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Preliminary experiments indicated that an acid casein co-precipitate could be produced by extrusion from skim milk powder (SMP). In assessing the problems encountered, experiments were designed to model and optimize the coagulation/washing process using response surface methodology (RSM), to minimize residual whey components and losses of fines. This study yielded useful information relative to improving our understanding of the coagulation mechanism and the most important variables affecting the process. In addition, RSM allowed multiresponse optimization of acid casein production using unique and newly developed optimization techniques. In order to simplify the process, an extruder die was designed to assist with the dewheying process, however, plugging problems occurred due to screw design limitations. Studies were implemented to determine the rheological behaviour of sodium caseinate and to evaluate the extruder performance in terms of energy consumption, and in terms of mixing and conveying through mathematical description of residence time distributions in the extruder. The knowledge gained from these studies was integrated to produce acid casein and sodium caseinate at pilot plant level and to conceive a plant layout of the process for the dairy industry. The process developed has many advantages, including the ability to produce a high quality product.

Preservation of food by freezing is a common method of processing. Of relatively recent origin is the freeze-drying method. This method has several advantages over other methods of preservation, but is not free of problems, one of which is the maintenance of appearance and texture. In the present study, the effects of freezing, thawing, freeze-drying, and reconstitution on the physico-chemical properties of Northwest variety strawberries with particular reference to textural characteristics were investigated. Very little prior work is reported with regards to the effect of these factors on fruits. Strawberries were frozen at two different rates of freezing - slow frozen at 0°F and quick frozen in a blast freezer at -20°F. Frozen berries were examined by physical and chemical methods to evaluate the changes. In a separate study, berries were thawed under standard conditions of relative humidity and temperature and the drip collected for analysis. Thawed berries were examined by both physical and chemical methods. To study the reconstitution behaviour of the berries, they were freeze-dried and reconstituted under standard conditions of berry to water ratio, temperature of water and time of reconstitution. Reconstituted berries and the remaining solutions were then examined. Measurements of the texture, color, total solids, alcohol insoluble solids, pectins, cellulose, ash, and constituents of ash were made on raw, frozen, thawed, and reconstituted berries. The results indicated the following conclusions: 1. An increase in percent soluble solids, pH, and titratable acids and a decrease in total solids and AIS of the berries were observed upon freezing. Slow frozen berries showed more pronounced effects. Smaller berries were observed to change the least. No significant differences were found in the other constituents. 2. Strawberries lose weight upon thawing depending on the chemical composition of the berries. An inverse relationship was observed between weight loss and total solids, AIS, pectic substances, cellulose, ash and mineral content of the berries. With gradual increase in the weight loss upon thawing, there was a progressive softening of the berries. A direct relationship was found between weight loss and the amount of pectic substances, sugars, titratable acids, ash, and minerals found in the drip. Slow freezing resulted in higher weight loss and smaller berries lost the least. 3. A linear relationship exists between weight loss of the berries upon thawing and the area of the drip. This method offers a convenient and quick procedure for evaluation of the quality of frozen strawberries, with the added advantage of collecting the drip and storing it for further analysis at a convenient time. 4. Ability to reconstitute was found to be related to rate of freezing and size of berry. Quick freezing and smaller berries gave the best results. 5. Direct relationship was found between the degree of reconstitution and total solids, AIS, pectic substances, cellulose, ash, and minerals. The amount of pectic substances, sugar, titratable acids, ash, and minerals leaching out of the berries into the reconstituting solution were smaller and were independent of the degree of reconstitution. 6. Individual berries showed a large variation in their chemical constituents, which was responsible for the differences in the thawing and reconstitution behavior of Northwest strawberries. / Graduation date: 1967

Graduation date: 1941

Graduation date: 1956