CN101156623B

CN101156623B - Combined drying method for preparing dehydrated vegetable and fruit

Info

Publication number: CN101156623B
Application number: CN2007101355059A
Authority: CN
Inventors: 崔政伟
Original assignee: Jiangnan University
Current assignee: Jiangnan University
Priority date: 2007-11-16
Filing date: 2007-11-16
Publication date: 2010-07-21
Anticipated expiration: 2027-11-16
Also published as: CN101156623A

Abstract

The invention relates to a dehydrating and drying method for the top-grade vegetable and fruit. After being sliced, the vegetable and the fruit are placed in a microwave vacuum dryer for being dried, the exerting microwave power density is between 0.5 w/g and 1.2 w/g (watt/gram), the vacuum rate is between 2.5KPa and 4.5KPa (remaining pressure), the materials to be dried can do reciprocating movement along with the drying dish in the microwave vacuum dryer. After being dehydrated by about 40-50 percent of the total moisture by the microwave vacuum drying, the materials are taken out and positioned on a stainless steel dish and then are positioned in a freezing dryer, and are frozen and sublimed dry under 25 DEG C below zero, the drying time is about 7-10 hours, and the moisture is loweredto the safe moisture of 6-7 percent. The preserving of the color, the scent, the taste, and the nutritious components of the dehydrated vegetable and fruit which are produced by the invention are quite approximate to that of the single freezing dried products, the volume is 60-70 percent of the volume of the single freezing dried products, the appearance and the organic structure are approximate too, the drying cost is low, and the energy can be saved by 40 percent above.

Description

The Aassociation drying of preparation dehydrated vegetables and fruit

Technical field

The present invention relates to food, processing of farm products field, particularly relate to the dehydrating processing method of fruit, vegetables.

Background technology

In numerous drying means, heated-air drying is owing to the baking temperature height, and drying time is long, and dried food quality is relatively poor, and change color is big, and the loss of color, smell and taste, nutrient is big, the institutional framework hardening, and rehydration is poor; Though traditional vacuum drying baking temperature is lower, because convection heat transfer' heat-transfer by convection exists hardly in the hothouse, but based on the heat conduction, so heat transfer rate is slow, drying time is still long, and the reservation of color, smell and taste and nutrition still has certain limit, institutional framework is hardening also, and rehydration is also poor; Cryodesiccated dry mass is best, and it basically can the original color of retaining food product and nutritional labeling or biologically active, and the profile of dry back product is constant substantially, and institutional framework is cellular, and rehydration is good.In food processings such as high-grade dehydrated vegetables, fruit, drying process is the key of decision product quality, and at present, high-grade dehydrated fruits and vegetables goods all are to adopt freeze drying process to produce, and traditional various drying processes can't be produced high-quality dehydrated fruits and vegetables.But freeze drying is apparatus expensive not only, and the operating cost height, need keep-25 ℃ low temperature, the high vacuum of 0.5Kpa, and about 20 hours drying times, production capacity is also limited, so production cost of products is very high.

Summary of the invention

The purpose of this invention is to provide a kind of new preparation dehydrated vegetables and the Aassociation drying of fruit, use the color, smell and taste and the nutrition of the product of this method drying, particularly mode of appearance and pure cryodesiccated vegetables and fruit are all very approaching, but total drying cost is more much lower than freeze drying, compare with pure freeze drying fruits and vegetables, can save energy more than 40%.

The objective of the invention is to realize by following technical scheme.

A kind of Aassociation drying for preparing dehydrated vegetables and fruit is characterized in that:

A, microwave drying: the section of vegetables and fruit is placed the microwave drying dish, carry out drying in the micro-wave vacuum device, the Microwave Power Density that applies is between 0.5～1.2 watt/gram, and vacuum is between 25～45Kpa; Slough in vegetables and the fruit 40～50% total moisture, form the partial desiccation material;

This moment, the volume of dried material was about 60～70% of original volume, did not produce buckling deformation, stopped micro-wave vacuum then;

B, freeze drying: the partial desiccation material that from the micro-wave vacuum device, takes out, put into freeze-dryer in the freeze drying dish of packing into, under-25 ℃ temperature, freeze fully; The lyophilization in freeze-dryer of material after freezing, about 7～10 hours of drying time, moisture is promptly reduced to 6～7% safe moisture, forms dehydrated vegetables and fruit.

