Fried vegetable food and method for preparing the same

Abstract

The present application provides a kind of fried vegetable food and its preparation method, including vegetable raw materials and the coating layer wrapped outside the vegetable raw materials, the coating layer is made of raw materials including mulberry leaf powder, malt dextrin, microcrystalline cellulose, starch and wheat flour.The present application realizes the unity of three functions of active moisture absorption, dense water resistance and structural support by the synergistic combination of mulberry leaf powder, malt dextrin and microcrystalline cellulose: mulberry leaf powder converts free water exuded by vegetables into bound water in a hydrogen bond combination, reducing water activity from the source;Malt dextrin fills the microcrack of starch network, improves the denseness of coating layer;Microcrystalline cellulose provides rigid skeleton support to prevent the collapse of coating layer due to moisture absorption.The three synergistically inhibit the plasticizing effect of moisture on the starch network of the coating layer, effectively prolong the crispness retention time, and at the same time, give the product the function of dietary fiber supplementation.

Description

Technical Field

[0001] This invention relates to the field of fried food technology, and more specifically to a fried vegetable food and its preparation method. Background Technology

[0002] Fried vegetable foods are a type of ready-to-eat product made by coating vegetable ingredients in batter or flour and then deep-frying them. They are popular with consumers because they combine the nutritional value of vegetables with the crispy texture of fried foods. These products are usually made with starch and wheat flour as the base coating materials, and are produced through processes such as preparing the batter, coating, and deep-frying.

[0003] However, existing fried vegetable products have long faced the problem of inconsistent crispness in coating during processing and distribution. High-temperature frying damages the internal structure of raw vegetables, causing cell rupture and the release of large amounts of free water. During storage, this water continuously migrates into the coating, acting as a plasticizer to penetrate the starch-protein network. This causes the glass transition temperature to gradually drop below ambient temperature, initiating a transition from a crisp, glassy state to a soft, rubbery state. The crispness is typically maintained for no more than 20-30 minutes. Furthermore, leafy vegetables have a waxy surface layer, and significant differences in surface energy between the front and back of the leaves and the vein areas result in insufficient wetting properties of conventional coatings, easily leading to "beading" and uneven coating thickness, with some areas charred and others undercooked. Current technologies often employ blanching or acid / alkali pretreatment to improve coating uniformity, but this damages the natural shape and color of the leaves.

[0004] Meanwhile, existing coating systems lack a systematic design to address moisture migration after frying. Although some technologies attempt to add a single hygroscopic component to delay softening, the coating network is prone to collapse and cracking after moisture absorption and expansion, which actually accelerates moisture penetration, making it difficult to balance structural support and moisture management. In terms of process control, key parameters such as slurry viscosity and draining time rely heavily on empirical descriptions and lack clear quantitative ranges, resulting in large batch-to-batch variations in coating thickness and difficulty in ensuring product quality consistency, which is detrimental to standardized management in continuous industrial production. Therefore, existing technologies require further development. Summary of the Invention

[0005] To address the shortcomings of existing technologies and solve the aforementioned problems, a fried vegetable food product and its preparation method are proposed, and the following technical solution is provided: A fried vegetable food product includes vegetable raw materials and a coating material wrapped around the vegetable raw materials, wherein the coating material comprises mulberry leaf powder, maltodextrin, microcrystalline cellulose, starch and wheat flour.

[0006] Further, by weight, the raw materials for making the coating layer include: 3-5 parts mulberry leaf powder, 15-20 parts maltodextrin, 2-4 parts microcrystalline cellulose, 50-55 parts starch, and 40-45 parts wheat flour.

[0007] Furthermore, the mulberry leaf powder has a dietary fiber content ≥ 35g / 100g and a water activity ≤ 0.6.

[0008] Furthermore, the glucose equivalent of the maltodextrin is less than 10%.

[0009] Furthermore, the starch is a mixture of phosphorylated distarch and high amylose corn starch in a mass ratio of 1:3-5; and the wheat flour is low-gluten wheat flour.

[0010] This invention also provides a method for preparing fried vegetable food, comprising the following steps: A dry powder containing mulberry leaf powder, maltodextrin, microcrystalline cellulose, starch and wheat flour is mixed with water at a weight ratio of 1:1.2-1.5 to obtain a slurry; vegetable raw materials are dipped into the slurry for coating; and the coated vegetable raw materials are deep-fried.

[0011] Furthermore, the viscosity of the slurry is 200-280 mPa·s, and after the vegetable raw material is immersed in the slurry for coating, it is drained for 5-8 seconds, and the thickness of the wet film of the coating layer is controlled to be 0.3-0.6 mm.

[0012] Furthermore, before the vegetable raw materials are immersed in the slurry, a pretreatment step is also included: immersing the vegetable raw materials in the adsorption liquid for 10-15 seconds, and then letting them stand at room temperature for 30-40 seconds; The adhering liquid comprises, by weight, 3-5 parts of octenyl succinate starch ester, 0.5-1.5 parts of konjac glucomannan, 1-2 parts of trehalose, 0.1-0.3 parts of citric acid, and 95 parts of water.

[0013] Furthermore, in the attachment liquid, the molecular weight of konjac glucomannan is greater than 1×10⁻⁶. 6 Da.

[0014] Furthermore, the attachment liquid is prepared by the following steps: mixing octenyl succinate starch ester, konjac glucomannan, trehalose and water, and adding citric acid to adjust the pH of the system to 4.5-5.5.

[0015] Furthermore, the total time for the pretreatment step, the coating step, and the frying step shall not exceed 3 minutes.

