The effect of glaze on the quality of frozen stored Alaska pollack (Theragra chalcogramma) fillets under stable and unstable conditions
Peter Žoldoš, Peter Popelka, Slavomír Marcinčák, Jozef Nagy, Lýdia Mesarčová, Monika Pipová, Pavlína Jevinová, Alena Nagyová, Pavel Maľa
Acta Veterinaria Brno
Frozen fillets (n = 288) of Alaska pollack (Theragra chalcogramma) were used to evaluate the effect of glaze on lipid oxidation and microbiological indicators during 6 months of freezing storage under stable (−18 °C) and unstable temperature (varying from −5 to −18 °C) conditions. The amount of glaze, moisture, fat and protein content were measured. Despite the low fat content in Alaska pollack, a positive effect of glazing and stable freezing conditions of storage on the range of oxidative
... ges of lipids expressed as thiobarbituric acid reactive substances was found. Total counts of viable cells slightly rose before the end of the storage period in both groups with commercially glazed fish. The average counts of psychrotrophs in each group () were at the same level, ranging from 9.1 ×10 3 CFU·g -1 to 1.1 × 10 4 CFU·g -1 . According to the microbiological results fillets stored under unstable conditions were considered to be acceptable, but sensory evaluation showed that at the end of frozen storage they could not be consumed because of rancidity. Based on our results, glaze application ranged from 10 to 15% guarantee of final quality, however, prevention of temperature fluctuation during storage is important to keep the quality of the frozen fillets. This is the first similar study in Alaska pollack. Fish fillets, glazing, frozen storage, lipid oxidation, temperature fluctuation One of the main requirements in food industry is to improve the conservation technologies of perishable foods to reach a final product with optimal quality (Chevalier et al. 2000) . Freezing followed by cold storage is an efficient method of preservation; however, final quality depends on the initial conditions of foodstuff as well as other factors during freezing, cold storage, and distribution (Johnston et al. 1994) . The application of a layer of ice to the surface of frozen products by spraying, brushing on water or by dipping, is widely used to protect the product from the effects of dehydration and oxidation during cold storage. The ice layer sublimes instead of the fish below and it also excludes air from the surface of the fish and thereby reduces the rate of oxidation (Bogh-Sorensen 2002) . Good glazing practice can be beneficial, particularly when other aspects of storage and transport are far from ideal, but poor glazing involving partial thawing of the fish and slow refreezing in cold storage may do more harm than good (Johnston et al. 1994) . Although freezing is an effective method of preserving foods, some deterioration in frozen food quality occurs during storage. The extent of quality loss depends on many factors, including the rate of freezing and thawing, storage temperature, temperature fluctuation, transportation, retail display and consumption (Bogh-Sorensen 2002) . In fatty species such as herring (Clupeidae), anchovy (Engraulidae), mackerel (Scombridae) and salmon (Salmonidae) the most serious cause of deterioration is oxidation. Despite this fact, also lean fish from Gadidae family are sensitive to lipid oxidation. Lipid oxidation typically results in formation of aldehydes, alkyl radicals and semialdehydes (Chen et al.