Freeze-dried Chinese yam biscuits and preparation method thereof

Abstract

The invention relates to the technical field of food processing, in particular to a freeze-dried Chinese yam biscuit and a preparation method thereof. The freeze-dried Chinese yam biscuit which is low in GI, good in flavor and crispy in texture is developed by screening the formula and considering the texture and flavor, and the freeze-dried pure raw Chinese yam biscuit has the problems that the structure is loose, the freeze-dried pure raw Chinese yam biscuit is prone to breakage under external force and adheres to teeth in the mouth, and the freeze-dried pure raw Chinese yam biscuit has the powder paste taste, the raw Chinese yam taste and the like. On the basis of maintaining the nutritional ingredients of the raw materials to the greatest extent, the freeze-dried biscuits are excellent in flavor, crisp in taste and friendly to diabetics, the defects that in the production process, products fall off residues, adhere to teeth, are heavy in raw taste and the like are overcome, meanwhile, the process is optimized, energy consumption is reduced to the minimum, and the problem that freeze-dried products are high in energy consumption is solved. The formula comprises the following components in parts by weight: 440 to 460 parts of common yam rhizome, 50 to 70 parts of henry steudnera tuber, 110 to 130 parts of milk, 10 to 15 parts of crystalline fructose, 8 to 12 parts of konjak, 15 to 25 parts of sesame and 0.5 to 1.0 part of theanine.

Description

Technical Field

[0001] The invention relates to the technical field of food processing, and in particular to a freeze-dried yam biscuit and a preparation method thereof. Background Art

[0002] Chinese yam, a food that serves both medicinal and edible functions, is rich in various nutrients and has benefits such as strengthening the spleen and stomach, benefiting the lungs and relieving coughs, lowering blood sugar, providing anti-inflammatory and immunomodulatory benefits. Traditional methods for preparing Chinese yam include stir-frying, deep-frying, and baking. These processing methods all suffer from varying degrees of loss or deterioration of the yam's nutritional value, failing to maintain its original nutritional value. While raw Chinese yam has high nutritional value, it has a short shelf life and is prone to browning and spoilage. In recent years, numerous studies have reported on the preparation of freeze-dried Chinese yam, such as patent CN103055096 B. Fresh Chinese yam is washed and cut into sections, then freeze-dried to obtain freeze-dried Chinese yam powder. This powder is then extracted to obtain a freeze-dried Chinese yam extract, which is then mixed with Atractylodes macrocephala and ginseng extracts, granulated with starch slurry, dried, granulated, and tableted. The prior art provides methods for preparing freeze-dried Chinese yam, which involves freeze-drying the Chinese yam before using it to prepare corresponding medicines or foods. We found that directly freeze-drying yam and then using it as a powder to prepare products has poor solubility due to the retained mucilage layer and extremely fine particles. However, destroying the tissue structure before drying not only improves solubility but also reduces the number of drying cycles, avoiding nutrient loss through multiple processing and achieving complete drying in one step. This not only preserves the nutritional content of the yam but also facilitates the development of ready-to-eat nutritious and healthy foods. Biscuits are a popular product that meet the dietary needs of today's consumers for convenience, fast delivery, nutrition, and deliciousness. Experiments have found that freeze-dried biscuits prepared solely from yam have problems such as loose structure, easy breakage due to external forces, stickiness, a powdery texture, and the taste of raw yam. Summary of the Invention

[0003] To address existing issues, the present invention provides freeze-dried yam biscuits and a preparation method thereof. Through the synergistic reconstruction of multiple components, while maximally preserving nutrients, the present invention produces freeze-dried biscuits with excellent flavor and a crispy texture. These biscuits address the shortcomings of existing freeze-dried pure yam biscuits, such as crumbly, sticky texture, and a strong raw taste. Furthermore, a phased heating technique is employed to optimize the process, reducing energy consumption and addressing the high energy consumption of freeze-dried products.

