※基础研究 食品科学 2016, Vol.37, No.23 57

Vacuum Freezing Properties of Blanched Apple Slices

WANG Haiou, FU Qingquan, CHEN Shoujiang, WANG Rongrong, ZHANG Wei, YANG Ping(School of Food Science, Nanjing Xiaozhuang University, Nanjing 211171, China)

Abstract: The vacuum freezing properties of blanched apple slices were investigated by comparing with traditional refrigerator freezing. Results showed that after 40 min vacuum freezing, a mass loss of 27.5% and the lowest frozen temperature of -27.6 ℃ were achieved in apple slices pretreated by blanching, while a mass loss of 22.9% and the lowest

frozen temperature of -26.5 ℃ were obtained in non-blanched apple slices. The total process of vacuum freezing was divided into low pressure flash evaporation stage, ice crystal formation stage and deep freezing stage. Vacuum freezing caused less microstructural changes and less significant cell disruption and contributed to smaller thawing loss and weaker relative electrical conductivity in frozen-thawed apple slices in contrast to refrigerator freezing. Blanching pretreatment before freezing caused more severe damage to cell microstructure in apple slices than non-blanching pretreatment, resulting in a significant increase in thawing loss and relative electrical conductivity in frozen-thawed apple slices.Key words: vacuum freezing; blanching pretreatment; apple slices; micro-structure

热烫处理苹果片真空冻结特性

王海鸥，扶庆权，陈守江，王蓉蓉，张 伟，杨 平

（南京晓庄学院食品科学学院，江苏 南京 211171）

摘  要：本研究与传统冰箱冷冻相比较，研究了热烫处理苹果片的真空冻结特性。真空冻结40 min后，经热烫处理

的苹果片冻结最低温度达－27.6 ℃，质量损失为27.5%，而未经热烫处理的苹果片的冻结最低温度和质量损失分别

为－26.5 ℃、22.9%。依据温度变化，苹果片真空冻结过程可分为：减压闪发段、冰晶形成段、深层冻结段。相对

于冰箱冷冻而言，真空冻结苹果片对组织微观结构改变小，冻融后汁液流失率低，电导率低，另外，冷冻前热烫处

理会引起更大的组织结构损坏，显著增加冻融后的汁液流失率和电导率。

关键词：真空冻结；热烫处理；苹果片；微观结构

DOI:10.7506/spkx1002-6630-201623010中图分类号：TS255.3 文献标志码：A 文章编号：1002-6630（2016）23-0057-07

引文格式：

WANG Haiou, FU Qingquan, CHEN Shoujiang, et al. Vacuum freezing properties of blanched apple slices[J]. 食品科学,

2016, 37(23): 57-63. DOI:10.7506/spkx1002-6630-201623010. http://www.spkx.net.cn

WANG Haiou, FU Qingquan, CHEN Shoujiang, et al. Vacuum freezing properties of blanched apple slices[J]. Food Science,

2016, 37(23): 57-63. (in English with Chinese abstract) DOI:10.7506/spkx1002-6630-201623010. http://www.spkx.net.cn

收稿日期：2016-07-24

基金项目：国家自然科学基金青年科学基金项目（31301592）；常州市科技支撑计划项目（CE20152017）；

江苏省教育厅自然科学基金项目（15KJB550008）；南京晓庄学院人才引进项目（2013xzrc04）

作者简介：王海鸥（1978—），男，副教授，博士，主要从事食品冷冻与干燥加工技术研究。E-mail：who1978@163.com

Freezing has become one of the most important unit

operations in food processing and preservation[1]. And it is the

necessary process for food vacuum freeze-drying[2]. Usually,

freezing consists of three stages[3-4]: precooling stage, phase

transition stage and tempering stage, during which the

sensible and latent heat from food product are removed by the

traditional refrigerator cooling system. As a very effective and

clean cooling technology, vacuum cooling is characterized by

the rapid evaporation of the water in the product itself, and

quick removal of the heat contained in the product[5-7]. It was

widely used in the processing of fruits, vegetables, meat, fish,

sauces, soups, bakery, and ready meals[8-9].

