EC Nutrition

Freezing is a reliable method of extending the shelf-life of muscle-based foods but it is associated with quality deteriorations if subjected to temperature fluctuations during the period of storage. The product may undergo freeze-defrost cycles, and this is to be expected in retail outlets, restaurants and homes, in places of inconsistent power supply. This phenomenon of freeze-defrost cycles adversely affects the safety and quality of the final product, and is of great concern to national food safety control authorities and consumers. This paper is a review of the extent of damage to food quality as a result of freeze-defrost operations. Three major aspects of product deteriorations are involved, with one depending on the other to interdependently and synergistically impact the quality of the final product. These include physicochemical characteristics, biochemical quality and microbiological safety. Physicochemically, freeze-defrost cycles disrupt muscle structure and denature muscle proteins affecting water-holding capacity, nutritional value and pH. It is noteworthy that changes in pH can transform food to support the growth of some pathogenic microbes. Some quality char- acteristics that are influenced by enzyme and/or microbial activity with increased freeze-defrost cycles include discolouration and this is linked to protein oxidation, with corresponding accumulation of thiobarbituric acid reactive substances, a measure of oxidative rancidity. Total volatile basic nitrogen (TVB-N) is also a chemical marker of spoilage in muscle foods that results in changes in odour, flavour and texture, as a result of enzymatic break down of protein and other nitrogenous compounds. The concentration of TVB-N increases with increased enzyme and/or microbial activity, and this is characteristic of freeze-defrost operations. Freeze-defrost cycles are therefore detrimental to product quality. Efforts targeted at sustaining the cold chain in muscle foods will go a long way in maintaining product safety and quality characteristics comparable to that of a fresh product. Should the cold chain be interrupted, refreezing is not recommended because any damage caused is irreversible and also exponential.

 Keywords: Freeze-defrost cycles; muscle foods; muscle protein; microbial/enzyme activity; food safety and quality

1. Popelka , et al. “Comparison of chemical, microbiological and histological changes in fresh, frozen and double frozen rainbow trout (Oncorhynchus mykiss)”. Acta Veterinaria Brno 83 (2014): 157-161.
2. Katekhaye “Effects of freeze thaw cycles abuse and refrigerated thawing on microbial quality of chevon”. International Journal of Interdisciplinary and Multidisciplinary Studies 1.8 (2014): 76-79.
3. Szymczak “Comparison of physicochemical and sensory changes in fresh and frozen herring (Clupeaharrengus L.) during mari- nating”. Journal of the Science of Food and Agriculture 91.1 (2011): 68-74.
4. “Evaluation and definition of potentially hazardous foods”. chapter 3: Factors influence microbial growth (2015).
5. Freezing and thawing
6. Ali , et al. “Effects of multiple freeze-thaw cycles on the quality of chicken breast meat”. Food Chemistry 173 (2015): 808-814.
7. Huff-Lonergan E and Lonergan “Mechanisms of water-holding capacity of meat: the role of postmortem biochemical and

structural changes”. Meat Science 71.1 (2005): 194-204.

8. Moller JKS and Skibsed “Myoglobins-The link between discolouration and lipid oxidation in muscle and meat”. Quimica Nova

29.6 (2006): 1270-1278.

9. Akhtar , et al. “Effect of thawing on meat quality: a comprehensive review”. Pakistan Journal of Food Sciences 23.4 (2013):

198-211.

10. Baygar , et al. “Effects of multiple freezing and refrigerator thawing cycles on the quality changes of sea bass (Dicentrarchus labrax)”. Iranian Journal of Fisheries Sciences 12.12 (2013): 289-300.
11. Manheem , et al. “Impacts of freeze-thawing on melanosis and quality change of precooked pacific white shrimp”. International Food Research Journal 20.3 (2013): 1277-1283.
12. Benjakul S and Bauer “Biochemical and physicochemical changes in catfish muscle as influenced by different freeze-thaw

cycles”. Food Chemistry 72.2 (2001): 207-217.

13. Perez-Alvarez JA and Fernandez-Lopez “Chemical and biochemical aspects of color in muscle foods”. Handbook of Meat, Poultry and Seafood Quality (2012). Nollet LML (editor) 2^nd edn. John Wiley & Sons.
14. Boonsumrej , et al. “Effects of freezing and thawing on the quality changes of tiger shrimp (Penaeus monodon) frozen by air- blast and cryogenic freezing”. Journal of Food Engineering 80.1 (2007): 292-299.