[0016] Due to the adoption of the above technical solutions, the beneficial technical effects of the present invention are as follows: 1. The fried vegetable food provided by this invention achieves a unified triple function of active moisture absorption, dense water blocking, and structural support through the synergistic combination of mulberry leaf powder, maltodextrin, and microcrystalline cellulose in the coating formula, while maintaining crispness and dietary fiber supplementation. Mulberry leaf powder, with its high dietary fiber content of ≥35g / 100g, converts free water exuded from vegetables into bound water through hydrogen bonding, reducing water activity at the source. Maltodextrin fills the microcracks in the starch network, improving the density of the coating and delaying the formation of water migration channels. Microcrystalline cellulose, as a rigid framework dispersed in the coating network, enhances structural support and prevents the coating from collapsing and deforming due to moisture absorption. The synergistic effect of these three components significantly inhibits the plasticizing effect of water on the coating starch network, effectively extending the crispness retention time. Simultaneously, the dietary fiber and polyphenolic antioxidant activity contributed by mulberry leaf powder endow the product with nutritional supplementation and oxidative protection functions not found in traditional fried foods.

[0017] 2. The coating formulation uses a blend of high-amylose corn starch and phosphorylated distarch as the main starches. These two starches form a dense film-forming structure through covalent cross-linking and a high-amylose crystalline network. Combined with low glucose equivalent (DE < 10%) maltodextrin filling the microcracks in the film-forming structure, and the rigid framework support of microcrystalline cellulose, a composite coating system with a high glass transition temperature is constructed. After frying, this coating effectively prevents the migration of internal moisture from the vegetables to the coating, delaying the transition of the coating from a glassy to a rubbery state. This significantly extends the crispness retention time of the product at room temperature compared to traditional coatings.

[0018] 3. In the preparation method of fried vegetable food provided by the present invention, the vegetable raw materials are first soaked in a pretreatment coating liquid before being coated with the slurry. The octenyl succinic starch ester in the coating liquid is amphiphilic and can form a molecular bridge between the waxy hydrophobic layer on the leaf surface and the hydrophilic slurry, significantly reducing the leaf surface contact angle; the high molecular weight konjac glucomannan fills the microscopic concave areas on the leaf surface, eliminating dead angles for adhesion. The two work synergistically to enable the slurry to spread evenly on the surface of leafy vegetables, overcoming problems such as uneven coating thickness, local exposure or powdering caused by the waxy layer on the leaf surface, and the coating thickness of the entire leaf surface tends to be uniform. Detailed Implementation

[0019] To enable those skilled in the art to better understand the technical solutions of the present invention, the technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Based on the embodiments in this application, other similar embodiments obtained by those skilled in the art without creative effort should all fall within the scope of protection of this application.

[0020] Unless otherwise specified in the examples, standard conditions or conditions recommended by the manufacturer should be followed. Reagents or instruments whose manufacturers are not specified are all commercially available products. Unless otherwise specified, all reagents used in the examples are commercially available.

[0021] A fried vegetable food product includes vegetable raw materials and a coating material wrapped around the vegetable raw materials, wherein the coating material comprises mulberry leaf powder, maltodextrin, microcrystalline cellulose, starch and wheat flour.

[0022] Conventional starch-wheat flour coating systems form a porous starch network after frying. This network maintains its glassy structure through van der Waals forces and hydrophobic interactions, but it has a weak affinity for water molecules. Free water exuded from vegetables easily penetrates into the network pores, lowering the system's glass transition temperature (Tg) through plasticization and inducing a brittle-to-tough transition. The fried vegetable food provided by this invention achieves a unified function of active moisture absorption, dense water barrier, and structural support through the synergistic combination of mulberry leaf powder, maltodextrin, and microcrystalline cellulose in the coating formula, thus maintaining a crisp and lasting texture while providing dietary fiber. Mulberry leaf powder is rich in soluble and insoluble dietary fiber (≥50 g / 100 g). Its molecular chains contain numerous free hydroxyl groups, which can convert free water exuded from vegetables into bound water through hydrogen bonding, reducing the system's water activity at the source and decreasing the plasticizing effect on the starch network. Maltodextrin, a low-molecular-weight polysaccharide, has linear dextran segments that can embed into microcracks caused by shrinkage during starch network film formation, filling pores, improving coating density, and blocking water migration channels. Microcrystalline cellulose (MCC) particles are physically dispersed within the coating network, providing rigid skeletal support and preventing the coating from collapsing or cracking due to localized stress concentration after moisture absorption, thus maintaining network integrity. The synergistic effect of these three components significantly inhibits the plasticizing effect of water on the coating starch network, resulting in a significantly longer crispness retention time compared to traditional coatings. Simultaneously, the dietary fiber and polyphenolic antioxidants contributed by mulberry leaf powder provide nutritional supplementation and oxidative protection functions not found in traditional fried foods.

[0023] The raw materials used to make the coating, by weight, include: 3-5 parts mulberry leaf powder, 15-20 parts maltodextrin, 2-4 parts microcrystalline cellulose, 50-55 parts starch, and 40-45 parts wheat flour.

[0024] Mulberry leaf powder dosage: 3-5 parts. Below 3 parts, insufficient hydrogen bonding sites result in limited ability to capture free water, making it difficult to significantly reduce water activity. Above 5 parts, a large amount of hydrophilic cellulose absorbs moisture and swells, exacerbating the overall water absorption of the coating, and the unique bitter taste of mulberry leaf powder is sensorily unacceptable. Maltodextrin dosage: 15-20 parts. Below 15 parts, insufficient filling of microcracks in the starch network leads to insignificant improvement in density. Above 20 parts, excessive maltodextrin causes abnormally high viscosity in the film-forming system, affecting slurry flowability, and uneven crystallization due to dextrin aggregation after film formation, creating new defects. Microcrystalline cellulose dosage: 2-4 parts. Below 2 parts, insufficient rigid particle density results in limited skeletal support. Above 4 parts, excessively dense MCC particle distribution affects film continuity, causing a grainy texture in the coating, deteriorating its texture and mouthfeel. A ratio of 50-55 parts starch to 40-45 parts wheat flour: the two form the basic film-forming framework of the coating, with starch providing sufficient film strength and wheat protein providing moderate protein network toughness. This ratio ensures that the coating forms an optimal glassy network structure.

