Christopher R. Daubert

The interdependency of protein-energy malnutrition, aging, and dysphagia.

Advancing age is increasingly associated with confounding chronic and acute ailments, predisposing elderly individuals to conditions such as malnutrition and swallowing dysfunction. This enhanced susceptibility to malnutrition and dysphagia in this aging demographic lends itself to exacerbating, disabling conditions that may result in increased morbidity and mortality in the event of an aspiration episode. Early identification of substandard nutritional status and subsequent interventiion in the elderly dysphagic population may circumvent the deleterious effects of malnutrition.

Sensory and mechanical aspects of cheese texture

Producing high quality dairy products requires precise control over factors determining product appearance, flavor and texture. Food texture is analyzed by descriptive sensory analysis. This method uses terms that depict the textural sensations perceived from first bite through mastication and swallowing. One component of sensory texture is mechanical properties, which are determined by empirical or fundamental methods. However, if one wants to understand the molecular basis of texture, then fundamental tests are required. Fundamental rheological properties are linked to network models, such as those for rubber elasticity or filled gels. These models predict how network interactions will alter rheological properties, providing a link from molecular interactions to sensory texture. In general, sensory and rheological terms that relate to the overall firmness and resiliency of cheese are highly correlated. However, sensory terms that describe the breakdown pattern, adhesiveness and cohesiveness of cheese, are weakly, if at all, correlated with rheological properties.

Gelation properties of dispersions containing polymerized and native whey protein isolate

Whey protein polymers (WP-polymers) were prepared by heating whey protein isolate below the critical concentration for gelation at neutral pH and low salt conditions. The effects of WP-polymers and salt types (CaCl2 or NaCl) on rheological properties (large-strain and small-strain analysis), water holding properties, turbidity and microstructure of heat-induced whey protein isolate gels were investigated. Replacement of native whey protein isolate with WP-polymers increased fracture stress, fracture modulus, held water, and the translucency of gels. With both salt types, the addition of WP-polymers changed the gel structure from particulate to fine-stranded. However, the effect of WP-polymers on rheological properties was salt specific. Addition of 20‐100% WP-polymers in the presence of 10 mM CaCl2 caused a continued increase in fracture stress. In contrast, protein dispersions containing 30 mM NaCl did not form self-supporting gels when

The effect of aging on low-fat, reduced-fat, and full-fat Cheddar cheese texture

60% WP-polymers were added. Dispersions containing 200 mM NaCl formed self supporting gels at all levels of WP-polymer addition but fracture stresses for gels containing 20‐100% WP were similar. Dispersions containing 80% WP-polymers and 200 mM NaCl had lower gel points (time and temperature) than dispersions with 80% WP-polymers and 10 mM CaCl2. It appeared that CaCl2 was more effective in increasing gel fracture stress while NaCl was more effective in decreasing gelation time. Different gel properties may be prepared by altering the amount of WP-polymers and salt types. q 2001 Elsevier Science Ltd. All rights reserved.

Rheological properties and microstructure of Cheddar cheese made with different fat contents.

This study investigated the effects of aging and fat content on the texture of Cheddar cheese, both mechanical and sensory aspects, over a 9-mo aging period. Cheeses of 6, 16, and 33% fat were tested at 0.5, 3, 6, and 9 mo of aging. Cheeses were evaluated by a trained sensory panel using an established texture lexicon as well as instrumental methods, which were used to probe cheese structure. Sensory analysis showed that low-fat cheeses were differentiated from full-fat cheeses by being more springy and firm and this difference widened as the cheeses aged. In addition, full-fat cheeses broke down more during chewing than the lower fat cheeses and the degree of breakdown increased with aging. Mechanical properties were divided by magnitude of deformation during the test and separated into 3 ranges: the linear viscoelastic region, the nonlinear region, and fracture point. These regions represent a stress/strain response from low to high magnitude, respectively. Strong relationships between sensory terms and rheological properties determined in the linear (maximum compliance) and nonlinear (critical stress and strain and a nonlinear shape factor) regions were revealed. Some correlations were seen with fracture values, but these were not as high as terms related to the nonlinear region of the cheeses. The correlations pointed to strain-weakening behavior being the critical mechanical property. This was associated with higher fat content cheeses breaking down more as strain increased up to fracture. Increased strain weakening associated with an increase in fat content was attributed to fat producing weak points in the protein network, which became initiation sites for fracture within the structure. This suggests that fat replacers need to serve this functional role.

RHEOLOGICAL AND PHYSICOCHEMICAL PROPERTIES OF DERIVATIZED WHEY PROTEIN CONCENTRATE POWDERS

Reduced- and low-fat cheeses are desired based on composition but often fall short on overall quality. One of the major problems with fat reduction in cheese is the development of a firm texture that does not break down during mastication, unlike that observed in full-fat cheeses. The objective of this investigation was to determine how the amount of fat affects the structure of Cheddar cheese from initial formation (2 wk) through 24 wk of aging. Cheeses were made with target fat contents of 3 to 33% (wt/wt) and moisture to protein ratios of 1.5:1. This allowed for comparisons based on relative amounts of fat and protein gel phases. Cheese microstructure was determined by confocal scanning laser microscopy combined with quantitative image analysis. Rheological analysis was used to determine changes in mechanical properties. Increasing fat content caused an increase in size of fat globules and a higher percentage of nonspherical globules. However, no changes in fat globules were observed with aging. Cheese rigidity (storage modulus) increased with fat content at 10°C, but differences attributable to fat were not apparent at 25°C. This was attributable to the storage modulus of fat approaching that of the protein gel; therefore, the amount of fat or gel phase did not have an effect on the cheese storage modulus. The rigidity of cheese decreased with storage and, because changes in the fat phase were not detected, it appeared to be attributable to changes in the gel network. It appeared that the diminished textural quality in low-fat Cheddar cheese is attributed to changes in the breakdown pattern during chewing, as altered by fat disrupting the cheese network.

