CN117044886A - Process for preparing dried natto product by micro-puffing method - Google Patents
Process for preparing dried natto product by micro-puffing method Download PDFInfo
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- CN117044886A CN117044886A CN202311133533.2A CN202311133533A CN117044886A CN 117044886 A CN117044886 A CN 117044886A CN 202311133533 A CN202311133533 A CN 202311133533A CN 117044886 A CN117044886 A CN 117044886A
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Classifications
-
- A—HUMAN NECESSITIES
- A23—FOODS OR FOODSTUFFS; TREATMENT THEREOF, NOT COVERED BY OTHER CLASSES
- A23L—FOODS, FOODSTUFFS, OR NON-ALCOHOLIC BEVERAGES, NOT COVERED BY SUBCLASSES A21D OR A23B-A23J; THEIR PREPARATION OR TREATMENT, e.g. COOKING, MODIFICATION OF NUTRITIVE QUALITIES, PHYSICAL TREATMENT; PRESERVATION OF FOODS OR FOODSTUFFS, IN GENERAL
- A23L11/00—Pulses, i.e. fruits of leguminous plants, for production of food; Products from legumes; Preparation or treatment thereof
- A23L11/50—Fermented pulses or legumes; Fermentation of pulses or legumes based on the addition of microorganisms
-
- A—HUMAN NECESSITIES
- A23—FOODS OR FOODSTUFFS; TREATMENT THEREOF, NOT COVERED BY OTHER CLASSES
- A23L—FOODS, FOODSTUFFS, OR NON-ALCOHOLIC BEVERAGES, NOT COVERED BY SUBCLASSES A21D OR A23B-A23J; THEIR PREPARATION OR TREATMENT, e.g. COOKING, MODIFICATION OF NUTRITIVE QUALITIES, PHYSICAL TREATMENT; PRESERVATION OF FOODS OR FOODSTUFFS, IN GENERAL
- A23L3/00—Preservation of foods or foodstuffs, in general, e.g. pasteurising, sterilising, specially adapted for foods or foodstuffs
- A23L3/36—Freezing; Subsequent thawing; Cooling
- A23L3/365—Thawing subsequent to freezing
-
- A—HUMAN NECESSITIES
- A23—FOODS OR FOODSTUFFS; TREATMENT THEREOF, NOT COVERED BY OTHER CLASSES
- A23L—FOODS, FOODSTUFFS, OR NON-ALCOHOLIC BEVERAGES, NOT COVERED BY SUBCLASSES A21D OR A23B-A23J; THEIR PREPARATION OR TREATMENT, e.g. COOKING, MODIFICATION OF NUTRITIVE QUALITIES, PHYSICAL TREATMENT; PRESERVATION OF FOODS OR FOODSTUFFS, IN GENERAL
- A23L33/00—Modifying nutritive qualities of foods; Dietetic products; Preparation or treatment thereof
-
- A—HUMAN NECESSITIES
- A23—FOODS OR FOODSTUFFS; TREATMENT THEREOF, NOT COVERED BY OTHER CLASSES
- A23P—SHAPING OR WORKING OF FOODSTUFFS, NOT FULLY COVERED BY A SINGLE OTHER SUBCLASS
- A23P30/00—Shaping or working of foodstuffs characterised by the process or apparatus
- A23P30/30—Puffing or expanding
- A23P30/32—Puffing or expanding by pressure release, e.g. explosion puffing; by vacuum treatment
-
- A—HUMAN NECESSITIES
- A23—FOODS OR FOODSTUFFS; TREATMENT THEREOF, NOT COVERED BY OTHER CLASSES
- A23V—INDEXING SCHEME RELATING TO FOODS, FOODSTUFFS OR NON-ALCOHOLIC BEVERAGES AND LACTIC OR PROPIONIC ACID BACTERIA USED IN FOODSTUFFS OR FOOD PREPARATION
- A23V2002/00—Food compositions, function of food ingredients or processes for food or foodstuffs
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- Life Sciences & Earth Sciences (AREA)
- Engineering & Computer Science (AREA)
- Polymers & Plastics (AREA)
- Food Science & Technology (AREA)
- Chemical & Material Sciences (AREA)
- Health & Medical Sciences (AREA)
- Nutrition Science (AREA)
- Botany (AREA)
- Agronomy & Crop Science (AREA)
- Microbiology (AREA)
- Biotechnology (AREA)
- Mycology (AREA)
- Beans For Foods Or Fodder (AREA)
Abstract
The invention belongs to the field of fermented food preparation, and relates to a process for preparing a dried natto product by a micro-puffing method, which comprises the following steps: pretreating beans to obtain fermented natto; pre-drying fermented natto, and then carrying out micro-puffing drying to obtain a dried natto product; micro-puffing and drying: pressurizing at 50-70deg.C, and standing for a period of time; instantly puffing under high pressure difference; continuously vacuumizing and drying; evacuating temperature is 50-70 deg.C, micro puffing pressure difference is 0.5-0.6MPa; wherein, the pre-drying comprises freeze thawing treatment and hot air drying; conditions of hot air drying: drying at 40-60deg.C to obtain natto with water content of 15-25%. The drying process adopts freeze thawing treatment, hot air drying and micro puffing drying, and the three processes are cooperated to form a set of drying process, so that the activity of nattokinase can be ensured, and the puffing result can be ensured, thereby improving the quality of natto.
Description
Technical Field
The invention belongs to the technical field of fermented food preparation, and particularly relates to a process for preparing a dried natto product by a micro-puffing method.
Background
Natto is a traditional fermented food, and is obtained by fermenting and cooking beans with Bacillus natto, and is characterized in that the beans are covered with viscous substances. The natto contains about 60% of water, 20% of crude protein, 8% of crude fat, 2% of crude fiber and 2% of ash. The natto food contains functional factors such as bacillus natto, nattokinase, polypeptides, vitamin K2 and the like, so that the natto has various physiological functions such as antithrombotic, antioxidant, blood sugar reducing, osteoporosis preventing, intestinal health regulating, alcohol dispelling and sobering-up and the like, and can be used as a traditional seasoning food and a health-care food. Among them, nattokinase is the most bioactive component in natto, and is a natural, safe, efficient and economical thrombolytic enzyme. Natto has become a health food with homology of medicine and food nowadays, and is deeply favored by Japanese people.
