Processing method of roasted sweet potatoes

Abstract

The invention relates to a processing method of roasted sweet potatoes. The processing method comprises the following steps: grading and screening sweet potatoes according to diameters; performing water bath cleaning on the screened sweet potatoes; uniformly arranging the cleaned sweet potatoes at intervals; baking the sweet potatoes in three stages from high temperature to low temperature; spraying the baked sweet potatoes, and performing gradient cooling to 15-25 DEG C; and freezing the center temperature of the sweet potatoes to-18 DEG C or below within 30 minutes, and storing the sweet potatoes. Through selection and setting of segmented cooling, a spray gradient cooling process is introduced and a quick-freezing process is combined, so that the taste and the quality of the roasted sweet potatoes are improved.

Description

Technical Field

[0001] This application belongs to the field of food processing, and specifically relates to a processing method for roasted sweet potatoes. Background Art

[0002] Roasted sweet potatoes, as a traditional food with a strong fragrance and a sweet and glutinous taste, are deeply loved by the public. The outer skin of freshly baked roasted sweet potatoes is slightly charred due to high-temperature baking, forming a crispy and hard texture, which forms a strong contrast with the moist, soft, and almost runny sweet potato flesh inside. This taste level is the most direct expectation of consumers for "freshly roasted". In addition, the freshly roasted state can awaken people's yearning for the traditional street atmosphere.

[0003] Although "freshly roasted" sweet potatoes have the above advantages, due to the different sizes of sweet potatoes, there are problems such as poor quality stability among the individuals in the same pot of roasted sweet potatoes. For example, small sweet potato pieces are already charred, while large sweet potato pieces are still undercooked inside, and it is difficult to separate the skin and flesh of the sweet potato pieces. In recent years, the following problems have also been faced: 1) The city has increasingly strict requirements for the city appearance and environment; 2) Consumers attach importance to the convenience of purchase and the hygiene status of products; 3) The shelf life of the finished product is short, generally for immediate consumption on the street as a street snack; 4) Limited by fresh sweet potato raw materials, the product has strong seasonality and it is difficult to achieve annual supply and enter the catering channel.

[0004] In order to solve the problems existing in the traditional food roasted sweet potatoes, researchers have developed frozen roasted sweet potatoes to achieve hygienic guarantee, instant consumption, and annual supply. However, as the storage time passes, frozen roasted sweet potatoes often have problems such as deterioration of taste, such as dryness and hardness and / or bland sweetness due to water loss and starch retrogradation after reheating. In addition, due to the need for long-term storage and reheating, the baking conditions of frozen roasted sweet potatoes are also different from those of "freshly roasted", and defects such as charred skin, undercooked inside, and difficult separation of skin and flesh are often caused by inappropriate baking conditions. Generally speaking, how to make frozen roasted sweet potatoes as close as possible to the "freshly roasted" state after reheating is a currently recognized difficult problem.

[0005] In the prior art, Chinese Patent Publication CN105077078A proposes a method of low-temperature baking after peeling and cutting, and then reheating with an oven. On the one hand, it is difficult for consumers who love traditional roasted sweet potatoes to recognize the appearance after peeling and cutting. On the other hand, the method of reheating with an oven is not convenient enough to meet the instant consumption needs. Korean Patent Publication KR1020240094618A proposes a baking method of heating up in stages to increase the sweetness, but it still needs to be peeled and cut into appropriate sizes. Chinese Patent Publication CN103478644A mentions a preparation method for roasted sweet potatoes, which uses a baking method of heating up first and then cooling down, making the starch granules in the sweet potatoes more easily digestible. These baking processes can improve the quality of roasted sweet potatoes in some aspects. However, generally speaking, it is difficult to ensure the integrity and quality stability of the sweet potato pieces of roasted sweet potatoes, and it is even more difficult to achieve the quality of "freshly roasted" comprehensively after reheating.

