Understanding the structure of chocolate

Edible mechanical metamaterials with designed fracture for mouthfeel control

Metamaterials can display unusual and superior properties that come from their carefully designed structure rather than their composition. Metamaterials have permeated large swatches of science, including electromagnetics and mechanics. Although metamaterials hold the promise for realizing technological advances, their potential to enhance interactions between humans and materials has largely remained unexplored. Here, we devise a class edible mechanical metamaterials with tailored fracture properties to control mouthfeel sensory experience. Using chocolate as a model material, we first demonstrate how to create and control the fracture anisotropy, and the number of cracks, and demonstrate that these properties are captured in mouthfeel experience. We further use topology optimization to rationally design edible metamaterials with maximally anisotropic fracture strength. Our work opens avenues for the use of metamaterials to control fracture and to enhance human-matter interactions.

Tailoring crystallization and physical properties of palm mid-fraction with sorbitan tristearate and sucrose stearate

This paper addresses sorbitan and sucrose ester in physical transformations of palm mid-fraction (PMF). Both emulsifiers influenced the crystallization properties of PMF, mainly due to emulsifier solubility, which affects its ability to interfere with the kinetics of solution-mediated phase transformations. DSC results corroborate the polymorphism analysis, indicating that the mechanism and rate of phase transformation depend on the chemical structure and amount of each emulsifier. The addition of sorbitan tristearate (STS) and sucrose stearate (S-370) increased the crystallization speed of the PMF and caused changes in the crystallization behavior. STS favored the β'→β transition, while S-370 stabilized the β'-form. We can conclude that the presence of emulsifiers dissimilar to the composition of PMF modified its physical structure, either by increasing the liquid fraction or by reducing molecular motion, facilitating or preventing polymorphic transformations.

Effect of solvent pre-treatment on the physicochemical, thermal profiles and morphological behavior of Mangifera pajang seed fat

In this work, the effect of solvent pre-treatment (hexane, petroleum ether and ethanol) on the physicochemical, thermal and morphology behavior of Mangifera pajang seed fat (MPSF) were investigated. Fat extraction was performed using Soxhlet method, and results showed that the yield, physicochemical, and crystalline structures of the MPSF were significantly (p < 0.05) influenced by the extraction solvents. Hexane gave the highest fat yield (7.67 %) with low unsaturation value (52.13 g iodine/g) compared with petroleum ether and ethanol. Hexane MPSF also had low oxidation rate (peroxide value of 1.1 mEq/g). Both non-stabilized and stabilized hexane MPSF showed a single melting endothermic peak at high temperature with onset, maximum peak and offset temperature of 16.23 ˚C-18.21 °C, 28.22 ˚C-31.25 °C and 34.85 ˚C-39.58 °C, respectively. Hexane MPSF crystallized rapidly at high temperature with single maximum peak starting at 16.51 ˚C-16.68 °C and ending at 0.23 ˚C-1.13 °C. In comparison with ethanol extract, hexane MPSF demonstrated a compact crystalline structure with a large densely packed center. Therefore, MPSF obtained from hexane presented better overall quality than those obtained from other extraction solvents. MPSF exhibited similar melting and morphological behavior to mango kernel fat and commercial cocoa butter. These results suggested that hexane was the best solvent for the extraction of MPSF. This fat also has the potential to be applied as a cocoa butter alternative fat or functional fat.

Development of a GC-FID method for the quantitative determination of polyglycerol polyricinoleate (PGPR) in foods