[0004] To achieve the above object, the present invention provides the following technical solutions:

[0005] A freeze-dried yam biscuit comprises the following components, measured by weight: 440-460 parts of Chinese yam, 50-70 parts of taro powder, 110-130 parts of milk, 10-15 parts of crystalline fructose, 8-12 parts of konjac powder, 15-25 parts of sesame seeds, and 0.5-1.0 part of theanine.

[0006] In one preferred embodiment, the freeze-dried yam biscuits comprise the following components, by weight: 450-460 parts of Chinese yam, 60-70 parts of taro, 120-130 parts of milk, 13-15 parts of crystalline fructose, 10-12 parts of konjac flour, 20-25 parts of sesame, and 0.7-1.0 parts of theanine.

[0007] In one preferred embodiment, the freeze-dried yam biscuits comprise the following components, by weight: 450 parts of Chinese yam, 60 parts of taro, 120 parts of milk, 15 parts of crystalline fructose, 10.8 parts of konjac flour, 20 parts of sesame, and 0.7 parts of theanine.

[0008] The present invention also claims a method for preparing the freeze-dried yam biscuits, which comprises the following steps:

[0009] 1) Wash and peel the Chinese yam, then cut it into pieces. Blend the pieces with milk to make yam puree.

[0010] 2) uniformly mixing taro powder, crystalline fructose, theanine, and konjac flour to obtain premix 1;

[0011] 3) Add premix 1 and sesame to the yam puree, mix well, put into a mold, perform vacuum freeze drying, and demold to obtain freeze-dried yam cake.

[0012] In one preferred embodiment, taro flour, sesame and konjac flour are mixed in a mixer at a rotation speed of 45 to 55 r / min for 3 to 5 minutes to obtain premix 1.

[0013] In one preferred embodiment, the drying curve of vacuum freeze drying is shown in the following table:

[0014] Temperature / (℃) -45～-35 -32～-28 -22～-18 -12～-8 -2～2 8～12 18～22 28～32 38～42 Time / (h) 0.6～1 2～2.5 2～2.5 2～2.5 0.5～0.7 0.5～0.7 0.5～0.7 0.5～0.7 6～7 Vacuum degree / (pa) 10 10 10 10 10 10 10 10

[0015] In one preferred embodiment, the drying curve of vacuum freeze drying is shown in the following table:

[0016] Temperature / (℃) -40 -30 -20 -10 0 10 20 30 40 Time / (h) 0.6～1 2～2.5 2～2.5 2～2.5 0.5～0.7 0.5～0.7 0.5～0.7 0.5～0.7 6～7 Vacuum degree / (pa) 5～10 5～10 5～10 5～10 5～10 5～10 5～10 5～10

[0017] In one preferred embodiment, the drying curve of vacuum freeze drying is shown in the following table:

[0018] Temperature / (℃) -40 -30 -20 -10 0 10 20 30 40 Time / (h) 1 2 2 2 0.5 0.5 0.5 0.5 6 Vacuum degree / (pa) - 10 10 10 10 10 10 10 10

[0019] After molding, the yam paste is first frozen at -35℃ to -45℃ for 0.6 to 1.0h. After the biscuits are frozen and formed, they are demolded. After demolding, vacuum is applied. When the vacuum degree is less than 10 Pa, freeze-drying is carried out according to the above drying curve. When the center temperature of the biscuit and the temperature of the freeze-drying chamber are close to 38℃, freeze-drying is completed to obtain freeze-dried yam cakes.

[0020] The present invention is further explained below:

[0021] The present invention uses crystalline fructose as a functional sweetener, replacing traditional sweeteners such as sucrose and white sugar, providing a sweet taste to the product, making it suitable for consumption by patients with chronic diseases such as diabetes, hypertension, and obesity. Furthermore, theanine, which has multiple functional activities and can protect the nervous system, is added. Theanine can alleviate brain tissue damage, inhibit brain nerve death, delay the occurrence of post-ischemic brain damage, and protect nerves. It also has excellent pharmacological effects in relieving stress, promoting sleep, relieving anxiety, combating depression, and improving learning ability and memory. Freeze-dried yam biscuits prepared using vacuum freeze drying have the effects of strengthening the spleen and stomach, benefiting the lungs and relieving coughs, lowering blood sugar, combating inflammation, and regulating the immune system.

