Preparation method of pineapple peel residue dietary fiber powder

Abstract

The present invention discloses a pineapple peel residue dietary fiber powder preparation method which is characterized by comprising the following steps: raw material pretreatment: pineapple processing by-product peel residues are selected and washed, and are added with clear water for pulping; adding a NaOH solution, alpha-amylase and papain into the obtained slurry for enzymolysis; carrying out coarse filtration on the enzymolysis slurry by using a screen, and then carrying out plate-frame pressure filtration; putting the crude fibers into steam explosion equipment; adding alkali liquor into the steam-exploded material, cooling, and adjusting the pH value with acetic acid; performing circulation treatment on the slurry by using a colloid mill; further crushing the feed liquid through a high-pressure jet mill; homogenizing and emulsifying the feed liquid treated by the jet mill; concentrating the homogenized material liquid by using membrane concentration equipment; and drying by using a spray drying method, and cooling. The pineapple by-product peel residue is used as a natural dietary fiber source, the process is simple and feasible, the raw material loss rate is low, the product yield is high, the dietary fiber dissolution rate and the particle fineness are improved, and meanwhile, the raw materials can be completely utilized.

Description

Technical Field

[0001] The invention relates to the technical field of food processing, in particular to a method for preparing pineapple peel residue dietary fiber powder. Background Art

[0002] Pineapple (Ananascomosus (L.) Merr), also known as pineapple and yellow pear, is rich in nutrients such as dietary fiber, vitamins, protein and minerals. It is an important tropical fruit resource in my country, with an average annual output of more than 1.6 million tons. In addition to fresh fruit sales, pineapples are often processed into canned fruits, juices and fruit powders. During the processing, pineapple peel residue byproducts such as peel, pomace and core are produced, accounting for about 50% of the total fruit weight. The nutritional components of pineapple peel residue are basically the same as those of the flesh, but the current processing utilization rate is low, and a large amount of peel residue is discarded as waste, causing serious waste of resources and environmental pollution. Therefore, the development of pineapple peel residue comprehensive utilization technology is of great significance to extend the pineapple industry chain and realize the high-value utilization of pineapples.

[0003] Dietary fiber is a general term for a class of carbohydrate polymers found in plants, mainly including cellulose, hemicellulose, lignin and pectin. As the seventh essential nutrient for the human body, it plays a significant role in inhibiting the increase of blood sugar after meals and improving gastrointestinal function. According to the solubility in water, dietary fiber can be divided into soluble dietary fiber (SDF) and insoluble dietary fiber (IDF). The content of SDF can be used as one of the key indicators for evaluating the quality of dietary fiber. If the content of SDF is above 10%, its good processing characteristics, physiological activity and health care functions can be maximized.

[0004] However, IDF has limited functional properties due to its dense structure and poor water solubility. The dietary fiber content in pineapple peel residue is very high, accounting for 65-75% of the dry matter weight, and can be used as a natural source of dietary fiber. However, the SDF content is extremely low and cannot meet the requirements of dietary balance. Therefore, it is necessary to adopt appropriate modification treatment methods to increase the SDF content in pineapple peel residue dietary fiber, while improving its macromolecular structure to give it good swelling and water retention. Summary of the invention

[0005] The invention aims to provide a method for preparing pineapple peel residue dietary fiber powder, which uses pineapple byproduct peel residue as a natural dietary fiber source, has a simple and feasible process, a low raw material loss rate, a high product yield, ensures high production efficiency and continuity, improves the dietary fiber dissolution rate and particle fineness, and can achieve full utilization of the raw materials.

