Acetaldehyde and ethanol are already present in detectable levels at the time of harvest, under aerobic conditions and in healthy, undamaged fruit. Both metabolites can be detected, at different concentrations, in all cultivars. Several hours after harvest, the levels of acetaldehyde in cultivars Summit, Těchlovan and Kordia were 6.41, 9.78 and 22.00 mg/l, respectively. Both ethanol and acetaldehyde accumulate to significant levels in anaerobically stored cherries, particularly in atmospheres with high levels of CO 2 . The highest levels of ethanol observed, after 31 days of exposure to anaerobic conditions, were in the cultivars Těchlovan (1,159 mg/l) and Summit (1,168 mg/l); both concentrations are are broadly similar. The metabolites decreased after a return to aerobic conditions, but remained higher than the levels first observed. Sweet cherries stored in anaerobic conditions are also sensitive to the development of off-flavours in the first 24 hours after opening the storage box. The very slow ripening of the fruit under anaerobic conditions was satisfactorily quantified by measuring the higher degree of fruit firmness, when the usual, visual attributes of ripeness were almost undetectable. Stems also remained green, in contrast to the usual browning that occurs under normal atmospheres. Discrimination analysis of various parameters observed gave a good resolution of different cultivars.
27tential of ultra-low oxygen (ULO) storage as a practical technique for extending sweet cherry shelf-life.
MATERIAL AND METHODS
Fruit preparationSweet cherries (Prunus avium cv. Těchlovan, Summit and Kordia) with stems attached were hand harvested on July 6, two days before the optimal harvest stage, from the commercial orchard Agro Stošíkovice at the Horticultural Faculty in Lednice. The fruits were sorted to exclude those with obvious defects or dissimilar states of maturity, based primarily on their appearance. Selected fruits were then transported into small boxes and during two hours they were chilled to 3°C before placing in the various gas mixtures.
Preparation of the atmospheres
Preparation of atmospheres:Immediately after cooling, the final atmosphere composition was obtained by flushing with nitrogen. To eliminate the possibly excessive influence of CO 2 as a respiration inhibitor, the chambers were connected to absorption tubes filled with solid tablets of KOH, which were mixed with an inert material (polystyrene). Gas mixtures were monitored twice a day, using a dual CO 2 /O 2 analyzer (Arelco, ARC, France).
Ethanol and acetaldehyde levelsThe cherries were temporarily stored in a freezer and then defrosted prior to analysis. The juice produced was filtered (25 mm diameter syringe filter, 0.2 μm nylon with glass, Alltech Associates Inc., Belgium). 1 μl aqueous samples were injected into a sample block fitted with Teflon, and analyzed with a gas chromatograph equipped with FID (Chrom 5, Laboratory Equipment, Prague). Separation was achieved on a packed column (Porapak P, 3 mm i.d., 120 cm length), gas...
