HortResearch Publication - Controlled atmosphere storage of Fuji apples
Fuji apples respond well to controlled atmosphere (CA) storage. Ranges of oxygen and carbon dioxide of 1 - 2.5% and 0.7 - 2% respectively, have been recommended in at least five countries. However, oxygen levels below 2% have been known to cause breakdown and alcoholic off-flavours, and carbon dioxide levels above 3% can cause internal carbon dioxide damage and cavity formation.
In HortResearch trials, Fuji apples were stored under 2% oxygen and 2% carbon dioxide. This atmosphere produced fruit which had :
• a firmer texture
• higher soluble solids
• less advanced background colour
• higher titratable acidity levels, and
• less greasiness
than air-stored fruit. However, the CA fruit also had a higher incidence and severity of watercore than air-stored fruit, although not to commercially significant levels. CA storage has been shown in later trials to dramatically slow the dissipation of watercore during storage; problems may occur with severely affected fruit at harvest.
The CA-stored Fuji were juicier, crisper, and more difficult to break down when chewed than air-stored fruit. A taste panel described the CA-stored fruit as having "higher acidic aroma and flavour" and a "fresh grass" aroma. However after 4 - 6 days out of CA storage, the CA-stored fruit lost some of their ability to produce volatiles and therefore aroma and flavour was perceived as lower than that of air-stored fruit.
The early harvested fruit were less mature than late harvested fruit, both at harvest and after storage, in either air or CA storage. Early harvested fruit were less greasy and had lower levels of watercore than late harvested fruit and had higher levels of firmness, titratable acidity and soluble solids. After CA storage, the early harvested fruit was still more acidic and firm than the later harvested Fuji. However, sweetness and "apple taste" decreased in the later harvested fruit. The opposite happened with the air-stored Fuji - it was the more mature, later harvested fruit which had the most sweetness and flavour, as detected by the sensory panel.
(Note : excess sweetness is often the result of over-mature fruit).
At harvest, and after storage in either air or CA, the fruit from Central Otago were firmer (generally 1kgf firmer), greasier and had a slightly higher incidence of watercore than fruit from Hawke’s Bay or Nelson.
Therefore, 2% oxygen and 2% carbon dioxide is a successful atmosphere for CA storage of Fuji, although further trials are required to optimise the storage environment for fruit from different districts and destined for different markets. After storage in this atmosphere, Fuji will be generally 0.5 kgf firmer than air stored fruit and have marginally higher soluble solids levels. Background colour of CA-stored Fuji was generally one colour grade less advanced than air-stored fruit and had 30% higher titratable acidity. Air-stored fruit developed more greasiness than CA-stored Fuji. The CA fruit had less disorders (12% of the fruit had some disorder) compared with the air-stored fruit of which 22% had disorders.
The CA-stored Fuji appears to the consumer as a "fresher" product. However, the taste and aroma of CA-stored Fuji decreased once the fruit was removed from CA store, so it should be sold and eaten soon after removal from CA storage
Watercore does not seem to disappear to the same extent in CA-stored fruit. Although the incidence of watercore in this trial was very low (7% watercore for CA-stored fruit compared with 4% watercore for air-stored fruit), in years where watercore is severe it could possibly be a problem where fruit is stored under CA .
HortResearch acknowledges ENZA New Zealand (International) for financial support.
New for HortNET, November 1996. Written and submitted by Helen Percy from ENZA Client Report 94/277.