阅读说明：本技术 一种紫薯营养米粉的加工方法 (Processing method of purple sweet potato nutritional rice noodles ) 是由 邹仙果 费洁羽 徐静 翁业勋 杨开 田宝明 孙培龙 于 2021-06-24 设计创作，主要内容包括：本发明公开了一种紫薯营养米粉的加工方法。本发明针对传统米面类型单一、营养价值低及在米面制作过程中会出现粘结、甚至不出丝等现象,调整早晚籼米的比例,添加紫薯以丰富米面类型及营养,确定了紫薯粉、可得然胶的最佳添加比和米面的最优干燥温度及时间,制得的紫薯米面品质好、营养丰富且耐储存,适宜各种人群食用。(The invention discloses a processing method of purple sweet potato nutritional rice noodles. Aiming at the phenomena that the traditional rice and flour has single type and low nutritional value, and the rice and flour can be bonded or even not shredded in the making process, the invention adjusts the proportion of long-shaped rice in the morning and evening, adds the purple sweet potato to enrich the type and the nutrition of the rice and flour, determines the optimal adding ratio of the purple sweet potato powder and the curdlan and the optimal drying temperature and time of the rice and flour, and the prepared purple sweet potato rice and flour has good quality, rich nutrition and long storage life and is suitable for various crowds to eat.)

1. A processing method of purple sweet potato nutritional rice flour comprises the following steps:

(1) soaking the mixture of long-shaped rice in the morning and evening at a mass ratio of 3-4: 1 in cold water for 5-8 h, draining, grinding into powder, and sieving to obtain rice flour; meanwhile, cleaning and cooking the purple sweet potatoes for 15-25 min, peeling, pressing into mashed purple sweet potatoes, drying, crushing and sieving to obtain purple sweet potato powder;

(2) taking rice flour, adding 15-20% of purple sweet potato powder and 0.8-1.2% of curdlan by mass, uniformly mixing, adding clear water, and mixing into rice pulp to prepare purple sweet potato rice flour;

(3) aging the prepared purple sweet potato rice noodles for 5-8 h, soaking the pine shreds in cold water for 10-15 min, folding and placing the rice noodle finished products into flour cakes, placing the flour cakes in a netted tray, and drying the flour cakes for 120-180 min at 40-50 ℃ to obtain the purple sweet potato nutritional rice noodles.

2. The method of claim 1, wherein the fineness of the rice flour and the purple potato flour in step (1) is 80 mesh.

3. The method as claimed in claim 1, wherein in step (1), the mashed purple sweet potatoes are dried in an electric heating constant temperature oven at 105 ℃ for 8h and then crushed by a broken food machine.

4. The method according to claim 1, wherein the drying temperature in the step (3) is 50 ℃ and the drying time is 180 min.

5. A method according to claim 1, wherein in step (3) the finished rice and flour product is folded and arranged into a pancake having dimensions of 20cm x 10cm x 2 cm.

(I) technical field

The invention relates to a processing method of purple sweet potato nutritional rice flour.

(II) technical background

The rice flour is also called as dang powder, dripping powder, rice flour or rice flour, and is usually prepared by using long-shaped rice as a raw material and carrying out the working procedures of washing, soaking, grinding into slurry, pasting, cooling, aging, packaging and the like. The edible oil is convenient to cook and tasty and refreshing to eat, is deeply loved by southern people, and has more than 2000 years of eating history in China. The time is shifted to the star, the times are prosperous and developed, rice flour is popular all over the world, and the rice flour is very popular in south-east Asia.

Generally, the higher the amylose content of rice, the better the quality of the rice flour produced, and it is easily retrograded. The amylose content of the early-season long-shaped rice is relatively high, most of rice flour can be made only by the early-season long-shaped rice, but if the amylose content is too high, the toughness of finished rice flour is possibly insufficient, the rice flour is easy to break and can be regenerated, and the gelatinization process of the rice flour is difficult. Therefore, a certain proportion of late long-shaped rice can be added into the early long-shaped rice, so that the prepared rice noodle can be quickly taken out and is not easy to break, and the taste is smooth without losing toughness. Therefore, the rice flour with the best quality and characteristics can be prepared by adjusting the mixing proportion of the long-shaped rice in the morning and at night.

