JPH03236752A - Additive for rice grain and usage thereof - Google Patents

Abstract

PURPOSE:To improve taste of cooked rice by adding an aqueous endopeptidase solution to rice grains and giving a suitable softness and stickiness to the cooked rice. CONSTITUTION:An aqueous solution containing <=0.05wt.% endopeptidase as an additive for rice grains is added to rice grains and rice cooking is carried out.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] This invention relates to an additive for rice grains comprising a proteolytic enzyme, particularly an endopeptidase, and a method for using the same.

[Conventional technology]

The taste of rice depends on the production stages such as the variety, place of production, cultivation method, and harvesting method, as well as the post-harvest processing stages such as drying, storage, and milling, and the cooking stage. It is said that the variety and place of production have a major influence on the taste of rice.

Traditionally, rice taste evaluation involves cooking white rice, having multiple examiners eat the cooked rice, and comparing various items such as the appearance, aroma, taste, stickiness, and hardness of the rice to be evaluated. This is done through a so-called sensory test, in which rice is repeatedly tested to see how superior or inferior it is to the standard rice used as the basis for evaluation, and the average value is taken.

In recent years, the composition and physical and chemical properties of rice have been scientifically measured and analyzed, and the correlation between them and the taste evaluation values obtained in the aforementioned sensory tests has been investigated, and finally, the scientifically obtained measured values. As a result of research that attempts to evaluate the quality of rice, it has been found that among the components that make up rice, the content ratio of amylose and amylopectin, which make up rice starch, is particularly important in evaluating the quality of rice. , protein content and water content.

Next, we will explain how the content of each component that makes up rice affects its taste. In general, Koshihikari and Sasanishiki are popular brands of rice with good taste in Japan. - As an example, Table 1 shows a comparison of the protein content and amylose content in starch of several brands of white rice, including Koshihikari and Sasanishiki, with standard milling degrees.

Table 1 (Protein content shows the weight ratio, and amylose content shows the ratio to 100% starch.) If the brand is the same, the content of each component is the same as shown in Table 1. Needless to say, the content of each ingredient varies slightly depending on the geological conditions (soil quality, water quality) of the region where it is grown, as well as weather conditions (temperature, sunshine hours, rainfall, etc.).

According to Table 1, Koshihikari and Sasanishiki have lower protein content and lower amylose content in starch than other general brands of rice. As is clear from this table, the lower the protein and amylose content, the better the taste.

Proteins are abundant in the cell walls of rice grains and are also present between starch molecules. The reason why rice with a lot of protein tastes bad is because protein inhibits water absorption into the rice grains during cooking, and starch does not gelatinize sufficiently. Similarly, amylose itself is thought to inhibit gelatinization due to its poor water absorption.

As mentioned above, in addition to the protein content and the amylose content ratio in starch that have a strong influence on the taste of rice, the moisture content of white rice also has a large effect on the taste in terms of stickiness and hardness. affect If the moisture content of white rice is around 15%, the rice will not crack even when soaked in water and will be cooked into perfect rice grains. Water absorption progresses rapidly from the ventral side of polished rice (where there are relatively many intercellular spaces for water to penetrate) to the endosperm, causing instantaneous cracks due to the volume strain caused by the difference in water content with the dorsal side (where the intercellular spaces are extremely small). When rice is raised and cooked, starch particles blow out from the cracks, resulting in sticky, low-quality rice that is neither chewy nor sticky.

Therefore, humidity control is carried out to maintain the moisture content of rice grains at 15% by adjusting the water content, which is the only adjustable component of the rice grains. However, 15% of rice is inherently bad in taste.
Even if the humidity is adjusted, the rice grains contain a lot of protein and the intercellular spaces are narrow, so water cannot be absorbed into every corner of the rice grains even when soaked. becomes.

[Problem to be solved by the invention]

This invention enables efficient gelatinization of starch when polished rice grains (white rice) are soaked in water and cooked, thereby producing rice grains that have appropriate softness and stickiness and become delicious cooked rice after cooking. The purpose of the present invention is to provide an additive for rice grains and a method for using the same.

[Means to solve the problem]

Endopeptidase is used as an additive for rice grains and is added to the rice cooking liquid or rice grains for cooking.

The additive is added to the rice grains or rice cooking liquid during rice cooking, or an aqueous solution of the additive is added to the rice grains in advance. The amount added should be 0.05% or less based on the weight of rice grains.

