PRODUCTION OF FUNCTIONAL BIO - YOGHURT MADE FROM CAMEL MILK, SKIM MILK RETENTATE AND FORTIFIED WITH SWEET POTATO POWDER

Abstract

The goal of this study was done to estimate the effect of partially replacement of camel's milk with skim milk retentate (SMR) as well as fortification with sweet potato powder (SPP) on the physicochemical, rheological, microbiological, microstructure and sensory properties of the resultant bio- yoghurt, during the storage. Yoghurt was made from camel milk as a control (C), and the other treatments were made from camel milk after replacing 30% or 40% of it by SMR, and fortified with 0, 1.5 and 3% SPP. Addition of (SM) aimed to overcome the problem of long coagulation time and the weak body arising by using camel milk. Results revealed that treatments of camel milk supplemented with (SMR) and (SPP) were more effective in increasing the total solids, protein, ash, total carbohydrates, acidity and total volatile fatty acid (TVFA). Curd firmness and syneresis were also affected, by the level of SMR and SPP. This fortification resulted in increasing the water holding capacity and lowering the susceptibility to syneresis in the supported yoghurt. Microbiological results revealed that the counts of L .delbruecii spp. bulgaricus, and S.thermophi lu s were increased up to 3 days of storage then decreased gradually thereafter , in all treatments till the end of the storage period , compared with control one. B .bifidum behaved another trend so it decreased gradually during the storage period. The survival rate of S.thermophills in treatments containing SMR and SPP was higher than that of both L . delbruecii spp . bulgaricus and B. bifidum . The viable cells of probiotic bacteria were maintained at the functional level (>106 cfu//ml) up to 10 days of storage. Scanning electron microscopy showed that the size of casein clusters and protein aggregates , the number and size of voids were not the same between the different treatments and was affected by the additives used . Sensory attributes showed that addition of SMR and SPP to camel milk improved greatly both the organoleptic properties, especially body & texture, the nutritive value and healthy benefits in the resultant yoghurt, compared to the control. The best treatment was yoghurt contained 40% SMR and 3% SPP. Control yoghurt was the lowest one in scoring and had very weak body (semi- liquid) and lack of acid flavor.