CN114451533A - High-quality raisin preparation method - Google Patents
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- 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
- A23L19/00—Products from fruits or vegetables; Preparation or treatment thereof
- A23L19/03—Products from fruits or vegetables; Preparation or treatment thereof consisting of whole pieces or fragments without mashing the original pieces
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- A—HUMAN NECESSITIES
- A23—FOODS OR FOODSTUFFS; TREATMENT THEREOF, NOT COVERED BY OTHER CLASSES
- A23B—PRESERVING, e.g. BY CANNING, MEAT, FISH, EGGS, FRUIT, VEGETABLES, EDIBLE SEEDS; CHEMICAL RIPENING OF FRUIT OR VEGETABLES; THE PRESERVED, RIPENED, OR CANNED PRODUCTS
- A23B7/00—Preservation or chemical ripening of fruit or vegetables
- A23B7/02—Dehydrating; Subsequent reconstitution
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- 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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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
- Y02A40/00—Adaptation technologies in agriculture, forestry, livestock or agroalimentary production
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Abstract
The invention discloses a method for making high-quality raisins, belonging to the technical field of agricultural product processing, which comprises the following steps: picking fresh 'seedless white' grapes which are not rotten, removing fruit stalks, washing off impurities, and extruding damaged and deformed grape grains in the picking and transporting processes; secondly, screening by adopting a vibrating screen to divide the grapes into big, middle and small types; thirdly, adopting a salt solution method to accurately distinguish the grapes with different ripeness degrees. Fourthly, the classified grapes are selected, catalytic infrared heating is carried out, and surface moisture is dried; fifthly, drying the grapes in a vacuum pulse mode; sixthly, carrying out catalytic infrared sterilization on the dried grapes, and finally carrying out vacuum packaging. Thereby obtaining the raisin product with the moisture content and the bacteria content reaching the standard and the uniform and consistent product quality. The method can produce high-quality raisin products with consistent quality, moisture content and bacteria content, and the products have good quality, no chemical residue and simple and reliable method.
Description
Technical Field
The invention belongs to the technical field of agricultural product processing, and relates to a method for making high-quality raisins.
Background
The grapes are strong in seasonality and concentrated in the market period, the water content of the fresh grapes is as high as 80%, the soluble solid content is high, and the grapes are easy to grow microorganisms to rot and deteriorate. The dried grapes are one of the important processing modes of the grapes except for fresh food, the prominent problems of concentrated grape harvesting period, easy decay and deterioration, short storage period, high transportation cost and the like can be solved, and the prepared raisins have unique taste and flavor which are not possessed by the fresh grapes, are popular with consumers and are also indispensable auxiliary materials in the food industry. Seedless white grapes are the most important dried variety, and about 95% of raisins are processed from "seedless white" grapes.
However, the following problems generally exist in the current raisin processing technology.
Firstly, the natural drying time is long. The traditional drying room can obtain good color and luster (emerald green) with a large probability after being dried, but the green product rate is usually lower than 35 percent; and the drying time is generally longer, usually 25-40 days, and the product quality problem is easily caused by the pollution of external microorganisms, insects and birds. .
Secondly, hot air drying is easy to brown. Color is an important indicator of consumer choice. If the fresh grapes are not treated by any chemical drying accelerator, a hot air drying technology is directly adopted, and the drying time is about 1-7 days. Although the drying efficiency can be greatly improved, the browning of the product is more serious, and the raisins with better color and luster are difficult to obtain.
And thirdly, the maturity of the fresh grapes is inconsistent, so that the physical and chemical characteristics of the raw materials are not uniform. Due to the difference of plant growing environment in the agricultural material growing process, the individual size, shape and maturity of grapes usually have difference. Even the maturity of grapes in the same orchard and the same harvest time and in the same plant is obviously different, so that the sizes and the soluble solid content of the grapes are obviously different. Under the same drying condition, the small-volume grapes are easy to cause over-drying and influence the mouthfeel; the grapes with larger volume are usually not completely dried, so that bacteria are easy to breed during storage, and the quality is reduced. During the process of making dry grapes, the inconsistency of the physical and chemical characteristics of the raw materials can directly cause the uneven and unstable quality of the dried products. This has become a significant problem affecting the mechanized drying of grapes.
In order to ensure the consistency of the quality of raisins, the prior classification method is to adopt a machine vision technology to classify the raisins after the raisins are dried and judge the color and the size of the raisins one by one. But the raisins with different soluble solid content can not be accurately distinguished based on the soluble content difference inside the grapes. And the classification equipment based on machine vision has large investment and high maintenance cost.
And fourthly, because the grapes are difficult to kill all microorganisms in the drying processing, the microorganisms of the raisin product exceed the standard sometimes, and the food safety problem is easily caused. At present, the common sterilization modes of dehydrated vegetables mainly comprise high-temperature steam sterilization, hot water blanching sterilization, chemical reagent sterilization and the like, but the high-temperature steam and hot water blanching sterilization easily causes the loss of nutritional ingredients of raisins, and the water content exceeds the standard. Chemical agent sterilization may have chemical residues with some controversy. Therefore, new sterilization techniques are needed.
