The fragrant rice cannot withstand the “scouring”

The fragrant rice cannot withstand the “scouring”

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Rice, also known as white rice or simply rice, is made by steaming rice and water and is the staple food and main source of energy for half of the world’s population. As people’s demand for delicious and healthy food continues to increase, rice aroma has become an important indicator for evaluating the sensory properties of rice. Researchers reported several types of rice aromas, which were described as bland, burnt, sour, buttery, biscuit, nutty, popcorn, potato, and floral.

Among them, 2-acetyl-1-pyrroline is the most important volatile compound in fragrant rice and has a popcorn-like aroma. In addition, starch, protein and lipid are the main components of rice. During the cooking process, the formation of aroma is also closely related to the complex chemical reactions between these components, including Maillard reaction, lipid oxidation, etc. The following introduces the effects of the main ingredients of rice and cooking methods on the aroma of rice.

The formation of ingredients and aroma in rice

Contribution of protein to the aroma of cooked rice: The impact of protein in rice on the aroma characteristics of rice is mainly reflected in two aspects: on the one hand, amino acids and peptides produced by protein hydrolysis participate in the Maillard reaction to generate aldehydes, ketones, furans, pyrazines, etc. Aroma compounds; on the other hand, proteins combine reversibly or irreversibly with aroma compounds through van der Waals forces, ionic bonds, hydrogen bonds and hydrophobic interactions, affecting the release of aroma compounds.

Contribution of lipids to cooked rice aroma: Lipid oxidation is another important pathway for the formation of cooked rice aroma. The process in which unsaturated fatty acids in oils and fats are slowly oxidized by oxygen molecules in the air is called lipid oxidation.

During the soaking and cooking process of rice, the activity of endogenous enzymes (lipase and lipoxygenase) for lipid oxidation increases, the decomposition of hydroperoxide, the volatile precursor in the original rice, is accelerated, and the starch-lipid complex Decomposed into fatty acids, unsaturated fatty acids generate conjugated hydroperoxy fatty acids, which are further auto-oxidized or enzymatically degraded into various volatile compounds, making the rice smell more fragrant.

In addition, lipid autooxidation or enzymatic degradation can generate various volatile compounds, including aldehydes, ketones, alcohols, and esters. Alcohols such as hexanol and octanol often have refreshing sweetness and aroma.

Contribution of starch to cooked rice aroma: Rice starch affects the formation of cooked rice aroma through Maillard reaction. During the cooking process, starch will absorb water, expand and gelatinize, causing significant changes in the distribution of water in the food matrix, thus affecting the viscosity of the system and the mobility of Maillard reactants, resulting in a reduction in the reaction rate.

At the same time, starch undergoes high-temperature degradation and enzymatic hydrolysis during the heating process, and the generated reducing sugars undergo Maillard reaction with amino acids to generate volatile aromatic compounds. As the cooking temperature increases and the cooking time increases, 2- The mass fraction of burnt aroma compounds such as acetyl-1-pyrroline gradually increases, and the rice becomes fragrant.

Effect of rice varieties on the aroma of cooked rice

Due to its sweet, nutty flavor and slightly sticky texture, urune rice is the most popular Japanese rice and is commonly used to make sushi and rice balls.

Mochi rice has a mild, slightly sweet taste. Due to its high starch content, this rice becomes very sticky when cooked, making it ideal for making rice cakes and candies. It can be seen that the influence of rice varieties on the aroma of cooked rice comes from the differences in starch types and contents in different rice varieties.

Chinese scientists are also actively studying the impact of the environment on the formation of rice starch. Recent research has found that temperature has a significant impact on starch formation in rice. By subjecting Yangnong No. 1 rice and Yangnong No. 6 rice to different daytime high temperature, nighttime high temperature and all-weather high temperature treatments, the starch content of the rice was significantly different.

The production process affects the formation of aroma

Washing: Washing the rice before cooking usually removes dust and remaining bran from the milling process. Some people like to put the rice in water and wash it repeatedly. This will cause the nutrients to be lost and the steamed rice will not have an attractive rice aroma. Therefore, when making rice, you should wash the rice moderately, no more than three times at most, and in When washing rice, do not rub the surface of the rice too hard.

Soaking: Different soaking temperatures and soaking times will lead to differences in the activity of endogenous enzymes in rice, thus affecting the formation and release of aroma during rice cooking.

It is reported that soaking at 50°C for 10 minutes can improve the aroma of rice. The reason is that compared with room temperature soaking, hot soaking makes the macromolecular structure inside and on the surface of rice unevenly distributed, forming a permeability channel through which volatile components can volatilize. , thereby promoting the release of aroma. It should be noted that if the soaking time is longer, the sweet compounds may be lost during the subsequent cooking process, resulting in a rancid, spoiled smell. Therefore, it is advisable to soak the rice in water for ten minutes. Doing so will also increase the viscosity of the rice.

If you continue to perform high-pressure treatment in the container after soaking, small molecular sugars can be pressed into the rice grains without loss, resulting in a sweeter taste. The content of alcohols, aldehydes and ketones in the rice treated in this way increases, which will also improve the aroma of the cooked rice.

Cooking methods: Common thermal cooking methods include steam cooking, electronic rice cooker cooking and microwave cooking. The advantage of steam cooking is that water is less likely to be lost during the cooking process and it is easier to produce aroma.

In our daily life, rice cookers are commonly used to cook rice, and rice cookers can be divided into normal-pressure rice cookers and high-pressure rice cookers according to whether they have pressure. The electronic rice cooker has an automatic temperature control device, which can better control the temperature and heating time in the pot, so that the cooked rice can fully emit aroma. The closed cooking environment prevents the aroma from dissipating easily.

Microwave cooking is popular because of its fast heating speed, uniform heating, safe operation and short cooking time. Microwave treatment can change the structural characteristics of rice starch, leading to the rearrangement of crystallization areas. It can also destroy the biological conformation of protein molecules such as lipase and lipoxygenase, and reduce the production of fatty acids.

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