A low-starch high-expansion fish feed for carnivorous fish and a method for preparing the same

Abstract

This invention discloses a low-starch, high-expansion feed for carnivorous fish and its preparation method, belonging to the field of aquatic feed technology. The feed consists of a protein source, functional fiber, starch, and oil. During preparation, a portion of emulsified oil is first mixed with the powder and then extruded using a twin-screw high-shear extrusion process. The mixture is then dried in stages, and finally, the remaining oil and heat-sensitive nutrients are loaded using vacuum spraying. This invention utilizes enzymatic hydrolysis of fishmeal peptides and fiber to construct a protein cross-linking network to replace the starch backbone, combined with a vacuum permeation process, solving the problems of low-starch feed's difficulty in extrusion, easy dispersion, and easy oxidation of high-oil content. The resulting product has a low starch content, an expansion rate of 2.10~2.60 times, a bulk density of 360~440 g / L, a weight loss rate of ≤6% in water over 4 hours, a starch gelatinization degree of ≥90%, and a high vitamin retention rate, making it particularly suitable for carnivorous fish.

Description

Technical Field

[0001] This invention belongs to the field of aquatic feed technology, specifically relating to a low-starch, high-expansion carnivorous fish feed and its preparation method. Background Technology

[0002] Carnivorous fish (such as largemouth bass, mandarin fish, and grouper) have seen a continuous increase in market demand due to their delicious taste and rich nutrition, driving the rapid development of large-scale aquaculture. In recent years, the production of carnivorous fish, represented by largemouth bass, has shown a significant growth trend nationwide, with some major producing areas experiencing huge annual increases. This species has become an important pillar for increasing the income of fishermen and the aquaculture industry in many regions. In the aquaculture process, feed is the core cost element, accounting for about 70% of the total cost, and its quality directly determines the economic benefits and sustainability of the industry.

[0003] However, the production of feed for carnivorous fish has long faced a contradiction between "physiological needs" and "processing technology". From a physiological and nutritional perspective, carnivorous fish have a very low capacity to utilize carbohydrates. Ideally, the starch content in their feed should be controlled below 7%; excessive starch intake can cause a series of serious problems: (1) physiological metabolic disorders: excessive sugar is converted into glycogen and fat in the liver, which can easily lead to hepatocyte hypertrophy, fatty liver, or even liver dysfunction, which in turn can cause metabolic diseases and seriously affect the health of fish; (2) decreased growth performance: the digestive system of carnivorous fish lacks sufficient amylase, and excessive starch increases the burden on the intestines, causing digestive disorders and reducing the absorption rate of key nutrients such as protein; (3) deterioration of muscle quality: glycogen after excessive starch conversion accumulates in the muscle, leading to increased water content in the fish meat, loose muscle fibers, and a decrease in the relative protein content, which seriously affects the taste, flavor, and commercial value of the fish meat; (4) aggravated water pollution: a large amount of undigested starch is discharged into the water with feces, which not only deteriorates the water quality but also increases the risk of eutrophication and the probability of fish stress-related diseases.

[0004] Furthermore, from a processing technology perspective, traditional extruded feed production lines heavily rely on starch as the "extrusion substrate." Starch gelatinizes under high temperature and pressure, acting as a crucial binder and imparting good pellet formability, expansion, and water stability. In actual production, if traditional raw materials such as wheat flour, corn flour, or tapioca starch are used, the addition ratio usually needs to reach 10% to 15% or higher to ensure smooth pelleting by the extruder and prevent pellet collapse. Forcibly reducing the starch content to below 7% (to meet the physiological needs of fish) often leads to insufficient extrusion, poor pellet formation, high starch content, poor water stability, and may even cause production line blockages and shutdowns.

[0005] Therefore, how to break through the dependence of traditional processes on high starch content while meeting the low-sugar physiological needs of carnivorous fish, and develop a feed formula and preparation process that can significantly reduce starch content while ensuring high extrusion degree, high water stability and high nutrient retention rate, has become one of the problems that urgently need to be solved by those skilled in the art. Summary of the Invention

[0006] In view of the shortcomings of the prior art, the present invention provides a low-starch, high-expansion feed for carnivorous fish and its preparation method. The present invention utilizes functional fiber sources to reconstruct the extrusion matrix of the material, combined with optimized protein source combinations and a refined processing technology throughout the entire process (biaxial differential conditioning, high-shear extrusion, and vacuum negative pressure spraying), achieving a starch content of less than 9% while simultaneously achieving high extrusion, excellent water stability, and efficient retention of heat-sensitive nutrients.

[0007] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a low-starch, high-expansion carnivorous fish feed, which comprises the following components by weight: 45-60 portions of protein source; 15-25 parts of oil source; 6-9 parts starch source; 3-6 parts of functional fiber source; 1-3 parts of additive premix; The protein sources include enzymatically hydrolyzed fish meal, plant protein sources, and animal by-product proteins. The functional fiber sources include ultrafine pulverized dietary fiber and chitin derivatives; The resulting feed pellets have a bulk density of 350 g / L to 450 g / L, a weight loss rate of ≤6% after soaking in still water at 25℃ for 4 hours, and a starch gelatinization degree of ≥90%.

[0008] Preferably, the weight parts and characteristics of each component in the protein source are as follows: the enzymatically hydrolyzed fish meal is 30-35 parts, and the small peptide content is ≥15%; the plant protein source is selected from at least one of pea protein isolate, soy protein isolate, or soy protein concentrate, and is 12-18 parts; the animal by-product protein is selected from at least one of chicken meal or meat and bone meal, and is 8-12 parts, and the collagen content of the animal by-product protein is ≥20%.

[0009] Preferably, the weight parts and characteristics of each component in the functional fiber source are as follows: the ultrafine pulverized dietary fiber is ultrafine pulverized wheat bran or beet pulp with a particle size equivalent to a 60-80 mesh sieve, and is 2.5-5 parts; the chitin derivative is at least one of modified chitosan or chitin, and is 0.5-1 parts.

[0010] Preferably, the oil source is a mixed oil that has undergone emulsification treatment; the mixed oil consists of the following components in parts by weight: 13-22 parts fish oil, 2-3 parts lecithin, and 0.01-0.1 parts antioxidant; the emulsification treatment is to mix the above components at 60-70°C and perform shear emulsification until the oil particle size in the system is ≤10μm.

