A method for preparing pre-cut french fries for frying

Abstract

The present application relates to the technical field of food processing and manufacturing, and particularly relates to a preparation method of pre-prepared potato strips / slices for frying. The pre-prepared potato strips / slices are prepared by the following method. The method is to replace the traditional blanching and hot air drying process with microwave treatment of potatoes, to realize full-dry production, and to achieve the purposes of water saving and better retention of nutrients. Two-stage microwave treatment is adopted, the first stage microwave is for the purpose of enzyme inactivation, and the second stage microwave is for the purpose of drying. The microwave heating process of the present application can not only reduce water consumption and waste in the processing, but also avoid the loss of nutritional components of potatoes caused by the blanching process, and can also inactivate the activity of polyphenol oxidase in potatoes and inhibit the growth of microorganisms on the surface of the pre-prepared potato strips for frying under cold storage. The pre-prepared potato strips / slices for frying prepared by the microwave process have a lower oil content and a more crisp taste after frying.

Description

Technical Field

[0001] This invention relates to the field of food processing and manufacturing technology, specifically to a method for preparing pre-made fried French fries. Background Technology

[0002] Currently, blanching with hot water, boiling water, or steam is the most commonly used commercial method due to its advantages such as simple operation and low cost. The main purpose of blanching is to inactivate the enzymes that cause browning in fruits and vegetables and reduce the microbial load to extend shelf life. However, blanching has disadvantages such as slow heat transfer, leaching of water-soluble nutrients, high energy consumption, generation of large amounts of wastewater, and environmental pollution. Therefore, there is an urgent need to research and develop alternative methods for blanching.

[0003] Microwaves are electromagnetic waves with frequencies ranging from 300MHz to 300GHz. Water molecules in the heated medium are polar molecules. Under the influence of a rapidly changing high-frequency electromagnetic field, their polar orientation changes with the external electric field, causing molecular motion and friction. The field energy of the microwave field is then converted into heat energy within the medium, raising the material's temperature and initiating a series of physicochemical processes, including thermochemical heating and expansion, thus achieving the purposes of microwave heating, drying, mold prevention, sterilization, and preservation. Compared to traditional heating methods, microwave heating offers advantages such as rapid heating, minimal heat loss, and ease of operation. It can shorten processing time, increase productivity, reduce costs, and improve product quality.

[0004] French fries / chips, a common snack in modern life, are popular with a wide range of people, especially children. However, blanching, an essential process in the traditional production of pre-made French fries / chips, easily causes the leaching of water-soluble nutrients and generates a large amount of wastewater, polluting the environment. Furthermore, blanching affects the heat and mass transfer efficiency during the frying process, thus increasing the oil content of the product. Extensive evidence shows that excessive fat intake increases the risk of obesity, type 2 diabetes, non-alcoholic fatty liver disease, and cardiovascular disease. Therefore, how to reduce fat intake in French fries / chips while maintaining their ideal flavor, and simultaneously saving water consumption during processing, has become a hot topic in the development of low-fat foods. Summary of the Invention

[0005] [Technical Issues]

[0006] The technical problem to be solved by this invention is the large amount of wastewater generated by the traditional blanching and heating process in the production of fried French fries / chips, which pollutes the environment and causes an increase in the oil content of fried French fries / chips.

[0007] [Technical Solution]

[0008] This invention uses two-stage microwave processing to treat French fries / chips, replacing traditional blanching and hot air drying processes, to achieve the goal of producing pre-made French fries / chips for frying using a completely dry method, thus saving water and better preserving nutrients.

[0009] The first objective of this invention is to provide a method for preparing pre-made French fries / chips for frying, wherein the method directly uses microwave treatment of potato fries / chips without blanching, thereby obtaining pre-made French fries / chips for frying.

[0010] In one embodiment of the present invention, the first microwave segment aims to inactivate enzymes and rapidly raise the center temperature of the potato strips to above 70°C within 0.5-3 minutes.