At present, rice and flour on the market mostly only use fine white rice as a raw material, and besides starch can provide energy for human bodies, the rice and flour contains few nutritional ingredients and has loss in the manufacturing process, so that various increasing requirements of people on nutrition, taste, color and the like cannot be fully met. The five-cereal rice flour is rich in nutrition and color, and the compound rice flour with unique taste, color and flexible texture can be developed by adding the five-cereal rice flour in order to change the single color, flavor and texture quality of the traditional rice flour, enrich the variety of the rice flour and improve the nutrition of the rice flour.

Purple potato (Solanum Tuberosum) belongs to Convolvulaceae annual herbaceous plant, is a sweet potato, and has purple black potato peel and purple to purple black meat quality. The purple sweet potato is rich in compounds such as anthocyanin, beta-carotene, glycoprotein, phenols and the like, and has the effects of resisting oxidation, removing free radicals, preventing fat accumulation of cardiovascular systems, constipation and colon cancer, blocking HIV infection and the like. In recent years, purple sweet potatoes have been developed for producing various products, such as purple sweet potato bread, purple sweet potato chips, purple sweet potato beverages, and the like, and relatively few studies and patents have been made on adding purple sweet potatoes to rice flour.

Patent application CN108967858A discloses a purple sweet potato rice flour. Patent application CN106136067A discloses a preparation method of purple sweet potato rice flour. Patent application 109566990A discloses a processing technology of purple sweet potato rice flour. Patent application CN108967856A discloses a stomach-regulating purple sweet potato rice flour which specifically comprises rice, purple sweet potato flour, honey, red date powder and American ginseng powder. Patent application CN108967847A discloses high dietary fiber purple sweet potato flour which comprises rice, purple sweet potato powder, kudzu root powder, yam powder and honey. Patent application 106722154A discloses purple sweet potato health rice flour with an antioxidant function and a preparation method thereof. Patent application CN108771111A discloses a purple sweet potato oat health rice flour and a preparation method thereof. Patent application CN105901584A discloses a purple sweet potato health-care rice flour and a preparation method thereof, which is specifically prepared by mixing purple sweet potato slices with cortex dictamni, sargentgloryvine stem, barbed skullcap herb, vietnamese sophora root, dahurian patrinia herb, Chinese pulsatilla root, mazzing, prepared common monkshood daughter root and dried ginger. Patent application CN110269187A discloses purple sweet potato nutritional noodles and a preparation method, which are added with chickpea, cyclocarya paliurus leaves, mulberry leaves, polygonatum odoratum, mulberry seeds, nostoc sphaeroides and purple sweet potato powder, dried by hot air and stored by filling nitrogen. Patent application CN112137048A discloses a processing technology of double-screw extrusion purple sweet potato rice flour, which comprises rice, purple sweet potato flour and a modifier (konjac glucomannan, guar gum and disodium hydrogen phosphate), and optimally designs the temperature of a zone III and the screw rotation speed of the double-screw extrusion.

The purple sweet potato rice flour is characterized in that the nutritional value of the rice flour is improved or the purple sweet potato rice flour with certain function orientation is prepared by adding purple sweet potatoes, other nutritional substances, nutritional enhancers and the like. However, the influence of different rice (the addition ratio of long-shaped rice in the morning and evening) on the quality of rice flour is not optimized in the above patents, and under the condition that purple potatoes (10-40% of the rice flour is added), the phenomenon that the quality characteristic of the rice flour is poor due to the fact that the rice flour is easy to adhere in the manufacturing process after the purple potatoes are added is not considered.

Disclosure of the invention

The invention provides a processing method of purple sweet potato nutritional rice and flour which is good in quality, rich in nutrition and durable in storage.

The technical scheme adopted by the invention is as follows:

a processing method of purple sweet potato nutritional rice flour comprises the following steps:

(1) soaking the mixture of long-shaped rice in the morning and evening at a mass ratio of 3-4: 1 in cold water for 5-8 h, draining, grinding into powder, and sieving to obtain rice flour; meanwhile, cleaning and cooking the purple sweet potatoes for 15-25 min, peeling, pressing into mashed purple sweet potatoes, drying, crushing and sieving to obtain purple sweet potato powder;

(2) taking rice flour, adding 15-20% of purple sweet potato powder and 0.8-1.2% of curdlan by mass, uniformly mixing, adding clear water, and mixing into rice pulp to prepare purple sweet potato rice flour;

(3) aging the prepared purple sweet potato rice noodles for 5-8 h, soaking the pine shreds in cold water for 10-15 min, folding and placing the rice noodle finished products into flour cakes, placing the flour cakes in a netted tray, and drying the flour cakes for 120-180 min at 40-50 ℃ to obtain the purple sweet potato nutritional rice noodles.

