Since the nutritional information is automatically calculated, we have to distinguish between lemons used without the peel and lemons used with the entire peel, for example, for marmalade. We also should distinguish between lemons and limes. Limes are greener and smaller and usually taste stronger and are also more aromatic, whereas lemons are considered to be sour.
From Wikipedia: “The lemon, Citrus limon (L.) Osbeck is a species of small evergreen tree in the flowering plant family Rutaceae, native to Asia.
The tree's ellipsoidal yellow fruit is used for culinary and non-culinary purposes throughout the world, primarily for its juice, which has both culinary and cleaning uses. The pulp and rind (zest) are also used in cooking and baking. The juice of the lemon is about 5% to 6% citric acid, which gives a sour taste. The distinctive sour taste of lemon juice makes it a key ingredient in drinks and foods such as lemonade and lemon meringue pie.”
“Lemons are a rich source of vitamin C, providing 64% of the Daily Value in a 100 g serving. Other essential nutrients, however, have insignificant content. Lemons contain numerous phytochemicals, including polyphenols, terpenes, and tannins. As with other citrus fruits, they have significant concentrations of citric acid (about 47 g/l in juice).”
“Lemon juice, rind, and zest are used in a wide variety of foods and drinks. Lemon juice is used to make lemonade, soft drinks, and cocktails. It is used in marinades for fish, where its acid neutralizes amines in fish by converting them into nonvolatile ammonium salts, and meat, where the acid partially hydrolyzes tough collagen fibers, tenderizing the meat, but the low pH denatures the proteins, causing them to dry out when cooked. Lemon juice is frequently used in the United Kingdom to add to pancakes, especially on Shrove Tuesday.
Lemon juice is also used as a short-term preservative on certain foods that tend to oxidize and turn brown after being sliced (enzymatic browning), such as apples, bananas, and avocados, where its acid denatures the enzymes.
Lemon juice and rind are used to make marmalade, lemon curd and lemon liqueur. Lemon slices and lemon rind are used as a garnish for food and drinks. Lemon zest, the grated outer rind of the fruit, is used to add flavor to baked goods, puddings, rice, and other dishes.
The leaves of the lemon tree are used to make a tea and for preparing cooked meats and seafoods.”
“Lemons were the primary commercial source of citric acid before the development of fermentation-based processes.”
As a cleaning agent
“The juice of the lemon may be used for cleaning. A halved lemon dipped in salt or baking powder is used to brighten copper cookware. The acid dissolves the tarnish and the abrasives assist the cleaning. As a sanitary kitchen deodorizer the juice can deodorize, remove grease, bleach stains, and disinfect; when mixed with baking soda, it removes stains from plastic food storage containers. The oil of the lemon's peel also has various uses. It is used as a wood cleaner and polish, where its solvent property is employed to dissolve old wax, fingerprints, and grime. Lemon oil and orange oil are also used as a nontoxic insecticide treatment.
A halved lemon is used as a finger moistener for those counting large amounts of bills, such as tellers and cashiers.”
“Lemon oil may be used in aromatherapy. Lemon oil aroma does not influence the human immune system, but may contribute to relaxation.”
“One educational science experiment involves attaching electrodes to a lemon and using it as a battery to produce "electric power". Although very low power, several lemon batteries can power a small digital watch. These experiments also work with other fruits and vegetables.
Lemon juice may be used as a simple invisible ink, developed by heat.”