Lyophilization effect on the fermentative and microbiological properties of kefir grains

MORETTI, ANA ; CORREA, MARIANA; GAMBA, RAÚL; LEÓN, ÁNGELA

Mar del Plata

Congreso; X Congreso Argentino de Microbiología General SAMIGE; 2014

SAMIGE

The effect of the kefir grains lyophilization on the physicochemical, microbiological and sensorial properties of the milk kefir was studied by our group. We lyophilized CIDCA AGK1 kefir grains (using UHT milk as cryoprotector) and stored them during 6 months at 4ºC. The different tests were made comparing fresh and lyophilized grains at months 0, 1, 3 and 6. The milk fermentation kinetics was assessed by inoculating fresh milk with kefir grains 10% v/v, followed of incubation at 30 °C. The pH drop was measured every hour. The microbiological composition was assessed during storage, by accounts of lactic acid bacteria and yeasts. Serial dilutions were made from the fermented products, and 100 ul from these dilutions were inoculated on MRS® and YGC® medium for the account of lactic acid bacteria and yeasts respectively. The physicochemical properties as protein composition, lipid content and acidity were assessed too. Cell free supernatants (CFS) were obtained from the fermented products by centrifugation and filtration. The CFS were used to study the antimicrobial activity against E.coli and Salmonella sp. We made a sensorial study in order to determine if there were differences between the fermented milk with lyophilized and fresh kefir grains. We found that LAB and yeasts survived the lyophilization process as well as the storing time, keeping their viability. The final account of LAB and yeasts from lyophilized grains after six months of storage was the same that the obtained with fresh grains; these microorganisms fermented lactose from the milk and produced lactic and acetic acid. CFS obtained from lyophilized and fresh grains didn?t show significant differences on the inhibitory activity against E. coli and Salmonella sp. Finally, there was no sensorial difference between the kefir obtained with lyophilized and fresh grains. Additionally, the fermented milk obtained with fresh and lyophilized grains got a high score, near 9, in the sensorial acceptability test. We concluded that the lyophilization process followed of a 6 months of storage doesn´t affect the fermentative, microbiological, bromatological, antimicrobial and sensorial properties of the kefir grain CIDCA AGK1. It gives us a perspective for a more thorough study of different drying strategies for the kefir grains.