[0011] In one embodiment of the present invention, preferably, the microwave power of the first segment is 800-1000W and the processing time is 60-90s.

[0012] In one embodiment of the present invention, the temperature of the potato strips reaches 70-98°C after the first stage of microwave treatment.

[0013] In one embodiment of the invention, potato fries or slices are quickly placed in a microwave device to prevent oxidative browning.

[0014] In one embodiment of the invention, both the cutting of potatoes and the microwave treatment are carried out in a nitrogen-filled environment to avoid oxidative browning.

[0015] In one embodiment of the present invention, in order to make the microwave processing more uniform, multiple microwave processing zones of 2-4 are set in the microwave processing cavity, and the processing time of each zone is controlled at 10-60 seconds. During the process of the material moving from the previous microwave processing zone to the next microwave processing zone, the potato strips / slices need to be flipped and their positions changed.

[0016] In one embodiment of the present invention, the second microwave stage maintains the temperature of the potato strips at 70-90°C, so that the moisture content of the dried potato strips is 50-70%.

[0017] In one embodiment of the present invention, the potato is in the form of strips or slices.

[0018] A second objective of this invention is to provide pre-made French fries / chips for frying prepared according to the above method. These pre-made French fries / chips only require refrigeration at 0-4°C and do not require freezing.

[0019] The third objective of this invention is to provide a method for preparing fried French fries / chips, wherein the method uses the above-mentioned pre-made French fries / chips for frying as raw materials, and frys them to obtain fried French fries / chips without the need for blanching before frying.

[0020] In one embodiment of the present invention, the frying conditions are: frying temperature 150-200℃, frying time 2-5min.

[0021] The fourth object of the present invention is to provide a fried French fry / chip prepared according to the above method.

[0022] The beneficial effects of this invention are:

[0023] (1) Microwave heating can be used to quickly deactivate the activity of polyphenol oxidase in potatoes, which helps to delay browning caused by oxidation during the re-drying process of potato strips / chips.

[0024] (2) Microwave treatment can reduce the moisture content on the surface of pre-made potato fries for frying and inhibit the growth of microorganisms on the surface of pre-made potato fries for frying under refrigeration.

[0025] (3) Microwave treatment can moderately increase the thickness of the outer shell of fried French fries from 1.14μm to 1.90-2.01μm, making them crispier.

[0026] (4) Using microwave heating instead of traditional blanching helps reduce water consumption during processing and avoids the loss of potato nutrients caused by blanching. It also significantly reduces the oil content of fried potato fries and improves their chewiness. Pre-made fried potato fries prepared by microwave treatment have an oil content reduced to less than 20% after frying, which is 40.5% of that obtained by blanching. Furthermore, compared to blanching, the chewiness improved from 206.55 to 722.14–786.03.

[0027] (5) The pre-made French fries / chips prepared by the present invention only need to be kept at 0-4℃ and do not need to be frozen. Detailed Implementation

[0028] The preferred embodiments of the present invention are described below. It should be understood that the embodiments are for better explanation of the present invention and are not intended to limit the present invention.

[0029] 1. Texture analysis methods:

[0030] The total texture (TPA) of fried potato chips was determined using a texture analyzer (TA.XT Plus, Stable Microsystems Ltd., Britain). A P35 probe was used, with a compression ratio of 60%, a trigger force of 5 g, and a test rate of 1 mm / s.

[0031] 2. Polyphenol oxidase analysis method:

[0032] Accurately weigh approximately 2.00 g of the surface area of ​​pre-fried potato fries and add 15.00 mL of pre-cooled phosphate buffer solution (pH 6.5, 0.1 mol / L). Homogenize for 3 min. Transfer the homogenate to a 10 mL centrifuge tube and centrifuge for 25 min (10000 g, 4℃). Collect the supernatant to obtain the crude PPO enzyme solution and store it at 4℃ for later use. Add 100 μL (0.2 mol / L) catechol solution to a 96-well plate, then add 150 μL (pH 5.5, 0.1 mol / L) phosphate buffer and 50 μL of crude enzyme solution sequentially. Mix well and immediately measure the absorbance at 410 nm. Record the absorbance every 30 s for a total of 2 min.