The vacuum cooling turns into vacuum freezing if the

vapor pressure in the vacuum chamber drop below 0.6 kPa,

58 2016, Vol.37, No.23 食品科学 ※基础研究

i.e., the saturation pressure of water at 0 ℃. So vacuum

freezing is known as a new special freezing technique that is

attracting more and more researchers’ interests. And some

studies on vacuum freezing of food have been reported

recently. Cogné et al.[10] developed a numerical simulation

to model heat and mass transfer during vacuum freezing

of puree droplet. Chen et al.[11] studied the morphological

changes of water during vacuum cooling and vacuum

freezing, finding that the liquid water inside the vessel in a

vacuum cooling system was frozen into two layers: irregular

porous layer on the top and dense layer on the bottom. In

order to simplify the food freeze-drying process and shorten

the drying time, the author proposed a novel freeze-drying

technology in which the traditional air-freezing or plate

freezing process of food product was replaced by vacuum

freezing conducted in the same vacuum freeze dryer[12]. And

some laboratory experiments were performed on fruits and

vegetables with this novel freeze-drying technology. Zhang

Haifeng et al.[13] analyzed the process characteristics of water

vaporization and solidization, the organizational structure and

mass loss during the vacuum freezing of fresh mutton.

In the freezing or drying process of fruits and

vegetables, blanching pretreatment is generally applied

in order to undermine and suppress the enzyme activity,

prevent nutrients loss, retain original colors and taste, reduce

bacterial contamination, and so on[14-19]. There is few report

on the vacuum freezing properties of fruits and vegetables

with blanching pretreatment. The main objectives of the

current study are to evaluate the vacuum freezing properties

of blanching-treated apple slices in contrast with traditional

refrigerator freezing method, including mass loss, temperature

variation, thawing loss, relative electrical conductivity and

micro-structure of the tissue in the apple materials. Due

to the fact that there have been lots of reports about the

influence of blanching pretreatment on the sensory and

nutritional qualities of apples[14-19], so these quality indices

were not involved in this experiments. This study aimed to

provide basic knowledge for improving the effect of vacuum

freezing in fruits and vegetables and promoting the practical

application of this novel freezing technique.

1 Materials and Methods

1.1 Materials

Fresh Fuji apples were obtained from a farm located

in Yantai, Shangdong, China. The apples were selected

according to apparent color and size. Then, the selected

apples were washed, pitted and cut into 3 cm × 3 cm × 0.5 cm slices. The initial moisture content of these apple

slices was (86.34 ± 0.52)% (mf). Some apple slices were

blanched for 1 min in 95 ℃ distilled water heated by an

induction cooking plate and then cooled quickly to room

temperature using cold distilled water according to the

method of Wang Yuchuan et al.[16]. The blanching parameters

were chosen on the basis of the literatures[17-19]. And it was

also verified by the pre-experiments that the chosen blanching

parameters can suppress the enzyme activity and retain good

colors for the fresh slices. The non-blanched apple slices

were taken as the control group.

1.2 Instruments and equipment

50F vacuum f r eeze d rye r N ingbo Sc i en t z

Biotechnology Co. Ltd.; BCD-182DTB freeze refrigerator

Hefei Meiling Co. Ltd.; YNK/TH-50 constant temperature

and humidity chamber Suzhou Unique Environmental

Test Equipment Co.; FE38-Standard conductivity meter

Mettler-Toledo Instruments Co. Ltd.; HNY-1102C shaker

Nuoji Instrument Co. Ltd..

