With an increasing consumption of lipids nowadays, decreasing the fat content in food products has become a trend. Chocolate is a fat-based suspension that contains about 30%wt fat. Reducing fat content causes an increase in the molten chocolate viscosity. This leads to 2 major issues: difficulties in the process and a loss of eating quality in the final product, reported to have poor in-mouth melting properties, remain hard, and difficult to swallow. Literature shows that optimizing the particle size distribution (PSD), that is, having one with an increased packing fraction, can decrease the viscosity of highly concentrated suspensions. This study focuses on the impact of the PSD and fat content on the rheological properties, melting behavior, and hardness of chocolate models (dispersions of sugar in fat). We show that optimizing the PSD while reducing the fat content to a critical amount (22%wt) can decrease the viscosity of the molten material and reduce the hardness of the crystallized chocolate models. Melting in the mouth, characterized by an in vitro collapse speed, is faster for the samples with an optimized PSD. The decrease in the viscosity by optimizing the PSD in systems with a constant fraction of medium phase is based on the decrease of interparticle contact, reducing the particle aggregates strength, and structure buildup during flow or meltdown. In its crystallized state, the particle network is less interconnected, providing less resistance to breakage and meltdown.

The addition of limonene, a low molecular weight hydrophobic compound, to chocolate was reported to decrease the hardness and the viscosity of chocolate, facilitating the production and improving the eating quality of reduced fat chocolate. The objective of this study is to understand the functionality of limonene in decreasing the viscosity and the hardness of chocolate, a fat (cocoa butter)-based particulate suspension. This study shows that chocolate hardness was decreased because limonene mixes with cocoa butter, affects its crystallization pattern and decreases its solid fat content. After checking that limonene does not significantly affect the continuous phase volume fraction, we show that limonene decreases chocolate viscosity by decreasing the viscosity of the continuous phase, cocoa butter. The addition of low quantities of limonene in cocoa butter leads to a great decrease in the liquid fat viscosity. The dependence of the viscosity on the ratio of cocoa butter to limonene analyzed using Kay's equation seems to indicate that limonene mixes with and within the cocoa butter triglycerides, diluting the fat and leading to a decrease in the overall fat viscosity.