Fresh natto has some disadvantages such as: (1) The presence of bad flavors (including beany flavor, ammonia flavor during fermentation, and off-flavors in "like toe odor", "mold decay flavor") in combination with special mouthfeel results in natto and its products not being very popular in our country; (2) short shelf life and high transportation and storage cost;
in addition, due to the insufficient knowledge of the natto and the longer preservation time of the fresh natto, the odor, the appearance and the internal quality of the natto are reduced to different degrees, the industrial production and development of the natto are limited, and the natto is dried by a drying means to ensure the variety and industrialization of the natto.
The common dry natto products in the market mainly comprise hot air drying, freeze drying, vacuum frying, spray drying and the like. However, the dried natto products currently on the market often have the following drawbacks: (1) The high temperature existing in the process damages natural active substances in natto, and especially has more obvious damage to nattokinase, and the existing research shows that the nattokinase can resist high temperature but the temperature cannot exceed 70 ℃; (2) The energy consumption in the drying process is large, the production capacity is small, and the equipment cost and the maintenance cost are expensive, so that the application of the method in industrial production is limited to a great extent.
Accordingly, in view of the above drawbacks, there is a need for developing a new process to produce a higher quality natto product.
Disclosure of Invention
The invention aims to provide a process for preparing a dried natto product by a micro-puffing method, which solves the problems of bad taste, inactivation of nattokinase and high energy consumption in the drying process of the existing dried natto.
The invention is realized by the following technical scheme:
the invention discloses a process for preparing a dried natto product by a micro-puffing method, which comprises the following steps:
pretreating beans to obtain fermented natto;
pre-drying fermented natto, and then carrying out micro-puffing drying to obtain a dried natto product;
the micro-puffing and drying method specifically comprises the following steps: pressurizing at 50-70deg.C, and standing for a period of time; instantly puffing under high pressure difference; continuously vacuumizing and drying;
evacuating temperature is 50-70 deg.C, micro puffing pressure difference is 0.5-0.6MPa;
wherein, the pre-drying comprises freeze thawing treatment and hot air drying;
the conditions of hot air drying are as follows: drying at 40-60deg.C to obtain natto with water content of 15-25%.
Further, the equipment used for micro-puffing drying comprises a puffing tank, a vacuum tank and a pneumatic valve, wherein the pneumatic valve is arranged between the puffing tank and the vacuum tank;
the puffing tank is used for placing a dried sample, applying pressure and heating; the expansion tank is connected with a steam generator and an air compressor.
Further, the micro-puffing and drying process specifically comprises the following steps:
(a) Preheating a puffing tank: closing a pneumatic valve connected with the vacuum tank, opening a steam generator, and heating the puffing tank to a preset temperature by utilizing steam;
(b) And (2) charging: after the temperature in the puffing tank reaches the preset temperature, placing fermented natto in the puffing tank, and sealing the puffing tank;
(c) Heating and pressurizing: the superheated steam generated by the steam generator continuously heats the expansion tank, and the steam generator is closed after the expansion temperature is reached;
connecting an air compressor with the expansion tank, pressurizing the expansion tank to a preset pressure of 0.4-0.5Mpa, and closing the air compressor;
opening a vacuum pump, and continuously pumping air in the vacuum tank until the vacuum degree reaches 0.098-0.1 MPa;
(d) Puffing: after the temperature rise and the pressurization in the puffing tank are completed, the vacuum tank is stopped for a period of time, and a pneumatic valve connected with the puffing tank is opened for instant puffing;
(e) And (3) drying: continuously vacuumizing at the vacuumizing temperature of 50-70 ℃ to dry;
(f) Cooling, opening the tank, and taking out the dried natto product.
Further, pretreatment comprises selecting, cleaning, soaking, steaming, inoculating bacteria and fermenting.
Further, the cooking conditions were: the temperature was 121℃and the time was 30min.
Further, the moisture content of the pre-dried natto is 17%, the puffing temperature is 60 ℃, and the vacuumizing temperature is 60 ℃.
Further, the dead time is 10-30min, and the evacuation time is 90-120min.
Further, the freezing and thawing treatment process comprises the following steps: freezing at-32deg.C for 120min, and thawing at 4deg.C for 180min.
Further, the temperature of the hot air drying was 50 ℃.
Compared with the prior art, the invention has the following beneficial technical effects:
the invention discloses a process for preparing a dried natto product by a micro-puffing method, wherein the drying process adopts freeze thawing treatment, hot air drying and micro-puffing drying, the freeze thawing treatment and the hot air drying belong to pre-drying, and the three processes are cooperated to form a set of drying process; freeze-thaw pretreatment has a significant impact on optimizing the texture characteristics and drying rate of the product. During the quick freezing process, ice crystals formed by the water in the cells destroy cell structures such as cell walls and fix the fiber structure of the materials. Therefore, when the material is thawed, the texture becomes relatively soft, which facilitates the subsequent puffing process, reduces the hardness of the dried product, and increases the crispness; in addition, the thawing phase results in dissociation of bound water within the cells, further facilitating acceleration of the drying process. And then the product is dried in advance by hot air and is subjected to micro-puffing drying, so that the obtained product is smooth and round in appearance, full in particles, obvious in texture and crisp to a certain extent, and the micro-puffing drying method is short in time consumption and low in equipment cost, and saves much for subsequent development. The differential pressure puffing generally needs a temperature higher than 90 ℃ Wen Caihang, and at the same time, nattokinase is deactivated, so that the activity of nattokinase and the puffing are both an important problem and a difficult point, no micro puffing technology is adopted to produce natto products at present, and the differential pressure puffing technology adopted by most fruits and vegetables is not suitable for natto products at present, especially the high temperature of 90 ℃ and above 90 ℃ is not suitable for natto products. According to the characteristics of natto, the invention can ensure the activity of natto kinase and the puffing result by the cooperation of a plurality of methods so as to improve the quality of natto, and through design research, the fermented natto is pre-dried, wherein the pre-drying comprises freeze thawing treatment and hot air drying, and the hot air drying conditions are as follows: drying at 40-60deg.C until the water content of natto is 15-35%. And then puffing, wherein the puffing conditions are as follows: the puffing temperature is 50-70deg.C, and the evacuating temperature is 50-70deg.C. Under such condition constraints, the quality of the obtained dried natto is relatively high.
