Effect of stabilizers on the physico-chemical and sensory attributes of thermized yoghurt

Abstract

Stabilized thermized yoghurt was produced by the addition of gelatin, carboxyl methyl cellulose (CMC) and corn starch, into yoghurt mix as stabilizers, each at 0, 0.5, 0.75 and 1.0% concentrations. The yoghurt samples produced after pasteurization of the mix, cooling, inoculation of starter culture and incubation for about 16 h were thermized at 75oC for 60 s followed by immediate cooling. Results show that titratable acidity value of the control samples (0% stabilizer) was 0.92 ± 0.03. CMC, when added to yoghurt mix at levels of 0.5% and above, depressed lactic acid production (compare 0.92 ± 0.03 of the control with 0.90 ± 0.01 of samples containing 0.5 and 0.75% CMC). This observation is in contrast to effects of corn starch and gelatin which enhanced lactic acid production (at least up to 0.75% concentration). This was also mirrored (in reverse order) in the pH values; as samples with higher titratable acidity had, expectedly, lower pH values. Addition of stabilizers decreased percent protein and ash contents due to dilution effect but increased total solids and specific gravity of the thermized yoghurt samples. Sensory results showed that addition of corn starch produced the most desirable flavour and taste which differed significantly (p < 0.05) from flavour and taste produced by gelatin but did not differ significantly (p ≥ 0.050) from that produced by CMC at 0.5 and 0.75% concentrations. Yoghurt containing CMC had the best mouth feel/consistency as well as appearance which did not differ significantly (p ≥ 0.05) from the mouth feel and appearance of yoghurt containing corn starch but differed significantly from yoghurt containing gelatin. Yoghurt containing CMC at 0.75% concentration was the most generally accepted. Key words: Stabilizers, thermized yoghurt, sensory attribute, physco-chemical.