Polyglycerol polyricinoleate (PGPR) is a powerful lipophilic emulsifier used in low-fat spreads and chocolate. It should be used at the lowest level at which the desired technological effect is achieved, not exceeding the specified maxima according to Annexe II to Regulation (EC) No 1333/2008. A gas chromatography-flame ionisation detection (GC-FID) method was developed for quantification of PGPR. This method is based on estimating the content of ricinoleic acid using 12-hydroxyoctadecanoic acid as an internal standard, from which the PGPR concentration was deduced. The method involved saponification, methylation, a two-step solid phase extraction (SPE) separation of the fatty acid methyl esters (FAMEs), silylation, and GC-FID analysis. The limits of detection and quantification of ricinoleic acid were 2.2 and 6.7 μg/mL, respectively, at 0.1 µL injection volume. Considering the average content of ricinoleic acid in PGPR (i.e. 86.63 ± 2.0 wt%) and the amount of food product that is used in the proposed protocol (i.e. 20 mg), this resulted in a LOD and LOQ of 0.76 and 2.32 μg PGPR per mg of food product, respectively. The developed method was validated by determining PGPR recovery from a high oleic sunflower oil (HOSO) solution, from chocolate spiked with a commercially available PGPR, and from commercially available low fat spreads with a known PGPR content. The actual recovery was more than 95% for all matrices, indicating the accuracy of the developed analytical technique. Moreover, the method proved to be very reproducible, with RSD < 4% for concentrations ranging from 0.2 to 5 wt%. The results showed that our proposed GC-FID method enables the reliable and quantitative determination of the PGPR concentration in commercial food products with various fat contents.

Effects of Low-melting-point Fractions of Cocoa Butter on Rice Bran Wax-corn Oil Mixtures: Thermal, Crystallization and Rheological Properties

The fatty acid compositions, polymorphism, solid fat content (SFC), thermal properties, microstructure and rheological properties of fat blends of rice bran wax and corn oil (RWC) with low-melting-point fractions of cocoa butter (LFCB) in the range of 20-50% were investigated. With the raising content of LFCB, the hardness, SFC, storage modulus (G') and loss modulus (G'') of blend samples increased. The unsaturated fatty acids of blend samples with different LFCB proportion were in the range of 60.42% to 71.25%. Two kinds of polymorphism were observed in blend samples, which were β'-Form and β-Form. During the crystallization process, the rice bran wax was first crystallized, and then induced a part of LFCB formed β'-Form crystals and another LFCB formed the β-Form crystals. The results show that the addition of LFCB could improve the plasticity of fat blends and reduce the difference in properties between them and commercial shortening.

Heat resistant chocolate development for subtropical and tropical climates: a review

Heat resistant chocolate (HRC) which can retain the desired texture and mouthfeel in tropical and subtropical climatic conditions has become a major research area in the chocolate industry. Liking of the chocolate products keeps on changing with the geographical conditions of the world due to the availability of ingredients from local resources and consumer's taste preferences. The geographical changes also bring about the change in climatic conditions and as such no chocolates have been formulated to withstand the hot tropical or sub-tropical temperature conditions. Textural issues and various storage related problems faced due to meltability of chocolate in different countries has opened up a broad research field of sustainable HRC manufacturing. Over the years, there are broadly three different approaches (fat modification, sugar structure modification and innovative process approach) to develop the HRC and all these scientific approaches have given different scientific insights about improving the heat resistance characteristics and textural stability of chocolate. There is a lack or coordinated fundamental and applied research related to cocoa butter polymorphism, and thermal-textural issues during product development/storage. This review paper is an attempt to describe the different scientific approaches for developing HRC and how they affect the physical/sensory chocolate attributes.

Physicochemical characteristics of anhydrous milk fat mixed with fully hydrogenated soybean oil

There is a growing demand for fats that confer structure, control the crystallization behavior, and maintain the polymorphic stability of lipid matrices in foods. In this context, milk fat has the potential to meet this demand due to its unique physicochemical properties. However, its use is limited at temperatures above 34 °C when thermal and mechanical resistance are desired. The addition of vegetable oil hard fats to milk fat can alter its physicochemical properties and increase its technological potential. This study evaluated the chemical composition and the physical properties of lipid bases made with anhydrous milk fat (AMF) and fully hydrogenated soybean oil (FHSBO) at the proportions of 90:10; 80:20; 70:30; 60:40; and 50:50 (% w/w). The increased in FHSBO concentration resulted in blends with higher melting point, which the addition of 10% of FHSBO increase the melting point in 12 °C of the lipid base. Also, FHSBO contributed for a higher thermal resistance conferred by the coexistence of polymorphs β' and β, which remained stable for 90 days. Co-crystallization was observed for all blends due to the total compatibility of milk fat with the fully hydrogenated soybean oil. The results suggest a potential of all blends for various technological applications, makes milk fat more appropriate to confer structure, and improve the polymorph stability in foods. The blends presenting singular characteristics according to the desired thermal stability, melting point, and polymorphic habit.