Further, the conditions designed to obtain the optimal freeze-thawing treatment are: quick-freezing for 120min at-32 ℃ and thawing for 180min at 4 ℃ has obvious influence on optimizing the texture characteristics and drying rate of the product.
Drawings
FIG. 1 is a schematic diagram of a micro-puffing drying device;
1, an air compressor; 2. a puffing tank; 3. a pneumatic valve; 4. a vacuum tank; 5. a steam generator; 6. a vacuum pump;
FIG. 2 is a diagram of the process of making natto; a, soaking soybeans; b, steaming soybeans; c, inoculating natto starter; d-fermenting for 18 h; e-refrigerating for 8 hours to obtain natto finished products;
FIG. 3 shows the effect of different factors on the moisture content after puffing; a is the influence of puffing temperature on the moisture content of the dried natto; b is the influence of the pre-drying water content on the water content of the dried natto; c is the influence of the evacuation temperature on the water content of the dried natto; d is the influence of the pre-drying temperature on the water content of the dried natto;
FIG. 4 is a sensory evaluation of puffed natto under various conditions; the influence of the moisture content of the pre-drying on the quality of natto products; b-influence of puffing temperature on quality of natto products; influence of C-evacuating temperature on quality of natto product; influence of D-predrying temperature on quality of natto product;
FIG. 5 is a contour plot and a 3D plot of the interaction of pre-dried moisture content with expansion temperature (AB), the interaction of pre-dried moisture content with evacuation temperature (AC), the interaction of expansion temperature with evacuation temperature (BC), illustrating the effect of three factors on the moisture content of expanded natto;
FIG. 6 is a contour plot and a 3D plot of the interaction of pre-drying moisture content with expansion temperature (AB), the interaction of pre-drying moisture content with evacuation temperature (AC), the interaction of expansion temperature with evacuation temperature (BC), illustrating the effect of three factors on the color difference of expanded natto;
FIG. 7 is a diagram of a finished natto product dried under two conditions, and the left diagram is a natto after hot air drying; the right panel shows micro-puffed dried natto.
Detailed Description
The objects, technical solutions and advantages of the present invention will be more apparent from the following detailed description with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the invention, i.e., the embodiments described are merely some, but not all, of the embodiments of the invention.
The components illustrated in the figures and described and shown in the embodiments of the invention may be arranged and designed in a wide variety of different configurations, and thus the detailed description of the embodiments of the invention provided in the figures below is not intended to limit the scope of the invention as claimed, but is merely representative of selected ones of the embodiments of the invention. All other embodiments, which can be made by a person skilled in the art without making any inventive effort, are intended to be within the scope of the present invention, based on the figures and embodiments of the present invention.
It should be noted that: the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, element, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, element, method, article, or apparatus.
The features and properties of the present invention are described in further detail below with reference to examples.
Micro-puffing working principle:
the pretreated beans are placed in a puffing tank 2 for heating and pressurizing, and are subjected to instant pressure relief after being subjected to heat preservation and pressure maintaining for a certain time, so that moisture of materials is quickly evaporated, the materials expand and cause texture change, and the subsequent dehydration and drying are completed in a vacuum state, so that a final product is obtained. The material texture change is slight due to the lower heating temperature, so the material is called micro-puffing. The micro-puffing drying device is schematically shown in fig. 1, and consists of three main components: the device comprises a puffing tank 2, a vacuum tank 4 and a pneumatic valve 3, wherein the puffing tank 2 is used for placing a dried sample, and applying pressure and heating; the pneumatic valve 3 separates the puffing tank 2 from the vacuum tank 4, and can instantaneously communicate the puffing tank 2 with the vacuum tank 4; the puffing tank 2 is connected with a steam generator 5 and an air compressor 1, and the vacuum tank 4 is connected with a vacuum pump 6.
The preparation method of the natto dry product comprises the following steps:
(1) Material and apparatus
The main materials are as follows: soybean, natto starter (Angel yeast Co., ltd.).
Experimental equipment and instrumentation as shown in table 1:
table 1 laboratory apparatus and equipment
(2) Experimental method
1. The processing technology comprises the following steps:
beans are selected, cleaned, soaked, steamed, inoculated with bacteria, fermented, palletized, pre-dried, micro-puffed dried, crushed or not crushed and vacuum bagged.
The method comprises the following specific steps:
beans: the beans are soybean, chickpea or black bean.
Carefully selecting: and selecting high-quality beans with consistent diameter specification, full grains and no spoilage.
Cleaning: the sand, dust and organic matters attached to the surface of the beans are removed by washing with flowing clean water for standby.
Soaking: putting beans in a container, adding purified water which is 2.5-3 times of the weight of the beans, soaking for 8 hours, fully absorbing water by the beans until the surface is free from wrinkles, drying the beans, and putting the beans in a material tray.
And (3) cooking: placing beans into an autoclave for cooking under the following conditions: the temperature is 121 ℃, the pressure is 120kPa, and the time is 20-90min.
Inoculating: and (3) cooling the steamed beans to 40 ℃, inoculating bacillus natto, and uniformly stirring.
Fermentation: the inoculated beans are placed in a constant temperature incubator at 40 ℃ for fermentation for 18 hours. After 18 hours, a layer of white film uniformly covered on the beans appears, and the preparation of the natto is completed. And (3) dishing: and directly and uniformly spreading the fermented natto material in a drying tray, and controlling the thickness of the natto material within 3 cm.
Predrying: in order to improve the quality of the product, the raw materials are usually subjected to certain pre-drying before drying, so that adverse changes in the drying and subsequent storage processes are reduced to the greatest extent, and the puffing effect can be better achieved by reducing the water content of natto.
The pre-drying of the micro-puffing dried natto is freeze thawing treatment and hot air drying. The freezing and thawing treatment is to quick-freeze natto in refrigerator at-32deg.C for 120min, and thawing at 4deg.C for 180min. And hot air drying, namely placing natto in an electrothermal blowing drying oven, setting the pre-drying temperature to be 40-60 ℃, and pre-drying the natto material until the water content is 15-35%.