[0022] The present invention adopts fresh Chinese yam and konjac flour to add in combination, and utilizes the combination of konjac flour and water molecules in yam to form a network structure to solve the problems of easy cracking and chipping of the product after freeze-drying. Taro flour is combined with fresh Chinese yam, and the taro flavor molecules neutralize the special flavor of fresh yam, so that the product has good flavor. In summary, under the conditions of taking into account flavor and texture, a freeze-dried yam biscuit with good flavor and crisp texture is developed, and the time required for vacuum freeze drying is shortened by adopting staged heating technology, thereby improving production efficiency and reducing production energy consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 1a is the SEM image of formula 2, Figure 1 b is the SEM result of formula 4;

[0024] Figure 2 The product diagrams of the present invention are shown in FIG. 2a for process 1, 2b for process 2, 2c for process 3, and 2d for process 4;

[0025] Figure 3 The temperature change curves of the products during the freeze-drying process of different freeze-drying processes of the present invention are shown. DETAILED DESCRIPTION

[0026] The present invention will be described in detail below with reference to the examples. The examples are only preferred embodiments of the present invention and are not intended to limit the present invention.

[0027] Example 1

[0028] Recipe Optimization

[0029] During the flavor optimization process, attempts were made to improve the product using fruit and vegetable raw materials (carrots, oranges, kale, apples, etc.), high-sugar raw materials (fermented glutinous rice, honey), fruit and vegetable powders (taro powder, cucumber powder, lychee powder, pineapple powder), and thickeners (guar gum, xanthan gum, sodium alginate, konjac flour, etc.), but the results were poor. Specifically, testing revealed that when high-moisture fruit ingredients such as oranges and apples were added at 5%, the product had the unique orange or apple flavor of the added ingredients. However, due to their high water content, the sample's moisture content was also increased, making the product fluffy, easy to break, and prone to falling into powder. When vegetable ingredients such as carrots and kale were added at 5%, they also imparted a unique flavor to the product. However, due to their high cellulose content, the fiber texture of these vegetable ingredients made the mouthfeel rough, and the flavor they imparted was unpleasant. When too little high-sugar ingredients such as fermented glutinous rice was added, there was no significant improvement in the product's taste. However, increasing the addition to 15% did impart a strong wine aroma to the product. However, the high sugar content in fermented glutinous rice increased the freeze-drying time and enhanced the product's hygroscopicity. Adding cucumber powder, lychee powder, or pineapple powder would make the freeze-dried product more hygroscopic. Thickeners such as guar gum, sodium alginate, and xanthan gum, when added at 2%, could increase the product's viscosity and thus improve its shape stability after freeze-drying, but the product's flavor was poor. Table 1 lists the recipes of some of the better freeze-dried yam cookies.

[0030] Table 1 Comparative group freeze-dried yam biscuit recipe

[0031]

[0032] Recipe 1: 440 parts of Chinese yam, 50 parts of taro, 110 parts of milk, 10 parts of crystalline fructose, 8 parts of konjac flour, 15 parts of sesame, and 0.5 parts of theanine.

[0033] Recipe 2: 450 parts of Chinese yam, 60 parts of taro, 120 parts of milk, 15 parts of crystalline fructose, 10.8 parts of konjac flour, 20 parts of sesame, and 0.7 part of theanine.

[0034] Recipe 3: 460 parts of Chinese yam, 70 parts of taro, 130 parts of milk, 15 parts of crystalline fructose, 12 parts of konjac flour, 25 parts of sesame, and 1.0 part of theanine.

[0035] Recipe 4: 450 parts of Chinese yam, 120 parts of milk, 15 parts of crystalline fructose, 20 parts of sesame, and 0.7 parts of theanine.

