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A study was conducted to characterize a novel on-line technique for determining resident time distribution in a twin-screw extruder using rice flour as the feed material. The technique was analyzed based on the electrical conductivity of the material in the die. Results indicated that the on-line method can effective determine the influence of screw configuration, feed flow rate and screw speed.

High moisture twin-screw extrusion processing completely inhibits protease in Arrowtooth flounder muscle at high temperature. The inactivation of protease is absent below 40 degree celsius (C) material temperature in the extruder die. Inactivation begins to take place at 50 degree C and accelerates at higher levels of temperature. Complete inactivation occurs when the temperature reaches 100 degree C, irrespective of screw speed and configuration. In general, low screw speed promotes the inactivation process.

An increase in the spacing or distance of reverse screw elements (RSEs) from the die increases specific mechanical energy (SME) input, expansion ratio (ER) and water solubility index (WSI) during twin-screw extrusion of rice flour and fish muscle blends. RSEs decrease Warner-Bratzler shear stress (W-B SS) and bulk density (BD). An increase in the fish muscles content of the blends decrease SME, ER and WSI, and increase W-B SS and BD. There is a linear relation between shear stress and BD, and solubility index and SME.

An initial velocity assay is used to evaluate the effect of various modifiers on protease activity in arrowtooth flounder mince. The assay is very sensitive: fresh mince is equivalent to fresh-frozen (0.25 y), but both are significantly (p < 0.001) higher than a 1.5 y frozen sample. Activity is inversely related to water content and pollock mince, and declines with increasing pH (6.5 to 9). Potato inhibitor and beef plasma inhibit 90% of activity at 1% (w/w), are 3× more effective than egg white, but whey protein concentrate is a poor inhibitor. Sucrose and sorbitol are inhibitory at high concentrations (10–15%). Sodium chloride at a concentration of 200 mM significantly (p < 0.001 ) enhances enzyme activity ( + 17%). [ABSTRACT FROM AUTHOR]

A crude protease extract from arrowtooth flounder (Atheresthes stomias) mince was used to separate muscle protein from commercial fisheries by-products. Pollock mince, frames, and skin were subjected to digestion by the enzyme extract for one hour at 55 deg.C. The frames were clean and free of adhering muscle tissue and skin samples were largely broken down. Mass and protein balances for skin and frames demonstrated proteolytic release of small peptides through marked increase in the mass and protein concentration in the liquid (soluble) fractions of the digests compared to controls. Frame digestion showed a protein mass transfer of 64.1% of the solid substrate to the liquid fraction during the course of the digestion. By the end of the skin digestion, 53.7% of the skin protein had transferred from the solid substrate to the liquid fraction. The apparent breakdown of skin and intervertebral cartilaginous tissues indicate a possible affinity of the enzyme for these substrates. Results demonstrate the potential of utilizing the arrowtooth protease as a processing aid in the recovery of proteins from fish processing by-products. [ABSTRACT FROM AUTHOR]

The effects of location and spacing of kneading elements on specificmechanical energy input and product attributes during twin-screw extrusion of pink salmon muscle and rice flour blends were investigated.Incorporation of kneading elements increased specific mechanical energy, expansion ratio and water solubility index, but decreased bulk density and Warner-Bratzler shear stress. The opposite trend was observed with increasing fish solids content except for shear stress, which was little affected by up to 30% fish solids concentration and in the expansion ratio range of 5 to 10. Water solubility index and Warner-Bratzler shear stress were linearly related to specific mechanical energy and bulk density, respectively. Results show that the magnitudes of the effects due to incorporation of kneading elements were different from that of reverse screw element and combination of reverse screw and kneading elements. [ABSTRACT FROM AUTHOR]