n. moayednia

The effect of different levels of inulin (0, 1.5 and 3 %) and probiotic bacteria including Lactobacillus acidophilus and Lactobacillus casei on chemical properties (pH and titratable acidity) and viable count of probiotic strain of sweet cream during 30 days for 15-day interval at 4°C were studied. All experiments were carried out in three replications. The results showed that during the refrigeration storage of samples, pH decreased and acidity increased significantly. The addition of inulin caused significant changes in pH, acidity and the viability of probiotic strains. By increasing the level of inulin to 3%, the pH of the cream samples decreased, and the acidity and counts of the probiotics increased significantly and this was more significant in Lactobacillus acidophilus, although the treatment containing Lactobacillus acidophilus had the highest acidity. The probiotic survival evaluation also indicated that inulin treatment at 3% level was the best treatment for increasing the viability of the probiotics in cream. The results showed that the addition of prebiotics, such as inulin, could play an important role in increasing the viability of probiotics. In general, changes in the chemical properties of sweet cream during the refrigeration were standard, which could be considered as a synbiotic product and sweet cream as a dairy product can also be considered as a good carrier for probiotic bacteria.

Two probiotic bacteria (Lb. acidophilus and B. lactis) were immobilized on the alginate coat of strawberry pieces and were added to the prepared sweet non fat dietary stirred yogurt. Physico-chemical parameters namely pH value, titratable acidity and synersis along with the viability of probiotic bacteria of the samples were evaluated over the 8 days of storage at 5 ºC at 2 day intervals. A significant decrease in pH value occurred after 6 and 8 days and the titratable acidity significantly increased after 8 days. Synersis did not show significant changes probably due to the presence of applied hygroscopic nature of some ingredients in the samples. Some free probiotic cells were identified in yogurt matrix of the samples due to the migration phenomenon. The decrease trend of embedded cells happened slower than the free ones. This might be due to the protective effects of alginate coat on the survival of probiotic bacteria surrounded by yogurt.

The “Encyclopedia of Fermented Fresh Milk” has classified Acidophilus and Bifidus milks as Non-traditional fermented milk products. These products contain Lactobacillus acidophilus and Bifidobacterium spp., respectively, that are known as probiotic microoganisms. In this study, some aspects of acidity development, pH measurement and bacterial counts were monitored when these micro-organisms were grown in milk. The starter cultures of L. acidophilus La-5 and Bifidobacterium lactis Bb-12, obtained from Chr. Hansen in Denmark, were each inoculated at the rate of 0.01 g 100 ml-1 in UHT milk and incubated at 37ºC for a duration of 5 h (Acidophilus and Bifidus milks). The same procedure was carried out with the same inoculation rates of two mentioned starters as mixed culture (Acidobifidus milk). The titratable acidity measurements and pH values of the single strains fermented milks were similar, but the sour taste of Acido-bifidus milk of the mixed starter culture was more tangible when compared with the two other fermented products. From the limited data available, it was evident from the preliminary studies that the growth of B. lactis in mixed cultures was better as compared to the single strain, and it is suggested that a lower inoculum rate of starter cultures or shorter fermentation period might be recommended for the development of Acido-bifidus milk.

Acidophilus milk after preparation, with the defined characteristics of pH, titratable acidity and viable counts of Lb. acidophilus, was kept at the refrigerator (5 °C) and changes of above mentioned parameters were evaluated during 21 days at 7-day intervals. The obtained results showed that the titratable acidity of product significantly (p≤0.05) increased over storage period, demonstrating the post acidification ability of Lb. acidophilus at low temperatures. The pH values of Acidophilus milk, due to the buffering capacity of milk, didn’t show significant (p≤0.05) decrease after 14 days, which this was contrary to the obtained result at 21 days of storage period. The viability of Lb. acidophilus significantly (p≤0.05) fell down in the first two assessments due to cold shock and increase of acidity and then raised at the last assessment due to the proteolytic activity of Lb. acidophilus, causing the liberation of nutritive amino acids.

The growth rate of two probiotic strains with documented health effects was studied in ultra-high temperature treated milk separately and beside each other. The probiotic strains were Lactobacillus acidophilus (La-5) and Bifidobacterium lactis (Bb-12). Fermentation was followed for 12 h at 37 ˚C and the samples were analyzed for pH, titratable acidity and viable counts of probiotic bacteria before incubation and at 2h intervals throughout the fermentation period. The obtained results showed that Lb. acidophilus had higher activity and growth rate than B. lactis when they were purely cultured in milk. Investigation on mixed culture inoculating the milk revealed that Lb. acidophilus had a stimulating effect on the growth rate of B. lactis, however, its growth wasn’t significantly affected by the presence of the latter bacteria.