1.3 Methods

1.3.1 Vacuum freezing and refrigerator freezing

A laboratory-scale vacuum freeze dryer and a freeze

refrigeratorwere used for the freezing operation of apple

samples which were divided into 4 groups (group A, B,

C, D). Apple slices of group A and group B were selected

from the blanched slices, and those of group C and group D

from the non-blanched slices. Group A and group C were

performed vacuum freezing operation for 40 min in the

vacuum freeze dryer. The refrigeration units of the freeze

dryer were switched on half an hour earlier to reduce the

cold trap temperature below -50 ℃, then apple slices of

group A and group C were put into the freeze dryer at the

same batch ensuring the two groups’ vacuum freezing were

performed under the same operation parameters such as the

environmental pressure and the cold trap temperature. Apple

slices in group B and D were put into the freeze refrigerator

to perform traditional freezing for 4 h at -30 ℃.

1.3.2 Mass loss analysis in vacuum freezing

Three slices of apple samples in each group were

randomly selected and individually weighed before and after

vacuum freezing to determine the mass loss (ML), taking

the average value of 3 slices as the final result. ML was

calculated as the percentage loss of initial weightmass using

the formula (1).

※基础研究 食品科学 2016, Vol.37, No.23 59

ML/%＝ ×100m0－m1m0

(1)

where m0/g and m1/g were the weight of apple slice

before and after vacuum freezing, respectively.

1.3.3 Sample temperature analysis in vacuum freezing

The temperature of the geometric center of apple

slices in each group was measured using the thermocouple

temperature sensors of the vacuum freeze dryer to determine

the sample temperature variation during vacuum freezing.

1.3.4 Thawing loss analysis

After freezing, 3 frozen slices were taken out from each

group, separately placed into a high-density polyethylene bag

and thawed in a constant temperature and humidity chamber

maintained at (20 ± 0.5) ℃ and (70 ± 5)% relative humidity

until the temperature in the geometric center of the samples

reached 4 ℃. Each thawing experiment was undertaken in

triplicate. Then thawing loss (TL) was calculated according

to the formula (2).

TL/%＝ ×100m2－m3

m2 (2)

where m2/g was the weight of samples before freezing;

m3/g was the weight of samples after thawing.

1.3.5 Relative electrical conductivity analysis

The method was based on Lebovka et al.[20]. The

relative electrical conductivity (REC) of fresh slices (before

blanching), blanched slices (after blanching), and freeze-

thawed slices in group A, B, C, D (after freeze-thawing)

were all measured with the following method. Ten small

apple slices with 1 cm in diameter were obtained from each

group using the 1 cm-diameter hole puncher, then were

washed twice with deionized water, placed in the Erlenmeyer

flask containing 100 mL deionized water, and measured

the initial conductivity E0 with the conductivity meter. The

second conductivity E1 was also measured after shaking

the Erlenmeyer flask for 1 h at temperature of 15 ℃ in the

shaker. Subsequently, the Erlenmeyer flask was boiled for

15 min on the electric furnace, then cooled down to the room

temperature and added with deionized water until achieving

the original weight before boiling. Finally, the third conductivity

E2 was measured. All the measurements were undertaken in

triplicate. REC was calculated as the formula (3).

REC/%＝ ×100E1－E0

E2 (3)

1.3.6 Micro-structure analysis by light microscope

The method was modified from that of Ignat et al.[21].

Some of the fresh, blanched and freeze-thawed slices in

group A, B, C, D were taken for micro-structure analyses by

light microscope. All the prepared apple slices were fixed in

Formalin acetic acid alcohol (FAA) solution (90% ethanol,

5% acetic acid, 5% formalin) for 3 d. After fixation, gradient

elution with 30%, 50%, 70%, 90% and 100% ethanol was

performed for 15 min in each ethanol concentration. Then

the slices were processed by an automatic histoprocessor

to embed the tissue in paraffin which was cut into 5 μm

paraffin-tissue slices with a tissue slicer. The paraffin-tissue

slices were baked to remove paraffin, stained with Safranin

O/Fast Green, and finally were sealed in glass slide to be

ready for microscope imaging.