[0006] The above technical objectives of the present invention are achieved through the following technical solutions:

[0007] A method for preparing pineapple peel residue dietary fiber powder comprises the following steps:

[0008] Step 1, raw material pretreatment: the pineapple processing by-product peel residue is selected and cleaned, and then pulped after adding 6 to 10 times the mass of clean water to obtain pineapple peel residue slurry;

[0009] Step 2, enzymolysis: adding NaOH solution to the obtained slurry to adjust its pH value, then adding a certain mass fraction of α-amylase and controlling the temperature and stirring for a period of time to allow it to cool, then adding a certain mass fraction of papain and continuing to stir for enzymolysis, boiling to inactivate the enzyme, and then cooling to obtain an enzymolysis slurry;

[0010] Step 3, washing: the enzymatic slurry is coarsely filtered through a 100-150 mesh screen, the coarse filter residue is repeatedly washed and sieved with clean water for 3-4 times, and then subjected to plate and frame filter pressing, and the filter residue is collected to obtain crude fiber;

[0011] Step 4, steam explosion: placing the obtained crude fiber into a steam explosion device, setting the pressure to 0.8-1.6 MPa, and maintaining the pressure for 60-180 seconds;

[0012] Step 5, alkaline hydrolysis: add 12 to 15 times the mass ratio of alkaline solution to the material after steam explosion, react at a temperature of 35 to 45 ° C for 45 to 60 minutes, cool to room temperature and adjust the pH to neutral with acetic acid;

[0013] Step 6: colloid mill treatment: the obtained slurry is circulated and treated at 2000-3000 r / min for 7-14 min using a colloid mill;

[0014] Step 7: high-pressure jet mill treatment: the prepared liquid is further crushed by a high-pressure jet mill at 80-110 MPa to make the fiber particle size less than 40 μm;

[0015] Step 8: High-pressure homogenization: homogenize and emulsify the liquid treated by the jet mill at a pressure of 45-60 MPa for 3-4 times;

[0016] Step 9, membrane concentration: the homogenized liquid is concentrated using a membrane concentration device to a solid content of 22-28%;

[0017] Step 10, spray drying: drying the obtained concentrated solution by spray drying, collecting the dry powder, and cooling it to below 40° C. to obtain pineapple peel residue dietary fiber powder.

[0018] Further: in step 1, the peel residue includes by-products such as pineapple peel, core and pulp residue after juicing, and the stems, leaves and rotten and deteriorated raw materials are selected.

[0019] Further: In step 2, the pH value of the slurry is adjusted to 6 by adding NaOH solution.

[0020] Further: in step 2, the mass fraction of α-amylase is 1.5-2.5%, the stirring temperature is 55-65° C., the stirring time is 60-120 min, the mass fraction of papain is 0.15-0.25%, the stirring time is 25-35 min, and the enzyme inactivation boiling time is 5 min.

[0021] Further: in step 2, the cooling temperature after adding α-amylase and stirring is 45-55°C.

[0022] Further: in step three, the plate and frame filter pressing accuracy is 30-50 μm, the pressure is 0.5-0.7 Mpa, and the moisture content of the filter residue is 45-55%.

[0023] Further: in step five, the alkali solution is a NaOH solution and its concentration is 6-10%.

[0024] Further: in step nine, the membrane concentration is a two-stage membrane concentration, the first stage is an ultrafiltration membrane, and the second stage is a reverse osmosis membrane.

[0025] Further: in step ten, the air inlet temperature of the spray drying method is 180-200°C, the air outlet temperature is 70-95°C, and the spraying method is centrifugal spraying, pressure spraying or convection spraying.

[0026] In summary, the present invention has the following beneficial effects:

[0027] First, the process of the present invention is simple and feasible, and the raw material conversion rate is high. The pineapple processing by-product peel residue is used as the raw material, and steam explosion combined with high-pressure jet mill and high-pressure homogenization modification technology are used to solve the problem that the raw material fiber structure is rough and difficult to degrade and utilize, so as to improve the modification efficiency of crude fiber and increase the proportion of soluble dietary fiber in the product, thereby realizing the complete utilization of by-products and avoiding the generation of secondary waste;

[0028] Second, the present invention pre-treats the raw materials by wet pulping and concentrates the liquid by membrane concentration, thereby avoiding flavor changes and nutrient loss caused by thermal processing, greatly shortening the production cycle, simplifying the process flow, reducing energy consumption, and ensuring the high efficiency and continuity of production, which is convenient for industrial production;

