Milk Fat Thermal Properties and Solid Fat Content in Emmental Cheese: A Differential Scanning Calorimetry Study

Crystal networks, partial coalescence, and rheological properties of milk fat fraction model systems

This study aimed to investigate the crystal network of bulk milk fat fractions and the partial coalescence, and the rheological properties of their oil-in-water (O/W) emulsions. Different milk fat fraction model systems were compared for their physicochemical properties, crystallization kinetics, and fat crystal networks across a range of temperatures. The extent of partial coalescence and rheological properties of the O/W emulsion prepared by different milk fat fractions were further analyzed. The results demonstrated that the ratio between saturated fatty acids (SFA) and unsaturated fatty acids and triacylglycerides (TAG) influenced the melting thermal behaviors, solid fat contents (SFC), and crystal networks of various milk fat fractions, which in turn influenced the partial coalescence and rheological characteristics of their O/W emulsions. Moreover, an excellent fit of the trend line confirmed that hardness increased exponentially with SFC. Trisaturated TAG in fractions with high melting points (HMF) such as milk fat fraction MF45, whose clarification temperature was 45°C, enriched long-chain SFA (saturated:unsaturated fatty acid = 2.2:1). We found that MF45 achieved higher SFC and hardness in the range of 0 to 40°C and, ultimately, formed a well-defined microstructural network with thick, rod-like crystals. Further, TAG in fractions with low melting points (LMF) such as MF10, whose clarification temperature was 10°C, were enriched with short-chain and unsaturated fatty acids (saturated:unsaturated fatty acid = 1.5:1), and a disordered crystal network in MF10, composed of randomly arranged, translucent platelets, was detected. Although fat globules of HMF and LMF were stabilized against coalescence, this could be attributed to a variety of mechanisms involving SFC, liquid fat, protective film around the fat globule, and minor lipids. According to the rheological profiles, all O/W emulsions exhibited weak viscoelastic "gel-like" structures [storage modulus (G') > loss modulus (G")] over most of the measured range. The G' values and apparent viscosity of HMF were greater than those of other fractions, indicating that the large and rigid crystals strengthen the networks more effectively.

Development of a method to determine the SFC in the fat phase of emulsions using TD-NMR FID-CPMG deconvolution

Fat crystallisation in emulsions is a complex process. One of the important parameters is the solid fat content (SFC). Up to now, there is no standardised method to measure the SFC in emulsions, let alone to determine the SFC of the fat inside droplets, thus avoiding the signal of the aqueous phase. This work evaluates the capabilities of deconvolution of the free induction decay (FID)-Carr-Purcell-Meiboom-Gill (CPMG) signal of emulsions. Three models were evaluated. The first model was a combination of a Gaussian function and a bi-exponential function (GBE model). The second model combined a Gaussian function with multiple exponential functions (GME model). The last model contained multiple Gaussian functions and multiple exponential functions (MGME model). The latter two models used a simplified CONTIN analysis. Based on the analysis of the determination coefficient R² , the calculated water content and the estimated SFC of nonemulsified two-phase systems, the GBE model was selected to analyse the FID-CPMG signal of emulsified systems. However, the results obtained with the other models did not differ substantially, and hence, they could be used to obtain a full relaxation time distribution. When the GBE model was applied on different emulsion systems, no significant differences in estimated SFC of the fat phase were found, thus indicating that the emulsion formulation (i.e. water-in-oil [W/O], oil-in-water [O/W] or water-in-oil-in-water [W/O/W]) only had a minor effect on the SFC in the systems considered here.

Contrastive analysis of lipid composition and thermal and crystallization behavior of olein/stearin fractionated by novel layer melt crystallization from palm oil

BACKGROUND

Melt crystallization is typically recognized as a highly efficient and green method for oil fractionation. This work concentrated on novel layer melt crystallization for preparing desirable olein and stearin products from palm oil and the evaluation of fraction quality. Layer melt crystallization was performed at various temperatures and the effects on fractions were evaluated using iodine value (IV), solid fat content (SFC) and melting point. The lipid composition, thermal and crystallization properties, and phase behaviors of the final optimized fractions were determined using gas chromatography, high-performance liquid chromatography-atmospheric pressure chemical ionization mass spectrometry and differential scanning calorimetry.