[0006] Accordingly, in the field of food processing, there is a need to improve the quality of frozen baked sweet potatoes after reheating after long-term storage. Summary of the Invention

[0007] In view of this, the present application aims to solve the problems of the quality stability of baked sweet potatoes and the difficulty in approaching the taste and texture of " freshly baked" sweet potatoes after reheating of frozen baked sweet potatoes stored for a long time.

[0008] In one aspect, the present application provides a processing method for baked sweet potatoes, comprising:

[0009] grading and screening sweet potatoes according to their diameter;

[0010] washing the screened sweet potatoes by water bath;

[0011] arranging the washed sweet potatoes in a uniformly spaced manner;

[0012] baking the sweet potatoes according to the following procedure:

[0013] The first stage: baking at 230°C to 250°C for 15 minutes to 25 minutes; the second stage: baking at 190°C to 210°C for 15 minutes to 25 minutes; and the third stage: baking at 145°C to 165°C for 15 minutes to 25 minutes;

[0014] spraying and gradient cooling the baked sweet potatoes to 15°C to 25°C, wherein the spraying and gradient cooling includes a process of at least two spraying operations, a time interval is set between adjacent two spraying operations, and the time interval is 1 minute to 3 minutes; the atomized liquid for the spraying operation is pure water (at room temperature), and the water spraying amount is 2 mL to 4 mL for each sweet potato;

[0015] freezing the central temperature of the sweet potatoes to below -18°C within 30 minutes and storing them.

[0016] Unless otherwise specified, all technical terms and scientific terms used herein have the same meanings as those commonly understood in the technical field to which the present application belongs. The following interpretations are supplements to those in the art and relate to the present application, but do not extrapolate to any related or unrelated situations, such as any patents or applications commonly used. Although any methods and materials similar or equivalent to those described herein can be used when practically testing the present application, the materials and methods described herein are preferred. Therefore, the terms used herein are intended to merely describe specific embodiments and are not intended to limit the present application.

[0017] In a specific embodiment, the processing method of the present application uses sweet potato varieties with a dry matter content of 22% to 35%.

[0018] Exemplary sweet potato varieties include: Zijinxiang, Xinxiang, or Yanshu 25, but are not limited thereto.

[0019] In some embodiments, the grading and screening includes screening sweet potatoes with a diameter difference of ≤5%.

[0020] Exemplarily, the diameter difference between each sweet potato is ≤5%, ≤4%, ≤3%, ≤2%, ≤1%.

[0021] In some embodiments, the grading and screening includes selecting sweet potatoes with an individual weight of 50 g to 400 g.

[0022] In some embodiments, before processing, the sweet potatoes are fully saccharified. Saccharification is achieved, for example, by storing at 10 to 15 °C for more than 2 to 4 weeks. Saccharification decomposes the starch in the sweet potatoes into sugars, thereby increasing the sweetness.

[0023] In a specific embodiment, the cleaning includes using a bubble cleaning machine or a high-pressure water gun for cleaning, but is not limited thereto, as long as it can remove surface impurities without causing the potato skin to fall off.

[0024] In some embodiments, the spacing of the uniform spacing arrangement is 2 cm to 3 cm. Exemplarily, the spacing is 2 cm, 2.5 cm, 3 cm.

[0025] In a specific embodiment, the sweet potatoes are arranged at intervals by laying the sweet potatoes flat at intervals on a breathable grill or baking tray.

[0026] In the processing method of the present application, the baking process sequentially includes three stages: the first stage, the second stage, and the third stage; the temperatures of the three stages decrease sequentially.

[0027] In the first stage, the sweet potatoes can be placed in an oven preheated to 230 °C to 250 °C and baked for 15 minutes to 25 minutes.

[0028] Exemplarily, the baking temperature in the first stage is 230 °C to 250 °C, for example, 245 °C, 246 °C, 247 °C, 248 °C, 249 °C, 250 °C, 251 °C, 252 °C, 253 °C, 254 °C, 255 °C.

[0029] Exemplarily, the baking duration in the first stage is 15 minutes, 16 minutes, 17 minutes, 18 minutes, 19 minutes, 20 minutes, 21 minutes, 22 minutes, 23 minutes, 24 minutes, 25 minutes.