[0029] Third, the present invention adopts physical modification and alkaline hydrolysis methods to treat fiber materials, so that dietary fiber can be fully utilized, eliminating the steps of alcohol precipitation and purification, which not only simplifies the process and improves the product yield, but also avoids the use of organic solvents, significantly reducing production costs and safety risks. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a flow chart of the operation steps of the present invention;

[0031] Figure 2 This is a comparison table of the content of SDF in the pineapple peel residue dietary fiber powder in the experimental group 1 of the present invention;

[0032] Figure 3 This is a comparison table of the effects of the inlet air temperature on the product yield and water content in the spray drying in Experimental Group 2 of the present invention;

[0033] Figure 4 This is a table for determining the water holding capacity, oil holding capacity, swelling capacity and cation exchange capacity of the pineapple peel residue dietary fiber powder in the experimental group 3 of the present invention. DETAILED DESCRIPTION

[0034] The present invention is further described in detail below in conjunction with the accompanying drawings.

[0035] In the description of the present invention, it is necessary to understand that the directions or positional relationships indicated by terms such as “upper”, “lower”, “left”, “right”, “front”, “back”, “inside” and “outside” are based on the directions or positional relationships shown in the accompanying drawings and are only for the convenience of describing the present invention and simplifying the description. They do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore should not be understood as a limitation on the present invention.

[0036] Example 1, reference Figure 1 , a method for preparing pineapple peel residue dietary fiber powder, comprising the following steps:

[0037] Step 1, raw material pretreatment: pineapple peel, core and pulp after juicing and other by-products such as pomace, i.e., removing stems, leaves and rotten and deteriorated raw material peel residues, after sorting and cleaning, adding 8 times the mass of clean water and beating, to obtain pineapple peel residue slurry;

[0038] Step 2, enzymolysis: add NaOH solution to the obtained slurry and adjust the pH value of the slurry to 6, then add a certain weight percentage of 2% α-amylase, stir at a temperature of 60°C for 90 minutes, and let it cool to 50°C, then add 0.2% weight percentage of papain and continue to stir for 30 minutes, then boil it for 5 minutes to kill the enzyme, and let it cool to room temperature to obtain an enzymolysis slurry;

[0039] Step 3, washing: the enzymatic slurry is coarsely filtered with a 130-mesh screen, the coarse filter residue is repeatedly washed and sieved with clean water for 4 times, and then filtered using a plate and frame filter with a precision of 40 μm and a pressure of 0.6 MPa to collect the filter residue crude fiber with a moisture content of 50%;

[0040] Step 4: Steam explosion: the obtained crude fiber is placed in a steam explosion device, and the pressure is set to 1.2 MPa, and the pressure is maintained for 120 seconds;

[0041] Step 5, alkaline hydrolysis: add 16 times the mass ratio of 8% NaOH solution to the material after steam explosion, react at 40°C for 70 minutes, cool to room temperature and adjust the pH to neutral with acetic acid;

[0042] Step 6: colloid mill treatment: the obtained slurry is circulated and treated at 2500r / min for 10min using a colloid mill;

[0043] Step 7: high-pressure jet mill treatment: the prepared liquid feed is further crushed by a high-pressure jet mill at 100 MPa to make the fiber particle size less than 40 μm;

[0044] Step 8: High-pressure homogenization: homogenize and emulsify the liquid treated by the jet mill at a pressure of 45 MPa for 4 times;

[0045] Step 9, membrane concentration: The homogenized liquid is concentrated using a two-stage membrane concentration device to a solid content of 26%;

[0046] Step 10, spray drying: drying the obtained concentrated solution by centrifugal spray drying method, and controlling the inlet air temperature to 180° C. and the outlet air temperature to 75° C., collecting the dried powder, and cooling it to below 40° C. to obtain pineapple peel residue dietary fiber powder.

