Li Jiangtao, lecturer of Central South University of Forestry and Technology, et al.: The effect of baking soda on the cooking and edible quality of brown rice

Brown rice is a whole grain obtained after less or no processing after the husk of rice is removed, and is rich in nutrients such as dietary fiber, oryzanol and γ-aminobutyric acid, and is a whole grain
richer in nutrients than refined white rice.
In recent years, brown rice has been used to make snack foods
such as gluten-free bread, brown rice milk and brown rice crackers due to its high nutritional value.
However, it is rare to report the use of brown rice as a staple food, mainly because brown rice has a long cooking time and poor
palatability.

As one of the common food additives, baking soda is often used as an auxiliary material for food such as meal replacement effervescent tablets, buckwheat steamed buns and bread, and has also been studied
in degrading toxins in food.
Studies have shown that applying baking soda to grain processing can significantly increase its eating quality
.
Zhang Yili, Mei Dongxu, Li Jiangtao* from the National Engineering Research Center for Deep Processing of Rice and By-products, College of Food Science and Engineering, Central South University of Forestry and Technology, took Yanfeng 47 brown rice as the research object to analyze the effects of different mass concentrations of baking soda solution on the sensory evaluation, cooking index, macroscopic morphology, chromaticity difference, texture difference, micromorphology structure and starch chain length distribution in rice soup, so as to explore the essence of the effect of different mass concentrations of baking soda solution on the cooking quality of brown rice.
This paper provides a theoretical basis
for the feasibility of baking soda applied to improve the cooking quality of brown rice.

1.
Effect of baking soda on the distribution of pullopectin branch chain length in brown rice soup

It can be seen from Figure 1 and Table 2 that the addition of baking soda can reduce the content of starch B2 chain and B3 chain in brown rice soup, and increase the content of B1 chain, which has no significant effect on the average polymerization degree of amylopectin in brown rice soup.
Adding 0.
4% baking soda can increase the A chain content of starch in brown rice soup, and the remaining mass concentration of baking soda can reduce
the A chain content of starch in brown rice soup.
It is speculated that, to a certain extent, baking soda will break the amylopectin in brown rice soup and form starch branches of the medium and long chain, and the short chain may also be degraded under the action of baking soda, forming small molecules
with a degree of polymerization below 6.
However, due to the low lye concentration and short heating time, the long branched chains of amylopectin were reduced, but there was no significant difference
in the average chain length.

2.
The effect of baking soda on the microstructure of brown rice

As shown in Figure 2, there is a difference
in the microstructure between raw brown rice (uncooked) and brown rice cooked with baking soda of different mass concentrations.
The surface of the raw brown rice particles is dense and smooth
.
After cooking, there are microscopic folds in the brown rice skin, obvious cracks and furrows in some areas, and breakages and holes also appear on the surface of some brown rice (Figures 2b, c, g).

Some areas of the BR-0.
0 surface are smoother, with smaller folds and fewer cracks, which is consistent
with the results of Liu Ming et al.
With the increase of baking soda mass concentration, brown rice surface folds and cracks increased (Figures 2c, d, e), especially BR-0.
4 and BR-0.
6, indicating that low and medium mass concentrations of baking soda had a significant effect
on the brown rice cortex.
The appearance of cracks on the surface of brown rice is conducive to the absorption of brown rice during the cooking process, and promotes the gelatinization of starch in the endosperm, thereby reducing the hardness and cooking time
of brown rice.
However, BR-0.
8 and BR-1.
0 (Fig.
2f, g) brown rice surface folds were significantly reduced, and the cortex became smoother because the outer surface of the brown rice cortex was destroyed by the high-quality concentration of baking soda, resulting in a smoother surface
.

3.
Effect of baking soda on the cooking characteristics of brown rice

As can be seen from Table 3, the addition of baking soda significantly shortens the optimal cooking time of brown rice (P<0.
05), and the higher the mass concentration of baking soda, the shorter the optimal cooking time, from 23.
42 min to 15.
91 min<b10>.
The water absorption capacity of rice grains is positively correlated
with the cooking quality of rice.
Compared to brown rice cooked without baking soda, brown rice has an increased
water absorption rate after steaming with baking soda solution.
Compared with BR-0.
0, the expansion rates of BR-0.
2, BR-0.
4, BR-0.
6, BR-0.
8 and BR-1.
0 are significantly increased
.

