Citrus is one of the most important com-mercial fruit crops grown in all continents of the world. Due to natural distinct flavors and medicinal value, people’s interest is increasing inits consumption. Citrus contains bioactivecompounds that lower the risk of colorectal, esophageal, gastric and stomach cancers, stroke and play protective role against many chronicdiseases. Beside this, citrus fruits also have asignificant role in improving blood lipid profilesand survival in the elderly.
In current citrus industry, citrus fruits areconsumed as raw or as processed juice whilefruit peel is produced in great quantities and due to unawareness, this highly valuable peelhaving renowned mass is regarded mainly as awaste. Citrus peel has significant economicvalue for its essential oil. If proper recyclingof this peel is performed, a valuable productcan be made from this natural gift in the formof peel oil. Interestingly, recent research studieshave revealed that fruit peel of citrus hasessential oils which provide antioxidant and antimicrobial properties. Essential oils of plants have been proven to be eco-friendly bio-control agent too.
Photosensitization is a potential problem withmany cold pressed citrus oils. Distillationtechniques are the most common fragranceyielding method. Since the last decade, consumersare becoming more conscious of the nutritionalvalue and safety of their health as well as food and ingredients while on the other hand, pestcontrol (bacterial & fungal) in the public healthsector continues to place heavy reliance upon theuse of synthetic chemicals. The present study wascarried out with the objectives to characterizecitrus peel oil in a range of citrus cultivars on the basis of physical, morphological and chemicalcharacters; to document potential use of oil as anantioxidant and antimicrobial additive.
Materials and methods
Plant material collection and extraction of essential oils
All citrus plant material used in this study wascollected from the in situ citrus repositorymaintained and authenticated by the citrus experts at the Institute of Horticultural Sciences (IHS),University of Agriculture, Faisalabad, Pakistan.An exclusive citrus gene pool has been established by the IHS following precise descriptive identi-fication of all available species at PostgraduateAgricultural Research Station (PARS) and Experimental Fruit Garden Square # 9. Maturefruits (in uniform size) of commonly grown citruscultivars viz. sweet oranges (Citrus sinensis Vars.Jaffa, Blood Red and Mosambi), Mandarins(Citrus reticulata Var. kinnow) and grapefruits (Citrus paradisi Var. Shamber) were collected from the Postgraduate Agricultural ResearchStation (PARS) and Experimental Fruit GardenSquare # 9, Institute of Horticultural Sciences, University of Agriculture, Faisalabad, Pakistan.To find out the quantity of essential oil contentsin peel; minimum 5 kilograms of peel of eachcultivars were collected. Conventional hydro-distillation method was used to extract the oil fromcitrus peel. The essential oils were dried over anhydrous sodium sulphate to remove any tracesof water and kept at 4° C until use. Extraction process was carried in triplicate to obtainreproducible results.
Analysis of essential oil
Five microliters of essential oil were diluted using 0.5 mL of n-hexane (0.5 mL) and analyzed with the Agilent 6890N GC was interfaced with aVG Analytical 70-250s double - focusing massspectrometer apparatus equipped with a 30 m ×0.32 mm fused capillary silica column coated withDB-5. Mass spectrometer was operated in the EImode at 70 eV and in the m/z range 40-500.Carrier gas helium was passed at a flow rate of 1.0 mL/min and the injector and the transfer linewere maintained at 250 and 280° C, respectively.The column temperature was kept constant at 60° C for 4 min and then programmed to rise to 240° C at 4° C/min with hold up time of 15 min at 240° C. Retention indices of the separated compounds were determined on the basis of ahomologous series of n-alkanes.The relative proportions of the essential oilconstituents were expressed as percentagesobtained by peak area normalization, and allrelative response factors were taken as one.
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