Graduation date: 1961

Thesis (Ph. D.)--University of Wisconsin--Madison, 1951. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 126-137).

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Graduation date: 1961

Graduation date: 1963

Thesis (Ph. D.)--University of Wisconsin--Madison, 1949. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves [71]-75).

Inaug.-Diss.--Giessen. / Lebenslauf. "Beiträge zur chemischen physiologie und pathologie ... Sonder-abdruck aus Band VII, Heft 1/3." "Literaturverzeichnis": p. 35.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1970. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliography.

A method was developed for the extraction of rennet from fresh frozen vells. Frozen vells were partially thawed and minced in a Hobart "Wonder worker." The tissue was treated with 2.0 per cent potassium alum and allowed to stand for 20 hours before sufficient 0.45 M disodium phosphate was added to bring the pH of the mixture to 5.7. Dry sodium chloride was added until the salt concentration in the moisture of the mixture was 10 per cent. The tissue was then mixed with 3/4-inch pumice gravel in a volume ratio of 1 to 2 and packed into extractor columns. The tissue was extracted continuously with a 10 per cent sodium chloride solution. The yield of enzyme and extract viscosity from 60 undried vells was compared with that from 60 dried vells. The undried vells yielded 2. 99 x 106 R.U. in 86 liters of extract and the dried vells yielded 3.03 x 106 R.U. in 74 liters of extract. The viscosities of the initial extracts were 5.8 and 6.2 centipoise respectively. Drying temperature, moisture content and pH had no effect on extract viscosity . Viscosities of extracts were viii reduced by aging the dried vells prior to extraction, adjusting sodium chloride to 10 per cent in extracting solutions, and adding 2 to 3 per cent potassium alum to undried vell tissue and holding for 20 hours before neutralizing to pH 5.7 %plusmn; 0.2 with disodium phosphate. The mean activity value of extracts representing 96,000 vells was 45.5 R.U. with a standard deviation of ± 19.57 for individual vells. This variation in enzyme content precluded useful comparisons of yield based on small numbers of individual whole vells.

The purpose of this research was to determine the effects of heating (including heating to ultra-high temperatures) homogenized ultrafiltered whole and skim milks on whey protein denaturation and milk's subsequent rennet coagulation properties: coagulation time, curd firmness, and microstructure. Whole and skim milk samples were ultrafiltered using a spiral wound ultrafiltration membrane system. Samples were preheated to 72°C for 58 s, held for 8 s then heated to 72, 89, 106, 123, or 140°C for more than 97 sand held for 4 s. The milk was then cooled to 60°C and homogenized, further cooled to 30°C, packaged into 120 ml sterile containers, and refrigerated overnight. Rennet coagulation time and curd firmness were monitored using a Formagraph . Milk and gel samples were fixed in 2.5% glutaraldehyde solution and examined by electron microscopy. Whey protein denaturation was determined by precipitating casein at pH 4.6 with .lN HCl and measuring protein content in the filtrate by the Kjeldahl procedure. Rennet coagulation time of milk increased as processing temperature was increased. Gel strength decreased with an increase in processing temperature. Ultrafiltration shortened rennet coagulation time and increased gel firmness. Ultra-high- temperature- heated whole and skim milks did not coagulate upon addition of rennet, but their concentrated counterparts did. Rennet coagulation of the concentrated milks was delayed by heating. Samples treated with ultra-high-temperature formed only a weak gel. The casein micelles in milk increased in size as a function of increasing processing temperature and concentration by ultrafiltration. Additional protein material adhered to the casein micelles after high-temperature processing and was especially noticeable in the samples treated with ultra-high-temperature. Whey protein denaturation increased as a function of increased heating temperature. The heated concentrated milks had higher levels of protein denaturation than the heated unconcentrated ones.