[0011] Preferably, the additive premix comprises the following components in parts by weight: 0.5 to 1 part of a non-starch binder, selected from one or more of sodium alginate and calcium lignosulfonate; 0.2 to 0.5 part of a puffing accelerator, selected from one or more of sodium bicarbonate, calcium dihydrogen phosphate, or transglutaminase; and the balance being vitamins, minerals, and palatability enhancers; wherein the sum of the parts by weight of the non-starch binder, puffing accelerator, vitamins, minerals, and palatability enhancers is 1 to 3 parts.

[0012] This invention provides a method for preparing the above-mentioned low-starch, high-expansion carnivorous fish feed, comprising the following steps: S1. Raw material pretreatment: Weigh the protein source, starch source, functional fiber source and additive premix according to the formula, and grind them to 60-80 mesh, mix them evenly, and obtain the mixed powder. S2. Preparation of oil source: Weigh fish oil, lecithin and antioxidant according to the formula, mix the above components at 60~70℃ and shear emulsify and stir until the oil particle size in the system is ≤10μm, and obtain emulsified mixed oil. S3. The mixed powder obtained in step S1 is fed into a biaxial differential speed conditioner, and saturated steam and a first portion of emulsified mixed oil accounting for 40% to 60% of the total weight of the emulsified mixed oil in step S2 are added. The mixture is then conditioned at 90 to 95°C to obtain the conditioned material. The amount of saturated steam added is 4% to 8% of the weight of the mixed powder. S4. Extrusion puffing: The conditioned material is fed into a twin-screw extruder and extruded and puffed through a high-shear screw configuration; S5. Drying and spraying: The expanded pellets are dried in sections, followed by vacuum spraying to obtain the finished feed.

[0013] Preferably, in step S4, the extrusion expansion is carried out in a twin-screw extruder, wherein the screw configuration of the twin-screw extruder is configured such that the length-to-diameter ratio L / D is 2.5:1 to 2.8:1 and the compression ratio is 3.5:1 to 4:1; and the melting section and metering section of the screw are provided with reverse thread elements and toothed shear discs, so that the die pressure during the extrusion process is maintained at 35 to 45 Bar.

[0014] Preferably, the extrusion puffing process parameters are: spindle speed of 450~550 rpm; temperature distribution of the puffing machine cylinder: 60~70℃ in the feeding section, 90~110℃ in the compression section, 125~135℃ in the melting section, and 115~120℃ in the die head; and the moisture content of the discharged material is controlled at 18~20%.

[0015] Preferably, in step S5, the segmented drying process is as follows: in the first stage, rapid drying is carried out at 110~115℃ until the surface moisture of the particles is ≤12% to complete the surface shaping; in the second stage, slow drying is carried out at 85~90℃ until the overall moisture of the particles is ≤10% to remove internal moisture.

[0016] Preferably, in step S5, the conditions and material composition of the vacuum spraying treatment are as follows: the vacuum degree is -0.08MPa to -0.09MPa; the spraying liquid is a mixture of the second part of emulsified mixed oil and heat-sensitive nutrient additive; wherein, the second part of emulsified mixed oil is the remaining amount after deducting the first part of emulsified mixed oil used in step S3 from the total weight of the emulsified mixed oil obtained in step S2.

[0017] Compared with the prior art, the present invention has the following beneficial effects: (1) This invention abandons the traditional approach of relying on high starch content (usually >20%) gelatinization to form a gel network in extruded feed, and constructs a dual network structure of "protein chemical cross-linking-fiber physical support", which realizes high extrusion degree and high stability of low starch formula.

[0018] (i) Enhanced protein cross-linking: By selecting enzymatically hydrolyzed fish meal with high small peptide content, plant protein rich in globulin, and animal by-products with high collagen content, protein molecular chains are induced to unfold under high temperature and high shear, promoting the oxidation of -SH groups to form a strong disulfide bond (-SS-) cross-linking network, which replaces the binding function of starch.

[0019] (ii) Fiber physical support: 60-80 mesh ultrafine pulverized dietary fiber and modified chitin derivatives are introduced. The fiber is distributed in a mesh under shear force, which plays a physical support role similar to the "steel bars" in concrete. This not only prevents the particles from collapsing in water, but also increases the internal porosity.

[0020] The aforementioned dual-network synergistic effect replaces the traditional binding function of starch, allowing the starch content in feed formulations to be reduced to 6%~9%, while ensuring that feed pellets have excellent expansibility (bulk weight 350~450g / L) and excellent water stability (weight loss rate ≤6% after soaking in still water at 25℃ for 4 hours), solving the common industry problem of low starch formulations being difficult to form and easy to disperse.

[0021] (2) The "stepwise emulsification + vacuum negative pressure spraying" process improves the oil loading and the retention rate of heat-sensitive components. To address the problems of screw slippage during extrusion of high-fat, low-starch systems and the deactivation of heat-sensitive additives at high temperatures, this invention employs a graded addition process: (i) During the conditioning stage, a portion of the oil that has undergone microemulsification is added in advance. By utilizing the surface activity of lecithin, the oil is evenly dispersed in the protein network, which avoids the "slippage" phenomenon caused by the oil forming a lubricating layer in the screw and ensures smooth puffing.

[0022] (ii) By utilizing the porous structure inside the puffed granules, the remaining emulsified oils and heat-sensitive nutritional additives (vitamins, enzymes, probiotics, etc.) are forcibly drawn into the depths of the granules under vacuum negative pressure, rather than remaining only on the surface.

[0023] This process not only avoids the deactivation of heat-sensitive components during high-temperature puffing and drying (significantly improving the retention rate of active ingredients), but also isolates oxygen, preventing the oxidation and rancidity of oils, thus greatly improving the nutritional value and shelf life of feed.

[0024] (3) The segmented drying process of "high-temperature rapid setting combined with low-temperature gradient dehumidification" eliminates the "hard core" phenomenon of particles and ensures uniform moisture content. To address the problem that traditional single-temperature drying easily leads to premature hardening of the particle surface and hinders internal moisture migration, thus forming a "hard core," this invention adopts a segmented temperature-controlled drying strategy: The first stage uses a relatively high temperature for rapid drying, which quickly solidifies and shapes the particle surface. The second stage uses a relatively low temperature for slow drying, establishing a moisture gradient from the inside out to guide the internal moisture to diffuse and drain out gradually.