[0047] Example 2, reference Figure 1 , a method for preparing pineapple peel residue dietary fiber powder, comprising the following steps:

[0048] Step 1, raw material pretreatment: the pineapple peel, core and pulp after juicing the fruit residue and other by-products, that is, the stems, leaves and rotten raw material peel residues are selected and cleaned, and 6 times the mass of clean water is added and pulped to obtain pineapple peel residue slurry;

[0049] Step 2, enzymolysis: add NaOH solution to the obtained slurry and adjust the pH value of the slurry to 6, then add 1.5% by weight of α-amylase, stir at 65°C for 120 minutes, and let it cool to 55°C, then add 0.15% by weight of papain and continue stirring for 35 minutes, then boil it for 5 minutes to inactivate the enzyme, and let it cool to room temperature to obtain an enzymolysis slurry;

[0050] Step 3, washing: the enzymatic slurry is coarsely filtered with a 100-mesh sieve, the coarse filter residue is repeatedly washed and sieved with clean water for 3 times, and then filtered using a plate and frame filter with a precision of 50 μm and a pressure of 0.5 MPa to collect the filter residue crude fiber with a moisture content of 55%;

[0051] Step 4, steam explosion: the obtained crude fiber is placed in a steam explosion device, and the pressure is set to 1.0 MPa, and the pressure maintenance time is 120 s;

[0052] Step 5, alkaline hydrolysis: add 12 times the mass ratio of 10% NaOH solution to the material after steam explosion, react at 35°C for 60 minutes, cool to room temperature and adjust the pH to neutral with acetic acid;

[0053] Step 6: colloid mill treatment: the obtained slurry is circulated in a colloid mill at 2000 r / min for 14 min;

[0054] Step 7: high-pressure jet mill treatment: the prepared liquid is further crushed by a high-pressure jet mill at 110 MPa to make the fiber particle size less than 40 μm;

[0055] Step 8: High-pressure homogenization: homogenize and emulsify the liquid treated by the jet mill at a pressure of 50 MPa for 3 times;

[0056] Step 9, membrane concentration: The homogenized liquid is concentrated using a bipolar membrane concentration device to a solid content of 22%;

[0057] Step 10, spray drying: drying the obtained concentrated solution by centrifugal spray drying method, and controlling the air inlet temperature to 200° C. and the air outlet temperature to 90° C., collecting the dried powder, and cooling it to below 40° C. to obtain pineapple peel residue dietary fiber powder.

[0058] Example 3, reference Figure 1 , a method for preparing pineapple peel residue dietary fiber powder, comprising the following steps:

[0059] Step 1, raw material pretreatment: pineapple peel, core and pulp after juicing and other by-products such as pomace, i.e., removing stems, leaves and rotten and deteriorated raw material peel residues, after sorting and washing, adding 10 times the mass of clean water and beating, to obtain pineapple peel residue slurry;

[0060] Step 2, enzymolysis: add NaOH solution to the obtained slurry and adjust the pH value of the slurry to 6, then add 2.5% by weight of α-amylase, stir at 55°C for 60 minutes, and let it cool to 45°C, then add 0.25% by weight of papain and continue stirring for 25 minutes, then boil it for 5 minutes to inactivate the enzyme, and let it cool to room temperature to obtain an enzymolysis slurry;

[0061] Step 3, washing: the enzymatic slurry is coarsely filtered with a 150-mesh screen, the coarse filter residue is repeatedly washed and sieved with clean water for 3 times, and then filtered using a plate and frame filter with a precision of 30 μm and a pressure of 0.7 MPa to collect the filter residue crude fiber with a moisture content of 45%;

[0062] Step 4: Steam explosion: the obtained crude fiber is placed in a steam explosion device, and the pressure is set to 0.8 MPa and the pressure maintenance time is 90 seconds;

[0063] Step 5, alkaline hydrolysis: add 15 times the mass ratio of 6% NaOH solution to the material after steam explosion, react at 45°C for 45 minutes, cool to room temperature and adjust the pH to neutral with acetic acid;

