Monoacylglycerols in dairy recombined cream: I. The effect on milk fat crystallization

Recent advances in studying crystallisation of mono- and di-glycerides at oil-water interfaces

This review focuses on the current understanding regarding lipid crystallisation at oil-water interfaces. The main aspects of crystallisation in bulk lipids will be introduced, allowing for a more comprehensive overview of the crystallisation processes within emulsions. Additionally, the properties of an emulsion and the impact of lipid crystallisation on emulsion stability will be discussed. The effect of different emulsifiers on lipid crystallisation at oil-water interfaces will also be reviewed, however, this will be limited to their impact on the interfacial crystallisation of monoglycerides and diglycerides. The final part of the review highlights the recent methodologies used to study crystallisation at oil-water interfaces.

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.

Effects of monoacylglycerols with different saturation degrees on physical and whipping properties of milk fat-based whipping creams

Milk fat-based whipping cream is primarily comprised of cream and whole milk. It has melt-in-the-mouth texture and unique milk flavor. However, milk fat-based whipping cream suffers from poor emulsion stability and foam firmness. The effects of monoacylglycerols (MAGs) with different saturation degrees (M1: 98% saturation, M2: 70% saturation and M3: 30% saturation) on emulsion properties (average particle size, viscosity, and emulsion stability) and whipping properties (overrun, firmness, shape retention ability, and foam stability) of milk fat-based whipping creams were investigated in this study. MAGs significantly decreased particle sizes (from 2.84 to 1.16 μm) and enhanced viscosity (from 350 to 490 cP) of the milk fat-based emulsions (emulsion without MAGs: M0, 5.01 μm, 298 cP) (P < 0.05). MAGs increased the stability of the milk fat-based emulsions with lesser phase separation during centrifugation tests and lower changes in particle sizes and viscosities during temperature cycling tests. Emulsion M1 with highest degree of saturation is less likely to destabilize and phase inverse. The decrease sharply in conductivity can be attributed to the entrapment of large amounts of air. Following that, the conductivity of M1 with low variation indicating high whipping resistance and less likely to coalescence and phase separation. Adding MAGs can significantly enhance overrun (M1: 205.3%, M2: 198.5%, M3: 141.4%) as compared to the control sample (M0: 97.9%) (P < 0.05). In emulsions containing MAGs with high degree of saturation (M1 and M2), firmness (M1: 95 g, M2: 109 g) and shape retention ability of the whipped creams were reduced as compared to control emulsion without MAG (M0: 173 g), but the foam stability (M1: 89%, M2: 91%) was enhanced (M0: 81%); M3 (firmness: 507 g; foam stability: 66%) has the contrasted effects. Whipping cream M2 demonstrated the best whipping properties with high overrun (198.46%), good firmness (109 g), shape retention ability and foam stability (91%). Good quality whipping creams can be obtained by selecting suitable MAGs.

Effect of stearic and oleic acid-based lipophilic emulsifiers on the crystallization of the fat blend and the stability of whipped cream

Effect of stearic acid-based lipophilic emulsifiers (sorbitan monostearate (Span-60), sucrose ester S-170, and lactic acid esters of monoglycerides (LACTEM)) and oleic acid-based lipophilic emulsifiers (sorbitan monooleate (Span-80) and sucrose ester O-170) on the crystallization of fat blend and the stability of whipped cream were studied. Span-60 and S-170 possessed strong nucleation inducing ability and good emulsifying properties. Thus, tiny and uniform crystals were formed in fat blends, small and ordered fat globules were distributed in emulsions, and air bubbles were effectively wrapped in firmly foam structures. The crystallization of the fat blend and the stability of whipped cream were slightly modified by LACTEM due to its poor nucleation inducing ability and moderate emulsifying characteristic. Span-80 and O-170 had weak nucleation inducing ability and poor emulsifying properties, therefore, loose crystals were formed in fat blends and some big fat globules were separated in emulsions, thereby decreasing the stability of whipped creams.