Pre-crystallization process in chocolate: Mechanism, importance and novel aspects

Pre-crystallization is an important step in the production of chocolate, which is defined as tempering of cocoa butter through primary and secondary nucleation. The goal of tempering is to obtain a sufficient amount of β_V polymorph of the right size. The pre-crystallization process has a great impact on the quality and production cost of final product. Development of chocolate technology requires the use of the most appropriate techniques and ingredients without negatively affecting the quality characteristics. Applications of novel technologies within the confectionery industry have allowed production of chocolate in sufficient quantities to meet the public needs. In order to provide and investigate the potential and usage of novel technologies, the present review focused on different pre-crystallization methods and factors affecting the processing conditions. Seeding and ultrasound-assisted pre-crystallization can be used as alternatives to conventional tempering process. However, in both methods, optimization of experimental conditions is required.

Production and characterization of promising β-stable seed crystals to modulate the crystallization of fat-based industrial products

Spray cooling or spray chilling is a technique for obtaining solid lipid microparticles (SLMs) within the diameter range in micrometers using low temperatures and no organic solvents. It is a low-cost technique and is easy to scale-up. The production of SLMs into β-form represents a technological challenge due to the fast crystallization given by the spray cooling system, which generally results in SLMs crystallized into the metastable polymorphic form α. This study focuses on the production and characterization of SLMs by spray cooling using hard fat soybean oil (HS) added of D-limonene or canola oil, aiming to their application as β-seed crystals into lipid systems. The β-seed crystals could turn into an alternative lipid material to be used in fat-based products that present the preferential β' crystallization, like palm oil, increasing its compatibility with cocoa butter (CB) and allowing for the development of substitutes. The obtained SLMs showed spherical geometry and no agglomeration during storage at 25 °C for up to 30 days, verified by scanning electron microscopy (SEM). The mean diameters (D₅₀) were between 150 and 200 μm and the β' and β-form, determined by X-ray diffraction (XRD), appeared immediately after the crystallization process by spray cooling using HS added of 5% D-limonene (the HS control sample presented only the α-form). The SLMs of this study demonstrated their potential use as β-seed crystals into lipid systems.

Potential of Milk Fat to Structure Semisolid Lipidic Systems: A Review

Food production and consumption patterns have changed dramatically in recent decades. The universe of oils and fats, in particular, has been changed due to the negative impacts of trans fatty acids produced industrially through the partial hydrogenation of vegetable oils. Regulations prohibiting its use have led the industry to produce semisolid lipid systems using chemical methods for modification of oils and fats, with limitations from a technological point of view and a lack of knowledge about the metabolization of the modified fats in the body. Milk fat is obtained from the complex biosynthesis in the mammary gland and can be a technological alternative for the modulation of the crystallization processes of semi-solids lipid systems, once it is naturally plastic at the usual processing, storage, and consumption temperatures. The natural plasticity of milk fat is due to its heterogeneous chemical composition, which contains more than 400 different fatty acids that structure approximately 64 million triacylglycerols, with a preferred polymorphic habit in β', besides other physical properties. Therefore, milk fat differs from any lipid raw material found in nature. This review will address the relationship between the chemical behavior and physical properties of semisolid lipids, demonstrating the potential of milk fat as an alternative to the commonly used modification processes.

