Effect of Freezing Process on the Texture of Vegetables

Part I. Texture Measurement for a Small Test Pieceof Carrot in Freezing Process

Abstract

In order to measure the change of mechanical properties of vegetables caused by freeze-thawing, the constant rate compressive rupture test with the Instron type instrument was proposed for the cylindrical small test piece which is adaptable to quick freeze process.
(1) It is possible to determine exactly, rapidly and simply with the same procedure for a large extent of the texture from raw firm samples to the blanched soft or the frozen and thawed tender test pieces of carrot.
(2) No effect of size of test pieces on the measurement of rupture stress, deformation ratio and apparent elastic modulus was obtained.
(3) Little deviations of the texture in the direction of elongation in the same individual of carrot were recognized. In a cross-sectional direction, it was found tendencies that phloem was slightly firm than xylem of raw and the blanched samples, but that reverse trends was after freeze-thawing.
(4) Raw carrot texture markedly decreased and the force-deformation curves bended down-wards by the preheat or freeze-thawing. Repture stress decreased the initial value to 10-45% on the blanching and furthermore decreased the value of blanching to half on the cooking. On the freeze-thawing, decrease ratios of rupture stress to the control were 13-20% of raw-freezing, 20-40% of blanching-freezing and 28-38% of cooking-freezing.