Browsing by Author "Dr. Mary Anne Drake, Committee Member"

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    Cheese Texture
    (2002-06-17) Brown, Jennifer Amber; Dr. Marcia Gumpertz, Committee Member; Dr. Mary Anne Drake, Committee Member; Dr. E. Allen Foegeding, Committee Chair; Dr. Christopher R. Daubert, Committee Member
    Cheese is a popular food due to its diversity in application, nutritional value, convenience, and good taste. Producing high quality cheeses that meet consumer expectations is crucial in order for cheese makers to remain competitive. These expectations include proper end-use functionality (shred, melt, stretch, etc.) and appropriate texture. Currently, there is not a complete understanding of what characteristics govern these aspects. This study seeks to determine what transitions occur during the early stages of maturation of certain cheeses, specifically, how the changes in physicochemical properties in young cheeses affect textural changes perceived when consumed. Mozzarella and Pizza cheeses were tested at 4, 10, 17, and 38 d of age; Process cheese was tested at 4 d of age. Rheological methods were employed to determine the linear, non-linear, and fracture properties of the cheeses. A trained sensory panel developed appropriate descriptive language and product-specific reference scales to evaluate cheese texture. Both sensorial and rheological methods differentiated the cheese varieties, and patterns were observed as the cheese aged. Rheological analysis showed the cheeses were viscoelastic gels with greater storage (G´, elastic) than loss (G'', viscous) moduli. The overall magnitude of G´ decreased as the cheeses aged; creep recovery analysis confirmed the loss of overall firmness with time. Five sensory terms differentiated the ages of the cheeses within varieties. Correlations between the sensory and rheological methods were observed. Principal component analysis revealed that combinations of both sensory and rheological parameters could distinguish the cheeses based upon variety and age. Comparison of certain large strain rheological methods was also done. Fracture stresses and fracture strains (or apparent strain) at three different strain rates (0.0047, 0.047, and 0.47 -1) were determined using both torsion and vane methods to see how the large strain properties compared in these cheeses. Overall, vane fracture stresses were lower than torsion fracture stresses. As the strain rate increased, the fracture stresses increased. Simple linear regression of the torsion and vane fracture stresses revealed that the torsion fracture stresses were 2.0 times higher than the vane fracture stresses (R²=0.66). Mozzarella is an anisotropic material since the body of this cheese has fibers that are oriented in a specific way. Methodology to appropriately evaluate the sensory perception of such materials was explored. No differences in any of the sensory terms were found between samples tested having the fibers oriented parallel to the force applied and samples tested having fibers perpendicular to the force applied. Finally, the thermal behavior of these cheeses was considered through use of differential scanning calorimetry. Two different heating schemes were used to determine if glass transitions occur in these cheeses and to characterize melting behavior. Glass transition temperatures were determined in the Process cheese. The heating profiles at elevated temperatures (i.e. during melting) were similar in all cheeses at all ages. It is likely that the transitions observed during melting are due to phase changes in certain lipids within the cheese. These results have significant implications in the cheese industry. An understanding of the transitions in both physical and chemical properties in young cheeses can help to explain what causes change in the perceptual texture, which may help in producing customized cheeses. Future testing should focus on how such parameters affect end-use functionality in order develop similar models which will help cheese makers to meet consumer demands.
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    Sensory and Instrumental Analysis of Pasteurized Dill Pickles Made from Acidified, Bulk Stored Cucumbers
    (2009-07-28) Kuhlman, Nicholas Grant; Dr. Lisa Ohehrl Dean, Committee Member; Dr. Roger F. McFeeters, Committee Chair; Dr. Mary Anne Drake, Committee Member
    Storing fresh cucumbers for an 8 to 12 week period in an acidified, non-fermented environment prior to processing would extend the time for processing locally grown cucumbers into pasteurized pickle products. The effect of acidified storage of fresh cucumbers for up to 120 days prior to their conversion to pasteurized dill pickles was evaluated. Cucumbers stored at 18ºC prior to pasteurization maintained a fresh, non-cured appearance as well as a firm texture. Equilibrated acid concentrations of 3.5% acetic acid also helped to reduce the amount of curing and maintained firmness in cucumber tissue. Dill pickles made from acidified, bulk stored cucumbers maintained a firm texture after pasteurization. However, the cured appearance of bulk stored cucumbers increased by 40% within 30 days of pasteurization so that it was much higher than the cured appearance of dill pickles made directly from the same lot of fresh cucumbers and stored for an equivalent period of time after pasteurization. Sour, sweet, bitter and vinegar intensities were similar for dill pickles prepared from either bulk stored or fresh cucumbers. Firmness, saltiness, and dill flavor while significantly different, differed by less than 1 point on a 15-point scale. The major flavor difference between pasteurized dill pickles made from stored acidified cucumbers and pickles made directly from fresh cucumbers is that pickles made from stored cucumbers had an “other†flavor. The intensity of this flavor was perceived at a similar level regardless of the brine composition or storage time of the cucumbers prior to pasteurization. Descriptors for this “other†flavor were chlorine, pool, barny and metallic. GCxGC-TOFMS analysis of volatile components in dill pickles prepared from bulk stored cucumbers and dill pickles prepared from fresh cucumbers resulted in detection of 24 components that were significantly different (p<0.05) between at least one treatment pair. Individual volatile components did not provide a clear basis for differentiation among different storage brine treatments. However, PCA analysis using the 24 components was able to differentiate treatments.