The slice thickness of vegetables and fruit is less than 10mm.Described microwave drying dish is made by tetrafluoroethene or virgin pp material.Described freeze drying dish is made by stainless steel.

When carrying out microwave drying, vegetables to be dried and fruit rotate in the micro-wave vacuum device or move back and forth, to eliminate the microwave focus that produces in the dry run.

The microwave drying cost that microwave system combines with vacuum system is more much lower than freeze drying, microwave vacuum drying technology combines the advantage of microwave and vacuum, promptly both reduced baking temperature, accelerated rate of drying again, have fast, characteristics such as efficient, low temperature, baking temperature can be controlled in 25～45 ℃ the scope, can keep the original color, smell and taste of material such as the food that is dried preferably, the loss of thermal sensitivity nutritions such as vitamin or active ingredient seldom, can obtain dry products quality preferably, drying cost is more much lower than freeze drying.But the product of this technology drying has bigger distortion at the later stage of drying product, with lyophilisation product big gap is arranged on mode of appearance.

The specific embodiment

By the following examples, the invention will be further described.

Embodiment 1:

Carrot is cut into the thick sheet of 6mm, get 2kg carrot slice thin layer and place the tetrafluoroethene dish, the micro-wave vacuum device of putting into microwave output power and be 2KW carries out drying, vacuum is 3.0Kpa (residual voltage), dry 16 minutes, sloughed 712g water, promptly removed in the raw sample 40.5% moisture (fresh carrot moisture about 88%, be total to moisture 1760g), sample carries out freeze drying 10 hours after taking out again, and the water content of taking out the back product is 6.4% (wet basis), and measuring its volume is 68.6% of pure freeze drying example, the retention rate of measuring carrotene is 97.1%, and the retention rate of pure freeze drying example carrotene is 98.5%.So it is very approaching to use the quality of the quality of carrot slice of this combined method preparation and pure freeze drying carrot slice, difference is also very little in appearance.

Embodiment 2:

Be cut into the thick thin slice of 3～5mm behind the apple peel, get 2kg apple flakes thin layer and place the tetrafluoroethene dish, the micro-wave vacuum device of putting into microwave output power and be 2KW carries out drying, vacuum is 3.0Kpa (residual voltage), dry 20 minutes, sloughed 910g water, promptly removed in the raw sample 50.5% moisture (fresh apple moisture about 90%, be total to moisture 1800g), sample carries out freeze drying 10 hours after taking out again, and the water content of taking out the back product is 6.9% (wet basis), and measuring its volume is 62.2% of pure freeze drying example, measuring ascorbic retention rate is 94.6%, and the ascorbic retention rate of pure freeze drying example is 97.4%.So it is very approaching to use the quality of the quality of apple flakes of this combined method preparation and pure freeze drying apple flakes, the color of product also difference is very little.

Claims

1. Aassociation drying for preparing dehydrated vegetables and fruit is characterized in that:

A, microwave drying: the section of vegetables and fruit is placed the microwave drying dish, carry out drying in the micro-wave vacuum device, the Microwave Power Density that applies is between 0.5～1.2 watt/gram, and vacuum is 3.0Kpa; Slough in vegetables and the fruit 40～50% total moisture, form the partial desiccation material;

2. prepare the Aassociation drying of dehydrated vegetables and fruit according to claim 1, it is characterized in that: the slice thickness of vegetables and fruit is less than 10mm.

3. prepare the Aassociation drying of dehydrated vegetables and fruit according to claim 1, it is characterized in that: described microwave drying dish is made by tetrafluoroethene or virgin pp material.

4. prepare the Aassociation drying of dehydrated vegetables and fruit according to claim 1, it is characterized in that: described freeze drying dish is made by stainless steel.

5. the Aassociation drying for preparing dehydrated vegetables and fruit according to claim 1, it is characterized in that: when carrying out microwave drying, vegetables to be dried and fruit rotate in the micro-wave vacuum device or move back and forth, to eliminate the microwave focus that produces in the dry run.