Shinichi Yoshikawa

The triacylglycerols (TAGs) containing saturated (S_at)‐unsaturated (U) fatty acid moieties (S_at‐U mixed acid TAGs) are widely present in most natural fats and employed in many industrial applications. The mixing behavior of different Sat‐U mixed acid TAGs acts important roles in the physicochemical properties TAG‐based materials. Among the three main mixing states of miscible, eutectic and molecular compound (MC) forming mixtures, fundamental research has been conducted on the MC crystals formed by different S_at‐U mixed acid TAGs to understand the structures, phase behavior and crystallization properties. This article reviews studies to date on the complex thermodynamic, kinetic and structural factors that affect the formation of MC crystals in binary and ternary mixtures of S_at‐U mixed acid TAGs (S_atUS_at, S_atS_atU, US_atU and UUS_at) through specific molecular interactions among the component TAGs. Furthermore, the application of the MC‐forming mixtures containing cacao butter to new types of cocoa butter alternative is reviewed.

Compound chocolates made of lauric-acid-based cocoa butter substitute (CBS) and cocoa butter (CB) often exhibit serious fat blooms caused by phase separation and polymorphic transformation of CB and CBS triacylglycerols. Herein, we found that the fat bloom of CBS-based chocolates could be completely inhibited by adding fat containing 1,3-dioleoyl-2-stearoyl-triacylglycerol (OSO) to CBS/CB blends. Unlike the CBS/CB chocolates that presented fat blooms within 3 wk under isothermal storage at 15, 20, and 25°C and 15 wk under thermal thawing storage at 15–25°C, no fat blooms appeared in the CBS/CB/OSO compound chocolates under any storage condition up to 6 months. The following key factors are involved in the addition of the OSO fats: the (1) concentration ratio of CB/OSO should be 1/1 such that CB/OSO can form molecular compound crystals and (2) total amount of CB+OSO in the CBS/CB/OSO blends should reach 20%. The solid fat content, hardness, and crystallisation rate of the CBS/CB/OSO blend-based chocolate compound were confirmed to be suitable for chocolate production.

This paper reports the precise analysis of the eutectic mixing behavior of 1,3-distearoyl-2-oleoyl-sn-glycerol (SOS) and trilaurin (LLL), as a typical model case of the mixture of cocoa butter (CB) and cocoa butter substitute (CBS). SOS was mixed with LLL at several mass fractions of LLL (w_LLL); the mixtures obtained were analyzed for polymorphic phase behavior using differential scanning calorimetry (DSC) and synchrotron radiation X-ray diffractometry (SR-XRD). In melt crystallization with constant-rate cooling, SOS and LLL formed eutectics in their metastable polymorphs, allowing the occurrence of a compatible solid solution at w_LLL ≥ 0.925. With subsequent heating, the resultant crystals transformed toward more stable polymorphs, then melted in a eutectic manner. For mixtures aged at 25 °C after melt crystallization, eutectics were found in the extended w_LLL region, even at w_LLL = 0.975. These results indicate that phase separation between SOS and LLL progressed in their solid solution under stabilization. The crystal growth of the separated SOS fraction may cause fat-bloom formation in compound chocolate containing CB and CBS. To solve this problem, the development of retardation techniques against phase separation is expected.

Some inorganic and organic crystals have been recently found to promote fat crystallization in thermodynamically stable polymorphs, though they lack long hydrocarbon chains. The novel promoters are talc, carbon nanotube, graphite, theobromine, ellagic acid dihydrate, and terephthalic acid, among which graphite surpasses the others in the promotion effect. To elucidate the mechanism, we investigated the influence of graphite surfaces on the crystallization manner of trilaurin in terms of crystal morphology, molecular orientation, and crystallographic features. Polarized optical microscopy, cryo-scanning electron microscopy, synchrotron X-ray diffractometry, and polarized Fourier-transform infrared spectroscopy combined with the attenuated total reflection sampling method were employed for the analyses. All the results suggested that the carbon hexagonal network plane of graphite surfaces have a high potential to facilitate the clustering of fat molecules against high thermal fluctuations in fat melt, the fat molecules form a layer structure parallel to the graphite surface, and the clusters tend to grow into thin plate crystals of the β phase at the temperatures corresponding to low supercooling. The β′ phase also has a larger chance to grow on the graphite surface as supercooling increases.