RESULTS

Increasing crystallization tube temperatures under the same jacket temperature increased the melting point and SFC, while decreasing the IV of the olein product. Opposite results were observed for the stearin product. Major fatty acids in fractions were determined as palmitic acid and oleic acid. 1,2-Dioleoyl-3-palmitoylglycerol and 1,3-dipalmitoyl-2-oleoylglycerol were identified as the main triacylglycerols in olein and stearin fractions, respectively. A critical effect of crystallization temperature on co-crystallization of oleins and stearins was revealed. A transition from plate-like crystal growth to spherulitic growth with spontaneous nucleation was indicated in palm oil and stearin fractions with increasing crystallization temperature. As for olein fractions, a temperature increase resulted in heterogeneous nucleation from instantaneous nucleation.

CONCLUSIONS

Novel layer melt crystallization was successfully applied and optimized for fractionating palm oil. The composition and property changes of obtained fractions were analyzed and explained at both macroscopic and microscopic levels. © 2021 Society of Chemical Industry.

Application of Thermal Methods to Analyze the Properties of Coffee Silverskin and Oil Extracted from the Studied Roasting By-Product

The aim of the study was to characterize the thermal properties of coffee silverskin and fat extracted from the material by using differential scanning calorimetry, modulated differential scanning calorimetry and thermogravimetry/derivative thermogravimetry. Additionally, the thermokinetic parameters, oxidative stability and fatty acid composition of the extracted oil were defined. Thermal decomposition of the studied coffee roasting by-product under oxygen occurred in three defined stages. The most significant changes in weight were observed in the region of 200–500 °C and correspond to polysaccharide decomposition. These results are in agreement with the data obtained from the differential scanning calorimetry curve. On the curve course of silverskin, two main exothermic peaks can be observed with a maximum at 265 and 340 °C. These exothermic events represent the transitions of hemicellulose and cellulose. Fat extracted from silverskin turned out to be a source of polyunsaturated fatty acids with the recommended n-6 to n-3 ratio reaching the value 4:1. The studied fat was characterized by low oxidative stability. Considering the obtained results, it can be stated that thermal analysis can provide fast and reliable data concerning the composition and properties of coffee silverskin and coffee silverskin oil.

Milk fat: opportunities, challenges and innovation

Milk fat is a high-value milk component that is processed mainly as butter, cheese, cream and whole milk powder. It is projected that approximately 35 million tonnes of milk fat will be produced globally by 2025. This surplus, enhances the need for diversification of milk fat products and the milk pool in general. Infant milk formula producers, for instance, have incorporated enzyme modified ("humanised") milk fat and fat globule phospholipids to better mimic human milk fat structures. Minor components like mono- and di-glycerides from milk fat are increasingly utilized as emulsifiers, replacing palm esters in premium-priced food products. This review examines the chemistry of milk fat and the technologies employed for its modification, fractionation and enrichment. Emerging processing technologies such as ultrasound, high pressure processing, supercritical fluid extraction and fractionation, can be employed to improve the nutritional and functional attributes of milk fat. The potential of recent developments in biological intervention, through dietary manipulation of milk fatty acid profiles in cattle also offers significant promise. Finally, this review provides evidence to help redress the imbalance in reported associations between milk fat consumption and human health, and elucidates the health benefits associated with consumption of milk fat and dairy products.

Short communication: Decrease of lipid profiles in cow milk by ultra-high-temperature treatment but not by pasteurization

Triglyceride (TG) and fatty acid profiles of raw (RM), pasteurized (PM, 85°C for 15 s), and indirect UHT-treated (UM, 135°C for 15 s) cow milk were investigated by a lipidomics approach. Ninety-four TG were identified and all were present at significantly lower concentrations in UM than in RM or PM, and free fatty acid contents were significantly higher in UM than in RM and PM, indicating that TG lipolysis occurred to a greater degree in UM than in RM and PM. In addition, UM contained significantly fewer unsaturated fatty acids (14 types) than those in RM and PM, including C14:1n-5, C15:1n-5, C16:1n-7, C17:1n-7, C18:1n9 cis, C18:2n-6 cis, C18:3n-3, C18:3n-6, C20:1, C20:2, C20:3n-6, C20:3n-3, C20:4n-6, and C20:5n-3. However, we detected no significant differences between RM and PM in these fatty acids. In conclusion, UHT treatment, but not pasteurization, caused loss of the nutritional quality and bioactivity of cow milk lipid profiles.

