One of the best applications for high pressure processing (HPP) has been the processing of avocado paste or guacamole so that micro-organisms are destroyed which improves shelf-life (Palou et al., 2000). It also allows for better retention of both colour and the delicate flavour, which would be badly damaged by any thermal process. As a non-thermal treatment to commercially pasteurise what is a delicate product, there are hints that HPP has considerable potential with the manufacture of other high value products besides avocado, seafood and hams.
One of the issues though with avocado paste has been how to improve its shelf-life, which would increase its commercial success further. One main factor and known for some time, is the inability to destroy polyphenol oxidase (PPO) activity which then continues after HPP processing to catalyse browning in the final product. It seems that greater pressure is required to inactivate the enzyme than the microbial cells, which are present in the product – mushroom PPO being one classic example (Weemaes et al., 1997). Subsequently, a better understanding of how PPO was also activated in some processes began to be explored (López-Malo et al., 1998).
A recent article has set out to identify why HPP treated avocado paste which is refrigerated for storage is rejected by consumers after nearly 20 days when its shelf-life is at least double that (Jacobo-Velázquez and Hernández-Brenes, 2011). Their study shows a sour or rancid flavour as the main sensory descriptors which put consumers off. A clearer understanding of the activity of PPO and lipoxygenase (no mention of a peroxidase), and the mechanisms by which rancid notes are generated in this particular process has been attempted. The study also provides some useful thoughts on shelf-life determination where two methods, a cut-off point determination and logistic regression are used.
References
Jacobo-Velázquez, D.A., Hernández-Brenes, C. (2011) Sensory Shelf-Life Limiting factor Of High Hydrostatic Pressure Processed Avocado Paste. J. Food Sci., Online version publ. 5th July 2011. DOI: 10.1111/j.1750-3841.2011.02259.x
López-Malo, A., Palou, E., Barbosa-Cánovas, G.V., Welti-Chanes, J., and Swanson, B.G. (1998) Polyphenoloxidase activity and color changes during storage in high hydrostatic pressure treated avocado puree. Food Res. Int. 31(8), pp. 549–556.
Palou, E., Hernandez-Salgado, C., Lápez-Malo, A., Barbosa-Cánovas, G.V., Swanson, B.G. and Welti-Chanes, J. (2000) High pressure processed guacamole. Innov. Food Sci. Emerg. Technol. 1, pp. 69–75.
Weemaes, C., Rubens, P., De Cordt, S., Ludikhuyze, L., Van den Broeck, I., Hendrickx, M., Heremans, K., and Tobback, P. (1997) Temperature sensitivity and pressure resistance of mushroom polyphenoloxidase. J. Food Sci. 62 pp. 261-266
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