Production of dry-cured ham: challenges and perspectives of research
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Dry-cured ham is a product belonging to a high-priced food category. Norwegian dry-cured ham is a young, local brand which has not been well studied. The careful investigation of the environmental parameters, meat properties, and processes taking place in the ham during processing was the main aspect of the present research. Due to the lack of scientific data on Norwegian dry-cured ham, the research represents a manifold work on the edge of two different scientific approaches – process engineering and biochemistry. On the one hand, dehydration processes throughout the production were studied. Osmotic dehydration in the process of salting was investigated. Drying kinetics was obtained for the drying process with corresponding dehydration curves. The use of models, describing the dehydration with high accuracy for both the salting and drying, was proposed. On the other hand, the production of food does not come down to just the investigation of processes involved in a certain technology. Biochemical changes in food products must be followed to understand the role of the technological processes used. During the production of dry-cured ham, there are three main technological processes, namely salting, post-salting and drying-ripening. Salting is used to suppress possible microbial contamination and to give the product a pleasant salty taste. The post-salting step is introduced to the technology to achieve salt equilibration in the tissues; the salt concentration and distribution significantly influence the next processing step. Drying-ripening is the longest step, mainly used to obtain a certain degree of biochemical change, which influences the final flavor of the dry-cured ham. Proteins are the most abundant organic structures in animal meat and, therefore, changes occurring in proteins are of special interest. The main biochemical change which occurs in proteins during dry-cured ham manufacture is the process called proteolysis. When proteins in ham are affected by the action of specific proteolytic enzymes, they are broken down into smaller parts – peptides and amino acids – which contribute to the final flavor and tenderness of the meat. In the present research, proteolytical changes were studied by means of two approaches: the investigation of the rate of protein breakage into smaller parts (proteolysis index) and the study of the activity of the main proteolytic enzymes during production. Peptides produced in Norwegian dry-cured ham and their quantitative kinetics during production were also studied. Several peptides were reported as suitable for use as “process biomarkers”. The thermal properties of Norwegian dry-cured ham, namely glass transition temperature (Tg) and the amount of unfreezable water (Wunf), were checked by Differential Scanning Calorimetry (DSC) in order to prove the conclusions made on the basis of biochemical experiments. The outcomes of the present study would help the Norwegian meat industry to obtain economic and quality benefits. The knowledge about meat dehydration during salting and drying can be implemented to calculate the final physico-chemical parameters of hams without high-costing experiments. The connection between the rate of proteolytical changes and the thermal properties of meat has been found and reported for the first time. The quantitative parameter for the found “process biomarkers” – the intensity of absorbance of the peptide ion measured by proteomic tools – can be used as an indicator of the completeness of the process. The results of the physico-chemical and biochemical experiments were also used to report to Norwegian local producers and the Norwegian Research Council in order to improve the quality and efficiency of production (project 225262/E40 – DryMeat).