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Lin Zhai

Document Type

Thesis - University Access Only

Award Date

2001

Degree Name

Master of Science (MS)

Department / School

Agricultural and Biosystems Engineering

Abstract

A new procedure was developed for preparing Cheddar cheese samples during heating and cooling for the scanning electron microscope (SEM). An image processing and analyzing algorithm was developed for evaluating Cheddar cheese microstructure during heating and cooling from the SEM images. A second-order geostatistical method ----semivariogram was used to automatically and objectively extract and quantify the fat globule's average size and density from the cheese SEM images. A modified exponential model was used for fitting the semivariogram curve derived from a Cheddar cheese SEM image. A least-square method was applied to fit semivariograms automatically and optimally. Two parameters of semivariogram, range of influence (abbreviated as range) and sill, were used to objectively and quantitatively evaluate the cheese microstructure features. Range represents the fat globule's average size and sill inversely represents the fat globule's spatial density. Four Cheddar cheeses with varying fat contents (44.1, 41.0, 27.1, 21.9% FDM (fat in dry matter)) and two Cheddar cheeses with different moisture (58.1 and 62.4% MNFP (moisture in non-fat portion)) at 2, 4, 12, and 24 weeks aging were used for studying the effect of fat content, moisture and maturation on the Cheddar cheese microstructure during heating and cooling. A statistical analysis ---- Least Significant Difference (LSD) was employed to analyze the quantified microstructure information. The results indicated that fat content, moisture and heating had significant effects on the Cheddar cheese microstructure, but cooling did not significantly affect the Cheddar cheese microstructure. Before heating, as the fat level decreased, the fat globules became smaller. The quantified fat globule's average size for the 12 weeks cheeses with fat content of 44.1, 41.0, 27.1, and 21.9% FDM were 10.1, 9. 6, 8.3, and 6.9 pixels, respectively. High fat cheese had larger fat globules than low fat cheese after being heated for the same time. After being heated for 20 seconds, the quantified fat globule's average size for the 12 weeks cheeses with fat content 44.1, 41.0, 27 .1, and 21.9% FDM were 15 .5 , 13 .5, 11.9, and 8.4 pixels, respectively. Thus, the microstructure of high fat cheese changed much more than that of low fat cheese during heating. Normal moisture cheese had larger fat globules than high moisture cheese after being heated for the same time. After being heated for 20 seconds, the quantified fat globule's average size for the 12 weeks cheeses with the moisture 58.1 % and 62.4% MNFP were 15.6 and 14.3 pixels, respectively. Aging had significant effect on the fat globule's average size of high fat Cheddar cheese, but did not have significant effect on that of low fat Cheddar cheese. The result of this research can provide useful information for cheese manufacturers to improve their product quality to meet customers' needs.

Library of Congress Subject Headings

Cheddare cheese -- Composition

Microstructure

Scanning electron microscopy

Format

application/pdf

Number of Pages

150

Publisher

South Dakota State University

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