[0064] Step 6: colloid mill treatment: the obtained slurry is circulated and treated in a colloid mill at 3000 r / min for 7 min;

[0065] Step 7: high-pressure jet mill treatment: the prepared liquid is further crushed by a high-pressure jet mill at 80 MPa to make the fiber particle size less than 40 μm;

[0066] Step 8: High-pressure homogenization: homogenize and emulsify the liquid treated by the jet mill at a pressure of 6 MPa for 4 times;

[0067] Step 9, membrane concentration: The homogenized liquid is concentrated using a bipolar membrane concentration device to a solid content of 28%;

[0068] Step 10, spray drying: drying the obtained concentrated solution by centrifugal spray drying, and controlling the air inlet temperature to 185° C. and the air outlet temperature to 80° C., collecting the dried powder, and cooling it to below 40° C. to obtain pineapple peel residue dietary fiber powder.

[0069] Set up a control group

[0070] Control group 1

[0071] The preparation method is basically the same as that of Example 2, except that in step 4, the steam explosion pressure is 1.6 MPa.

[0072] Control group 2

[0073] The preparation method is basically the same as that of Example 2, except that in step 4, the steam explosion pressure is 0.8 MPa.

[0074] Control group 3

[0075] The preparation method is basically the same as that in Example 2, except that in step 4, the steam explosion pressure maintenance time is 60 seconds.

[0076] Control group 4

[0077] The preparation method is basically the same as that in Example 2, except that in step 4, the steam explosion pressure maintenance time is 180 s.

[0078] Control group 5

[0079] The preparation method is basically the same as that in Example 1, except that in step 5, the alkaline hydrolysis time is 40 minutes.

[0080] Control group 6

[0081] The preparation method is basically the same as that in Example 1, except that in step 5, the alkaline hydrolysis time is 80 minutes.

[0082] Control group 7

[0083] The preparation method is basically the same as that of Example 3, except that in step 10, the outlet air temperature of the spray drying is 70°C.

[0084] Control group 8

[0085] The preparation method is basically the same as that of Example 3, except that in step 10, the outlet air temperature of the spray drying is 90°C.

[0086] Control group 9

[0087] The pretreatment, enzymolysis and washing of the raw materials are basically the same as steps 1 to 3 in Example 1. The washed materials are placed in a 60° C. oven and dried to a moisture content of less than 6%, and then crushed and passed through a 60-mesh sieve to obtain pineapple peel residue dietary fiber powder.

[0088] Setting up the experimental group

[0089] Experimental Group 1 ( Figure 2 )

[0090] The effects of steam explosion pressure, pressure maintenance time and alkaline hydrolysis time on the SDF content of the product were investigated respectively, and the SDF content in the pineapple peel residue dietary fiber powder prepared in Examples 1-2 and Control Groups 1-6 and 9 was determined by enzyme-gravimetric method (Table 1).

[0091] Table 1 Product SDF content

[0092] sample Steam explosion pressure / MPa Pressure maintenance time / s Alkaline hydrolysis time / min SDF / % Example 1 1.2 120 70 28.6 Example 2 1.0 150 60 26.4 Comparative Example 1 0.8 120 70 23.7 Comparative Example 2 1.6 120 70 27.3 Comparative Example 3 1.2 60 70 24.1 Comparative Example 4 1.2 180 70 27.0 Comparative Example 5 1.0 150 40 23.1 Comparative Example 6 1.0 150 80 25.9 Comparative Example 9 / / / 6.3

[0093] Note: “ / ” means not to perform this process.

[0094] By comparing Example 1 with Comparative Examples 1 to 4 and 9, it can be seen that steam explosion can significantly increase the SDF content, indicating that steam explosion promotes the glycosidic bond cleavage of insoluble macromolecular substances such as cellulose and hemicellulose to form soluble SDF; and under the conditions of steam explosion pressure of 1.2 MPa and pressure maintenance time of 120 s, the SDF content is the highest. This is because under too low pressure or pressure maintenance time, the degree of expansion and disintegration of the material is low, which is not conducive to the cracking and conversion of IDF into SDF, but too high pressure or pressure maintenance time will cause SDF to be partially degraded into small molecular sugars, which will reduce the SDF content.