Micro-puffing: putting natto materials into a puffing tank 2 of micro puffing equipment for puffing under the following conditions: the puffing temperature is preset to be 50-90 ℃, air is introduced to keep the pressure in the puffing tank 2 at 0.4-0.5Mpa, the vacuum tank 4 is vacuumized until the vacuum degree reaches 0.098-0.1 MPa, the vacuum tank is kept for 10-30min, then the pressure is rapidly released within 1-5s, the vacuum tank 4 is continuously vacuumized, the vacuum degree reaches 0.098-0.1 MPa, and the vacuum is pumped for 90-120min at the temperature of 50-90 ℃.
Crushing: and (3) putting the obtained natto product into a pulverizer to pulverize and screen into particles with uniform size or directly obtaining the dried natto product without pulverization.
Vacuum packaging: and (5) putting the natto product into a vacuum packaging machine according to a certain weight for sub-packaging.
2. Micro puffing process flow of natto
(a) Preheating a puffing tank 2: the pneumatic valve 3 connected with the vacuum tank 4 is closed, the steam generator 5 is opened, and the puffing tank 2 is heated to a set temperature by steam.
(b) And (2) charging: when the temperature in the puffing tank 2 reaches the preset temperature, the processed materials are flatly paved on a tray, a feeding cabin door of the puffing tank 2 is opened, the materials are rapidly placed in the tray, then the cabin door is closed, and the puffing tank 2 is sealed.
(c) Heating and pressurizing: the superheated steam generated by the steam generator 5 continues to heat the expansion tank 2, and after the material reaches the expansion temperature, the steam generator 5 is turned off and is disconnected with the expansion tank 2. The air inlet valve is opened, the air compressor 1 is connected with the expansion tank 2, the expansion tank 2 is pressurized to a preset pressure, and then the air inlet valve is closed.
(d) Vacuumizing: after the pressurization is completed or at the same time, the vacuum pump 6 is turned on, and the vacuum tank 4 is continuously evacuated.
(e) Puffing: after the vacuum tank 4 reaches the preset vacuum degree, the pneumatic valve 3 (time 1-3 seconds) connected with the vacuum tank 4 and the puffing tank 2 is opened, the material is puffed, and a large amount of water in the material is taken away.
(f) And (3) drying: and continuously vacuumizing for a certain time at a preset temperature.
(g) And (3) cooling: when the vacuumizing time is up, a circulating cooling water valve of the puffing tank 2 is opened, the puffing tank 2 is cooled to about 35 ℃, cooling water is closed, and a pressure relief valve is opened, so that the pressure in the tank is the same as that in the atmosphere.
(h) Opening the pot: and opening the puffing tank 2, taking out the product, and performing relevant detection.
(3) Sensory evaluation and physical and chemical index detection
1. Measurement of Water content
Reference is made to the method for measuring the moisture in national standard GB 5009.3-2016 food. The measurement was performed by a direct drying method.
2. Chromatic aberration
And photographing the dried natto in different drying stages by using a digital camera to obtain a three-channel color image, and performing color analysis on the obtained image by using ImajeJ software to obtain color change in the natto drying process. L is a brightness index, where l=0 represents deep black, l=100 represents white, a and b are chroma indexes, a and b represent two directions of the same rectangular coordinate, and a=0 represents gray; the larger the absolute value of +a, the closer the representative color is to pure red; the larger the absolute value of a is, the closer the representative color is to pure green. b=zero is gray; the larger the +b value, the closer the representative color is to pure yellow; the larger the absolute value of b, the closer the representative color is to pure blue. The color difference of natto, generally expressed as Δe, is smaller, representing the smaller color difference between the measured sample and fresh natto, and the Δe value is calculated as follows:
wherein:
L 0 *、a 0 *、b 0 * Respectively representing the color value of fresh natto; l, a, b represent the color values of the samples, respectively.
3. Sensory evaluation
The sensory evaluation standards of natto comprise five aspects of color, flavor, taste, texture and appearance, wherein the sensory evaluation score of natto is 50 points at the highest and 0 points at the lowest, 10 people are used for blind evaluation and scoring, the average value is taken, and the sensory evaluation standards are shown in Table 2.
TABLE 2 organoleptic scoring criteria for natto
(4) Single factor test
1. Influence of soybean cooking time on natto fermentation result
Putting soybeans into an autoclave for cooking under the following conditions: the temperature is 121 ℃, and the time is 20min, 30min, 50min, 60min and 90min respectively. Experiments show that the conditions of the fermented natto have important influence on the preparation of natto, and the steps of preparing natto are as follows: selecting beans, soaking, steaming, inoculating and fermenting, wherein the steaming process adopts an autoclave at 121 ℃ for 30min to optimize, the color of the fermented natto is yellow brown, and the wire drawing is obvious. The fermentation optimization process is shown in fig. 2.
1. The influence of the pre-drying water content on the quality of the micro-puffed natto is explored
The pre-dried water content of natto was set to 15%, 20%, 25%, 30%, 35%, and other conditions were fixed, and the water content, sensory evaluation, and color of natto were measured. As can be seen from the data of fig. 3-B, fig. 4-a and table 3, the moisture content of the micro-puffed natto increases with the increase of the pre-dried moisture content; the color difference value is firstly reduced and then increased; at the same time, sensory evaluation was continuously reduced. The analytical reasons may be that the higher pre-dried moisture content hinders the loss of moisture, resulting in an increase in the final moisture content of the natto. Regarding the variation of the color difference value, the pre-drying moisture content is in the range of 25-35%, and an excessively high moisture content of natto may be a cause of the generation of large color difference. Under the condition that the pre-drying water content is 15%, the moisture loss in the puffing process is too rapid because the termination moisture content of the natto is low, so that the color difference value is increased. As regards the continuous decline of the organoleptic evaluation, one possible explanation is that in the section where the pre-dried moisture content is 30% -35%, the too high moisture content of the natto makes it insufficiently dry, which further leads to a decrease in the hardness and brittleness of the product, thereby affecting the organoleptic score. And the optimal pre-drying water content is determined to be 20% by comprehensively considering the factors and experimental results.
