Influence of Stabilizers on the Fermentation Rate and Nutritive Value of Set Yoghurt

Abstract

Stabilized yoghurt samples were produced by reconstituting powdered milk in water along with sugar and 0, 0.5 and 1.0 % concentrations of carboxyl methyl cellulose (CMC), Corn starch and gum acacia before fermentation. The yoghurt samples were either produced as short set yoghurt by incubating at 42 oC for 5 hours or incubating at 30 ± 2 oC (room conditions) for 24 hours as long set yoghurt. Samples were analyzed at intervals of 1 h for 5 h for the short set yoghurt and at intervals of 4 h for 24 h for long set yoghurt. The proximate, physicochemical, niacin content, microbial and sensory evaluation were carried out in the yoghurt samples as fermentation progressed for both short set and long set yoghurt. Results showed that the addition of stabilizers reduced moisture content from 88.54 ± 0.02 % (no stabilizer) to 84.59 ± 0.02 % (CMC), 85.59 ± 0.02 % (corn starch) and 86.70 ± 0.02 % (gum acacia). Due to dilution effect, addition of stabilizers depressed protein contents from 3.37 ± 0.04 % (no stabilizer) to 3.28 ± 0.51 % (CMC), 3.08 ± 0.03 % (corn starch) and 3.32 ± 0.03 % (gum acacia). Total solids increased on addition of stabilizers from 11.64 ± 0.02 % (no stabilizer) to 15.41 ± 0.02 % (CMC), 14.47 ± 0.02 % (corn starch) and 13.30 ± 0.02 % (gum acacia). Increase in stabilizer concentration and fermentation time decreased moisture content but increased total solids, protein, fat, ash and sugars. The viscosity of the yoghurt samples significantly (p < 0.05) increased with addition of stabilizers from 1.48 ± 0.03 Cp (no stabilizer) to 78.03 ± 1.14 Cp (CMC), 2.74 ± 0.04 Cp (corn starch) and 1.99 ± 0.03 Cp (gum acacia), with CMC having the highest increase (p < 0.05) and gum acacia the least. Viscosity significantly increased (p < 0.05) as stabilizer concentration and fermentation time increased. Although CMC increased the pH from 6.19 ± 0.03 (no stabilizer) to 6.26 ± 0.02, corn starch did not affect pH (6.18 ± 0.02) while gum acacia reduced pH to 5.94 ± 0.03. Increase in stabilizer concentration and fermentation time increased pH. Addition of stabilizers increased the titratable acidity from 0.29 ± 0.01 % (no stabilizer) to 0.39 ± 0.01 %( CMC), 0.32 ± 0.01 % (corn starch) and 0.45 ± 0.00 % (gum acacia). Lactic acid production reduced as concentration of stabilizers increased, but increased as fermentation time increased. Vitamin B3 (niacin) increased with the addition of stabilizers from 0.15 ± 0.00 (no stabilizer) to 0.175 ± 0.02 mg/ml (CMC), 0.185 ± 0.01 mg/ml (corn starch) and 0.185 ± 0.00 mg/ml (gum acacia). Niacin production increased as stabilizer concentration and fermentation time increased. The total viable bacteria significantly (p < 0.05) reduced with increase in concentration of stabilizer and fermentation time, while lactic acid bacteria decreased with increase in stabilizer concentration it increased as the fermentation time increased. Significant (p < 0.05) interactions were observed between stabilizers and their concentrations for all parameters studied. Sensory results indicated that yoghurt produced with 1.0 % concentration of CMC gave the best mouth feel while yoghurt produced with corn starch produced the most desirable taste and flavor. Results showed that reaction rates were higher for the short set yoghurt for all parameters studied, resulting to achieving an equivalent effect in 5 h in short set yoghurt compared to the same effect achieved in 24 h in the long set yoghurt.