Structure and mechanical properties of anisotropic agar gels obtained via unidirectional freezing.

The controllable formation of anisotropic gel structures is presently sought for the development of foods with novel textures. Here, we used unidirectional freezing to generate agar gels consisting of a honeycomb-like porous network of elongated and aligned pores. A custom-built Peltier system allowed for control of the freezing front velocity throughout the agar gels. A higher freezing velocity (10 µm/s) led to smaller pore sizes compared to the slower freezing velocity tested (2 µm/s). Texture analysis highlighted the significantly higher Young's modulus in the gels when compressed in the axial vs. radial direction - a direct consequence of the unidirectional freezing. The proton spin-spin relaxation time revealed greater water mobility in the unidirectionally frozen gel with larger pores. This study serves as the basis for the development of anisotropic hydrocolloid gels with a tunable microstructure and texture.

A hybrid approach to oil structuring - combining wax oleogels and capillary suspensions.

There is continuing interest in finding new approaches to gel liquid oil for processed food applications. Here, we combined oleogels and capillary suspensions to generate model oil-continuous networks consisting of a wax oleogel and a water-bridged, glass particle network. The composition map tested comprised 30 vol% polar or non-polar glass beads dispersed in a 70 vol% non-particle phase consisting of water (≤9 vol%) as well as 2 wt% hexatriacontane as oleogelator in canola oil. While the hexatriacontane wax alone gelled the oil, presence of the glass beads (but no water) prevented oleogelation. Self-supporting capillary networks formed with polar particles and 1 vol% water or non-polar glass beads and 3 vol% water in canola oil. The capillary suspensions demonstrated significant differences in rheological behaviour as the polar particles yielded much higher elastic moduli than their non-polar particle counterparts. Polar hybrids were weakened by inclusion of the wax whereas the non-polar particle hybrid network displayed elastic moduli greater than the respective contributions of both capillary and wax gel networks. This hybrid method of oleogelation can be applied to virtually any food particles and uses minimal water and wax.

Demulsification of water-in-oil emulsions stabilized with glycerol monostearate crystals.

HYPOTHESIS: Colloidal particles can be used to generate water-in-oil (W/O) emulsions resistant against coalescence. Demulsification is possible with addition of low molecular weight surfactants to the emulsion continuous oil phase. Whether surfactants demulsify particle-stabilized W/O emulsions depends on their ability to modify the wettability of interfacially-bound particles. EXPERIMENTAL: Crystals of glycerol monostearate (GMS) were prepared followed by water addition to generate GMS-stabilized W/O emulsions. The surfactants sorbitan monooleate (SMO), sorbitan monolaurate (SML), citric acid esters of monoglycerides (CITREM), sorbitan trioleate (STO), propylene glycol monolaurate (PgML), and polyglycerol polyricinoleate (PGPR) were added to the emulsion oil phase. Emulsion microstructure was characterized by light microscopy and cryo-scanning electron microscopy. Surfactant activity and crystal wetting were characterized by interfacial tension and three-phase contact angle measurements. Salt release from within the emulsions was used to assess demulsifier efficacy. FINDINGS: Emulsions stabilized by platelet-like GMS crystals were generated. Of the six surfactants, SMO, SML, and CITREM were effective demulsifiers whereas STO, PgML, and PGPR were ineffective. The former three sufficiently modified the wettability of GMS crystals on the droplet surface, as they adsorbed to both the oil-water interface and GMS crystal surface. Emulsion destabilization was associated with faster NaCl release from the emulsion internal phase.

Structure-rheology relationship in monoolein liquid crystals.

