Non-Invasive Determination of Freezing Effects in Blueberry Fruit Tissue by Magnetic Resonance Imaging

Water and sugar distribution in a single blueberry were mapped both before and after freeze/thaw using magnetic resonance imaging. Images were obtained using a slice selective spin echo pulse sequence which included a T₁ inversion recovery time period, allowing selection of either the water signal or the sugar signal. Freeze/thaw results in the rupture of water retaining membranes within discrete locations of the fruit tissue. This causes a change in the ratio of motion modified water (i.e., hydrogen bonded or chemically exchanged) to unmodified (i.e. mobile and not chemically exchanged) in those regions, as well as a concomitant change in sugar concentration, due to diffusion to other tissues.