In the European Union alone, some 88-90 million tons of food waste are produced every year. IN the UNitesd States this reaches 100 millions tons ageragely. The processing of fruit and vegetables alone involves a waste that can reach 30% of the total product. Although considered common waste products, seeds, husks and peels contain bioactive molecules such as oils, coenzymes, pro-vitamins, vitamins and polyphenols. Fruit and vegetable wastes are made up of secondary metabolites that have been explored for phenolics, dietary fiber and other bioactive compounds. Research suggests that essential nutrients and phytochemicals are abundant in fruit peels and seeds. For example, the peel of grapes, lemons, avocados and mango seeds contain 15% more phenolic compounds than the pulp. Various countries have directed food industries to ensure low food waste. As such, bioactive compounds such as antimicrobials and antioxidants have been introduced as viable solutions to improve the shelf life of food products.
A range of natural products found in fruit peels have antimicrobial, cytotoxic and antioxidant properties. The use of fruit peels as sources of biologically active molecules could be helpful in preventing spoilage bacteria (Pseudomonas) and food poisoning caused by Staphylococcus aureus. Edible coatings (eco-packaging) are thin layers on the surfaces of foods that improve shelf life and help maintain the characteristics and functionality of foods. A research team has synthesized an apple peel-based coating for beef meatballs. They revealed that the application of the edible film inhibited lipid oxidation and suppressed the growth of the microbes tested. Growing evidence points to the improvement in the shelf life of several food products (cupcakes, shrimp, strawberries and tofu) by coating them with edible films derived from fruit peels.
Interestingly, some studies have found that adding powdered fruit peels to probiotic yogurts improved the growth of Lactobacillus spp. In fact, pectin is a prebiotic fiber for some bacterial species. Fruit peels, which represent a significant part of industrial food by-products, have not been used as a valuable resource. The agri-food industry is looking for new solutions for various reasons. One of these is sustainability and all the collateral associated with the problem, such as fighting waste, saving water and energy, depleting resources and reducing the use of plastic materials. While generally considered an unhealthy and unwanted byproduct, the wide range of natural products in fruit peels, including peptides, steroids, alkaloids, and polyphenols, among others, could have significant benefits for human health. Examples are given below which, due to the timing and breadth of the topic, will be greatly reduced.
Citrus peels contain bioactive compounds and have been conventionally used in some regions of the world to treat coughs, muscle and intestinal aches, digestive problems, and skin inflammation. Who has never experienced the infusion of bay leaves and lemon peel (the “canary”) for a bad digestion or stomach cramps? Polyphenol nobiletin is found in the fruit peels of several citrus fruits (including oranges) and research has shown its antioxidant, anti-inflammatory and anticancer activity. Another study reported the inhibition of nuclear factor kappa -B (NF-κB) by nobiletin in mouse models, with protective action on neuroinflammation, a pivotal component in multiple sclerosis and similar diseases. Furthermore, in vivo studies have reported the protective effects of nobiletine against various types of cancer. Hesperidin present in C. sinensis and C. reticulata has shown potent anti-inflammatory, antimicrobial, antioxidant and chemopreventive effects.
Additionally, hesperidin has also been used as a supplemental dietary product as its deficiency leads to nocturnal leg weakness, pain and cramps. It is no coincidence that many commercial preparations used for capillary fragility contain extracts from blueberry, vine (Vitis vinifera) and even citrus fruits. They are better known as vitamin P complex and exert a tonic action on the walls of blood vessels, preventing them from stiffening and the tendency to bleed. They also collaborate with vitamin C to repair vascular collagen and protect it from inflammation. The polymethoxy-flavones from Japanese citrus peels, “hebesu”, have shown potent anti-neuroinflammatory effects by inhibiting the expression of interleukin (IL)-1β. The peels of Citrus unshiu and C. reticulata are used as raw drugs in Japan and referred to as “Chimpi”. Several coumarins, which are natural anticoagulants, have been isolated from the fruit peels of C. hystrix.
Some coumarins (isoimperatorin, bergamottin and oxo-peucedanine) inhibit the butyryl-cholinesterase enzyme, a liver and blood enzyme that is used to deactivate muscle-numbing drugs. Other coumarins (eg oxo-peucedanin) from the same plant can block the production of the inducible nitric oxide synthase (iNOS) enzyme in animal macrophages. This enzyme is partly responsible for cardiovascular collapse in the case of septicemia. The fruit peels of Elaeagnus rhamnoides contain a quinone, musizine, caulilexin C and a nor-sesquiterpene. Nor-sesquiterpene was shown to exert antiviral activity on the herpes simplex virus 2 (HSV-2) in a virus reduction yield test. Musizine, a derivative of naphthalene, was also found to be anti-HSV-2 although it was less potent. Pomegranate (Punica granatum) peels contain punicagranin, a pyrrolizidine alkaloid with anti-inflammatory effects that is not toxic to macrophage immune cells.
The polyphenol-rich fraction of Annona crassiflora fruit peels has antioxidant effects that may have potential clinical applications in the treatment of diabetes. Steroid alkaloids such as solamargine, solasodine and solasonine (cousins of solanine in tomatoes, eggplant and potatoes) are present in the fruit peels of Solanum melongena, the common long eggplant. They are cytotoxic to cervical, liver and breast cancer cell lines. Carbazole alkaloids such as claulansin K, claulansin J, carbazole-3-carboxylic acid, etc. were found in the husks of Clausena lansium. It has been reported that claulansin K and clausolanamide inhibit digestive α-glucosidase, interfering with the intestinal absorption of glucose and therefore lowering blood sugar. In contrast, claulansin J showed a moderate antibacterial effect against Staphylococcus aureus of common septicemia and other lethal skin infections.
Ataluntum found in the peels of the fruit of Atalantia monophylla, a lemon-like tree that grows in Thailand and India, is a potent cytotoxic compound for cholangiocarcinoma (biliary tract cancer) cells. Other benzoyl tyramines of Atalantia monophylla showed antitumor activity against the HeLa, HCT116 and MCF-7 cell lines. One study extracted flavones from fruit peels of Wisteria floribunda (Japanese wisteria), and found several promising candidates for inhibition of platelet-derived growth factor (PDGF) -induced proliferation on arterial muscle cells (VSMC). These include syringaresinol and (-)- pinoresinol. This means that they could be useful in countering atherosclerosis induced by hypertension. Finally, the fruit peels of W. floribunda contain phytosteroids such as β-sitosterol and β-sitosterol glucopyranoside which contribute to the action of the previous polyphenols on the proliferation of VSMCs.
Looks like, therefore, it’s not just for pork that nothing is thrown away….
- Edited by Dr. Gianfrancesco Cormaci, PhD, specialist in Clinical Biochemistry.
Hussain H et al. Curr Issues Mol Biol 2022; 44(5):1960-94.
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Dott. Gianfrancesco Cormaci
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