[0030] In a specific embodiment, after the first stage, the temperature at the center of the sweet potato is 68 °C to 90 °C, such as 68 °C, 69 °C, 70 °C, 71 °C, 72 °C, 73 °C, 74 °C, 75 °C, 76 °C, 77 °C, 78 °C, 90 °C.

[0031] Preferably, the baking temperature in the first stage is 250 °C and the baking duration is 20 minutes.

[0032] In the second stage, the oven temperature can be adjusted to 190 to 210 °C and baked for 15 to 25 minutes.

[0033] Exemplarily, the baking temperature in the second stage is 190 °C to 210 °C, for example, 195 °C, 196 °C, 197 °C, 198 °C, 199 °C, 200 °C, 201 °C, 202 °C, 203 °C, 204 °C, 205 °C.

[0034] Exemplarily, the baking duration in the second stage is 15 minutes, 16 minutes, 17 minutes, 18 minutes, 19 minutes, 20 minutes, 21 minutes, 22 minutes, 23 minutes, 24 minutes, 25 minutes.

[0035] In a specific embodiment, after the second stage, the temperature at the center of the sweet potato is 93 °C to 97 °C, such as 93 °C, 94 °C, 95 °C, 96 °C, 97 °C.

[0036] Preferably, the baking temperature in the second stage is 200 °C and the baking duration is 20 minutes.

[0037] In the third stage, the oven temperature can be adjusted to 145 to 165 °C and baked for 15 to 25 minutes.

[0038] Exemplarily, the baking temperature in the third stage is 145 °C to 165 °C, for example, 150 °C, 155 °C, 156 °C, 157 °C, 158 °C, 159 °C, 160 °C, 161 °C, 162 °C, 163 °C, 164 °C, 165 °C.

[0039] Exemplarily, the baking duration in the third stage is 15 minutes, 16 minutes, 17 minutes, 18 minutes, 19 minutes, 20 minutes, 21 minutes, 22 minutes, 23 minutes, 24 minutes, 25 minutes.

[0040] In a specific embodiment, after the third stage, the temperature at the center of the sweet potato is 98 °C to 102 °C, such as 98 °C, 99 °C, 100 °C, 101 °C, 102 °C.

[0041] Preferably, the baking temperature in the third stage is 160 °C and the baking duration is 20 minutes.

[0042] In some embodiments, the total duration of the baking process is 50 to 70 minutes, such as 50 minutes, 52 minutes, 54 minutes, 56 minutes, 58 minutes, 60 minutes, 62 minutes, 64 minutes, 66 minutes, 68 minutes, 70 minutes.

[0043] In one embodiment, the spray gradient cooling includes a process of at least two spray operations, with a time interval set between adjacent two spray operations. The time interval is from 1 minute to 3 minutes (e.g., 2 minutes); the atomized liquid for the spray operation is pure water (at room temperature), and the water spray amount is 2 mL to 4 mL per sweet potato.

[0044] In one embodiment, the duration of each spray operation is 15 seconds - 20 seconds, preferably 15 seconds.

[0045] In one embodiment, the spray gradient cooling is a process of two spray operations.

[0046] In one embodiment, the water spray amount is 3 mL per sweet potato.

[0047] No spraying is performed during the interval between each spray operation.

[0048] In a specific embodiment, after the spray gradient cooling, the central temperature of the sweet potato is cooled to 12 to 20 °C, such as 12 °C, 13 °C, 14 °C, 15 °C, 16 °C, 17 °C, 18 °C, 19 °C, 20 °C.

[0049] In the processing method of the present application, the freezing step includes freezing the central temperature of the sweet potato to below -18 °C within 20 minutes - 30 minutes.

[0050] In some embodiments, the freezing step includes freezing the central temperature of the sweet potato to below -18 °C within 25 minutes.

[0051] The freezing step can be achieved, for example, by a speed device, such as placing it in a quick-freezing device with a freezing temperature of -30 to -40 °C.