A new lipophilic spin-trapping flow-injection electron spin resonance (LFI-ESR) system was developed for quantitative detection of DMPO spin-adduct of alkoxyl radical (RO•), which was produced by thermal decomposition of an azo-initiator (AIBN) in ethyl acetate at 70 °C. The 50% and 75% inhibition dose (ID₅₀ and ID₇₅) of a series of lipophilic antioxidants, such as tocopherol derivatives (αToc, βToc, γToc, δToc, Toc, αTocM, βTocM, γTocM, TocM, TRX, and 7TocM), a lipophilic phenol (BHT), and unsaturated fatty acids (Ole, Lin, and Lic), were determined by monitoring the ESR signal intensity of the DMPO spin-adducts of RO• radical (DMPO/OR). On the basis of the observed ID₅₀ and ID₇₅ values, the lipophilic alkoxyl radical eliminating capacities (L-AREC) of these lipophilic antioxidants were determined using TRX as a standard. The evaluated L-AREC values are directly connected to the second order rate constants for the RO• radical induced hydrogen atom abstractions from the hydroxyl groups of the phenolic antioxidants, as well as from the allylic methylene groups of unsaturated fatty acids. The L-AREC values estimated by LFI-ESR method are concluded to be a practical and reliable indicator that reflect the inhibiting abilities of lipophilic antioxidants towards the radical chain reaction involved in the autoxidation processes of unsaturated fatty acids.

This paper reports the effects of adding talc particles on the physical properties of palm oil (PO)‐based shortening formed by working refined PO (RPO) after rapid cooling. We examined the thermal and viscoelastic behavior of RPO in bulk fat systems, and the polymorphism and hardness of the shortening in the presence and absence of talc particles. In addition, the microstructure of fat crystals formed was observed. The effects of talc addition are summarized as follows: (i) When RPO was cooled at a rate of 5°C/min, crystallization of the high‐melting fraction, including tripalmitoylglycerol (PPP) and 1,3‐dipalmitoyl‐2‐oleoyl glycerol (POP), was preferentially promoted to form small‐sized microcrystals. During cooling, the increase in the viscoelasticity of RPO was suppressed at low temperatures. (ii) When the shortening was stored at 5°C, β′‐crystallization of 1‐palmitoyl‐2,3‐dioleoyl glycerol (POO) and β‐crystallization, probably of a molecular compound (MC) of POP and 1,2‐dipalmitoyl‐3‐oleoyl glycerol (PPO), were delayed compared to β′‐crystallization of PPP and POP. During storage, the homogeneity of the fat crystal dispersion improved and the hardness of the shortening decreased. These results indicate that talc improved the physical properties of the PO‐based shortening by changing the crystallization kinetics and the networking processes of the fat crystals.Practical applications: The present study showed that adding talc particles effectively improved the physical properties of palm oil (PO)‐based shortening during storage. This is considered beneficial for resolving problems in the quality control of PO‐based products, such as post‐hardening and the formation of granular crystals due to low rates of crystallization.Storage modulus (G′) of refined palm oil (RPO) with and without talc particles in bulk fat systems, obtained from dynamic viscoelasticity measurements during cooling at a rate of 5°C/min. Adding talc particles drastically changed the three‐stage increases in G′ of pure RPO, promoting the first‐stage increase but suppressing subsequent increases at low temperatures.

We recently found that new types of additives including talc promoted the crystallization of monoacid saturated triacylglycerols (TAGs) in stable polymorphs. This study reports the effects of size and concentration of talc particles and cooling rate on the crystallization of trilauroylglycerol (LLL), tripalmitoylglycerol (PPP), and 1,3‐dipalmitoyl‐2‐oleoyl glycerol (POP). Talc particles were mixed with molten TAGs, and the mixtures were then cooled at designated cooling rates. Polymorphic crystallization was observed by simultaneous use of X‐ray diffractometry and differential scanning calorimetry and by polarized optical microscopy. The following results were obtained: (i) talc promoted the crystallization of LLL in stable polymorphs with decreasing particle size and increasing concentration; (ii) the promotional effects were influenced by the cooling rate; (iii) the same behavior was observed for PPP and POP; and (iv) hydrophobic modification of talc surfaces did not affect the promotional effects. These results indicate that talc particles having median sizes of less than 2.5 μm and concentrations exceeding 0.1 wt.% effectively promote fat crystallization, and that the promotional effects can be maximized by choosing proper cooling rates according to the target fats. Furthermore, we propose a model of the heterogeneous nucleation of TAG crystals taking account of the molecular adsorption on cleavage surfaces of talc.Practical applications: Talc is widely approved as a food‐grade ingredient, and the additive effects on various triacylglycerols widen its applicability to fat‐based food and cosmetic materials.With grinding, talc particles exhibit anisotropic surfaces: cleavage surfaces are hydrophobic, and edge (lateral) surfaces are hydrophilic. Hydrophobic modification of the edge surfaces does not affect the additive effects of talc particles on fat crystallization, indicating adsorption of fat molecules on the cleavage surfaces.