Effect of Fractionation and Chemical Characteristics on the Crystallization Behavior of Milk Fat

The experiments reported in this study provided a more comprehensive insight into the effect of chemical composition on the crystallization behavior of milk fat (MF). MF was fractionated between 20 and 40 °C into nine fractions with different melting points and was first subjected to the heating step (L20, L30, L40, and S40) followed by the cooling phase (SS40, SL40, SS30, SL30, and LL40). Furthermore, the species of fatty acids (FAs) and triglycerides (TAGs) of the MF fractions were identified. The thermodynamics, crystallization behavior, and polymorphs were determined using differential scanning calorimetry, pulsed nuclear magnetic resonance, and X-ray diffraction, respectively. The results indicated that L40 yielded the highest percentage (∼35% of the total MF) of all the fractions. Enthalpies of the melting and crystallization processes of solid fat content in this study were related to the different FA and TAG compositions of MF and its fractions. High melting fractions (HMFs) were enriched with long-chain saturated fatty acids and tri-saturated (S3) TAGs, and low melting fractions (LMFs) were enriched with short-chain unsaturated FAs and tri-unsaturated (U3) TAGs. Moreover, the various nucleation mechanisms of MF fractions were identified according to the Avrami equation. The polymorphic transformation from a β' form of double chain length structures to a β form of triple chain length occurred in the native MF and HMFs, whereas the LMFs displayed almost no crystals. PRACTICAL APPLICATION: This study represented the first time that nine fractions were obtained using MF fractionation via a heating step, followed by a cooling phase. Furthermore, the chemical composition of MF fractions was investigated. The results obtained from this study might be of specific value in understanding the functional properties of fat-based dairy food in both storage conditions and real-time applications.

Evaluation of the effects of mild heat in bovine milk by time resolved fluorescence

Heat treatment of milk and dairy products are indispensable for the dairy industry. This thermal processing intends to extend shelf life, improve quality of the milk and minimize the health risks associated with milk and dairy products. The use of time-resolved fluorescence techniques to identify conformation and structure changes ok milk fat and proteins could help understand the temperature effects in bovine milk. This study aimed to use fluorescence lifetimes to evaluate the effects of heating fresh cow milk up to 85 °C. We observed different tendencies for fluorescence lifetimes submitted to different heating temperatures. The longer lifetime values decreased for temperatures higher than room temperature until it reached a minimum value near 40 °C and it slowly increased again for temperatures higher than 40 °C, indicating two distinct processes. These results indicate that time-resolved fluorescence can assist on the analysis of heating effects in fluid milk.

Rheology of Swiss Cheese Fondue

Cheese fondue is a popular Swiss dish prepared by melting cheese under the addition of wine, starch, and seasoning. The flow behavior or rheology of fondue is crucial for mouthfeel, flavor release, and the tendency of fondue to cling to the bread. Fondue is a complex multiphase system whose rheology is determined by the interactions of its colloidal ingredients. We establish cheese fondue as a water-continuous system with dispersed fat droplets, charged caseins, and starch granules. Irreversible phase separation, a common issue in fondue preparation, may be prevented by addition of a critical minimum starch concentration. Fondue was found to be a shear-thinning yield stress fluid, which is desirable for mouthfeel and facilitates fondue to cling to the bread for consumption. Fondue showed a viscoelastic stress response around the gel point (G' ≈ G″), which is proposed as crucial for the balance of orally perceived gumminess (G') and liquidity (G″). Ethanol addition and lowering pH toward the isoelectric point of casein, as associated with wine addition, decrease fondue viscosity due to a decrease in casein micelle size. Below the isoelectric point of casein, fondue is unstable and phase separates, potentially impeding fondue digestion. Thus, fondue rheology is governed by the complex colloidal interactions within its ingredients, and ultimately determines fondue eating experience.

Symposium review: Structure-function relationships in cheese

The quality and commercial value of cheese are primarily determined by its physico-chemical properties (e.g., melt, stretch, flow, and color), specific sensory attributes (e.g., flavor, texture, and mouthfeel), usage characteristics (e.g., convenience), and nutritional properties (e.g., nutrient profile, bioavailability, and digestibility). Many of these functionalities are determined by cheese structure, requiring an appropriate understanding of the relationships between structure and functionality to design bespoke functionalities. This review provides an overview of a broad range of functional properties of cheese and how they are influenced by the structural organization of cheese components and their interactions, as well as how they are influenced by environmental factors (e.g., pH and temperature).

