Influence of harvest time on quality of ‘valencia’ oranges and juice

Abstract

‘Valencia’ oranges were harvested from Feb. to June 2007, and the effects of harvest time on fruit and juice quality were investigated. After reaching a peak in peel color in March, peel regreening occurred and juice content decreased. Soluble solids content (SSC) remained constant at 10.3% to 11.0% regardless of harvest time. However, juice from later harvested fruit had much lower titratable acidity (TA). Thus, the SSC : TA ratio steadily increased from 10.4 in February to 25.5 in June-harvested fruit. When individual sugars and acids were analyzed, it was found that the ratio increased due to a decrease in citric acid and an increase of sucrose over the season. Pectin content in juice increased with delayed harvest time, possibly due to a softening of albedo and membrane tissues that resulted in small amounts of these materials entering the juice during processing. Ascorbic acid content decreased throughout the harvest season. Phenolic hydroxycinnamic acids (HCAs), an unidentified alkaloid (UA), flavonoids including narirutin (NR), 6,8-di-C-glucosyl apigenin (DCGA) and narirutin-4´-O-glucoside (NRG), as well as limonoids including limonin glucoside (LG), nomilin glucoside (NG), nomilinic acid glucoside (NAG), limonin (L) and nomilin (N) aglycones were measured over the season. Total levels of the HCAs decreased continually until May then increased in June, and the alkaloid, UA, continually increased during the entire harvest season. Contents of flavonoids decreased or remained constant. Limonoids, including L and N, the major bitterness contributors, decreased over the season except LG and NG, which peaked in May. Volatile production for most compounds increased with delayed harvest time at least until May, including acetaldehyde, octanal, hexanal, decanal, ethanol, hexanol, E-2-hexenol, linalool, octanol, á-pinene, mycene, limonene, ethyl butanoate, ethyl hexanoate and methyl butanoate. Some compounds, such as methanol, valencene and ethyl acetate decreased with delayed harvest. Z-3-Hexenol and á-terpineol showed similar patterns, decreasing in April and May and increasing thereafter. The results indicate that fruit harvested in earlier in the season had better quality in terms of higher juice content, better SSC/TA ratio (April to May, 15.1–18.6 ratio), higher levels of ascorbic acid, flavonoids and other secondary metabolites. However, fruit harvested later in the season likely had more aroma and lower levels of bitter components.