[0095] By comparing Example 2 with Comparative Examples 5 to 6 and 9, it can be seen that alkali treatment can promote the decomposition of IDF into SDF, thereby increasing the SDF content; at the same time, the SDF content at an alkaline hydrolysis time of 60 min is higher than that at 40 and 80 min. This is because under alkaline conditions, IDF will partially decompose into soluble SDF, which increases the SDF concentration of the slurry. As the alkaline hydrolysis time increases, the dissolved SDF will further degrade, resulting in a decrease in the SDF content.

[0096] Experimental Group 2 ( Figure 3 )

[0097] Investigating the effect of spray drying inlet air temperature on product yield and moisture content

[0098] The yield and moisture content of the pineapple peel residue dietary fiber powder prepared by the methods of Example 3 and Control Groups 7 to 9 were determined.

[0099] Yield determination: The pineapple peel residue dietary fiber powder collected by spray drying is weighed as m, the mass of the pineapple peel residue raw material consumed is M, and the dry matter content of the raw material is n.

[0100] The product yield is: m / (M×n)×100%.

[0101] Determination of moisture content: Weigh 1g of pineapple peel residue dietary fiber powder and put it into the moisture meter for determination (Table 2).

[0102] Table 2 Product yield and water content

[0103] sample Air outlet temperature / ℃ Yield / % Moisture content / % Example 3 80 81.9 4.75 Control group 7 70 72.0 5.68 Control group 8 95 75.3 4.72 Control group 9 / / 5.54

[0104] Note: “ / ” means not to perform this process.

[0105] It can be seen from the data in Table 2 that the product yield at an outlet air temperature of 80°C is higher than that at 70°C and 95°C. This is because the drying temperature is too low to completely dry the liquid droplets after spraying, resulting in some particles sticking to the wall, thereby reducing the powder yield; if the temperature is too high, SDF and small molecular sugars in the liquid will melt and hang on the wall, which will also affect the product yield, and the product will be burnt and agglomerated; in addition, compared with hot air drying, the moisture content of the product prepared under suitable spray drying conditions is lower, indicating that spray drying is more efficient, and the powder fluidity, uniformity and dispersibility are better, which is convenient for the continuous production of powder materials.

[0106] Experimental Group 3 ( Figure 4 )

[0107] The water holding capacity, oil holding capacity, swelling capacity and cation exchange capacity of the pineapple peel residue dietary fiber powder prepared in Examples 1 to 3 and Control Group 9 were measured (Table 3).

[0108] Table 3 Physical and chemical properties of the products

[0109]

[0110] The physical and chemical properties of dietary fiber have an important influence on physiological functions and are important indicators for measuring its quality. Dietary fiber increases the swelling power of dietary fiber materials and absorbs fat in food by absorbing water and oil. It fully exerts the volumetric effect of fillers and the effect of lowering cholesterol in the gastrointestinal tract, increasing the volume and frequency of human bowel movements, thereby indirectly reducing the pressure on the rectum and urinary system.

[0111] In addition, dietary fiber contains carboxyl and hydroxyl side chain groups in its structure, which can exchange with Na+ and K+ in the intestines, promote the excretion of K+ and Na+ through the digestive tract, and reduce the incidence of cardiovascular diseases.

[0112] As can be seen from Table 3, the method of the present invention can effectively improve the water holding capacity, oil holding capacity, swelling capacity and cation exchange capacity of the pineapple peel residue dietary fiber powder, and improve the physical and chemical properties of the product.

[0113] This specific embodiment is only an explanation of the present invention, and it is not a limitation of the present invention. After reading this specification, those skilled in the art can make creative modifications to this embodiment as needed, but as long as it is within the scope of the claims of the present invention, it will be protected by the patent law.

