Effect of Different Maturity (Measured as IAD index)
on Storability of Apples in CA-bags
I. Lunde Knutsen, E. Vangdal and J. Børve
Bioforsk Ullensvang, N-5781 Lofthus
[email protected]
Norwegian Institute for Agriculture and Environmental Research
Non-destructive methods to determine ripeness of apple fruits are an important research topic. Recently a portable
spectrometer measuring indirectly chlorophyll content, given as an IAD index, was made commercial available. The IAD index
could thus give an indication of fruit ripeness. Non-destructive methods give possibility to grade fruits before storage and
estimate storage potential. To test the potential usefulness of the equipment apples were measured and divided into
groups with presumably different maturity and thus possible different storage potential and stored in CA- conditions and
regular air.
C
B
A
Figure 1:A) The DA-meter from TR-Turoni snc, Forli, Italia used to measure IAD index. B) Apples from same harvest day with IAD index > 0.81 and
< 0.65 looked differently also after storage for one month in regular air. C) Storage of apples in controlled atmosphere bags.
Material and methods
At the main harvest four pallet sized boxes of apples of the cultivar ‘Aroma’ were assessed for maturity using a DA-meter (TR-Turoni
snc, Forli, Italia). This portable spectrometer gives an IAD- index, which is based on the differences in absorption between 670 and 720
nm indicating chlorophyll content. The apples were divided into three groups based on different IAD index; < 0.65, 0.66-0.80 and 0.81>,
where the lower values indicated more mature apples. The apples were stored for three months in regular air at 1°C and at 2 °C in CAbags with 2% O2 and 2% CO2. The apples were assessed for fungal decay and physiological disorder in addition to quality parameters at
harvest time, after three months of cold storage and thereafter 14 days at 20°C to simulate shelf life. Quality parameters included
ground and cover colour, IAD index, firmness, starch, sugar and acid content.
30
50
45
20
15
1°C NA
2°C CA
10
5
A
0
<0.65
IAD
0.66-0.8
index groups
>0.81
Decayed apples (%)
Decayed apples (%)
25
40
35
30
25
1°C NA
2°C CA
20
15
10
5
B
0
<0.65
IAD
0.66-0.8
index groups
>0.81
Figure 2: Apples of the cultivar ‘Aroma’ with different maturity (measured as IAD index) were assessed for both fungal decay and physiological
disorders (decayed apples %) after stored three months at 1°C in natural atmosphere (NA) or 2 °C in CA-bag (2% O2 and 2% CO2) (CA) (Figure 2A)
and then 14 days at 20°C (Figure 2B).
Results and discussion
At the start of the experiment apples from the different IAD index groups were different in subjectively judged ground colour and cover
colour but similar in firmness, acid, sugar and starch content. After three months at cold storage both apples stored in regular air and in
CA-bags were still different in ground and cover colour and IAD index. In CA-bags acid content were significantly higher for above 0.81
group than for the < 0.65 group. After 14 days at 20°C apples with IAD index > 0.81 were different from < 0.65 group in ground colour
and IAD index, but other parameters assessed were similar.
After three months the apples stored in CA-bags had only 2% visible decay but up to 27% decay when stored in regular air (figure 2A).
Senescent breakdown was the most important physiological disorder and accounted for about 90% of the decay after cold storage. The
apples with IAD index < 0.65 were more decayed than apples from the other groups. After 14 days at 20°C apples with IAD index < 0.65
and between 0.66-0.80 stored in CA- bags had developed about 5% decay, apples from the last group developed no decay (figure 2B).
The apples with IAD index < 0.65 stored in regular air had developed 45% decay after 14 days at 20°C and apples from the other groups
had developed about 20% decay. Fungal decay, primarily bitter rot, accounted for about 50% of the decay. It is clear that apples stored
in CA-bags were less vulnerable for decay than apples in regular air at all maturity stages. Apples that had low IAD index at harvest time
developed more decay after three months of storage.
Conclusion
Apples that were sorted into the low IAD index group at harvest had higher risk of developing physiological disorder and fungal decay
than apples with higher values in both cold storage and after simulated shelf life. The non-destructive IAD index is a promising tool to
sort ‘Aroma’ apples into different maturity groups, hence determine the storage potential. More investigation should be conducted to
better understand the potential of the DA-meter in commercial use.
www.bioforsk.no