Many of us may be familiar with candied “citron” in fruitcake. Some may say that any food-like substance appearing in fruitcake could not possibly be healthy. This post explores health benefits of orange peel in particular. The peeling orange image came from a 2015 Natural Remedies post on recycling of orange peel for various purposes. Dr Andrew Weill’s website put its own two cents on orange peel health benefits.Just be careful about the pesticides. This post is taking a different approach to address medicinal properties.
After the production of orange juice, citrus peel oil is extracted and used in fragrances, cleaning fluids, cosmetics, and aroma therapy. Compounds in citrus peel oil may be antimicrobial and insecticidal. Limonene is the major volatile compound in citrus peel oils. The compounds in orange peel oil will be affected by the type of orange, the time of harvest, soil conditions, and disease status. 
Citrus peel pectin has been presented in the pectin and butyrate post on this site as a means of generating short chain fatty acids by fermentation by intestinal bacteria. Econugenetics has a compound called Pectasol. This produce is less than 13 kDa and less than 5% eserification. . Around slide 15 of the Isaac Eliaz slide share we find out what is meant by modified pectin.
Dr Isaac’s slide share does a a good job covering many of the several dozen peer reviewed studies on activation of galectin-3 by their product.
What is galectin-3?
According to UniProt.org, Galectin-3, “Galactose-specific lectin which
- binds IgE.
- May mediate with the alpha-3, beta-1 integrin the stimulation by CSPG4 of endothelial cells migration.
- Together with DMBT1, required for terminal differentiation of columnar epithelial cells during early embryogenesis (By similarity).
- In the nucleus: acts as a pre-mRNA splicing factor.
- Involved in acute inflammatory responses including neutrophil activation and adhesion, chemoattraction of monocytes macrophages, opsonization of apoptotic neutrophils, and activation of mast cells.
- Together with TRIM16, coordinates the recognition of membrane damage with mobilization of the core autophagy regulators ATG16L1 and BECN1 in response to damaged endomembranes”
Galectin-3 is a mere 250 amino acids in length with an approximate molecular mass of about 26 kDa… about twice the mass of Pectasol. These images came from Protein Atlas. According to this site the expression is high in colonic endocrine cells and enterocytes (but not microvilli), but not detected in endothelial cells.
How does Pectasol get into our blood stream?
We don’t know, really.
- We don’t know how it gets out of our blood either.
- We don’t know if the gut microbiome consumes Pectasol
- We don’t know if other polysaccharides will work as well or even better
What else is in orange peel?
This list is not exhaustive. Should we decide to go the organic, natural, non processed route, it’d be nice to know what we are putting in our bodies besides pectin
Huanglongbing (HLB, or citrus greening), associated with the bacterium Candidatus Liberibacter asiaticus (CLas), is a multi billion dollar threat to Florida’s Valencia orange industry. Fruits and juice from HLB-diseased trees are also associated with low soluble sugar and ethyl butanoate, as well as high acid, limonoid, and flavonoid content.  These authors wanted to know how the various fertilizers and pesticides affected teh chemicals in Valencia orange peel. The analyzed for several dozen terpenes only to determine that regardless of HLB status or types of treatments, limonene was always about 90% of the total terpenes. 
Note that this is not the entire list, but a small part. Note that limonene is aways around 90% of the total.
Flavonoids are polyphenolic compounds found in plants. A group out of Singapore used pressurized hot water to extract compounds from orange peel. Pressurized hot water can be achieved at home with a pressure cooker. The authors used several presured temperatures. Table 1 compares water extraction under pressure with methanol extraction. The authors cite references about the dipole moment of water being reduced under tempraturer and pressure.  In Table 1 we will assume that RSD is the standard deviation divided by the mean and multiplied by 100.
- Gallic acid is a cyclooxygenase 2 inhibitor and plant metabolite
- p-coumaric acid is a free radical scavenger
- ferulic acid is an anti-oxidant and has anti-inflammatory properties.
- narirutin is an anti-inflammatory disaccharide
- hesperidin is a disaccharide found in citrus and a potential mutagen according to PubChem. Herperidin seems to be anti-inflammatory according to one PubMed abstract.
Note that this table expresses in units of mg of flavonoid per kg of orange peel. The authors only produced 314.56 mg, or 0.314 g, of gallic acid with a day of extraction at 60oC. They extracted 35,702mg, or 36 g, of Neperidin! Orange peel is starting to seem like a serious source of antioxidants. This luke warm “pressure cooker” extraction yields just a little more than 10x the amount of Hesperidin as does the methanol extraction, something a lay person would never do at home.
The authors used two colorimetric assays to measure antioxidant capacity: DPPH assay and the ABST assay. In the DPPH assay, less is more. The less extract it takes to inhibit 50% of the reaction, When it comes to the ABTS assay, more equivalent Vitamin C units is more anti-oxidant power. It is clear that going up to 120oC reduces the anti-oxidant power in some way.
Processing orange peel at home?
The pressurized extraction at 60oC might be difficult for most to do at home. However, 100oC is only the boiling temperature of water. This post is public simply to exchange ideas on how to do this. This post is absolutely not meant to discourage anyone from Pectasol. The fact that orange peel has more healing compounds than just the pectin gives one pause as to whether buying the processed stuff will lead to a return on the investment. This post has not gotten into targets of the terpene limonene or if there’s enough limonene in a reasonable amount of orange peel to make a difference. Perhaps the pleasant aroma can make a difference in terms of aromatherapy. The flavonoids in orange peel certainly seem like something not to discard.
- Eliaz I. Letter to the Editor: Not all modified citrus pectins are the same: size does matter. Am J Physiol Heart Circ Physiol. 2019 May 1;316(5):H1232-H1233. PMC free article
- Sun X, Yang H, Zhao W, Bourcier E, Baldwin EA, Plotto A, Irey M, Bai J. Huanglongbing and Foliar Spray Programs Affect the Chemical Profile of “Valencia” Orange Peel Oil. Front Plant Sci. 2021 Apr 6;12:611449. PMC free article
- Leo CH, Foo SY, Tan JCW, Tan UX, Chua CK, Ong ES. Green Extraction of Orange Peel Waste Reduces TNFα-Induced Vascular Inflammation and Endothelial Dysfunction. Antioxidants (Basel). 2022 Sep 7;11(9):1768. PMC free article
This paper comes out of t