Claims

1. A method for preparing pineapple peel residue dietary fiber powder, characterized in that: The following steps are involved: Step 1, raw material pretreatment: the pineapple processing by-product peel residue is selected and cleaned, and then pulped after adding 6 to 10 times the mass of clean water to obtain pineapple peel residue slurry; Step 2, enzymolysis: adding NaOH solution to the obtained slurry to adjust its pH value, then adding a certain mass fraction of α-amylase and controlling the temperature and stirring for a period of time to allow it to cool, then adding a certain mass fraction of papain and continuing to stir for enzymolysis, boiling to inactivate the enzyme, and then cooling to obtain an enzymolysis slurry; Step 3, washing: the enzymatic slurry is coarsely filtered through a 100-150 mesh screen, the coarse filter residue is repeatedly washed and sieved with clean water for 3-4 times, and then subjected to plate and frame filter pressing, and the filter residue is collected to obtain crude fiber; Step 4, steam explosion: placing the obtained crude fiber into a steam explosion device, setting the pressure to 0.8-1.6 MPa, and maintaining the pressure for 60-180 seconds; Step 5, alkaline hydrolysis: add 12 to 15 times the mass ratio of alkaline solution to the material after steam explosion, react at a temperature of 35 to 45 ° C for 45 to 60 minutes, cool to room temperature and adjust the pH to neutral with acetic acid; Step 6: colloid mill treatment: the obtained slurry is circulated and treated at 2000-3000 r / min for 7-14 min using a colloid mill; Step 7: high-pressure jet mill treatment: the prepared liquid is further crushed by a high-pressure jet mill at 80-110 MPa to make the fiber particle size less than 40 μm; Step 8: High-pressure homogenization: homogenize and emulsify the liquid treated by the jet mill at a pressure of 45-60 MPa for 3-4 times; Step 9, membrane concentration: the homogenized liquid is concentrated using a membrane concentration device to a solid content of 22-28%; Step 10, spray drying: drying the obtained concentrated solution by spray drying, collecting the dry powder, and cooling it to below 40° C. to obtain pineapple peel residue dietary fiber powder.

2. The method for preparing a pineapple peel residue dietary fiber powder according to claim 1, wherein: In step one, the peel residue includes by-products such as pineapple peel, core and pulp residue after juicing, and the stems, leaves and rotten and deteriorated raw materials are selected.

3. The method for preparing a pineapple peel residue dietary fiber powder according to claim 1, wherein: In step 2, the pH value of the slurry is adjusted to 6 by adding NaOH solution.

4. The method for preparing a pineapple peel residue dietary fiber powder according to claim 1, wherein: In step 2, the mass fraction of α-amylase is 1.5-2.5%, the stirring temperature is 55-65° C., the stirring time is 60-120 min, the mass fraction of papain is 0.15-0.25%, the stirring time is 25-35 min, and the enzyme inactivation boiling time is 5 min.

5. The method for preparing a pineapple peel residue dietary fiber powder according to claim 1, wherein: In step 2, the cooling temperature after adding α-amylase and stirring is 45-55°C.

6. The method for preparing a pineapple peel residue dietary fiber powder according to claim 1, wherein: In step three, the plate and frame filter pressing accuracy is 30-50 μm, the pressure is 0.5-0.7 Mpa, and the moisture content of the filter residue is 45-55%.

7. The method for preparing a pineapple peel residue dietary fiber powder according to claim 1, wherein: In step 5, the alkali solution is a NaOH solution and its concentration is 6-10%.

8. The method for preparing a pineapple peel residue dietary fiber powder according to claim 1, wherein: In step nine, the membrane concentration is a two-stage membrane concentration, wherein the first stage is an ultrafiltration membrane and the second stage is a reverse osmosis membrane.

9. The method for preparing a pineapple peel residue dietary fiber powder according to claim 1, wherein: In step ten, the inlet air temperature of the spray drying method is 180-200° C., the outlet air temperature is 70-95° C., and the spraying method is one of centrifugal spraying, pressure spraying or convection spraying.

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