KEEPING QUALITY OF YOGHURT IN STORAGE AS INFLUENCED BY INCLUSION OF BLACK CUMIN (Nigella sativa) SEED OIL EXTRACTS

Abstract

As a result of negative and potential life-threatening side effects of chemical preservatives used in dairy products, it is worthwhile to seek alternative toxic free preservatives from natural sources for diary food products. As such, phytochemical constituents of Nigella sativa seed oil extract (NSOE) were determined before being utilized in the preservation of yoghurt produced at concentrations of (T2)2, (T3)4, (T4)6, (T5)8, and (T6)10 % and (T1) 0.1 % of Sodium benzoate which served as control in their respective treated groups. The yoghurt samples were refrigerated for 42 days and their physical, chemical and microbial and sensory properties were evaluated at 7 days’ interval. The Nigella sativa oil extract revealed the presence of phenols, flavonoids, tannins, terpenoids, saponins, alkaloids, reducing sugar, anthraquinones, cardiac glycosides and steroids while protein was absent. Quantitatively, tannins (17.05 ± 0.24 mg/g) were relatively highest phytoconstituents while alkaloids (45.77 ± 0.56 µg/g) and saponins (29.37 ± 5.06 µg/g) were in minor quantities. A significant (p< 0.01) difference was observed in the mean pH of the yoghurt samples with T5 and T6 (8 and 10 % v/v NSOE infused) having the lowest mean pH value (3.55) and the highest pH value(4.61) was observed for yoghurt included with 6 % v/v NSOE. The mean of the titratable acidity of the yoghurt is significantly (p< 0.01) affected. A significant (p< 0.01) difference was observed in the mean of non-fat solid values of the yoghurt samples with T1 (0.1% Benzoic acid), having the lowest value of 29.35, the highest non-fat solid values were observed for yoghurt infused with 10% v/v NSOE (33.22). Also There is no significant (p>0.01) difference in the total solid mean values of (NSOE) infused yoghurt no significant (p>0.01) difference in the viscosity mean of the yoghurt samples. The moisture content mean value of T1 (0.1% Benzoic acid infused) have the highest value of 68.28 as compared to T6 (63.02). The mean fat content value of the yoghurt samples with T6 having the highest value (3.68), the lowest was observed in T1 (2.12). there was a significant difference (P< 0.01) for the values of crude protein highest was observed in T6 (7.76). Significant (p< 0.01) differences were observed in the mean value of the ash content of the all the yoghurt samples (T1 - T6). The mean value of bacteria count for the control (0.1% Benzoic acid ) is 27.14 cfu/mL which is the highest as compared to T6 having the lowest value 13.09 cfu/mL. Finally, no significant (p> 0.01) difference in the mean values of colour, consistency, flavour and overall acceptability during the cold storage for all the treatment. Conclusively, the inclusion of Nigella sativa seed oil in yoghurt could lead to production of a better keeping quality yoghurt. And as acceptable alternative to chemical preservation