Effect of Freezing Process on the Texture of Vegetables

Part II. Measurement of the Puncture Curves of Carrot in Freezing Process

Abstract

A constant rate puncture test with the Instron type instrument for the cross sectional test piece of carrot was proposed in order to measure the texture of vegetables affected by freezing process. The results obtained can be summarized as follows.
(1) Cross sectional test piece of carrot was punctured from cortex to a center pith with a cylindrical plunger, hemisphere tip of 4mm in diameter at a rate of 10mm/min. Larger diameter of plunger gave not sharp puncture curve. Higher rate of puncture showed slightly larger stress than the lower rate but resulted in overshoot of the puncture distance.
(2) The distances of characteristic peaks on the puncture curve agreed with the extent by the histological measurement, i.e., centripetal deviation of the texture in a specimen may be obtained by the reading of the curves.
(3) Texture of raw carrot is markedly reduced by the preheat. Puncture force of cortex showed lower than the peak of cambium but the strain increased. On freeze-thawing, the puncture strain more increased and the force-deformation curves bended similarly in the case of compression. Decrease ratio of firmness to that of control sample showed rather small but the same trend in the case of compression.