¹H‐NMR Study of the Impact of High Pressure and Thermal Processing on Cell Membrane Integrity of Onions

Abstract

Proton nuclear magnetic resonance (¹H-NMR) relaxometry was used to study the effects of high pressure and thermal processing on membrane permeability and cell compartmentalization, important components of plant tissue texture. High pressure treated onions were subjected to pressure levels from 20 to 200 MPa at 5 min hold time at initial temperatures of 5 and 20 °C. Thermally treated onions were exposed for 30 min at temperatures from 40 to 90 °C. Loss of membrane integrity was clearly shown by changes in transverse relaxation time (T(2)) of water at temperatures of 60 °C and above. Destabilization effects on membranes exposed to high pressure were observed at 200 MPa as indicated by T(2) measurements and cryo-scanning electron microscopy (Cryo-SEM). T(2) relaxation successfully discriminated different degrees of membrane damage based on the T(2) shift of the vacuolar component. Analyses of the average water self-diffusion coefficient indicated less restricted diffusion after membrane rupture occurred in cases of severe thermal treatments. Milder processing treatments yielded lower average diffusion coefficients than the controls. ¹H-NMR proved to be an effective method for quantification of cell membrane damage in onions and allowed for the comparison of different food processes based on their impact on tissue integrity.

Influence of Cell Integrity on Textural Properties of Raw, High Pressure, and Thermally Processed Onions

“…The results on cell viability agree with the results of 1 H‐NMR T 2 (Gonzalez and others 2010b), electrolyte leakage, and pyruvate analysis (Gonzalez and others 2010c), methods used to determine cell integrity after high pressure and thermal processing. Butz and others (1994) also observed microscopic damage of the tonoplast of onion epidermal cells that were associated with 300 MPa treatments and detected changes in enzymatic activity associated with membrane damage above 100 MPa.…”

Onion Cells After High Pressure and Thermal Processing: Comparison of Membrane Integrity Changes Using Different Analytical Methods and Impact on Tissue Texture

“…Tissue stiffness was determined from the initial slope of a force/deformation curve in a puncture test of the onion disks following either high pressure or thermal treatments (Mohsenin 1986; Bourne 2002). Figure 5 illustrates a comparison of the changes in cell membrane integrity as determined by the different methods we evaluated in this article and in 2 others, for example, pyruvate content, ion leakage (% of total conductivity), cell viability, or % of relative stained area (Gonzalez 2010a) and 1 H‐NMR T 2 (Gonzalez 2010b). …”

“…The different methods described previously were used to evaluate onion cell membrane integrity and were compared to the previously obtained cell viability (Gonzalez 2010a) and 1 H–NMR T 2 (Gonzalez 2010b) results. The relationship between membrane integrity and texture quality was evaluated.…”

“…In this article, an enzymatic method that measures the amount of pyruvate formed in onion tissue (Anthon and Barrett 2006; Schwimmer and Weston 1961) is also proposed for use in determination of changes in cell membrane integrity after high pressure and thermal processing. The results of different membrane permeability and/or integrity methods that allow for the quantification of cell integrity after high pressure and thermal processing, for example, pyruvate analysis, ion leakage, cell viability (Gonzalez and others 2010a), and 1 H‐NMR T 2 (Gonzalez and others 2010b) are summarized and the impact of membrane integrity on the texture component of quality is determined.…”

Recent Developments in High Pressure Processing of Foods

“…HPT (100 and 400 MPa, 5 °C) of onion led to better extraction of At 400 MPa, the extraction of quercetin glucoside increased to 33 %, but there was no change in antioxidant activity (Roldan et al 2009 ). Gonzalez et al ( 2010a ) used proton nuclear magnetic resonance ( 1 H-NMR) relaxometry to study the effects of HP and thermal processing on membrane permeability and cell compartmentalization. Loss of membrane integrity was clearly shown by changes in transverse relaxation time in thermally processed sample.…”