A full additive QM/MM scheme for the computation of molecular crystals with extension to many-body expansions

An additive quantum mechanics/molecular mechanics (QM/MM) model for the theoretical investigation of molecular crystals (AC-QM/MM) is presented. At the one-body level, a single molecule is chosen as the QM region. The MM region around it consists of a finite cluster of explicit MM atoms, represented by point charges and Lennard-Jones potentials, with additional background charges to mimic periodic electrostatics. Cluster charges are QM-derived and calculated self-consistently to ensure a polarizable embedding. We have also considered the extension to many-body QM corrections, calculating the interactions of a central molecule to neighboring units in the crystal. Full gradient expressions have been derived, also including symmetry information. The scheme allows for the calculation of molecular properties as well as unconstrained optimizations of the molecular geometry and cell parameters with respect to the lattice energy. Benchmarking the approach with the X23 reference set confirms the convergence pattern of the many-body extension although a comparison to plane-wave density functional theory reveals a systematic overestimation of cohesive energies by 6-16 kJ mol^-1. While the scheme primarily aims to provide an inexpensive and flexible way to model a molecule in a crystal environment, it can also be used to reach highly accurate cohesive energies by the straightforward application of wave function correlated approaches. Calculations with local coupled cluster with singles, doubles, and perturbative triples, albeit limited to numerical gradients, show an impressive agreement with experimental estimates for small molecular crystals.

Phase transitions in polymorphic materials probed using space-resolved diffusing wave spectroscopy

We use space-resolved dynamic light scattering in the highly multiple scattering regime (Photon Correlation Imaging Diffusing Wave Spectroscopy, PCI-DWS) to investigate temperature-induced phase transitions in polymorphic materials. We study paraffin wax as a simple model system and chocolate, a prototypical example of fat-based products exhibiting complex, history-dependent phase transitions. We find that microscopic dynamics measured using PCI-DWS show remarkable, non-monotonic behavior upon heating: they transiently accelerate when crossing phase transition and slow down above the transition temperature. Sub-micron resolution measurements of the local drift of the sample surface reveal that the speed-up of the dynamics is due to the strain field induced by the change in density at transition temperature. The transition temperatures obtained from PCI-DWS are found to be in excellent agreement with those inferred from complementary differential scanning calorimetry and X-ray scattering experiments, thereby validating PCI-DWS as a new, powerful tool for the characterization of phase transitions in complex soft matter. Finally, we demonstrate the unique possibilities afforded by space-resolved DWS by investigating the spatially heterogeneous response of poorly manufactured or composite chocolate samples.

Effects of Fat Polymorphic Transformation and Nonfat Particle Size Distribution on the Surface Changes of Untempered Model Chocolate, Based on Solid Cocoa Mass

This study aims to understand the bloom process in untempered chocolate by investigating the polymorphic transformation of cocoa butter and changes in chocolate surface. Cocoa mass with varying particle size distributions (PSD) were used to produce untempered model chocolate. Optical microscopy showed that during 25 d of storage, the chocolate surface gradually became honeycombed in appearance with dark spots surrounded by white sandy bloom areas. In conjunction with X-ray diffraction this indicates that the polymorphic transformation of form IV cocoa butter to more stable form V crystals caused the observed surface changes with the most significant changes occurring within 6 d. As bloom developed the surface whiteness increased, but the PSD of nonfat particles showed limited impact on the changes in whiteness. Moreover, scanning electron microscopy showed separated fat crystals on fat-rich dark spots and empty spaces between particles in bloom areas suggesting redistribution of fat in the chocolate matrix.

PRACTICAL APPLICATION

The results reported in this work can facilitate the understanding of fat bloom formation in untempered chocolate with respect to the changes in microstructure and surface appearances. It also contributes to show the details of IV-to-V polymorphic transformation in the fat phase as time went by.