HYPOTHESES: Monoolein liquid crystals find use in foods and pharmaceuticals. Our hypotheses were: (a) liquid crystal symmetry dominates yielding and large deformation, and (b) strain rate frequency superposition (SRFS) may be used to determine mesophase long and short relaxation times. EXPERIMENTS: Liquid crystal microstructure and rheology were characterised as a function of temperature and composition. Their structure was assessed using small angle X-ray scattering (SAXS) and polarised light microscopy. Small and large deformation rheology was characterised using frequency and amplitude sweeps, large amplitude oscillatory shear tests, and SRFS. FINDINGS: We have contributed to the structure-rheology relationship governing the properties of the lamellar, cubic, and hexagonal mesophases. Initially, we characterised a number of monoolein-water binary phase transitions, which showed similar behaviour with earlier efforts. Frequency sweeps revealed that the cubic phases had the highest elasticity followed by the lamellar and hexagonal phases. The stiffening and thickening ratios, extracted from the Lissajous-Bowditch plots, were used to quantify intra-cycle non-linearities. The cubic phases displayed abrupt yielding with more pronounced stiffening and thinning behaviour compared to the others. Each liquid crystal phase displayed unique rheological behaviour upon large deformation and, by linking rheology with SAXS and composition, we show that their symmetry defined their rheology.

Effects of Sorbitan Monostearate and Stearyl Alcohol on the Physicochemical Parameters of Sunflower-Wax-Based Oleogels.

A rising health concern with saturated fatty acids allowed researchers to look into the science of replacing these fats with unsaturated fatty acids. Oleogelation is a technique to structure edible oil using gelators. The present study looked for the effect of solid emulsifiers; namely, sorbitan monostearate (SP) and stearyl alcohol (SA), on the physicochemical parameters of oleogels. All the oleogels were formulated using 5% sunflower wax (SW) in sunflower oil (SO). The formulated oleogels displayed irregular-shaped wax crystals on their surface. The bright-field and polarized microscopy showed the fiber/needle network of wax crystals. Formulations consisting of 10 mg (0.05% w/w) of both the emulsifiers (SA10 and SP10) in 20 g of oleogels displayed the appearance of a dense wax crystal network. The SP and SA underwent co-crystallization with wax molecules, which enhanced crystal growth and increased the density and size of the wax crystals. The XRD and FTIR studies suggested the presence of a similar ß' polymorph to that of the triacylglycerols' arrangement. The incorporation of SA and SP in wax crystal packing might have resulted in a lower crystallization rate in SA10 and SP10. Evaluation of the thermal properties of oleogels through DSC showed better gel recurrence of high melting enthalpy. These formulations also displayed a sustained release of curcumin. Despite the variations in several properties (e.g., microstructures, crystallite size, thermal properties, and nutrient release), the emulsifiers did not affect the mechanical properties of the oleogel. The meager amounts of both the emulsifiers were able to modulate the nutrient release from the oleogels without affecting their mechanical properties in comparison to the control sample.

Rice bran wax effects on cocoa butter crystallisation and tempering.

The effects of up to 5 wt% rice bran wax (RBX) on the crystallisation, tempering and storage stability of cocoa butter (CB) and a model dark chocolate were assessed. Presence of RBX significantly accelerated tempering and the formation of the desirable form V polymorph in CB. The form V to VI transition in both CB and chocolate was slowed in the presence of RBX during temperature-cycling, with addition of 1 wt% wax effectively reducing the extent of bloom formation in model chocolate following two weeks of temperature-cycling from 25 to 29 °C. Overall, this study has shown that RBX may be considered a viable seed material to accelerate tempering of CB and retard fat bloom in chocolate.

Temperature-dependent properties of fat in adipose tissue from pork, beef and lamb. Part 1: microstructural, thermal, and spectroscopic characterisation.

We investigated the temperature-dependent microstructure and thermal properties of back fat adipose tissue from pork, beef and lamb. Microstructural characterisation via electron, confocal and light microscopy showed that the back fats were structurally similar and consisted of fat dispersed as discrete units within a protein matrix akin to a closed cell foam. Differential scanning calorimetry showed distinct fat melting profiles for each of the tissues, which were ascribed to differences in fatty acid profile. Fat crystal organisation, melting and re-solidification signatures unique to each adipose tissue were found via X-ray diffraction and Raman spectroscopy. Overall, we found that the temperature-dependent microstructure of adipose fat was intricately linked to the fat phase melting behaviour, and importantly, to its protein matrix at elevated temperatures. Such understanding is necessary to provide the required insights to effectively replicate the functionality of adipose tissue using plant-based materials.