Insights into the mechanism of the formation of the most stable crystal polymorph of milk fat in model protein matrices

The effect of incorporation and presence of various ingredients in a model sodium caseinate-based imitation cheese matrix on the polymorphism of milk fat was comprehensively described using powder x-ray diffraction, differential scanning calorimetry, and microscopy. With anhydrous milk fat (AMF) in bulk used as control, the embedding of AMF as droplets in a protein matrix was found to result in a greater extent of formation of the β polymorph than AMF alone and AMF homogenized with water and salts solution. The use of other protein matrices such as soy and whey protein isolate gels revealed that the nature of the protein and other factors associated with it (i.e., hydrophobicity and molecular structure) do not seem to play a role in the formation of the β polymorph. These results indicated that the most important factor in the formation of the β polymorph is the physical constraints imposed by a solid protein matrix, which forces the triacylglycerols in milk fat to arrange themselves in the most stable crystal polymorph. Characterization of the crystal structure of milk fat or fats in general within a food matrix could provide insights into the complex thermal and rheological behavior of foods with added fats.

Spatial Distribution of Lactococcus lactis Colonies Modulates the Production of Major Metabolites during the Ripening of a Model Cheese

In cheese, lactic acid bacteria are immobilized at the coagulation step and grow as colonies. The spatial distribution of bacterial colonies is characterized by the size and number of colonies for a given bacterial population within cheese. Our objective was to demonstrate that different spatial distributions, which lead to differences in the exchange surface between the colonies and the cheese matrix, can influence the ripening process. The strategy was to generate cheeses with the same growth and acidification of a Lactococcus lactis strain with two different spatial distributions, big and small colonies, to monitor the production of the major ripening metabolites, including sugars, organic acids, peptides, free amino acids, and volatile metabolites, over 1 month of ripening. The monitored metabolites were qualitatively the same for both cheeses, but many of them were more abundant in the small-colony cheeses than in the big-colony cheeses over 1 month of ripening. Therefore, the results obtained showed that two different spatial distributions of L. lactis modulated the ripening time course by generating moderate but significant differences in the rates of production or consumption for many of the metabolites commonly monitored throughout ripening. The present work further explores the immobilization of bacteria as colonies within cheese and highlights the consequences of this immobilization on cheese ripening.

Characteristics and Feasibility of Trans-Free Plastic Fats through Lipozyme TL IM-Catalyzed Interesterification of Palm Stearin and Akebia trifoliata Variety Australis Seed Oil

Akebia trifoliata var. australis seed oil (ASO) was used as an edible oil in China. However, in-depth research studies on ASO have yet to be conducted for production of plastic fats in food industry. In this work, an immobilized lipase from Thermomyces lanuginosus (TL IM) was employed to catalyze palm stearin (PS) with different ratios of ASO in a laboratory-scale operation at 60 °C. The physical properties [e.g., fatty acid profile, slip melting point (SMP), solid fat content (SFC), polymorphic form, and microstructure] of physical blends (PBs) were analyzed and compared with those of the interesterified products (IPs). Results showed that SMPs of IPs (33.20-37.60 °C) decreased compared with those of PBs (48.03-49.30 °C). Meanwhile, IPs showed a good SFC range from 16.11% to 28.29% at 25 °C with mostly β' polymorphic forms determined by X-ray diffraction analysis. It should be mentioned that no trans fatty acids (TFAs) were detected in any products, suggesting much more health-benefits of IPs. Texture tests showed that PBs (3318.19 ± 86.67 g) were markedly harder than IPs (557.02 ± 12.75 g). Conclusively, our study demonstrated that ASO can be utilized to produce trans-free plastic fats with good qualities through lipase-catalyzed interesterification.

Multiscale structures of lipids in foods as parameters affecting fatty acid bioavailability and lipid metabolism

On a nutritional standpoint, lipids are now being studied beyond their energy content and fatty acid (FA) profiles. Dietary FA are building blocks of a huge diversity of more complex molecules such as triacylglycerols (TAG) and phospholipids (PL), themselves organised in supramolecular structures presenting different thermal behaviours. They are generally embedded in complex food matrixes. Recent reports have revealed that molecular and supramolecular structures of lipids and their liquid or solid state at the body temperature influence both the digestibility and metabolism of dietary FA. The aim of the present review is to highlight recent knowledge on the impact on FA digestion, absorption and metabolism of: (i) the intramolecular structure of TAG; (ii) the nature of the lipid molecules carrying FA; (iii) the supramolecular organization and physical state of lipids in native and formulated food products and (iv) the food matrix. Further work should be accomplished now to obtain a more reliable body of evidence and integrate these data in future dietary recommendations. Additionally, innovative lipid formulations in which the health beneficial effects of either native or recomposed structures of lipids will be taken into account can be foreseen.