[0033] 3. Method for determining oil content:

[0034] The oil content of freeze-dried fried French fries was determined using the Soxhlet extraction method.

[0035] 4. Method for measuring the outer shell thickness of French fries:

[0036] The French fries were cut along their cross-section into slices approximately 1 mm thick. The slices were then magnified under an electron microscope and photographed. The thickness of the French fries' outer shell was then measured using Adobe Photoshop.

[0037] Example 1

[0038] Select potatoes free from insect holes, sprouts, diseases, and rot, wash and drain them, then cut them into 1cm x 1cm strips, 5cm in length, according to actual production needs. Lay the potato strips flat on a conveyor belt and feed them into the processing chamber of a microwave unit for two-stage microwave treatment. The first stage uses a microwave frequency of 2450MHz and a power of 1000W, with four microwave processing zones. Each zone is processed for 15 seconds. The potato strips / slices need to be turned and repositioned as they move from one microwave processing zone to the next. After 60 seconds of the first microwave treatment, the center temperature of the potato strips reaches 95℃. The second stage involves microwave drying, maintaining the potato strips at 80℃ until the moisture content reaches 65%. Shortening is then used, and the frying temperature is set to 180℃ for 3.5 minutes.

[0039] Example 2

[0040] The potatoes were processed according to the method in Example 1, except that the microwave power of the first stage was set to 1000W, three microwave processing zones were set, and the processing time of each zone was controlled at 30s. After 90s of processing, the center temperature of the potato strips reached 97°C. The second stage was microwave drying, maintaining the temperature of the potato strips at 80°C, so that the potato strips were dried to a moisture content of 65%. Other conditions were the same as in Example 1.

[0041] Example 3

[0042] The potatoes were processed according to the method in Example 1, except that the microwave power of the first stage was set to 800W, two microwave processing zones were set, and the processing time of each zone was controlled at 25s. After processing for 50s, the center temperature of the potato strips reached 80°C. The second stage was microwave drying, maintaining the temperature of the potato strips at 80°C, so that the potato strips were dried to a moisture content of 65%. Other conditions were the same as in Example 1.

[0043] Example 4

[0044] Potato fries were prepared using the method described in Example 1, with the only difference being that the first microwave power was set to 1200W, two microwave processing zones were set up, and the processing time for each zone was controlled at 15 seconds, for a total of 30 seconds, so that the center temperature of the potato fries reached 90°C. The second microwave drying stage maintained the temperature of the potato fries at 80°C, drying them to a moisture content of 65%. Other conditions were the same as in Example 1.

[0045] Example 5

[0046] Potato fries were prepared using the method described in Example 1, with the only difference being that the first microwave power was set to 900W, four microwave processing zones were set up, and the processing time for each zone was controlled at 30s, for a total of 120s, so that the center temperature of the potato fries reached 98°C. The second microwave drying stage maintained the temperature of the potato fries at 80°C, drying them to a moisture content of 65%, with other conditions remaining the same as in Example 1.

[0047] Comparative Example 1

[0048] The microwave treatment in Example 1 was replaced with blanching, where the cut potato strips were blanched. The potato strips were placed in boiling water at 85-95°C for 7-10 minutes. Other conditions or parameters were the same as in Example 1.

[0049] Comparative Example 2

[0050] The microwave processing in Example 1 is omitted, while other conditions or parameters are the same as in Comparative Example 1.