1.4 Statistics

Statistical analysis of variance (ANOVA) was performed

using SPSS 20.0 software. Tests of significant differences

between means were determined by Duncan’s multiple range

tests at a significance level at 0.05 (P<0.05).

2 Results and Discussion

2.1 ML analysis in vacuum freezing

00

10

20

30

10 20Time/min

30 40

ML

/%

group Agroup C

group A. blanched apple slices; group C. non-blanched apple slices. The same below.

Fig. 1 ML of apple slices after different times of vacuum freezing

During vacuum freezing the water in the apple slices

evaporated from liquid to vapor along with the performing

time causing the result of continual ML. As shown in Fig. 1,

ML in group A (27.5%) after vacuum freezing for 40 min was

significantly higher than that of group C (22.9%, P<0.05).

Due to the blanching pretreatment, the ML in group A was

increased by 32.35%, 21.85%, 20.26%, 20.00% at 10, 20, 30,

40 min of the vacuum-freezing performing time compared

with that in group C, respectively. Water evaporation rate (ML

rate) varied with a slowing down trend. The first 10 min was

the rapidest and main evaporation stage, contributing to more

than half of the total ML in 40 min.

During the vacuum cooling and freezing process, water

evaporation in apple slices was driven by the difference

between the water vapor pressure on materials and the

60 2016, Vol.37, No.23 食品科学 ※基础研究

pressure in the vacuum chamber. ML and frozen temperature

are the main indicators of vacuum freezing performance which

is affected by some factors including the initial temperature

of the material, moisture status and micro-structure of

the inner tissue, vacuum pressure, vacuum performing

time, the cold trap temperature and so on[10-11]. In our

experiments, vacuum freezing operations of group A and C

were performed at the same batch in the same equipment,

ensuring that the material initial temperature and the vacuum

processing conditions of the two groups were consistent. The

significant difference of ML between group A and C may be

mainly caused by the moisture status and micro-structure of

material tissue. This might be due to the fact that blanching

pretreatment resulted in some changes to the cell wall micro-

structure, contributing to the more ML in group A.

ML was inevitable phenomenon of vacuum freezing,

which lead to different results for food different processing.

ML was undesirable for the manufacturers if the vacuum-

frozen materials were used as instant freezing products

for the preserving purpose, and should be controlled as

small as possible to reduce the economic losses. However,

ML was desirable if the vacuum-freezing processing was

used as the purpose of freezing stage in freeze-drying

technology, and should be controlled as more as possible

to obtain the maximum dehydration mass and the lowest

freezing temperature in favor of enhancing freeze-drying

performances.

2.2 Sample temperature analysis in vacuum freezing

Sample temperature variation was caused by the phase

change of the moisture in the apple slices themselves,

including evaporation from liquid to vapor and freezing from

liquid to solid ice[10]. As shown in Fig. 2, the vacuum freezing

process can be divided into 3 stages according the change

curve of sample temperature which presented a similar trend

in the studies of Zhang Haifeng et al.[13].

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40Time/min

-30-25-20-15-10-505

10

Tem

pera

ture

/

group Agroup C

Fig. 2 Temperature changes of apple slices during vacuum freezing

The first stage: pressure-reducing and flashing stage.

The pressure in the vacuum chamber dropped to saturation

vapor pressure at the initial temperature of apple slices after

2 min of vacuum pumping, reaching to the flash-point of

water evaporation. Then rapid evaporation and boiling status

of water in apple slices happened, removing large quantity

of heat from samples themselves and leading to a rapid

reduction in sample temperature (dropped below -10 ℃).

The temperature curves of group A and C almost overlapped,

showing no obvious difference in slices temperature variation

caused by the blanching pretreatment.

The second stage: ice formation stage. Apple slice

samples turn into a super-cooling sate due to the happening

of the flashing evaporation. And ice crystals in samples were

gradually formed releasing a lot of latent heat, which slowed

down the temperature reduction rate of samples caused by the

removed heat of water evaporation. This stage lasted about

10 min, the temperature curve dropped with a slighter slope

compared with the first stage. Moreover, the temperature

curves of group A and C slightly separated showing that the

blanched samples had a lower temperature.

