Browning of Food and its Types : Maillard reaction and Caramelization

• Browning is the process by which foods turn brown due to certain special chemical reactions. 
• During pre-preparation, processing, or storing of food, browning is a common color shift that can be seen in the food. 
• It can be found in varying degrees in some food materials. Depending on the food and extent of reaction, the color that is generated can vary from cream or a light yellow to a dark brown or even a black. 
• Browning reaction may be desirable or undesirable. The aroma, flavor, and color of the product are influenced by browning reactions, which are responsible for the bread crust, all baked products, potato crisps, toasted nuts, roasted coffee beans, and many other processed foods.
• Foods dehydrated like milk, eggs, dry fruits, citrus fruit juice concentrates, sliced fruits, canned milk, and coconut all show adverse effects of browning reactions. Controlled browning is necessary even in foods where browning is desired because excessive browning can produce an undesirable product.
• Browning of foods can be either non-enzymatic (caramelization or Maillard reaction) or enzymatic.

Non enzymatic browning

Non enzymatic browning is a process which produce brown pigments in food but without activity of enzymes. Non- enzymatic browning is Maillard reaction, caramelization, ascorbic acid browning.

1. Maillard reaction

•  Maillard reaction are also called carbonyl-amine reaction. Protein and sugar combine during the Maillard process. In a combination of amino acids and reducing sugars, the Maillard reaction causes the development of brown color. 
• The brown colour formed contributes to the aroma, flavor, and colour of many ready to eat cereals, baked food, malted barley etc.
• Higher the proportion of reducing sugar, the darker the crust on baked foods, the type of amino acid, temperature, and moisture are some of the variables that impact this factor.

Mechanism of Maillard reactions

• The amino group of the amino acid and the carbonyl group of the reducing sugar combine, forming an N-substituted glucosamine (along with water) as the first step in the Maillard reaction process.
• Now, The Amadori rearrangement converts the glucosamine into ketoamides.
• These Ketosamines can be further reacted with to produce reductones, butanedione, methylglyoxal, and a number of other short-chain hydrolytic fission products.
• Melanoidins and other brown nitrogenous polymers can also be produced by the ketosamines. This imparts the characteristic brown color to the food.

2. Caramelization

•  Caramelization is the process of sugar turning dark when cooked to a high temperature (160 deg C) without water or amino acids. 
• Sugar is broken down into a number of compounds due to intense heat. It involves in pyrolysis of sugar. caramelization widely used in cooking to achieve a brown color and and distinctive flavor.
• While the development of caramel flavor and color in caramel custard is a desirable change whereas uncontrolled heating of sugar can lead to objectionable burnt colour and flavour.

3. Ascorbic acid browning

•  Ascorbic acid present in foods endures oxidation, creating a compound that results in the production of a dark pigment and discoloration. In pickles, ascorbic acid is present.
• The process may be slowed down by low storing temperatures.

Enzymatic browning

•  Enzymatic browning refers to the color change that occurs in vegetables, fruits, etc. when enzymes are present.
• Light color due to the presence of oxidative enzymes, vegetables and fruits turn darker when exposed to air.
• When cutting, bruising, or other tissue damage disturb the cellular structure, enzymatic browning takes place in those vegetables and fruits. Apple, banana, pears, brinjal and potatoes undergo enzymatic browning.

• Only phenolic-compound-containing fruits and veggies experience enzyme-induced discoloration. These phenolic substances serve as the substrate, and the subsequent oxidative reaction is seen in the presence of oxygen and under the influence of enzymes.
• Enzymatic browning happens when the fruit’s phenols are oxidized to produce quinones by the enzyme polyphenol oxidase or other enzymes. Quinones can then polymerize to create melanin, which are what give dark compounds their color.
• By preventing the enzyme from working properly, browning can be slowed down.
• Lemon juice contains an acid which can stop enzymes working properly as enzymes often work best at a certain pH. For example, the water and sugar in jam prevent browning by stopping oxygen from the air from reaching the enzymes.

Methods of controlling enzymatic browning of food

The different types of enzymatic browning can be controlled into two major categories: physical and chemical methods.

Physical methods

Heat treatments: Heat treatment of food, such as blanching or baking, denaturants enzymes and destroys the compounds that cause browning. For example, blanching is used in the production of wine, tea, the processing of nuts and pork, and the freezing of vegetables.

Irradiation: Food irradiation using UV-C, gamma rays, x-rays and electron beams is another tool for enhancing food shelf life. Ionizing radiation prevents the development of the microorganisms that cause food spoilage and delays the maturation and growth of vegetables and fruits.

Cold treatments: The most effective methods to preserve food and keep it from getting spoiled are refrigeration and freezing. Fresh vegetables and fruits retain their natural flavor, color, and appearance when refrigerated. Refrigeration is also used for distribution and retailing of fruit and vegetables.

Chemical methods

Acidification: Like other enzymes, browning enzymes have a specific pH range where they are active. Food additives like acidifying agents and acidity controllers are frequently used to maintain an appropriate pH level in food items. Anti-browning substances include acids like citric acid, ascorbic acid, and glutathione.

Chelating agents: Copper serves as a coenzyme for polyphenol oxidase, which is why copper chelating chemicals prevent this enzyme from performing. Various chelating substances, including citric acid, sorbic acid, polyphosphates, hinokitiol, kojic acid, EDTA, porphyrins, poly carboxylic acids, and diverse proteins, have been researched and used in various sectors of the food industry.

Antioxidants: Many antioxidants are used as food additives in the food industry. These substances interact with oxygen to prevent browning. Examples of anti-browning antioxidants include ascorbic acid, N-acetylcysteine, L-cysteine, 4-hexylresorcinol, erythorbic acid, cysteine hydrochloride, and glutathione.

Difference between Maillard reaction and caramelization