[0025] Furthermore, the mulberry leaf powder has a dietary fiber content ≥ 35g / 100g and a water activity ≤ 0.6.

[0026] The dietary fiber content requirement of ≥40 g / 100 g is based on the fact that the ability of mulberry leaf powder to capture free water essentially depends on the number of free hydroxyl groups per unit mass. The higher the dietary fiber content, the greater the density of active sites that can participate in hydrogen bonding. When the content is below 35 g / 100 g, the hydrogen bonding sites provided by 3-5 servings are insufficient to effectively capture the free water exuded from vegetables, and the hygroscopic function cannot be fully utilized. The water activity requirement of ≤0.6 is intended to ensure the stability of mulberry leaf powder as a dry powder raw material. When the water activity is higher than 0.6, the free water content in mulberry leaf powder increases, causing it to pre-consume some of the functional capacity of maltodextrin and MCC when mixed with other dry powders. Furthermore, mulberry leaf powder with high water activity is prone to clumping and deterioration, affecting the uniformity of slurry preparation.

[0027] Furthermore, the glucose equivalent of the maltodextrin is less than 10%.

[0028] The glucose equivalent (DE value) reflects the degree of hydrolysis of maltodextrin molecular chains. The lower the DE value, the higher the average degree of polymerization and the longer the molecular chains. Maltodextrin with a DE value <10% has a high average degree of polymerization. Its linear dextran long chain segments can embed themselves into the microcracks of the starch network in a multi-point winding manner and form cross-links with the starch chain segments through inter-segment hydrogen bonding, permanently sealing the cracks. On the other hand, maltodextrin with a high DE value (>10%) has shorter molecular chains, making it difficult to form effective winding, resulting in poor filling effect. Furthermore, it is prone to caramelization and Maillard reaction after high-temperature frying, causing abnormal browning of the coating and affecting the product color.

[0029] In addition, low DE value maltodextrin has low hygroscopicity and will not damage the filled cracks due to its own water absorption, which is conducive to maintaining the long-term compactness of the coating.

[0030] Furthermore, the starch is a mixture of phosphorylated distarch and high amylose corn starch in a mass ratio of 1:3-5; and the wheat flour is low-gluten wheat flour.

[0031] Phosphorylated distarch is a product modified by covalently cross-linking starch with phosphate groups. The introduction of phosphate ester bonds forms a covalent bridging structure between adjacent starch chains, significantly improving the heat degradation resistance and hydrolysis resistance of the starch network. This allows the coating to maintain a dense network structure during high-temperature frying without network collapse due to excessive thermal gelatinization. Simultaneously, the cross-linking structure imparts a high Tg to the coating, delaying the transition from a glassy to a rubbery state. High-amylose corn starch contains over 70% amylose. During cooling, the amylose molecules form a highly ordered crystalline network through intermolecular hydrogen bonds. After film formation, it exhibits extremely low air and moisture permeability, effectively creating a dense physical barrier within the coating and preventing the migration of moisture from the vegetables into the coating. The mass ratio of phosphorylated distarch to high-amylose corn starch is set within the range of 1:3-5 to ensure that the dense crystalline network of high-amylose corn starch is the main component, while the covalent cross-linking of phosphorylated distarch is auxiliary. The two components interpenetrate during film formation, forming a dual stable structure of "covalent cross-linking-physical crystallization." When the ratio is less than 1:3, the high amylose content is too dominant, resulting in excessively brittle film that is easily broken. When the ratio is greater than 1:5, the cross-linking density of phosphorylated distarch is insufficient, failing to effectively prevent the high amylose network from swelling and deforming in high-humidity environments. Low-gluten wheat flour has a lower protein content (approximately 8%-9%), resulting in a weaker gluten network formed during slurry preparation and frying. This prevents the coating from becoming too dense and hard due to excessive gluten toughness. Instead, it acts as an elastic buffer within the starch network, giving the coating moderate toughness and preventing cracking caused by localized stress concentration during mechanical handling and thermal expansion and contraction.

[0032] This invention also provides a method for preparing fried vegetable food, comprising the following steps: A dry powder containing mulberry leaf powder, maltodextrin, microcrystalline cellulose, starch and wheat flour is mixed with water at a weight ratio of 1:1.2-1.5 to obtain a slurry; vegetable raw materials are dipped into the slurry for coating; and the coated vegetable raw materials are deep-fried.

[0033] Furthermore, the viscosity of the slurry is 200-280 mPa·s, and after the vegetable raw material is immersed in the slurry for coating, it is drained for 5-8 seconds, and the thickness of the wet film of the coating layer is controlled to be 0.3-0.6 mm.

[0034] The dry powder to water weight ratio of 1:1.2-1.5 was determined through rheological optimization: below 1:1.2, the slurry solid content is too high, the system viscosity exceeds the upper limit of the process window (>280 mPa·s), the slurry fluidity is poor, and the coating on the vegetable surface is uneven; above 1:1.5, the slurry solid content is too low, the system viscosity is below the lower limit of the process window (<200 mPa·s), the slurry adhesion to the vegetable surface is insufficient, the wet film after draining is too thin, and the shape after frying is slightly poor. This ratio range is interrelated with the slurry viscosity range (200-280 mPa·s) and draining time (5-8 seconds), together forming a complete process quantitative control system. This ensures that the wet film thickness is precisely controlled within the range of 0.3-0.6 mm, achieving a high degree of consistency in quality between batches, and is suitable for standardized management in industrial continuous production.

[0035] Furthermore, before the vegetable raw materials are immersed in the slurry, a pretreatment step is also included: immersing the vegetable raw materials in the adhering liquid for 10-15 seconds, and then letting them stand at room temperature for 30-40 seconds; by weight, the adhering liquid includes: 3-5 parts of octenyl succinic acid starch ester, 0.5-1.5 parts of konjac glucomannan, 1-2 parts of trehalose, 0.1-0.3 parts of food-grade citric acid, and 95 parts of water.