[0036] The production process of freeze-dried yam biscuits is as follows:

[0037] 1. Select fresh high-quality yam, wash and peel it, weigh it, cut it into slices or dices, and add it into a blender with milk to blend;

[0038] 2. Add taro powder, crystalline fructose, theanine, and konjac flour according to the above weight into a kneading machine (parameter settings: speed set to 50 r / min, mixing time 5 min) and mix to obtain premix 1;

[0039] 3. Add premix 1 and sesame seeds to the yam puree in sequence and mix well;

[0040] 4. Pour the prepared slurry into the mold and smooth it with a scraper;

[0041] 5. Place the plasticized biscuits in the freeze-drying chamber of a vacuum freeze dryer and introduce the drying curve, as shown in the table below. First, freeze at -35°C to -45°C for 1 hour. After the biscuits are frozen and formed, demold them. After demolding, vacuumize them and freeze-dry them according to the drying curve in Table 2 under the condition that the vacuum degree is less than 10 Pa. When the center temperature of the biscuits and the freeze-drying chamber temperature are close to 38°C, freeze-drying is completed to obtain freeze-dried yam cakes.

[0042] Table 2 Drying curve

[0043] Temperature / (℃) -40 -30 -20 -10 0 10 20 30 40 Time / (h) 1 2 2 2 0.5 0.5 0.5 0.5 6 Vacuum degree / (pa) - 10 10 10 10 10 10 10 10

[0044] 8. When the center temperature of the biscuits and the temperature of the freeze-drying chamber are close to 38°C and the weight of the material is constant, the biscuits are removed from the chamber and demoulded to obtain freeze-dried yam biscuits;

[0045] 9. Aluminum foil bag packaging.

[0046] Among them, testing is carried out after the freeze-drying is completed to ensure that all products have been freeze-dried.

[0047] The sensory test of the formula was carried out, and the test contents were as follows:

[0048] A sensory evaluation panel consisting of 20 individuals who had undergone at least one sensory evaluation training was randomly selected to conduct sensory testing on the products prepared according to the recipes in Examples 1-3 and Comparative Group 1. The low-GI freeze-dried yam biscuits were evaluated for appearance, flavor, tooth stickiness, and crumbing. The evaluation criteria are shown in Table 3. The evaluation results are shown in Table 4.

[0049] Table 3 Sensory evaluation score sheet

[0050]

[0051] Table 4 Sensory evaluation results of freeze-dried yam biscuits

[0052] project color shape Flavor Adhesiveness Degree of chipping Total score Recipe 1 9.0 8.17 723 7.50 8.20 40.1 Recipe 2 9.0 8.65 7.47 757 8.11 40.8 Recipe 3 9.0 8.04 7.16 7.36 7.50 39.06 Recipe 4 8.86 4.00 3.71 4.03 2.15 2275 Comparison group 1-1 8.85 4.02 3.67 4.00 2.13 22.67 Comparison group 1-2 8.18 5.67 4.67 5.67 3.44 27.63 Comparison groups 1-3 8.16 6.01 5.87 6.66 7.14 3384 Comparison groups 1-4 8.76 8.14 7.45 7.24 8.07 39.66 Comparison groups 1-5 3.33 2.13 8.15 3.67 2.73 20.01 Comparison groups 1-6 7.88 4.61 3.42 5.67 444 26.02 Comparative groups 1-7 7.61 6.01 4.87 666 7.14 3229 Comparison groups 1-8 7.43 5.78 4.66 7.01 7.48 32.36

[0053] Through sensory evaluation, it can be concluded that compared with the control group 1-1, the addition of taro powder and fresh cucumber improved the product flavor, while the addition of maltodextrin did not improve the product flavor. However, the addition of fresh cucumbers resulted in an excessively high moisture content in the product, and the product had a poor appearance and was prone to falling off after freeze-drying. As the amount of taro powder added increased, more taro powder combined with the water molecules in the yam mud increased the wet-base solid content, thereby giving the freeze-dried product a better appearance and good flavor. By comparing the total scores of the sensory evaluations of Examples 1-3 and Control Groups 1-1 to 1-8, the total scores of Examples 1-3 and Control Group 1-4 were higher than those of the other control group formulas. It can be concluded that when the amount of taro powder added reached 60g, the flavor and appearance of the freeze-dried product could be improved. However, the freeze-dried product still had problems with falling off and sticking to teeth, so further optimization was carried out. The raw materials and amounts of the optimized freeze-dried yam biscuits are shown in Table 5.

