Effects of temperature, pH, salt concentration and pre-heating treatment on enzymatic processes in cod and herring roe
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In recent years, an increasing attention has been paid to producing high value products from fish byproduct, such as fish roe. However, the nutritional and sensory properties of the roe products can be affected by many factors during the processing, such as fish species, pH, salt concentration and temperature. The objective of the present thesis is to characterize and compare proteolytic and lipolytic activities in cod roe and herring roe under different temperature, salt concentration and pH.The proteolytic activities of unsalted cod roe were highest at 50℃, regardless of the pH value. Cod roe extracts with salt, compared with extracts without salt, have shown a much higher proteolytic activity at pH 5, but a much lower activity at pH 7. The proteolytic enzymes of herring roe, both salted and unsalted, were less active that those of cod roe. The lipolytic enzymes of cod and herring roe were mostly found to have maximum activities at 50℃ and pH 7, and were higher in herring roe than cod roe. The present study also showed that heating at 50℃ did not completely inactivate the proteolytic and lipolytic enzymes while the enzymatic activities were inactivated after heating for 10 minutes at 60 and 70℃. From the results we conclude that fish species, salt concentration, pH and temperature all have influence on the proteolytic and lipolytic activities in fish roe. To inactivate proteolytic and lipolytic activities in cod and herring roe, temperatures above 50℃ is needed.