Goal: When you have finished this laboratory exercise you will understand
- the quality changes occurring in frozen foods during different stages of food distribution
and you will learn
- about the effects of the time and temperature on the frozen food product quality at different stages of the cold chain.
The quality of frozen foods is significantly influenced by the storage and transport conditions. The most detrimental factor is the storage temperature.
Major consideration must be given to using the lowest storage and transport temperatures that are feasible for extending the storage life.
Fluctuations in the temperature result in changes in product temperature, adversely affecting the quality and reducing the storage life of a food.
We have selected frozen strawberries and frozen chicken thighs for this experiment.
The experiments will be conducted at different times and temperatures during different stages of the frozen chain (producer, transport, wholesale, retail and finally home freezer) to obtain information on changes in food quality.
Freezing is the preferred method of food preservation when the quality maintenance of a food product is a key concern.
Frozen products are exposed to variable ambient conditions during freezing, storage or transportation resulting in the loss of quality. Therefore, with proper pre-freezing preparation and freezing techniques, the majority of quality deterioration is expected to occur during the distribution period.
The most important parameter resulting in adverse quality change is the cumulative effect of time and temperature change during storage condition.
The quality loss in frozen foods can be predicted using experimentally obtained data on acceptable time for storage and kinetic analysis of changes occurring during the frozen stage.
This laboratory exercise will involve quality changes in frozen strawberries and in frozen chicken thighs starting from the production stage to the home freezer.
Quality changes occuring during different stages of distribution will be determined to learn the effects of the time and temperature parameters on changes in the product quality.
Analysis of data will include investigating changes during different stages of a distribution protocol to identify stages where the major losses are occurring.
In this experiment, we obtained data on the quality loss in frozen strawberries and chicken thighs held under different temperatures and time periods.
Using the data we will
1. Investigate the changes in individual stages to identify where the major losses are occurring.
2. Investigate the combined effects of time and temperature on the percent quality losses. We will note that a reduction of either storage temperature or time in the identified stage can help reduce the quality loss for a given product.
- In your experiments, during which stage did the major quality losses occur in the frozen strawberries and in the frozen chicken thighs. Did these changes occur at the same stage or different? Why?
- Review published literature to identify and discuss key reactions that cause loss in quality of frozen strawberries and chicken thighs.
- Why is it necessary to determine the "cumulative" effect of time and temperature on product quality?
- Almonacid-Merino, S.F., and Torres, J.A. (1993). Mathematical models to evaluate temperature abuse effects during distribution of refrigerated solid foods. J. Food Eng. 20: 223-245
- Bhattacharya, M., Langstaff, T.M., and Berzonsky, W.A. (2003). Effect of frozen storage and freeze-thaw cycles on the rheological and baking properties of frozen doughs. Food Res. Int. 36: 365-372.
- Giannakourou, M.C. and Taokis, P.S. (2003). Kinetic modeling of vitamin C loss in frozen green vegetables under variable storage conditions. Food Chem. 83: 33-41.