Aiming at the problems, a novel grape drying method is provided by combining a salt solution classification method, a vacuum pulsation drying technology and a catalytic infrared heating technology.
The grape appearance size difference is combined, and the grape can be classified through vibrating screens with different apertures. Grapes have different ripeness degrees, soluble solid contents are different, and the density is also different. Therefore, grapes with the same size and different ripeness degrees can be further graded by configuring salt solutions with different concentrations.
The catalytic infrared heating technology is that under the action of catalyst, natural gas and oxygen are made to produce oxidation reaction to produce carbon dioxide and water and infrared energy is radiated. The catalytic infrared is a flame-free reaction, the temperature of the catalytic infrared is lower than the ignition point, no open fire exists, no explosion hidden danger exists, and the catalytic infrared is safe and reliable. Compared with the traditional electric infrared, the catalytic infrared energy is directly converted from natural gas into infrared heating, and the energy utilization efficiency is higher. The catalytic infrared has a strong surface heating effect and can quickly remove the moisture on the surface of the material. Compared with the traditional high-temperature steam and blanching sterilization, the device has the advantages of rapid heating, high heat transfer efficiency, energy conservation, environmental protection and no chemical residue.
The vacuum pulse drying technology is developed on the basis of the common vacuum drying technology, and the equilibrium state of the evaporation of the water on the surface of the material can be continuously broken by adopting continuous periodic pressure switching, so that the drying process is accelerated; in addition, the continuous pulse change of the pressure in the drying chamber can also enable the micro pore canals of the drying materials to be continuously expanded and contracted and even communicated with each other, thereby effectively promoting the transmission of the water in the drying materials to the outside and maintaining higher drying speed. Compared with common vacuum drying, the technology has the advantages of high drying efficiency, good product quality and the like.
Therefore, the invention effectively combines the salt solution classification method, the vacuum pulsation drying technology and the catalytic infrared heating technology. On the premise of accurately classifying the grapes and ensuring the consistency of the physical and chemical characteristics of the grapes, high-quality raisin products with consistent product quality and standard water content and bacteria content are quickly produced.
Disclosure of Invention
The invention aims to provide a method for making high-quality raisins, which is characterized by comprising the following steps:
(1) selecting raw materials, selecting fresh 'seedless white' grapes which are not rotten, removing fruit stalks, washing off impurities, and removing grape grains which are extruded, damaged and deformed in the picking and transporting processes;
(2) grading and screening the particles, namely screening the particles in sequence by adopting 4 layers of vibrating screens, and storing the grape raw materials with large, medium and small transverse diameters of the grapes;
(3) grading according to the phenomenon that grape particles float or sink in a salt solution, namely, preparing sodium chloride solutions with the concentrations of 120,140, 160 and 180g/L by utilizing the principle that grape particles with different maturity have different densities, placing the grapes graded in the step (2) in the salt solution with the lowest concentration at first, fishing out suspended grape particles and collecting the grape particles according to the phenomenon that the grapes float and sink, fishing out the grape particles which sink and placing the grape particles in the salt solution with higher concentration at next time, and fishing out the grape particles which float upwards, fishing out the grape particles which sink, placing the grape sample which sink in the salt solution with higher concentration continuously and sequentially carrying out the steps until the grading of the sample is finished. The material is divided into grapes with salt solution concentration less than 120, (120,140], (140,160], (160,180], > 180g/L, respectively defined as grapes with lower, middle, high and higher ripeness degrees.
(4) Removing the surface moisture of each level of grapes obtained in the step (3) by adopting catalytic infrared heating, selecting grapes classified in size and maturity, placing the grapes on a double-layer conveyor belt, enabling the conveyor belts to be different in height, installing catalytic infrared heating above the conveyor belts, enabling rolling in the falling process of the materials to realize automatic turning, and facilitating uniform heating of the materials to remove the surface moisture; the speed of the conveyor belt is adjustable, so that the sterilization time is adjusted;
(5) performing vacuum pulse drying on the grapes with the surface moisture removed in the step (4), flatly laying the grapes with the surface moisture removed in a single layer mode in a vacuum box, pumping to a rated vacuum state, setting a drying temperature, and performing vacuum drying; when the vacuum maintaining time is over, switching to a rated normal pressure state, performing normal pressure drying, when the normal pressure maintaining time is over, switching to a vacuum state again, and circulating in sequence; stop until the dry basis moisture content of the material decreased to 0.25 + -0.05 g/g and record the total drying time.
(6) The dried grapes are subjected to catalytic infrared sterilization and are placed on a double-layer conveyor belt, the conveyor belt is different in height, catalytic infrared heating is arranged above the conveyor belt, automatic turning can be achieved by rolling in the falling process of the materials, and uniform heating sterilization of the materials is facilitated; the speed of the conveying belt is adjustable, and the heating time can be adjusted.
(7) And (3) product quality detection, namely sampling the grapes dried and sterilized in the step (6) by adopting a nine-point method, respectively detecting 4 physicochemical quality indexes of the soluble solid content, the color difference value, the product water content and the total bacteria residual activity rate after the drying is finished, and taking the average value as a final detection result. Respectively calculating logarithmic values of the color difference value, the total bacteria number survival rate, the soluble solid content and the uniform coefficient of the product water content for comparing test results;
(8) and finally, carrying out vacuum packaging. Thereby obtaining the raisin product with the moisture content and the bacteria content reaching the standard and the uniform and consistent product quality.
