الفهرس 
SOME CITRUS PEELS AS A SOURCE OF ANTIOXIDANTS IN DIFFERENT VEGETABLE OILS AND ITS APPLICATIONS IN SOME FUNCTIONAL FOODSOnly 14 pages are availabe for public view
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Abstract
By-products of food processing industries have added value by identification and
isolation of their bioactive compounds. Consequently, the present study was conducted on the
orange peels (OP), mandarin peels (MP) and lemon peels (LP) to achieve the following five goals: (1) Determination of chemical composition and essential oils of citrus peels.
(2) Investigating bioactive compounds such as phenolics, flavonoids, vitamin C and dietary fibers.
(3) Determination of the antioxidant activity of citrus peels.
(4) Comparing among citrus peels and their ethanolic extract as a source of natural antioxidants
in some edible oils to extend its shelf life.
(5) Preparing some functional food products containing citrus peels.
The main results obtained in the present study can be summarized as follows:
A) Chemical composition of orange, mandarin and lemon peels.
1) The moisture content ranged between 70.05 % for LP to 77.82 % for MP, while the moisture content of OP lied in between being 72.33 %.
2) The crude protein content of OP, MP and LP ranged from 4.44 % to 9.91 % on dry weight basis (DW). The OP exhibited significantly (p ≤ 0.05) the least crude protein content (4.44%), on contrary to LP which possessed significantly (p ≤ 0.05) the highest content (9.91 %).
3) The LP had significantly (p ≤ 0.05) the highest crude oil content (12.79 %) and the OP exhibited crude oil content of 8.64 %, while the MP was tailed behind since it had 10.1% crude oil content.
4) The LP possessed significantly (p ≤ 0.05) the highest ash content (15.13 %), on contrary to MP that had 10.37 % ash content. As for OP, it had ash content being in between the aforementioned two values (10.41%) (DW).
5) A range from 62.17 % to 76.51 % (DW) was figured out for the carbohydrate content for the three types of peels. The OP had significantly (p ≤ 0.05) the highest content of total carbohydrate (76.51 %) followed by LP (72.9 %) and MP had significantly (p ≤ 0.05) the least carbohydrate content (62.17%).
6) The MP had significantly (p ≤ 0.05) the highest total sugars content (33.35 %) and OP exhibited total sugars of 32.82 %, while the LP was tailed behind, since it had 30.7 % total sugars content.
7) The ascorbic acid content of OP, MP and LP ranged from 29.43 to 44.36 mg / 100 g (DW). The LP exhibited significantly (p ≤ 0.05) the least ascorbic acid content (29.43 mg / 100g), on contrary to MP which possessed significantly (p ≤ 0.05) the
highest content (44.36 mg / 100g), while the ascorbic acid content of OP lied in between (35.27 mg /100 g).
B) Fiber and pectin content in orange, mandarin and lemon peels.
1) Orange peel had significantly (p ≤ 0.05) the highest crude fiber content (8.73 %),followed by LP (6.51 %), whereas, MP exhibited significantly (p ≤ 0.05) the lowest crude fiber content (5.48 %).
2) The MP had significantly (p ≤ 0.05) the highest contents of NDF (21.83 %) and hemicellulose (10.89 %), followed by OP which was 17.85 % NDF and 4.33 %
hemicellulose, then LP 12.43 % NDF and 1.11 % hemicellulose. However, OP had
significantly (p ≤ 0.05) the highest contents of ADF (13.52 %) and cellulose (12.4 84 %), followed by LP being 11.32 % ADF and 10.18 % cellulose, followed by MP which had 10.94 % ADF and 9.87 % cellulose.
3) Lemon peel had significantly (p ≤ 0.05) the highest content of lignin (1.14 %), followed by OP (1.12 %) and MP (1.07 %).
4) It can be observed that the pectin content for each of MP and LP were comparable (17.72 and 19.04 %, respectively), while OP had significantly (p ≤ 0.05) the highest
content of pectin (25.84 %) as compared with MP and LP.
C) Minerals content of orange, mandarin and lemon peels.
1) The significant (p ≤ 0.05) high content of calcium was in LP (2185.19 mg /100 g), followed by OP (1147.15 mg / 100 g) and MP (683.2 mg / 100 g).
2) The LP was significantly (p ≤ 0.05) higher in sodium content (1164 mg /100 g), followed by OP (623 mg / 100 g) and MP (614 mg /100 g). On the other hand, the amount of potassium was higher in OP (7670 mg / 100 g) and MP (6140 mg /100
g) compared to LP (2667 mg / 100 g).
3) Iron, a very important mineral was found in OP in a considerable amount
(63.0 mg /100 g), LP (54.9 mg / 100 g) and MP (48.8 mg / 100 g). Magnesium
followed the same trend, it was found in OP, MP and LP as follows: (81.0, 69.7 and 92.1 mg / 100 g, respectively)
4) There were trace amounts of copper and manganese in OP (4.0 and 4.5 mg / 100g, respectively) in MP (5.7 and 3.2 mg / 100 g, respectively) and in LP
(7.8 and 5.3 mg /100 g, respectively). Also, there was a trace amount of zinc in OP, MP and LP.
D) Essential oils content of orange, mandarin and lemon peels.
The amount of essential oils ranged from 0.87 % in LP to 2.4 % in OP, while the MP lied in between being 1.9 %. The essential oils in OP, MP and LP have been analyzed using GC-MS apparatus to identify different components in the citrus peels. The main components in the essential oil of OP and MP were D-limonene (94.91 % and 77.85 %,
respectively), the other main components in OP were β- myrcene (2.96 %), α- pinene (1.17 %) and finally linalool (0.97 %). Furthermore, the other main components in MP were ᵞ -terpinene (13.83 %), α-pinene (3.1 %), β-myrcene (2.36 %), β-pinene (1.75 %) and
finally α-thujene (1.09 %). In contrast, the main components in LP were α- terpineol (50.64 %), followed by terpinen-4-ol (27.54 %), linalool (7.89 %), Z-citral (7.12 %) and finally
trans-caryophyllene (6.81 %), which is mainly different from OP and MP essential oils components.