The third stage: deep freezing stage. Water evaporation

and freezing in slices get on simultaneously along with

the continuation of vacuum freezing. And the temperature

curves slowly leveled off at the limit frozen temperature at

-27.6 ℃ in group A and -26.5 ℃ in group C, following by

a slight rise. At this stage, most of water in the slices was

frozen and water evaporation gradually weakened. Even at

the later stage, sublimation drying happened due to the heat

transferring from ambient environment to the slices, which

contributed to the slight rise in slices temperature.

It is well known that vacuum freezing has an amazing

freezing rate in contrast to traditional refrigerator freezing,

which was verified by the above analyses of sample

temperature in vacuum freezing. And the temperature

variation and ML variation of apple slices showed a close

relation in Fig. 1 and Fig. 2. The more and faster ML, the

more and faster temperature reduction, which reflected

the energy conservation principle during vacuum freezing

process in some sense.

2.3 TL analysis

TL is an important indicator for the integrity in the cell

tissue of frozen products. Thawing experiments of samples

in this study were performed under the same temperature

and humidity. TL of the 4 groups was presented in Fig. 3.

TL in group B was highest (27.67%), followed by group

D (24.94%), group A (21.87%) and the lowest group C

(10.71%). The difference between any two groups in TL

※基础研究 食品科学 2016, Vol.37, No.23 61

was significant except group B and D (P<0.05). It can be

concluded that blanching pretreatment caused more TL in

terms of the same freezing method. Many available studies

revealed that a series of changes in tissues of fruits and

vegetables will happened during blanching pretreatment,

including degeneration of inner cell protoplasm, increase in

cell membrane permeability, extracellular and intracellular

water exchange, increase in tissue elasticity and toughness

and so on[22]. In this study, blanching pretreatment caused

about 104% and 11% increase in TL for the vacuum freezing

and the refrigerator freezing, respectively. This was probably

due to micro-structure damage on cell tissue of apple slices

caused by the blanching pretreatment.

c

a

c

b

A B C Dgroup

0

10

20

30

TL

/%

group A. vacuum-frozen apple slices with blanching pretreatment; group B.

refrigerator-frozen apple slices with blanching pretreatment; group C: vacuum-

frozen apple slices without blanching pretreatment; group D: refrigerator-

frozen apple slices without blanching pretreatment. The same in Fig. 4.

Fig. 3 TL of frozen-thawed apple slices from 4 groups

And TL in the refrigerator freezing method were

significantly higher than that in the vacuum freezing method.

This was probably due to the formation of larger ice crystals

in the extracellular or intracellular space because of extremely

slow freezing rate in refrigerator freezing, leading to more

disruption of cells[23-24].

2.4 REC analysis

contr

ol

blanc

hing

thawing

in gr

oup A

thawing

in gr

oup B

thawing

in gr

oup C

thawing

in gr

oup D

group

010203040506070

RE

C/% a

b

cd

b

c

Fig. 4 Relative electrical conductivity of apple slices after different treatments

REC is an important indicator to measure permeability of

cell membrane. Higher REC value represents greater damage

of membrane intactness. The REC results were shown in Fig. 4.

After blanching pretreatment and/or the freeze-thawing

treatment in all groups, the RECs in the slices were increased

with different degrees compared with the raw fresh slices. A

similar difference trend of REC in group A, B, C and D was

observed in Fig. 4 as TL in Fig. 3. The highest REC value of

63.45% was found in the thawing slices of group B, following

down by 58.62% in thawing slices of group D, 55.77% in

thawing slices of group A, 40.66% in thawing slices of group

C, 39.33% in the blanched slices (blanching) and 31.22% in

the raw fresh slices (control group). A significant difference

in REC was observed between any two groups except the

pair of blanching and thawing in group C, thawing in group

A and thawing in group D. It can be concluded from the REC

results that refrigerator freezing conducted more damage to

cell tissue than vacuum freezing, and combined treatments of

blanching and freezing conducted a further more damage on

the micro-structure of apple tissue than the single one.

