Investigations of the Chemical Composition and Aromatic Properties of Peel Essential Oils throughout the Complete Phase of Fruit Development for Two Cultivars of Sweet Orange (Citrus sinensis (L.) Osb.)

Abstract

The peel essential oil (PEO) of sweet orange is used for flavoring liquors or foods and in the perfumery and cosmetics industry. The fruit maturity stage can modify the essential oil composition and aromatic properties, but little information is available on the evolution of PEO during the entire time set of fruit development. In this study, the yield, chemical composition and aromatic profile over the three phases of orange development were monitored. Four fruit traits (peel color, weight, acidity and sweetness) were recorded to characterize fruit development. Fruits of two sweet orange cultivars were sampled every two weeks from June to May of the next year. PEO was obtained by hydrodistillation and analyzed by gas chromatography coupled with a flame ionization detector (GC-FID). Compounds were identified with GC coupled with mass spectrometry (GC/MS). Ten expert panelists using the descriptor intensity method described the aromatic profile of PEO samples. The PEO composition was richer in oxygenated compounds at early fruit development stages, with an aromatic profile presenting greener notes. During fruit growth (Phases I and II), limonene's proportion increased considerably as a few aliphatic aldehydes brought the characteristic of orange aroma. During fruit maturation (from November to March), the PEO composition and aromatic profile were relatively stable. Later, some modifications were observed. Regardless of the fruit development stage, the two sweet oranges presented distinct PEO compositions and aromatic profiles. These results constitute a temporal reference for the chemical and aromatic evolution of sweet orange PEO in the fruit development process under Mediterranean conditions. During the first two phases of fruit development, many changes occur in the PEO composition and aroma, suggesting that their exploitation could create new products.

Keywords: GC-FID; GC/MS; fruit growth; fruit maturity; oxygenated compounds; sensorial analysis.

Figure 1

Dot plots representing the evolution of phenological parameters at different dates of fruit development. The vertical bar on each dot represents the standard deviation. (A) fruit weight (W) (in g); (B) citrus color index (CCI) of the flavedo; (C) titrated acidity (AC) expressed in % of citric acid; and (D) total soluble solid (TSS) content expressed in °Brix.

Figure 2

Dot plots representing the evolution of the average weight (g) of essential oil per fruit (A), the average weight (g) of essential oil per 100 g of dried peel (B) and the average weight (g) of essential oil per 100 g of fresh fruit (C) throughout fruit development. The vertical bar represents the standard deviation, and the letter in each plot represents the statistical group according to Tukey’s test (p ≤ 0.05) of differences between cultivars at each date.

Figure 3

Stacked bar plot representing the mean proportion of major chemical families of the “Cara Cara navel” sweet orange cultivar during fruit development.

Figure 4

Biplots of principal component analysis representing the diversity of the PEO composition of each sampling date (in black) and the contribution of the 33 main aromatic compounds (in blue). Each sampling date represents the average composition of each compound of the five repetitions of “Cara Cara Navel” sweet orange.

Figure 5

Stacked histogram representing the evolution of the 15 main compounds between January and May for the PEO of the two cultivars. When the proportion of a compound in “Cara Cara Navel” was superior to that in “Madame Vinous”, the bar is red, and in the opposite situation, the bar is green. *—Significant differences between the two varieties. The asterisk indicates a significant difference with the Kruskal-Wallis test (p < 0.05).

Figure 6

Bar plots representing the evolution of the five sensory descriptors of “Cara Cara Navel” (A) and “Madame Vinous” (B) sweet oranges during fruit development. The vertical bar represents the standard deviation, and the letter represents the statistical group according to Tukey’s test.

Figure 7

Correlation circles between PEO compounds and aromatic descriptors using partial least squares regression. Compounds are represented in blue, and aromatic descriptors are represented in orange. The inner circle corresponds to a correlation of (±) 0.5, and the outer circle corresponds to (±) 1. (A) “Cara Cara Navel” and (B) “Madame Vinous”.