The viscoelastic properties of processed cheeses depend on their thermal history and fat polymorphism

Both the composition and the thermal kinetics that are applied to processed cheeses can affect their texture. This study investigated the effect of the storage conditions and thermal history on the viscoelastic properties of processed cheese and the physical properties of the fat phase. The microstructure of processed cheese has been characterized. Using a combination of physical techniques such as rheometry, differential scanning calorimetry, and X-ray diffraction, the partial crystallization of fat and the polymorphism of triacylglycerols (TG; main constituents of milk fat) were related to changes in the elastic modulus and tan δ as a function of temperature. In the small emulsion droplets (<1 μm) dispersed in processed cheeses, the solid fat phase was studied at a molecular level and showed differences as a function of the thermal history. Storage of processed cheese at 4 °C and its equilibration at 25 °C lead to partial crystallization of the fat phase, with the formation of a β' 2 L (40.9 Å) structure; on cooling at 2 °C min(-1), the formation of an α 3 L (65.8 Å) structure was characterized. The cooling of processed cheese from 60 to -10 °C leads to the formation of a single type of crystal: α 3 L (72 Å). Structural reorganizations of the solid fat phase characterized on heating allowed the interpretation of the elastic modulus evolution of processed cheese. This study evidenced polymorphism of TG in a complex food product such as processed cheese and allowed a better understanding of the viscoelastic properties as a function of the thermal history.

Crystallization and polymorphism of triacylglycerols contribute to the rheological properties of processed cheese

The thermal, rheological, and structural behaviors of a spreadable processed cheese were studied by complementary techniques including differential scanning calorimetry (DSC), rheology, and X-ray diffraction as a function of temperature. In this product, fat is present as a dispersed phase. Thermal and rheological properties were studied at different cooling rates between 0.5 and 10 degrees C min(-1) from 60 to 3 degrees C. Crystallization properties of fat were monitored at a cooling rate of -2 degrees C min(-1) from 60 to -10 degrees C. Fat triacylglycerols (TGs) crystallized at 15 degrees C in a triple-chain length 3Lalpha (72 A) structure correlated to exothermic events and to the sudden increase in the rheological moduli G' and G''. Upon heating at 2 degrees C min(-1), the polymorphic transition of TGs evidence the melting of the 3Lalpha structure and the formation of a 2Lbeta' (36.7-41.5 A) structure. Melting of the latter follows. These transformations coincide with thermal events observed by DSC and the decrease in two steps of the rheological moduli. The influence of fat crystallization, melting, and polymorphism upon the viscoelastic properties is clearly demonstrated upon both heating and cooling.

Multiscale characterization of the organization of triglycerides and phospholipids in emmental cheese: from the microscopic to the molecular level

The chemical composition and properties of lipids, both triglycerides and phospholipids, play a major role in the functional and nutritional properties of food products. In this study, the suprastructure of fat, solid fat content, and crystallographic properties of triglycerides were investigated in hard-type cheeses from the microscopic scale to the molecular level using the combination of relevant techniques. Two industrial cheeses with different oiling off properties were compared with experimental cheeses manufactured in the laboratory. Microstructural analysis performed using confocal laser scanning microscopy showed that milk processing led to the disruption of fat globules with the formation of nonglobular fat. For a similar fatty acid composition, oiling off was mainly related to the fat in dry matter content and to the suprastructure of fat in cheese. An exogenous fluorescent phospholipid permitted the localization of milk phospholipids in the cheese matrix, which mainly remain around fat inclusions after disruption of the milk fat globule membrane, and to show heterogeneities. We also showed using differential scanning calorimetry that the suprastructure of fat did not affect the solid fat content in cheese at 4 degrees C: 71.6 +/- 4.9%. The organization of triglyceride molecules in fat crystals, elucidated at a molecular level using X-ray diffraction, corresponded to the coexistence of 2 lamellar structures (2L 40.5 angstroms and 3L 54.6 angstroms) with four polymorphic forms: alpha, two beta' and beta. A schematic representation of the multiscale organization of triglycerides and phospholipids in cheese is proposed.