Economics and management in the sphere of ict department: management and marketing

Caramels, fondants and jellies as centres and fillings

W.P. (Bill) Edwards, in Science and Technology of Enrobed and Filled Chocolate, Confectionery and Bakery Products, 2009

7.2.3 Crystallisation

Sugar confectionery can be neatly divided into those products that are intended to crystallise and those that are not. Figure 7.1 shows the different sugar to glucose syrup ratios for a number of different products. In products that are intended to crystallise there is a high ratio of sugar to glucose while in those products where crystallisation is undesirable there is a much lower ratio. Where crystallisation has occured, the solid and the liquid phase will have different compositions. The factors that control the tendency to crystallise are the sucrose to glucose syrup solids ratio, the total solids and the temperature.

Fig. 7.1. Different sugar to glucose syrup ratios for a number of different products.
The horizontal line between 70 and 80% soluble solids represents the stability, that is, the solids should be above this line to avoid biodeterioration. Products that are intended not to grain, for example high boilings are made with sucrose to glucose ratios at the left of the diagram. Products like fudge and fondant paste are on the right of the diagram. Toffees, gums and pastilles occupy the middle of the diagram as non-crystallising products. Nougat is an unusual product, as some varieties do not grain while other varieties do grain. Clearly the non-graining nougats are to the left of the diagram while the graining varieties are to the right.

Glass Transition and Crystallization in Foods

Yong Wang, Tuyen Truong, in Non-Equilibrium States and Glass Transitions in Foods, 2017

7.2.3 Glass Transition and Crystallization of Sugar Mixtures

Many sugar products are used in mixture to achieve desirable taste or texture of food. Thus the kinetics of glass transition and crystallization in sugar mixture has been investigated in a wide range. Aiming to inhibit the crystallization in dried products by raising T_g through the addition of high molecular weight compounds, mixing the crystallizing sugar with other substances effectively reduces crystallization rate (Meste et al., 2002). The crystallization temperature (T_cr) is higher in lactose/trehalose systems than pure lactose or trehalose, because the molecules of lactose and trehalose in binary sugar systems need more energy to form stable nucleus due to molecular interactions (Fan and Roos, 2016a). However, the T_g almost remained constant when the composition changed in lactose/trehalose mixtures comparing with either pure lactose or trehalose. When the concentration of lactose increased gradually from 0% to 100% in the mixture of lactose/sucrose, the temperature difference of T_cr − T_g also increased from 64°C to 76°C (Arvanitoyanis and Blanshard, 1994). Mazzobre et al. (2001) found only one glass transition temperature in the thermograms of low moisture lactose-trehalose mixtures, which indicated the compatibility among the two sugars. Addition either of lactose, trehalose, or raffinose could increase the crystallization temperature of sucrose for about 30°C, when the additive sugar comprised 10% of the mixture (Saleki-Gerhardt and Zografi, 1994). The sugar additives can accumulate at the solid-particle interface as an adsorbed layer, which might be the reason to inhibit any nucleation that initiated on the surface of the particle. Additive levels of 10 and 20% (w/w) of corn syrup solids and their fractions interfered with crystallization of amorphous sucrose, whereas levels 50% of corn syrup prevented crystallization of sucrose (Gabarra and Hartel, 1998). An increased ratio of raffinose or trehalose in the sugar mixture system containing sucrose increased the glass transition temperature and decreased the melting enthalpy, enhancing sucrose stability (Amaro et al., 2015).
Crystallization of amorphous sugars was assumed to begin as the material is transformed from glass into the rubber at T_g, and proceed with a rate determined by T − T_g (Roos and Karel, 1992). At temperatures close to T_g, the crystallization time was too long for practical purposes for lactose and 8:2 lactose-trehalose mixtures in freeze-dried systems, and at temperatures near (T_g + 60°C) almost instantaneous crystallization occurred (Mazzobre et al., 2003). It is beneficial for the food industry to develop methods that delay or avoid sugar crystallization during storage conditions that regularly would allow the amorphous system to crystallize. Since the rubbery state above the glass transition temperature was metastable, a supercooled liquid-like state, and the state of crystallization depends on viscosity (Roos and Karel, 1991). Ebrahimi et al. (2015) investigated the highly-porous lactose by using sucrose, glucose, or fructose as templating agent, which resulted in a decrease in the glass-transition temperatures of the spray-dried mixtures, and lead to higher values for T − T_g and higher crystallization rates for lactose during spray drying. Fructose was reported to be able to delay the crystallization of amorphous sucrose probably because of increased viscosity above glass transition temperature. Since fructose increased crystallization temperature of sucrose about 30°C, and the crystallization exotherms were also broad showing delayed crystallization (Roos and Karel, 1991). This phenomenon has been utilized in the manufacture of hard candy by using the mixture of sucrose and fructose.