ADSA Foundation Scholar Award: defining dairy flavors

Production and consumption of dairy foods continue to increase annually. Further, new ingredient applications for dairy foods continue to expand. With continued production and consumption, there is also increased competition. Increased competition exists regionally, nationally, and globally. Processors as well as product developers must find ways to maximize existing markets and expand into new markets. A consistent high quality product is necessary to maintain competitiveness. Although microbial safety and stability are key ways to define quality, flavor is one method of defining quality that is often assumed or overlooked. The aggressive and competitive nature of today's market demands more precise and powerful tools for defining flavor and flavor quality. Traditional as well as more recent methods for evaluating dairy flavor are reviewed. The application of defining sensory flavors to fundamental research on flavor chemistry, product understanding, and effective marketing is addressed.     

ADSA Foundation Scholar Award. Formation and physical properties of milk protein gels

Gelation of milk proteins is the crucial first step in both cheese and yogurt manufacture. Several types of milk gels are discussed, with an emphasis on recent developments in our understanding of how these gels are formed and some of their key physical properties. Areas discussed include the latest dual-binding model for casein micelles; some recent developments in rennet-induced gelation; review of the methods that have been used to monitor milk coagulation; and a discussion of some of the possible causes for the wheying-off defect in yogurts. Casein micelles are the primary building blocks of casein-based gels; however, controversy about its structure continues. The latest model proposed for the formation of casein micelles is the dual-binding model proposed by Horne, 1998, which suggests that casein micelles are formed as a result of two binding mechanisms, namely hydrophobic attraction and colloidal calcium phosphate (CCP) bridging. Most previous models for the casein micelle have treated milk gelation from the viewpoint of simple particle destabilization and aggregation, but they have not been able to explain several unusual rheological properties of milk gels. Although there have been many techniques used to monitor the milk gelation process over the past few decades, only a few appear attractive as possible in-vat coagulation sensors. Another important aspect of milk gels is the defect in yogurts called wheying-off, which is the appearance of whey on the gel surface. The factors responsible for its occurrence are still unclear, but they have been investigated in model acid gel systems.     

ADSA Foundation Scholar Award: Possibilities and challenges of exopolysaccharide-producing lactic cultures in dairy foods

Exopolysaccharides (EPS) from lactic acid bacteria are a diverse group of polysaccharides exhibiting various functional properties. Two forms of EPS are produced by lactic acid bacteria: capsular and unattached. Capsular EPS does not cause ropiness nor does production of unattached EPS ensure ropiness. The functions of EPS in dairy products are not completely understood. This is for 2 main reasons: the major variations among exopolysaccharides even from the same group of micro-organisms, which makes it difficult to apply information from one EPS to others, and the lack of availability of techniques with the ability to observe the microstructure and distribution of the highly hydrated EPS in fermented dairy products. The introduction of relatively new microscopic techniques such as confocal scanning laser microscopy and cryo-scanning electron microscopy made it possible to directly observe the distribution of fully hydrated EPS in dairy products. Recently, EPS produced by nonropy strains have drawn the attention of the dairy industry. This is because of the ability of some nonropy strains to produce large capsular and unattached EPS that would improve the texture of dairy products without causing the undesirable slippery mouthfeel produced by the ropy strains. Factors affecting functions of EPS are their molecular characteristics and ability to interact with milk proteins. Studying the interaction between EPS and milk proteins is complex because EPS are gradually produced during fermentation, unlike polysaccharides added directly to milk to stabilize the fermented product. The concentration and possibly molecular characteristics of EPS and protein characteristics such as charge and hydrophobicity change during fermentation. Consequently, the interaction of EPS with proteins might also change during fermentation. Exopolysaccharides provide functions that benefit reduced-fat cheeses. They bind water and increase the moisture in the nonfat portion, interfere with protein-protein interactions and reduce the rigidity of the protein network, and increase viscosity of the serum phase. This review discusses the production of capsular EPS and their role in structure formation in fermented milk, the mechanism of ropiness formation, and applications of EPS-producing cultures in reduced-fat cheeses.     