[0036] Leafy vegetables are covered with a cuticle and a waxy layer, mainly composed of hydrophobic substances such as long-chain alkanes, fatty alcohols, and wax esters. The contact angle with hydrophilic coatings can reach over 110°, causing the coating to bead up on the leaf surface instead of spreading evenly. Octenyl succinate starch ester (OSA starch) is an amphiphilic modified starch containing both hydrophobic octenyl succinate side chains and a hydrophilic dextran backbone. The hydrophobic side chains are anchored to the waxy layer on the leaf surface through hydrophobic interactions, while the hydrophilic backbone faces outwards, creating a hydrophilic interface layer covering the waxy layer. This significantly reduces the leaf contact angle from over 110° to below 35°, allowing the subsequent coating to completely wet and spread on the leaf surface, overcoming the "beading" phenomenon. Konjac glucomannan (KGM) is a high molecular weight polysaccharide linked by β-1,4 glycosidic bonds, with highly flexible and strongly hydrophilic molecular chains. High molecular weight KGM (>1×10⁻⁶) 6The Da solution exhibits significant non-Newtonian fluid properties (pseudoplasticity). In a static state, it has high viscosity, effectively filling microscopic depressions on the leaf surface (such as stomata and vein grooves) and eliminating adhesion dead zones. Under shear conditions, the viscosity rapidly decreases, ensuring the fluidity of the coating solution during immersion. The synergistic effect of KGM and OSA starch achieves uniform wetting of the entire leaf surface from macroscopic to microscopic levels, resulting in a consistent coating thickness across the entire leaf surface. This fundamentally solves the problems of localized exposure, powdering, and uneven thickness caused by the heterogeneity of the leaf surface in traditional coating methods. Trehalose, after adsorbing onto the vegetable surface in the coating solution, forms a glycoprotective film. During high-temperature frying, it replaces water molecules and forms hydrogen bonds with proteins on the magnesium porphyrin ring of chlorophyll, delaying the high-temperature demagnesiation reaction and effectively protecting natural pigments such as chlorophyll from thermal degradation, maintaining the product's bright green color. Citric acid adjusts the pH of the coating solution to 4.5-5.5, inhibiting the catalytic activity of polyphenol oxidase (PPO) (PPO's optimal pH is 5.5-6.5) through an acidified environment. This prevents the oxidative polymerization of polyphenols in vegetables during processing, thus preventing the formation of brown substances and effectively inhibiting enzymatic browning, protecting the product's color. Soaking for 10-15 seconds ensures that OSA starch and KGM are fully adsorbed onto the leaf surface; subsequently, allowing it to stand for 30-40 seconds allows some of the water in the coating solution to evaporate, transitioning the coating film from a liquid to a gel state. This increases the film's cohesion, ensuring it doesn't detach from the slurry during subsequent coating operations, thereby maintaining the integrity of the molecular bridging interface layer.

[0037] Furthermore, in the attachment liquid, the molecular weight of konjac glucomannan is greater than 1×10⁻⁶. 6 Da.

[0038] KGM's ability to fill microscopic depressions on leaf surfaces depends on the hydrodynamic volume of its molecular chains and its gel strength. Molecular weight greater than 1×10⁻⁶ 6 The high molecular weight KGM in Da, with its extended molecular chains, can cover a significantly larger area in aqueous solution than low molecular weight KGM, effectively bridging openings in leaf depressions and forming bridging structures to fill these spaces. Simultaneously, the physical entanglement between high molecular weight KGM segments is denser, resulting in a stronger gel network formed during static loading, which maintains interfacial integrity under the shearing action of the coating process. When the KGM molecular weight is below 1×10⁻⁶, the molecular weight of KGM is significantly lower. 6 At this stage, the molecular chains are relatively short and cannot cross microscopic depressions such as stomata (10-30μm in diameter) on the leaf surface, resulting in a significant decrease in filling effect; the solution gel strength is insufficient, and the film formed after standing is easily dispersed during the coating process, losing its homogenization function.

[0039] Furthermore, the attachment liquid is prepared by the following steps: mixing octenyl succinate starch ester, konjac glucomannan, trehalose and water, and adding citric acid to adjust the pH of the system to 4.5-5.5.

[0040] This preparation method specifies mixing all solid components first, then adjusting the pH. KGM exhibits the optimal hydration and swelling rate under neutral to weakly alkaline conditions, and the hydrophobic modified group orientation of octenyl succinate starch ester is more stable at higher pH levels. If acid is added before adding KGM, the low pH environment will inhibit the effective hydration and chain segment extension of KGM, resulting in lower solution viscosity and weakened interfacial filling function. Adding citric acid to adjust the pH to 4.5-5.5 after thorough hydration and mixing of all components preserves the optimal hydration state of KGM while achieving the inhibitory effect on polyphenol oxidase (PPO). The pH range of 4.5-5.5 is chosen to balance two objectives: above 5.5, the PPO inhibition effect is insufficient; below 4.5, the strongly acidic environment will cause the hydrophobic modified ester bonds of octenyl succinate starch ester to hydrolyze during long-term storage, affecting product quality stability. Furthermore, excessively low pH increases the corrosiveness to vegetable cell membranes, affecting the morphological integrity of vegetables.

[0041] Furthermore, the total time for the pretreatment step, the coating step, and the frying step shall not exceed 3 minutes.

[0042] Even after being removed from the cell, cellular respiration continues in vegetable tissues. Polyphenolic substrates oxidize slowly under the combined action of PPO and oxygen in the air; the longer the exposure time, the greater the accumulation of enzymatic and non-enzymatic browning. Simultaneously, surface moisture continues to evaporate from vegetables at room temperature, and prolonged exposure leads to wilting and water loss in the leaves, affecting the adhesion between the coating and the vegetables. Strictly controlling the total process time to within 3 minutes ensures that all processing steps are completed before the polyphenol oxidation reaction reaches a sensory threshold. Frying and shaping are also completed while the vegetables have sufficient moisture content and firm texture, ensuring a bright color, intact shape, and good adhesion between the coating and the vegetables. This time constraint also promotes a continuous and efficient production process, highly compatible with industrial assembly line operations.

