This paper deals with the principles of starch pasting and aging as well as their role in cooking for food quality improvement, nutrient protection, and applications in food processing.

Starch pasting and aging

1.1 Starch pasting

The raw starch molecules are tightly arranged by intermolecular hydrogen bonding, forming bundles of micelles, with very small gaps between them, which makes it difficult for water molecules to penetrate, and the raw starch with micellar structure is called β-starch.

β-starch in water after heating, part of the micelle is dissolved and form a void, so the water molecules into the interior, and the remaining part of the starch molecules, the micelle is gradually dissolved, the void is gradually expanding, starch particles due to water absorption, the volume of expansion of tens of times, the raw starch micelles that is, the disappearance of this phenomenon is known as the phenomenon of dilatancy.

Continuing heating, the micelles are all collapsed, forming starch single molecule, and surrounded by water, and become solution state, this phenomenon is called pasting, and the starch in this state is called α-starch.

1.2 Aging of starch

After the pasteurized α-starch is placed at or below room temperature, it will become opaque or even coagulate and become precipitate, and this phenomenon is called aging of starch. This is due to the paste after the starch molecules at low temperature and automatically arranged into order, adjacent molecules of hydrogen bonding and gradually restore the formation of dense, highly crystalline starch molecules micro beams of the reason.

Application of starch in cooking

2.1 Effects of starch pasting on dietary quality.

(1) Improve the digestion and absorption rate of food: The pasteurized starch becomes loose and conducive to the action of amylase enzyme because it destroys the bundle structure of natural starch, thus improving its digestion and absorption rate in human body. Generally, food ingredients containing starch should be made starch pasteurized in cooking before consumption. Many convenience foods, such as instant rice, instant porridge, instant noodles is the use of starch pasting, so that the raw starch into. α – starch, in order to improve the □ feeling and improve the digestibility.

(2) for dishes in the paste: starch in the cooking process is often used for some raw materials for the paste, the surface of the raw materials by the paste is a layer of starch paste, thicker than the batter to be much thicker. By hanging the paste of the raw materials are generally fried, the temperature is very high (generally 200 ℃ ~ 220 ℃ or so), starch in this high-temperature effect, has undergone drastic changes, first of all, starch due to the role of high temperatures, which the rapid evaporation of water, starch molecules between the hydrogen bond breaking and rapid dextrination to generate dextrin, the majority of which dextrin and the action of high temperatures and the occurrence of the hydrogen bond breaking, the loss of water molecules occurring Sugar caramelization, the formation of burnt starch. Burnt starch has the characteristics of crispness, crunchiness and fragrance, so the surface of the fried raw materials has a layer of tough and crispy shell, and it feels crispy.

2.2 The effect of starch aging on diet.

(1) Factors affecting starch aging are:

a. Type of starch; the type of starch mainly refers to the proportion of straight-chain starch and branched-chain starch and the size of molecular weight; straight-chain starch is more easy to be aged than branched-chain starch; starch with medium degree of polymerization is easy to be aged.

b. Water content of food; starch is easy to be aged when the water content of food is 30%-60%, and starch is not easy to be aged when the water content is less than 10% or when there is a lot of water.

(2) Measures to prevent and retard the aging of starch.

a. Temperature; the most suitable temperature for aging is 2~4℃, and aging is not easy to happen when it is higher than 60℃ and lower than -20℃.

b. Moisture; the aging phenomenon of starch is easy to happen when the water content of food is between 30% and 60%, and the aging phenomenon is not easy to happen when the water content of food is below 10% in dry state or more than 60% of water.

2.3 Properties of starch in other applications.

As starch is rich in resources, has many varieties and adjustable denaturation methods, it can be used in modern food industry as food additives or food processing aids to play the functions of thickening, stabilizing, emulsifying, bonding, filling and excipient, etc., and it can save the cost, improve the processing performance, and give the products unique texture, and to a certain extent improve the quality of the products.

(1) Dairy products: Modified starch used in dairy products provides creamy structure and shelf stability during dairy processing. For example, cross-linked modified starch is usually added in yogurt production. The cross-linked starch molecules have cross-linked ester bonds that are much stronger than the hydrogen bonds of starch molecules, and the molecular weight is larger than that of the original starch, which strengthens and maintains the hydrogen bonds, and acts as a bridge between molecules, so that when the starch is heated in water, the granules still maintain varying degrees of integrity, which inhibits granule rupture and decreases in viscosity, and provides a unique processing tolerance. Viscosity is formed when starch is pasted, giving yogurt a smooth and delicate organization. The addition of modified starch with unique rheological properties in the production of milk beverages can enhance the taste and provide a light flavor.

(2) Flavorings: Modified starch can not only thicken the flavorings, improve the quality and stability of flavorings, but also reduce the production cost and greatly improve the competitiveness of the products. One of the modified starch pre-gelatinized starch, can give the food “slurry” or “granular” organization, whether in a highly acidic or low-acid environment are applicable, so that the product in the appearance and □ sense are improved. In short, we often cook dishes, we should be reasonable application of starch paste and aging properties, scientific cooking, more preservation of the nutrients of the dishes, so that the color, aroma, taste and shape of the dishes to achieve better results, but also to a certain extent to ensure that our physical health.