When the coarse cereals are added in the rice flour production, the phenomena of bonding, even no silk and the like often occur in the production process of the product due to the change of system moisture, texture and the like. Curdlan is a tasteless irreversible edible gel, and the strength of the gel is improved along with the rise of heating temperature and concentration, so that the water holding capacity, cohesiveness, stability and the like of food can be improved. The invention adjusts the proportion of long-shaped rice in the morning and evening on the basis of the traditional rice and flour preparation process, adds the purple sweet potatoes to enrich the types and nutrition of the rice and flour, determines the optimal addition ratio of the purple sweet potato powder and the curdlan and the optimal drying temperature and time of the rice and flour by detecting the rehydration rate, the ripeness and breakage rate, the pulp discharge rate, the transmittance, the iodine blue value and the sensory evaluation of the rice and flour, and prepares the purple sweet potato nutritional rice and flour which has good quality, rich nutrition and long shelf life, and is suitable for various crowds to eat.

Preferably, the fineness of the rice flour and the purple sweet potato flour in the step (1) is 80 meshes.

Preferably, the mashed purple sweet potatoes in the step (1) are dried in an electric heating constant-temperature oven at 105 ℃ for 8 hours and then crushed by a wall-breaking food machine.

Preferably, the drying temperature in the step (3) is 50 ℃, and the drying time is 180 min.

Preferably, in the step (3), the finished rice and flour products are folded and placed into 20cm × 10cm × 2cm cakes when the rice and flour are dried, the drying temperature of a drying oven is 50 ℃, and the drying time is 180 min.

The invention has the following beneficial effects: according to the invention, the proportion of the long-shaped rice in the morning and the evening is adjusted, the purple sweet potatoes are added to enrich the types and the nutrition of the rice and the flour, the optimal adding ratio of the purple sweet potato powder and the curdlan and the optimal drying temperature and time of the rice and the flour are determined, and the prepared purple sweet potato rice and flour has good quality, rich nutrition and long storage life and is suitable for various crowds to eat.

(IV) description of the drawings

FIG. 1 is a schematic view of the process of the present invention.

(V) detailed description of the preferred embodiments

For the purpose of enhancing understanding of the present invention, the present invention will be described in further detail with reference to specific examples, which are provided for illustration only and are not intended to limit the scope of the present invention.

The raw materials and instruments used in the examples were as follows:

cottage farmhouse early indica rice, purchased from Murraya Koenigii food factories in Lujiang county;

savory beautiful shrimp king soft rice (late long-shaped rice) purchased from Tai Liang Rice industry Co., Ltd, Dongguan, Guangdong province;

blenders, philips;

rice flour machine, guangzhou xuzhong food machinery ltd;

an electric heating constant temperature air blast drying oven, Shanghai Jing hong experiment equipment Co.

The detection method of the rehydration rate comprises the following steps: selecting a clean utensil, placing the utensil in an electric heating constant-temperature oven, and drying the utensil to constant weight. Soaking the finished rice flour at normal temperature (25 ℃) for rehydration for 5min, weighing rehydrated rice flour with a certain mass in a utensil, drying the surface moisture by using filter paper, weighing, placing the rehydrated rice flour in an electric heating constant-temperature oven for drying for 2-4 h, taking out, cooling to room temperature, and weighing; then putting the mixture into the oven again for drying for 1h, taking out the mixture, cooling the mixture to room temperature, and weighing the mixture again; the constant weight is calculated when the mass difference between the two times is less than 0.002 g.

The method for detecting the rate of cooked strips breaking comprises the following steps: selecting 30 noodles of 20cm from the finished rice and flour, weighing m per group, and collecting 10 noodles₁Placing in a vessel, adding boiling water at a ratio of 1:15, and covering for 2 min.Then taking out the rice flour, dispersing the rice flour in supercooled water on a porcelain dish, separating rice flour with a thickness of more than 10cm from rice flour with a thickness of less than 10cm, weighing m respectively₂And m₃. The breaking rate was calculated according to equation (1).

Wherein "R₁"represents the breaking rate; m is₂Representing the quality of rice and flour with the length less than 10 cm; m is₃Represents the rice-flour mass with the length of more than 10 cm; according to the T/CCOA 4-2019 standard, the rate of cooked broken strips of the rice and the flour should be lower than 10%.