[0043] The vegetable raw materials used in the following examples and comparative examples are perilla leaves, mulberry leaf powder (purchased from Taizhou Wangpai Food Co., Ltd.), maltodextrin (purchased from Guangzhou Juyuan Biotechnology Co., Ltd.), microcrystalline cellulose (purchased from Guangzhou Heshun Biotechnology Co., Ltd.), low-gluten wheat flour (purchased from Wuhan Zhengyou Food Co., Ltd.), ordinary wheat flour (purchased from Heilongjiang Liangshi Agricultural Development Co., Ltd.), phosphorylated distarch (purchased from Guangzhou Xinxiangyuan Biotechnology Co., Ltd.), high amylose corn starch (purchased from Qingdao Huazhiyuan Food Additives Co., Ltd.), corn starch (purchased from Guangzhou Juyuan Biotechnology Co., Ltd.), octenyl succinate starch ester (purchased from Hebei Yuanle Biotechnology Co., Ltd.), konjac glucomannan (purchased from Xi'an Bainiankang Biotechnology Co., Ltd.), and trehalose (purchased from Jiangsu Pize Biotechnology Co., Ltd.).

[0044] The following are examples and comparative test methods: Evaluation method for crispness retention time: After the product is removed from the oven, it is placed in an environment of 25℃ and 55% relative humidity. The breaking force is measured every 10 minutes using a texture analyzer (probe speed 1 mm / s, target deformation 2 mm). The point at which the breaking force decreases to 50% of the initial value is the endpoint of the crispness retention time. Coating powder removal rate: The percentage of the area of ​​the leaf not covered by the coating to the total projected area of ​​the leaf surface is the powder removal rate. The dietary fiber content of the product is determined according to the enzyme gravimetric method of GB / T 22224-2008, and is characterized as the percentage of total dietary fiber mass to sample mass (g / 100g).

[0045] Example 1 The coating formula, by weight, includes: 4 parts mulberry leaf powder, 17 parts maltodextrin, 3 parts microcrystalline cellulose, 52 parts high amylose corn starch, and 42 parts ordinary wheat flour.

[0046] The mulberry leaf powder has a dietary fiber content ≥ 25g / 100g and a water activity ≤ 0.6.

[0047] Preparation steps: Mix the above dry powder with water at a weight ratio of 1:1.35 to obtain a slurry with a viscosity of about 240 mPa·s; immerse perilla leaves in the slurry to coat them, drain for 6 seconds (the wet film thickness of the coating is about 0.45 mm), and deep-fry at 170℃ for 90 seconds; the total time is about 2.5 minutes.

[0048] The resulting product was bright green in color, with a uniform coating thickness and no exposed spots on the entire leaf surface. It maintained its crispness for 85 minutes. The dietary fiber content was measured at 2.1 g / 100 g of product. Due to the lack of pretreatment with an adhesive liquid, there was a difference in wettability between the waxy layer on the perilla leaf surface and the hydrophilic slurry. Slight powder shedding occurred at the leaf vein edges, and the coating was slightly thinner in microscopic depressions on the leaf surface, but the overall uniformity was within acceptable limits. Ordinary high-amylose corn starch relies solely on hydrogen bonds between amylose molecules to form a crystalline network, lacking the assistance of covalent cross-linking structures, resulting in limited density of the water-blocking barrier formed after frying. Mulberry leaf powder provides hydrogen bond water absorption sites, maltodextrin fills microcracks, and microcrystalline cellulose provides skeletal support. The synergistic effect of these three components significantly improved the crispness retention time compared to traditional coating methods, but the water-blocking properties of the starch network itself still have room for improvement.

[0049] Example 2 The coating formula, by weight, includes: 3 parts mulberry leaf powder, 15 parts maltodextrin, 2 parts microcrystalline cellulose, 50 parts starch, and 40 parts low-gluten wheat flour.

[0050] The mulberry leaf powder has a dietary fiber content ≥ 25g / 100g and a water activity ≤ 0.6.

[0051] Preparation steps: Same as in Example 1.

[0052] The resulting product maintained its crispness for 68 minutes. The product was macroscopically completely coated, with no significant exposure on the entire leaf surface. Similar to Example 1, due to the lack of pretreatment with the coating liquid, the waxy layer on the leaf surface resulted in slight powdering at the vein edges, and the coating was thinner in the concave areas of the leaf surface. Only 3 parts of mulberry leaf powder were used, and the number of free hydroxyl groups provided by its abundant dietary fiber was at the lower limit of the formulation range, resulting in a weaker ability to capture free water exuded from the vegetables via hydrogen bonding compared to Example 1. The reduction in water activity was limited, and the inhibition of the starch network plasticizing effect was insufficient, leading to a crispness retention time approximately 20% shorter than in Example 1. However, even at the lower limit of the formulation, 68 minutes still far exceeds traditional coating methods, demonstrating the effectiveness of the ternary synergistic system.

[0053] Example 3 The coating formula, by weight, includes: 5 parts mulberry leaf powder, 20 parts maltodextrin, 4 parts microcrystalline cellulose, 55 parts starch, and 45 parts low-gluten wheat flour.

[0054] The mulberry leaf powder has a dietary fiber content ≥ 25g / 100g and a water activity ≤ 0.6.

[0055] Preparation steps: Same as in Example 1.

[0056] The resulting product maintained its crispness for 89 minutes; the coating was a deep golden yellow, slightly darker than in Example 1 due to the pigment contribution from the mulberry leaf powder itself; the product had a slightly bitter taste, but it was still acceptable in the overall flavor. The dietary fiber content was significantly increased to 3.4 g / 100g. With mulberry leaf powder increased to 5 parts, the density of hydroxyl groups that could participate in hydrogen bonding in the coating per unit mass was greatly increased, resulting in the strongest ability to capture free water, thus achieving the highest crispness retention time of 89 minutes among the ordinary starch group. However, the flavonoids and alkaloids naturally present in mulberry leaf powder were already perceptible to the taste at 5 parts, producing a slight bitter aftertaste. In addition, the hygroscopic swelling effect of the high cellulose content began to appear, but because it was still within the formulation window, the coating structure did not collapse.