[0025] This process effectively balances the difference in the rate of surface shaping and internal dehumidification, avoids the obstruction of internal moisture escape by surface hardening shrinkage, significantly reduces the proportion of "hard core" in the finished particles, ensures that the overall moisture content is uniformly reduced to below 10%, and improves the product's storage resistance. Attached Figure Description

[0026] Figure 1 The graph shows the total oil content data of Examples 1-3 and Comparative Examples 1-3 of the present invention; Figure 2 The graph shows the starch content and corresponding swelling data of Examples 1-3 and Comparative Examples 1-3 of the present invention; Figure 3 The graph shows the starch content and corresponding bulk density data of Examples 1-3 and Comparative Examples 1-3 of the present invention; Figure 4The starch content and corresponding water stability of Examples 1-3 and Comparative Examples 1-3 of the present invention; Figure 5 The graphs show the starch gelatinization degree data of Examples 1-3 and Comparative Examples 1-3 of this invention; Figure 6 The graphs show the vitamin C retention rate and lipid oxidation value of Examples 1-3 and Comparative Examples 1-3 of the present invention. Detailed Implementation

[0027] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0029] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0030] This invention provides a low-starch, high-expansion carnivorous fish feed and its preparation method. By constructing a "protein-fiber" dual network structure to replace the binding and expansion functions of traditional starch, and by combining stepwise emulsification, vacuum penetration and segmented drying processes, the problems of difficult pellet formation, poor water stability and low nutrient retention in low-starch formulations are solved.

[0031] The low-starch, high-expansion carnivorous fish feed disclosed in this invention comprises the following components by weight: 45-60 parts of protein source, 15-25 parts of oil source, 6-9 parts of starch source, 3-6 parts of functional fiber source, and 1-3 parts of additive premix.

[0032] The protein source consists of: enzymatically hydrolyzed fish meal (30-35 parts, small peptide content ≥15%), plant protein source (12-18 parts, selected from at least one of pea / soy protein isolate or protein concentrate), and animal by-product protein (8-12 parts, selected from at least one of chicken meal / meat and bone meal, collagen content ≥20%).

[0033] Small peptides in enzymatically hydrolyzed fishmeal undergo Maillard reactions and protein cross-linking under high temperature and high shear during extrusion, forming a preliminary chemical cross-linked network. Collagen from animal by-products provides strong physical binding force after gelatinization upon heating. Plant protein serves as the skeletal support. These three components work synergistically to construct a high-strength granular skeleton even with a starch content of only 6-9%, ensuring a bulk density of 350-450 g / L and a weight loss of ≤6% after soaking in water for 4 hours.

[0034] The functional fiber source consists of: 2.5 to 5 parts of ultrafine pulverized dietary fiber (wheat bran or beet pulp with a particle size equivalent to a 60 to 80 mesh sieve) and chitin derivatives (0.5 to 1 part of modified chitosan or chitin).

[0035] The ultra-fine particle size of 60-80 mesh allows it to fill the gaps in the protein network evenly, acting as the sand and gravel in "reinforced concrete" and enhancing the density of the particles; the chitin derivative has unique cationic properties, which can form electrostatic complexes with negatively charged protein molecules, further strengthening the network structure and preventing the particles from collapsing rapidly in water.

[0036] The oil source is composed of fish oil (13-22 parts), lecithin (2-3 parts), and antioxidants (0.01-0.1 parts).

[0037] Shear emulsification at 60-70℃ ensures that the oil particle size is ≤10μm. These tiny oil droplets are more evenly dispersed in the material matrix, preventing screw slippage caused by excessive lubrication from large droplets during extrusion. Simultaneously, lecithin, as a natural emulsifier, improves the compatibility of the oil with the protein / starch interface.

[0038] The additive premix contains a non-starch binder (0.5 to 1 part, selected from one or more of sodium alginate and calcium lignosulfonate) to assist in particle strength at room temperature; a puffing accelerator (0.2 to 0.5 part, selected from one or more of sodium bicarbonate, calcium dihydrogen phosphate, or transglutaminase) to regulate the puffing ratio; and the balance of vitamins, minerals, and palatability enhancers.

[0039] This invention provides a method for preparing the above-mentioned low-starch, high-expansion carnivorous fish feed (including five steps: raw material pretreatment, oil emulsification, conditioning, extrusion puffing, drying, and spraying), as detailed below: S1. Raw material pretreatment: Weigh the protein source, starch source, functional fiber source and additive premix according to the above formula, pulverize to 60-80 mesh, mix evenly, and obtain mixed powder.

[0040] S2. Preparation of oil source: Weigh fish oil, lecithin and antioxidant according to the above formula, mix the above components at 60~70℃ and shear emulsify and stir until the oil particle size in the system is ≤10μm, and obtain emulsified mixed oil.

[0041] S3. The mixed powder obtained in step S1 is fed into a biaxial differential speed conditioner, and saturated steam and a first portion of emulsified mixed oil accounting for 40% to 60% of the total weight of the emulsified mixed oil in step S2 are added. The mixture is then conditioned at 90 to 95°C to obtain the conditioned material. The amount of saturated steam added is 4% to 8% of the weight of the mixed powder. Adding a portion of grease at this point (the first part) utilizes the lubricating properties of grease to reduce energy consumption, while also preventing the material from becoming too wet and sticking to the walls due to adding all the grease. The conditioning temperature of 90~95℃ ensures that the material entering the machine has reached the critical point of protein denaturation, shortening the maturation time in the extruder.

[0042] S4. Extrusion Extrusion: The conditioned material is fed into a twin-screw extruder; Equipment configuration: A twin-screw extruder with a length-to-diameter ratio (L / D) of 2.5:1~2.8:1 and a compression ratio of 3.5:1~4:1 is adopted, with reverse screw elements and toothed shear discs installed in the melting and metering sections; Process parameters: Spindle speed 450~550 rpm, barrel temperature gradient distribution (feed section 60~70℃ → compression section 90~110℃ → melting section 125~135℃ → die head 115~120℃); die head pressure maintained at 35~45 Bar; moisture content of the discharged material controlled at 18~20%.