ADSA Foundation Scholar Award: Early-life exposure to hyperthermia: Productive and physiological outcomes,costs, and opportunities

Global rising temperature is a considerable threat to livestock production and an impediment to animal welfare. In fact, the 5 warmest years on record have occurred since 2016. Although the effect of heat stress on lactating cattle is well recognized and extensively studied, it is increasingly evident that rising temperatures will affect dairy cattle of all ages and lactation states. However, the extent and consequences of this effect are less understood and often overlooked in the literature and dairy industry. Early-life experiences, such as exposure to hyperthermia, can have life-long implications for health and productivity. This review highlights the body of work surrounding the effects of heat-stress exposure in young dairy cattle, including the prenatal fetus (in utero), postnatal calves (preweaning), and growing heifers, which are all categories that are typically not considered for heat-stress abatement on farm. Insights into the physiological and molecular mechanisms that might explain the adverse phenotypic outcomes of heat-stress exposure at different stages of development are also discussed. The estimated economic loss of in utero hyperthermia is addressed, and the ties between biological findings and opportunities for the application of cooling management interventions on farm are also presented. Our research highlights the importance of heat-stress abatement strategies for dry-pregnant cows to ensure optimal multigenerational productivity and showcases the benefits of cooling neonatal calves and growing heifers. Understanding the implications of heat stress at all life stages from a physiological, molecular, economic, and welfare perspective will lead to the development of novel and refined practices and interventions to help overcome the long-lasting effects of climate change in the dairy industry.     

ADSA Foundation Scholar Award--An integrated science-based approach to dairy food safety: Listeria monocytogenes as a model system

Transmission of food- and milkborne pathogens often involves complex interactions among the pathogen, the environment, and one or multiple host species. A complete understanding of these interactions is critical to allow the development of science-based, effective intervention strategies for foodborne infectious diseases. This article summarizes our studies on the transmission, ecology, pathogenesis and population genetics of Listeria monocytogenes, which we have used as model for a food- and milkborne pathogen that infects multiple hosts and also has considerable ability to survive and multiply in nonhost environments. Application of molecular subtyping tools in conjunction with phenotypic characterization of selected strains has allowed us to define distinct L. monocytogenes subtypes and clonal groups that appear to differ in relevant phenotypic characteristics that may affect their abilities to be transmitted through food systems. For example, a genetic group designated as lineage I has been shown to be not only more common among human listeriosis cases than among animal cases, but lineage I strains also appear to show an increased in vitro ability to spread intracellularly from host cell to host cell. These findings are consistent with the fact that while genetically diverse strains may be classified to one bacterial species, these strains often differ from one another in important genetic and phenotypic characteristics. I thus propose that evolutionary- and molecular subtyping-based definitions of bacterial subtypes and clonal groups will provide critical insight into the microbial ecology of dairy food systems, including not only foodborne pathogens, but also organisms important for dairy fermentation and spoilage.     

ADSA Foundation Scholar Award: Implementing waste solutions for dairy and livestock farms

Water quality in the United States is threatened by contamination with nutrients, primarily nitrogen (N) and phosphorus (P). Animal manure can be a valuable resource for farmers, providing nutrients, improving soil structure, and increasing vegetative cover to reduce erosion potential. At the same time, application of manure nutrients in excess of crop requirements can result in environmental contamination. Concentrated animal agriculture has been identified as a significant source of nutrient contamination of surface water, nitrogen contamination of groundwater, and ammonia emission. Areas facing the dilemma of an economically important livestock industry concentrated in an environmentally sensitive area have few options. If agricultural practices continue as they have in the past, despite the significant changes in agricultural intensity and changing environmental conditions, continued damage to water resources and a loss of fishing and recreational activity are inevitable. If agricultural productivity is reduced, however, the maintenance of a stable farm economy, a viable rural economy, and a reliable domestic food supply are seriously threatened. The identification and implementation of solutions to the generation of excess manure in confined animal feeding operations are necessary to enable such agricultural operations to thrive in environmentally sensitive areas such as the Chesapeake Bay Watershed. This paper will review an innovative collaborative approach to the development of a manure and litter solutions strategy by a diverse array of potential problem-solvers.     

