Uporedno ispitivanje odabranih parametara kvaliteta marinirane skuše pakovane u vakuumu i modifikovanoj atmosferi / Comparative study of selected quality parameters of marinated mackerel packed in vacuum and modified atmosphere

The marinating process is one of the oldest preservation methods of fish, and is often used in Europe. This method is commonly used for preservation of the fish with a higher fat content, such as sardines, mackerel, herring, but for the crustaceans and molluscs as well. Generally, shelf life and safety of the marinated fish and seafood, without temperature treatment, depends on the type of organic acid which is used for marinating, and the concentration of salt. It is known that the pH values lower than 4.5 are sufficient to prolong the shelf life of the fish. However, the low pH values of the marinade may cause strong acidic taste. The terms marinade or marinated fish refer to fish products consisting of fresh, frozen, or salted fish or portions of fish treated with an edible organic acid, usually acetic acid. After completing marinating, fish is usually packed in vacuum or modified atmosphere, which is a way to prolong shelf life of marinated fish. The aim of food, including fish labelling is to provide consumers with key information about the fish, and especially on storage conditions and expiration date of the product. In this regard, nowadays, food industry in particular is characterized by the development of food packaging segment. The aim of the study within this PhD thesis was to investigate the influence of packaging of salted and marinated fish (mackerel) in vacuum and modified atmosphere on the shelf life and selected quality parameters. In the experiment it has been used commercial size mackerel (a mass of 350-400 g), which is treated in the manner customary for industrial plant which deals with processing of fish. Fish is processed so that for salting, marinating, and packaging has been used primarily processed fish carcasses. The fish was divided into two subgroups, first which was treated only with saline (10% salt), and a second subgroup which was marinated in a 10% salt and 0.5% acetic acid. The fish was treated for twenty-four hours. The first sub-group is divided into two groups, one of which is packaged in a vacuum (the first group), and the second group in modified atmosphere (40% CO2 + 60% N2). In the same way the other sub-groups were divided and packed in a vacuum (the third group), or a modified atmosphere (40% CO2 + 60% N2) (fourth group). All samples were stored under the same controlled conditions, and storage temperature was 4 ° C. At the beginning of the experiment and every ten days, during the fifty days, were conducted microbiological (total bacteria count, the total number of Enterobacteriaceae, the psychrotrophs number, the number of anaerobic bacteria, the number of lactic acid bacteria), the chemical (the basic chemical composition, the content of total volatile nitrogen, malondialdehyde and histamine), physico-chemical (aw value and pH value), and sensory analysis. Basic chemical composition and aw value was determined in samples taken on test day. Salting and especially marination, significantly affects the change in the chemical composition of fish meat, since it leads to a significant reduction in water content, an increase in fat content and the content of ash. These processes affect the reduction of aw value of fish meat. In the samples of marinated fish, especially in the samples packaged in a modified atmosphere, it was determined significantly lower number of bacteria in the tested group compared to samples which were treated with salt solution, and which are packed under vacuum. In all tested groups of samples the highest increase was observed in the aerobic mesophilic bacteria followed by psychrotrophic bacteria, while increasing in the number of enterobacteria was least pronounced. Increase in the number of enterobacteria was determined till 40. day and then decreasing to the end of the study. Significant growth of lactic acid bacteria and the number of anaerobic bacteria was observed from the thirtieth to the fiftieth day of the study and it was approximately on the same level. The content of total volatile nitrogen was significantly higher in the samples which were marinated and were packed under vacuum. Within this group of samples at the end of examination the content of total volatile nitrogen was above the recommended value for this type of fish. The way of preparing fish and method of packaging were influenced on increase in malondialdehyde content. Malondialdehyde content was lowest in the samples of marinated fish packed in a modified atmosphere. Since the beginning the pH value of the fish meat was significantly lower in marinated samples compared to samples which were treated only with saline. The decrease of pH during storing was less pronounced in samples marinated and packaged in a vacuum as well as in those packaged in a modified atmosphere. The content of histamine increased in mackerel samples of all the groups, and was most pronounced in samples of salted mackerel packed in vacuum. At the end of the study the average histamine content in all samples was less than regulated maximum allowed in fish meat. Sensory evaluation of total acceptability of samples of mackerel at the end of the study was significantly higher in samples of marinated fish, while samples of salted fish packed in vacuum had the sensory evaluation of the overall acceptability less than satisfactory.