2. Exploring the influence of expansion temperature on the quality of micro-expanded natto
The puffing temperature is set to be 50 ℃,60 ℃, 70 ℃, 80 ℃, 90 ℃ respectively, other puffing conditions are fixed, and the moisture content, sensory evaluation and color of the natto are measured. From fig. 3-a, fig. 4-B and table 3, it can be seen that as the puffing temperature increases, the moisture content of the micro-puffed natto decreases continuously, the color difference value decreases and increases, and the sensory evaluation tends to increase and decrease. The analytical reasons may be that the higher the puffing temperature is, the more advantageous the moisture loss is, and the final moisture content of the natto is reduced. In the expansion temperature range of 50-70 ℃, the color difference value is continuously reduced along with the increase of the expansion temperature. However, when the puffing temperature reaches 80 ℃ and above, the moisture evaporation rate on the surface of natto is lower than the rate at which the moisture inside the natto diffuses to the surface due to the excessive temperature, which may trigger a browning reaction, resulting in an increase in color difference. In addition, too low a puffing temperature limits the moisture diffusion and puffing degree inside the natto, and as a result, the final moisture content of the natto is too high, which affects the crispness thereof, and thus adversely affects the sensory scores. However, as the puffing temperature increases, the crispness of the natto increases and the color difference value decreases, which results in an increase in the sensory score, but peaks at 60 ℃. Subsequently, the color difference increases due to the excessive puffing temperature, and the sensory score correspondingly decreases. In addition, when the temperature exceeds 70 ℃, the activity of nattokinase is also difficult to maintain. Therefore, the above analysis results are combined, and the puffing temperature is preferably 60 ℃.
3. The influence of the evacuation temperature on the quality of the micro-puffed natto is explored
Setting the evacuation temperature at 50deg.C, 60deg.C, 70deg.C, 80deg.C, and 90deg.C, fixing other puffing conditions, and measuring water content, sensory evaluation and color of puffed natto. From fig. 3-C, fig. 4-C and table 3, it can be seen that as the evacuation temperature increases, the moisture content of the micro-puffed natto decreases and then becomes gentle, the color difference value decreases and then increases, and the sensory score increases and then decreases. The analytical reasons may be that the evacuation process is long in duration, and when the evacuation temperature reaches 70 ℃, the evacuation and drying are performed for a long time, a hard shell is formed on the surface of the natto, which makes the dissipation of water in the natto difficult, so that the final water content change of the natto is not obvious any more. At the same time, this hardening of the surface may also affect the mouthfeel of the natto, making it stiffer, resulting in a decrease in organoleptic scores. Thus, in combination with all of the above analyses, it is appropriate to evacuate the temperature of 60 ℃.
4. The influence of the predrying temperature on the quality of the micro-puffed natto is explored
Setting hot air drying temperature at 40deg.C, 45deg.C, 50deg.C, 55deg.C, 60deg.C, fixing other puffing conditions, and measuring water content, sensory evaluation and color of puffed natto. The moisture content of the micro-puffed natto firstly obviously decreases, and then the decrease amplitude is gradually slowed down until the micro-puffed natto tends to be stable. In addition, the sensory scores gradually increased with increasing pre-drying temperature. However, the change in color difference value is not significant compared to the pre-drying temperature, indicating that the pre-drying temperature has little effect on the color difference value. In addition, in order to ensure that the kinase activity in natto is not impaired, the temperature of the predrying should be as low as possible in theory. Considering the combination of moisture content, sensory score, color difference and maintenance of kinase activity, a pre-drying temperature of 50℃appears to be a desirable choice. In view of the above, a pre-drying temperature of 50℃is suitable.
The single-factor experimental analysis shows that the lower the pre-drying moisture content is, the higher the puffing temperature and the evacuating temperature are, the lower the moisture content of the finally obtained natto product is, and the temperature has a great influence on the moisture content of the puffed natto. The micro-puffing dried natto has good quality, the pre-drying water content is 20%, the puffing temperature is 60 ℃, the evacuating temperature is 60 ℃, the pre-drying temperature is 50 ℃, the quality of the natto product dried by micro-puffing is good, and the quality of all aspects of sensory evaluation is good.
TABLE 3 influence of different factors on color difference values
(5) Response surface optimization experiment
1. Factor and level of response surface optimization experiments
Three factors with larger influence are obtained through single factor experiments, and the design response surface experimental factor level table 4 has determined three factors with influence on micro puffing of dried natto: pre-drying water ratio (A), puffing temperature (B), evacuating temperature (C), and water content Y of dried natto 1 And color difference Y 2 As a dependent variable, a three-factor quadratic regression orthogonal rotation combination test was performed, and the horizontal setting and the coding values of each factor are shown in table 4. Other process parameters are fixed: the dead time is 12min, the evacuation time is 90min, and the puffing pressure difference is 0.5-0.6MPa.
Optimizing the conditions of the micro-puffing dry natto by utilizing the Box-Behnken model design response, determining each process condition, selecting a reaction curved surface redesign model selected by three factors and two levels for testing, performing variance analysis on the model to determine the technical parameters, and finally adopting more optimized process conditions to form a response curved surface regression model.
The experimental design method and the data of the study are given in tables 5 and 6. In Table 5, 17 examples are shown, and the influence of various pre-drying water contents, puffing temperatures and evacuations on the water contents and color difference values of natto can be seen from Table 5, and the optimal puffing conditions can be further selected.