The detection method of the pulp discharge rate comprises the following steps: taking 20 pieces of 20cm rice from the finished rice flour, weighing m₄Adding 1L boiling water, boiling for 5min, taking out all rice flour, cooling, adding the solution into 1L volumetric flask, and shaking to desired volume. Shaking up, measuring 100mL of solution, transferring into a dried vessel, and weighing₅Drying in 105 deg.C electric heating oven to constant weight, weighing₆The pulp discharge value was calculated as follows:

wherein "R₂"represents the spitting value; "M" represents the moisture content of the sample; according to the T/CCOA 4-2019 standard, the paste discharge value of the rice and flour is lower than 15%.

The transmittance detection method comprises the following steps: the transmittance is the ratio of transmitted light to incident light flux, under the same conditions, the transmittance is in direct proportion to the transparency of the extracting solution, 5.0g of fresh rice flour is weighed and placed in a 250mL beaker, 100mL of boiling water is added for soaking for 2min, the soaked supernatant is selected for color comparison at 620nm, and the blank group is distilled water.

The iodine blue value detection method comprises the following steps: the iodine blue value can represent the content of amylose dissolved in water, wherein the higher the content of soluble amylose, the better the mouthfeel and viscoelasticity of the rice flour. Weighing 5.0g of fresh finished rice flour, placing in a 250mL beaker, adding 100mL of boiling water, soaking for 2min, taking supernatant, filtering with filter paper, taking 10mL of filtrate, placing in a 100mL volumetric flask, adding 1mL of 0.1mol/L HCl and 1mL of iodine solution, and then fixing the volume with distilled water. And (3) carrying out color comparison on the liquid in the volumetric flask at the wavelength of 620nm, and reading a light absorption value to obtain an iodine blue value of the extracting solution. The blank group was substituted for the filtrate with distilled water.

Sensory evaluation method: by adopting an 8-person scoring method, the total score is 40, the score is excellent above 34, the score is good 33-28, the score is qualified 27-24, and the score is unqualified below 23; expressed in terms of average score calculation.

Example 1:

weighing early long-shaped rice and late long-shaped rice according to the mass ratio of 3:1, uniformly mixing the two long-shaped rice, soaking the two long-shaped rice in cold water for 5 hours, taking out the rice and putting the rice into a stirrer for crushing, and sieving the crushed rice flour with a 80-mesh sieve to obtain the rice flour. Cleaning purple sweet potato, steaming for 20min, peeling, pressing into mashed purple sweet potato, oven drying at 105 deg.C for 8 hr in an electric heating constant temperature oven, pulverizing in a wall-breaking food machine, and sieving with 80 mesh sieve to obtain purple sweet potato powder.

Mixing the sieved rice flour with 15% purple sweet potato powder and 0.9% curdlan, adding sufficient water into a water tank of a rice flour machine, turning on a heating button until the rice flour machine begins to emit steam, and preparing rice pulp. And pouring the mixed rice slurry into a preheated rice flour machine, turning on a fan inside the machine and starting the machine to make rice flour.

The prepared rice and flour are well connected by a container, and then the container is sealed by a preservative film for aging for 6 hours. And then soaking the rice flour in cold water for 10min, loosening the filaments, and finally drying the purple sweet potato rice flour at 50 ℃ for 180min to obtain a finished product. And detecting rehydration rate, cooked and broken rate, pulp discharge rate, transmittance, iodine blue value and sensory evaluation of the finished rice and flour.

Through analysis and detection, the rehydration rate of the prepared purple sweet potato rice noodles is 59.56%, the breaking rate is 5.66%, the pulp discharge value is 2.95%, the transmittance is 0.932, and the iodine blue value is 0.180; sensory score 34.3.

Example 2:

according to the following steps of 18: 5, weighing early long-shaped rice and late long-shaped rice, mixing the two long-shaped rice uniformly, and soaking the mixture for 6 hours by using cold water. Taking out rice, putting into a stirrer, crushing, and sieving the crushed rice flour with a 80-mesh sieve. Cleaning purple sweet potato, steaming for 20min, peeling, pressing into mashed purple sweet potato, oven drying at 105 deg.C for 8 hr in an electric heating constant temperature oven, pulverizing in a wall-breaking food machine, and sieving with 80 mesh sieve to obtain purple sweet potato powder.

Mixing the sieved rice flour with 18% of purple sweet potato powder and 1.0% of curdlan, adding sufficient water into a water tank of a rice flour machine, turning on a heating button until the rice flour machine starts to emit steam, and preparing rice pulp. And pouring the mixed rice slurry into a preheated rice flour machine, turning on a fan inside the machine and starting the machine to make rice flour.

