Untargeted metabolomics analysis of Gannan navel orange at different storage periods under room temperature using HS-SPME-GC-MS and UPLC-Q-TOF/MS.

Navel orange remains metabolized continuously during postharvest storage, but few studies have monitored the changes of these metabolites. Therefore, HS-SPME-GC-MS and UPLC-Q-TOF/MS were used to comprehensively investigate the dynamic changes of the components of Gannan navel orange during storage at room temperature. A total of 62 volatile components and 68 non-volatile components were identified. Principal Component Analysis and Partial Least Squares Discriminant Analysis showed that navel orange under different storage periods were clearly distinguished. Combined with VIP > 1 and p < 0.05, 19 volatile and 27 non-volatile differential metabolites were obtained. KEGG enrichment analysis revealed that flavonoid biosynthesis (map00941) was the primary metabolic pathway. The middle storage period had a higher antioxidant enzyme activity, but the malondialdehyde content was the opposite. These results reveal the changes of postharvest components of Gannan navel orange, providing a theoretical basis for the storage and product development of navel orange.

Variations in phenolic acids and antioxidant activity of navel orange at different growth stages.

Ripe navel orange has abundant amounts of phenolic compounds. Few studies monitored changes in these compounds during ripening. In this study, the effects of navel orange maturation on dynamic changes in antioxidant activity, total phenolic content (TPC), total flavonoid content (TFC) and phenolic acids were investigated. Five growth stages of navel orange were studied, and nine phenolic acids were detected via high performance liquid chromatography-triple quadrupole mass spectrometry (HPLC-QQQ-MS). Results showed that antioxidant activity, TFC and TPC decreased gradually with fruit ripening. The concentrations of most phenolic acids also declined during fruit maturation, except for free fractions of sinapic acid and bound fractions of ferulic and caffeic acids. Ferulic acid was the most dominant of all phenolic acids at all growth stages. Partial least-squares showed significant differences among fruits of different maturities. A significant correlation between antioxidant capacity, TPC, TFC and some phenolic acids was found.

Volatile composition changes in navel orange at different growth stages by HS-SPME-GC-MS.

This study investigated the changes in volatile organic compounds (VOCs) of navel orange during fruit maturation. The volatiles in navel orange from July (young fruit period) to November (commercial maturation period) were separated by headspace solid-phase microextraction (HS-SPME) and analyzed using gas chromatography-mass spectrometry (GC-MS). Fifty-seven VOCs were identified and classified into five groups. Through principal component analysis, the samples of different months were discriminated, and one-way analysis of variance showed that 55 volatiles significantly differed during growth. Among the VOCs, the relative concentration of monoterpenes increased with maturity, and D-limonene was the component with the highest content. Similar behavior was exhibited for aldehydes, reaching the maximum content in November. On the contrary, esters decreased its concentration from July to November. The concentration of sesquiterpenes gradually increased, reaching the maximum level between August and November. Moreover, alcohols reached theirs largest content in September, ß-Linalool had the highest content among the alcohols. These results provided important theoretical support for the development of navel orange components and comprehensively elucidate the flavor characteristics during the ripening of navel orange.