2.5 Micro-structure analysis by light microscope

100 µm 100 µm

a b

100 µm 100 µm

c d

100 µm 100 µm

e f

a. control group; b. blanching group; c. thawing in group A;

d. thawing in group B; e. thawing in group C; f. thawing in group D.

Fig. 5 Photomicrographs of apple tissues after different treatments

Fig. 5 shows the photomicrographs of apple tissue under different treatment conditions, in which thin layers lined cells surface profile. It was observed from Fig. 5a that cells in untreated fresh apple were regular in shape, arranged in order and appeared plump with an apparent consistent cell wall structure. However, blanching treatment caused the loss of turgidity of the cells, appearing irregular in cell shape, distortion in tissue and disorderly in arrangement (Fig. 5b), which was

62 2016, Vol.37, No.23 食品科学 ※基础研究

verified by the apparent phenomenon that blanched apple slices presented relatively more soft in tissue and smaller in volume-size compared with untreated fresh ones.

Fig. 5c shows the cell tissue of vacuum-freeze-thawed apple slices with blanching pretreatment, in which a similar tissue morphology as Fig. 5b was observed except that a small quantity of cell walls were disrupted. The cell tissue of vacuum-freeze-thawed apple samples without blanching pretreatment was shown in Fig. 5e with fewer structural changes in contrast to Fig. 5c, even retaining many regular and plump cells similar to those in Fig. 5a.

Cells in refrigerator-freeze-thawed apple slices with (Fig. 5d) and without (Fig. 5f) blanching pretreatment appeared more distortion and disruption in cell walls compared to Fig. 5c and Fig. 5e. It is well known that ice crystal size is closely related to the freezing rate. Vacuum freezing were performed with a much faster freezing rate than refrigerator freezing, resulting in smaller and more uniform ice crystals in the extracellular and intracellular region. In contrast, larger ice crystals in apple tissue were formed during refrigerator freezing contributing to more cell disruption and morphological changes.

It can be concluded from Fig. 5 that vacuum freezing without blanching pretreatment (Fig. 5e) caused the smallest morphological changes and the lowest breakage to apple cell tissue, flowing increasingly by Fig. 5c, f and d. And the aforementioned difference of ML, thawing loss and relative electrical conductivity in different treatments groups could be attributed to the micro-structural changes at cellular level in the sample tissue.

In Fig.1, ML in group A was significantly higher than that in group C. It might be due to that blanching pretreatment on apple slices softened cells tissue, enhanced cells permeability and promoted more water evaporation or ML during vacuum freezing. And TL in Fig. 2 and relative electrical conductivity in Fig. 3 indirectly reflect the degree of structural changes in apple cells shown in Fig. 5. For example, vacuum-freeze-thawed apple samples without blanching pretreatment had the smallest TL value and REC value which was confirmed by the minimum structural changes in Fig. 5e. Refrigerator-freeze-thawed apple samples with blanching pretreatment had the highest TL value and REC value conforming to the highest degree of disruption in cells tissue.

And for the purpose of freezing preservation, the least micro-structure disruption in Fig. 5e (vacuum freezing

without blanching pretreatment) was desired and accepted in priority in order to achieve a good quality of frozen products. However, the micro-structure changes on apples tissue due to blanching treatment and freezing methods would also cause different drying properties if the frozen products were used for vacuum freeze drying[25-26], which needed further studies in the near future.