The vibrating screen is made of high-density polyethylene plastics, and the diameters of circular meshes of the vibrating screen are 18 mm, 15 mm, 12 mm and 9mm in sequence.
The grape raw materials which are divided into big, medium and small grapes according to the transverse diameter of the grapes are divided into grape particles with the diameter larger than 18, (15, 18), (12, 15), (9, 12) and smaller than 9mm according to the diameters of sieve meshes of 18, 15, 12 and 9 mm.
The catalytic infrared heating condition is as follows: the temperature of the catalytic infrared generator is 380-420 ℃, the distance between the conveyor belt and the catalytic infrared generator above the conveyor belt is 16-20 cm, and the heating time is 60-6000 s.
The vacuum pulse drying conditions are as follows: the pressure of the drying chamber in a rated vacuum state is 0-10 kPa, the pressure of the drying chamber in a rated normal pressure state is 95-101 kPa, the drying temperature is 60-85 ℃, the vacuum holding time is 1-15 min, and the normal pressure holding time is 2-10 min;
the catalytic infrared heating condition is as follows: the temperature of the catalytic infrared generator is 380-420 ℃, the distance between the conveyor belt and the catalytic infrared generator above the conveyor belt is 16-20 cm, and the heating time is 60-6000 s.
The quality detection of the grapes specifically comprises the following steps:
1) soluble solid content: the content of soluble solid is determined by NY/T2637-2014 standard,
the larger the value of the content uniformity coefficient of the soluble solid matters is, the better the drying uniformity is, and the calculation formula is as follows:
in the formula, M1jIs the soluble solids content of the jth sample point,oBrix；
expressed as the average soluble solid content, g.g-1(ii) a j represents the number of the different sample points,the value range is 1-9;
2) color difference value: and pouring a proper amount of raisin into a white vessel, and detecting the L, a and b values of the sample by using a color difference meter. The L value represents the brightness of the sample, the a value represents the red-green degree of the sample, and the b value represents the yellow-blue degree of the sample; Δ E represents the color difference value, the greater this value, the greater the change in color of the dried grapes compared to the fresh grapes; the color difference value Δ E is calculated as follows:
in the formula: l is0、a0、b0Respectively, the color value of fresh grape, L*、a*、b*Respectively, the color values of the dried grape products.
The larger the color difference value uniformity coefficient is, the better the drying uniformity is, and the calculation formula is as follows:
in the formula, M2jThe color difference value of the jth sampling point is obtained;
representing the average color difference value; j represents the number of different sampling points, and the value range is 1-9;
3} water content of the product: the water content of the product is determined by a drying method in the national food safety standard GB 5009.3-2016, the larger the uniform coefficient value of the water content of the product is, the better the drying uniformity is, and the calculation formula is as follows:
in the formula, M3jThe water content of the product at the jth sampling point is obtained;
to representAverage product water content; j represents the number of different sampling points, and the value range is 1-9;
4) the total number of bacteria remaining rate: the bactericidal effect is expressed by a logarithmic value of the survival rate of the total number of bacteria, and the total number of colonies is determined by referring to the GB47892-2010 standard;
the larger the value of the uniform coefficient of the total number of bacteria and the better the drying uniformity, the calculation formula is as follows:
in the formula, M4jThe bacterial count survival rate of the jth sampling point is the bacterial count survival rate of the jth sampling point;
represents the average total number of bacteria remaining rate; j represents the number of different sampling points, and the value range is 1-9.
The invention has the beneficial effects that the high-quality raisin product which has consistent product quality and reaches the water content and the bacteria content standards is provided, the product quality is good, no chemical residue is generated, and the method is simple and reliable. Has the following characteristics:
(1) the grape drying and sterilizing treatment is realized by adopting an effective salt solution classification method, a vacuum pulsation drying technology and a catalytic infrared heating technology, and the grape drying and sterilizing treatment device has the advantages of high drying speed, uniform drying, good product quality and simplicity in operation.
(2) Realize the material classification based on the difference of the physical and chemical characteristics of the grapes, in particular the difference of maturity. And (3) distinguishing the content of soluble solids by adopting a salt solution method based on the density difference of the grapes, and further accurately distinguishing the maturity. Compared with the traditional method of distinguishing the maturity of grapes by depending on the size and color of the grapes, the method has the characteristics of simplicity, reliability, high efficiency and the like, and avoids the damage of materials in the material screening and classifying process to a greater extent.
(3) The pretreatment of the fresh grapes is carried out without any chemical reagent except the salt solution. The catalytic infrared drying technology is adopted to carry out surface rapid dehydration on the grapes classified by means of the salt solution, so that the time consumption of the subsequent drying stage is favorably shortened, and the energy consumption is reduced. Compared with the traditional grape drying method, the method has the advantages of nature, greenness and no pollution, and the operation method is simple and easy to understand.
