Changes on Acidic parameters and probiotic survival in the kefir using Lactobacillus acidophilus and Lactobacillus paracasei complementary probiotics during cold preservation

BACKGROUND: Kefir is a fermented milk product containing some beneficial anticarcinogenic organic compounds with nutritional benefits made it one of the natural dairy beverage extensively consumes. OBJECTIVES: The present study was conducted to assess the effect of two selective probiotics on the values of acidic criteria and probiotic survival in the kefir produced in this study.METHODS: In the first step, the cow milk, which preheated at 90 oC for 5 min, was inoculated with the commercial starter and divided in two groups. They complemented with L. acidophilus LA-5 and L. paracasei 431 and incubated at 30 oC for 6 h. They were then preserved at refrigerated temperature up to 14 d and sampling was carried out to evaluate the changes of values of organic acids (lactic acid and acetic acid), pH, titratable acidity and survival of probiotic complemented bacteria on 1th, 7th, and 14 d. RESULTS: The pH values of L. acidophilus LA-5 and L. paracasei 431were 4.34 and 4.36 at the beginning of cold storage and reached 4.27 and 4.31 in the day of 14. The acidity of L. acidophilus LA-5 complemented kefir on the 1st day was 0.80 g/100 g greater than L. paracasei 431one showed 0.72 g/100 g. Lactic acid was ranging from 1.57 to 2.40 g/100 mL (from 1st to 14th day) or 2.17 to 2.42 g/100 mL, while kefirs respectively complemented to L. acidophilus and L. paracasei 431. In the kefirs complemented with L. acidophilus and L. paracasei 431, respectively acetic acid was stable during 14 d (from 0.11 to 0.13 g/100 mL) but increased in the later kefir (from 0.11 to 0.23 g/100 mL). The survival of both bacteria was greater than 7 log CFU/g in the kefir.CONCLUSIONS: Adding the L. acidophilus LA-5 and L. paracacei 431 can moderate the acidity of the kefir and extend the survival of complementary probiotics at a standard level during two weeks of cold preservation.