Fruit enzymes like papain and bromelain are proteolytic enzymes, meaning they break down proteins into smaller peptides or amino acids. These enzymes are naturally found in certain fruits and have various applications in the food, pharmaceutical, and cosmetic industries. Chemical Properties: • Proteolytic Activity: Papain catalyzes the hydrolysis of peptide bonds in proteins, particularly those involving basic amino acids like lysine and arginine. • Optimal pH: Papain exhibits optimal activity in a slightly acidic to neutral pH range (5.5 to 7.0). • Temperature Sensitivity: Papain is relatively heat-stable but can be denatured at very high temperatures (above 70°C). Its activity can be retained over a broad temperature range, typically between 30°C and 60°C. • Inhibition: Papain's activity can be inhibited by specific chemical inhibitors, such as iodoacetate and heavy metal ions like copper and mercury, which react with its active site.

Salicylic acid is a beta-hydroxy acid (BHA) that is widely used in skincare, particularly for treating acne and other skin conditions. It is a naturally occurring compound found in plants like willow bark, but it is also synthesized for use in pharmaceuticals and cosmetics. Salicylic acid is well-known for its exfoliating, anti-inflammatory, and keratolytic (skin-shedding) properties. Chemical Properties 1. Structure: o Salicylic acid consists of a benzene ring with two functional groups: a hydroxyl group (-OH) attached to the ortho position (carbon 2) and a carboxylic acid group (-COOH) attached to the carbon 1 position. This structure makes it a beta-hydroxy acid (BHA), distinguishing it from alpha-hydroxy acids (AHAs) like glycolic acid and lactic acid. o The hydroxyl group is attached to the benzene ring in the ortho position relative to the carboxylic acid group, giving salicylic acid its specific properties. 2. Solubility: o Salicylic acid is sparingly soluble in water (about 2 g/L at room temperature) but is more soluble in organic solvents such as ethanol, acetone, and ether. o This limited solubility in water makes it less irritating when applied to the skin, as it penetrates slowly and reduces the likelihood of over-exfoliation. 3. Acidity: o Salicylic acid is a weak acid with a pKa of 2.97, meaning it partially dissociates in water to release hydrogen ions (H+). Its acidic nature contributes to its ability to exfoliate the skin by dissolving the bonds between dead skin cells. o The carboxylic acid group contributes to its overall acidity, while the hydroxyl group allows for hydrogen bonding and interaction with other molecules. 4. Exfoliating Properties: o Salicylic acid is keratolytic, meaning it helps to shed the outer layer of the skin (stratum corneum) by breaking down keratin, a protein that holds skin cells together. This action makes it highly effective in treating acne, as it can penetrate into the pores, dissolve excess oil, and prevent clogged pores. o Unlike AHAs, which are water-soluble and primarily work on the skin's surface, salicylic acid is oil-soluble, allowing it to penetrate deeper into the pores and exfoliate from within. 5. Anti-Inflammatory Properties: o Salicylic acid is derived from salicin, a compound related to aspirin (acetylsalicylic acid). It shares similar anti-inflammatory properties, making it beneficial for calming irritated skin and reducing redness associated with acne. o Its anti-inflammatory effects are due to its ability to inhibit the production of certain inflammatory mediators, such as prostaglandins.

Glycolic acid is the simplest alpha-hydroxy acid (AHA) and is widely used in skincare products due to its effective exfoliating properties. It is naturally derived from sugar cane but can also be synthesized. Glycolic acid is highly valued in dermatology and cosmetics for its ability to improve skin texture and tone. Chemical Properties 1. Structure: o Glycolic acid has a simple structure with two carbon atoms. The molecule consists of a hydroxyl group (-OH) attached to the alpha carbon, which is adjacent to the carboxylic acid group (-COOH). o The presence of both the hydroxyl and carboxylic acid groups gives glycolic acid its unique chemical properties. 2. Solubility: o Glycolic acid is highly soluble in water, which makes it easy to formulate in aqueous-based skincare products. o It is also soluble in alcohols and some organic solvents, but its solubility in non-polar solvents is limited. 3. Acidity: o Glycolic acid is a relatively strong acid among AHAs, with a pKa of around 3.83. This indicates that it readily dissociates in water to release hydrogen ions (H+), contributing to its acidic nature. o When used in skincare, the pH of glycolic acid formulations is usually adjusted to ensure safety and efficacy, often ranging between 3.0 and 4.0. 4. Exfoliating Properties: o Glycolic acid’s small molecular size allows it to penetrate the skin more easily than other AHAs. It works by breaking down the bonds between dead skin cells, promoting their removal and revealing fresher, smoother skin underneath. o This property makes it effective in treating various skin conditions such as hyperpigmentation, fine lines, acne, and uneven skin texture. 5. Hygroscopic Nature: o Glycolic acid is hygroscopic, meaning it can attract and retain moisture from the environment. This property can help increase skin hydration when used in lower concentrations in skincare products. 6. Chemical Reactivity: o Glycolic acid can react with bases to form glycolate salts, which are sometimes used in different industrial and cosmetic applications. o It can also undergo esterification reactions with alcohols, producing glycolic esters, which may be used in some formulations.

Lactic acid is an organic acid that plays a crucial role in various biological processes and is widely used in the food, pharmaceutical, and cosmetic industries. It is naturally produced in the body during anaerobic respiration and is found in fermented foods like yogurt and sourdough bread. Lactic acid is also a key ingredient in skincare products due to its exfoliating and hydrating properties. Chemical Properties 1. Structure: o Lactic acid is a hydroxycarboxylic acid with a hydroxyl group (-OH) and a carboxyl group (-COOH) attached to the same carbon atom, making it an alpha-hydroxy acid (AHA). o It exists in two optical isomers: L-lactic acid (L-enantiomer) and D-lactic acid (D-enantiomer), with L-lactic acid being the form commonly found in the human body. 2. Solubility: o Lactic acid is highly soluble in water, which makes it easy to incorporate into aqueous formulations for various applications. o It is also soluble in ethanol and other polar organic solvents, although it is less soluble in non-polar solvents. 3. Acidity: o Lactic acid is a weak acid with a pKa of approximately 3.86, indicating that it partially dissociates in water to release hydrogen ions (H+), contributing to its acidic nature. o Its acidity allows it to lower the pH of solutions, making it useful in products designed to exfoliate the skin or preserve food. 4. Hygroscopic Nature: o Lactic acid is hygroscopic, meaning it has the ability to attract and retain moisture from the environment. This property makes it valuable in skincare products for its moisturizing and humectant effects.