[0054] Table 5 Freeze-dried yam biscuit recipe

[0055]

[0056] The freeze-dried yam biscuits were prepared and the freeze-dried drying curve was the same as above. Multiple repeated tests were performed to ensure that all products were freeze-dried.

[0057] The TPA texture test was performed on the freeze-dried yam cakes of the control group in Table 5 and formulas 1-3. The specific process is as follows:

[0058] The hardness of the low-GI freeze-dried yam biscuits prepared according to the recipes in Examples 1-3 and Comparative Group 2 was measured using a TA-XT physical property analyzer. The TA-XT physical property analyzer used a P2 probe in puncture mode. The measurement parameters were: pre-test speed 1.0 mm / s, test speed 1.0 mm / s, post-test speed 2 mm / s, test distance 1.5 mm, and trigger force 5 g. Five replicates were run for each treatment. The test results are shown in the table.

[0059] Table 6 Texture results of freeze-dried yam biscuits

[0060] project Hardness (g) Recipe 1 342.8±17.6 Recipe 2 347.91±19.4 Recipe 3 320.3±24.1 Comparative group 2-1 141.1±12.6 Comparative group 2-2 250.5±27.8 Comparison group 2-3 860.9±21.5 Comparative groups 2-4 191.7±29.2 Comparative groups 2-5 248.4±6.1 Comparative groups 2-6 733.8±16.1

[0061] Konjac flour and round-shell psyllium seed powder are all dietary fibers, can have thickening effect after interacting with water molecules.As can be seen from the texture results of table 6, adding konjac flour and round-shell psyllium seed husk powder improves the hardness of product, and product hardness increases along with the increase of addition.When the addition of round-shell psyllium seed husk powder (comparison group 2-6) and konjac flour (comparison group 2-3) reaches 22.5g, freeze-dried product has high hardness, needs greater strength when chewing.For the hardness of group 2-1, 2-2 and 2-5, all lower than formula group, illustrate that product is more fluffy compared to internal structure, when edible, there will be phenomenons such as fragmentation, falling off, and round-shell psyllium seed husk powder is easier to produce viscosity after being combined with water, also easier to stick teeth.To sum up, select konjac flour as thickening agent, and konjac flour addition when about 10.8g, freeze-dried product hardness is suitable and difficult for falling off.

[0062] In order to enrich the unsaturated fatty acid content in the product, components containing unsaturated fatty acids were added based on the base material formula of the comparative group. After multiple optimizations, it was determined that adding 20-25 portions of sesame seeds had the best effect. On the one hand, the addition of sesame seeds will significantly increase the unsaturated fatty acid content in the product, and compared to other nuts rich in unsaturated fatty acids, sesame seeds have a small particle size and can be added to the product without being crushed, which can greatly reduce the fat oxidation and rancidity during the subsequent storage of the product. On the other hand, after adding 20-25 portions of sesame seeds, the functional ratio of linoleic acid in the food is not less than 2.5% E, and the functional ratio of α-linoleic acid is not less than 0.4% E.

[0063] The results of scanning electron microscopy of formula 4 and formula 2 are as follows: Figure 1 shown. Figure 1 a and Figure 1 b are scanning electron micrographs of formula 2 and formula 4. The electron micrographs show that in formula 2, after adding taro and konjac, the ingredients form a network structure through hydrogen bonds, which wraps around the outside of the yam starch molecules and other components.

[0064] Example 2

[0065] Drying process optimization

[0066] The preparation method of freeze-dried yam biscuits is as follows:

[0067] 1. Prepare 450 parts of yam, 60 parts of taro, 120 parts of milk, 15 parts of crystalline fructose, 20 parts of sesame, 10.8 parts of konjac flour, and 0.7 parts of theanine.

