The extraction of nitrogenous compounds from cod (Cadus morhua) offal by enzymic hydrolysis with papain, the membrane separation of the peptides in the soluble fraction and their freeze and membrane concentration were investigated with the aim of obtaining a high yield of functional products. The following aspects were covered: kinetics of the hydrolysis and of the enzyme inactivation, separation of insoluble solids and yield of nitrogen under different operating conditions (water to fish offal ratio, temperature and particle size of the raw material). Three of the processing options -the hydrolyses, without and with added water, and the water extraction of the minced fish offal followed by hydrolysis of the residue- gave nitrogen yields of 51%, 62% and 69% of the total nitrogen in the fish offal, and required water: fish offal ratios of 0,1 and 1.86 respectively. The peptides in the hydrolysate supernatants were not amenable to membrane separation but those in the water extract supernatant could be split by pH precipitation and ultrafiltration. Eight functional properties of the potential products were evaluated. The hydrolysate supernatants lacked most of them except for high solubility but their low ash content and the particular molecular weight distribution of their peptides may be useful in special feeding diets. The pH precipitate and the concentrate from the ultrafiltration of the supernatant from the pH precipitation exhibited all the functional properties tested to some extent. The precipitate exhibited low solubility and high buffering capacity, high viscosity and good foaming properties. The concentrate had good solubility, gel strength and emulsifying properties.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:378685 |
| Date | January 1987 |
| Creators | Vega, R. |
| Publisher | University of Reading |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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