[0043] S5. Drying and spraying: The expanded granules are dried in sections and then vacuum sprayed; the details are as follows.

[0044] Segmented drying: First stage: rapid drying at 110~115℃, which quickly reduces the surface moisture of the particles to ≤12%, forming a hard shell to fix the shape and prevent particle deformation; Second stage: slow drying at 85~90℃, which utilizes the difference in internal and external moisture gradient to slowly remove internal moisture to ≤10% overall; This process effectively eliminates the "dry outside and wet inside" hard core phenomenon and ensures consistent quality inside and outside the particles.

[0045] Vacuum spraying process parameters: vacuum degree -0.08MPa to -0.09MPa; the spraying liquid is composed of a second part of emulsified mixed oil and a heat-sensitive nutrient additive; wherein, the second part of emulsified mixed oil is the remaining amount after deducting the first part of emulsified mixed oil used in step S3 from the total weight of the emulsified mixed oil obtained in step S2.

[0046] This step utilizes negative pressure to force the oil into the microporous structure inside the pellet, rather than adhering it to the surface. This not only significantly increases the oil content of the feed but also does not affect the appearance and hardness of the pellet. More importantly, the heat-sensitive additive bypasses the high-temperature extrusion and drying processes, directly entering the pellet and being protected by the oil, significantly improving retention rate and antioxidant stability.

[0047] This invention enables the preparation of feed pellets with low bulk density (350-450 g / L), high water stability (4-hour weight loss ≤6%), and high gelatinization (≥90%) under conditions of starch content (6-9 parts). The core of this invention lies in constructing a dual network structure combining a "protein-fiber physical framework" and "Maillard reaction chemical cross-linking," replacing the traditional feed's reliance on the simple starch gelatinization binding mechanism. The specific principle is explained below: This invention involves a Maillard reaction between small peptides / proteins (derived from enzymatically hydrolyzed fish meal and chicken meal) and a small amount of reducing sugars (derived from starch hydrolysis or naturally occurring in the raw materials) in a high-temperature extrusion process (125~135℃). The resulting intermediates and polymers can form covalent cross-links between protein molecules. This "protein-sugar" cross-linking network acts like glue, tightly binding loose fibers and protein particles together, thus achieving high water stability even under low starch conditions (weight loss ≤6% after 4 hours of soaking).

[0048] Excessive reaction can lead to lysine degradation and reduced nutritional value. This invention controls the extrusion puffing process in step S4, limiting the melting zone temperature to 125-135°C. Under these conditions, the free amino groups (-NH2) of small peptides in the protein source (enzymatically hydrolyzed fish meal) undergo a specific condensation reaction (i.e., Maillard reaction) with the active carbonyl groups (>C=O) of reducing sugars (such as glucose, fructose, etc.), forming a stable covalent cross-linked network. This avoids severe charring caused by high temperatures (>140°C) or prolonged heating, thereby minimizing lysine loss and ensuring the biological value of the protein.

[0049] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments: Enzymatically hydrolyzed fish meal: small peptide content ≥15%, purchased from a well-known biotechnology company; Plant protein source: Pea protein isolate (protein content ≥85%); Animal by-product protein: chicken meal (collagen content ≥20%). Ultra-fine pulverized dietary fiber: Ultra-fine pulverized wheat bran, with a particle size passing through a 60-80 mesh sieve.

[0050] Chitosan derivatives: Modified chitosan (degree of deacetylation ≥ 90%); Mixed oils: Fish oil, lecithin, and antioxidants (ethoxyquinoline) are mixed in a certain proportion.

[0051] Example 1 The low-starch, high-expansion carnivorous fish feed in this embodiment has the following formula by weight: Protein sources (55 portions in total): 30 portions of enzymatically hydrolyzed fish meal (small peptide content ≥15%), 15 portions of pea protein isolate, and 10 portions of chicken meal (collagen content ≥20%). Oil sources (total 20 parts): 17 parts fish oil, 2.95 parts lecithin, 0.05 parts antioxidant; Starch source: 7 parts corn starch; Functional fiber source (3.5 parts in total): 3 parts ultrafine pulverized wheat bran (particle size passed through 60-80 mesh sieve), 0.5 parts modified chitosan; Additive premix (2 parts total): 0.7 parts sodium alginate, 0.3 parts sodium bicarbonate, and the remainder of vitamins, minerals, and palatability enhancers.

[0052] The specific steps for preparing the above-mentioned low-starch, high-expansion carnivorous fish feed are as follows: S1. Raw material pretreatment: Crush all dry powder raw materials except for oil sources, pass them through a 60-80 mesh sieve, mix them evenly, and obtain mixed powder.

[0053] S2. Preparation of oil source: Fish oil, lecithin and antioxidant are sheared and emulsified at 65°C until the oil particle size is ≤10μm to obtain emulsified mixed oil.

[0054] S3. Conditioning: The mixed powder is fed into a dual-shaft differential speed conditioner, saturated steam (6% of the weight of the mixed powder) is introduced, and 50% (i.e., 10 parts) of the total amount of the above emulsified mixed oil is added. The mixture is then conditioned at 92°C for 2 minutes to obtain the conditioned material.

[0055] S4. Extrusion Extrusion: The conditioned material is fed into a twin-screw extruder (L / D=2.6:1, compression ratio 3.8:1); and the melting and metering sections of the screw are equipped with reverse thread elements and toothed shear discs; process parameters: speed 500 rpm; temperature gradient: feed section 65℃ → compression section 100℃ → melting section 130℃ → die head 118℃; die head pressure 40 Bar; outlet moisture 19%.

[0056] S5. Drying and Spraying: The expanded pellets are dried in stages. Stage 1 drying: rapid drying at 112℃ until the surface moisture content is ≤12%. Stage 2 drying: slow drying at 88℃ until the overall moisture content is ≤10%. Then, vacuum spraying is performed. Vacuum spraying is carried out at a vacuum degree of -0.085MPa to spray the remaining 50% emulsified mixed oil (containing heat-sensitive vitamins) into the pellets, so that the oil penetrates into the pellets to obtain the finished feed.

