Improving the yield of Mozzarella cheese by phospholipase treatment of milk.

Part-skim Mozzarella cheese was manufactured from milk hydrolyzed with fungal phospholipase A1 prior to renneting. The phospholipase treatment reduced fat losses in whey and cooking water and increased cheese yield as a result of improved fat and moisture retention in the cheese curd. The amount of phospholipids in the whey was reduced because of improved retention of lysophospholipids in the cheese curd. Water binding in the fresh curds and young cheeses up to 3 wk of storage was investigated by a 1H nuclear magnetic resonance spin-spin relaxation technique. In the fresh curds, 2 dominant water fractions were present, characterized by average spin-spin relaxation times (T2) of 14 and 86 to 89 ms, respectively. These 2 fractions of low- and high-molecular-mobility water were similar in all cheeses and presumed to represent water associated with the casein matrix and water present in the pores. A few hours after manufacture, cheeses made with phospholipase showed decreased T2 of the high-mobility fraction, indicating improved water-holding capacity. It is suggested that lysophospholipids released from the fat globule membranes act as surface-active agents in the cheese curd, helping emulsification of water and fat during processing and reducing syneresis. During 3 wk of storage after manufacture, the mobility of both water fractions increased in all cheeses, but was highest in the cheeses made with phospholipase. The increase in mobility during the first weeks of storage has earlier been ascribed to structural changes in the protein matrix, which in principle could be accelerated because of the higher moisture content. However, the microstructure of phospholipase-treated cheese was investigated by confocal laser scanning microscopy and found to be very similar to the control cheese during processing and up to 28 d of storage. In addition, flowability, stretchability, and browning were acceptable and similar in all the manufactured cheeses. Thus, phospholipase hydrolysis of cheese milk improved the cheese yield without changing the cheese microstructure, and resulted in cheese with functional properties that were identical to traditional Mozzarella cheese.

Commercial slaughter methods used on Atlantic salmon: determination of the onset of brain failure by electroencephalography.

This study investigated the effect of exsanguination without prior stunning, or carbon dioxide narcosis followed by exsanguination, or percussive stunning or spiking the brain, on the time taken to abolish the visual evoked responses (VERS) of farmed Atlantic salmon. Only percussive stunning and spiking killed the fish immediately and the other two methods resulted in aversive reactions by the fish. The VERS were lost between 148 and 440 seconds after exsanguination without stunning, and between 300 and 554 seconds after carbon dioxide narcosis followed by exsanguination. During both these procedures the fish showed strong aversive behaviour. In contrast, percussive stunning and spiking the brain could result in the immediate loss of VERS and no aversive reactions from the fish if the stun was applied correctly.

Processing of marine foods.

For the Norwegian fish industry, it is an objective to increase the production of value added products in order to improve profitability. This paper will briefly present four areas of important research tasks in this field. To aid in the identification of the species present in a product, we have applied the method called Random Amplification of Polymorphic DNA (RAPD). This technique is used to produce a fingerprint of DNA contained in the sample. The application of DNA typing for species identification in fish products is presented. The nutritional aspects of foods are important. Although the low death rate from coronary heart disease among the Eskimos of Greenland has been suggested to stem in large part from their consumption of fish, one should keep in mind that the daily diet of Eskimos living in the traditional way consists of substantial quantities of meat and fat (blubber) from seals and whales. A recent study as to whether seal and whale oils are more effective than cod liver oil in changing biological parameters that might be important in explaining low incidence of coronary heart disease, asthma and psoriasis among Greenland Eskimos will be presented. Commercial processing of fish must take the development of rigor mortis into consideration since it affects yield and fish flesh quality. Influence of early processing (pre-rigor) on fish quality and yield is also discussed. There are significant differences among fish species in gross chemical composition and morphological structure. Depending on the properties of the flesh and the way it is treated, it may gain or lose water. The relationship between structure and liquid-holding properties of cod and salmon muscle as a function of temperature is presented.