The fracture toughness of pea testa in relation to temperature abuse during frozen storage

Obtaining information on the textural quality of food materials in SI units is desirable for objective quality control. Adapting standard materials testing methods to biological specimens has the potential of providing such objective measurements. Based on the approach of linear elastic fracture mechanics, a tear test was used to measure the fracture toughness of the testa of frozen peas. The mean fracture toughness obtained for an extension rate of 0.13 mm s(-1) was 212 J m(-2). The effect of extension rate was investigated and showed that fracture toughness increased with increasing extension rate. Measurement of fracture toughness was applied to identify the effect of ''temperature abuse'' in the pea testa. Following three thaw-freeze cycles, the specimen became more fragile and fracture toughness of pea testa decreased by about 18%. Brightfield microscopy and low temperature scanning electron microscopy were used to observe tissue changes resulting from temperature abuse. Cell rupture in the osteosclereids and parenchyma layers was associated with temperature-abused tissue. Slow freezing during the thaw-freeze cycles caused formation of large ice crystals which disrupted the pea testa tissue. (C) 1997 Published by Elsevier Science Ltd on behalf of the Canadian Institute of Food Science and Technology.