Document Type

Dissertation - Open Access

Award Date


Degree Name

Doctor of Philosophy (PhD)

Department / School

Dairy Science

First Advisor

Lloyd Metzger


Spore formers are observed as the common spoilage-causing microflora in milk and dairy products. Their spore-forming ability increases their survivability during heat treatment which leads to their presence in a final product. Spore-forming bacteria have ability to produce many types of spoilage-causing enzymes which are potential to influence quality and functionality of the final product. Many researchers have studied the ability of spore formers to induce a spoilage in various dairy products but as per our knowledge, their spoilage-causing activities are not described in a detail for cultured dairy products. In our first objective, we have studied the ability of the common dairy spore formers to degrade milk proteins, fat, phospholipids, common stabilizers, and exopolysaccharides at typical sour cream (24ºC) and yogurt (42ºC) fermentation temperatures. The ability of spore-forming strains to the degradation of tested components was starch > xanthan gum > protein = gelatin > phospholipid > pectin > fat at 24°C, and starch > protein = gelatin > xanthan gum > phospholipids > pectin > fat at 42°C. Results indicated that exopolysaccharides produced by commercial yogurt and sour cream cultures were susceptible to the degradation by spore formers. In our second objective, we have studied the influence of proteolytic and lipolytic spore formers on rheology, texture, physicochemical, sensory, and microstructure of sour cream. Spore formers had grown during sour cream fermentation and had influenced its texture by inducing limited level of proteolysis but not shown any lipolytic activity in sour cream. This study indicated that the contamination of proteolytic spore formers during fermentation can bring batch to batch variations in manufacture sour cream. In our third objective, we have evaluated the influence of proteolytic spore formers on cottage cheese yield, physicochemical, textural, and sensory attributes. Proteolytic spore formers was inoculated in milk and cream dressing. Results indicated lower yield, higher grit, influenced texture for cottage cheese inoculated with proteolytic spore formers, and also observed for bitterness in cottage cheese at the end of shelf life. Cottage cheese mixed with contaminated cream dressing had shown bitterness in cottage cheese without affecting its texture.

Library of Congress Subject Headings

Sporeforming bacteria.
Dairy products -- Contamination.
Microbial contamination.



Number of Pages



South Dakota State University

Included in

Dairy Science Commons



Rights Statement

In Copyright