Date of Award:

1991

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Nutrition, Dietetics, and Food Sciences

Department name when degree awarded

Nutrition and Food Science

Advisor/Chair:

Donald J. McMahon

Abstract

Ice cream mix (12% fat, 11% milk solids nonfat, 12.5% sugar, and 4.5% corn syrup solids) was fermented with Lactobacillus acidophilus and Bifidobacterium bifidum. Half of the mix was heat treated at 82°C for 30 minutes and cooled to 40-41°C. The other half was warmed to 40-41°C and inoculated with the starter cultures. Both were made into ice cream and stored at -29°C. Survival of L. acidophilus and B. bifidum and of β-galactosidase activity were monitored during 17 weeks of frozen storage. Reinforced clostridial medium was used to enumerate culture bacteria. Colony counts, after fermentation, for both L. acidophilus and B. bifidum were about 5 x 108. The population of cultures decreased less than one log cycle after initial freezing. After 17 weeks storage the bacterial counts were 1 x 107 for B. bifidum and were 4 x 106 for L. acidophilus. During the same period, β-galactosidase activity decreased only 31%. Therefore, frozen fermented dairy products provide a good vehicle to supply β-galactosidase enzymes to people who are lactose maldigestors.

Frozen fermented ice cream was prepared at four different pH's (5.0, 5.5, 6.0, 6.5) by blending fermented mix with unfermented mix and then was frozen to produce samples for sensory evaluation. All samples were strawberry flavored. These were then evaluated by 88 judges. The preferred pH, based on overall acceptance, was 5.5. A second sensory evaluation was conducted to compare heat-treated with non-heat-treated ice cream. There were no significant differences in appearance, texture, flavor, and overall acceptance between the two samples.

Our study shows that ice cream is a suitable vehicle for delivering these beneficial microorganisms and enzymes to consumers.

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