Impact of Citrus reticulata Peel Extract and Bifidobacterium longum on Staphylococcus aureus during Cold Storage of Functional Yoghurt

This study aimed to evaluates the effect of Citrus reticulate peel extract and Bifidobacterium longum on Staphylococcus aureus inoculated in milk used for manufacturing of yoghurt an attempt to improve the safety of yoghurt. Seven batches of yoghurt were prepared from cow's milk with Streptococcus thermophilus and Lactobacillus bulgaricus then inoculated with S. aureus, the first batch was a control (containing no probiotic bacteria, Citrus reticulata or S. aureus), the second batch contains S. aureus only, and the third batch contains B.longum. The following two batches (4,5) contain both citrus reticulata at concentrations of 0.5 and 1%. The remaining 6(th), 7(th) batches contain B. longum and Citrus reticulata 0.5 and 1%, respectively. The yoghurt batches were examined physically and bacteriologically at zero time and after 3, 5, 10, and 12 days of refrigerated storage. The reduction percent of S. aureus count once the storage term has expired (12 days) was <56%, < 94,8% in yoghurt containing Citrus reticulata at concentrations of 0.5 and 1%, respectively. While the reduction percent in the case of yoghurt containing B. longum was < 95.4% But in the case of the combined addition of both citrus reticulata and B. longum, the reduction percent was < 96.2% and < 96.8% for 0.5 and 1% added citrus reticulata and B. longum, respectively. At the same time, in the control positive batch, the increase percent of S. aureus after the storage time has ended (Twelve days) was > 96.4%. This study offers important insights into the potentially beneficial uses of citrus peels, in particular, Citrus reticulata peel extract and B. longum as functional food additions in manufacture of yoghurt.