**3.1.1 Precooling process of kiwi**

The kiwi was produced in Shengxi Province, after harvested, they was transported to lab in 24 hours.

Traditional storage process of kiwi: kiwi is precooled rapidly from 29°C to 3°C in 3 hours and be stored in the storehouse of which the ambient temperature is 3°C and the relative humidity is 85%.

The variable cooling rate precooling process of kiwi: the kiwi was precooled rapidly from 29°C to 5°C in 2.5 hours, then change the precooling rate, the kiwi was cooled slowly to 3°C in 24 hours ,then to 0°C in 10 hours ,then to -0.8°C in 10 hours, and at last to the storage temperature -1.3°C in 10 hours, stored in the ice-temperature storehouse at -1.3°C and its relative humidity is 85%.

2.5 <sup>24</sup> <sup>10</sup> <sup>10</sup> <sup>10</sup> 29C 5C 3C 0C 0.8C 1.3 C *hours hours hours hours hours*

#### **3.1.2 Precooling process of pear**

The pear was produced in Xingjian Province, and after harvest they were transported to lab in 48 hours.

Traditional storage process of pear: pear was precooled rapidly from 29ºC to 3ºC in 3 hours and was stored in the storehouse of which the ambient temperature is 3ºC and the relative humidity is 85%.

Fig. 11. Curves of kiwi respiration v.s. storage time

Fig.12 Curves of kiwi water-soluble vitamin C v.s. storage time

and is stored in the vicinity of ice temperature.

does not meet with the common views.

From Fig.11, it can be found that the kiwi has two reparatory peaks under the traditional storage condition, while under the condition of the ice temperature, there is only one reparatory peak, and on both storage conditions, the time to show the first reparatory peak is almost the same. The main reason is that when kiwi was put into the storehouse, the stimulation of the low temperature strengthened the respiration rate to protect itself in cold environment. So there is a minor reparatory peak in both the storage conditions. As for the second reparatory peak under the traditional condition, the reason is that the kiwi belongs to breathing-type fruit, the reparatory peak is delayed under the traditional storage condition. But as the the fruit precooled at variable cooling rate and stored in ice temperature, it dosen't has the second reparatory peak .The main reason for that is in the pre-cooling process with different cooling rate, the kiwi has adapted the surrounding well

403

Compared the respiration rate of the two storage conditions, it can be found that the respiratory rate decline rapidly in the vicinity of freezing point, which doesn't match the law of temperature coefficient. From the two figures, the temperature difference between these two storage conditions is only 4.3ºC, but the ratio of respiration rate is about 5, which

The variable-rate pre-cooling process of kiwi: the kiwi was precooled rapidly from 29ºC to 5ºC in 3 hours, then cooled the kiwi slowly to 3ºC in 24 hours, then to 0ºC in 10 hours, then to -1ºC in 10 hours, and at last to the storage temperature -1.7ºC in 10 hours, after that stored the kiwi in the freezing storehouse at -1.3ºCand its relative humidity is 85%.

3 24 10 10 10 29 C 5 C 3 C 0 C 1 C 1.7 C *hours hours hours hours hours*

#### **3.1.3 Precooling process of peach**

The peach was produced in Beijin City, and after harvested they were transported into lab in 24 hours.

Traditional storage process of peach, A: the peach was precooled rapidly from 28ºC to 2.5ºC in 3.5 hours and be stored in the storehouse of which the ambient temperature is 3ºC and the relative humidity is 85%.

In order to verify the influence of the precooling at different cooling rate on the storage of peach, two precooling experiments were carried out, after the precooling, the peaches were stored in the storehouse at -0.7ºC with a relative humidity of 85%.