As shown in Table 3, with the increase of the mass concentration of baking soda, the pH value of brown rice soup shows a trend of first increasing and then almost unchanged, because baking soda is alkaline when dissolved in water, and it is a strong alkaline weak salt, and the pH value will not continue to increase due to the increase
of its addition after dissolving in water 。 At the same time, when the mass concentration of baking soda was not more than 0.
6 g/100 mL, the relative content of brown rice soup solids continued to decrease with the increase of baking soda mass concentration.
When the mass concentration of baking soda was greater than 0.
6 g/100 mL, the relative content of brown rice soup solids increased with the increase of baking soda mass concentration.
Among them, the relative content of brown rice soup solids of BR-0.
2 and BR-1.
0 was close to
BR-0.
0.

4.
The effect of baking soda on the appearance of brown rice

As can be seen from Figure 3, the overall particle of BR-0.
0 is complete, the volume expansion is small, the surface is smooth, the white is less, the rice grain is loose and the viscosity is poor
.
BR-0.
2~BR-1.
0 can obviously observe that the gap between rice grains becomes smaller and the viscosity becomes stronger
.
Brown rice absorbs water and expands during cooking, and the brown rice cortex breaks due to the expansion of the endosperm, forming a white color
.
With the increase of the mass concentration of baking soda, the whiteness of brown rice gradually increased, indicating that the addition of baking soda is conducive to the water absorption expansion and gelatinization of brown rice during the cooking process, improving the cooking properties of brown rice, making brown rice softer, and thus improving the edible quality
of brown rice.
Add baking soda and steam brown rice, yellow brown rice gradually deepens as the mass concentration of baking soda increases; Among them, BR-0.
4 and BR-0.
6 brown rice are yellowish-white, and BR-0.
8 and BR-1.
0 brown rice gradually turn yellow-brown
.

5.
The effect of baking soda on the apparent color of brown rice

As can be seen from Table 4, with the increase of the mass concentration of baking soda, the L* value of brown rice decreases, the b* value increases, and the a* value first rises and then
decreases.
This means that the brown rice darkens in appearance and deepens
in yellow.
Because the conformation of proteins is more likely to change in an alkaline environment, it is speculated that the proteins in brown rice are heated under alkaline conditions to oxidize some amino acids and turn yellow, and some flavonoids in the brown rice cortex change color, resulting in a deepening
color of brown rice.
It can be seen from Table 4 that compared with brown rice cooked without baking soda solution, the ΔE value of brown rice cooked with baking soda was significantly increased.
This shows that after cooking brown rice with baking soda solution, the overall color change of brown rice is large, which is consistent with
the overall color change of brown rice observed in Figure 3.

6.
Effect of baking soda on texture characteristics of brown rice

It can be seen from Table 5 that compared with brown rice cooked without baking soda, the hardness of brown rice was significantly reduced after baking soda cooking with a mass concentration of 0.
2, 0.
4, 0.
6, 0.
8 g/100 mL and 1.
0 g/100 mL.
The viscosity of BR-0.
2 was significantly reduced, the absolute value of BR-1.
0 viscosity increased significantly, and the chewiness of brown rice was significantly reduced
after steaming baking soda with mass concentrations of 0.
4, 0.
6, 0.
8, 1.
0 g/100 mL.
Higher hardness and chewiness are associated
with less hydration of starch granules in brown rice.
The addition of baking soda causes obvious grooves and cracks on the surface of brown rice, and holes appear in some places; During the cooking process, the water can quickly migrate to the inside of the rice grain, accelerate the hydration of the starch, fully gelatinize the starch, reduce the hardness and chewiness of brown rice, and increase the taste quality
.

7.
The effect of baking soda on sensory evaluation of brown rice

From the comprehensive score of Table 6, it can be seen that the sensory quality of BR-0.
0 brown rice is poor, the cracking of brown rice is not obvious after cooking, and there is a certain rice bran flavor, poor viscosity, hard taste and not easy to chew.

After adding baking soda, the overall score of brown rice first increased and then
decreased.
BR-0.
2 and BR-0.
4 brown rice improved in sensory evaluation in terms of appearance, taste, palatability and texture in addition to odor.
BR-0.
6~BR-1.
0 brown rice presents a strong alkaline taste in the smell, which greatly affects the score
of brown rice.
The low score of brown rice may be due to the brown rice cortex, which makes it difficult for
brown rice to absorb water.
It can be seen that under the condition of a certain mass concentration of baking soda, the protein denaturation in brown rice and the effect of hindering starch absorption and gelatinization are weakened, thereby comprehensively improving the sensory quality of brown rice, but excessive high-quality concentration of baking soda will reduce the sensory quality of brown rice.
BR-0.
4 brown rice has the highest sensory comprehensive score, and its appearance, palatability and texture are significantly improved
.

Conclusion