keywords: Yoghurt, Moringa oleifera, microbial quality, storage, shelf-life, preservative
Yoghurt is one of the most popular fermented dairy products widely consumed all over the world. It is obtained by lactic acid fermentation of milk by the action of a starter culture containing Streptococcus thermophilus and Lactobacillus delibrueckii. This study investigated the effect of Moringa oleifera seed flour on the microbial quality of freshly produced and shelf life stability of yoghurt after the storage period of 28 days under refrigeration and ambient temperature (5±1 and 27±10C), respectively. Moringa oleifera seed flour was incorporated into yoghurt at concentrations of 0.5, 1, 1.5, 2 and 2.5%. The microbial enumeration was observed using Nutrient, MacConkey and Potato dextrose agar media. The result indicated that addition of Moringa oleifera seed flour at various concentration has remarkable effect on bacteria, yeast and mold count. Microbial count (total aerobic count) decreased with advance storage period for samples A1 –E1 at the various concentrations for bacteria cells rang from 3.70 -2.30 X 106, 4.06 – 2.21 X 106, 4.35 – 2.10 X 106, 5.30 – 1.40 X 106 and 6.30 – 1.15 X 10 cfu/ml for samples stored under refrigeration temperature, respectively. The result for samples stored under ambient temperature for bacteria cells count ranged from 1.30 X 106 – 9.97 for control, 3.70 X 106 - 2.80 X 106 , 4.06 X 106 – 2.68 X 106, 4.35 X 106 – 2.45 X 106, 5.30 X 106 – 2.33 X 106 and 6.30 X 106 – 2.25 X cfu/ml for samples A2 – E2, respectively. However, samples with concentration of 2.5% stored in the refrigerator and ambient temperature showed high inhibitory effect of (1.15 X 106 and 2.25 X 106) after the storage period. Yeast and mold count were detected only from samples with concentration of 2% (1.24 X 106) and 2.5% (1.84 X 106) from ambient temperature after the period of storage, but absent from all samples stored under refrigeration temperature, except control samples (fresh) which showed growth in the third (3rd) and fourth (4th) week of storage (1.22 X 106 and 1.53 X 106) period. Notably, Coliform counts were not detected in all samples for both control (fresh) and treated samples throughout the storage period. Therefore, it can be concluded that the use of Moringa oleifera seed flour can serve as a preservative since it led to retarded microbial growth in the yoghurt produced, thereby, improving its quality and shelf-life stability.