Temperature-dependent properties of fat in adipose tissue from pork, beef and lamb. Part 2: rheology and texture.

Matching the texture of fat in plant-based meat alternatives requires an in-depth understanding of the rheology of animal adipose tissue which, to-date, remains under-studied. Here, we characterised the small and large deformation behaviour of back fat from pork, beef, and lamb, with the underlying goal being the establishment of the temperature-dependent structure-function relationship governing the texture and rheology of adipose tissue. The dynamic rheological behaviour of the back fats was characterised via frequency and amplitude sweeps and large amplitude oscillatory strain (LAOS), as well as texture analysis via puncture tests. At 20 °C, prior to heating, the small and large deformation properties of adipose tissue were dominated by the solid fat phase within the adipose cells. Upon heating to 80 °C, with the fat phase molten, the protein network underpinning the structure of the back fats conferred elastic behaviour to the tissues, and the now-molten oil partly leaked from the adipocytes into the surrounding interstitial space. Upon re-cooling, a bicontinuous network of fat crystals and protein contributed to back fat rheology. Large deformation rheology revealed animal species-specific differences. Prior to heating, pork back fat was characterised by soft yielding behaviour while beef and lamb back fat showed abrupt yielding and intra-cycle strain stiffening. Post-heating, lamb showed the highest stiffness, compared to pork and beef, as well as non-linearities in its stress-strain relationship obtained via LAOS. Such fundamental understanding is essential to provide the required insights to replicate the functionality of adipose tissue using plant-based materials.

Sugar-sugar interactions in oil suspensions containing surfactants and effects on macroscopic phenomena.

Surfactants are used in confectionery production to control the viscosity and yield value of molten chocolate. To develop a deeper understanding of the structure-function relationship of surfactants in food-related particle suspensions, the apparent viscosity, yield value, sedimentation, and particle interactions of 10 wt% confectioner's sugar-in-canola oil suspensions were investigated in the presence of up to 1 wt% commercial soy lecithin, polyglycerol polyricinoleate (PGPR), citric acid esters of monoacylglycerols (CITREM) or ammonium phosphatides (AMP). Atomic force microscopy (AFM) was used to measure attractive forces at the nano-Newton scale between a sugar substrate and a sugar crystal-functionalized AFM cantilever in an oil environment. For all but PGPR, addition of surfactant reduced the adhesion force between sugar surfaces up to a critical concentration above which the force increased, implying the presence of additional interactions. This critical concentration was assumed to be when monolayer coverage of the sugar surfaces by surfactant occurred (0.05 wt% for lecithin, 0.10 wt% for CITREM and AMP). No critical concentration was found for PGPR, with its greatest effect for each analysis occurring at the highest concentrations tested (0.60 and 1.00 wt%). The significance of these interactions on macroscopic phenomena such as apparent viscosity and sedimentation was also assessed. Like with the AFM data, there was an optimal concentration of added surfactant above which viscosity increased. Sedimentation rate greatly decreased with addition of PGPR while being only slightly affected by addition of lecithin, CITREM and AMP. An argument regarding their efficacy was made based on the relative sizes of the polar headgroup and nonpolar tail groups of the molecules, which contributed to how they adsorbed to the sugar surface. Overall, these results suggested that surfactant properties such as molecular weight and head group properties played an important role in modifying the interactions between sugar crystals in an oil-continuous environment.

The presence of crystalline sugar limits the influence of emulsifiers on cocoa butter crystallization.

The effects of 2 wt% emulsifier and crystalline sugar on the isothermal solidification and polymorphic behavior of cocoa butter were evaluated. The emulsifiers investigated were commercial soy lecithin, polyglycerol polyricinoleate (PGPR), citric acid esters of mono- and diacylglycerols (CITREM) and ammonium phosphatides (AP). All emulsifiers accelerated cocoa butter nucleation and growth from the melt, with PGPR showing the smallest enhancement. Lecithin and AP minimally affected the polymorphic form IV-to-V transition contrary to PGPR and CITREM, whichboth promoted the formation of form V crystals. The presence of sugar alone accelerated cocoa butter solidification while limiting the ability of the emulsifiers to do so. Sugar alone, and in the presence of emulsifier, hindered the polymorphic form IV-to-V transition. This study shows that the effects of emulsifiers on the isothermal crystallization of cocoa butter can be muted in the presence of crystalline sugar, suggesting a complex interplay dependent on emulsifier molecular structure.