干酪流变学性质及其对质地的影响

综述了关于流变学性质方面的构成因素、影响因素、作用机理、对质地的影响以及酪蛋白凝胶结构的形成机理和它对流变学特性的影响。同时讨论了分子问相互作用对流变学性质的作用机理和加工条件对它的影响情况。通过对流变学和质地性质的研究，将有助于干酪生产者更好的地预测和控制产品的质量。     

ADSA Foundation Scholar Award. Critical issues affecting the future of dairy industry: individual contributions in the scope of a global approach.

Several constraints that have been affecting the dairy industry are identified in a critical fashion, and directions are given with an emphasis on food processing implemented at the postproduction level. The rationale for modifications aimed at enhancing the appeal of condensed dairy products should be consubstantiated in strengthening of organoleptic characteristics, improvement of nutraceutical impact, and reduction of polluting power. This enumeration follows an order of increasing time scale required for consumer perception and increasing size scale associated with expected impact. Pursuance of such streamlines should lead to manufacture of dairy products that resemble nature more closely in terms of milk coagulation, milk fat modification, milk fermentation, whey fermentation, and starter culture addition. Directions for research and development anticipated as useful and effective in this endeavor, and which have been previously and consistently adopted in the development of an individual research program, are characterization and development of alternative rennets from plant sources, development of starter and nonstarter cultures from adventitious microflora, utilization of probiotic strains as starter cultures, upgrading of whey via physical or fermentation routes, and modification of milk fat via lipase-mediated interesterification reactions.     

Use of time–temperature superposition to study the rheological properties of cheese during heating and cooling

The objective of this study was to investigate the time–temperature superposition behaviour of the rheological properties of cheese during heating and cooling. A standard part‐skim Mozzarella cheese and a fat‐free cheese were used for the study. Fourier transform mechanical spectroscopy was used to simultaneously study the rheological properties over a range of frequencies from 0.08 to 8 Hz while samples were being heated from 10 to 90 °C or cooled from 90 to 10 °C at the rate of 1 °C min^?1. Master curves of storage modulus (G′), loss modulus (G′′) and loss tangent were obtained using a reference temperature of 70 °C.     

Effect of increasing the protein-to-fat ratio and reducing fat content on the chemical and physical properties of processed cheese product

Scientific studies indicate that the intake of dietary fat and saturated fats in the modern Western diet is excessive and contributes adversely to health, lifestyle, and longevity. In response, manufacturers of cheese and processed cheese products (PCP) are pursuing the development of products with reduced fat contents. The present study investigated the effect of altering the fat level (13.8, 18.2, 22.7, 27.9, and 32.5 g/100 g) in PCP on their chemical and physical properties. The PCP were formulated in triplicate to different fat levels using Cheddar cheese, skim milk cheese, anhydrous milk fat, emulsifying salt (ES), NaCl, and water. The formulations were designed to give fixed moisture (~53 g/100 g) and ES:protein ratio (0.105). The resultant PCP, and their water-soluble extracts (WSE), prepared from a macerated blend of PCP and water at a weight ratio of 1:2, were analyzed at 4 d. Reducing the fat content significantly increased the firmness of the unheated PCP and reduced the flowability and maximum loss tangent (fluidity) of the melted PCP. These changes coincided with increases in the levels of total protein, water-soluble protein, water-insoluble protein, and water-soluble Ca, and a decrease in the molar ratio of water-soluble Ca to soluble P. However, both water-soluble Ca and water-soluble protein decreased when expressed as percentages of total protein and total Ca, respectively, in the PCP. The high level of protein was a major factor contributing to the deterioration in physical properties as the fat content of PCP was reduced. Diluting the protein content or reducing the potential of the protein to aggregate, and thereby form structures that contribute to rigidity, may provide a means for improving quality of reduced-fat PCP by using natural cheese with lower intact casein content and lower calcium:casein ratio, for example, or by decreasing the ratio of sodium phosphate to sodium citrate-based ES.     