(4) The vacuum pulse drying technology is adopted to quickly dehydrate and dry the classified grapes, and compared with the traditional vacuum drying mode, the vacuum pulse drying method has the advantage of high efficiency; compared with the traditional hot air drying, the method avoids the excessive contact of the materials with oxygen for a long time, and can effectively inhibit the oxidative deterioration of thermosensitive components; and the processed grapes have better quality and better quality consistency.
(5) In the later processing stage, the catalytic infrared drying technology is adopted to sterilize the dried grape product, no chemical reagent pollution is caused, a new way is opened up for sterilizing the dried grape product, and the storage period of the product can be effectively prolonged.
Drawings
FIG. 1 is a flow chart of an embodiment of raisin preparation;
FIG. 2 is a schematic view of the transverse diameter of a grape pip;
FIG. 3 is a schematic diagram of the salt solution method classification;
FIG. 4 is a schematic illustration of a catalytic infrared heating process;
FIG. 5 is a schematic view of a sample collection method.
1-grape grain, 2-transverse diameter, 3-liquid storage tank, 4-low concentration salt solution, 5-high concentration salt solution, 6-catalytic infrared heater, 7-conveying belt, 8-material tray, and 9-sampling point.
Detailed Description
The invention provides a method for making high-quality raisins, which is further described by combining the accompanying drawings and specific implementation examples.
FIG. 1 is a flow chart of an embodiment of raisin preparation; the preparation of the high-quality raisin shown in figure 1 comprises the following steps:
(1) picking fresh 'seedless white' grapes which are not rotten, removing fruit stalks, washing off impurities, and removing grape grains which are extruded, damaged and deformed in the picking and transporting processes;
(2) and (3) grading and screening the particles, namely screening the particles in sequence by adopting 4 layers of vibrating screens, wherein the vibrating screens are made of high-density polyethylene plastics, and the diameters of circular meshes of the vibrating screens are 18 mm, 15 mm, 12 mm and 9mm in sequence. As shown in FIG. 2, the grapes can be divided into materials with diameters of > 18, (15,18], (12,15], (9,12], < 9mm in sequence according to the transverse diameters of the grapes (shown in FIG. 2). As grapes with larger diameters are dried for longer time and grapes with undersize diameters are dried for poorer product phase, the materials with the transverse diameters of (15,18], (12,15], (9, 12) are selected as processing raw materials and are respectively defined as grapes with large, medium and small diameters;
(3) grading is carried out according to the phenomenon that grape particles float or sink in a salt solution, namely, sodium chloride solutions with the concentrations of 120,140, 160 and 180g/L are prepared by utilizing the principle that grape particles with different maturity have different densities, and grading is carried out according to the phenomenon that the grape particles float or sink in the salt solution. As shown in fig. 3, the grapes with the graded sizes are firstly placed in the salt solution with the lowest concentration, the suspended grape particles are fished out and collected according to the floating and sinking phenomena on the grapes, the grapes which sink are fished out and then placed in the salt solution with the next higher concentration, similarly, the grape particles which float up are fished out, the grape samples which sink are fished out and continuously placed in the salt solution with the higher concentration, and the steps are sequentially carried out until the grading of the samples is completed. The material is divided into grapes with salt solution concentration less than 120, (120,140], (140,160], (160,180], > 180g/L, respectively defined as grapes with lower, middle, high and higher ripeness degrees.
(4) Removing the surface moisture of the grapes at all levels obtained in the step (3) by adopting catalytic infrared heating, selecting grapes classified according to size and maturity, placing the grapes on a double-layer conveyor belt as shown in fig. 4, wherein the conveyor belts are different in height, catalytic infrared heating is arranged above the grapes, rolling of the materials in the falling process can realize automatic turning, and the catalytic infrared heating is beneficial to uniform heating of the materials to remove the surface moisture; the speed of the conveyor belt is adjustable, thereby adjusting the sterilization time. The catalytic infrared heating condition is as follows: the temperature of the catalytic infrared generator is 380-420 ℃, the distance between the conveyor belt and the catalytic infrared generator above the conveyor belt is 16-20 cm, and the heating time is 60-6000 s.
(5) Carrying out vacuum pulse drying on the grapes, flatly laying the materials in a single layer, placing the materials in a vacuum box, pumping the materials to a rated vacuum state, setting the drying temperature, and carrying out vacuum drying. And when the vacuum maintaining time is over, switching to a rated normal pressure state, performing normal pressure drying, when the normal pressure maintaining time is over, switching to the vacuum state again, circulating in sequence until the dry basis moisture content of the material is reduced to 0.25 +/-0.05 g/g, and recording the total drying time.
The vacuum pulse drying conditions are as follows: the pressure of the drying chamber in a rated vacuum state is 0-10 kPa, the pressure of the drying chamber in a rated normal pressure state is 95-101 kPa, the drying temperature is 60-85 ℃, the vacuum holding time is 1-15 min, and the normal pressure holding time is 2-10 min.
(6) The dried grapes are subjected to catalytic infrared sterilization and are placed on a double-layer conveyor belt, the conveyor belt is different in height, catalytic infrared heating is arranged above the conveyor belt, automatic turning can be achieved by rolling in the falling process of the materials, and uniform heating sterilization of the materials is facilitated; the speed of the conveying belt is adjustable, and the heating time can be adjusted. The catalytic infrared heating condition is as follows: the temperature of the catalytic infrared generator is 380-420 ℃, the distance between the conveyor belt and the catalytic infrared generator above the conveyor belt is 16-20 cm, and the heating time is 60-6000 s.