[0057] Example 2 The low-starch, high-expansion carnivorous fish feed in this embodiment has the following formula by weight: Protein sources (45 portions in total): 25 portions of enzymatically hydrolyzed fish meal (small peptide content ≥15%), 12 portions of pea protein isolate, and 8 portions of chicken meal (collagen content ≥20%). Oil source (15 parts total): 12.5 parts fish oil, 2.45 parts lecithin, 0.05 parts antioxidant; Starch source: 6 parts corn starch; Functional fiber source (3 parts in total): 2.5 parts ultrafine pulverized wheat bran (particle size passed through 60-80 mesh sieve), 0.5 parts modified chitosan; Additive premix (1 part total): 0.5 parts sodium alginate, 0.2 parts calcium dihydrogen phosphate, and the remainder of vitamins, minerals, and palatability enhancers.

[0058] The specific steps for preparing the above-mentioned low-starch, high-expansion carnivorous fish feed are as follows: S1. Raw material pretreatment: Crush all dry powder raw materials except for oil sources, pass them through a 60-80 mesh sieve, mix them evenly, and obtain mixed powder.

[0059] S2. Preparation of oil source: Fish oil, lecithin and antioxidant are sheared and emulsified at 60°C until the oil particle size is ≤10μm to obtain emulsified mixed oil.

[0060] S3. Conditioning: The mixed powder is fed into a dual-shaft differential speed conditioner, saturated steam (accounting for 4% of the weight of the mixed powder) is introduced, and 40% (i.e. 6 parts) of the total amount of the above emulsified mixed oil is added. Conditioning is carried out at 90°C for 2 minutes to obtain the conditioned material.

[0061] S4. Extrusion Extrusion: The conditioned material is fed into a twin-screw extruder (L / D=2.5:1, compression ratio 3.5:1); and the melting and metering sections of the screw are equipped with reverse thread elements and toothed shear discs; process parameters: speed 450 rpm; temperature gradient: feed section 60℃ → compression section 90℃ → melting section 125℃ → die head 115℃; die head pressure 35 Bar; outlet moisture 18%.

[0062] S5. Drying and Spraying: The expanded pellets are dried in stages. Stage 1 drying: rapid drying at 110℃ until the surface moisture content is ≤12%. Stage 2 drying: slow drying at 85℃ until the overall moisture content is ≤10%. Then, vacuum spraying is performed. Vacuum spraying is carried out at a vacuum degree of -0.08MPa to spray the remaining 60% emulsified mixed oil (containing heat-sensitive vitamins) into the pellets, so that the oil penetrates into the pellets to obtain the finished feed.

[0063] Example 3 The low-starch, high-expansion carnivorous fish feed in this embodiment has the following formula by weight: Protein sources (60 portions in total): 30 portions of enzymatically hydrolyzed fish meal (small peptide content ≥15%), 18 portions of pea protein isolate, and 12 portions of chicken meal (collagen content ≥20%). Oil sources (25 parts total): 21.9 parts fish oil, 3 parts lecithin, 0.1 parts antioxidant; Starch source: 9 parts tapioca starch; Functional fiber source (6 parts in total): 5 parts ultrafine pulverized wheat bran (particle size passed through 60-80 mesh sieve), 1 part modified chitosan; Additive premix (3 parts total): 1 part sodium alginate, 0.5 parts transglutaminase, and the remainder of vitamins, minerals, and palatability enhancers.

[0064] The specific steps for preparing the above-mentioned low-starch, high-expansion carnivorous fish feed are as follows: S1. Raw material pretreatment: Crush all dry powder raw materials except for oil sources, pass them through a 60-80 mesh sieve, mix them evenly, and obtain mixed powder.

[0065] S2. Preparation of oil source: Fish oil, lecithin and antioxidant are sheared and emulsified at 70°C until the oil particle size is ≤10μm to obtain emulsified mixed oil.

[0066] S3. Conditioning: The mixed powder is fed into a dual-shaft differential speed conditioner, saturated steam (8% of the weight of the mixed powder) is introduced, and 60% (i.e., 15 parts) of the total amount of the above emulsified mixed oil is added. The mixture is then conditioned at 95°C for 150 seconds to obtain the conditioned material.

[0067] S4. Extrusion Extrusion: The conditioned material is fed into a twin-screw extruder (L / D=2.8:1, compression ratio 4:1); and the melting section and metering section of the screw are equipped with reverse thread elements and toothed shear discs; process parameters: speed 550 rpm; temperature gradient: feed section 70℃ → compression section 110℃ → melting section 135℃ → die head 120℃; die head pressure 45 Bar; outlet moisture 20%.

[0068] S5. Drying and Spraying: The expanded pellets are dried in stages. Stage 1 drying: rapid drying at 115℃ until the surface moisture content is ≤12%. Stage 2 drying: slow drying at 90℃ until the overall moisture content is ≤10%. Then, vacuum spraying is performed. Vacuum spraying is carried out at a vacuum degree of -0.09MPa to spray the remaining 40% emulsified mixed oil (containing heat-sensitive vitamins) into the pellets, so that the oil penetrates into the pellets to obtain the finished feed.

[0069] Comparative Example 1 This comparative example aims to verify the necessity of enzymatically hydrolyzed fish meal (rich in small peptides) in the Maillard reaction and the construction of protein cross-linking networks. Compared with Example 1, this comparative example does not use enzymatically hydrolyzed fish meal, but replaces it with an equal weight of ordinary steamed fish meal (which, upon testing, had a small peptide content of <5% and a significantly lower free amino acid content than enzymatically hydrolyzed fish meal); the types and amounts of the remaining components (pea protein, chicken meal, starch, fiber, oil, and additives) are completely consistent with those in Example 1; and the preparation process is exactly the same; as detailed below.

[0070] The formula for this comparative carnivorous fish feed, by weight, is as follows: Protein sources (55 portions in total): 30 portions of ordinary steamed fish meal (tested to contain <5% small peptides), 15 portions of pea protein isolate, and 10 portions of chicken meal; Oil sources (total 20 parts): 17 parts fish oil, 2.95 parts lecithin, 0.05 parts antioxidant; Starch source: 7 parts corn starch; Functional fiber source (3.5 parts in total): 3 parts ultrafine pulverized wheat bran, 0.5 parts modified chitosan; Additive premix (2 parts total): 0.7 parts sodium alginate, 0.3 parts sodium bicarbonate, and the remainder of vitamins, minerals, and palatability enhancers.

