Aspartame was used, casein micelles formed double longitudinal polymers. In comparison sugar caused casein micelles to form clusters. Data show that type of sweetener impacts state of association of casein micelles and thus effects microstructure. Keywords: cultured, dairy, fermentation, structure, sweetener Principal component analysis of yogurt revealed high consumer acceptability for sweetness characteristics and lower consumer acceptability for samples with plain yogurt character (Barnes et al., 1991). Hence consumers want the sweetness in yogurt but health reasons dictate decreased intake of calories and reduction of sugars. To decrease calories in yogurt, artificial sweeteners have been incorporated (Nabros & Gelandi, 1986;Keating & White, 1990). Farooq and Haque (1992) reported that nonfat yogurts with Aspartame, a popular peptide based sweetener, had half the calories per serving compared to regular yogurt containing 3.25% fat and 4% sucrose. Mozaffar and Haque (1992) and Haque (1993) have shown that amphipathic peptides (like Aspartame) effect protein-protein association, which is a primary requisite during gel formation. On the other hand sugars such as sucrose are traditionally used by enzymologists to stabilize enzyme proteins (Choi & Kosikowski, 1985). Such hydrophilic solutes impact water structuring and hence influence protein-protein association (Kalab & Harwalkar, 1972). This in turn may impact the amount of entrapped water or pore dimensions. The size of pores of the casein micelle network is a major factor affecting susceptibility of yogurt to syneresis (Harwalkar & Kalab, 1986). Various factors such as heating of milk, total solids content, pH, lactic acid bacteria and thickening agents have been reported to affect the microstructure of yogurt . It would be interesting to see the effect of a peptide sweetener, Aspartame, compared to a carbohydrate sweetener, sucrose, on yogurt gel network formation.Yogurt was made as described earlier by Farooq and Haque (1992) with slight modification. Yogurt mixes were prepared in 1 l batches. Fluid skim milk with 9% milk solids not fat (MSNF) was obtained from the Mississippi State University Dairy Plant. Other ingredients added on weight per volume basis were 0.5% modified food starch, 3% non fat dry milk (NDM), 0.02% Aspartame (NutraSweet Co., Deerfield, IL), and 3% maltodextrin or 3% sugar. The overall total solids (TS) content was 15.5% (Table 1). Every effort was taken to keep TS constant to avoid its impact on microstructure Harwalkar & Kalab, 1986). Ingredients were throughly mixed in fluid skim milk heated to 60˚C and homogenized at 35.15 and 140.62 kg/cm 2 . This was followed by batch past...

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