Effect of Date Pit Powder on quality properties and survival of Probiotic bacteria in Set Yogurt

Date pit is one of the major waste of date processing plants and a rich source of dietary fiber and contains high levels of phenolic compounds so potentially can improve the growth and survival of probiotic bacteria. In this research, the effect of adding date pit powder on some quality properties and viability of probiotic bacteria in set yogurt was investigated. In this study, the date pits were first separated from dates and after washing and drying, they were powdered and sieved. After fat removal by N-hexane, they were re-dried and sieved to make the date pit powder with high fiber content. The date pit powder was added at three levels of 0.5, 1 and 2 percent to set yoghurt containing Lactobacillus acidophilus LA-5 and Bifidobacterium lactis Bb-12. During the 21 days of storage in the refrigerator, physic- chemical (pH, acidity, dry matter, syneresis) , sensory properties and viability of probiotic bacteria were evaluated on days of 1, 7, 14, and 21. The results showed that with increasing the amount of date pit powder, the pH of all samples decreased during the first day and storage period with more reduction rate in B. Lactis content yogurt while the acidity and dry matter percentage, especially in samples with 2% date pit powder, were increased. Increasing the amount of date pit powder resulted in a reduction in the percentage of syneresis from 29% to 24% in first day, although during the storage, it increased and reached 33%. However, there was no difference in the water separation between the samples of yogurt containing two different probiotic bacteria. By increasing the concentration of date pit powder, probiotic counts in all samples from 8.2 (log cfu ml-1) was improved to about 9.5 (log cfu ml-1), although it decreased during storage and decreased to at least 7.4 (log cfu ml-1), but never exceeded the recommended limits For probiotic products (107 cfu g-1). The highest probiotics survival at the end of the storage period was observed in samples containing 2% date pit powder. The sensory evaluation showed higher score in color, flavor and overall acceptance of yogurt when date pit powder was added to samples but it declined during storage period. However, by the end of the second week, all sensory characteristics were well evaluated. In general based on the results, one percent date pit powder was led to improve survival of probiotic bacteria, physico- chemical and sensory characteristics of yogurt, for up to two weeks after production.