Publisher Summary The crystalline structure of foods is important to product quality, texture, and stability. It is this crystalline structure and other structural elements that determine product appearance, mechanical properties during handling, mouthfeel during consumption, and shelf stability. To control crystallization, it is necessary to have an understanding of the phase behavior of the system, some knowledge of nucleation and growth kinetics, and the effects of both formulation and processing conditions on this kinetics. In foods, two circumstances for controlling the formation of crystals can be distinguished: those where the crystals provide an element of structure in the product and those where crystallization is a separation process. There are many factors that influence crystallization in food products. In many products, the goal of crystallization is to generate a certain texture or appearance that makes the product acceptable. Thus, nucleating many crystals that remain small within the product itself is often the goal. There must be many crystals with small mean size and narrow distribution. The crystals also must have the proper shape and/or polymorph to enhance stability of the product during storage and distribution. However, in other types of products, crystallization is undesired even though the system is supersaturated. In these cases, techniques are used to prevent crystallization from occurring during storage, because this leads to unacceptable product quality.

Crystallization in Foods

Numerical modelling technology offers an efficient and powerful tool for simulating the heating/cooling processes in the food industry. The use of numerical methods such as finite difference, finite element and finite volume analysis to describe the heating/cooling processes in the food industry has produced a large number of models. However, the accuracy of numerical models can further be improved by more information about the surface heat and mass transfer coefficients, food properties, volume change during processes and sensitivity analysis for justifying the acceptability of assumptions in modelling. More research should also be stressed on incorporation of numerical heat and mass transfer models with other models for directly evaluating the safety and quality of a food product during heating/cooling processes. It is expected that more research will be carried out on the heat and mass transfer through porous foods, microwave heating and turbulence flow in heating/cooling processes.

Recent developments in numerical modelling of heating and cooling processes in the food industry—a review

From hardening of marshmallow to graining of hard candies, moisture plays a critical role in determining the quality and shelf life of sugar-based confections. Water is important during the manufacturing of confections, is an important factor in governing texture, and is often the limiting parameter during storage that controls shelf life. Thus, an understanding of water relations in confections is critical to controlling quality. Water content, which is controlled during candy manufacturing through an understanding of boiling point elevation, is one of the most important parameters that governs the texture of candies. For example, the texture of caramel progresses from soft and runny to hard and brittle as the moisture content decreases. However, knowledge of water content by itself is insufficient to controlling stability and shelf life. Understanding water activity, or the ratio of vapor pressures, is necessary to control shelf life. A difference in water activity, either between candy and air or between two domains within the candy, is the driving force for moisture migration in confections. When the difference in water activity is large, moisture migration is rapid, although the rate of moisture migration depends on the nature of resistances to water diffusion. Barrier packaging films protect the candy from air whereas edible films inhibit moisture migration between different moisture domains within a confection. More recently, the concept of glass transition, or the polymer science approach, has supplemented water activity as a critical parameter related to candy stability. Confections with low moisture content, such as hard candy, cotton candy, and some caramels and toffees, may contain sugars in the amorphous or glassy state. As long as these products remain below their glass transition temperature, they remain stable for very long times. However, certain glassy sugars tend to be hygroscopic, rapidly picking up moisture from the air, which causes significant changes that lead to the end of shelf life. These products need to be protected from moisture uptake during storage. This review summarizes the concepts of water content, water activity, and glass transition and documents their importance to quality and shelf life of confections.

Moisture and Shelf Life in Sugar Confections

The smoothness and perceived quality of an ice cream depends in large part on the small size of ice crystals in the product. Understanding the mechanisms responsible for producing the disc-shaped crystals found in ice cream will greatly aid manufacturers in predicting how processing and formulation changes will affect their product. Because ice cream mix is opaque, it has not yet been possible to observe ice crystallization in ice cream in situ. Studies to date, therefore, have used analogues or have related observed effects to a hypothesized mechanism. Still, some elements of the crystallization mechanism are well accepted. Because of the large supercooling at the freezer wall, ice nucleates there before being swept into the bulk of the freezer. In the bulk, heat and mass transfer cause some crystals to melt and others to grow. By the time the ice cream reaches the freezer exit, the ice crystals have become small, rounded discs.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1541-4337.2009.00101.x

Mechanisms of Ice Crystallization in Ice Cream Production

Effects of freezing and temperature fluctuations during frozen storage on frozen dough and bread quality

Computer simulation of ice recrystallization in ice cream during storage

Three-dimensional model of phase transition of thin sucrose films during drying.

Sucrose crystal growth from stagnant sucrose syrups in thin films was monitored by videomicroscopy at different temperatures and concentrations in order to obtain sucrose crystal growth rates as a function of sucrose total solids at four temperatures (40, 55, 70, and 82 °C). Total solids were varied from 70% to 95%, creating supersaturation values (based on concentration units in weight percent) of 1.02−1.3 at each temperature. Growth rates for individual crystals at each temperature under stagnant growth conditions in thin films were monitored by an image analysis system for up to 30 min. Additionally, theoretical growth rates based on diffusion-limited sucrose growth models were obtained at the same temperatures. A concentration gradient model was compared to a model based on chemical potential differences. At 40, 55, and 70 °C, growth rates decreased at very high supersaturation values, whereas at 82 °C growth rates continued to increase with supersaturation (within experimental limits). The diffusion-...

Sucrose crystallization kinetics in thin films at elevated temperatures and supersaturations

Computer modeling of sugar crystallization during drying of thin sugar films

A computer simulation was developed to model drying, moisture sorption and crystallization, during processing and storage of confectionery products. The three-dimensional model analyzed simultaneously heat and moisture transfer, accounting for shrinkage, with temperature and moisture-dependent transport properties. Kinetics of crystal growth at different solution conditions were determined experimentally. Predicted crystal growth rates were evaluated from crystallization kinetics based on supersaturation, temperature, and state of the solution. The influence of growth on the solution concentration and drying rate were taken into account. The model predicted quality and storage stability based on correlations with the calculated sugar concentration, crystallinity and phase state. Simulation results were in agreement with theory and experimental results. Industrial relevance: The goal of this work was to develop a model for quality and storage stability determination of confectionary products using crystallization of sugar shell in hard panning process as example. The model developed can successfully predict the concentration profile and growth of sugar crystals in a thin film and it’s industrial relevance is evident by the industrial financial support.

E. Ben-Yoseph

Papers

Computer simulation of ice recrystallization in ice cream during storage

Three-dimensional model of phase transition of thin sucrose films during drying.

Sucrose crystallization kinetics in thin films at elevated temperatures and supersaturations

Computer modeling of sugar crystallization during drying of thin sugar films

Computer simulation of sugar crystallization in confectionery products