By using Design experert 8.0.6 software, a regression fit equation based on the quadratic response can be established to study the response values of different influence factors (including water content of the product, color difference values) in table 5. The regression equation model of the secondary response surface of each factor to the water content and color difference value index of the product is obtained as follows:
Y 1 ＝6.59+2.07A-0.61B-0.86C-0.24AB-0.40AC+1.03BC+1.29A 2 +0.50
B 2 +0.27C 2
Y 2 ＝2.80+0.33A-0.036B+0.28C+2.23AB+1.25AC-1.00BC+1.83A2+1.18
B2+1.03C2
based on the data in Table 5, the model was found to have p < 0.0001, indicating that the regression model was extremely significant, meaning that its effect was quite large, the mismatch term p was 0.9034 (p > 0.05) and was not significant, indicating that the experimental model was well-characterized and the regression model was reasonable. From the data of the F value, the three factors influencing the moisture content of the dried natto are the pre-drying moisture content, the evacuating temperature and the puffing temperature in sequence, wherein the primary term A, C is extremely remarkable (p < 0.01), which indicates that the pre-drying moisture content and the evacuating temperature have extremely remarkable influence on the moisture content of the product, and the interactive term BC is extremely remarkable (p < 0.01), which indicates that the interaction between the puffing temperature and the evacuating temperature is extremely remarkable. The determination coefficient R of each equation is known by checking the regression coefficient 2 The values are all larger than 0.95, which indicates that the three factors and the quadratic term thereof explain the model fitting degree of each response value change. The analysis of variance results of the model are shown in table 6. The primary and secondary orders of three factors can be judged according to the size of the F value, the primary and secondary orders affecting the water content of the dried natto are A & gtC & gtB, the primary and secondary orders affecting the color of the dried natto are A & gtC & gtB, and the p value can be seen from A, C and A 2 Has extremely remarkable influence (p is less than 0.01) on the water content of the dried natto, A, B, C, BC, A 2 Has significant influence on the water content of the dried natto (p is less than 0.05); AB. AC, BC, A 2 、B 2 、C 2 Has obvious influence on the color and luster of the dried natto (p is less than 0.05), AB, AC, BC, A 2 、B 2 、C 2 Has very obvious influence on the color of the dried natto (p is less than 0.01). In addition, the mismatching term of each model is larger than 0.05, the mismatching term is not obvious, and the regression equation fitting degree is good.
2. Response surface analysis of influence of each factor level on natto product quality
(a) Influence of three factors on water content of puffed natto
The response values and other factors influencing the response values can be observed more clearly by drawing a response surface 3D graph through Design-Expert 8.0.6, so that the relation between the response values and other factors is explored better, and a better production scheme is obtained. According to fig. 5AB, it was found that the moisture content of natto was drastically reduced during the expansion temperature rise. According to fig. 5CD, when the puffing temperature is a central level value, the moisture content of the dried natto is rapidly reduced with the increase of the evacuation temperature, and then gradually recovered, and the moisture content thereof is less than that of the previously dried natto, thereby obtaining a more excellent product. As can be seen from fig. 5EF, the moisture content of the micro-puffed natto gradually decreases with increasing evacuation temperature and puffing temperature and finally reaches equilibrium. When the puffing temperature is too low, enough energy cannot be provided for puffing, so that the puffing effect is poor; when the concentration of the active ingredients is too high, a protective film is formed on the surface of the raw materials too early, which is not beneficial to the sufficient diffusion of moisture, and the activity of nattokinase is greatly affected by the too high concentration, so that the characteristics of natto per se cannot be exerted. As the evacuation temperature and the puffing temperature rise, the water content of natto decreases.
As can be seen from fig. 5AB, the interaction between the pre-drying moisture content and the puffing temperature has a significant effect on the moisture content of the dried natto, the gradient of the response surface corresponding to the pre-drying moisture content is steeper, and the gradient of the response surface corresponding to the puffing temperature is relatively gentle, which means that the effect of the pre-drying moisture content on the moisture content of the dried natto is more obvious than the puffing temperature. According to fig. 5CD, the pre-dried moisture content had a significant effect on the moisture content of the dried natto, while the puffing temperature did not have a significant correlation, but it had a more significant effect on the moisture content of the dried natto, which was in full agreement with the results of the analysis of variance. As can be seen from fig. 5EF, the interaction of the bulking temperature and the evacuating temperature has no significant effect on the moisture content of the dried natto, and the bulking temperature has a more significant effect on the moisture content of the dried natto than the evacuating temperature, consistent with the analysis of variance.
(b) Influence of three factors on color difference of puffed natto
As can be seen from fig. 6AB, the color difference value of the dried natto becomes stable after decreasing with increasing the pre-drying water content, and becomes stable after decreasing with increasing the puffing temperature; as can be seen from fig. 6CD, when the puffing temperature is a central level value, the color difference value of the dried natto is decreased first and then slowly increased as the pre-drying moisture content is increased, and is slowly decreased as the evacuation temperature is increased. From fig. 6EF, it can be seen that the color difference value of the dried natto shows a slow rising trend with rising puffing temperature, but the variation is not obvious; when the evacuation temperature rises, the color difference value of the dried natto also shows a tendency of slowly rising; when the combined values of the puffing temperature and the evacuation temperature reach a certain level, the color difference value of the dried natto appears to be minimum, indicating that in this case, the color difference value of the dried natto is at the minimum level. In summary, the color stability is severely affected as the puffing temperature and evacuation temperature are increased.
As can be seen from fig. 6AB, the effect of the cross-action of the pre-drying moisture content and the puffing temperature on the color difference of the natto is more remarkable, the gradient of the response surface corresponding to the pre-drying moisture content is steeper, and the gradient of the response surface corresponding to the puffing temperature is gentler than that of the response surface corresponding to the puffing temperature, which indicates that the effect of the pre-drying moisture content on the color difference of the natto after drying is more remarkable than that of the puffing temperature. Similarly, as can be seen from fig. 6CD, the effect of interaction of both the pre-drying moisture content and the evacuation temperature on the color difference of the dried natto was found to be more remarkable by the micro-puffing drying, and the effect of the evacuation temperature on the color difference of the dried natto was more remarkable than the pre-drying moisture content. From fig. 6EF, it can be seen that the interaction of the bulking temperature and the evacuation temperature was not significant for the color difference of the dried natto, and the evacuation temperature had a more pronounced effect on the color difference of the dried natto than the bulking temperature, consistent with the analysis of variance.
(c) Model verification
For the evaluation index of each puffed product, the higher the puffing degree is, the better the color and luster are, and meanwhile, the lower the water content is, so that the better the quality of the product is. Although the trend of these indices varies, sensory evaluation is the primary index and color is the secondary index for puffed natto products. Therefore, the puffing degree is optimized through Design Expert8.0 software, the optimal process conditions for obtaining the puffing degree are that the pre-drying moisture content is 16.89%, the puffing temperature is 65.65 ℃, the evacuating temperature is 64.26 ℃, and the optimal process conditions are adjusted to be in consideration of the convenience of experimental operation: the pre-drying moisture content 17% puffing temperature 60 ℃ and the evacuating temperature 60 ℃. In order to test the reliability of the result obtained by the response surface method, the conclusion of the response surface method is found to be credible through 3 parallel experiments by adopting the optimization conditions. Based on the method, the sensory evaluation total score 48 of the variable-temperature micro-puffing drying of the natto is obtained, the water content of the natto is about 3.95%, the color difference value is about 6.86, and the relative difference of the data is very small, which shows that the model performs well in the variable-temperature differential-pressure puffing drying process, so that the model is recommended to be applied to the control of the natto puffing drying process.