[For production]

When endopeptidase is added to the cooking liquid or rice grains,
A protein that chemically acts on the cell walls of rice grains and protein granules that are unevenly distributed between starch particles, hydrolyzing the peptide bonds of the protein internally and changing the properties of the protein, thereby inhibiting water absorption into the interior of the rice grain. The effect of starch is weakened, the degree of gelatinization of starch is high, and the rice becomes sticky. When the amount of endopeptidase added is less than 0.05%, the viscosity increases, which affects the taste, but when it exceeds 0.05%, the lactic acid-like odor of the enzyme itself becomes strong, and the deterioration of flavor is more likely to be a factor than the effect of increased viscosity. In fact, it has the opposite effect.

[Embodiments of the invention]

Add endopeptidase to the rice cooking liquid at a rate of 0.00 per rice grain weight.
5%, 0.015%, 0. A test was conducted to measure the hardness and stickiness of the cooked rice by cooking rice with the addition of f13% and 0.05%. Michikogane, a Hokkaido variety, was used as the sample rice, and the hardness and stickiness of the rice was evaluated using a texturometer.

Hardness, stickiness, and balance measured by a texturometer are used as factors to determine the quality of rice taste.

A texturometer uses a plunger to press and pull rice grains placed in a saucer in a manner that matches the chewing speed of a human, and measures the hardness and stickiness of rice grains using the compression and tension forces. The tensile force, or stickiness, is divided by the pressing force, or hardness, and this value is determined as the degree of balance, and it is generally said that the greater the degree of balance, the better the taste for Japanese people. The test results were as follows.

Rice cooked without endopeptidase has hardness H = 2JI, stickiness - H = 0.19, and balance - H/H.
= 0.08, whereas the one containing 0.005% endopeptidase had hardness H = 2.34, stickiness - H = 0.20, and balance -〇/H = 0.09. Yes, there was a slight difference, but no significant difference was found.

[At 1,015% addition, hardness H = 2.32,
The viscosity-H=0.23 and the balance degree-H/H=0.10, and the effect of the addition is somewhat recognized.

In addition, when adding 0.03%, hardness H = 2.26 and stickiness - H = 0.31. The degree of balance -H/H=0.14, which was a statistically significant difference, and the effect of improving taste was clearly recognized. When adding 0105%, the hardness H=2.
27, Stickiness-H=0.33, Balance degree-H/H=0
．． 15, which is the same improvement in balance as when adding 0.005%, but when you open the rice cooker, you will start to feel a lactic acid-like odor caused by the enzyme, and increasing the amount beyond this will actually reduce the taste. It became a thing.

In the test, endopeptidase was added to the rice cooking liquid during rice cooking, but similar results can be obtained by adding endopeptidase to the rice grains and then adding the rice cooking liquid afterwards.

Furthermore, even if the additive for rice grains is dissolved in water and sprayed to absorb it from the surface of the rice grains into the rice grains when conditioning the humidity of the rice grains, some effects may be obtained, although some elution may occur during cooking. I can.

In addition, rice grains are prepared by infiltrating a certain amount of the rice grain additive into the interior of the rice grains or coating the surface of the rice grains, and then mixed with untreated white rice grains at the time of measuring and packaging or cooking rice. You can still get the appropriate effect.

It is known that endopeptidase can be produced by culturing Bacillus subtilis species in the Bacillus layer.

〔Effect of the invention〕

By adding the rice grain additive of the present invention to polished rice grains,
In order to hydrolyze the peptide bonds of proteins that are unevenly distributed in the cell walls of rice grains and inhibit water absorption from within the proteins, the permeability of the cooking liquid to the cell walls during rice cooking is improved, and the efficiency of gelatinization of starch is increased. In addition to improving the stickiness of rice grains, it can also improve the taste of rice grains by softening them.

Claims (4)

[Claims] (1) An additive for rice grains characterized by comprising endopeptidase. (2) A method of using a rice grain additive comprising endopeptidase, which comprises adding the rice grain additive to a rice cooking liquid or rice grains to cook rice. (3) A method of using an additive for rice grains, which comprises adding to rice grains in air an aqueous solution in which an additive for rice grains consisting of endopeptidase is dissolved. (4) The amount of the additive for rice grains is 0.05 relative to the weight of rice grains.
% or less, the method for using the rice grain additive according to claim (2) or (3).