Effect of curing on the shelf life of ambersweet oranges (<i>Citrus Sinensis</i> Osbeck) stored at ambient tropical condition

Abstract

Curing is a pre-storage treatment that can be carried out on certain products by using natural environmentallyfriendly conditions. Sweet orange fruits from 2007 and 2008 harvests were subjected to curing treatment by exposing them in the sun at 35₀ -39₀ C or cool air at room temperature. The fruits were allowed to dry to 1, 3, 5, 7, and 9% weight loss before storage in normal atmosphere at 28₀ C and 85% relative humidity. The incidence of infection was higher in sun-cured fruits. The causal organisms were Penicillium digitatum, Phytophthora sp. and Alternaria citri. Incidence was lowest in fruits cured in the shade to 7% weight loss. Juice content was higher in shade-cured fruits but was unaffected by the level of drying. Juice content also decreased significantly with storage. Weight loss was higher in sun-cured fruits, was dependent on level of treatment and increased with storage in both sun and shade methods. Colour change to yellow was faster with sun curing and fruits initially cured to 7% weight loss in shade retained the attractive greenish-yellow colour for 9 weeks. Titratable acidity (TA) was higher in shade-cured fruits and it decreased with storage while total soluble solid (TSS) content ranged from 10.20 to 12.90₀ Brix. Sun-cured fruits had higher TSS and it increased slightly with level of curing in both methods. More ascorbic acid was retained by shade curing to higher levels. Fruit firmness and stoniness were significantly affected by curing method. Sun-cured fruits had harder, leathery rinds giving the effect of moderate stoniness. Curing in the shade to an initial 7% weight loss resulted into fruits that were the most stable for storage. Despite the reduction in weight, juice content and ascorbic acid concentration of cured fruits, natural pre-storage curing is convenient and has potential advantage in extending the storage life of orange fruits.

Keywords: Fruit, Sun-cured, Shade-cured, Weight Loss, Storage,