Date of Award:

5-1970

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Nutrition, Dietetics, and Food Sciences

Department name when degree awarded

Food Science and Technology

Committee Chair(s)

L. Elmer Olson

Committee

L. Elmer Olson

Committee

Gene W. Miller

Committee

Harris Van Orden

Committee

J. Clair Theurer

Abstract

PART I

The precursors for the biosynthesis of raffinose in sugarbeets were studied.

An enzyme preparation was obtained from the sugarbeet (Beta vulgaris) root. Incubation of this enzyme with (X-galactose-1-phosphate, Uridine triphosphate (UTP), Adenosine triphosphate (ATP), Magnesium chloride (MgCl2), and L- cysteine at pH 5, 10°c for 6 hours formed a compound which was identified as raffinose by a hydrolysis method and thin- layer chromatography. The same result was obtained when Uridinediphosphate (UDP)-galactose was incubated with sucrose, ATP , MgCl2, and L- cysteine in the presence of the beet enzyme preparation. These reactions suggested that the sugarbeet contained an enzyme system capable of transferring a galactose unit from X-galactose-1-phosphate or UDP-galactose to sucrose, forming raffinose. The galactosylation of sucrose via UDP- galactose was further confirmed using sucrose-UL-C14 as one of the substrates. Radioactive raffinose was identified on a radio-autograph.

The involvement of UDP-galactose in the raffinose synthesis is believed to be of more significance in vivo. A preliminary study indicated there are at least five main categories of nucleotide compounds in beet root tissues. It is suggested that a sugar nucleotide pool is present in the sugarbeet for transglycosylation among various sugars. A reaction similar to the above using UDP-glucose-UL-c14 and Nicotinamide adenine dinucleotide instead of UDP-galactose resulted in the formation of labeled raffinose. This suggested that an UDP-glucose-4-epimerase activity in beet tissues may be responsible for the conversion of UDP-glucose to UDP-galactose for the raffinose synthesis.

The possible participation of galactinol in the raffinose synthesis in sugarbeets was investigated. An experiment using galactinol, sucrose-UL-C14 and ATP as reactants with the sugarbeet enzyme did not give positive results.

The presence of X-galactosidase activity in the beet enzyme preparation was noted. Incubation of the enzyme at 37°C with raffinose and stachyose respectively liberated galactose as a common product. It is suggested that X-galactosidase is the enzyme responsible for the breakdown of raffinose in the sugarbeet. The turn-over of galactose liberated from raffinose by this hydrolytic enzyme is discussed.

The separation of X-galactosidase from raffinose synthetase was attempted. Some difficulties involved are discussed.

A study of the effects of pH and temperature on the enzyme activities showed that pH 5 and low temperatures (0-15°C) are favorable for the raffinose synthesis, while high temperatures (above 15°C) favored X-galactosidase activity. Raffinose was formed when UDP-galactose and sucrose were incubated with the enzyme preparation at 0°C for 24 hours. This would account for the accumulation of raffinose during cold storage since at low temperatures X-galactosidase activity is retarded while raffinose synthetase seems to be unaffected.

PART II

Incubation of 30 milligrams commercial sweet almond emulsin (800 units/mg) with 2.5 BX molasses which contained 1. 5 mg raffinose in 3 milliliters 0.1 M acetate buffer at pH 6, 35°C for one day resulted in a complete hydrolysis of raffinose in the digest. No sucrose inversion occurred under the above conditions.

Checksum

9cb82088efcf62576b127f4ae9300608

Download

Included in

Food Science Commons

Share

COinS

Copyright for this work is retained by the student. If you have any questions regarding the inclusion of this work in the Digital Commons, please email us at .