[0057] Example 4 The coating formula, by weight, includes: 4 parts mulberry leaf powder, 17 parts maltodextrin, 3 parts microcrystalline cellulose, 52 parts starch (phosphorylated distarch: high amylose corn starch = 1:3), and 42 parts low-gluten wheat flour.

[0058] The mulberry leaf powder has a dietary fiber content ≥ 35g / 100g and a water activity ≤ 0.6; the maltodextrin has a glucose equivalent of less than 10%. Preparation steps: Same as in Example 1.

[0059] The resulting product is golden in color, with a uniform coating thickness and no exposed spots on the entire leaf surface. It maintains its crispness for 96 minutes. The dietary fiber content was measured at 2.2 g / 100 g of product. Compared to Example 1, the introduction of phosphorylated distarch to form a dual network of covalent cross-linking and physical crystallization significantly improved the water resistance of the coating and further delayed the transition from a glassy to a rubbery state, thus significantly extending the crispness retention time. Due to the lack of pretreatment with an adhesion liquid, the "beading" phenomenon caused by the waxy layer on the leaf surface was not completely eliminated, and there was very slight powdering at the leaf vein edges. The amount of mulberry leaf powder used was 4 parts; the product had no bitter taste and overall high acceptability.

[0060] Example 5 The coating formula, by weight, includes: 4 parts mulberry leaf powder, 17 parts maltodextrin, 3 parts microcrystalline cellulose, 52 parts starch (phosphorylated distarch: high amylose corn starch = 1:5), and 42 parts low-gluten wheat flour.

[0061] The mulberry leaf powder has a dietary fiber content ≥ 35g / 100g and a water activity ≤ 0.6; the maltodextrin has a glucose equivalent of less than 10%. Preparation steps: Same as in Example 1.

[0062] The resulting product was a light golden-yellow color with a relatively hard and brittle coating, maintaining its crispness for 104 minutes. Further increasing the proportion of high-amylose corn starch increased the crystalline network in the coating, creating a denser physical barrier and further reducing the rate of moisture migration after frying, resulting in the optimal crispness retention time among all coating formulations. However, the high amylose content also increased film-forming brittleness, leading to significant coating rigidity after cooling and a pronounced crispness, with slightly less flexibility than in Example 4. Due to the absence of an adhesive liquid, a small amount of powder accumulated in the leaf depressions. The mulberry leaf powder dosage was 4 parts, with no obvious bitterness. The dietary fiber content was measured at 2.1 g / 100 g of product.

[0063] Example 6 The coating formula, by weight, includes: 4 parts mulberry leaf powder, 17 parts maltodextrin, 3 parts microcrystalline cellulose, 52 parts starch (phosphorylated distarch: high amylose corn starch = 1:4), and 42 parts low-gluten wheat flour.

[0064] The mulberry leaf powder has a dietary fiber content ≥ 35g / 100g and a water activity ≤ 0.6; the maltodextrin has a glucose equivalent of less than 10%. The formulation of the adhesion liquid, by weight, includes: 4 parts of octenyl succinate starch ester, KGM (Mw=2×10 6 1 part Da, 1.5 parts trehalose, 0.2 parts citric acid, 95 parts water; adjust pH to 5.0.

[0065] Preparation steps: Mix the above dry powder with water at a weight ratio of 1:1.35 to prepare a slurry with a viscosity of about 240 mPa·s; first immerse the perilla leaves in the coating liquid for 12 seconds, let them stand at room temperature for 35 seconds, then immerse them in the slurry to coat them, drain the liquid for 6 seconds (the wet film thickness of the coating layer is about 0.45 mm), and deep-fry at 170℃ for 90 seconds; the total time is about 2.5 minutes.

[0066] The resulting product exhibits a vibrant green color, significantly superior to the example without the coating solution. The coating thickness is highly uniform across the entire leaf surface, with no exposed spots. The veins are well-filled, with no powder shedding or accumulation. The crispness is maintained for 87 minutes; it is crisp and palatable, without bitterness, and contains 2.3 g / 100g of dietary fiber. The amphiphilic molecular structure of OSA starch (4 parts) in the coating solution constructs a hydrophilic interface layer on the waxy layer of the leaf surface, significantly reducing the subsequent coating contact angle and achieving complete wetting and spreading. KGM (molecular weight 2×10⁻⁶) 6 (1 part Da) fills the microscopic depressions such as stomata and vein grooves on the leaves, eliminating dead zones for adhesion. The two work synergistically to make the coating thickness uniform across the entire leaf surface, a uniformity unattainable in the examples without the adhesion liquid. The adhesion liquid, at pH 5.0, effectively inhibits polyphenol oxidase activity, and trehalose protects chlorophyll from thermal degradation during frying, resulting in a bright green color in the finished product. The 1:4 ratio of compound starch is a middle proportion in the formula, offering a good balance between water resistance and crispness, and the crispness retention time (87 minutes) is above average in the compound group.

[0067] Example 7 The coating formula, by weight, includes: 3 parts mulberry leaf powder, 15 parts maltodextrin, 2 parts microcrystalline cellulose, 55 parts starch (phosphorylated distarch: high amylose corn starch = 1:3), and 45 parts low-gluten wheat flour.

[0068] The mulberry leaf powder has a dietary fiber content ≥ 35g / 100g and a water activity ≤ 0.6; the maltodextrin has a glucose equivalent of less than 10%. The formulation of the adhesion liquid, by weight, includes: 3 parts octenyl succinate starch ester, KGM (Mw=1.5×10 6 0.5 parts Da, 1 part trehalose, 0.3 parts citric acid, 95 parts water; adjust pH to 4.5.

