Technology for three-dimensional microwave air-jet drying of persimmon slices

Abstract

The present invention relates to a method for three-dimensional microwave air-jet drying of persimmon slices, comprising steps of grading and cleaning, slicing, microwave heating, steam de-astringency, hot-air reverse primary drying, negative-pressure intermittent secondary drying, cooling and packaging. In the present invention, high-temperature (60-70° C.) high-pressure annularly sprayed citric acid and 40% alcohol vapor (rotating at 360°) are adopted to remove astringency of persimmons, wherein high temperature causes more intense Brownian motion of liquid molecules; high pressure improves permeation and diffusion speed of de-astringency liquid in the persimmon slices; citric acid plays a membrane breaking role on persimmon cell membranes; and 40% alcohol vapor is allowed to rapidly diffuse into cells, so that tannin is polymerized into insoluble gel from a soluble state, thereby achieving a uniform and rapid de-astringency effect.

Claims

1. A method for three-dimensional microwave air-jet drying of persimmon slices, comprising the following steps: (1) selecting and cleaning fresh, complete and pest-free persimmons; (2) peeling the persimmons and removing pedicels by a manual peeling method; (3) vertically cutting each peeled persimmon into two halves first, and then slicing with a water jet cutter to obtain 4-5 mm thick persimmon slices, wherein an anti-browning aqueous solution is used for slicing, the anti-browning aqueous solution contains an aqueous solution prepared from 0.5% NaCl+1% vitamin C+0.5% citric acid, and persimmon pieces are cut with the water jet cutter formed by a pressurized gun head; (4) spreading the persimmon slices on a mesh tray, placing the mesh tray in a microwave tunnel oven for 3 min at 1500W; (5) using 10% citric acid and 40% ethanol as de-astringency liquid for de-astringency at temperature of 60-70° C. and pressure of 0.3-0.4 MPa, annularly spraying de-astringency liquid vapor at 3600 around the persimmon slices at a rotation speed of 2-3 rad/min in a first rotary direction, and performing de-astringency operation for 8-10 min; (6) performing hot-air rotary drying on the persimmon slices for 35-40 min at the rotation speed of 2-3 rad/min in a second rotary direction which is reverse to the first rotary direction, wherein the temperature of the hot air is 70-80° C.; (7) placing the persimmon slices in the microwave tunnel oven again, evacuating the microwave tunnel oven, and drying the persimmon slices for 15 min at 1000W and a vacuum degree of −0.10 to −0.12 MPa until the moisture content of each persimmon slice is less than 10%; (8) taking out the dried persimmon slices, cooling the dried persimmon slices, and then performing nitrogen-filled packaging to obtain packaged dried persimmon slices.

2. The method for three-dimensional microwave air-jet drying of persimmon slices according to claim 1, wherein the cutting speed is 230-350 mm/min; the diameter of a water nozzle is 0.46 mm; the diameter of an abrasive nozzle is 1.6 mm; and the jet pressure is 210 MPa.

Description

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

(1) The present invention will be further described in detail with reference to accompanying drawings through specific embodiments. The following embodiments are only illustrative and not restrictive, and shall not be used to limit the protection scope of the present invention.

(2) With the continuous expansion of persimmon planting areas in China, the yield of persimmons is constantly increased. However, the persimmons are relatively high in moisture content and not easy to store. The persimmons in the market are mainly fresh-eaten and processed into dried persimmons, so that the persimmons are single in variety and cannot satisfy taste and needs of consumers. Therefore, it is urgent to perform profound processing on the persimmons. Persimmon slices are loved and sought after by the consumers due to rich nutrients, excellent taste, long storage period and other advantages and characteristics. However, the production of the dried persimmon slices is mostly limited in family kitchens; and the industrial production starts late. The purposes of the present invention are to provide a set of rapid batch drying method for persimmon slices with good shrinkage uniformity and without browning and solve the critical technical problems.

