New Zealand Journal of Crop and Horticultural Science abstracts
Approaches to optimising surface coatings for fruits
NIGEL H. BANKS
JONATHAN G. M. CUTTING
SUE E. NICHOLSON
Department of Plant Science and Centre
for Postharvest and Refrigeration Research
Massey University
Private Bag 11 222
Palmerston North, New Zealand
Abstract A mathematical model predicted that final water
vapour permeance in surface-coated fruits would depend upon water permeance of
the coating but not the proportion of pores blocked on the fruit surface. In
contrast, predicted final oxygen (O2) permeance depended upon numbers of pores
blocked but not O2 permeance of the coating. Predicted variation in internal
atmosphere composition caused by coatings that blocked different proportions of
pores on the model fruit surface was consistent with data from two experiments
on coated apples (Malus domestica Borkh.). A new equation was developed
to characterise the relationship between internal carbon dioxide (CO2) and O2
levels resulting from different coating treatments. Two graphical approaches to
assess surface coatings for fresh fruits are presented. In the first, a plot of
water vapour permeance against internal O2 was used to identify the most
suitable of three surface coatings for reducing water loss in `Royal Gala'
apples at 20deg.C. The second method used a plot of internal CO2 versus
internal O2 in coated fruit to identify the crop's internal lower O2 limit
(LOLi), which lies just below the optimum internal O2 level
for modified atmosphere effects. Coatings containing different concentrations
of carboxymethyl cellulose produced internal O2 levels ranging from almost
0 to 16 kPa in `Granny Smith' apples at 20deg.C. The
LOLi of these fruit was estimated using the new equation to
be c. 0.8 kPa O2. Large fruit-to-fruit variability with some coating
treatments indicated that uniformity of response may be as important as average
response in selection of coatings. Risks cannot be separated from benefits when
using surface coatings to gain modified atmosphere benefits, making their use
to achieve modified atmosphere benefits more risk-laden than for other
purposes.
Keywords anaerobiosis; apple; internal atmosphere; lower
oxygen limit; modified atmosphere; optimisation; permeance; surface coating;
water loss; wax
New Zealand Journal of Crop and Horticultural Science, 1997, Vol. 25:
261-272
0114-0671/97/2503-0261 $7.00/0 (c) The Royal Society of New Zealand
1997
PDF file of entire paper: medium quality (928K); (scanned from paper original: notes about this process)
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