(7) And (3) product quality detection, as shown in fig. 5, spreading the articles in a tray, sampling by a nine-point method, respectively detecting the content of soluble solids, the color difference value, the water content of the material (product water content) after drying and 4 physicochemical quality indexes of the total bacteria survival rate, and taking the average value as a final detection result. And calculating the log values of the color difference value, the total bacteria count survival rate, the soluble solid content and the uniform coefficient of the product water content respectively for comparing test results.
(8) And finally, carrying out vacuum packaging. Thereby obtaining the raisin product with the moisture content and the bacteria content reaching the standard and the uniform and consistent product quality.
In steps (4) and (6) of the present embodiment, the temperature, irradiation distance, and treatment time of the infrared radiation plate can be adjusted as needed. The temperature of the infrared radiation plate is high, the irradiation distance is short, and the processing time can be correspondingly shortened.
The specific method for detecting the quality of the grapes is as follows.
Soluble solid content: the soluble solid content was determined using NY/T2637-2014.
The larger the value of the coefficient of uniformity of the content of the soluble solid matters is, the better the drying uniformity is, and the calculation formula is as follows:
in the formula, M1jIs the soluble solids content of the jth sample point,oBrix；
expressed as the average soluble solid content, g.g-1(ii) a j represents the number of different sampling points, and the value range is 1-9;
color difference value: and pouring a proper amount of raisin into a white vessel, and detecting the L, a and b values of the sample by using a color difference meter. The L value represents the brightness of the sample, the a value represents the red-green degree of the sample, and the b value represents the yellow-blue degree of the sample. Δ E represents the color difference value, and the larger the value, the larger the change in color of the dried grapes compared to the fresh grapes. The color difference value Δ E is calculated as follows:
in the formula: l is0、a0、b0Respectively, the color value of fresh grape, L*、a*、b*Respectively, the color values of the dried grape products.
The larger the color difference value uniformity coefficient is, the better the drying uniformity is, and the calculation formula is as follows:
in the formula, M2jThe color difference value of the jth sampling point is obtained;
representing the average color difference value; j represents the number of different sampling points, and the value range is 1-9;
③ the water content of the product: the water content of the product is measured by a drying method in the national food safety standard GB 5009.3-2016.
The larger the value of the uniform coefficient of the water content of the product is, the better the drying uniformity is, and the calculation formula is as follows:
in the formula, M3jThe water content of the product at the jth sampling point is obtained;
representing the average product water content; j represents the number of different sampling points, and the value range is 1-9;
fourthly, the residual rate of the total number of bacteria: the bactericidal effect is expressed by a logarithmic value of the survival rate of the total number of bacteria. The total number of colonies was determined according to the GB47892-2010 standard.
The larger the value of the uniform coefficient of the total number of bacteria and the better the drying uniformity, the calculation formula is as follows:
in the formula, M4jThe bacterial count survival rate of the jth sampling point is the bacterial count survival rate of the jth sampling point;
represents the average total number of bacteria remaining rate; j represents the number of different sampling points, and the value range is 1-9;
comparative example 1
Picking fresh 'seedless white' grapes which are not rotten, removing fruit stalks, washing off impurities, and removing grape grains which are extruded, damaged and deformed in the picking and transporting processes;
② directly placing the cleaned grapes in a cool and ventilated place for drying in the shade until the moisture content of the dry material is reduced to 0.25 +/-0.05 g/g. And recording the total drying time, sampling and measuring the color difference value, the logarithm value of the total bacterial count residual-activity rate, the content of soluble solids and the water content of the product, and calculating the logarithm values of the color difference value, the total bacterial count residual-activity rate and the uniformity coefficient of the content of the soluble solids and the water content of the product.
Comparative example 2
Picking fresh 'seedless white' grapes which are not rotten, removing fruit stalks, washing off impurities, and removing grape grains which are extruded, damaged and deformed in the picking and transporting processes;
② taking the cleaned grapes, directly placing the cleaned grapes in a hot air oven at 75 ℃ for drying until the moisture content of the dry material is reduced to 0.25 +/-0.05 g/g. And recording the total drying time, sampling and measuring the color difference value, the logarithm value of the total bacterial count residual activity rate, the content of soluble solid matters and the water content of the product, and calculating the logarithm values of the color difference value, the total bacterial count residual activity rate and the uniformity coefficient of the content of the soluble solid matters and the water content of the product.