(3) A method for three-dimensional microwave air-jet drying of persimmon slices comprises the following steps:

(4) (1) Grading and cleaning: selecting and cleaning fresh, complete and pest-free hard persimmons;

(5) (2) Peeling: peeling the hard persimmons and removing pedicels by a manual peeling method;

(6) (3) Slicing: vertically cutting each peeled hard persimmon into two halves first, and then slicing with a water jet cutter, wherein the persimmon slices are preferably 4-5 mm thick; to prevent the fruits from oxidative browning in contact with air, color protection measures should be taken in the slicing process; therefore, ultra-high-pressure water-jet cutting technology is adopted to cut the hard persimmons; a broad-spectrum natural anti-browning aqueous solution is prepared, containing an aqueous solution prepared from 0.5% NaCl+1% vitamin C+0.5% citric acid; the water jet cutter formed by a high-pressure micro-gun head is adopted to cut persimmon pieces; the solution can be recycled; the cutting thickness is 5-6 mm; the cutting speed is 230-350 mm/min; the diameter of a water nozzle is 0.46 mm; the diameter of an abrasive nozzle is 1.6 mm; the jet pressure is 210 MPa; and a layer of water film is formed on cut surfaces of the fruit pieces after completing the cutting, wherein the water film has effects of oxygen isolation and color protection, and can effectively inhibit surface browning.

(7) An ultra-high-pressure water jet cutter cutting technology is adopted to slice the persimmons, thereby inhibiting browning and maintaining cell integrity and nutrition; high-pressure water is adopted to clean and grind the cut surfaces while cutting; in addition, a natural anti-browning aqueous solution is used to replace clear water to form the water jet cutter through the high-pressure micro-gun head, so that the layer of water film is formed on the cut surfaces of the fruit pieces after completing the cutting; and the water film has effects of oxygen isolation and color protection, and can effectively inhibit surface browning.

(8) (4) Microwave heating: spreading the persimmon slices on a mesh-like tray, placing the mesh-like tray in a microwave tunnel, and rapidly heating interiors and exteriors of the persimmons for 3 min under a microwave power of 1500 W;

(9) (5) Vapor de-astringency: using 10% citric acid and 40% ethanol as de-astringency liquid, annularly spraying de-astringency liquid vapor (rotating at 360° at a rotation speed of 2-3 rad/min) at high temperature (60-70° C.) and high pressure (0.3-0.4 MPa), and performing de-astringency operation for 8-10 min.

(10) A 360° rotary spraying de-astringency technology (gas fumigation) of mixed vapor of high-temperature high-pressure citric acid and 40% alcohol is used to improve the diffusion and permeation effect of the de-astringency liquid, greatly improve the de-astringency uniformity and shorten the operation time of de-astringency.

(11) (6) Hot-air reverse primary drying: performing hot-air reverse 360° rotary drying for 35-40 min at the rotation speed of 2-3 rad/min, wherein the temperature of hot air is 70-80° C.

(12) A microwave tunnel drying way is adopted to increase the internal temperature of the persimmons and accelerate the internal moisture migration; the external heating air (60-70° C.) is used for reversely rotating and drying at 360° to increase the surface moisture vaporization rate and realize relatively uniform internal and external moisture loss, so that the persimmons have good shrinkage uniformity and high apparent quality.

(13) (7) Negative-pressure intermittent secondary drying: placing the persimmon slices in the device with ultrasonic waves again, evacuating the device, and performing intermittent drying for 15 min at a vacuum degree of −0.10 to −0.12 MPa and a microwave power of 1000 W until the moisture content is less than 10%.

(14) A microwave tunnel way is adopted to heat and dry; hot air and mixed vapor of high-temperature citric acid and 40% alcohol move 360° towards each other to form convective vortex and accelerate moisture loss; a three-phase coupled drying way is adopted to greatly improve the drying efficiency and greatly shorten the drying time.

(15) The microwave tunnel drying and the hot-air reverse 360° rotary drying are adopted to improve the persimmon drying uniformity and correspondingly improve the rehydration property.

(16) (8) Cooling and packaging: taking out the dried persimmon slices, cooling to room temperature, and then performing nitrogen-filled packaging to obtain dried persimmon slices.