The use of sulphur as a method of postharvest disease control and colour retention
in litchis is soon to be restricted by the European Union. It is therefore essential that
new postharvest treatments and packaging techniques be developed in order to
retain internal and external fruit qualities and thus allow for export. Good litchi
quality is not only important for the export market but also for use on the local
market.
In this study, alternative methods for postharvest quality control were investigated
with the aim of extending the litchi storage life to 40 days under modified storage.
Packaging the fruit in polypropylene bags significantly decreased fruit water loss and
resulted in an increase in shelf life, as determined by red colour and overall rind
appearance. There was no distinct advantage of amodified atmosphere. The use of
a punnet, lined with absorbent sheeting and placed within the sealed polypropylene
bag, further improved the shelf life. The absorbent sheeting reduced the amount of
free water and resulted in little pathogen infection, while the punnet was effective in
protecting the fruit from damage. It was notable that most water loss occurred within
the first 10 days of storage and that the majority would actually take place during the
cooling phase. A hydrocooling technique was therefore investigated and was found
to not significantly decrease water loss, possibly due to not hydrocooling the fruit for
a long enough period of time.
Temperature management was extremely important for both colour retention and
pathogen control. It was found that treatments stored at 5.5QC showed better colour
retention after the 40 days storage than the 1QC storage treatment. The higher
storage temperature, however, enhances the potential for postharvest diseases.
Three compounds, namely ISR 2000, 'Biosave' and F10, were tested for pathogen
control. 'Biosave' showed the best results with the most effective concentration
being 100 mill water and good pathogen control occurred when storage was at 10 C.
Polyphenol oxidase (PPO) activity in the litchi rind was evaluated as it is thought to
be closely related to browning of litchi fruit, probably due to the degradation of
phenolics by PPO. Brown fruit had a high PPO activity whilst red fruit had much
lower activity. It was also shown that PPO activity decrease over storage time,
possibly due to product inhibition of the enzyme.
The internal quality of the fruit was determined using the T88: acid ratio of the pulp,
as it is well correlated to mean eating quality. For fruit to have excellent taste, it must
have a T88: acid ratio of between 31:1 and 60:1. All the fruit had a ratio that met
this criterion and would therefore ensure good eating quality. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2006.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ukzn/oai:http://researchspace.ukzn.ac.za:10413/3833 |
| Date | January 2006 |
| Creators | Archibald, Alison Joy. |
| Contributors | Bower, John P., Bertling, Isa. |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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