Vapour heat treatment of 'Hass' and 'Fuerte' avocado (Persea americana Mill.) fruit for extending storage life.
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Date
1998
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Abstract
In an attempt to extend storage life of 'Hass' and 'Fuerte' avocado {Persea americana
Mill.) fruit postharvest vapour heat treatments were used. Vapour heat treatment
temperature regimes were 36, 38, 40 and 42°C for either 1, 2, 4 or 8 hours. After vapour
heat treatment, fruit were cold stored at 3.5°C, for 5 or 6 weeks each. On removal from cold
storage fruit were evaluated for firmness, and ripened at room temperature. Once ripe fruit
were evaluated for heat/cold damage, days to ripening, weight loss and physiological
disorders. These experiments were conducted during the 1996 and 1997 'Fuerte' and 'Hass'
avocado seasons.
Electron microscope analysis of vapour heat treated fruit revealed heat damage to the
epidermis and fruit organelles of certain treatments. The effect of vapour heat treatment on
protein synthesis on 'Fuerte' and 'Hass' avocado was investigated using gel electrophoresis,
to determine if presumed heat shock proteins were synthesized under the treatment
conditions. The activity of pectin methyl esterase was also investigated on the heat treated
'Fuerte' and 'Hass' avocados, to investigate if heat alters the activity of this enzyme.
All experiments showed that vapour heat treatment extended 'Fuerte' and 'Hass' avocado
storage and shelf life. Evaluation of the time/temperature combination for vapour heat
treatment for each cultivar indicated that extension of shelf life was, in some cases, limited
by rind heat damage. For the 1996 season, the best time/temperature combination for
'Fuerte' was at 38°C between 4 to 8 hours, 40°C between 4 to 8 hours and 42°C between
2 to 4 hours. For 'Hass', best results were achieved at 38°C between 4 to 8 hours. For the
1997 season, 'Fuerte's best time/temperature combination were at 36°C for 8 hours, 42°C
between 1 to 2 hours and marginal results at 38°C between 4 to 8 hours. For 'Hass' the best
time/temperature combination were achieved at 38°C and 40°C for 8 hours. Analysis of
fruit flesh protein indicated changes associated with vapour heat treatment, and even
induction of new proteins, perhaps heat shock proteins, giving 'Fuerte' and 'Hass' avocados
beneficial characteristics such as an extension of shelf life. There was a decline in activity
of pectin methyl esterase after vapour heat treatment, which was associated with a longer
shelf life.
Description
Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 1998.
Keywords
Avocado--Storage., Avocado--Postharvest technology, Avocado--Postharvest physiology., Theses--Horticultural science.