3 Conclusions

The vacuum freezing properties of blanching-treated

apple slices were investigated in this study by comparing

with the traditional refrigerator freezing. Results from this

work demonstrated that blanching pretreatment provided

significant increase in ML of apple slices during vacuum

freezing. In addition, more than half of the ML and most of

temperature reduction happened within the first 10 min of the

vacuum freezing period. The total process of vacuum freezing

can be divided into 3 stages: pressure-reducing and flashing

stage, ice formation stage and deep freezing stage. Based on

the analyses of thawing loss, relative electrical conductivity

and photomicrographs, it has been concluded that vacuum

freezing causes less micro-structural changes and disruption

to apple cells tissue and contributes to smaller TL and REC

value in contrast to refrigerator freezing, and that blanching

treatment before freezing conducts further damage to cell

micro-structure than non-blanching pretreatment.

References:

[1] PRETAMO G, PALOMARES L, SANZ P. Broccoli (Brasica oleracea) treated under pressure-shift freezing process[J]. European

Food Research and Technology, 2004, 219(6): 598-604. DOI:10.1007/

s00217-004-1022-2.

[2] PALACIOS I, GUILLAMON E, GARCIA-LAFUENTE A, et al.

Effects of freeze-drying treatment on the aromatic profile of tuber spp.

truffles[J]. Journal of Food Processing and Preservation, 2014, 38(3):

768-773. DOI:10.1111/jfpp.12028.

[3] BRONFENBRENER L, RABEEA M A. Kinetic approach to modeling

the freezing porous media: application to the food freezing[J].

Chemical Engineering and Processing: Process Intensification, 2015,

87: 110-123. DOI:10.1016/j.cep.2014.11.008.

[4] XANTHAKIS E, LE-BAIL A, RAMASWAMY H. Development of

an innovative microwave assisted food freezing process[J]. Innovative

Food Science & Emerging Technologies, 2014, 26: 176-181.

DOI:10.1016/j.ifset.2014.04.003.

[5] LIU E, HU X, LIU S. Theoretical simulation and experimental

study on effect of vacuum pre-cooling for postharvest leaf lettuce[J].

Research on Crops, 2014, 15(4): 443-449.

[6] SCHMIDT F C, LAURINDO J B. Alternative processing strategies

to reduce the weight loss of cooked chicken breast fillets subjected to

vacuum cooling[J]. Journal of Food Engineering, 2014, 128: 10-16.

DOI:10.1016/j.jfoodeng.2013.12.006.

※基础研究 食品科学 2016, Vol.37, No.23 63

[7] FENG C H, DRUMMOND L, ZHANG Z H, et al. Effects of

processing parameters on immersion vacuum cooling time and

physico-chemical properties of pork hams[J]. Meat science, 2013,

95(2): 425-432. DOI:10.1016/j.meatsci.2013.04.057.

[8] SUN D W, ZHENG L. Vacuum cooling technology for the agri-food

industry: past, present and future[J]. Journal of Food Engineering,

2006, 77(2): 203-214. DOI:10.1016/j.jfoodeng.2005.06.023.

[9] MCDONALD K, SUN D W. Vacuum cooling technology for the food

processing industry: a review[J]. Journal of Food Engineering, 2000,

45(2): 55-65. DOI:10.1016/S0260-8774(00)00041-8.

[10] COGNÉ C, NGUYEN P U, LANOISELLÉ J L, et al. Modeling

heat and mass transfer during vacuum freezing of puree droplet[J].

International Journal of Refrigeration, 2013, 36(4): 1319-1326.

DOI:10.1016/j.ijrefrig.2013.02.003.

[11] CHENG H P, LIN C T. The morphological visualization of the water in

vacuum cooling and freezing process[J]. Journal of Food Engineering,

2007, 78(2): 569-576. DOI:10.1016/j.jfoodeng.2005.10.025.

[12] WANG Haiou, HU Zhichao, TU Kang, et al. Application of vacuum-

cooling pretreatment to microwave freeze drying of carrot slices[J].

Transactions of the Chinese Society of Agricultural Engineering, 2011,

27(7): 358-363. DOI:10.3969/j.issn.1002-6819.2011.07.063.

