Date of Award
1-1-2023
Document Type
Dissertation
Degree Name
Ph.D. in Biological Science
First Advisor
Erik Hom
Second Advisor
Colin Jackson
Third Advisor
Clifford Ochs
School
University of Mississippi
Relational Format
dissertation/thesis
Abstract
Kefir is a fermented beverage that has become increasingly popular because of its proposed probiotic functions. It can be classified into two types: milk kefir and water kefir depending on the medium and inoculated starter culture. This dissertation summarizes work exploring the similarities and differences between milk and water kefir with respect to sensory properties and microbial composition. For the kefir sensory test, six milk and six water kefirs were evaluated on the sensory attributes (color, aroma, taste, and mouthfeel). Milk kefirs were assessed as sour and cheesy, followed by a creamy and thick mouthfeel. In contrast, water kefirs were described as sweet with an appealing color and smooth mouthfeel. Regarding the microbial characteristics, whole community shotgun metagenomic sequencing (SMS) was used to characterize the microbial diversity of 32 milk kefir grains (MKGs) and 34 water kefir grains (WKGs) that were obtained from various geographical locations around the world. Lactobacillus kefiranofaciens was identified as the predominant species in all MKGs (except NPM), consistent with prior literature demonstrating the importance of this species in milk kefir. It is surprising to find that Zymomonas mobilis was the predominant species in most of the WKGs (30 out of 34) considering this species was rarely reported from the literature. Principal Component Analysis (PCA) of microbial composition based on SMS data showed a tight clustering of 28 out of 32 MKGs, and 33 out of 34 WKGs. To understand the effect of medium on the growth characteristics of kefir grains, a reciprocal transplantation experiment was conducted on 14 WKGs, among which two WKGs (JES and MES) were selected for metagenomic analysis. The growth of all 14 WKGs (except JES) were significantly inhibited by milk, however, an increased multiplication ability was observed when recultivated with sugar water. The microbial composition of both the JES and USS changed as the culture medium changed. The milk favored the growth of certain microorganisms belonging to the phylum Firmicutes and Actinobacteria, and genus Bifidobacterium and Acetobacter. In contrast, the sugar water particularly favored the growth of Zymomonas species (e.g. Zymomonas mobilis).
Recommended Citation
Li, Xia, "Milk and water kefir: microbial diversity and sensory properties" (2023). Electronic Theses and Dissertations. 2694.
https://egrove.olemiss.edu/etd/2694