Evaluation and Utilisation of Fish Protein Isolate Products

after 20 seconds of operating instrument at 5-7˚C, speed setting 6, system switch 6.Measurements were done in triplicate.2.2.7 Viscosity (Brabender® viscograph E)The Brabender viscosity of CPS samples was determined using a Brabender® ViscographE coaxial viscometer (Brabender® OHG, Duisburg, Germany) based on Gunnarsson et al.,(2005) but with some modification. The Viscograph E is a rotational viscometer designedto measure “viscosity” as a time and temperature dependent parameters. This instrumentmeasures a resistance of the sample against flow. It is assumed that this resistance isproportional to the viscosity of the system. The term “Brabender viscosity” is used fordescribing the resistance (Kristbergsson and Sigfusson 2002). The instrument offers theability to measure Brabender-viscosity of viscous materials during a heating cycle. Itconsists of an electronic measuring system, a measuring bowl (100 mm height, 90 mmdiameter) containing eight (8) protruding pins, and a seven (7) pin stirrer (Fig. 2). Themeasuring bowl, containing the sample (approximately 450 g) is placed in a temperaturecontrolledholder and rotates on a vertical axis forcing the sample to be pressed against thepin-style stirrer (Photo 2.4 (R), Annex 2). Torque on the pins is measured and expressed as“viscosity” in Brabender units (BU). The force exerted on the stirrer depends on theresistance of the sample. The instrument was designed for carbohydrate-based materials,but has also been used to study ”viscosity” in other food materials such as chocolate, juiceand other liquid, and semi-liquid foods and for testing the “viscosity” of materials in thechemical-cosmetics and textile industries (Kristbergsson and Sigfusson 2002).Figure 2. Measuring bowl and the pin-style stirred used for the Brabender® viscograph E,(From: Kristbergsson and Sigfusson 2002).Starting temperature was 5˚C, heating rate 1.5˚C/min, and maximum temperature 45˚Cwith a holding time 3 minutes, then cooling rate of 1.5˚C/min to 5˚C. Measuring cartridgewas 700 cmg (0.7 Nm) and speed of the bowl 7 rpm. Sample quantity was 450 g of CPSwithout addition of water or other additives. The measurements were done in duplicate.Different measuring rates (cmg) and speed (revolutions per minute) [350 and 65, 1000 and75, 1000 and 85, 250 and 55, 700 and 55] were tested to measure different proteinsolutions having different pH. The best measuring range and speed to study viscositychanges of protein samples were 700 cmg and 75 rpm respectively which were used duringmeasuring all test samples. The temperature of the sample should be 0 to 2˚C at the18