[13] ZHANG Haifeng, BAI Jie. Vacuum cooling and freezing of mutton[J]. Meat Research, 2008(9): 62-65.

[14] JAISWAL A K, GUPTA S, ABU-GHANNAM N. Kinetic evaluation of colour, texture, polyphenols and antioxidant capacity of Irish York cabbage after blanching treatment[J]. Food Chemistry, 2012, 131(1): 63-72. DOI:10.1016/j.foodchem.2011.08.032.

[15] CANET W, ALVAREZ M D, LUNA P, et al. Blanching effects on chemistry, quality and structure of green beans (cv. Moncayo)[J]. European Food Research and Technology, 2005, 220(3/4): 421-430. DOI:10.1007/s00217-004-1051-x.

[16] WANG Y, ZHANG M, MUJUMDAR A S, et al. Effect of blanching on microwave freeze drying of stem lettuce cubes in a circular conduit drying chamber[J]. Journal of Food Engineering, 2012, 113(2): 177-185.DOI:10.1016/j.jfoodeng.2012.06.007.

[17] DOYMAZ I. Effect of citric acid and blanching pre-treatments on drying and rehydration of Amasya red apples[J]. Food and Bioproducts Processing, 2010, 88(2/3): 124-132. DOI:10.1016/j.fbp.2009.09.003.

[18] GONZÁLEZ-FÉSLER M, SALVATORI D, GÓMEZ P, et al. Convective air drying of apples as affected by blanching and calcium impregnation[J]. Journal of Food Engineering, 2008, 87(3): 323-332. DOI:10.1016/j.jfoodeng.2007.12.007.

[19] BEVERIDGE T, WEINTRAUB S E. Effect of blanching pretreatment on color and texture of apple slices at various water activities[J]. Food Research International, 1995, 28(1): 83-86. DOI:10.1016/0963-9969(95)93335-R.

[20] LEBOVKA N I, PRAPORSCIC I, VOROBIEV E. Effect of moderate thermal and pulsed electric field treatments on textural properties of carrots, potatoes and apples[J]. Innovative Food Science & Emerging Technologies, 2004, 5(1): 9-16. DOI:10.1016/j.ifset.2003.12.001.

[21] IGNAT A, MANZOCCO L, MAIFRENI M, et a l . Surface decontamination of fresh-cut apple by pulsed light: effects on structure, colour and sensory properties[J]. Postharvest Biology and Technology, 2014, 91: 122-127. DOI:10.1016/j.postharvbio.2014.01.005.

[22] SANJUAN N, CLEMENTE G, BON J, et al. The effect of blanching on the quality of dehydrated broccoli florets[J]. European Food Research and Technology, 2001, 213(6): 474-479. DOI:10.1007/s002170100401.

[23] LI B, SUN D W. Novel methods for rapid freezing and thawing of foods-a review[J]. Journal of Food Engineering, 2002, 54(3): 175-182. DOI:10.1016/S0260-8774(01)00209-6.

[24] BOONSUMREJ S, CHAIWANICHSIRI S, TANTRATIAN S, et al. Effects of freezing and thawing on the quality changes of tiger shrimp (Penaeus monodon) frozen by air-blast and cryogenic freezing[J]. Journal of Food Engineering, 2007, 80(1): 292-299. DOI:10.1016/j.jfoodeng.2006.04.059.

[25] KOCHS M, KORBER C H, HESCHEL I, et al. The influence of the freezing process on vapour transport during sublimation in vacuum-freeze-drying of macroscopic samples[J]. International Journal of Heat and Mass Transfer, 1993, 36(7): 1727-1738. DOI:10.1016/S0017-9310(05)80159-0.

[26] KRAMER M, SENNHENN B, LEE G. Freeze-drying using vacuum-induced surface freezing[J]. Journal of Pharmaceutical Sciences, 2002, 91(2): 433-443. DOI:10.1002/jps.10035.