Destructuring and restructuring of foods during gastric digestion.

All foods harbor unique length scale-dependent structural features that can influence the release, transport, and utilization of macro- or micronutrients in the human gastrointestinal tract. In this regard, food destructuring and restructuring processes during gastric passage significantly influence downstream nutrient assimilation and feelings of satiety. This review begins with a synopsis of the effects of oral processing on food structure. Then, stomach-centric factors that contribute to the efficacy of gastric digestion are discussed, and exemplified by comparing the intragastric de- and restructuring of a number of common foods. The mechanisms of how intragastric structuring influences gastric emptying and its relationship to human satiety are then discussed. Finally, recently developed, non-destructive instrumental approaches used to quantitively and qualitatively characterize food behavior during gastric destructuring and restructuring are described.

Effect of Increasing the Dietary Protein Content of Breakfast on Subjective Appetite, Short-Term Food Intake and Diet-Induced Thermogenesis in Children.

Dietary protein affects energy balance by decreasing food intake (FI) and increasing energy expenditure through diet-induced thermogenesis (DIT) in adults. Our objective was to investigate the effects of increasing the dietary protein in an isocaloric breakfast on subjective appetite, FI, blood glucose, and DIT in 9-14 y children. Two randomized repeated measures designs were used. In experiment 1, 17 children (9 boys, 8 girls) consumed isocaloric meals (450 kcal) on four separate mornings containing: 7 g (control), 15 g (low protein, LP), 30 g (medium protein, MP) or 45 g (high protein, HP) of protein. Blood glucose and subjective appetite were measured at baseline and regular intervals for 4 h, and FI was measured at 4 h. In experiment 2, 9 children (6 boys, 3 girls) consumed the control or HP breakfast on two separate mornings, and both DIT and subjective appetite were determined over 5 h. In experiment 1, all dietary protein treatments suppressed subjective appetite compared to control (p < 0.001), and the HP breakfast suppressed FI compared with the LP breakfast and control (p < 0.05). In experiment 2, DIT was higher after HP than control (p < 0.05). In conclusion, increasing the dietary protein content of breakfast had favorable effects on satiety, FI, and DIT in children.

Effect of White Potatoes on Subjective Appetite, Food Intake, and Glycemic Response in Healthy Older Adults.

The objective of this study was to determine the effect of white potato cooking methods on subjective appetite, short-term food intake (FI), and glycemic response in healthy older adults. Using a within-subject, repeated-measures design, 20 participants (age: 70.4 ± 0.6 y) completed, in random order, five treatment conditions: three potato treatments (baked potatoes, mashed potatoes, and French fries), an isocaloric control treatment (white bread), or a fasting condition (meal skipping). Subjective appetite and glycemic response were measured for 120 min using visual analogue scales and capillary blood samples, respectively. Lunch FI was measured with an ad libitum pizza meal at 120 min. Change from baseline subjective appetite (p < 0.001) and lunch FI (p < 0.001) were lower after all test treatments compared with meal skipping (p < 0.001), but did not differ among test treatments. Cumulative FI (test treatment + lunch FI) did not differ among treatment conditions. Blood glucose concentrations were higher after all test treatments compared with meal skipping (p < 0.001), but were not different from each other. In healthy older adults, white potatoes suppressed subjective appetite and lunch FI compared with meal skipping, suggesting white potatoes do not bypass regulatory control mechanisms of FI.

Displacement of interfacially-bound monoglyceride crystals in water-in-oil emulsions by a non-ionic surfactant.

