Thermal Characterization of Food Products

Introduction 

“Jelly bears”, the well-known German “Gummibären”, are similar to the English “jelly baby” sweets in appearance, taste and consistency.

They are ideal products with which to demonstrate the potential applications of thermal analysis in the food industry. Between their production date and the time when they are finally eaten, jelly bears are exposed to widely different conditions such as temperature fluctuations, different frequencies, mechanical stress and different media.

These changing conditions can be simulated using thermal analysis instrumentation and the properties of the product determined from the measurement results.

Jelly bears consist mainly of gelatin, a protein product, and different types of sugar. The carbohydrate content can be up to 78 percent by weight.

Due to the fact that the raw mass is obtained by heating the different ingredients and that the mechanical properties of the finished products contribute decisively to their enjoyment and taste, thermal analysis can provide an important contribution to maintaining constant quality and for the optimization of the production and the product properties.

Experimental Details

Two different sorts of jelly bears manufactured in different countries were used as samples and are referred to as Sample A and Sample B. The samples were stored in a refrigerator prior to use. To eliminate the possible influence of different additives such as colorants, only red jelly bears were analyzed. The following thermal analysis instruments were used:

• DSC822^e with IntraCooler
  
• TGA/SDTA851^e
  
• TMA/SDTA841^e with automated liquid nitrogen cooling
  
• DMA/SDTA861^e 

DSC and TGA measurements were performed using 40-µL aluminum crucibles with pierced lids. Small sample quantities were used for the TGA measurements because the samples tended to foam at the onset of decomposition.

Results 

DSC

Figure 1 shows the DSC measurement curves of Samples A and B. One of the samples (Sample B) was also dried in air for half a day before measurement. All three curves showed a glass transition, a broad endothermic peak corresponding to the loss of moisture, and endothermic behavior at the end of the measurement due to decomposition. The glass transition temperatures of the two fresh samples at about −25 °C differ only slightly. The moisture content of Sample A was about 25% higher than that of Sample B. This can be seen from the normalized integral of the peak area. All three samples decompose at about 112 °C. The moisture content of the dried sample is lower. This is apparent from the smaller normalized peak area and the higher glass transition temperature, T_g, of −19 °C. Water acts as a plasticizer in this material, so the drier the sample, the higher the T_g

TGA

The mass loss of Sample B as a function of temperature was measured by TGA (Fig. 2). The vaporization process below 100 °C is followed by a multi-step decomposition process beginning at 112.7 °C. This value is in good agreement with the onset of decomposition determined by DSC.

TMA 

The glass transition can also be measured by TMA. In this technique, the glass transition is observed as a change in the linear coefficient of expansion of the material as it changes from the glassy to the rubbery state.

Summary

Two different sorts of jelly bears were analyzed using four different thermal analysis techniques. DSC and TMA were used to determine glass transition temperatures. The values obtained depend on the moisture content. This can be determined using TGA and DSC, which also allow the onset of decomposition to be determined

The most interesting results with respect to the end use (consumption) of jelly bears were obtained from the mechanical methods TMA and DMA. The swelling behavior in liquid media and creep behavior were determined by TMA, and the frequency-dependent behavior could be predicted from the DMA measurements. Table 1 summarizes the measurement results obtained with the four techniques

_{Thermal Characterization of Food Products | Thermal Analysis Application No. UC 244 | Application published in METTLER TOLEDO Thermal Analysis UserCom 24}