Effects of Heat Treatment on Composition and Nutritive Value of Herring Meal
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1. The effect of heat treatment on quality of herring meal has been investigated using a rotating autoclave operated under variable conditions (meal moisture: 1.1% - 41%; meal temperature: 96° C – 132° C; heating time: 0-2 hrs). 2. In terms of proximate chemical analyses all heat treated meals, containing 82.5-85.0% protein on a dry weight basis, would be considered of a very high grade. 3. Short heat treatments at about 125° C appeared to stabilize the lipid phase towards oxidation during storage: After four weeks an unheated reference meal had a carbonyl number of 323 mmol CO/kg fat whereas heat treated meals had values in the range of 74-91 mmol CO /kg fat. Corresponding iodine numbers were on the average 100 g I2/100 g fat for the unheated meal and 120 g I2/100 g fat for heat treated meals. 4. Analyses indicated some slight decrease in amino acids of the herring meals resulting from the heat treatments. 5. No clear correlation was found between available lysine and conditions of heat treatment, but there was a tendency for availability to decrease with increasing moisture content during prolonged heating of meals. 6. During the heat treatments, pepsin digestibility for dry meals dropped to 66% while that for wet meals dropped at most to about 33% with reference to freeze dried meals. 7. Pepsin digestibility was well correlated with values for nutritive criteria obtained in animal feeding tests. 8. Apparent indigestibility of individual amino acids In two selected meals showed some increase due to heat treatment.