[0052] Optionally, after the freezing step, the processing method of the present application further includes a step of packaging the frozen sweet potato. The packaging methods can be, for example, plastic bag packaging, plastic box packaging, vacuum packaging, aluminum foil packaging, etc.

[0053] In the processing method of the present application, after the freezing step, it includes storing the frozen sweet potato below -18 °C.

[0054] On the other hand, the processing method of the present application further includes the following step: a step of reheating the above-mentioned stored frozen roasted sweet potato, and the reheating is microwave heating.

[0055] In the manufacturing method of the present application, the reheating step heats the central temperature of the sweet potato to 90 to 100 °C, such as 90 °C, 91 °C, 92 °C, 93 °C, 94 °C, 95 °C, 96 °C, 97 °C, 98 °C, 99 °C, 100 °C.

[0056] In the manufacturing method of the present application, the microwave heating duration in the reheating step is 1.5 to 2.5 minutes.

[0057] In a specific embodiment, reheating is not carried out by baking.

[0058] In a specific embodiment, the thawing step is not included before the reheating step.

[0059] In this article, "thawing" refers to the process of raising the temperature of frozen food by certain methods and means, gradually melting the ice crystals, and restoring it to the state before freezing or a state close to the state before freezing. Thawing includes low-temperature thawing, room-temperature thawing, water thawing, microwave thawing, thawing board thawing, etc. Low-temperature thawing includes placing frozen food in the refrigerator's cold storage compartment to thaw slowly at a low temperature. Room-temperature thawing includes placing frozen food at room temperature to thaw naturally. Water thawing includes thawing frozen food in flowing tap water or soaking the food in water. Microwave thawing includes using the microwaves of a microwave oven to cause the polar molecules in the food to move and generate heat, thereby achieving the purpose of thawing. When using microwave thawing, appropriate thawing power and time need to be selected to avoid overheating the food. Thawing board thawing includes using a thawing board made of special metal materials, placing the frozen food on it, and using the good thermal conductivity of the metal to accelerate thawing.

[0060] The inventors have conducted long-term exploration on the processing process of sweet potatoes and found that the mutual cooperation of specific spaced arrangements, segmented temperature reduction, and spray gradient temperature reduction is the key to improving the quality stability and taste of roasted sweet potatoes.

[0061] On the one hand, the sweet potatoes obtained by the baking process of the present invention have a strong fragrance, appropriate sweetness, and good glutinousness. Through the setting of the baking process, the processing method of the present application prolongs the saccharification time of sweet potatoes in the second stage, making them basically cooked, improving the sweetness and flavor of the product. In the third stage, the sweetness and flavor of the product are further improved, while preventing the loss of sugar in the product; the cooperation of the first to third stages avoids excessive water loss of the product and maintains good glutinousness. At the same time, the spray gradient cooling in cooperation with the specific three-stage baking further improves the glutinousness.

[0062] On the other hand, the roasted sweet potatoes obtained by the processing method of the present application reach a state where the skin and flesh are completely separated. It is speculated that in the first stage of baking, the sweet potato quickly heats up from the outer skin to the center, and the epidermis quickly takes shape. While in the spray gradient cooling step, the hot epidermis of the sweet potato quickly cools down and shrinks, achieving a state where the sweet potato is completely separated from the pulp. At the same time, this state can be reproduced after long-term (more than 1 year) frozen storage and reheating, which is amazing. BRIEF DESCRIPTION OF THE DRAWINGS

[0063] Figure 1 A diagram showing the baking temperature and duration settings in the stage baking step in the embodiment.

[0064] Figure 2 A schematic diagram of the spaced arrangement of sweet potatoes.

[0065] Figure 3 A schematic diagram of a spray device for realizing spray gradient cooling.

[0066] 1: Baking tray; 2: Sweet potato; 3: Spray device; 4: Spray head.

[0067] The drawings of this application are only drawn for illustrative purposes, to show possible implementation manners, and are not intended to reflect actual sizes, scales or materials. Detailed implementation manners

[0068] The following describes the preferred implementation manners of the present invention. The present invention is not limited to the following preferred implementation manners. It should be noted that for those skilled in the art, based on the inventive concept of this invention, several deformations and improvements made all fall within the protection scope of the present invention. Reagents not indicating the manufacturer can all be conventional products obtained through commercial purchase.

