Addition of orange by-products (dry peel) in orange jam: evaluation of physicochemical characteristics, bioactive compounds and antioxidant activity

Citrus fruits (Rutaceae) are an important source of bioactive compounds such as ascorbic and hydroxycinnamic acids. Citrus peels contain significant amounts of phenolic compounds especially phenolic acids and flavonoids.

The citrus fruit residues, which are usually discarded as waste can be used as nutraceutical resources. The utilization of these bioactive rich citrus residues can serve for the production of novel products or for the improvement of those already in use. Orange peel contains significant amounts of phenolic compounds especially phenolic acids and flavonoids, thus we can consider it a potential material for the formulation of nutraceuticals and food preservatives and may be used as a possible functional ingredient in alimentary products such as marmalade.

The industrial manufacture of fruit jams requires constant gel strength during production; consequently, commercial pectin is added to minimize the effect of the variability of native fruit pectin. Orange marmalade is generally prepared by boiling fruit pulp with sugar, pectin, acid and other ingredient (preservatives, coloring, and flavorings).

The aim of this study was to investigate the effect of adding dry (Citrus x sinensis) peel to orange marmalades as an alternative to pectin, and to evaluate product stability.

The product stability and the antioxidant effect on shelf life of this enriched marmalade were evaluated. In particular, the hydroxymethylfurfural formation in correlation with major bioactive compounds, antioxidant assay, total phenols and anthocyans were estimated during storage at 18 and 30 °C for 140 days. The level of phenols ranged from 70.27 to 152.01 mg/100 g for control samples and from 108.18–146.02 mg/100 g for enriched samples. Obtained data show that incorporation of orange peel in marmalade production can be a valid use of this by-product. After storage, the enriched samples at 18°C maintained the analytical parameters better than the samples stored at 30°C.