Dispersed phase design for improved low-calorie chocolate

Chocolate represents a structured material with a continuous phase of crystallised cacao butter in which sugar crystals, non-fat cocoa solids and milk solids (in case of milk chocolate) are dispersed. In its molten state chocolate can be described as a suspension containing several dispersed, solid phases which affect the flow behaviour with their volume fraction, specific size, shape and surface property characteristics. In conventional chocolate the fat content, is about 30 %wt which equates to a dispersed phase volume of solids of about 0.45. Decreasing the fat content, i.e., increasing the dispersed volume fraction, to obtain a less calorific chocolate is not a viable option since the accompanied increase in viscosity of the chocolate in its molten state will impact negatively on the processing behaviour and sensory characteristics . However, it is possible and has been demonstrated, to modulate the particle size distribution to achieve more efficient packing of the particles and, hence, higher volume fractions without affecting the viscosity behaviour to an undesirable extent. The drawback of this approach is that particles above the generally accepted size limit above which grittiness tends to be observed during consumption is well exceeded. Other methods such as substituting the fat phase by a water-in-oil emulsion, use of fat replacers such as Salatrim for 'direct' removal or replacement of fat, and the use of increased emulsifier levels including emulsifier blends to allow for an increased solids content by increasing interparticle lubrication to maintain an acceptable viscosity level, have sensory properties or consumer acceptance negatives associated with them. In this industrial case project we propose investigating innovative approaches for the dispersed phase design to formulate low calorie chocolate hypothesised on overcoming the limitations outlined above. Initially, we will build on our previous work on modulating the particle size distribution of the filler phase by introducing a novel soft solid filler phase. It is hypothesised that the grittiness threshold for solid filler particles does not apply to soft solid particles. This needs to be tested. The type of soft solid particles we propose introducing are hydrocolloid or protein based dry particles that swell and become 'soft' in mouth. This may be achieved with conventionally available material, or powders that have undergone extrusion processing for physical modification. For example, for a conventional xanthan gum requiring high shear input for dispersion and subsequent dissolution in water, it has been shown extrusion processing imparts a rapid swelling and dispersing characteristics. In this project we propose exploring whether extrusion in a lipophilic phase that may or may not be miscible with cacao butter will produce swellable soft particles. A further novel filler phase that may be introduced into chocolate is a second non-aqueous liquid phase which may or may not need stabilisation by suitable emulsifiers. In its molten state the chocolate then will have a dispersed droplet phase and a dispersed solid phase, i.e., it will be a hybrid between an emulsion and a suspension. We will study the rheological behaviour of such a material, which has scarcely been reported, based on a simplified chocolate model system. Finally, we will investigate whether the non-fat cocoa solids phase has potential for exploitation. There is a lack of understanding of the role non-fat cocoa solids play from a material science point of view which will be addressed. With an enhanced understanding, suitable, preferably physical, modifications may become obvious that will contribute to the design of an improved low calorie chocolate based on dispersed phase innovation design.