The Effect of Fruit Maturity on Physicochemical Properties and Polyphenols in Citron Fruit (Citrus medica var. medica Proper.)

The harvest time and type of plant part have important roles in obtaining maximum amounts of active substances from medicinal plants. Medicinal plants vary in terms of phenological stages and maturity and each medicinal plant can be evaluated separately in research. Determining the exact time of harvest and selecting a plant organ for maximum yield of secondary metabolites can be very important and economically effective. Othroj-Saghir (Citrus medica var. medica Proper) or Othroje-Kabir (Citrus medica var. macrocarpa) is one of the most important citrus species. The southern provinces of Iran, especially the southern cities of Fars province, are the largest areas in which this species is cultivated. In addition to fruit juice, other parts of the fruit especially the flavedo, can be used for medicinal purposes and in food industries. In this study, for the first time, some physical and biochemical changes of different parts of Citrus medica var medica fruits were evaluated during fruit ripening. Also, some active substances (i.e. essential oil content, flavonoid components, etc.) of the flavedo were measured as the most important medicinal parts of the fruit through different stages of ripening.

In this study, the effects of fruit ripening on the biochemical properties of different parts of Citron fruit were evaluated. A factorial experiment was set up according to a randomized complete block design (RCBD) with two factors and four replications. The first factor included four levels: different stages of fruit maturity (green mature, intermediate, yellow ripe and over ripe stage). The second factor had four levels: the different parts of the Citron fruit (i.e. outer skin or flavedo, inner skin or albedo, pulp and juice). The most important measured traits were flavon and flavonols, total flavonoids, total phenolic compounds and antioxidant activity. Physical changes in different parts of the fruit (fresh and dry weight of flavedo and albedo, fresh weight of fruit, fruit diameter and height of fruit, etc.) were measured. Assessments also carried out to identify several features of fruit juice such as acidity, total soluble solids (TSS), titrable acidity (TA) and vitamin C during fruit ripening. Chemical measurements were aimed at determining the most important phytochemical compounds of the flavedo section during fruit ripening. These features included the essential oil percentage and yield, chlorophyll content and polyphenols constituents (rutin, trans-ferulic acid, hesperidin, hesperetin and quercetin by HPLC).

The results showed that the fruit maturity stage significantly affected most of the studied traits. The highest amounts of flavon and flavonols (0.377 mg quercetin/g dry weight) and total flavonoids (16.38 mg quercetin/g dry weight) were measured in the flavedo at the over ripe stage. The antioxidant activity initially increased during fruit ripening, but it decreased slightly (75.0%) from the yellow stage to the over ripe stage. The lowest rate of antioxidant activity (53.6%) was observed in the green stage and the highest rate (78.4%) was measured in the yellow ripe stage. The highest amounts of antioxidant activity (83.3% and 73.8%) were measured in the albedo and flavedo samples, respectively, and the lowest amount (54.1%) was recorded in the pulp section. The highest amount of flavedo essential oil (2.37%v/w) was measured in intermediate stage. The chlorophyll content with maturity progress was decreased. Progress in fruit maturity was reduced the most components of polyphenols. The maximum amount of hesperidin, as an important phenolic component, was identified in the peel of Citron fruit (1.86 mg/g dry weight) at the green mature stage. Its amount decreased through the stages of maturity, so that the lowest amount (0.68 mg/g dry weight) was measured at the over ripe stage.

In general, the stage of maturity and plant part had important effects on the amount of biochemical traits. The flavedo part of Citron fruit showed superior medicinal properties. Different active substances react variedly during maturity and so the preferable composition should be harvested according to the desired conditions. The best stages to reach maximum essential oil percentage and polyphenol components are the early stages of maturity (i.e. green mature and intermediate stages).