[0071] The specific steps for preparing the above-mentioned low-starch, high-expansion carnivorous fish feed are as follows: S1. Raw material pretreatment: Crush all dry powder raw materials except for oil sources, pass them through a 60-80 mesh sieve, mix them evenly, and obtain mixed powder.

[0072] S2. Preparation of oil source: Fish oil, lecithin and antioxidant are sheared and emulsified at 65°C until the oil particle size is ≤10μm to obtain emulsified mixed oil.

[0073] S3. Conditioning: The mixed powder is fed into a dual-shaft differential speed conditioner, saturated steam (6% of the weight of the mixed powder) is introduced, and 50% (i.e., 10 parts) of the total amount of the above emulsified mixed oil is added. The mixture is then conditioned at 92°C for 2 minutes to obtain the conditioned material.

[0074] S4. Extrusion Extrusion: The conditioned material is fed into a twin-screw extruder (L / D=2.6:1, compression ratio 3.8:1); and the melting and metering sections of the screw are equipped with reverse thread elements and toothed shear discs; process parameters: speed 500 rpm; temperature gradient: feed section 65℃ → compression section 100℃ → melting section 130℃ → die head 118℃; die head pressure 40 Bar; outlet moisture 19%.

[0075] S5. Drying and Spraying: The expanded pellets are dried in stages. Stage 1 drying: rapid drying at 112℃ until the surface moisture content is ≤12%. Stage 2 drying: slow drying at 88℃ until the overall moisture content is ≤10%. Then, vacuum spraying is performed. Vacuum spraying is carried out at a vacuum degree of -0.085MPa to spray the remaining 50% emulsified mixed oil (containing heat-sensitive vitamins) into the pellets, so that the oil penetrates into the pellets to obtain the finished feed.

[0076] Comparative Example 2 This comparative example aims to verify the effects of the "stepwise emulsification + vacuum spraying" process on high oil loading, nutrient protection, and particle stability. The raw material formulation is completely consistent with that of Example 1, but the preparation process has been adjusted: S3. Conditioning treatment: 100% of the emulsified mixed oil (i.e., 20 parts) is added during the conditioning stage and mixed into the powder along with saturated steam; S5. The vacuum spraying step is omitted, and the expanded particles are directly dried in stages (stage 112°C, stage 2 88°C) until the moisture content is ≤10%. Details are as follows.

[0077] The carnivorous fish feed used in this comparative example is formulated as follows, by weight: Protein sources (55 portions in total): 30 portions of enzymatically hydrolyzed fish meal (small peptide content ≥15%), 15 portions of pea protein isolate, and 10 portions of chicken meal (collagen content ≥20%). Oil sources (total 20 parts): 17 parts fish oil, 2.95 parts lecithin, 0.05 parts antioxidant; Starch source: 7 parts corn starch; Functional fiber source (3.5 parts in total): 3 parts ultrafine pulverized wheat bran (particle size passed through 60-80 mesh sieve), 0.5 parts modified chitosan; Additive premix (2 parts total): 0.7 parts sodium alginate, 0.3 parts sodium bicarbonate, and the remainder of vitamins, minerals, and palatability enhancers.

[0078] The specific steps for preparing the above-mentioned low-starch, high-expansion carnivorous fish feed are as follows: S1. Raw material pretreatment: Crush all dry powder raw materials except for oil sources, pass them through a 60-80 mesh sieve, mix them evenly, and obtain mixed powder.

[0079] S2. Preparation of oil source: Fish oil, lecithin and antioxidant are sheared and emulsified at 65°C until the oil particle size is ≤10μm to obtain emulsified mixed oil.

[0080] S3. Conditioning: The mixed powder is fed into a twin-shaft differential speed conditioner, saturated steam (6% of the weight of the mixed powder) is introduced, and all the above-mentioned emulsified mixed oils (i.e., 20 parts) are added. The mixture is then conditioned at 92°C for 2 minutes to obtain the conditioned material.

[0081] S4. Extrusion Extrusion: The conditioned material is fed into a twin-screw extruder (L / D=2.6:1, compression ratio 3.8:1); and the melting and metering sections of the screw are equipped with reverse thread elements and toothed shear discs; process parameters: speed 500 rpm; temperature gradient: feed section 65℃ → compression section 100℃ → melting section 130℃ → die head 118℃; die head pressure 40 Bar; outlet moisture 19%.

[0082] S5. Drying: The expanded pellets are dried in stages. Stage 1 drying: rapid drying at 112℃ until the surface moisture content is ≤12%. Stage 2 drying: slow drying at 88℃ until the overall moisture content is ≤10%, to obtain the finished feed.

[0083] Comparative Example 3 This comparative example represents a traditional method for preparing conventional carnivorous fish feed.

[0084] Raw material formula (by weight): Protein source (35 parts): 25 parts regular fish meal, 10 parts soybean meal; Starch source (25 parts): 25 parts corn starch (far higher than the 6-9 parts of this invention); Oil source (12 parts): 12 parts fish oil; Other: 3 parts mineral and vitamin premix, 2 parts binder (α-starch), 3 parts water.

[0085] Note: Contains no functional fiber sources (wheat bran, chitosan) and no enzymatically hydrolyzed fish meal.

[0086] The single-screw extrusion process is adopted, and the specific steps are as follows: (1) Mixing and conditioning: Mix all dry powder raw materials with oil and water, and condition with steam to 90°C.

[0087] (2) Extrusion puffing: The material enters a single-screw extruder and is shaped by the gelatinization and expansion force of the high starch content. The die temperature is 110℃, and there is no special shearing configuration design.

[0088] Drying: The single-layer dryer dries the product to a moisture content of ≤10% in one pass at 100℃.

[0089] Spraying: No vacuum spraying; if additional grease is required, simply spray the surface.