Relationships between cheese-processing conditions and curd and cheese properties to improve the yield of Idiazabal cheese made in small artisan dairies: A multivariate approach

Very diverse cutting and cooking intensity processes are currently used in small artisan dairies to manufacture Idiazabal cheese. The combination of the technical settings used during cheese manufacturing is known to affect cheese composition and yield, as well as whey losses. However, the information regarding the effect on microstructure and texture of cheese is scarce, especially in commercial productions. Therefore, the effect of moderate- and high-intensity cutting and cooking processes on whey losses, curd-grain characteristics, microstructure and cheese properties, and yield were analyzed. Three trials were monitored in each of 2 different small dairies during the cheesemaking of Idiazabal cheese, which is a semihard cheese made from raw sheep milk. The role and know-how of the cheesemakers are crucial in these productions because they determine the cutting point and handle semi-automatic vats. The 2 dairies studied used the following settings: dairy A used moderate-intensity cutting and cooking conditions, and dairy B used high-intensity cutting and cooking settings. Multiple relationships between cheese-processing conditions and curd, whey, and cheese properties as well as yield were obtained from a partial least square regression analysis. An increased amount of fat and casein losses were generated due to a combination of an excessively firm gel at cutting point together with high-intensity cutting and cooking processes. The microstructural analysis revealed that the porosity of the protein matrix of curd grains after cooking and cheese after pressing was the main feature affected, developing a less porous structure with a more intense process. Moderate-intensity cutting and cooking processes were associated with a higher cheese yield, regardless of the longer pressing process applied. No significant differences were observed in cheese composition. After 1 mo of ripening, however, the cheese was more brittle and adhesive when the high-intensity cutting and cooking process was applied. This could be associated with the composition, characteristics, and size distribution of curd grains due to differences in the compaction degree during pressing. These results could help to modify specific conditions used in cheesemaking, especially improving the process in those small dairies where the role of the cheesemaker is crucial.     

Transport phenomena in a model cheese: The influence of the charge and shape of solutes on diffusion

During cheese ripening, microorganisms grow as immobilized colonies, metabolizing substrates present in the matrix and generating products from enzymatic reactions. Local factors that limit the rates of diffusion, either within the general cheese matrix or near the colonies, may influence the metabolic activity of the bacteria during ripening, affecting the final quality of the cheese. The objective of this study was to determine the diffusion coefficients of solutes as a function of their different physicochemical characteristics (size, charge, and shape) in an ultrafiltrate (UF) model cheese (based on ultrafiltered milk) to enable better understanding of the ripening mechanisms. Diffusion coefficients of fluorescein isothiocyanate (FITC)-dextrans (4 kDa to 2 MDa) and FITC-labeled dairy proteins (α-lactalbumin, β-lactoglobulin, and BSA) were measured using the technique of fluorescence recovery after photobleaching (FRAP). This study showed that macromolecules up to 2 MDa and proteins could diffuse through the UF model cheese. The larger FITC-dextrans were not more hindered by the structure of the UF model cheese compared with the smaller ones. Any decrease in the diffusion coefficients of solutes was related only to their hydrodynamic radii. The FITC-dextran diffusion data were fitted to an obstruction model, resulting in a constant obstruction factor (k ~0.42). Diffusion in the model cheese was sensitive to the physicochemical characteristics of the solute. The FITC-dairy proteins studied (rigid and negatively charged molecules) were hindered to a greater degree than the FITC-dextrans (flexible and charge-neutral molecules) in the UF model cheese. The existence of steric and electrostatic interactions between the protein matrix of the UF model cheese and the FITC-dairy proteins could explain the decrease in diffusion compared with FITC-dextrans.     

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

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.     

