Preparation and applications in confectionery of co-crystalline sugar products and a novel hydrated form of sucrose
The formation of the solid crystalline phase of sugars plays an important role in many food products. The conventional crystallisation of sucrose gives solid, dense cubic crystals that have a limited surface area. On the other hand, co-crystallisation of sucrose is a process where a second ingredient is added to a supersaturated sucrose solution before crystallisation. The crystals obtained reveal a sponge-like appearance with considerable void space and interstices with the additive ingredient located in these interstices. The crystalline sugar products are said to be dry, granular, free-flowing and readily dispersible in water. It was shown that the co-crystallisation process improves the properties of a product such as its solubility, wettability and emulsification. Even though a number of patents have been reported on the subject, little research works have been published. In particular, little information was available on the thermal properties of the materials formed and the crystalline characteristics of the agglomerate matrix. In a preliminary work, the co-crystallisation of sucrose with honey was investigated. The Differential Scanning Calorimetry (DSC) and X-ray analyses showed that neither glucose nor fructose crystallised during the process. Nevertheless, glucose crystallised in the monohydrate form upon storage when a granulated honey was used. In addition, different types of glucose were co-crystallised with sucrose in the proportions glucose-sucrose 10/90, 15/85 and 20/80. The DSC analysis showed varying crystallisation behaviour depending on the type of glucose used. The co-crystallisation of glucose with sucrose was extended to the proportions 85/15, 90/10 and 95/5. The process was adapted to glucose as main ingredient. During the characterisation of the co-crystalline materials by DSC, an extra peak around 150°C was observed that could not be assigned to the second ingredient added or to a new crystalline phase formed by the constituents of the materials. The study of different sources of sucrose showed different behaviours by DSC analysis concerning this first melting peak. It was found that the purest sugar in terms of mineral salt content gave the highest intensity for this peak at 150°C. Further work under specific conditions of temperature and relative humidity permitted to isolate this phase believed to be due to a hydrated form of sucrose. Finally, the process of co-crystallisation of glucose with sucrose was scaled up to 5kg. The DSC traces showed that the ingredient present in minority did not crystallise during the process and remained in the amorphous form even after several months of storage. The materials thus prepared were used in confectionery applications. A co-crystalline material containing 10% of glucose was tested in chocolate but proved to thicken it up. This result was believed to be due to the porosity of the co-crystalline product. As a consequence, its potential for fat retention was studied. The co-crystalline material was found to reduce the migration of hazelnut oil in a dark chocolate coating. Furthermore, pressed sweets were prepared with co-crystalline materials containing 10 and 90% of glucose respectively. They showed good tabletting properties even without the use of binding agent. The tablets prepared had a crushing strength similar to superior to those prepared with a granulated powder. They also showed good flavour retention.