Barbara la Gatta

Protein Modifications in Cooked Pork Products

Abstract Heat treatment induces protein modifications in both cooked whole cuts of meat and in products such as emulsion sausages. Cooking results in shrinkage and water loss with the main proteins changing through conformational rearrangements, oxidation of amino acid residues, and polymeric aggregation (as supramolecular structures). The proteomes of whole-cut meats (e.g., Parma and “Praga” cooked hams) and comminuted pork (e.g., mortadella and wurstel) products have been compared to raw pork using traditional proteomics approaches employing two-dimensional gel electrophoresis (2-DE) coupled to image analysis and mass spectrometry (MS). These studies revealed that other than heat-induced breakdown of part of the myosin heavy chains, the 2-DE pattern of cooked ham was highly similar to that of raw pork. However, MS-based analysis showed protein modifications, including extensive oxidation of methionines. In contrast, likely due to emulsification, comminuted sausages were characterized by an abundant insoluble protein fraction. Interestingly, in comminuted sausages, tropomyosin and myosin light chains were exclusively found in the insoluble protein fraction, whereas actin was found in each supramolecular structure. Experimental evidence showed that the protein aggregation systems of cooked hams and emulsion sausages reflected the processing conditions and were definitely different, the former being characterized mainly by disulfide bridges and the latter by additional covalent interprotein links.

Fatty acid profile and coagulating ability of milk from Jersey and Friesian cows fed whole flaxseed

The experiment was carried out to evaluate the effects of a moderate level of flaxseed administration on milk coagulation properties and fatty acid profile of milk from two different breeds. The experiment was performed on 20 Italian Friesian cows and 20 Jersey cows divided into 2 groups of 10 animals each. The experimental diets were (1) a traditional diet (CON) administrated as unifeed and no supplemental fat and (2) a diet supplemented with 0·5 kg/d of whole flaxseed (FS). Cows were milked twice daily and milk yield was recorded. Milk samples were analysed at 1, 15, and 30 d of the experiment for composition, pH, and milk coagulation properties. To verify the effects of flaxseed administration on the coagulation properties of milk from Friesian and Jersey cows, an electrophoresis study on casein fractions was performed. Milk fatty acid profile can be improved by administrating a moderate level of flaxseed in the diet, however, milk fatty acid profile from Friesian and Jersey cows showed different contents of C18 : 1 trans-11, SFA and MUFA. The results demonstrated that milk coagulating ability can be increased by flaxseed administration in both breeds as a result of different aggregation of casein micelles.

Characterization of Silter Cheeses Produced in Valley and Alpine Pastures by a Proteomic Approach

Silter is an Italian hard cheese manufactured with milk produced by cows fed at different altitude, valley or alpine pasture. The chemical, rheological and sensory properties of cheeses can be affected by the modification in milk composition due to the breed which at different altitude causes the modification of protein content, κ-CN glycosylation, plasmin activity, and coagulation properties. The influence of milk plasmin activity on dairy production was investigated in seven Silter cheeses, four produced in the valley and three from alpine mountain through alkaline urea-polyacrylamide gel electrophoresis; two-dimensional gel electrophoresis coupled to mass spectrometry and image analysis. Results demonstrated that Silter cheese obtained from cows reared in alpine pasture is characterized by a more evident proteolysis, determining high levels of β-CN and αs1-CN fragments. Therefore, the most relevant fragmentation was attributed to a more intense activity of plasmin and to a different dosage of rennet to make up for the reduced coagulation properties of alpine milk.