Michael H. Tunick

Chemistry of structure-function relationships in cheese

Proceedings of an American Chemical Society Symposium held in Chicago, August 1993. Contributors evaluate the current status of cheesemaking and highlight the information that will be essential for new developments. The papers are arranged within sections devoted to physical chemistry of cheese text

Rheology and microstructure of low-fat Mozzarella cheese

The contributions of fat and moisture content to Mozzarella cheese texture were investigated to provide a basis for developing low-fat cheese with consumer acceptability. The characteristics of low-fat high-moisture (LFHM) experimental Mozzarella cheeses before and after 6 weeks of refrigerated storage were compared with those of high-fat low-moisture controls. High levels of either moisture in nonfat substance or fat in dry matter (FDM) were accompanied by decreases in hardness, complex viscosity, and elastic modulus and increases in meltability during the storage time. Starter culture bacteria were observed at the surface of the fat droplets, the latter having a tendency to coalesce during storage. Development of texture and meltability in LFHM Mozzarella appeared to be directly related to increased proteolysis of αs1-casein observed during storage. These results show the feasibility of making Mozzarella cheese containing <25% FDM with textural properties similar to those of a full-fat cheese if the product contains enough moisture and is stored under refrigeration for several weeks.

Effects of Skim Milk Homogenization on Proteolysis and Rheology of Mozzarella Cheese

Abstract The influence of milk homogenization on proteolysis and functional properties of Mozzarella cheese was examined in an effort to develop low-fat Mozzarella with desirable textural and melting properties. Two-stage homogenization of skim milk at 6870/3430 kPa prior to the addition of nonhomogenized cream did not inhibit the meltability of full-fat or low-fat cheeses, when compared with cheeses made from nonhomogenized milk, but the meltability of full-fat cheese made from homogenized milk was greatly decreased. Homogenization of whole or skim milk had no significant effect on other rheological parameters or on proteolysis of αs1-casein in full-fat and low-fat cheeses. Refrigerated storage at 4 °C caused meltability and proteolysis to increase and the other parameters to decrease. Differences in fat content caused significant changes in hardness, springiness and meltability. Fat globule size and homogenization of protein affected proteolysis and rheology much less than fat content and storage time.

Reorganization of casein submicelles in Mozzarella cheese during storage

Abstract To gain a better understanding of the factors involved in textural changes in Mozzarella cheese during storage, electron microscopic imaging was used to compare the ultrastructure of the protein matrix on the day of stretching (0 weeks) and after 6 weeks of storage at 4 °C. Low-fat and full-fat cheeses were prepared from nonhomogenized milk and from milk homogenized at 10.3 and 17.2 MPa. Analysis of the stained electron density distribution in image transforms of the protein matrix revealed that spacing patterns of regular structures with the dimensions of casein submicelles changed during storage, in most cases forming larger aggregates at longer average spacings, but there were no significant changes in total electron density between fresh and stored cheeses. These effects were related to proteolysis. Submicelles in low-fat cheeses homogenized at 17.2 MPa reorganized differently, a likely result of decreased proteolysis. Submicelles formed part of a new membrane around fat globules in cheeses made from homogenized milk, as previously observed. Changes in submicelle size and distribution could explain some of the differences in texture properties between fresh and stored Mozzarella cheeses, and between products made from homogenized and nonhomogenized milk.

Food texture analysis in the 21st century.

Food texture encompasses physical characteristics perceived by the senses. Research in this area must be multidisciplinary in nature, accounting for fracture of food, sounds it makes during biting and chewing, its microstructure, muscle movements during mastication, swallowing, and acceptability. Food texture thus encompasses chemistry, physics, physiology, and psychology. This brief review of the field covers the areas of recent research in food texture and specifies where further understanding is needed.

Dairy Products and Health: Recent Insights.

Milk, cheese, yogurt, and other dairy products have long been known to provide good nutrition. Major healthful contributors to the diets of many people include the protein, minerals, vitamins, and fatty acids present in milk. Recent studies have shown that consumption of dairy products appears to be beneficial in muscle building, lowering blood pressure and low-density lipoprotein cholesterol, and preventing tooth decay, diabetes, cancer, and obesity. Additional benefits might be provided by organic milk and by probiotic microorganisms using milk products as a vehicle. New research on dairy products and nutrition will improve our understanding of the connections between these products, the bioactive compounds in them, and their effects on the human body.

CRITICAL EVALUATION OF CRISPY AND CRUNCHY TEXTURES: A REVIEW

Crispness and crunchiness are important factors in the enjoyment of many foods, but they are defined differently among dictionaries, consumers, and researchers. Sensory, mechanical, and acoustic methods have been used to provide data on crispness and crunchiness. Sensory measurements include biting force and sound intensity. Mechanical techniques resemble mastication and include flex, shear, and compression. Acoustical techniques measure frequency, intensity, and number of sound events. Water and oil content contribute to crispness and crunchiness, which also have temporal aspects. Information in the literature is compared in this article to develop definitions of crispness and crunchiness.