HYPOTHESIS: Micron and nano-scale particles are increasingly used to stabilize water-in-oil (W/O) emulsions. Though remarkably stable, the resulting emulsions can be broken by adding low molecular weight surfactants that modify the wettability of the interfacially-adsorbed particles. EXPERIMENTS: W/O emulsions were prepared using lipophilic crystals of the monoglyceride glycerol monostearate (GMS), followed by addition of sorbitan monooleate (SMO) at concentrations below and above its critical micelle concentration (CMC). Systematic measurements of interfacial tension and three-phase contact angles, as well as characterization of emulsion sedimentation and microstructure, were used to assess GMS crystal wettability and emulsion destabilization. FINDINGS: GMS crystals formed shells around the dispersed droplets, resulting in emulsions stable against breakdown under quiescent conditions. With SMO concentrations added below CMC, emulsion stability was not significantly affected. At SMO concentrations above CMC, the integrity of the crystalline shell was markedly affected. Notably, the GMS crystals transitioned from preferential oil-wet to water-wet behavior, eventually leading to their diffusion into the droplets. Therefore, in-situ modification of particle wettability at the oil-water interface was responsible for emulsion breakdown. Findings from this study may provide a pathway for the design of particle-stabilized W/O emulsions with controllable breakdown properties for applications such as tailored release of aqueous bioactive compounds.

Morphology and Structure of Solid Lipid Nanoparticles Loaded with High Concentrations of ß-Carotene.

Solid lipid nanoparticles (SLNs) containing up to 37.5 wt % all-trans ß-carotene in the lipid phase are potential water-dispersible food colorants. SLNs have been made by hot-melt high-pressure homogenization with fully hydrogenated sunflower oil and with polysorbate 80 and sunflower lecithin as stabilizers. Atomic force microscopy revealed the SLNs had thin platelet structures most likely derived from the triglyceride crystal ß-form, as detected by X-ray diffraction. No indications of crystalline ß-carotene were detected. High-performance liquid chromatography analysis showed the extensive isomerization of ß-carotene into more than 10 cis isomers, suggesting that it is present as an amorphous mixture. The high ß-carotene loadings did not affect the triglyceride crystal structure and the morphology of the SLNs. It is suggested the SLNs consist of a platelet core of crystalline triglyceride surrounded by an amorphous ß-carotene-containing layer. The layered structure is suggested to affect the coloring power of the SLNs at ß-carotene loadings above 15 wt % of the lipid phase.

Interfacial ordering of tristearin induced by glycerol monooleate and PGPR: A coarse-grained molecular dynamics study.

We use coarse-grained molecular dynamics simulations to study the effect of surfactant structure on the ordering of bulk tristearin at an oil-water interface. In the absence of surfactant, tristearin acyl chains are marginally aligned normal to the interface. The surfactant glycerol monooleate (GMO), a common small-molecule monoacylglycerol (MW: 357 g/mol), preferentially adsorbs to the oil-water interface, displacing more of the tristearin as its concentration increases. The tristearin that remains at the interface is closely aligned normal to the interface. Adjacent to the interface, bulk tristearin increasingly aligns with its acyl chains entwined with the GMO acyl chain, which also preferentially aligns normal to the interface. In contrast, polyglycerol polyricinoleate (PGPR), a bulkier, polymeric surfactant (MW: 1398 g/mol for a molecule with five monomers), both displaces tristearin from the interface and reduces the alignment of the molecules that remain. We suggest that the similar fatty acid moieties of GMO (oleic acid) and tristearin (stearic acid) lead to liquid-state association and alignment, the latter of which can then serve as a template onto which tristearin crystals can nucleate. Conversely, by both displacing tristearin from the interface and reducing alignment below that of the surfactant-free system, PGPR eliminates the possibility of tristearin interfacial crystallisation.

Oleogelation of emulsified oil delays in vitro intestinal lipid digestion.

