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J. KRISTENSEN, Protein Technology, Alfa Laval Separation A/S, Maskinvej 5, Soborg, DK-2860, Denmark For turning fish protein into a protein isolate the raw material has to be kept as fresh as possible, and the temperature has to be kept low, to enable a high yield and good gelling ability. Also during each of the process steps the temperature has to be kept low and under control. Therefore, the critic part in designing the process is to minimize any temperature increases and reduce shear over each step in the process. Only cold water can be added to reach the optimal solubilisation of the protein. Air in-mix has to eliminate specific in the first part of the process because this can create large process problems at later stages. The solubilisation take place when the pH is adjusted upwards, and time to reach the optimal ph is very critical. During the adjustment of pH from 7 to approximate 11 the fish / water slurry go through a cycle, from a simple low viscosity product, to a very high viscosity paste, and back to a low viscosity product. Therefore, reaching the optimized pH is critical for all further process steps. At the low viscosity, insolubles and phorforlipids have to be removed by filtration or centrifugation. When processing oily raw material, removal of oils in this stage can be very difficult, since proteins are reactive and prone to emulsify oils, so only very gentle filtration or centrifuging methods can to chosen. Air incorporation during fluid transfer may create foam that disturb good separation For precipitation of the protein, separation has to be done momentarily and precise in order to facilitate proper flocculation of the proteins, so that the protein efficient can be recovered either by screening or by decanter centrifuge. The type of acid used is important to avoid corrosion on the stainless steel equipment. The neutralization of recovered isolate should be carried out rapidly to minimize damage to the functional proteins. Proper pH of the final isolate is important to proper protein dispersion and gelatinizing.
Session 3, Fish protein recovery using pH shifts
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