The prepared rice and flour are well connected by a container, and then the container is sealed by a preservative film for aging for 5 hours. And then soaking the rice flour in cold water for 12min, loosening the filaments, and finally drying the purple sweet potato rice flour at 50 ℃ for 180min to obtain a finished product. Through analysis and detection, the rehydration rate of the prepared purple sweet potato rice noodles is 58.33%, the breaking rate is 5.13%, the pulp discharge value is 2.83%, the transmittance is 0.898, and the iodine blue value is 0.181; sensory score 34.8.

Example 3:

weighing early long-shaped rice and late long-shaped rice according to the mass ratio of 36:11, mixing the two long-shaped rice uniformly, and soaking the rice in cold water for 7 hours. Taking out rice, putting into a stirrer, crushing, and sieving the crushed rice flour with a 80-mesh sieve. Cleaning purple sweet potato, steaming for 20min, peeling, pressing into mashed purple sweet potato, oven drying at 105 deg.C for 8 hr in an electric heating constant temperature oven, pulverizing in a wall-breaking food machine, and sieving with 80 mesh sieve to obtain purple sweet potato powder.

Mixing the sieved rice flour with 16% of purple sweet potato powder and 0.8% of curdlan, adding sufficient water into a water tank of a rice flour machine, turning on a heating button until the rice flour machine starts to emit steam, and preparing rice pulp. And pouring the mixed rice slurry into a preheated rice flour machine, turning on a fan inside the machine and starting the machine to make rice flour.

The prepared rice and flour are well connected by a container, and then the container is sealed by a preservative film for aging for 7 hours. And then soaking the rice flour in cold water for 11min, loosening the filaments, and finally drying the purple sweet potato rice flour at 50 ℃ for 180min to obtain a finished product. Through analysis and detection, the rehydration rate of the prepared purple sweet potato rice noodles is 56.86%, the breaking rate is 4.91%, the pulp discharge value is 2.78%, the transmittance is 0.833, and the iodine blue value is 0.181; sensory score 35.4 points.

Example 4:

weighing early long-shaped rice and late long-shaped rice according to the mass ratio of 4:1, mixing the two long-shaped rice uniformly, and soaking the rice in cold water for 8 hours. Taking out rice, putting into a stirrer, crushing, and sieving the crushed rice flour with a 80-mesh sieve. Cleaning purple sweet potato, steaming for 20min, peeling, pressing into mashed purple sweet potato, oven drying at 105 deg.C for 8 hr in an electric heating constant temperature oven, pulverizing in a wall-breaking food machine, and sieving with 80 mesh sieve to obtain purple sweet potato powder.

Mixing the sieved rice flour with 19% purple sweet potato powder and 0.9% curdlan, adding sufficient water into a water tank of a rice flour machine, turning on a heating button until the rice flour machine begins to emit steam, and preparing rice pulp. And pouring the mixed rice slurry into a preheated rice flour machine, turning on a fan inside the machine and starting the machine to make rice flour.

The prepared rice and flour are well connected by a container, and then the container is sealed by a preservative film for aging for 6.5 h. And then soaking the rice flour in cold water for 12min, loosening the filaments, and finally drying the purple sweet potato rice flour at 50 ℃ for 180min to obtain a finished product. Through analysis and detection, the rehydration rate of the prepared purple sweet potato rice noodles is 54.33%, the breaking rate is 4.21%, the pulp discharge value is 2.64%, the transmittance is 0.732, and the iodine blue value is 0.180; sensory score 35.5 points.

Example 5:

weighing early long-shaped rice and late long-shaped rice according to the mass ratio of 4:1, mixing the two long-shaped rice uniformly, and soaking in cold water for 7.5 h. Cleaning purple sweet potato, steaming for 20min, peeling, pressing into mashed purple sweet potato, oven drying at 105 deg.C for 8 hr in an electric heating constant temperature oven, pulverizing in a wall-breaking food machine, and sieving with 80 mesh sieve to obtain purple sweet potato powder.

Mixing the sieved rice flour with 20% of purple sweet potato powder and 1.1% of curdlan. Adding sufficient water into the water tank of the rice flour machine, and turning on the heating button until the rice flour machine begins to emit steam to prepare rice milk. And pouring the mixed rice slurry into a preheated rice flour machine, turning on a fan inside the machine and starting the machine to make rice flour.