Effect of high-pressure processing on reduction of Listeria monocytogenes in packaged Queso Fresco

The effect of high-hydrostatic-pressure processing (HPP) on the survival of a 5-strain rifampicin-resistant cocktail of Listeria monocytogenes in Queso Fresco (QF) was evaluated as a postpackaging intervention. Queso Fresco was made using pasteurized, homogenized milk, and was starter-free and not pressed. In phase 1, QF slices (12.7 × 7.6 × 1 cm), weighing from 52 to 66 g, were surface inoculated with L. monocytogenes (ca. 5.0 log10 cfu/g) and individually double vacuum packaged. The slices were then warmed to either 20 or 40°C and HPP treated at 200, 400, and 600 MPa for hold times of 5, 10, 15, or 20 min. Treatment at 600 MPa was most effective in reducing L. monocytogenes to below the detection level of 0.91 log10 cfu/g at all hold times and temperatures. High-hydrostatic-pressure processing at 40°C, 400 MPa, and hold time ≥ 15 min was effective but resulted in wheying-off and textural changes. In phase 2, L. monocytogenes was inoculated either on the slices (ca. 5.0 log10 cfu/g; ON) or in the curds (ca. 7.0 log10 cfu/g; IN) before the cheese block was formed and sliced. The slices were treated at 20°C and 600 MPa at hold times of 3, 10, and 20 min, and then stored at 4 and 10°C for 60 d. For both treatments, L. monocytogenes became less resistant to pressure as hold time increased, with greater percentages of injured cells at 3 and 10 min than at 20 min, at which the lethality of the process increased. For the IN treatment, with hold times of 3 and 10 min, growth of L. monocytogenes increased the first week of storage, but was delayed for 1 wk, with a hold time of 20 min. Longer lag times in growth of L. monocytogenes during storage at 4°C were observed for the ON treatment at hold times of 10 and 20 min, indicating that the IN treatment may have provided a more protective environment with less injury to the cells than the ON treatment. Similarly, HPP treatment for 10 min followed by storage at 4°C was the best method for suppressing the growth of the endogenous microflora with bacterial counts remaining below the level of detection for 2 out of the 3 QF samples for up to 84 d. Lag times in growth were not observed during storage of QF at 10°C. Although HPP reduced L. monocytogenes immediately after processing, a second preservation technique is necessary to control growth of L. monocytogenes during cold storage. However, the results also showed that HPP would be effective for slowing the growth of microorganisms that can shorten the shelf life of QF.

Effect of heat and homogenization on in vitro digestion of milk

Central to commercial fluid milk processing is the use of high temperature, short time (HTST) pasteurization to ensure the safety and quality of milk, and homogenization to prevent creaming of fat-containing milk. Ultra-high-temperature sterilization is also applied to milk and is typically used to extend the shelf life of refrigerated, specialty milk products or to provide shelf-stable milk. The structures of the milk proteins and lipids are affected by processing but little information is available on the effects of the individual processes or sequences of processes on digestibility. In this study, raw whole milk was subjected to homogenization, HTST pasteurization, and homogenization followed by HTST or UHT processing. Raw skim milk was subjected to the same heating regimens. In vitro gastrointestinal digestion using a fasting model was then used to detect the processing-induced changes in the proteins and lipids. Using sodium dodecyl sulfate-PAGE, gastric pepsin digestion of the milk samples showed rapid elimination of the casein and α-lactalbumin bands, persistence of the β-lactoglobulin bands, and appearance of casein and whey peptide bands. The bands for β-lactoglobulin were eliminated within the first 15min of intestinal pancreatin digestion. The remaining proteins and peptides of raw, HTST, and UHT skim samples were digested rapidly within the first 15min of intestinal digestion, but intestinal digestion of raw and HTST pasteurized whole milk showed some persistence of the peptides throughout digestion. The availability of more lipid droplets upon homogenization, with greater surface area available for interaction with the peptides, led to persistence of the smaller peptide bands and thus slower intestinal digestion when followed by HTST pasteurization but not by UHT processing, in which the denatured proteins may be more accessible to the digestive enzymes. Homogenization and heat processing also affected the ζ-potential and free fatty acid release during intestinal digestion. Stearic and oleic acids were broken down faster than other fatty acids due to their positions on the outside of the triglyceride molecule. Five different casein phosphopeptide sequences were observed after gastric digestion, and 31 sequences were found after intestinal digestion, with activities yet to be explored. Processing affects milk structure and thus digestion and is an important factor to consider in design of foods that affect health and nutrition.

Electron-Density Patterns in Low-Fat Mozzarella Cheeses During Refrigerated Storage

Consumer demand for palatable low-fat foods has prompted the development and production of a wide variety of new foods. Consumer interest in low-fat dairy products has increased dramatically, and among the many new and improved dairy foods are some Mozzarella cheeses that have suitable textural properties yet contain less fat than part-skim varieties (Tunick et al., 1991). We further improved the textural properties of low-fat Mozzarella cheeses by adjusting the proportions of ingredients and processing conditions (Tunick et al., 1993). High levels of moisture in the non-fat substance significantly decreased the hardness, complex viscosity and elastic modulus, and the meltability increased during storage. These improvements in textural properties appeared to be most directly related to increased proteolysis under conditions of high moisture.