The effect of inulin, inoculum's level and different temperatures on the growth and metabolism of Lactobacillus acidophilus La5 in milk

The biological activity of probiotics is affected by various environmental factors which can influence the performance as well as the growth of probiotics for increasing the health of the consumers. This study aims to investigate the effect of inulin, concentrate 0.5, 1, 1.5 and 2% of the primary culture and temperature of 35, 38, 41 and 44°C on the growth and metabolism of L. acidophilus La5 in UHT milk. In order to achieve this, the milk fermented with L. acidophilus La5 (as the culture ferment) was used for incubating the milk sample; incubation at 35, 38, 41 and 44°C were used in order to find the optimum temperature for the growth of microorganisms. The acidity and the pH of the milk samples were measured during 0, 2, 4 and 8 h and lactobacillus counts were performed at 0.4 and 8 h after the incubation period. In order to measure the effect of inulin, 0.5% (w/v) was added to the milk samples, and the resulted samples together with the control sample, were kept at 41°C. Then the acidity, pH and the total number of L. acidophilus of milk samples were determined during the above mentioned periods. Every of above operations were replicate ten times; then, utilizing statistical tests, the average of acidity, pH and enumeration of L. acidophilus were compared with one another during the above mentioned periods. The findings of the study indicat that, lactobacillus count and the amount of acidity in the incubated milk samples at 41 and 44°C were significantly greater than the other temperatures (P<0.05). The growth rate of the bacterium in samples containing 2% of starter culture during the fourth h of incubation was significantly greater than the other samples (P<0.05). However, this difference in 8 h after the incubation was not significant (P>0.05). Concerning the use of prebiotic inulin, the number of L. acidophilus and the acidity of milk samples containing inulin was significantly greater than the number of the bacterium in control sample (P<0.05). It is concluded from this study that, the best alternative temperature for this purpose is an incubation temperature ranging from 41 to 44°C. Addition of inulin enhance significantly the growth of L. acidophilus La5.