[0090] Test data and effect analysis: The physicochemical properties of the feed pellets obtained in Examples 1-3 and Comparative Examples 1-3 of this invention were tested. The testing methods for each property are as follows: (1) Starch content: The starch content was determined by enzymatic hydrolysis according to GB / T 20958-2007 "Determination of Starch Content in Feed".

[0091] (2) Bulk density: The bulk density was determined using an HGT-1000 bulk density meter, referring to the method for determining bulk density in the appendix of GB / T 6438-2007 "Determination of Crude Ash in Feed" (referring to NY / T 1102-2006 "Determination of Bulk Density in Compound Feed"). The results are expressed in g / L.

[0092] (3) Expansion degree: Twenty whole particles were randomly selected using vernier calipers, and their cross-sectional diameters were measured. The average value was calculated, and this average value was divided by the nominal diameter of the extrusion die to obtain the degree of expansion. The formula is: E=D particle / D die ; where D particle D is the average value. die This is the nominal diameter.

[0093] (4) Stability in water (4h weight loss rate): (i) Take about 10g of finished product granules with uniform particle size (accurate to 0.01g) and place them in distilled water at 25±1℃ for soaking.

[0094] (ii) Keep the water still during the soaking process and avoid human disturbance.

[0095] (iii) After 4 hours, carefully remove the particles, drain the surface moisture for 30 seconds, and dry them in an oven at 105℃ until constant weight.

[0096] Calculate the weight loss rate: Weight loss rate (%) = [(W0 - W1) / W0] × 100%; where W0 is the initial dry weight and W1 is the weight after drying after soaking. Each group of samples was measured in triplicate, and the average value was taken.

[0097] (5) Starch gelatinization degree: The glucose oxidase-peroxidase method (GOPOD method) was used for determination.

[0098] Principle: Amylase is used to hydrolyze gelatinized starch into glucose, and the gelatinized starch content is estimated by measuring the glucose content; another sample is taken and completely hydrolyzed with perchloric acid to determine the total starch content.

[0099] Calculation formula: Degree of gelatinization (%) = (gelatinized starch content / total starch content) × 100%.

[0100] (6) Oil content (crude fat) of particles: According to GB / T 6433-2006 "Determination of Crude Fat in Feed", Soxhlet extraction (ether extraction) was used, and the extraction time was not less than 6 hours.

[0101] (7) Vitamin C retention rate: The determination was performed using high performance liquid chromatography (HPLC).

[0102] Chromatographic conditions: C18 reversed-phase column; mobile phase: 0.05 mol / L potassium dihydrogen phosphate solution (pH adjusted to 3.0): methanol = 95:5; flow rate: 1.0 mL / min; detection wavelength: 254 nm.

[0103] Calculation method: Compare the vitamin C content in the finished product after extrusion and puffing with the mixed powder before conditioning (the theoretical addition amount is uniformly 200mg / kg), and calculate the retention percentage.

[0104] (8) Oxidation value of oils and fats (peroxide value, TBV): According to GB / T 5538-2005 "Determination of Peroxide Value of Animal and Vegetable Oils", the iodometric method was used for determination, and the results are expressed in milliequivalents per kilogram (meq / kg).

[0105] The performance comparison test results of the above embodiments and comparative examples are shown in Table 1 below, and their test graphs are shown in the figure below. Figures 1-6 As shown: Table 1

[0106] As can be seen from Table 1, this invention has significant progress, as detailed below: (1) Comparative Example 3 had a starch content as high as 25 parts, but its expansion was only 1.40 times, and its bulk density was as high as 565 g / L. The dense particle structure was not conducive to feeding by carnivorous fish. Comparative Example 1 (low starch but no small peptides) had an expansion as low as 1.35 times, indicating that it lacked protein cross-linking network support and the material could not form a stable bubble structure, resulting in expansion failure. In this invention (Examples 1-3), under the condition of starch content of 6.0-9.0 parts, a high expansion of 2.10-2.60 times was achieved by constructing a "protein-fiber" dual network and Maillard reaction cross-linking, and the bulk density was significantly reduced to 360-440 g / L. This shows that the present invention broke through the technical barrier of "low starch is difficult to expand" and achieved high expansion under low starch conditions.

[0107] (2) Comparing Example 1 and Comparative Example 1, it can be seen that both have the same starch content and the same process parameters; the only difference is that Comparative Example 1 uses ordinary fish meal. As can be seen from the table, the expansion degree of Comparative Example 1 is as low as 1.35, the weight loss rate in water is as high as 18.6%, and the bulk density is high (485g / L). This is because Comparative Example 1 uses ordinary fish meal (low content of small peptides), which cannot undergo sufficient Maillard reaction under high extrusion temperature, resulting in the lack of chemical cross-linking inside the particles. However, Example 1 utilizes the high content of small peptides in enzymatically hydrolyzed fish meal, which undergo Maillard reaction with reducing sugars during extrusion and combine with the physical bonding of collagen to construct a high-strength three-dimensional network. This makes its weight loss rate in water as low as 3.8% under low starch conditions, which is far better than traditional high starch feed (9.1%). This shows that the chemical cross-linking network formed by Maillard reaction is the core of maintaining the stability of low starch particles.

[0108] (3) Comparing Example 1 and Comparative Example 2, it can be seen that: Comparative Example 2 added all the oil during conditioning (without vacuum spraying). Although the expansion was acceptable (2.30), the surface was severely oil-seeped, causing the vitamin C retention rate to plummet to 62.5% (due to high-temperature oxidation damage), and the oil oxidation value soared to 5.1 (extremely prone to rancidity). In contrast, Example 1 used stepwise emulsification + vacuum spraying. Part of the oil was emulsified first for lubrication and extrusion, and the remaining oil was forcibly penetrated into the pores inside the particles under low-temperature vacuum conditions. Not only was more than 20% of the oil successfully loaded, but the oil was also locked inside the particles. The vitamin C retention rate was as high as 93.5%, the oil oxidation value was as low as 1.2 meq / kg, and the particle surface was dry. This shows that the stepwise addition and vacuum penetration process of the present invention effectively solves the common problems of oil seepage, nutrient loss and oxidative rancidity in the production of high-oil feed, and significantly improves the bioavailability and storage stability of the product.