The prepared rice and flour are well connected by a container, and then the container is sealed by a preservative film for aging for 8 hours. And then soaking the rice flour in cold water for 10min, loosening the filaments, and finally drying the purple sweet potato rice flour at 50 ℃ for 180min to obtain a finished product. Through analysis and detection, the rehydration rate of the prepared purple sweet potato rice noodles is 55.45%, the breaking rate is 4.59%, the pulp discharge value is 2.69%, the transmittance is 0.799, and the iodine blue value is 0.180; sensory score 36.1 points.

Comparative example 1:

weighing early long-shaped rice and late long-shaped rice according to the mass ratio of 2:1, mixing the two long-shaped rice uniformly, and soaking the rice in cold water for 5 hours. Taking out rice, putting into a stirrer, crushing, and sieving the crushed rice flour with a 80-mesh sieve. Cleaning purple sweet potato, steaming for 20min, peeling, pressing into mashed purple sweet potato, oven drying at 105 deg.C for 8 hr in an electric heating constant temperature oven, pulverizing in a wall-breaking food machine, and sieving with 80 mesh sieve to obtain purple sweet potato powder.

Mixing the sieved rice flour with 15% purple sweet potato powder, adding enough water into water tank of rice flour machine, turning on heating button until the rice flour machine begins to emit steam, and concocting to obtain rice milk. And pouring the mixed rice slurry into a preheated rice flour machine, turning on a fan inside the machine and starting the machine to make rice flour.

The prepared rice and flour are well connected by a container, and then the container is sealed by a preservative film for aging for 6 hours. Then soaking the rice flour in cold water for 15min, loosening, and finally drying the purple sweet potato rice flour at 50 ℃ for 180 min. The rice flour is bonded to a certain extent, and analysis and detection show that the rehydration rate of the prepared purple sweet potato rice flour is 61.21%, the breaking rate is 7.82%, the pulp discharge value is 4.92%, the transmittance is 0.734, and the iodine blue value is 0.151; sensory score 27.3.

Comparative example 2:

soaking early long-shaped rice in cold water for 5h, taking out the rice, putting into a stirrer, crushing, and sieving the crushed rice flour with a 80-mesh sieve. Cleaning purple sweet potato, steaming for 20min, peeling, pressing into mashed purple sweet potato, oven drying at 105 deg.C for 8 hr in an electric heating constant temperature oven, pulverizing in a wall-breaking food machine, and sieving with 80 mesh sieve to obtain purple sweet potato powder.

Mixing the sieved rice flour with 15% purple sweet potato powder, adding enough water into water tank of rice flour machine, turning on heating button until the rice flour machine begins to emit steam, and concocting to obtain rice milk. And pouring the mixed rice slurry into a preheated rice flour machine, turning on a fan inside the machine and starting the machine to make rice flour.

The prepared rice and flour are well connected by a container, and then the container is sealed by a preservative film for aging for 6 hours. Then soaking the rice flour in cold water for 15min, loosening, and finally drying the purple sweet potato rice flour at 50 ℃ for 180 min. The rice flour is bonded to a certain extent, and analysis and detection show that the rehydration rate of the prepared purple sweet potato rice flour is 65.21%, the breaking rate is 8.42%, the pulp discharge value is 6.81%, the transmittance is 0.604, and the iodine blue value is 0.129; sensory score 25.8.

Comparative example 3:

weighing early long-shaped rice and late long-shaped rice according to the mass ratio of 4:1, mixing the two long-shaped rice uniformly, and soaking the rice in cold water for 8 hours. Taking out rice, putting into a stirrer, crushing, and sieving the crushed rice flour with a 80-mesh sieve. Cleaning purple sweet potato, steaming for 20min, peeling, pressing into mashed purple sweet potato, oven drying at 105 deg.C for 8 hr in an electric heating constant temperature oven, pulverizing in a wall-breaking food machine, and sieving with 80 mesh sieve to obtain purple sweet potato powder.

Mixing the sieved rice flour with 25% purple sweet potato powder, adding enough water into water tank of rice flour machine, turning on heating button until the rice flour machine begins to emit steam, and making rice slurry. And pouring the mixed rice slurry into a preheated rice flour machine, turning on a fan inside the machine and starting the machine to make rice flour. The prepared purple sweet potato rice flour is seriously bonded and can not be shredded.

Table 1: comparison of physicochemical properties of the purple sweet potato rice noodles in examples and comparative examples