Date of Award

2014

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

First Advisor

Ibrahim, Salam A.

Abstract

This study investigated the impact of ten selected gums (carrageenan, carrageenan-maltodextrin, guar, locust bean, pectin, pectin- dextrose, pectin-carrageenan, guar-locust bean-carrageenan, inulin, and xanthan) on the growth of eight Lactobacillus strains in laboratory media. The bacterial population for eight Lactobacillus strains was determined in modified basal media at different concentration (0%, 0.25% and 0.5% w/v) of gums stored up to 12 hours at 37 °C. Findings show significant differences (p < 0.05) between the treated and control sample. Guar was found to be the best gum to enhance growth of L. rhamnosus GG B101, L. rhamnosus GG B101, L. delbrueckii subsp. bulgaricus SD35, L. delbrueckii subsp. bulgaricus SD33, L. acidophilus SD 16, L. acidophilus EF7, L. reuteri DSM20016, L. reuteri CF2-2F during 12 hours of storage at 37 C in laboratory media. The population of L. rhamnosus GGB101 in the samples containing gums were significantly (p < 0.05) higher than the control without gums. Samples containing 0.5% gums showed slightly higher bacterial population than those with 0.25% of gum. A minimum of 12 hour of incubation period was shown to be adequate to reach a bacterial population of 6 log CFU/mL in the presence of gums. Addition of guar (0.5%) led to the highest (1.31 log CFU/mL) increase in population of the treated L. rhamnosus GGB101 over the control. There was no marked (p < 0.05) change in pH and titratable acidity. Four different gums (carrageenan, carrageenan-maltodextrin, pectin-carrageenan, guar-locust bean-carrageenan) were selected to determine the effect on the growth, viability and betagalactosidase activity of four selected Lactobacillus strains (L. rhamnosus GG B101, L. rhamnosus GG B101, L. reuteri DSM20016, L. reuteri CF2-2F). Effect of the four selected gums on thegrowth L. rhamnosus GG B101, L. rhamnosus GG B101, L. reuteri DSM20016 in milk were compared to those in modified basal media. Results showed that xanthan induced highest growth of L. rhamnosus GG B103, L. rhamnosus GG B101 in milk whereas carrageenanmaltodextrin led to highest growth of L. reuteri DSM 20016 in the media. Marked differences (p < 0.05) in viability were observed between milk samples containing gums and the control. The presence of carrageenan-maltodextrin led to the highest viable counts (8.76 ± 0.03 log CFU/mL) of L. rhamnosus GGB103 during storage. The average population of L. rhamnosus GGB101 and Lactobacillus rhamnosus GGB103 was 8 log CFU/mL, whereas that of Lactobacillus reuteri DSM20016 and Lactobacillus reuteri SD2112 decreased slightly ( 0.15-0.64 log CFU/mL) to 7 log CFU/mL during the storage period. Viable counts were retained at 7-8 log CFU with no significant difference in the control versus treated strains except in the presence of carrageenanmaltodex. Guar-locust bean-carrageenan led to significant (p < 0.05) highest levels of β-gal activity of L. rhamnosus GGB103 (1287 ± 4.24 Miller units/ mL) compared to the control (78 ± 2.83 Miller units/ mL). L. rhamnosus GG B101and L. rhamnosus GG B103 were the best strains to attain enhanced levels of β-galactosidase activity. This shows that the inclusion of carrageenan-maltodextrin and guar-locust bean-carrageenan in milk could improve growth, viability and achieve an enhanced level of β-galactosidase activity in L. rhamnosus GG B101 and L. rhamnosus GG B103. The information gleaned from this study could be used in the food industry to improve the quality of probiotic functional foods and thereby contribute to the alleviation of lactose malabsorption.

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