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 caninfluence the performance as well as the growth of probiotics for increasing the health of theconsumers. 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 metabolismof 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; incubationat 35, 38, 41 and 44°C were used in order to find the optimum temperature for the growth ofmicroorganisms. The acidity and the pH of the milk samples were measured during 0, 2, 4and 8 h and lactobacillus counts were performed at 0.4 and 8 h after the incubation period. Inorder to measure the effect of inulin, 0.5% (w/v) was added to the milk samples, and theresulted samples together with the control sample, were kept at 41°C. Then the acidity, pHand the total number of L. acidophilus of milk samples were determined during the abovementioned periods. Every of above operations were replicate ten times; then, utilizingstatistical tests, the average of acidity, pH and enumeration of L. acidophilus were comparedwith 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°Cwere significantly greater than the other temperatures (P<0.05). The growth rate of thebacterium in samples containing 2% of starter culture during the fourth h of incubation wassignificantly greater than the other samples (P<0.05). However, this difference in 8 h after theincubation was not significant (P>0.05). Concerning the use of prebiotic inulin, the numberof L. acidophilus and the acidity of milk samples containing inulin was significantly greaterthan the number of the bacterium in control sample (P<0.05). It is concluded from this studythat, the best alternative temperature for this purpose is an incubation temperature rangingfrom 41 to 44°C. Addition of inulin enhance significantly the growth of L. acidophilus La5.