TABLE 4 factor level encoding table
TABLE 5 response surface test design and results
TABLE 6 regression equation analysis of variance table
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(6) Influence of drying mode on quality of dried natto
Spreading fermented fresh natto on a tray, placing into a hot air drying oven, respectively performing hot air drying at different drying temperatures (50deg.C, 60deg.C, 70deg.C, 80deg.C, 90deg.C), drying for a certain time, and respectively measuring index such as water content, color, and sensory evaluation of natto.
As a result, it was found that the time required for drying natto to a water content of 3% or less was different from one another at different hot air drying temperatures. In general, the higher the hot air drying temperature, the shorter the drying time used. Drying is required at 50 ℃ for 30 hours, 60 ℃ for 24 hours, 70 ℃ for 18 hours, 80 ℃ for 12 hours and 90 ℃ for 6 hours. The activity of high Wen Xiana bean kinase is obviously reduced, and the effect cannot be better exerted.
As shown in Table 3 and Table 7, the color difference of the micro-puffed dried natto was found to be superior to that of hot air drying by color difference analysis. The appearance of the natto dried by hot air is provided with a plurality of folds, is not smooth, is rugged and is not attractive in appearance, and is not easy to be accepted and loved by people as natto snack food. On the contrary, the micro-puffing dried natto particles are round, smooth and flat, and have the fragrance of soybeans. As can be seen in fig. 7, the micro-puffed dried natto is intact and flat in morphology; the natto dried by hot air has poor brittleness and obvious folds. The natto dried with hot air alone was accompanied by a slight ammonia smell and also was not crisp enough; the micro-puffed dried natto has no bad smell of natto, has a certain soybean flavor, and has obvious crisp and crisp degree.
TABLE 7 color difference values for Hot air drying
(7) Influence factor analysis
The nature of nattokinase is protein, but the activity and performance of the nattokinase are extremely easy to be limited by the environmental temperature, the stability of the nattokinase at 37 ℃ is very high, the relative average enzyme activity can reach 93%, the relative enzyme activity can be maintained above 95% under the condition of 47-60 ℃, and the activity of the nattokinase is estimated according to the existing research background, so that the nattokinase can resist high temperature but the temperature cannot exceed 70 ℃. Therefore, the influence of high temperature on the enzyme activity is larger, but the influence of low-temperature storage on the quality of nattokinase is not obvious, and in experiments, shoumeyan et al show that the repeated freezing and thawing has little influence on the activity of the nattokinase, even if the repeated freezing and thawing is carried out eight times, the activity still reaches over 78 percent, and in addition, the research reports that the enzyme activity is basically unchanged after the nattokinase is stored for seven days at the temperature of minus 20 ℃, so that the low-temperature storage of the nattokinase is not lost as a better storage mode, and the influence of freezing on the nattokinase is not great.
The fresh natto is mainly dried by vacuum freeze drying and hot air drying. Vacuum freeze drying is widely used in biological products. In order to avoid the damage of thalli and enzymes in the drying process, a protective agent can be added appropriately. Hot air drying is one of the most common modes in industrial production, and compared with a freeze dryer, the hot air dryer is low in price and low in energy consumption. By reasonably adjusting the drying temperature, the effective biological activity in the fresh natto can be maintained. Compared with the hot air dried and micro-puffed dried natto, the hot air dried natto has the advantages of serious shrinkage, unattractive shape and long drying time, the influence of the excessive hot air drying temperature on nattokinase is large, and the natto dried by the micro-puffing equipment has the advantages of attractive appearance, certain puffing effect, obvious crisp and crisp degree, light yellow color, no ammonia smell as heavy as fresh natto, and obviously reduced bitter taste along with light soybean smell.
Through single factor experiments, under the optimal condition, the texture, appearance and taste of the natto reach the optimal state. The pre-drying water content was set at 20%, the puffing temperature was set at 60 ℃, the evacuation temperature was set at 60 ℃, and the pre-drying temperature was set at 50 ℃. And the moisture content and delta E are used as response values, and the response surface of the dried natto is optimized, so that the optimal drying condition is that the pre-drying moisture content is 16.89%, the puffing temperature is set to 65.65 ℃ and the evacuating temperature is set to 64.26 ℃. Under the given conditions, the lowest moisture content and ΔE of the dried natto can be obtained. To better evaluate the experimental results, a pre-dried moisture content of 17%, a puffing temperature of 60 ℃, and an evacuation temperature of 60 ℃ were selected for the response surface test. The water content of the product of the micro-puffed natto is 3.95%, the color difference value is 6.86, the comprehensive score of the sensory score is 48 minutes, the test result has smaller difference with the predicted value, the result of response surface optimization is proved to have credibility, and the theoretical basis can be provided for the subsequent production and application. The micro-puffing dried natto can improve the quality of natto, maintain the special nutritional value and color increase of natto, and prolong the shelf life.
According to the invention, the water content, color and sense evaluation indexes of the natto under different drying conditions are researched and analyzed, the natto is dried in three modes of freeze thawing treatment, hot air drying and micro-puffing drying, and the optimal technological condition of the micro-puffing dried natto is selected, and the possible activity of the micro-puffing dried natto is predicted.
In view of the points, the micro-puffing dried natto is superior to the hot air dried natto product. The micro-puffed dried natto is greatly improved in appearance and smell, so that people can more easily accept the natto and the natto product thereof. The natto prepared by the micro-puffing drying method is superior to the traditional drying method in appearance, smell and taste by drying the natto by hot air at 50 ℃ for 24 hours. Therefore, the micro-puffing drying mode is selected to produce the natto, so that the quality of the natto can be ensured to a certain extent, the production cost is low, the efficiency is high, and the method is suitable for industrial production.