Emulsifying and Foaming Properties of a Derivatized Whey Protein Ingredient

ABSTRACT The gelling ability of whey proteins provides important textural and water holding properties in many foods. However, because many products cannot be heated to the temperature needed for thermal gelation of whey proteins, cold-set gelation of whey proteins could be very advantageous to the food industry. A derivatization procedure for the production of a cold gelling whey protein isolate (WPI) consisting of protein hydration, pH adjustment, thermal gelation, freeze drying, and milling was applied to three commercial whey protein concentrates (WPC). The resulting derivatized WPC powders were reconstituted in water and evaluated through a range of rheological and physical property studies. The effects of temperature, concentration, and shear on viscosity as well as water holding capacity and intrinsic viscosity were assessed. Although the composition of the starting materials influenced the functionality of the final derivatized powders, all samples exhibited a dramatic increase in thickening and water holding ability. All samples were able to form cold-set weak gel structures suitable for contributing viscosity and texture to a wide range of food systems.

Glycosylation and expanded utility of a modified whey protein ingredient via carbohydrate conjugation at low pH.

A derivatization procedure for the production of a cold gelling whey protein isolate (WPI) has been identified. The cold gelling derivatized whey protein isolate (dWPI) imparted greater viscosity and water holding ability when rehydrated at room temperature than unmodified whey powders. The objective of this study was to further characterize the foaming and emulsifying functionality of the derivatized ingredient. Samples were prepared by hydrating dWPI and WPI in deionized water and, when needed, adjusting the sample pH from 3.4 to 6.8, with 6M NaOH. Yield stress, drainage, and overrun were measured for 6.5% WPI and dWPI foams. Emulsifying capacity and creaming stability were determined for various WPI and dWPI emulsions. The overrun of dWPI foams was approximately 50% lower than WPI foams at pH 3.4 and 6.8. Foams of the derivatized ingredient were significantly more stable than WPI foams. The derivatized ingredient displayed a similar emulsifying capacity to WPI at pH 3.4 and pH 7.0, and differences were not observed in creaming of dWPI and WPI emulsions. Information on foaming and emulsifying ability of derivatized protein ingredients will expedite the development of applications with the novel dairy ingredient, particularly in those foods desiring an all-natural, or all dairy, food label.

Effect of disulfide interactions and hydrolysis on the thermal aggregation of β-lactoglobulin.

Whey protein, at one time considered a by-product of the cheese-making process, is now commonly used in foods for its thickening and emulsifying properties. Currently, approximately 30% of these proteinaceous resources remain under-utilized. Previously, an acidified, thermally treated whey protein concentrate (mWPC) was developed to produce a cold-set thickening ingredient. Mass spectroscopy revealed an approximate 2.5-fold decrease in the lactosylation of beta-lactoglobulin in mWPC starting materials compared with commercial whey protein concentrates, manufactured at a higher pH. Potentially, this should increase the number of reactive sites that remain available for carbohydrate attachment. With this study, the formation of glycoprotein complexes was demonstrated between the mWPC ingredient and lactose, naturally occurring in mWPC powders, or between mWPC protein components with dextran (35 to 45 and 100 to 200 kDa) materials at low pH. In fact, additional dry heating of mWPC powders showed a 3-fold increase in the amount of lactosylated beta-lactoglobulin. Evidence of Maillard reactivity was suggested using colorimetry, o-phthaldialdehyde assays, and sodium dodecyl sulfate PAGE followed by glycoprotein staining. Resultant glycoprotein dispersions exhibited altered functionality, in which case steady shear and small amplitude oscillatory rheology parameters were shown to be dependent on the specific reducing sugar present. Furthermore, the emulsion stability of mWPC-dextran fractions was 2 to 3 times greater than either mWPC or commercial WPC dispersions based on creaming index values. The water-holding capacity of all test samples decreased with additional heating steps; however, mWPC-dextran powders still retained nearly 6 times their weight of water. Scanning electron microscopy revealed that mWPC-dextran conjugates formed a porous network that differed significantly from the dense network observed with mWPC samples. This porosity likely affected both the rheological and water-binding properties of mWPC-dextran complexes. Taken together, these results suggest that the functionality of mWPC ingredients can be enhanced by conjugation with carbohydrate materials at low pH, especially with regard to improving the emulsifying attributes.

Rheological properties of fine-stranded whey protein isolate gels

The roles of sulfhydryl/disulfide interactions and acid/pepsin hydrolysis on β-lactoglobulin (β-lg) thermal aggregation at acidic pH 3.35 and 2 were studied using rheology, sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), transmission electron microscopy (TEM), and Western blotting. Pepsin promoted additional hydrolysis compared to the acid-hydrolyzed control sample based on a 12% increase in free amino groups. Hydrolysis with pepsin also resulted in an increase in the apparent viscosity by 2 logs upon heating 8% β-lg solutions at pH 3.35. Seemingly, hydrolysis promoted thermal aggregation of β-lg, correlating well with viscosity increases. Large microgels were observed in heated pepsin hydrolysates using TEM, supporting the increased viscosities of these dispersions. During thermal aggregation (85 °C, 3 h) of β-lg at pH 3.35, beyond the existence of limited disulfide interactions, acid hydrolysis and noncovalent interactions more likely play a crucial role in defining the functionality of acidified powdered modified whey ingredients.