Rapid Method Based on Proton Spin-Spin Relaxation Time for Evaluation of Freezing Damage in Frozen Fruit and Vegetable

Abstract

This study proposed the use of nuclear magnetic resonance (NMR) technique based on proton spin–spin relaxation time (T2) of water to indicate freezing damage in frozen fruit and vegetable. T2 value can be used to indicate water content in the cells of samples. The results showed that T2 values of frozen-thawed samples were lower than those of fresh (undamaged) samples. This is because of the cell membrane damage due to the formation of ice crystals, leading to leakage of water. The microstructural changes of frozen-thawed barley coleoptile tissue and apple parenchyma tissue were evident when observed using a high-resolution three-dimensional X-ray microscope and an optical microscope, respectively. Changes in the T2 value could be related directly to the microstructural changes of barley coleoptile tissue and apple parenchyma tissue. T2 value can be measured in far less time than conventional methods and is considered a rapid and effective method to indicate freezing damage in frozen foods. Practical Applications Freezing damage (e.g., cell shrinkage, membrane damage and loss of water holding capacity) caused by ice crystal formation affects the quality of frozen food products after thawing. This study proposed an alternative nuclear magnetic resonance (NMR) technique based on proton spin–spin relaxation time (T2) of water to indicate freezing damage in frozen fruit and vegetable. NMR measurement of T2 value can be performed in far less time than conventional freezing damage measurements (e.g., electrical conductivity and microscopy) and thus can be used as a rapid and reliable technique for determination of water in food samples and subsequently can be used to indicate freezing damage caused by ice crystal formation.