Example 1
Picking fresh 'seedless white' grapes which are not rotten, removing fruit stalks, washing off impurities, and removing grape grains which are extruded, damaged and deformed in the picking and transporting processes;
sequentially screening by adopting 4 layers of vibrating screens, wherein the vibrating screens are made of high-density polyethylene plastics, the diameters of circular meshes of the vibrating screens are sequentially 18 mm, 15 mm, 12 mm and 9mm, and as shown in figure 2, the vibrating screens can be sequentially divided into materials with the diameters larger than 18, (15,18], (12,15], (9, 12) and less than 9mm according to the transverse diameter of the grapes, and the medium-diameter grapes with the transverse diameter of (12,15] mm are selected as raw materials;
thirdly, preparing sodium chloride solution with the concentration of 120 g/L, 140 g/L, 160 g/L and 180g/L by utilizing the principle that grape particles with different maturity have different densities, and classifying according to the floating or sinking phenomenon of the grape particles in the salt solution. As shown in fig. 3, the grapes with medium diameter are firstly placed in the salt solution with lowest concentration, the suspended grape particles are fished out and collected according to the floating and sinking phenomenon on the grapes, the grapes which sink are fished out and then placed in the salt solution with higher concentration next, similarly, the grape particles which float up are fished out, the grape samples which sink are fished out and continuously placed in the salt solution with higher concentration, and the steps are sequentially carried out until the samples are classified. The material is divided into grapes with salt solution concentration less than 120, (120,140], (140,160], (160,180], > 180g/L, which are respectively defined as grapes with lower, low, medium, high and high ripeness, then grapes with medium ripeness are selected for standby.
Selecting grapes with medium diameter and medium maturity, placing the grapes on a double-layer conveyor belt, wherein the conveyor belt is different in height, catalytic infrared heating is arranged above the grapes, rolling of the materials in the falling process can realize automatic turning, and the grapes are beneficial to uniform heating of the materials to remove surface moisture; the conveyor belt speed is adjustable to adjust the heating time. The catalytic infrared heating condition is as follows: the temperature of the catalytic infrared generator is 400 ℃, the distance between the conveyor belt and the catalytic infrared generator above the conveyor belt is 18cm, and the heating time is 300 s.
Fifthly, carrying out vacuum pulse drying on the grapes, flatly laying the materials in a single layer, placing the materials in a vacuum box, pumping the materials to a rated vacuum state of 5 +/-2 kPa, setting the drying temperature to be 75 ℃, and carrying out vacuum drying. Setting vacuum holding time for 10min, switching to a rated normal pressure state of 99 +/-2 kPa for normal pressure drying when the vacuum holding time is over, setting normal pressure holding time for 4min, switching to the rated vacuum state again when the normal pressure holding time is over, and circulating in sequence.
Stop until the dry basis moisture content of the material decreased to 0.25 + -0.05 g/g and record the total drying time.
Sixthly, carrying out catalytic infrared sterilization on the dried grapes, and placing the grapes on a double-layer conveyor belt, wherein the positions of the conveyor belt are different, and catalytic infrared heating is arranged above the conveyor belt. The catalytic infrared heating condition is as follows: the temperature of the catalytic infrared generator is 400 ℃, the distance between the conveyor belt and the catalytic infrared generator above is 18cm, and the heating time is 240 s.
As shown in fig. 5, the articles are spread in the tray, and sampled by the nine-point method, and the content of soluble solids, the color difference value, the water content of the material (product water content) at the end of drying, and the residual rate of total bacteria are detected by 4 physicochemical quality indexes, and the average value is taken as the final detection result. And calculating the log values of the color difference value, the total bacteria number survival rate and the uniformity coefficients of the soluble solid content and the water content of the product respectively for comparing test results, wherein the specific results are shown in Table 1.
Example 2
Picking fresh 'seedless white' grapes which are not rotten, removing fruit stalks, washing off impurities, and removing grape grains which are extruded, damaged and deformed in the picking and transporting processes;
sequentially screening by adopting 4 layers of vibrating screens, wherein the vibrating screens are made of high-density polyethylene plastics, the diameters of circular meshes of the vibrating screens are sequentially 18 mm, 15 mm, 12 mm and 9mm, and as shown in figure 2, the vibrating screens can be sequentially divided into materials with the diameters of more than 18, (15,18], (12,15], (9, 12) and less than 9mm according to the transverse diameter of the grapes, and small-diameter grapes with the transverse diameter of (9, 12) mm are selected as raw materials;
thirdly, preparing sodium chloride solution with the concentration of 120 g/L, 140 g/L, 160 g/L and 180g/L by utilizing the principle that grape particles with different maturity have different densities, and classifying according to the floating or sinking phenomenon of the grape particles in the salt solution. As shown in fig. 3, the grapes with medium diameter are firstly placed in the salt solution with lowest concentration, the suspended grape particles are fished out and collected according to the floating and sinking phenomenon on the grapes, the grapes which sink are fished out and then placed in the salt solution with higher concentration next, similarly, the grape particles which float up are fished out, the grape samples which sink are fished out and continuously placed in the salt solution with higher concentration, and the steps are sequentially carried out until the samples are classified. The material is divided into grapes with salt solution concentration less than 120, (120,140], (140,160], (160,180], > 180g/L, respectively defined as grapes with lower, low, medium, high and higher ripeness, then grapes with higher ripeness are selected for standby.
Selecting grapes 1 with small diameter and high maturity, placing the grapes on a double-layer conveyor belt 3, wherein the positions of the conveyor belt 3 are different, a catalytic infrared heater 2 is arranged above the grapes, and the grapes 1 can be automatically turned over when rolling in the falling process, so that the grapes can be uniformly heated to remove surface moisture; the conveyor belt speed is adjustable to adjust the heating time. The catalytic infrared heating condition is as follows: the temperature of the catalytic infrared generator is 420 ℃, the distance between the conveyor belt and the catalytic infrared generator above the conveyor belt is 16cm, and the heating time is 180 s.
