Document Type

Dissertation - Open Access

Award Date

2016

Degree Name

Doctor of Philosophy (PhD)

Department

Dairy Science

First Advisor

Sanjeev K. Anand

Keywords

biofilms, enzymes, exopolymers, membranes

Abstract

In the concentration of cheese whey by membrane filtration processes, fouling is a major limiting factor that leads to flux decline and affects product quality. The growth of biofilms on membranes contributes to biofouling. Biofilms are very difficult to eliminate, and will serve as the seed for additional biofilm development and product contamination. The biofilm matrix is composed mainly of microbial exopolymeric substances (EPS), and therefore EPS is thought to help bacteria to adhere and form biofilms by acting as a cementing agent. The first research project under this study was conducted with the aim of elucidating the role of the EPS produced by lactic acid starter cultures on reverse osmosis (RO) membranes. A second study was designed to investigate the role of EPS produced by spore forming bacteria on RO membrane biofilms. A third study was conducted to evaluate the application of Catalase (Cat) on spores and biofilms formed by spore forming bacteria that produce EPS. Finally, the fourth study evaluated the application of natural depolymerases from bacteriophages and bacteria to disrupt biofilms. In the first research project we observed that the EPS of Streptococcus thermophilus strain 3534 enhanced biofilm formation but the EPS of Lactococcus lactis ssp. cremoris strain JFR inhibited the attachment and biofilm formation to RO membranes. This was associated to the cell-surface hydrophobicity of the strains, which was affected by the EPS production. In the second study a greater biofilm formation was observed for a Bacillus strain that produced poly glutamic acid, and it was established that hydrophobicity of the EPS, regardless of whether it is composed of polysaccharides or poly-amino acids, played an important role in biofilm formation on RO membranes. Food grade Cat preparations significantly reduced the number of spores in milk and the viable counts of EPS producing Bacillus cells on RO biofilms, showing a great potential in antimicrobial cleaning formulations in the dairy industry. In our final study the application of crude enzymes from different EPS degrading microorganisms although resulted in poor reductions, when they were applied to biofilm formed by single resistant species, revealed the importance of choosing compatible hydrolytic enzymes due to strong specificity for greater effectiveness.

Library of Congress Subject Headings

Dairy processing

Biofilms

Membrane separation

Membranes (Technology)

Microbial exopolysaccharides

Fouling

Description

Includes bibliographical references (page 147-174)

Format

application/pdf

Number of Pages

186

Publisher

South Dakota State University

Rights

Copyright © 2016 Nuria Garcia-Fernandez

Included in

Dairy Science Commons

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