[0069] Example 1 Processing of "Purple Crystal Fragrance" roasted sweet potatoes

[0070] Select 10 kg of "Purple Crystal Fragrance" sweet potatoes, grade them into 100 - 150 g per piece, with a diameter difference ≤ 5%.

[0071] After cleaning with a high-pressure water gun, drain.

[0072] Arrange the sweet potatoes on a breathable grill at intervals of about 2.5 cm.

[0073] Baking stage:

[0074] 1. Bake at 250°C for 20 minutes. At the beginning, the Maillard reaction occurs, with aroma generated, and the central temperature reaches 71.2°C;

[0075] 2. Bake at 200°C for 20 minutes. Continuously and slowly saccharify and ripen, lower the temperature to prevent burning, and the central temperature reaches 94.5°C;

[0076] 3. Bake at 160°C for 20 minutes. Continue to saccharify and ripen, then lower the temperature to prevent burning, and the central temperature rises to 99.3°C;

[0077] Spray gradient cooling: Spray pure water, repeat twice, with a single spraying duration of 15 seconds, and an interval of 2 minutes between the two times; the total water spraying amount is 3 mL per piece and cool to 15°C.

[0078] Quick freezing and packaging: Quick freeze at -35°C for 25 minutes, and store at -20°C for 15 months after packaging.

[0079] Reheating: Take out the stored sweet potatoes without thawing. For 98.5 grams of frozen sweet potatoes, heat them in the microwave at high power for 2 minutes until the center temperature of the sweet potato pieces reaches 95°C, and then let them cool naturally to a palatable temperature.

[0080] Comparative Example 1

[0081] This comparative example uses a method similar to that of Example 1, and a single temperature is used for baking in the baking stage: bake at 250°C for 60 minutes; other operating methods are the same as those in Example 1.

[0082] Comparative Example 2

[0083] This comparative example uses a method similar to that of Example 1, and a single temperature is used for baking in the baking stage: bake at 200°C for 60 minutes; other operating methods are the same as those in Example 1.

[0084] Comparative Example 3

[0085] This comparative example uses a method similar to that of Example 1, and a single temperature is used for baking in the baking stage: bake at 160°C for 60 minutes; other operating methods are the same as those in Example 1.

[0086] Comparative Example 4

[0087] This comparative example uses a method similar to that of Example 1, and replaces "arrange the sweet potatoes on the breathable grill at intervals of 2 - 3 cm" with "arrange the sweet potatoes on the breathable grill with an interval of 0 cm (arranged closely)"; other operating methods are the same as those in Example 1.

[0088] Comparative Example 5

[0089] This comparative example uses a method similar to that of Example 1, and replaces the spray gradient cooling with "natural cooling"; other operating methods are the same as those in Example 1.

[0090] Sensory evaluation of sweet potatoes in Example 1 - Comparative Example 5

[0091] The sweet potatoes baked in the above different examples and comparative examples were subjected to sensory evaluation according to the following criteria.

[0092] Aroma: The aroma of the sweet potato itself and the fragrance produced during processing, scored from 1 - 5, the higher the score, the better the aroma.

[0093] Sweetness: The level of sweetness, scored from 1 - 5, the higher the score, the better the sweetness.

[0094] Waxy texture: According to the waxy texture during eating, scored from 1 - 5, the higher the score, the better the waxy texture.

[0095] The degree of skin - flesh separation was scored according to the following criteria 1 - 5:

[0096] 1 point: The skin - flesh separation rate is 10 - 20%, the sweet potato flesh is unevenly cooked, and there are large particles of uncooked sweet potato pieces;

[0097] 2 points: The skin - flesh separation rate is 20 - 40%, containing small particles of unripened sweet potato pieces;

[0098] 3 points: The skin - flesh separation rate is 40 - 60%, and the sweet potato flesh is evenly ripened;

[0099] 4 points: The skin - flesh separation rate is 60 - 80%, and the sweet potato flesh is fully ripened;

[0100] 5 points: The skin - flesh separation rate is 80 - 100%, and the sweet potato flesh is fully and evenly ripened.