[0068] 2. Select fresh, high-quality yam, wash, peel, weigh, and cut into slices or dices. Add the slices and milk into a blender and blend.

[0069] 3. Add taro powder, crystalline fructose, theanine, and konjac flour according to the above weight into a kneading machine (parameter settings: speed set to 50 r / min, mixing time 5 min) and mix to obtain premix 1;

[0070] 4. Add premix 1 and sesame seeds to the yam puree in sequence and mix well;

[0071] 5. Pour the prepared slurry into the mold and smooth it with a scraper;

[0072] 6. Vacuum freeze drying: Freeze the shaped biscuits at -35℃~-45℃ for 1.0h. After the biscuits are frozen and formed, vacuumize them. When the vacuum degree is less than 10pa, freeze-dry according to the drying curve in Table 7. When the center temperature of the biscuits and the temperature of the freeze-drying chamber are close to 38℃, freeze-drying is completed to obtain freeze-dried yam biscuits.

[0073] Table 7 Vacuum freeze drying conditions

[0074]

[0075] By comparing the temperature changes during the freeze-drying process ( Figure 3 ), energy consumption (Table 8) and the appearance of the freeze-dried product ( Figure 2 ) showed that the shortest freeze-drying time of process 2 drying curve was 15h, the lowest energy consumption was 102KW·h, and the freeze-dried product obtained ( Figure 2 b) No cracking occurs. However, the freeze-drying time of process 4 is the longest at 22h and cracks appear in the freeze-dried product picture (2d). This is because the ice crystals formed during the quick freezing process are removed first while the ice crystals inside are still there during the rapid heating process. When entering the analytical drying stage, the internal and external heating performances are different, resulting in cracks. Comprehensive product appearance and energy consumption. Process 1 ( Figure 2 a) and process 3( Figure 2 c) Due to the longer drying time, the color and texture are also worse than process 2. In summary, process 2 is selected as the optimal process.

[0076] Table 8 Energy consumption of freeze-drying process

[0077] Process 1 Craft 2 Craft 3 Craft 4 Energy consumption (KW·h) 115.6 102 122.4 149.6

[0078] Under the same process conditions, drying other formulations using Process 2 revealed that different formulations had different optimal processes. For example, under the same process, control groups 1-5 were not completely freeze-dried, requiring an additional 1-3 hours to reach the freeze-drying endpoint. This may be due to the varying water content and composition of the ingredients in the different formulations, which affected their optimal drying curves.

[0079] Example 3 Preparation Process Comparison

[0080] The difference between Example 3 and Formula 2 is that the freeze-dried yam biscuits are prepared using yam powder obtained after vacuum freeze drying. The water content of fresh yam is 78%.

[0081] The preparation method of freeze-dried yam biscuits is as follows:

[0082] 1. Wash and slice fresh Chinese yam (5 mm thick) and freeze-dry directly under vacuum. Grind the freeze-dried Chinese yam slices into powder using a crusher to obtain Chinese yam powder.

[0083] 2. Freeze the shaped biscuits at -35℃~-45℃ for 1.0h. After the biscuits are frozen and formed, vacuum them. When the vacuum degree is less than 10Pa, freeze at 5℃ / h. When the center temperature of the biscuits and the freeze-drying chamber temperature are close to 38℃, freeze-drying is completed.

[0084] 3. Prepare 351 parts of water, 99 parts of yam powder, 60 parts of taro, 120 parts of milk, 15 parts of crystalline fructose, 20 parts of sesame seeds, 10.8 parts of konjac flour, and 0.7 parts of theanine.

