Physicochemical and Rheological Characteristics of Stirred Yogurt Fortified with Vitamin B₁₂ and Melatonin

Vitamin B-12 and melatonin were added to whole milk-stirred yogurt to evaluate its physicochemical (fat, protein, total solids, moisture, syneresis, and color), rheological (flow behavior and dynamic rheology), and color characteristics as L, a*, and b* and color change ( increment E). For this, five treatments (T) were elaborated as follows: T1 = yogurt (Y) without vitamin B-12 and melatonin, T2 = Y with 3 mu g/L of B-12, T3 = Y with 5 mg/L of melatonin, T4 = Y with 2 mu g/L of B-12 and 3 mg/L of melatonin, and T5 = Y with 3 mu g/L of B-12 and 5 mg/L of melatonin. The fortification of yogurt with vitamin B-12 and melatonin modified (P<0.05) the content of fat, moisture, and syneresis. Treatment 5 presented the lowest content of fat and the largest content of moisture (P<0.05). Treatment 4 had the largest syneresis at day 1, and at day 14, there was not differences in syneresis among treatments (P>0.05). Regarding color, luminosity (L*) did not have significant differences (P>0.05) among treatments and neither among storage days, except for T5 that presented the lowest value at day 14. Regarding parameter a*, all treatments presented negative values (tendency to green), and T2, T3, and T5 showed significant differences (P<0.05) trough time. No significant differences (P>0.05) were observed for the b* values neither among treatments nor among time. The highest value in Delta E, compare to the control, was observed in T5. Regarding flow behavior, T1 showed a significantly different (P<0.05) higher flow behavior (n) than the rest of the treatments. In general, all the samples indicate an increase (P<0.05) in the flow behavior (n) through the storage time. And the consistency index (K) showed significant difference (P<0.05) between T1 and T2 and T3 and T4. In conclusion, the addition of vitamin B-12 and melatonin to yogurt generates changes in the physicochemical and rheological properties; likewise, the addition of melatonin in combination with vitamin B-12 showed that the viscoelastic characteristics of the fortified yogurts are like the control yogurt. Since these, treatment 5 presented the most similar values of rheology and syneresis compared to the control, so this combination of B-12 and melatonin could be employed to develop a new functional yogurt.