The effect of high pressure processing on clingstone and freestone peach cell integrity and enzymatic browning reactions

- Browning reactions in HPP treated peaches correlated better to cell integrity than the enzyme or phenolics.
- Above 200 MPa, HPP induces loss of membrane permeability and sub-cellular compartmentalization.
- 1H NMR and microscopic evaluation were effective methods for determination of membrane integrity.

HPP-treated fruits and vegetables may undergo undesirable enzymatic browning reactions due to loss of membrane permeability and sub-cellular compartmentalization. Clingstone and freestone peaches were treated from 100 to 500 MPa for 10 min and evaluated for polyphenol oxidase (PPO) activity, color, total phenols, and for cell integrity using light microscopy and 1H NMR. Significant changes in membrane integrity following HPP above 200 MPa were determined by T2 shifts in the vacuolar compartment from initial levels of 0.79 (clingstone) or 0.88 (freestone) to approximately 0.60-0.68. Clingstone peaches treated at 300, 400 and 500 MPa showed significant decreases (5, 12 and 7%) in % water of the vacuolar compartment and simultaneous increases in the cytoplasmic compartment (4, 8 and 5%). Additionally, there was a reduction in the number of viable cells from an initial 57-58% to 0 and 14% in clingstone and freestone peaches, respectively. These results correlated with the development of increased browning.Industrial relevanceClingstone peaches are firm-textured and therefore are preserved primarily through canning, which desirably softens the texture. In this study we evaluated the use of high pressure processing - at a range of MPa levels - for preservation, and found that enzymatic browning took place after 2 weeks in refrigerated storage if processing occurred above 200 MPa. Analytical tools were developed to follow the onset of the browning, and in future work preventative measures will be studied to minimize this reaction.