[0085] 2. Add yam powder, water and milk into blender and blend;

[0086] 3. Add taro powder, crystalline fructose, theanine, and konjac flour according to the above weight into a kneading machine (parameter settings: speed set to 50 r / min, mixing time 5 min) and mix to obtain premix 1;

[0087] 4. Add premix 1 and sesame seeds to the yam puree in sequence and mix well;

[0088] 5. Pour the prepared slurry into the mold and smooth it with a scraper;

[0089] 6. Vacuum freeze drying: Freeze the shaped biscuits at -35℃~-45℃ for 1.0h. After the biscuits are frozen and formed, vacuum them. When the vacuum degree is less than 10pa, freeze-dry according to process 2. When the center temperature of the biscuits and the temperature of the freeze-drying chamber are close to 38℃, freeze-drying is completed to obtain freeze-dried yam biscuits.

[0090] Texture testing and sensory evaluation of Recipe 2 and Example 3 showed that the freeze-dried yam flour-based biscuits scored lower for appearance and crumbing. This suggests that adding water in the same proportion as the moisture content makes it difficult to restore the yam's original viscosity, resulting in easy crumbing and poor appearance. Example 3 had a lower hardness, which corresponds to its sensory evaluation of easy crumbing.

[0091] Table 9 Texture characteristics and sensory evaluation of freeze-dried yam biscuits

[0092]

[0093] Example 4

[0094] The difference between Example 4 and Recipe 2 is that the fresh yam is washed, cut into pieces, and cooked (steamed in boiling water for 30 minutes) before preparing the freeze-dried yam biscuits.

[0095] The preparation method of freeze-dried yam biscuits is as follows:

[0096] 1. Wash and cut fresh yam into pieces and steam in a steamer for 30 minutes to get cooked yam;

[0097] 2. Prepare 450 parts of cooked yam, 60 parts of taro, 120 parts of milk, 15 parts of crystalline fructose, 20 parts of sesame seeds, 10.8 parts of konjac flour, and 0.7 parts of theanine.

[0098] 2. Add the cooked yam and milk into a blender and blend;

[0099] 3. Add taro powder, crystalline fructose, theanine, and konjac flour according to the above weight into a kneading machine (parameter settings: speed set to 50 r / min, mixing time 5 min) and mix to obtain premix 1;

[0100] 4. Add premix 1 and sesame seeds to the yam puree in sequence and mix well;

[0101] 5. Pour the prepared slurry into the mold and smooth it with a scraper;

[0102] 6. Vacuum freeze drying: Freeze the shaped biscuits at -35℃~-45℃ for 1.0h. After the biscuits are frozen and formed, vacuum them. When the vacuum degree is less than 10pa, freeze-dry according to process 2. When the center temperature of the biscuits and the temperature of the freeze-drying chamber are close to 38℃, freeze-drying is completed to obtain freeze-dried yam biscuits.

[0103] Texture testing and sensory evaluation of Recipe 2 and Example 4 showed that the freeze-dried yam biscuits prepared by first cooking the yam resulted in a lower stickiness score. This indicates that cooking the yam causes starch gelatinization, which increases the consistency of the product, resulting in a sticky texture and a higher hardness. Furthermore, cooking the yam also increases the glycemic index of the product, as shown in Table 11. This is because starch gelatinization increases the content of digestible starch and reduces the content of resistant starch, resulting in a fast-digesting product.

[0104] Table 10 Texture characteristics and sensory evaluation of freeze-dried yam biscuits

[0105]