[0109] In summary, this invention, through the synergistic effect of specific formulation design (enzymatically hydrolyzed fish meal + functional fiber) and process (stepwise emulsification + vacuum spraying + segmented drying), successfully solves the problems of difficult molding, poor stability, and nutrient loss in the production of low-starch, high-oil fish feed, with significant technical effects.

[0110] The present invention provides a detailed description of a low-starch, high-expansion carnivorous fish feed and its preparation method. Specific examples have been used to illustrate the principles and implementation methods of the invention. These examples are merely illustrative and are intended to aid in understanding the method and core concepts of the invention. It should be noted that those skilled in the art can make various improvements and modifications to the invention without departing from its principles, and these improvements and modifications also fall within the scope of protection of the claims.

Claims

1. A low-starch, high-expansion carnivorous fish feed, characterized in that, Formulated by weight, it includes the following components: 45-60 portions of protein source; 15-25 parts of oil source; 6-9 parts starch source; 3-6 parts of functional fiber source; 1-3 parts of additive premix; The protein sources include enzymatically hydrolyzed fish meal, plant protein sources, and animal by-product proteins. The functional fiber sources include ultrafine pulverized dietary fiber and chitin derivatives; The resulting feed pellets have a bulk density of 350 g / L to 450 g / L, a weight loss rate of ≤6% after soaking in still water at 25℃ for 4 hours, and a starch gelatinization degree of ≥90%.

2. The low-starch, high-expansion carnivorous fish feed according to claim 1, characterized in that, The weight parts and characteristics of each component in the protein source are as follows: the enzymatically hydrolyzed fish meal is 25-30 parts, and the small peptide content of the enzymatically hydrolyzed fish meal is ≥15%; the plant protein source is selected from at least one of pea protein isolate, soy protein isolate, or soy protein concentrate, and is 12-18 parts; the animal by-product protein is selected from at least one of chicken meal or meat and bone meal, and is 8-12 parts, and the collagen content of the animal by-product protein is ≥20%.

3. The low-starch, high-expansion carnivorous fish feed according to claim 1, characterized in that, The weight parts and characteristics of each component in the functional fiber source are as follows: the ultrafine pulverized dietary fiber is ultrafine pulverized wheat bran or beet pulp with a particle size equivalent to a 60-80 mesh sieve, and is 2.5-5 parts; the chitin derivative is at least one of modified chitosan or chitin, and is 0.5-1 parts.

4. The low-starch, high-expansion carnivorous fish feed according to claim 1, characterized in that, The oil source is a mixed oil that has undergone emulsification treatment; the mixed oil consists of the following components in parts by weight: 13-22 parts fish oil, 2-3 parts lecithin, and 0.01-0.1 parts antioxidant; the emulsification treatment is to mix the above components at 60-70°C and perform shear emulsification until the oil particle size in the system is ≤10μm.

5. The low-starch, high-expansion carnivorous fish feed according to claim 1, characterized in that, The additive premix comprises the following components in parts by weight: 0.5 to 1 part of a non-starch binder, selected from one or more of sodium alginate and calcium lignosulfonate; 0.2 to 0.5 part of a puffing accelerator, selected from one or more of sodium bicarbonate, calcium dihydrogen phosphate, or transglutaminase; and the balance being vitamins, minerals, and palatability enhancers; wherein the sum of the parts by weight of the non-starch binder, puffing accelerator, vitamins, minerals, and palatability enhancers is 1 to 3 parts.

6. A method for preparing a low-starch, high-expansion carnivorous fish feed as described in any one of claims 1-5, characterized in that, Includes the following steps: S1. Raw material pretreatment: Weigh the protein source, starch source, functional fiber source and additive premix according to the formula, and grind them to 60-80 mesh, mix them evenly, and obtain the mixed powder. S2. Preparation of oil source: Weigh fish oil, lecithin and antioxidant according to the formula, mix the above components at 60~70℃ and shear emulsify and stir until the oil particle size in the system is ≤10μm, and obtain emulsified mixed oil. S3. The mixed powder obtained in step S1 is fed into a biaxial differential speed conditioner, and saturated steam and a first portion of emulsified mixed oil accounting for 40% to 60% of the total weight of the emulsified mixed oil in step S2 are added. The mixture is then conditioned at 90 to 95°C to obtain the conditioned material. The amount of saturated steam added is 4% to 8% of the weight of the mixed powder. S4. Extrusion puffing: The conditioned material is fed into a twin-screw extruder and extruded and puffed through a high-shear screw configuration; S5. Drying and spraying: The expanded pellets are dried in sections, followed by vacuum spraying to obtain the finished feed.

7. The preparation method according to claim 6, characterized in that, In step S4, the extrusion expansion is carried out in a twin-screw extruder. The screw configuration of the twin-screw extruder is configured such that the length-to-diameter ratio L / D is 2.5:1 to 2.8:1 and the compression ratio is 3.5:1 to 4:

1. Furthermore, the melting section and metering section of the screw are equipped with reverse thread elements and toothed shear discs, so that the die pressure during the extrusion process is maintained at 35 to 45 Bar.

8. The preparation method according to claim 6, characterized in that, In step S4, the process parameters for extrusion puffing are as follows: spindle speed is 450~550 rpm; the temperature distribution of the puffing machine cylinder is as follows: feeding section 60~70℃, compression section 90~110℃, melting section 125~135℃, die head temperature 115~120℃; and the moisture content of the discharged material is controlled at 18~20%.

9. The preparation method according to claim 6, characterized in that, In step S5, the segmented drying process is as follows: in the first stage, rapid drying is carried out at 110~115℃ until the surface moisture of the particles is ≤12% to complete the surface shaping; in the second stage, slow drying is carried out at 85~90℃ until the overall moisture of the particles is ≤10% to remove internal moisture.

10. The preparation method according to claim 6, characterized in that, In step S5, the conditions and material composition of the vacuum spraying treatment are as follows: the vacuum degree is -0.08 MPa to -0.09 MPa; the spraying liquid is composed of a second part of emulsified mixed oil and a heat-sensitive nutrient additive; wherein, the second part of emulsified mixed oil is the remaining amount after deducting the first part of emulsified mixed oil used in step S3 from the total weight of the emulsified mixed oil obtained in step S2.

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