Texture of frozen vegetables: Effect of freezing rate on green beans

Abstract The texture of green beans after blanching, freezing and cooking was measured with a shear press. Each processing step reduced shear resistance about the same amount. Visible damage to the vegetable tissues was caused by freezing, but not by blanching or cooking. Very rapid freezing by immersion in liquid nitrogen prevented damage and reduced the texture degradation. When the freezing rate was slightly slower than that required for perfect preservation, immature cells of the inner parenchyma were the first to be damaged. Further reduction of the freezing rate caused breakage of other cell walls in this tissue, and separation of walls in the outer part of the pod. When the freezing rate was changed during freezing, the part of the bean that froze rapidly was not damaged, whereas that which froze slowly was damaged. Decreasing the freezing rate during freezing did not damage the portion of the bean already frozen. Sensory appraisal panels were able to distinguish texture differences in beans frozen at various rates when there were visible differences in the amounts of cell wall damage.