Effects of pressure processing on strawberry studied by nuclear magnetic resonance

Abstract

Two different nuclear magnetic resonance techniques, namely magnetic resonance imaging and 1H-HR-MAS NMR spectroscopy, have been employed to study the extent of the damage caused by relatively low pressures (100–200 MPa) in strawberry. MRI maps showed important changes in the relaxation behavior of water molecules in pressurized samples. These differences increased with the pressure level applied. ADC values clearly showed the destruction of biological barriers and the loss of cell compartments produced by pressure. This induced major water redistribution in the tissues and; therefore, substantial changes in the interactions between water molecules and their environment. Relaxation times in T1 and T2 maps clearly depicted these pressure induced modifications. Moreover, NMR spectroscopy showed significant differences in the main sugars content in control and pressurized samples. Sucrose hydrolysis seems to be enhanced by the pressure treatment. The research data presented in this paper show a deep insight into the phenomena which take place during pressure processing in a soft plant tissue. The Nuclear Magnetic Resonance (NMR) techniques employed offered the opportunity of studying the whole product without any preparative manipulation which could mask the pressure effects. The results obtained should be useful to understand how and why pressure causes damage to vegetal tissues and, therefore, to design optimized high-pressure treatments which minimize this damage.