[0069] Preparation steps: Mix the above dry powder with water at a weight ratio of 1:1.2 to prepare a slurry with a viscosity of about 280 mPa·s; immerse the washed and drained perilla leaves in the coating liquid for 10 seconds, let them stand at room temperature for 30 seconds, then immerse them in the slurry to coat them, drain the liquid for 8 seconds (the wet film thickness of the coating layer is about 0.3 mm), and deep-fry at 170℃ for 50 seconds; the total time is about 2 minutes.

[0070] The resulting product is a beautiful blend of purple and green, with the characteristic purple and green hues of perilla leaves well preserved, and the leaves retain their original shape. The coating is thin and even, with no exposed veins, and the powder loss rate across the entire leaf surface is only 7.5%. It maintains its crispness for 110 minutes. The coating is extremely thin (0.3mm), resulting in a light and crisp texture with a prominent, characteristic perilla aroma. It contains 3 parts mulberry leaf powder and has no bitter taste.

[0071] This embodiment is a typical example of a thin-film coating process. The wet film coating is only 0.3 mm thick, and the frying time is only 50 seconds, far shorter than the 90 seconds in other embodiments. A thin coating means a shorter water migration path, which theoretically presents a greater challenge in preventing water loss. However, the cross-linked-crystallization network of the compound starch and the interfacial layer of the coating solution work synergistically to still achieve excellent crispness retention. Adjusting the pH of the coating solution to 4.5 provides the strongest inhibition of PPO, and with the entire process taking only 2 minutes, enzymatic browning is maximally suppressed, and the natural purple-green color of the perilla leaves is prominently preserved. The powder removal rate is only 7.5%, verifying the significant improvement in coating adhesion achieved by the coating solution treatment.

[0072] Example 8 The coating formula, by weight, includes: 5 parts mulberry leaf powder, 20 parts maltodextrin, 4 parts microcrystalline cellulose, 50 parts starch (phosphorylated distarch: high amylose corn starch = 1:5), and 40 parts low-gluten wheat flour.

[0073] The mulberry leaf powder has a dietary fiber content ≥ 35g / 100g and a water activity ≤ 0.6; the maltodextrin has a glucose equivalent of less than 10%. The formulation of the adhesion liquid, by weight, includes: 5 parts of octenyl succinate starch ester, KGM (Mw=2.5×10⁻⁶). 6 1.5 parts Da, 2 parts trehalose, 0.1 parts citric acid, 95 parts water; adjust pH to 5.5.

[0074] Preparation steps: Mix the above dry powder with water at a weight ratio of 1:1.5 to prepare a slurry with a viscosity of about 200 mPa·s; immerse the washed and drained perilla leaves in the coating liquid for 15 seconds, let them stand at room temperature for 40 seconds, then immerse them in the slurry to coat them, drain the liquid for 5 seconds (the wet film thickness of the coating layer is about 0.6 mm), and deep-fry at 170℃ for 150 seconds; the total time is about 3 minutes.

[0075] The resulting product had a slightly darker yellow hue, with less retention of the bright green color compared to Examples 6 and 7. The pH of the adhering solution (5.5) was at the critical upper limit of PPO inhibition, resulting in a weaker inhibition effect. Furthermore, the long frying time of 150 seconds and high temperature exacerbated the enzymatic browning and Maillard reaction catalyzed by residual PPO, leading to a darker color. The purple color of the perilla leaves was still discernible, but the overall color was quite deep. The leaf coating was dense and uniform, with good filling of the vein depressions, and no exposed or powdery areas on the entire leaf surface, resulting in excellent appearance integrity. The KGM molecular weight was as high as 2.5 × 10⁻⁶. 6The filling effect and interface layer strength are the best among all embodiments. The coating has a distinct crispness and a clear cracking sound when chewed, but its flexibility is relatively low. Five parts of mulberry leaf powder contribute a perceptible, slightly bitter aftertaste. The dietary fiber content is 3.4 g / 100g, the highest among all embodiments. The crispness retention time is 79 minutes.

[0076] This embodiment pushes all water-blocking and structural protection factors to their limits: the coating starch is used in a 1:5 extreme ratio to maximize the proportion of the crystalline network; the coating liquid constructs a complete hydrophilic interface to eliminate weak points where water can penetrate; and frying for 150 seconds allows the coating to be fully dehydrated and set. However, color protection factors are weakened: only 0.1 parts of citric acid are used, and the pH is adjusted to 5.5. At the same time, the frying time of 150 seconds far exceeds the conventional 90 seconds, and prolonged high-temperature exposure exacerbates pigment degradation and browning reactions.

[0077] Comparative Example 1 This comparative example uses existing technology, as detailed below: The coating formula, by weight, includes: 52 parts corn starch and 42 parts ordinary wheat flour.

[0078] Preparation steps: Mix the above dry powder with water at a weight ratio of 1:1.35 to obtain a slurry with a viscosity of about 240 mPa·s; immerse perilla leaves in the slurry to coat them, drain for 6 seconds (the wet film thickness of the coating is about 0.45 mm), and deep-fry at 170℃ for 90 seconds; the total time is about 2.5 minutes.

[0079] The resulting product, after high-temperature frying, had a dull color, and the leaves wilted and deformed due to lack of protection, exhibiting poor morphological integrity. The crispness was maintained for only 26 minutes. The traditional starch-wheat flour coating lacked active moisture absorption, dense water-blocking properties, and a rigid framework. Free water exuded from the vegetables quickly entered the network pores, producing a strong plasticizing effect on the starch. The coating rapidly transformed from a glassy state to a rubbery state, resulting in significant softening. Furthermore, the lack of pretreatment with an adhesive liquid led to beading of the waxy layer on the leaf surface, resulting in uneven coating thickness, localized scorching and undercooked areas, and numerous areas of powder loss and exposed skin.

