Date of Award:

12-2009

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Nutrition, Dietetics, and Food Sciences

Advisor/Chair:

Dr. Donald J. McMahon

Abstract

This study determined the impact of starches on the properties of low fat rennet curd as measured by microstructural and instrumental analysis. In experiment 1, 17 starches were initially screened for swelling power, impact of curd yield at 5 g/L and 10 g/L in milk, and settling in rennet-induced partially acidified low fat curd. Starches examined were narrowed down to five in experiment 2; they included: modified waxy corn starch, waxy rice starch, instant tapioca starch, dextrin, and a modified tapioca starch. These starches were added to skim milk to make rennet-induced partially acidified milk gels. Gels were made by adding starch to skim milk, heating to gelatinize starch, followed by addition of rennet and glucono-delta-lactone (GDL) to induce gelation. Once gels were set they were cut and centrifuged to sediment the curd. The amount of starch lost in whey was quantified to estimate starch retention in the curd. Confocal laser scanning microscopy was used to determine starch impact on curd microstructure. Curds yields were 13.1%, 18.4%, 20.7%, 21.5%, 23.5%, and 13.2% for control gel, and gels containing waxy corn, waxy rice, instant tapioca, modified tapioca and dextrin starches, respectively. Estimated starch retentions in the curds were 71%, 90%, 90%, 21%, and 1% for these curds. Waxy corn, waxy rice, and instant tapioca starches have the potential to improve the texture of low fat cheese because they are retained well in the protein network during coagulation and concentration of the milk proteins, and they generate interruptions in curd network that may help limit extensive protein-protein interactions. Modified tapioca starch causes the protein structure of the curd to be very loose, but it was not retained optimally in the curd. Also, because there were few distinct starch particles in the modified tapioca curd network, it is likely that when it is subjected to all the cheesemaking steps the same loose protein structure would not be observed. Dextrin was not retained well in the curd, nor did it disrupt the protein network, making it unsuitable for use in low fat cheese. In experiment 3, low fat cheddar cheeses were made with waxy corn starch, waxy rice starch, modified tapioca starch, and instant tapioca starch. Modified tapioca starch did not increase the moisture content of the cheese. Waxy corn starch, waxy rice starch, and instant tapioca starch all increased the moisture content of the cheeses significantly. However, when moisture contents of cheeses were over 61%, the body of the cheese visibly softened during storage, making the cheese very pasty. When starch-containing cheeses had moisture levels lower than that, the curd did not knit together well.

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Food Science Commons

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