Invited review: Sensory and mechanical properties of cheese texture

Instrumental mechanical properties (instrumental tests that measure force and deformation over time) of cheese and cheese texture (sensory perception of cheese structure) are critical attributes. Accurate measurement of these properties requires both instrumental and sensory testing. Fundamental rheological and fracture tests provide accurate measurement of mechanical properties that can be described based on chemical and structural models. Sensory testing likewise covers a range of possible tests with selection of the specific test dependent of the specific goal desired. Establishing relationships between instrumental and sensory tests requires careful selection of tests and consideration and analysis of the results. A review of these tests and a critical analysis of establishing relationships between instrumental and sensory tests is presented.     

Microstructure and rheological properties of Iranian white cheese coagulated at various temperatures

The effect of milk coagulation temperature on the composition, microstructure monitored using scanning electron micrographs, opacity measured by a Hunter lab system, and rheological behavior measured by uniaxial compression and small amplitude oscillatory shear were studied. Three treatments of Iranian White cheese were made by applying coagulation temperatures of 34, 37, and 41.5°C during the cheese-making procedure. A higher coagulation temperature resulted in increased fat and protein contents, and decreased the moisture content and ratio of moisture to protein. The highest temperature (41.5°C) had a significant effect on the opacity of Iranian White cheese. Milk coagulation at this temperature decreased the whiteness index (Hunter L value) and increased the yellowness index (Hunter b value) of the aged product compared with cheeses coagulated at lower temperatures. Microstructure of the cheese coagulated at 41.5°C was more compact and undisturbed, reflecting the higher values of stress at fracture and storage modulus measured for this treatment.     

Effect of selected Hofmeister salts on textural and rheological properties of nonfat cheese

Three Hofmeister salts (HS; sodium sulfate, sodium thiocyanate, and sodium chloride) were evaluated for their effect on the textural and rheological properties of nonfat cheese. Nonfat cheese, made by direct acidification, were sliced into discs (diameter = 50 mm, thickness = 2 mm) and incubated with agitation (6 h at 22°C) in 50 mL of a synthetic Cheddar cheese aqueous phase buffer (pH 5.4). The 3 HS were added at 5 concentrations (0.1, 0.25, 0.5, 0.75, and 1.0 M) to the buffer. Post-incubation, cheese slices were air dried and equilibrated in air-tight bags for 18 h at 5°C before analysis. Small amplitude oscillatory rheology properties, including the dynamic moduli and loss tangent, were measured during heating from 5 to 85°C. Hardness was determined by texture profile analysis. Acid-base buffering was performed to observe changes in the indigenous insoluble (colloidal) calcium phosphate (CCP). Moisture content decreased with increasing HS concentration. Cheeses incubated in high concentrations of SCN⁻ softened earlier (i.e., loss tangent = 1) compared with other HS treatments. Higher melting temperature values were observed for cheeses incubated in high concentrations of SO₄²⁻. Hardness decreased in cheeses incubated in buffers with high concentrations of SCN⁻. The indigenous CCP profile of nonfat cheese was not greatly affected by incubation in Cl⁻ or SCN⁻, whereas buffers with high concentrations of SO₄²⁻ reduced the acid-base buffering contributed by CCP. The use of high concentrations (1.0 M) of SCN⁻ for incubation of cheeses resulted in a softer protein matrix at high temperatures due to the chaotropic effect of SCN⁻, which weakened hydrophobic interactions between CN. Cheese samples incubated in 1.0 M SO₄²⁻ buffers exhibited a stiffer protein matrix at high temperatures due to the kosmotropic effect of SO₄²⁻, which helped to strengthen hydrophobic interactions in the proteins during the heating step. This study showed that HS influenced the texture and rheology of nonfat cheese probably by altering the strength of hydrophobic interactions between CN.     

