Delayed storage and controlled atmosphere storage of nectarines: two strategies to prevent woolliness

Abstract

Both delayed storage (DS) of nectarine (Prunus persica cv. Flavortop) fruits held for 48 h at 20°C before storage, and controlled atmosphere (CA) storage, fruits stored at 10% CO2, 3% O2, alleviated or prevented chilling injury manifested as woolliness in nectarine fruits stored for 4 or 6 weeks at 0°C. Control fruits showed 80 and 100% woolliness during ripening after 4 or 6 weeks at 0°C, respectively. DS and CA were similar in their beneficial effect after 4 weeks and CA was better after 6 weeks storage. The two storage processes appeared to prevent woolliness by different mechanisms. DS initiated ripening so that at removal from storage polygalacturonase (PG) activity was higher and pectin esterase (PE) activity lower than in control fruits. The PG activity increased further during ripening, and normal softening occurred in DS fruits. There was no difference in mRNA abundance of PG and PE between DS and control fruits. CA repressed both mRNA levels and activity of PG during storage, but allowed recovery of activity during ripening. Endoglucanase (EGase) activity declined during ripening in all fruits, but control fruits retained more activity than DS or CA fruits. The EGase mRNA level was high in control fruits during ripening after storage, and almost undetectable in all treatments at all other times. We postulate that the ratio between PG/PE either at removal (DS) or during ripening (CA) will determine whether woolliness develops or not.