At present, the vacuum freeze-drying technology is the most common drying mode for processing the dried natto, the damage degree of the vacuum freeze-drying technology to cells is minimum, but the energy consumed in the freeze-drying process is very much, the capacity is very small, and the equipment cost and the maintenance cost are relatively high, so that the wide application of the freeze-drying technology in industry is restricted to a great extent. However, the fermented natto is subjected to freeze thawing treatment at the temperature of minus 32 ℃, the frozen and thawed natto is subjected to hot air drying treatment, the water content is 17% at the temperature of 50 ℃, and the fermented natto is subjected to micro puffing drying, so that the obtained product is smooth and round in appearance, full in particles and obvious in texture and has a certain crisp texture. The micro-puffing drying method has the advantages of short time consumption, low equipment cost and great saving for subsequent development.
However, no relevant standard exists in the current detection of nattokinase, so that the nattokinase activity of the micro-puffed natto is not measured at present, further research and exploration are needed in the later time, the activity of the nattokinase can only be estimated according to the current research background, and the nattokinase can resist high temperature but the temperature cannot exceed 70 ℃, thus laying a certain foundation for the later research.
The heat-resistant temperature of nattokinase is 60-70 ℃, and the maintenance of the activity of nattokinase is an important problem and difficulty. As mentioned above, no puffing process is currently used to produce natto puffed artwork. And the pressure difference adopted by most fruits and vegetables is not suitable for natto products at present, and especially, the high temperature of 90 ℃ and above 90 ℃ is not suitable for natto products. According to the characteristics of natto, the quality of natto is improved through the cooperation of various methods.
The invention is based on the research of the natto drying method, and researches the optimal process of natto drying by a micro-puffing drying method, which provides theoretical basis for the subsequent large-scale production application, and the production process flow comprises the steps of pre-drying fermented natto, wherein the pre-drying comprises freeze thawing treatment and hot air drying. The conditions of the freeze thawing treatment are as follows: quick-freezing at-32deg.C for 120min, and thawing at 4deg.C for 180min. The conditions of hot air drying are as follows: drying at 50deg.C until the water content of natto is 17%. And then puffing, wherein the puffing conditions are as follows: the puffing temperature is 60 ℃, the evacuating temperature is 60 ℃, the dead time is 12min, and the puffing pressure difference is 0.5-0.6Mpa.
Finally, it should be noted that: the above embodiments are only for illustrating the technical aspects of the present invention and not for limiting the same, and although the present invention has been described in detail with reference to the above embodiments, it should be understood by those of ordinary skill in the art that: modifications and equivalents may be made to the specific embodiments of the invention without departing from the spirit and scope of the invention, which is intended to be covered by the claims.
Claims (9)
1. A process for preparing a dried natto product by a micro-puffing method is characterized by comprising the following steps:
pretreating beans to obtain fermented natto;
pre-drying fermented natto, and then carrying out micro-puffing drying to obtain a dried natto product;
the micro-puffing and drying method specifically comprises the following steps: pressurizing at 50-70deg.C, and standing for a period of time; instantly puffing under high pressure difference; continuously vacuumizing and drying;
evacuating temperature is 50-70 deg.C, micro puffing pressure difference is 0.5-0.6MPa;
wherein, the pre-drying comprises freeze thawing treatment and hot air drying;
the conditions of hot air drying are as follows: drying at 40-60deg.C to obtain natto with water content of 15-25%.
2. The process for preparing a dried natto product by a micro-puffing method according to claim 1, wherein the equipment for micro-puffing and drying comprises a puffing tank (2), a vacuum tank (4) and a pneumatic valve (3), wherein the pneumatic valve (3) is arranged between the puffing tank (2) and the vacuum tank (4);
a puffing tank (2) for placing a dried sample, applying pressure and heating; the expansion tank (2) is connected with a steam generator (5) and an air compressor (1).
3. The process for preparing a dried natto product by a micro-puffing method according to claim 2, wherein the micro-puffing drying process specifically comprises the following steps:
(a) Preheating a puffing tank (2): closing a pneumatic valve (3) connected with the vacuum tank (4), opening a steam generator (5), and heating the puffing tank (2) to a preset temperature by utilizing steam;
(b) And (2) charging: after the temperature in the puffing tank (2) reaches the preset temperature, placing fermented natto in the puffing tank (2), and sealing the puffing tank (2);
(c) Heating and pressurizing: the superheated steam generated by the steam generator (5) continuously heats the puffing tank (2), and the steam generator (5) is closed after the puffing temperature is reached;
connecting the air compressor (1) with the expansion tank (2), pressurizing the expansion tank (2) to a preset pressure of 0.4-0.5Mpa, and closing the air compressor (1);
opening a vacuum pump (6), and continuously pumping air in the vacuum tank (4) until the vacuum degree reaches 0.098-0.1 MPa;
(d) Puffing: after the temperature rise and the pressurization in the puffing tank (2) are completed, the vacuum tank (4) and a pneumatic valve (3) connected with the puffing tank (2) are opened for a period of time to carry out instant puffing;
(e) And (3) drying: continuously vacuumizing at the vacuumizing temperature of 50-70 ℃ to dry;
(f) Cooling, opening the tank, and taking out the dried natto product.
4. The process for preparing a dried natto product by a micro-puffing method according to claim 1, wherein the pretreatment comprises selecting, cleaning, soaking, steaming, inoculating and fermenting.
5. The process for preparing a dried natto product by a micro-puffing method according to claim 4, wherein the cooking conditions are as follows: the temperature was 121℃and the time was 30min.
6. The process for preparing a dried natto product by a micro-puffing method according to claim 1, wherein the moisture content of the pre-dried natto is 17%, the puffing temperature is 60 ℃, and the vacuumizing temperature is 60 ℃.
7. The process for preparing a dried natto product by a micro-puffing method according to claim 1, wherein the dead time is 10-30min and the evacuation time is 90-120min.
8. The process for preparing a dried natto product by a micro-puffing method according to claim 1, wherein the freezing and thawing treatment comprises the following steps: freezing at-32deg.C for 120min, and thawing at 4deg.C for 180min.
9. The process for preparing a dried natto product by a micro-puffing method according to claim 1, wherein the temperature of hot air drying is 50 ℃.
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