[0080] Comparative Example 2 This comparative example does not contain mulberry leaf powder; all other formulations and preparation steps are the same as in Example 1, as follows: The coating formula, by weight, includes: 17 parts maltodextrin, 3 parts microcrystalline cellulose, 52 parts high amylose corn starch, and 42 parts ordinary wheat flour.

[0081] Preparation steps: Mix the above dry powder with water at a weight ratio of 1:1.35 to obtain a slurry with a viscosity of about 240 mPa·s; immerse perilla leaves in the slurry to coat them, drain for 6 seconds (the wet film thickness of the coating is about 0.45 mm), and deep-fry at 170℃ for 90 seconds; the total time is about 2.5 minutes.

[0082] The resulting coating was lighter in color than that of Example 1; due to the absence of bitterness, the flavor was purer, but slight powdering still occurred, and the crispness was maintained for 34 minutes.

[0083] Comparative Example 3 This comparative example does not contain maltodextrin; all other formulations and preparation steps are the same as in Example 1, as follows: The coating formula, by weight, includes: 4 parts mulberry leaf powder, 3 parts microcrystalline cellulose, 52 parts high amylose corn starch, and 42 parts ordinary wheat flour.

[0084] Preparation steps: Mix the above dry powder with water at a weight ratio of 1:1.35 to obtain a slurry with a viscosity of about 240 mPa·s; immerse perilla leaves in the slurry to coat them, drain for 6 seconds (the wet film thickness of the coating is about 0.45 mm), and deep-fry at 170℃ for 90 seconds; the total time is about 2.5 minutes.

[0085] The resulting coating exhibits enlarged microcracks, and after prolonged storage, fine cracks or pores easily appear on the surface of the coating, accelerating softening and oil oxidation. The absence of maltodextrin and the lack of fillers with low DE values ​​(<10%) prevent abnormal browning such as caramelization; the color remains normal, and the crispness is maintained for 47 minutes.

[0086] Comparative Example 4 This comparative example does not contain microcrystalline cellulose, and all other formulations and preparation steps are the same as in Example 1, as follows: The coating formula, by weight, includes: 4 parts mulberry leaf powder, 17 parts maltodextrin, 52 parts high amylose corn starch, and 42 parts ordinary wheat flour.

[0087] Preparation steps: Mix the above dry powder with water at a weight ratio of 1:1.35 to obtain a slurry with a viscosity of about 240 mPa·s; immerse perilla leaves in the slurry to coat them, drain for 6 seconds (the wet film thickness of the coating is about 0.45 mm), and deep-fry at 170℃ for 90 seconds; the total time is about 2.5 minutes.

[0088] The resulting product exhibits visible dents, cracks, or peeling of the coating, resulting in poor surface smoothness. Initially, it retains some crispness after frying, but quickly becomes tough after absorbing moisture, accompanied by noticeable collapse and deformation. The crispness is maintained for 31 minutes.

[0089] Microcrystalline cellulose, acting as a rigid framework, plays a crucial structural support role in the coating network. Without microcrystalline cellulose, the mulberry leaf powder fibers swell upon absorbing water, and the resulting swelling stress has nowhere to dissipate, easily leading to stress concentration in localized areas of the coating, causing the network to collapse and crack. Once the coating cracks, a large amount of internal moisture escapes, and the crispness is rapidly lost, deteriorating much faster than when mulberry leaf powder or maltodextrin is simply lacking.

[0090] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A fried vegetable food product, comprising vegetable raw materials and a coating layer covering the outside of the vegetable raw materials, characterized in that, The coating material includes mulberry leaf powder, maltodextrin, microcrystalline cellulose, starch, and wheat flour.

2. The fried vegetable food according to claim 1, characterized in that, The raw materials used to make the coating, by weight, include: 3-5 parts mulberry leaf powder, 15-20 parts maltodextrin, 2-4 parts microcrystalline cellulose, 50-55 parts starch, and 40-45 parts wheat flour.

3. The fried vegetable food according to claim 1, characterized in that, The mulberry leaf powder has a dietary fiber content of ≥35g / 100g and a water activity of ≤0.

6.

4. The fried vegetable food according to claim 1, characterized in that, The glucose equivalent of the maltodextrin is less than 10%.

5. The fried vegetable food according to claim 1, characterized in that, The starch is a mixture of phosphorylated distarch and high amylose corn starch in a mass ratio of 1:3-5; and the wheat flour is low-gluten wheat flour.

6. A method for preparing a fried vegetable food product as described in any one of claims 1-5, characterized in that, Includes the following steps: A dry powder containing mulberry leaf powder, maltodextrin, microcrystalline cellulose, starch and wheat flour is mixed with water at a weight ratio of 1:1.2-1.5 to obtain a slurry; vegetable raw materials are dipped into the slurry for coating; and the coated vegetable raw materials are deep-fried.

7. The method for preparing fried vegetable food according to claim 6, characterized in that, Before the vegetable raw materials are immersed in the slurry, a pretreatment step is also included: immersing the vegetable raw materials in the adsorption liquid for 10-15 seconds, and then letting them stand at room temperature for 30-40 seconds; The adhering liquid comprises, by weight, 3-5 parts of octenyl succinate starch ester, 0.5-1.5 parts of konjac glucomannan, 1-2 parts of trehalose, 0.1-0.3 parts of citric acid, and 95 parts of water.

8. The method for preparing fried vegetable food according to claim 7, characterized in that, In the attachment liquid, the molecular weight of konjac glucomannan is greater than 1×10⁻⁶. 6 Da.

9. The method for preparing fried vegetable food according to claim 7, characterized in that, The adhesion liquid is prepared by the following steps: octenyl succinate starch ester, konjac glucomannan, trehalose and water are mixed, and citric acid is added to adjust the pH of the system to 4.5-5.

5.

10. The method for preparing fried vegetable food according to claim 7, characterized in that, The total time for the pretreatment step, coating step, and frying step shall not exceed 3 minutes.