Masters Theses

Date of Award


Degree Type


Degree Name

Master of Science


Food Science and Technology

Major Professor

P. Michael Davidson

Committee Members

H. O. Jaynes, B. J. DeMott, J. B. MacLaren, R. A. McLean


Buttermilk was made by three methods: conventional fermentation, direct acidification, and a combination of both. The conventional method involved adding a culture to skim milk followed by incubation at 23±1°C until a pH of 4.5 was reached; the direct acidification method involved the addition of lactic acid to skim milk to reduce the pH to 4.5; in the combination method the pH of the skim milk was reduced to 5.2 with lactic acid followed by inoculation with a bacterial culture as in the traditional fermentation. Two frozen concentrated starter cultures were used. The first contained Streptococcus lactis and/or S. cremoris and the second contained S. lactis and/or S. cremoris plus a strain of Leuconostoc. After fermentation, 0.1% (w/v) potassium sorbate was added to half of each of the cultured samples. The samples were then stored at 4°C and analyzed for various microbiological, chemical, and physical attributes at 0, 2, 4, 6, and 8 days. A 62 member consumer taste panel ranked the samples by preference. The psychrotrophic count and viscosity were not affected by the processing methods, the presence of potassium sorbate, or the culture used (P>0.G5). No coliforms were found in any buttermilk samples. The number of lactic acid bacteria was affected only by culture type (P<0.01), and not by processing method or the presence of potassium sorbate (P>0.05). The use of the titratable acidity test appeared to be a more reliable means of measuring acid development than pH because of less variation in the former. The processing method (P<0.01), culture type (P<0.01) and presence of potassium sorbate (P<0.10) had significant effects on the amounts of diacetyl and acetoin found. The concentration of acetoin increased significantly over time, while the concentration of diacetyl remained fairly constant. Those sensory panel members who normally consume buttermilk were able to detect the presence of potassium sorbate and tended to prefer the samples without the added sorbate, but the buttermilk non-consumers were not able to detect a difference in the samples. The consumer panel was not able to distinguish between the methods of production. The direct acidification-fermentation technique appeared to be a viable alternative to the conventional processing method for buttermilk. This method could result in a reduced processing time and a more consistent product through closer supervision.

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