Fifthly, carrying out vacuum pulse drying on the grapes, flatly laying the grapes in a single layer mode, placing the grapes in a vacuum box, pumping the grapes to a rated vacuum state of 5 +/-2 kPa, setting the drying temperature to be 85 ℃, and carrying out vacuum drying. Setting vacuum holding time for 10min, switching to a rated normal pressure state of 99 +/-2 kPa for normal pressure drying when the vacuum holding time is over, setting normal pressure holding time for 4min, switching to the rated vacuum state again when the normal pressure holding time is over, and circulating in sequence.
Stop until the dry basis moisture content of the material decreased to 0.25 + -0.05 g/g and record the total drying time.
Sixthly, carrying out catalytic infrared sterilization on the dried grapes, and placing the grapes on a double-layer conveyor belt, wherein the positions of the conveyor belt are different, and catalytic infrared heating is arranged above the conveyor belt. The catalytic infrared heating condition is as follows: the temperature of the catalytic infrared generator is 420 ℃, the distance between the conveyor belt and the catalytic infrared generator above the conveyor belt is 16cm, and the heating time is 180 s.
As shown in fig. 5, the grapes 1 are flatly placed in the tray 4, sampling is performed by a nine-point method, 4 physicochemical quality indexes, namely, the content of soluble solids, the color difference value, the water content of the material (the water content of the product) at the end of drying and the residual rate of the total number of bacteria, are respectively detected, and the average value is taken as the final detection result. And calculating the log values of the color difference value, the total bacteria number survival rate and the uniformity coefficients of the soluble solid content and the water content of the product respectively for comparing test results, wherein the specific results are shown in Table 1.
As can be seen from the results in Table 1, the drying time of the examples 1 and 2 of the present invention is significantly smaller than the logarithmic value of the survival rate of the total number of bacteria in the comparative examples 1 and 2, and the quality is superior. The color difference value, the log value of the total number of bacteria and the survival rate, the content of soluble solid matters and the uniformity coefficient of the water content index of the product are far superior to those of naturally aired and hot air dried raisins, and the uniformity of the quality is better.
Table 1 comparison of comparative examples and examples
Claims (7)
1. A method for making high-quality raisins is characterized by comprising the following steps:
(1) selecting raw materials, selecting fresh 'seedless white' grapes which are not rotten, removing fruit stalks, washing off impurities, and removing grape grains which are extruded, damaged and deformed in the picking and transporting processes;
(2) grading and screening the particles, namely screening the particles in sequence by adopting 4 layers of vibrating screens, and storing the grape raw materials with large, medium and small transverse diameters of the grapes;
(3) grading according to the phenomenon that grape particles float or sink in a salt solution, namely, preparing sodium chloride solutions with the concentrations of 120,140, 160 and 180g/L by utilizing the principle that grape particles with different maturity have different densities, placing the grapes graded in the step (2) in the salt solution with the lowest concentration at first, fishing out suspended grape particles and collecting the grape particles according to the phenomenon that the grapes float and sink, fishing out the grape particles which sink and placing the grape particles in the salt solution with higher concentration at next time, and fishing out the grape particles which float upwards, fishing out the grape particles which sink, placing the grape sample which sink in the salt solution with higher concentration continuously and sequentially carrying out the steps until the grading of the sample is finished. The material is divided into grapes with salt solution concentration less than 120, (120,140], (140,160], (160,180], > 180g/L, respectively defined as grapes with lower, middle, high and higher ripeness degrees.
(4) Removing the surface moisture of each level of grapes obtained in the step (3) by adopting catalytic infrared heating, selecting grapes classified in size and maturity, placing the grapes on a double-layer conveyor belt, enabling the conveyor belts to be different in height, installing catalytic infrared heating above the conveyor belts, enabling rolling in the falling process of the materials to realize automatic turning, and facilitating uniform heating of the materials to remove the surface moisture; the speed of the conveyor belt is adjustable, so that the sterilization time is adjusted;
(5) performing vacuum pulse drying on the grapes with the surface moisture removed in the step (4), flatly laying the grapes with the surface moisture removed in a single layer mode in a vacuum box, pumping to a rated vacuum state, setting a drying temperature, and performing vacuum drying; when the vacuum maintaining time is over, switching to a rated normal pressure state, performing normal pressure drying, when the normal pressure maintaining time is over, switching to a vacuum state again, and circulating in sequence; stop until the dry basis moisture content of the material decreased to 0.25 + -0.05 g/g and record the total drying time.
(6) The dried grapes are subjected to catalytic infrared sterilization and are placed on a double-layer conveyor belt, the conveyor belt is different in height, catalytic infrared heating is arranged above the conveyor belt, automatic turning can be achieved by rolling in the falling process of the materials, and uniform heating sterilization of the materials is facilitated; the speed of the conveying belt is adjustable, and the heating time can be adjusted.