Delaying fat bloom formation in dark chocolate by adding sorbitan monostearate or cocoa butter stearin

Two formulations of dark chocolate were developed by adding cocoa butter stearin (CBSt) or sorbitan monostearate (SMS) and compared to a standard formulation in order to investigate fat bloom formation over time. Fat bloom was monitored by Whiteness Index (WI), melting behavior and polymorphism determinations, in bars stored during 90 days at 20 °C and under oscillating temperature between 20 and 32 °C. All samples stored at 20 °C did not develop fat bloom and the required β(V) form was maintained. Under oscillating storage condition, samples with CBSt (6.0%, w/w) and SMS (0.15%, w/w) delayed the surface fat bloom formation by at least 45 and 15 days, respectively, compared to standard chocolate, observed visually and through WI increments. The β(V) to β(VI) polymorphic transition correlated well with the WI, and also with changes in DSC thermograms, confirming the higher effectiveness of specific triacylglycerol (mainly StOSt) in delaying bloom formation.

On the quantitative phase analysis and amorphous content of triacylglycerols materials by X-ray Rietveld method

The characterization of fat components becomes very useful for formulation of shortening, margarines and fat products due to their unique properties of plasticity, texture, solubility, and aeration. However, X-ray diffraction experiments on such materials are usually limited to a qualitative evaluation of the polymorphic properties based only on the characteristic d-spacing peak intensities. In this work, interesting results based on the Rietveld Method have supported both a Quantitative Phase Analysis and Degree of Crystallinity study on industrial and academic appealing samples, such as triacylglycerol standards, fully hydrogenated vegetable oils (hardfats) and cocoa butter. This useful approach to the area of oils and fats can provide valuable information about the polymorphism and its relationship to the application of lipid materials in food science and technology. Here, the discrimination between β and β' polymorphs on samples made of mixtures or blended hardfats was attained, and the results have shown a relevant contrast in comparison to a purely qualitative approach. Assessment of amorphous content on cocoa butter samples was achieved by isolating its contribution from the total X-ray diffraction background via mathematical tools during the whole pattern fitting.

Cocoa butter symmetrical monounsaturated triacylglycerols: separation by solvent fractionation and application as crystallization modifier

Symmetrical monounsaturated triacylglycerols-also known as SUS (saturated unsaturated saturated triacylglycerols)-are the main triacylglycerols present in cocoa butter (CB), exhibiting decisive influence in the tempering process conditions and sensorial characteristics in chocolate products. CBs with lower amounts of SUS do not crystallize adequately in chocolate processing, generating a low quality product with higher susceptibility to fat bloom formation. In this context, fractions with higher contents of SUS triacylglycerols were obtained by solvent fractionation of cocoa butter, under four operating conditions varying crystallization temperatures (17, 18, 20 and 22 °C) and sample/acetone solvent ratios (1:7 and 1:5, in w/v). After solvent evaporation, CB fractions were evaluated in terms of triacylglycerol profile, solid fat content and melting point. The solvent fractionation performed at 17 °C with a 1:7 ratio of cocoa butter:acetone favored the separation of a higher concentrated SUS stearin (denominated as S17) with 7.1% increment in SUS triacylglycerols, mainly StOSt-1-stearyl-2-oleoyl-stearin (26.9%) and POSt-1-palmitoyl-2-oleoyl-stearin (45.0%). Additionally, S17 was added to pure cocoa butter at three different proportions of CB:S17 (95:5, 90:10 and 80:20, in w/w) and the blend was evaluated by isothermal crystallization (at 17.5 °C) and consistency (at 10, 15 and 20 °C). Compared to the pure cocoa butter, at 10 °C, the blend with 20% stearin (80:20) showed an increment of 67% in the consistency and considerable higher crystallization rates at 17.5 °C were found, confirming the potential contribution of the SUS triacylglycerols as crystallization modifiers of CB.

Crystallinity properties and crystallization behavior of chocolate fat blends

Cocoa butter (CB) provides unique crystallization characteristics to chocolates and confectionary products; hence, it is an important value-add product. However, other alternative fats that minimally affect the crystallization behaviour of chocolates and confectionary products are now being increasingly used. This study analyzed the crystallization behaviour of CB, cocoa butter substitutes (CBSs), and their blends. Blends were prepared using CBS concentrations: 5, 10, 15, 20 and 37.5%. CB, CBS, and their blends were evaluated by following analysis: solid fat content, isothermal analysis, polarized light microscopic, thermal behaviour, X-ray diffraction and consistency. Crystallization analysis showed an incompatibility between the 2 fats, with a reduction in the crystallinity and increase in liquid content in all the blends. Eutectic crystallization at 20 °C was only observed for the blend containing 20% CBSs. This was considered as a positive result because previous studies have indicated that CBS concentration in CB blends should not be more than 5%.