[0106] Example 5

[0107] Glycemic index measurement

[0108] Formula 1, Formula 2, and Formula 3 were tested for their expected glycemic index according to the method reported by Goni et al. (1997) (Isabel , Alejandra Garcia-Alonso, Fulgencio Saura-Calixto. A starch hydrolysis procedure to estimate glycemic index, Nutrition Research, Volume 17, Issue 3, 1997, Pages 427-437.) to determine the expected glycemic index of the sample and make certain improvements. First, 500 mg of sample was placed in a centrifuge tube and mixed with 20 mL of 0.05 M phosphate buffer (pH 7.0). The pH was adjusted to 1 with 3 mol / L hydrochloric acid, and 1 mL of 0.05 mol / L pepsin solution (50 mg of pepsin dissolved in 10 mL of hydrochloric acid solution) was added. The mixture was reacted in a 37°C water bath shaker for 30 min. Subsequently, 5 mL of 1 mol / L NaOH solution was added to adjust the pH to 6.9, and the volume was adjusted to 50 mL with phosphate buffer solution. At this time, 0.1 mL of the digestion sample was taken and recorded as the 0 h sample. Finally, 0.5 mL of 1% α-amylase (1 g of α-amylase was dissolved in 10 mL of deionized water and the supernatant after stirring and centrifugation) was added. The mixture was reacted in a 37°C constant temperature water bath shaker for 180 min. At different reaction time points (15, 30, 60, 90, 120 and 180 min), 0.1 mL of digestion fluid was collected, placed in a centrifuge tube containing 1.9 mL of anhydrous ethanol, mixed evenly, and centrifuged (10,000 rad / min, 2 min). The supernatant was aspirated and the glucose content was measured by DNS to calculate the hydrolysis rate.

[0109] Hydrolysis rate (%) = (reducing sugar release amount at sampling time point * 0.9 / sample starch amount) * 100%.

[0110] The hydrolysis index (HI) was calculated based on the ratio of the area under the hydrolysis curve of the sample to that of the reference sample (white bread).

[0111] Glycemic index (eGI) = 39.7 + 0.549 HI.

[0112] The test results are shown in Table 9. The eGI values of Formula 1, Formula 2 and Formula 3 are 52.16, 53.45 and 54.82 respectively.

[0113] Table 11 Expected Glycemic Index

[0114] Recipe 1 Recipe 2 Recipe 3 Example 4 HI (hydrolysis index) 22.68 25.04 27.52 103.92 eGI (expected glycemic index) 52.16 53.45 54.82 96.76

[0115] The eGI values of the three formulas were all lower than 55, indicating that the freeze-dried yam biscuits were low GI products.

[0116] The embodiment described above is only one of the preferred specific implementation methods of the present invention. Common changes and substitutions made by those skilled in the art within the scope of the technical solution of the present invention should be included in the protection scope of the present invention.

Claims

1. A freeze-dried yam biscuit, characterized in that: The invention comprises the following components in parts by weight: 440-460 parts of Chinese yam, 50-70 parts of taro powder, 110-130 parts of milk, 10-15 parts of crystalline fructose, 8-12 parts of konjac powder, 15-25 parts of sesame seeds and 0.5-1.0 parts of theanine.

2. The freeze-dried yam biscuit according to claim 1, characterized in that: The invention comprises the following components in parts by weight: 450-460 parts of Chinese yam, 60-70 parts of taro, 120-130 parts of milk, 13-15 parts of crystalline fructose, 10-12 parts of konjac flour, 20-25 parts of sesame and 0.7-1.0 parts of theanine.

3. The freeze-dried yam biscuit according to claim 1, characterized in that: The invention comprises the following components in parts by weight: 450 parts of Chinese yam, 60 parts of taro, 120 parts of milk, 15 parts of crystalline fructose, 10.8 parts of konjac flour, 20 parts of sesame and 0.7 part of theanine.

4. A method for preparing the freeze-dried yam biscuits according to any one of claims 1 to 3, characterized in that: The steps include: 1) Wash and peel the Chinese yam, then cut it into pieces. Blend the pieces with milk to make yam puree. 2) mixing taro powder, crystalline fructose, theanine, and konjac flour to obtain premix 1; 3) Add premix 1 and sesame to the yam puree, mix well, put into a mold, perform vacuum freeze drying, and demold to obtain freeze-dried yam cake.

5. The preparation method according to claim 4, characterized in that Mix taro powder, crystallized fructose, theanine and konjac powder in a mixer at a speed of 45 to 55 rpm for 3 to 5 minutes to obtain premix 1.

6. The preparation method according to claim 4, characterized in that The drying curve of vacuum freeze drying is shown in the following table: 。 7. The preparation method according to claim 6, characterized in that The drying curve of vacuum freeze drying is shown in the following table: 。 8. The preparation method according to claim 7, characterized in that The drying curve of vacuum freeze drying is shown in the following table: 。

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