[0051] Comparative Example 3

[0052] Potato strips were prepared according to the method in Example 1, with the only difference being that the first microwave power was set to 600W, two microwave treatment zones were set, and the treatment time for each zone was controlled at 15s, with a total treatment time of 30s to bring the center temperature of the potato strips to 60°C. The second microwave drying stage maintained the potato strips at 60°C until the moisture content reached 65%, with other conditions remaining the same as in Example 1. The resulting potato strips were prone to browning during the second microwave drying stage, indicating that if the center temperature of the potato did not reach 70°C after the first microwave treatment, the polyphenol oxidase in the potato could not be deactivated.

[0053] Comparative Example 4

[0054] Potato fries were prepared using the method described in Example 1, with the only difference being that the first microwave power was set to 1500W, four microwave treatment zones were set up, and the treatment time for each zone was controlled at 30 seconds, for a total of 120 seconds, so that the center temperature of the potato fries reached 98°C. After the first microwave treatment, the moisture content of the potato fries had decreased to 42%, and local charring and smoking occurred.

[0055] Comparative Example 5

[0056] Potato fries were prepared according to the method in Example 1, with the only difference being that the first microwave power was set to 1000W, one microwave treatment area was set, and the treatment lasted for 60 seconds, so that the center temperature of the potato fries reached 95°C. The second microwave drying stage maintained the temperature of the potato fries at 80°C, drying them to a moisture content of 65%, with other conditions remaining the same as in Example 1. Because the potato fries did not undergo multiple microwave treatments, turning, or changing, the resulting product had poor uniformity. Regarding the second microwave drying stage, some potato fries were prone to enzymatic browning at this stage.

[0057] Multiple experiments revealed that insufficient microwave power or processing time failed to reduce the oil content of the fries or improve their texture, such as hardness, elasticity, stickiness, and chewiness. Excessive microwave power or processing time, before frying, caused a rapid decrease in moisture content, resulting in a burnt taste. Furthermore, the fried fries had a harder texture compared to those produced using conventional methods (Comparative Example 1), and a thicker outer shell. Fries that were not microwaved in multiple areas, turned, and rotated resulted in poor product uniformity, and some fries were prone to enzymatic browning during the microwave drying stage.

[0058] Table 1 Texture analysis of French fries

[0059]

[0060] Table 2. Analysis of relevant characteristics of fried French fries

[0061]

[0062] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Anyone skilled in the art can make various modifications and alterations without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be determined by the claims.

Claims

1. A method for preparing pre-made French fries / chips for frying, characterized in that, The method includes the following steps: The cut potato fries / slices are laid flat on a conveyor belt and fed into the processing chamber of a microwave device for two-stage microwave processing. No blanching is required to obtain pre-made potato fries / slices for frying. The first microwave processing chamber is equipped with 2-4 microwave processing zones. The processing time for each microwave processing zone is controlled at 10-60 seconds. During the process of moving the material from the previous microwave processing zone to the next microwave processing zone, the potato strips / slices need to be turned over and their positions changed. Within 0.5-3 minutes, the core temperature of the potato is rapidly raised to above 70°C to quickly inactivate the enzymes. The power of the first microwave processing stage is 800-1000W, and the processing time is 60-90s; The second stage of microwave treatment maintains the temperature of the potato fries / chips at 70-90℃, resulting in a moisture content of 50-70% after drying.

2. The method according to claim 1, characterized in that, Both potato cutting and microwave treatment were carried out in a nitrogen-filled environment to prevent oxidative browning.

3. The method according to claim 1, characterized in that, After the first stage of microwave treatment, the temperature of the potato strips / slices reaches 70-98℃.

4. A method for preparing fried French fries / chips, characterized in that, The method uses pre-made French fries / chips for frying obtained by any one of claims 1-3 as raw material, and frys them to obtain fried French fries / chips. No blanching treatment is required before frying. The frying conditions are: frying temperature 150-200℃, frying time 2-5min.

5. A fried French fry / chip prepared according to the method of claim 4.

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