Date of Award:

8-2021

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Nutrition, Dietetics, and Food Sciences

Committee Chair(s)

Marie Walsh

Committee

Marie Walsh

Committee

Donald McMahon

Committee

Brian Nummer

Committee

Silvana Martini

Committee

Sean Johnson

Abstract

Lipases are currently used in food technology for the modification of fats and oils. Lipase can synthesize, hydrolyze, and rearrange fatty acids, thus, resulting in their extensive use in industrial applications. The thermal stability of lipase is an essential characteristic for this application. Thermophilic bacteria are an important source for producing thermostable lipases because of their tolerance to high heat. Lipolytic enzymes can be purified using several purification methods, but these purification processes are often expensive and complex.Results from this study showed that lipases can be extract from thermophilic bacteria (Geobacillius stearothermophilus (GS) and Anoxybacillus flavithermus (AF)). Molecular weight of the lipase from (LGS) was approximately 42 kDa, and approximately 33 kDa for the lipase from AF (LAF). Ethanol precipitation and heat treatment are simple methods for enzyme purification and can result in high enzyme yields with moderate purification folds compared to more complex methods.

This study has shown the characterization of both LGS and LAF. The optimal Ph for LGS activity was at Ph 7.5 and the optimum enzyme activity of LAF was at Ph 8.0. Both enzymes were stable at a Ph range of 6 to 8 over 12 h at 4 °C, and the thermostability of both enzymes was between 20 to 80 °C. LGS had the highest Vmax value with p-nitrophenyl acetate while its lowest Km value was with p-nitrophenyl dodecanoic. LAF had the highest Vmax with p-nitrophenyl myristate, and its lowest Km with p-nitrophenyloctanoate. LGS preferentially hydrolyzed p-nitrophenyl acetate and p-nitrophenyl octanoate while the LAF preferentially hydrolyzed p-nitrophenyl myristate and p-nitrophenyl dodecanoate.

Results showed both lipase enzymes were successfully immobilized using silica beads. Both immobilized lipases were used to interesterify SBO with PA and change the chemical composition and melting point of the oil. PA concentration significantly decreased after 24 h at all reaction ratios, and the TAG concentration was significantly different after interesterification. FFA concentration changed after SBO interesterification, and the melting points of the samples increased from 4 °C to 40 °C. The results suggest that both immobilized lipases have suitable properties for oil interesterification and industrial applications.

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Available for download on Saturday, August 01, 2026

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