Soft matter food physics--the physics of food and cooking

This review discusses the (soft matter) physics of food. Although food is generally not considered as a typical model system for fundamental (soft matter) physics, a number of basic principles can be found in the interplay between the basic components of foods, water, oil/fat, proteins and carbohydrates. The review starts with the introduction and behavior of food-relevant molecules and discusses food-relevant properties and applications from their fundamental (multiscale) behavior. Typical food aspects from 'hard matter systems', such as chocolates or crystalline fats, to 'soft matter' in emulsions, dough, pasta and meat are covered and can be explained on a molecular basis. An important conclusion is the point that the macroscopic properties and the perception are defined by the molecular interplay on all length and time scales.

The effect of formulative parameters on the size and physical stability of SLN based on "green" components

Cocoa butter (CB) is a largely used excipient in pharmaceutical field. Aim of this work was to set formulative parameters for the preparation of SLN based on "green" lipid matrix for drug delivery as natural, both human and environmental safe systems. Double emulsion technique (w1/o/w2) was selected for SLN preparation. The effect on the dimensional properties of different surfactants (Tween 80 and PEG 40 monostearate) and co-surfactants (PEG400 monostearate, Emulium® Kappa2 and Plurol®Stearique) at different concentrations was evaluated. Stability tests were performed. SLN dispersions were exsiccated and the effect of the dried process on SLN size was evaluated. The influence of temperature on SLN dimensions was investigated at 37 °C. MTT test was performed on raw materials and formulations. The w1/o/w2 is suitable, rapid and economic technique for the preparation of CB SLN. Tween 80-Plurol Stearique combination gives the best results: particles size less than 400 nm and PI of about 0.4 are obtained when PS 2% is used. Both raw materials and formulations are safe. The importance to evaluate the effect of different surfactant and/or co-surfactant on the dimensional properties of SLN is evident by selecting substances with preferable safety profiles, and favorable environmental properties to develop stable "green" SLN.

Crystallization modifiers in lipid systems

Crystallization of fats is a determinant physical event affecting the structure and properties of fat-based products. The stability of these processed foods is regulated by changes in the physical state of fats and alterations in their crystallization behavior. Problems like polymorphic transitions, oil migration, fat bloom development, slow crystallization and formation of crystalline aggregates stand out. The change of the crystallization behavior of lipid systems has been a strategic issue for the processing of foods, aiming at taylor made products, reducing costs, improving quality, and increasing the applicability and stability of different industrial fats. In this connection, advances in understanding the complex mechanisms that govern fat crystallization led to the development of strategies in order to modulate the conventional processes of fat structuration, based on the use of crystallization modifiers. Different components have been evaluated, such as specific triacyglycerols, partial glycerides (monoacylglycerols and diacylglycerols), free fatty acids, phospholipids and emulsifiers. The knowledge and expertise on the influence of these specific additives or minor lipids on the crystallization behavior of fat systems represents a focus of current interest for the industrial processing of oils and fats. This article presents a comprehensive review on the use of crystallization modifiers in lipid systems, especially for palm oil, cocoa butter and general purpose fats, highlighting: i) the removal, addition or fractionation of minor lipids in fat bases; ii) the use of nucleating agents to modify the crystallization process; iii) control of crystallization in lipid bases by using emulsifiers. The addition of these components into lipid systems is discussed in relation to the phenomena of nucleation, crystal growth, morphology, thermal behavior and polymorphism, with the intention of providing the reader with a complete panorama of the associated mechanisms with crystallization of fats and oils.