Oleogelation is shown to delay the in vitro digestion of soybean oil (SBO) dispersed within an oil-in-water (O/W) emulsion. Rice bran wax (RBX) was used as an oleogelator at concentrations of 0, 0.25, 0.5, 1 and 4 wt% of the emulsions. All emulsions, which contained 1 wt% whey protein and 20 wt% oil and were prepared via hot homogenization, were kinetically stable against phase separation during the experimental timeframe (4 weeks), except at 4 wt% RBX where wax crystals 3-5 µm in length appeared within the dispersed oil phase, and which resulted in some emulsion instability. Rheological and thermal analysis of the emulsions and their corresponding SBO-RBX blends showed that the RBX led to formation of rigid oil droplets. Both in vitro gastric and intestinal digestion resulted in extensive oil droplet coalescence in all emulsions. Free fatty acid (FFA) release profiles showed that dispersed phase oleogelation delayed intestinal lipid digestion, with this effect enhanced up to 1 wt% RBX. A further increase to 4 wt% increased the rate of lipid digestion, which was ascribed to emulsion instability resulting from growth of intra-droplet RBX crystals.

Regression modelling of the impact of confectioner's sugar and temperature on palm oil crystallization and rheology.

The relationship between microscopic and macroscopic properties in fat-continuous dispersions is multifaceted compared to bulk oils, which limits the ability to extrapolate results from bulk systems towards complex formulations. The impact of confectioner's sugar on the crystallization and rheology of palm oil (PO) and mid-fraction blend (PMF) was investigated in this study. Adding sugar significantly increased storage modulus (G') and firmness (F) of the oils while exhibiting increased sensitivity towards processing conditions. Multiple regression analysis was used to create predictive models that correct for the effects caused by confectioner's sugar, such as altered fat crystal morphology and increased network rigidity, through the binary variable ζ. With limited studies on the use of PO in confectionery applications, these models may be used by industry as tools for production that do not rely on anecdote and overcome any shortcomings associated with the extrapolation from bulk systems.

Structure and rheology of oleogels made from rice bran wax and rice bran oil.

Structural and rheological properties of oleogels consisting of 0.5-25 wt% rice bran wax (RBX) in rice bran oil (RBO) were explored. RBX was an efficient, thermoreversible oleogelator capable of structuring RBO at concentrations as low as 0.5 wt% RBX. A qualitative temperature-composition phase diagram showed that oleogels containing higher concentrations of RBX were expectedly the most resistant to melting. In oleogels at higher RBX concentrations, polarized light microscopy revealed the presence of a network of interlinked, long aspect ratio wax crystal needles up to 50 µm long. Upon heating, RBX crystals did not undergo any structural transition, based on the constant short spacings at ~ 4.16 and ~ 3.73 Å, indicative of an orthorhombic subcell, and d001 long spacing at 74-76 Šthat persisted until RBX fusion. This long spacing was ascribed to the presence of wax esters consisting of long-chain saturated fatty acids (C24 and C22) esterified to C28 - C34 saturated fatty alcohols. During cooling from 90 to 20 °C, the increase in oleogel viscosity resulting from the RBX liquid-solid phase transition was corroborated by DSC-based crystallization onset and enthalpy data. Similarly, elastic moduli and hardness both rose with increasing RBX concentration. This study, which demonstrated that RBX can structure RBO with distinct concentration-dependent properties, serves as the foundation for the development of oleogel-based approaches to saturated and trans fats replacement in processed foods.

Effect of Emulsifier Concentration and Physical State on the In Vitro Digestion Behavior of Oil-in-Water Emulsions.

The influence of emulsifier physical state and concentration on the in vitro digestion of oil-in-water (O/W) emulsions was investigated. Two citrated monoacylglycerols, glyceryl stearate citrate (GSC, bulk mp of 55-65 °C) and glyceryl oleate citrate (GOC, bulk mp of 0-10 °C), were used at 0.5 or 5 wt % of the emulsions to generate 20 wt % soybean oil O/W emulsions. Oil droplet lipolysis was slower in emulsions with 0.5 wt % emulsifier versus in those with 5 wt % emulsifier, resulting from the reduced surface-to-volume ratio in emulsions at 0.5 wt % emulsifier and the increased concentration of hydrolyzable groups at 5 wt % emulsifier. When excluding gastric digestion, all emulsions were similarly digested, confirming that emulsion intestinal digestion was highly dependent on gastric preprocessing. Finally, at a given emulsifier concentration, GSC-based emulsions with an interfacial crystalline shell experienced a decreased rate of intestinal lipid digestion compared with their GOC-based counterparts, confirming that emulsifier physical state played a role in lipid digestion.