(7) And (3) product quality detection, namely sampling the grapes dried and sterilized in the step (6) by adopting a nine-point method, respectively detecting 4 physicochemical quality indexes of the soluble solid content, the color difference value, the product water content and the total bacteria residual activity rate after the drying is finished, and taking the average value as a final detection result. Respectively calculating logarithmic values of the color difference value, the total bacteria number survival rate, the soluble solid content and the uniform coefficient of the product water content for comparing test results;
(8) and finally, carrying out vacuum packaging. Thereby obtaining the raisin product with the moisture content and the bacteria content reaching the standard and the uniform and consistent product quality.
2. The method for making high-quality raisins according to claim 1, wherein the vibrating screen is made of high-density polyethylene plastic, and the diameter of the circular mesh of the vibrating screen is 18 mm, 15 mm, 12 mm and 9mm in sequence.
3. A method for preparing high-quality dried grapes according to claim 1, wherein the grape raw materials with large, medium and small transverse diameters are selected from grape granules with diameters > 18, 15-18, 12-15, 9-12 and < 9mm according to the diameters of the sieve meshes of 18, 15, 12 and 9 mm.
4. The method for preparing high-quality raisin according to claim 1, wherein the catalytic infrared heating condition is as follows: the temperature of the catalytic infrared generator is 380-420 ℃, the distance between the conveyor belt and the catalytic infrared generator above the conveyor belt is 16-20 cm, and the heating time is 60-6000 s.
5. The method for preparing high-quality raisins according to claim 1, wherein the vacuum pulse drying conditions are as follows: the pressure of the drying chamber in a rated vacuum state is 0-10 kPa, the pressure of the drying chamber in a rated normal pressure state is 95-101 kPa, the drying temperature is 60-85 ℃, the vacuum holding time is 1-15 min, and the normal pressure holding time is 2-10 min.
6. The method for preparing high-quality raisin according to claim 1, wherein the catalytic infrared heating condition is as follows: the temperature of the catalytic infrared generator is 380-420 ℃, the distance between the conveyor belt and the catalytic infrared generator above the conveyor belt is 16-20 cm, and the heating time is 60-6000 s.
7. The method for making high-quality raisins according to claim 1, wherein the quality detection of the grapes specifically comprises:
1) soluble solid content: the content of soluble solid is determined by NY/T2637-2014 standard,
the larger the value of the uniformity coefficient of the soluble solid content is, the better the drying uniformity is, and the calculation formula is as follows:
in the formula, M1jIs the soluble solids content of the jth sample point,oBrix；
expressed as the average soluble solid content, g.g-1(ii) a j represents the number of different sampling points, and the value range is 1-9;
2) color difference value: and pouring a proper amount of raisin into a white vessel, and detecting the L, a and b values of the sample by using a color difference meter. The L value represents the brightness of the sample, the a value represents the red-green degree of the sample, and the b value represents the yellow-blue degree of the sample; Δ E represents the color difference value, the greater this value, the greater the change in color of the dried grapes compared to the fresh grapes; the color difference value Δ E is calculated as follows:
in the formula: l is0、a0、b0Respectively, the color value of fresh grape, L*、a*、b*Respectively, the color values of the dried grape products.
The larger the value of the uniformity coefficient of the color difference value is, the better the drying uniformity is, and the calculation formula is as follows:
in the formula, M2jIs the color difference value of the jth sampling point;
representing the average color difference value; j represents the number of different sampling points, and the value range is 1-9;
3} water content of product: the water content of the product is determined by a drying method in the national food safety standard GB 5009.3-2016, the larger the uniform coefficient value of the water content of the product is, the better the drying uniformity is, and the calculation formula is as follows:
in the formula, M3jThe water content of the product at the jth sampling point is obtained;
representing the average product water content; j represents the number of different sampling points, and the value range is 1-9;
4) the total number of bacteria remaining rate: the bactericidal effect is expressed by a logarithmic value of the survival rate of the total number of bacteria, and the total number of colonies is determined by referring to the GB47892-2010 standard;
the larger the value of the uniform coefficient of the total number of bacteria and the better the drying uniformity, the calculation formula is as follows:
in the formula, M4jThe ratio of the total number of bacteria remaining at the jth sampling point;
represents the average total number of bacteria remaining rate; j represents the number of different sampling points, and the value range is 1-9.
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| CN101690609A (en) * | 2009-10-23 | 2010-04-07 | 中国农业大学 | A method for processing green raisin and preserved grape |
| CN103028555A (en) * | 2012-12-03 | 2013-04-10 | 天津理工大学 | Raisin color sorting detection method based on HSI (Hue-Saturation-Intensity) color features |
| CN111567828A (en) * | 2020-06-02 | 2020-08-25 | 山东省海通食品有限公司 | Raisin cleaning device and raisin cleaning method thereof |
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| CN101690609A (en) * | 2009-10-23 | 2010-04-07 | 中国农业大学 | A method for processing green raisin and preserved grape |
| CN103028555A (en) * | 2012-12-03 | 2013-04-10 | 天津理工大学 | Raisin color sorting detection method based on HSI (Hue-Saturation-Intensity) color features |
| CN111567828A (en) * | 2020-06-02 | 2020-08-25 | 山东省海通食品有限公司 | Raisin cleaning device and raisin cleaning method thereof |
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