Non-destructive measurements of internal maturity of Feijoa (Acca sellowiana) : a 90 credits thesis presented in partial fulfilment of the requirements for the Master degree of AgriScience in Horticulture at Massey University, Palmerston North, New Zealand
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Date
2015
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Massey University
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Abstract
Feijoa (Acca sellowiana) is a delicious fruit with a narrow window for harvest and a
limited postharvest life. In New Zealand, feijoa fruit is required to have at least 6
weeks postharvest life in cool storage plus 6 days shelf life under room temperature in
order to be exported to global markets. Slightly immature feijoa fruit (maturity stage 2)
can be stored for more than 6 weeks plus few days’ shelf life. However, the variation
of maturity is large even among individual fruits harvested from the same tree at the
same time, and currently, there is no way to segregate fruit non-destructively based on
the internal maturity of feijoa at harvest time. The problem with current industry
segregation practice is that the external features of feijoa, such as shape, size, and
weight cannot segregate fruit with different maturity. It is inevitably that some more
mature fruit will rot quickly and affect overall batch quality during storage. It is vital
to have a non-destructive assessment of fruit internal maturity at harvest time. Then
fruit with different maturity can be divided into different batches with more mature
fruit put on sale on local market and less mature fruit put into storage. As a result, the
fruit loss rate and overall fruit quality can be improved. Therefore, in this study,
efforts were made to explore a non-destructive method to estimate the internal
maturity of feijoa fruit and correlate that maturity with performance during storage.
The non-destructive measurements in this experiment included fruit weight,
compression firmness, and skin colour. Four feijoa varieties: ‘Kakariki’, ‘Barton’,
‘Anatoki’, and ‘Wiki-Tu’ were selected for this experiment. For each variety, 945
fruit samples were harvested at approximately one week before becoming fully
mature (standard commercial harvesting) and sent to the lab in Massey. All the fruit
were divided into three groups based on their skin colour (from darkest green to
lightest green). 45 fruit (three replicated batches of 15) from each colour group were
measured immediately for weight, firmness, maturity, skin colour, Brix, and titratable
acidity (TA). Then all the other fruit samples from the same colour group were
randomly divided into three groups that were kept in cool storage for 4 weeks, 6
weeks and 8 weeks respectively. Once cool storage was completed, those samples
were taken out and firmness and skin colour were measured (non-destructive
measurements). Then all the samples were retained at 20°C. Half of these fruits were
assessed for quality attributes 3 days later, and the other half were measured 6 days
after cool storage. All fruit were cut open for final visual assessment of maturity
according to the maturity index developed by Plant & Food Research Institute. The
data of internal maturity and initial fruit quality (weight, firmness, and skin colour)
for each fruit was used to draw scatterplots in order to find out the correlation
between estimated maturity at harvest, final fruit internal maturity and fruit quality
after storage.
The correlation (R2) between internal maturity and compression firmness found on
‘Kakariki’ was 0.6 to 0.5. The correlation for ‘Barton’ and ‘Wiki-Tu’ was weaker
than that of ‘Kakariki’ (R2 from 0.6 to 0.2). The correlation between firmness and
internal maturity for samples of ‘Anatoki’ were weak. The simulated segregation
based on firmness for ‘Kakariki’ and ‘Barton’ indicated that the firmness segregation
at harvest time could be very useful on eliminating potentially bad fruit during cool
storage. A non-destructive method for ‘Kakariki’ and ‘Barton’ fruit based on initial
firmness is therefore now available that would allow successful segregation of fruit
with potential for long term storage. However, this segregation would not work well
on ‘Anatoki’. No significant correlation was found between skin colour, fruit weight
and the internal maturity of feijoa fruit either at harvest time or after storage.
There was a very large variation in fruit quality at harvest time and during the storage
periods. Samples of ‘Wiki-Tu’ indicated that this variety could have the best storage
performance among the 4 varieties testes. ‘Anatoki’ may also have a reasonable
storage potential with less flavour.
The feijoa fruit may not be stored well when covered with polyethylene film, as it
may harm the storability of the fruit. Too immature fruit should not be harvested as
well, as it would never be able to ripen properly during the postharvest period.
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Keywords
Feijoa, Storage