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Document Type

Thesis - University Access Only

Award Date

2000

Degree Name

Master of Science (MS)

Department / School

Agricultural and Biosystems Engineering

Abstract

Functional and rheological properties of different cheeses were characterized using three different methods namely dynamic test, melt profile analysis, and stress relaxation test. Cheddar cheeses with four different fat content (15.3, 22.8, 37.3 and 45.6% fat dry matter – FDM), two different moisture content (58.1 and 62.4% moisture in non fat portion – MNFP) at 2, 4, 12 and 24 weeks old and Pizza and Mozzarella cheese (41.0% and 43.0% FDM) at 1 week old were used in this study. In dynamic testing, time sweep mode at a constant frequency of 1 Hz and strain 0.5% was used to characterize elastic (G”) and viscous (G”) properties of the cheese during heating from 25 to 60oC and cooling from 60 to 25oC. G’ decreased from 9.0 to 0.07 MPa during heating and increased from 0.07 to 9.0 MPa during cooling of Cheddar cheese. G” showed similar trend as G’. The reduction in fat content of Cheddar cheese increased G’ from 5.5 to 9.0 MPa and increased G” from 2.5 to 6.0 MPa at 25oC. A similar trend was observed at other temperatures. Proteolysis during ripening of cheese lead to decrease in G’ and G” value for different fat level Cheddar cheese at 60oC but differences were not statistically significant at 25oC. However, G’ increased for high moisture cheddar cheese (62.4% MNFP) from 1.6 to 4.4 MPa at 25oC and differences were not statistically significant at 60oC. Mozzarella cheese showed distinct G’ and G” characteristics during heating and cooling. Melt profile analysis of cheese was conducted by applying a constant weight of ~50g to cheese sample of 7mm in height and 28.5mm in diameter heated in an oven maintained at 70oC. Cheese temperature and all in height were recorded as a function of time. The decrease in height showed two-distinct transition region. The temperatures at which the first and second transitions occur were termed as softening and melting point of cheese. Softening point (Ts) of cheeses increased from 53.1 to 56.8oC with reduction in fat content of cheddar cheese (45.3 to 15.3% FDM) and decreased from 56.8 to 49.2oC with aging (2 week to 24 week) for four different fat content cheddar cheeses. Also, Ts decreased from 51oC to 46.2oC with an increase in moisture content (58.1 to 62.4% MNFP) of cheddar cheese at 2-week and increased from 46.2 to 50.9oC with aging (2 week to 24 week) for high moisture cheese. Melting point (Tm) showed mixed trend due to aging for cheddar cheese. Stress relaxation experiments were conducted by heating cheese sample of 22mm diameter and 17.5mm height at 40, 50, 60oC in an aluminum cup with an inner diameter of 22mm and depth of 17.5mm. The plunger of 18mm diameter, which was attached to Sintech machine, was allowed to compress the cheese instantaneously to 10% deformation. The relaxation of stress was recorded as a function of time. Generalized Maxwell and empirical Peleg models were used to characterized the stress relaxation behavior of melted cheese. The effect of fat content, moisture content, and age of cheese on stress relaxation behavior was studied. The Peleg model best described the stress relaxation behavior of melted cheese (cheeses above 50oC) and eight element Maxwell model predicted better than three element Maxwell and six element Maxwell models. The stress relaxation experiment differentiated the viscoelastic nature of different cheeses due to reduction of fat content, increase in moisture, increase melting temperature and age of cheese. Comparing the three methods that were used to evaluate the functionality of the cheeses, dynamic rheological test differentiated the cheese quantitatively better compared to other methods. Dynamic rheology and stress relaxation tests are better tools to systematically study cheese functionality whereas the melt profile test can be used for applied research.

Library of Congress Subject Headings

Cheese

Cheese -- Testing

Format

application/pdf

Number of Pages

143

Publisher

South Dakota State University

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