Modulation of the crystallization of rapeseed oil using lipases and the impact on ice cream properties

We investigated the possibility to use rapeseed as a main oil in ice cream formulations by changing its functionality when using different kinds of lipases. Through a 24 h-emulsification and a centrifugation, the modified oils were further used as functional ingredients. All lipolysis was first assessed as a function of time by ¹³C NMR, where triglycerides consumption and the formation of low-molecular polar lipids (LMPL: monoacylglycerol and free fatty acids, FFAs) were selectively identified and compared. The more the FFAs, the sooner the crystallization (from -55 to -10 °C) and the later the melting temperatures (from -17 to 6 °C) measured by differential scanning calorimetry. These modifications were exploited in ice cream formulations with a significant impact on overall hardness (range of 60-216 N) and flowing during defrosting (from 1.29 to 0.35g/min). The global behavior of products can be controlled by the composition of LMPL within oil.

Thickening mechanism of recombined dairy cream stored at 4 °C: Changes in the composition and structure of milk protein under different sterilization intensities

This work elucidates the mechanism involved in the effect of varying sterilization intensities on RDC thickening via comparative analysis of the changes in the composition and structure of RDC interfacial protein after storage at 4 °C and at 25 °C. The results showed that pasteurized RDCs (75 °C for 16 s, 90 °C for 5 min) and high-temperature sterilized RDCs (105 °C for 3 min, 115 °C for 7 min and 121 °C for 7 min) did not thicken during storage at 25 °C, and had lower viscosities and higher Ca²⁺ concentrations than those stored at 4 °C. Whey protein (WP) aggregates were found to have been adsorbed at the interface of high-temperature treated RDCs stored at 4 °C, leading to the aggregation of fat globules and, consequently, reversible thickening. However, high-temperature sterilized RDCs underwent into irreversible thickening at 10 d, 7 d and 3 d. This phenomenon was attributed to the large amount of heat-induced whey protein and κ-casein complex that was absorbed on the oil-water interface, with Ca²⁺ bonded to form bridging flocculation, which altered the secondary structure of the interfacial protein to one with increased β-sheet content and decreased random coil content.

Effect of Different Polymerization Degrees and Fatty Acids of Polyglycerol Esters on the Physical Properties and Whippability of Recombined Dairy Cream

Polyglycerol esters (PGEs) are used as emulsifiers in recombined dairy cream (RDC) to improve product quality. In this study, the effects of four PGEs with different polymerization degrees and esterification on the particle size, viscosity, zeta potential, and microrheology of RDC emulsions were investigated, and the whipping time, overrun, serum loss, and firmness of the RDC emulsions were recorded. The results show that the addition of the PGEs reduced the particle size (from 2.75 μm to 1.48-1.73 μm) and increased the viscosity (from 41.92 cP to 73.50-100 cP) and stability (from 0.354 to 0.105-0.128), which were related to the change in interfacial properties and the weakening of Brownian motion, but there were differences in the effect on the whipping behavior of the RDCs. Although the addition of 0.9% triglyceride monolaurate gave the emulsion the best stability, the RDC had a longer whipping time (318 s) and a lower overrun (116.6%). Comparatively, the 0.7-0.9% concentrations of PGE55 and tripolycerol monostearate (TMS) provided RDC with good stability and aeration characteristics, allowing inflation within 100 s and expansion rates of up to 218.24% and 186.88%, respectively. In addition, the higher degree of polymerization of polyglyceryl-10 monstearate (PMS) did not work well at any concentration. These results contribute to understanding the mechanism of action of PGEs and improving the quality of RDC.

The effect of emulsifier type on the secondary crystallisation of monoacylglycerol and triacylglycerols in model dairy emulsions

Dairy emulsions contain an intrinsically heterogeneous lipid phase, whose components undergo crystallisation in a manner that is critical to dairy product formulation, storage, and sensory perception. Further complexity is engendered by the diverse array of interfacially-active molecules naturally present within the serum of dairy systems, and those that are added for specific formulation purposes, all of which interact at the lipid-serum interface and modify the impact of lipid crystals on dairy emulsion stability. The work described in this article addresses this complexity, with a specific focus on the impact of temperature cycling and the effect of emulsifier type on the formation and persistence of lipid crystals at lipid-solution interfaces. Profile analysis tensiometry experiments were performed using single droplets of the low melting fraction of dairy lipids, in the presence and absence of emulsifiers (Tween 80 and whey protein isolate, WPI) and during the temperature cycling, to study the formation of monoacylglycerol (MAG) crystals at the lipid-solution interface. Companion experiments on the same lipid systems, and at the same cooling and heating rates, were undertaken with synchrotron small angle X-ray scattering, to specifically analyse the effect of emulsifier type on the formation of triacylglycerol (TAG) crystals at the lipid-solution interface of a model dairy emulsion. These two complementary techniques have revealed that Tween 80 molecules delay MAG and TAG crystal formation by lowering the temperature at which the crystallisation occurs during two cooling cycles. WPI molecules delay the crystallisation of MAGs and TAGs during the first cooling cycle, while MAG crystals form without delay during the second cooling cycle at the same temperature as MAG crystals in an emulsifier free system. The crystallisation of TAGs is inhibited during the second cooling cycle. The observed differences in crystallisation behaviour at the interface upon temperature cycling can provide further insight into the impact of emulsifiers on the long-term stability of emulsion-based dairy systems during storage.