[0101] The evenness of sweet potato piece ripening is scored from 1 to 5 according to the degree of evenness. The higher the score, the better the evenness.

[0102] The freshness of the epidermis is scored from 1 to 5 according to the following criteria:

[0103] 1 point: The epidermis is hard, the color is dull, and the skin - flesh adhesion degree is about 80%;

[0104] 2 points: The epidermis is relatively hard, the color is somewhat dull, and the skin - flesh adhesion degree is about 60%;

[0105] 3 points: The epidermis is relatively fresh, and the skin - flesh adhesion degree is about 40%;

[0106] 4 points: The epidermis is fresh, and the skin - flesh adhesion degree is about 20%;

[0107] 5 points: The epidermis is fresh and soft, and the skin - flesh adhesion degree is less than 10%.

[0108] Evaluate the sweet potatoes baked in the above - mentioned examples and comparative examples according to the above criteria. The evaluation results are as follows:

[0109] Table 1. Evaluation of sweet, fragrant, and glutinous properties of Example 1 and Comparative Examples 1 - 3

[0110]

[0111] Table 2. Quality evaluation of Example 1 and Comparative Example 4

[0112]

[0113] Table 3. Quality evaluation of Example 1 and Comparative Example 5

[0114]

[0115] From the above results, it can be concluded that the sweet potatoes baked by the method of Example 1 of the present application have a charred yellow surface, a fresh and soft epidermis, a strong fragrance, a good sweetness, a good glutinousness, the sweet potato flesh is fully and evenly ripened, the epidermis is fresh and soft, the skin - flesh separation rate is above 90%, and the overall taste is delicious and the quality stability is good.

Claims

1. A processing method for roasted sweet potatoes, the method comprising the following steps: (1) Classify and screen sweet potatoes according to their diameter size; (2) Wash the screened sweet potatoes by water bath; (3) Arrange the washed sweet potatoes in a uniform interval; (4) Roast the sweet potatoes according to the following procedure: The first stage: roast at 230°C to 250°C for 15 minutes to 25 minutes; The second stage: roast at 190°C to 210°C for 15 minutes to 25 minutes; and The third stage: roast at 145°C to 165°C for 15 minutes to 25 minutes; (5) Spray gradient cooling: Gradiently cool the baked sweet potatoes by spraying to 15°C to 25°C, where The spray gradient cooling includes a process of at least two spray operations, and the duration of each spray operation is 15 seconds - 20 seconds; A time interval is set between two adjacent spray operations, and the time interval is 1 minute to 3 minutes; The atomized liquid for the spray operation is pure water, and the water spray amount is 2 mL to 4 mL per sweet potato; (6) Freeze the central temperature of the sweet potatoes below -18°C within 30 minutes and store them.

2. The processing method according to claim 1, characterized in that, In the step (3), the interval for arranging in a uniform interval is 2 cm to 3 cm.

3. The processing method according to claim 1, characterized in that, In the step (4), the roasting temperature in the first stage is 250°C and the roasting duration is 20 minutes.

4. The processing method according to claim 1, characterized in that, In the step (4), the roasting temperature in the second stage is 200°C and the roasting duration is 20 minutes.

5. The processing method according to claim 1, wherein In the step (4), the roasting temperature in the third stage is 160°C and the roasting duration is 20 minutes.

6. The processing method according to claim 1, wherein, In the step (5), the spray gradient cooling includes a process of two spray operations.

7. The processing method according to claim 1, characterized in that, In the step (5), the duration of each spray operation is 15 seconds.

8. The processing method according to claim 1, wherein, In the step (5), the time interval is 2 minutes.

9. The processing method according to claim 1, characterized in that, In the step (5), the water spray amount is 3 mL per sweet potato.

10. The processing method according to any one of claims 1-9, characterized in that, It further includes a step of reheating the stored roasted sweet potatoes.

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