Effect of trisodium citrate concentration and cooking time on the physicochemical properties of pasteurized process cheese

The effects of the concentration of trisodium citrate (TSC) emulsifying salt (0.25 to 2.75%) and holding time (0 to 20 min) on the textural, rheological, and microstructural properties of pasteurized process Cheddar cheese were studied using a central composite rotatable design. The loss tangent parameter (from small amplitude oscillatory rheology), extent of flow (derived from the University of Wisconsin Meltprofiler), and melt area (from the Schreiber test) all indicated that the meltability of process cheese decreased with increased concentration of TSC and that holding time led to a slight reduction in meltability. Hardness increased as the concentration of TSC increased. Fluorescence micrographs indicated that the size of fat droplets decreased with an increase in the concentration of TSC and with longer holding times. Acid-base titration curves indicated that the buffering peak at pH 4.8, which is due to residual colloidal calcium phosphate, decreased as the concentration of TSC increased. The soluble phosphate content increased as concentration of TSC increased. However, the insoluble Ca decreased with increasing concentration of TSC. The results of this study suggest that TSC chelated Ca from colloidal calcium phosphate and dispersed casein; the citrate-Ca complex remained trapped within the process cheese matrix. Increasing the concentration of TSC helped to improve fat emulsification and casein dispersion during cooking, both of which probably helped to reinforce the structure of process cheese.     

Effect of frozen storage on the proteolytic and rheological properties of soft caprine milk cheese

Freezing and long-term frozen storage had minimal impact on the rheology and proteolysis of soft cheese made from caprine milk. Plain soft cheeses were obtained from a grade A goat dairy in Georgia and received 4 storage treatments: fresh refrigerated control (C), aged at 4°C for 28 d; frozen control (FC), stored at −20°C for 2 d before being thawed and aged in the same way as C cheese; and 3-mo frozen (3MF), or 6-mo frozen (6MF), stored at −20°C for 3 or 6 mo before being thawed and aged. Soft cheeses had fragile textures that showed minimal change after freezing or over 28 d of aging at 4°C. The only exceptions were the FC cheeses, which, after frozen storage and aging for 1 d at 4°C, were significantly softer than the other cheeses, and less chewy than the other frozen cheeses. Moreover, after 28 d of aging at 4°C, the FC cheeses tended to have the lowest viscoelastic values. Slight variation was noted in protein distribution among the storage treatment, although no significant proteolysis occurred during refrigerated aging. The creation and removal of ice crystals in the cheese matrix and the limited proteolysis of the caseins showed only slight impact on cheese texture, suggesting that frozen storage of soft cheeses may be possible for year-round supply with minimal loss of textural quality.     

An approach to improve the baking properties and determine the onset of browning in fat-free mozzarella cheese

Compared with low-moisture part-skim mozzarella and mozzarella cheese, bake performance of low-fat and fat-free mozzarella on pizza has a lot to desire. We hypothesized that a water-soaking pretreatment step of low-fat and fat-free cheese shreds before baking would improve pizza baking performance. The study also examined the correlation of the onset of cheese browning with the rate of moisture loss, changes in cheese surface temperature, and 3-dimensional (3D) plot L* a* b* CIELAB color analysis. The pretreatment of soaking cheese shreds in water improved the baking properties of fat-free mozzarella cheese on pizza. Compared with the control sample, which demonstrated significant shred identity, poor shred melt, fusion, and stretch during a pizza bake with fat-free mozzarella, the soaked cheese (SC) sample demonstrated satisfactory cheese melt, fusion, and stretch. In addition, the SC sample had desired browning as opposed to the control sample's excessive browning. The additional moisture from the soaking pretreatment aided in delaying the onset of cheese browning in the SC sample when compared with the control sample. For both the control and SC samples, there was a strong correlation between the onset of cheese browning with the peak of moisture-loss rate, and an increase in cheese surface temperature (>100°C). The color analysis of the 3D plot confirmed the relationship between the onset of cheese browning and the shift in L* (lightness), a* (red-green color), and b* (blue-yellow) values. According to the study's findings, soaking cheese shreds before baking can help improve bake performance on pizza. Furthermore, 3 measurement tools used in the study, (1) moisture-loss rate, (2) cheese surface temperature, and (3) 3D plot CIELAB color, were useful in determining the onset of cheese browning and can be applied to different intervention strategies to control cheese browning during pizza baking.