Rhizopus oryzae Lipase, a Promising Industrial Enzyme: Biochemical Characteristics, Production and Biocatalytic Applications

Lipases are biocatalysts with a significant potential to enable a shift from current pollutant manufacturing processes to environmentally sustainable approaches. The main reason of this prospect is their catalytic versatility as they carry out several industrially relevant reactions as hydrolysis of fats in water/lipid interface and synthesis reactions in solvent-free or non-aqueous media such as transesterification, interesterification and esterification. Because of the outstanding traits of Rhizopus oryzae lipase (ROL), 1,3-specificity, high enantioselectivity and stability in organic media, its application in energy, food and pharmaceutical industrial sector has been widely studied. Significant advances have been made in the biochemical characterisation of ROL particularly in how its activity and stability are affected by the presence of its prosequence. In addition, native and heterologous production of ROL, the latter in cell factories like Escherichia coli, Saccharomyces cerevisiae and Komagataella phaffii (Pichia pastoris), have been thoroughly described. Therefore, in this review, we summarise the current knowledge about R. oryzae lipase (i) biochemical characteristics, (ii) production strategies and (iii) potential industrial applications.

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.

Influence of interfacial adsorption of glyceryl monostearate and proteins on fat crystallization behavior and stability of whipped-frozen emulsions

The effect of interfacial competitive adsorption of glyceryl monostearate (GMS) with proteins and GMS-fat (anhydrous milk fat; coconut oil) interactions on the fat crystallization behavior and stability of whipped-frozen emulsions were investigated. The results indicated GMS retarded the nucleation of emulsified anhydrous milk fat, but accelerated crystal growth. A contrasting outcome was elicited by emulsified coconut oil. Increasing GMS concentration strengthened and weakened the structural networking within anhydrous milk fat and coconut oil emulsions, respectively, which was evidenced by the oscillatory rheology results. Anhydrous milk fat whipped-frozen emulsions were characterized by increased partial coalescence degree with increasing GMS concentration. However, lower partial destabilization index and insignificant effect of GMS was found in coconut oil systems. Confocal laser scanning micrographs revealed that big clumps of fat globules were present at air bubble surfaces in anhydrous milk fat whipped-frozen emulsions, while only some individual fat globules were observed in coconut oil systems.

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.

Effect of solubilised carbon dioxide at low partial pressure on crystallisation behaviour, microstructure and texture of anhydrous milk fat

The crystallisation and melting behaviour, fat polymorphs, microstructure and texture of anhydrous milk fat (AMF) was investigated in the presence of dissolved CO₂ (0-2000ppm) under two crystallising conditions (non-isothermal versus isothermal). CO₂ was found to induce higher onset crystallisation temperature during cooling from 35 to 5°C at 0.5°Cmin^-1. X-ray scattering analysis showed that, in the presence of dissolved CO_2, this rapid crystallisation caused the formation of unstable, α polymorph fat crystals. For milk fat crystallised under isothermal condition at 25°C for 48h, dissolved CO₂ improved solid fat content, slightly depressed melting temperature and exhibited a sharper melting peak. Microstructure of AMF visualised by Polarised light microscopy of crystallised AMF showed that increasing dissolved CO₂ concentration was associated with smaller crystal size and greater crystal number. The bulk properties of the fat appeared to mirror the microstructural differences, in that the texture of CO₂-treated AMF was harder under isothermal condition but became softer than untreated AMF under cooling condition. The results of this study are of significance in understanding how CO₂ treatment might be used to modulate the crystallisation behaviour of milkfat and thereby the structural development and physical functionality of fat-containing dairy products.