Structural and functional properties of probiotic strains as affected by multi-stress adaptation process and subsequent freezing

Consumers have become more aware of the importance of consuming foods and products that boost health. This is one of the reasons why the probiotic industry has been booming for the past several decades. Clinical studies have shown that when consumed in sufficient numbers, probiotics are capable of exerting certain beneficial characteristics on the host. However, their shortfall is their sensitivity to environmental stress factors, which alter their physiological state and thereby hinder their viability and functionality. The reality is, probiotics must endure various technological and gastrointestinal (GIT) stress factors before they arrive at their active site in the intestines. This therefore means that robust strains capable of withstanding threats to viability and functionality during production and after ingestion are a must. Moreover, understanding which food matrices facilitate viability during storage and in the conditions of the GIT can help in developing probiotic products that deliver on their claims. Much research has been conducted focused on producing stress tolerant probiotic strains. For example, by exposing cells to a sub-lethal dose of stress, this produces a stress response that later allows them to survive a more lethal dose of the same stress, a process known as stress adaptation. Adaptation to one stress is known to provide protection against other stresses, this is called cross protection. Research has also shown that adapting cells to multiple stress factors is better than adaptation to just one. Strains that undergo this type of manipulation must be assessed once more for retention of their probiotic properties. Taking that into consideration, the current study aimed to determine whether long term storage of multi-stress adapted (acid, bile and temperature) strains altered their functional and structural properties when compared to non-adapted and freshly adapted cells. In the first experimental chapter, five probiotic strains (Bifidobacterium bifidum LMG 11041, Bifidobacterium. longum LMG 13197, Bifidobacterium longum Bb46, Lactobacillus acidophilus LA14 150B and Lactobacillus plantarum) were sequentially adapted to acid, bile and temperature. The results show that after exposure to each stress factor, the strains not only survived better, but were capable of proliferating. Investigation into acid and bile tolerance showed insignificant differences in the strains’ ability to withstand acidic conditions p>0.05 However, bile resistance was better for the non-adapted cells compared to their adapted counterparts. Results from bile salt hydrolase (BSH) assay showed that only freshly-adapted cells and non-adapted L. acidophilus could hydrolyse bile salts. However, this did not enable these cells to survive bile exposure better than the cells that tested negative for BSH. The bile resistance was therefore attributed to other stress response genes. The freshly-adapted cells could, however, be beneficial for reducing serum blood cholesterol, which has been linked to BSH activity. The tests for antimicrobial activity showed that inhibition by old-adapted L. plantarum was significantly lower than non- and freshly adapted counterparts (p

Dissertation (MSc (Microbiology))--University of Pretoria, 2019.

Microbiology and Plant Pathology

MSc (Microbiology)

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