(1)the pre-cooling process of peach at slow cooling rate, B: the peach was precooled from 28ºC to 5ºC in 3.5 hours, then cooled the peach slowly to 3ºC in 3.5 hours, then to 1.7ºC in 24 hours ,then to 1ºC in 24 hours, then to 0.5ºC in 24 hours ,then to 0ºC in 24 hours, then to - 0.3ºC in 24 hours, and at last to the storage temperature 0.7ºC in 24 hours, after that stored the peach in the freezing storehouse at -1.3ºC and its relative humidity is 85%. slow cooling rate,B:

$$\begin{array}{c} 28^{\circ}\text{C} \xrightarrow{3.5h} \text{S}^{\circ}\text{C} \xrightarrow{-35h} \text{S}^{\circ}\text{C} \xrightarrow{24h} \text{1.7°C} \xrightarrow{24h} \text{1.0°C} \xrightarrow{24h} \text{0.5°C} \xrightarrow{24h} \text{0.5°C} \\ \xrightarrow{24h} \text{-0.3°C} \xrightarrow{24h} \text{-0.7°C} \end{array}$$

(2) the precooling process of peach at fast cooling rate, C: the peach was precooled from 28ºC to 5ºC in 3.5 hours, then cooled the peach slowly to 2.5ºC in 24 hours, then to the storage temperature 0.7ºC in 24 hours. After that, stored the peach in the freezing storehouse at -0.7ºC and its relative humidity is 85%.

②rapid cooling rate, C:

$$28^{\circ}\text{C} \xrightarrow{3.5h} 0.5^{\circ}\text{C} \xrightarrow{-24h} 2.5^{\circ}\text{C} \xrightarrow{-24h} 0.5^{\circ}\text{C} \xrightarrow{-24h} -0.7^{\circ}\text{C}$$

#### **3.1.4 Measurement of respiration rate and nutrients**

During the experiments, according to different types of fruit, different fruit has different components in fruits were measured, including the respiration rate, the water-soluble vitamin C, the total sugar, the acidity. The respiration rate is determined by gas flow processes, the vitamin C is measured by GB 6195-86 (Chinese), the total sugar is measured GB 6194-86 (Chinese) and the acidity is measured by GB 12293-90 (Chinese). Except the measurement of respiration, six samples were measured and the average value of 6 measurements was used in the analysis.

#### **3.2 Experimental results and discussion**

#### **3.2.1 Experimental results and analysis of kiwi**

Fig.11 and Fig. 12 show curves of the respiration rate of kiwi and the change of watersoluble vitamin C over storage time in preservation process.

The variable-rate pre-cooling process of kiwi: the kiwi was precooled rapidly from 29ºC to 5ºC in 3 hours, then cooled the kiwi slowly to 3ºC in 24 hours, then to 0ºC in 10 hours, then to -1ºC in 10 hours, and at last to the storage temperature -1.7ºC in 10 hours, after that stored

3 24 10 10 10 29 C 5 C 3 C 0 C 1 C 1.7 C *hours hours hours hours hours*

The peach was produced in Beijin City, and after harvested they were transported into lab in

Traditional storage process of peach, A: the peach was precooled rapidly from 28ºC to 2.5ºC in 3.5 hours and be stored in the storehouse of which the ambient temperature is 3ºC and the

In order to verify the influence of the precooling at different cooling rate on the storage of peach, two precooling experiments were carried out, after the precooling, the peaches were

(1)the pre-cooling process of peach at slow cooling rate, B: the peach was precooled from 28ºC to 5ºC in 3.5 hours, then cooled the peach slowly to 3ºC in 3.5 hours, then to 1.7ºC in 24 hours ,then to 1ºC in 24 hours, then to 0.5ºC in 24 hours ,then to 0ºC in 24 hours, then to - 0.3ºC in 24 hours, and at last to the storage temperature 0.7ºC in 24 hours, after that stored

3.5 35 24 24 24 24

*hhh h h h*

28 C 5 C 3 C 1.7 C 1.0 C 0.5 C 0 C

(2) the precooling process of peach at fast cooling rate, C: the peach was precooled from 28ºC to 5ºC in 3.5 hours, then cooled the peach slowly to 2.5ºC in 24 hours, then to the storage temperature 0.7ºC in 24 hours. After that, stored the peach in the freezing storehouse

3.5 <sup>24</sup> <sup>24</sup> <sup>24</sup> 28 C 0.5 C 2.5 C 0.5 C 0.7 C *hhhh*

During the experiments, according to different types of fruit, different fruit has different components in fruits were measured, including the respiration rate, the water-soluble vitamin C, the total sugar, the acidity. The respiration rate is determined by gas flow processes, the vitamin C is measured by GB 6195-86 (Chinese), the total sugar is measured GB 6194-86 (Chinese) and the acidity is measured by GB 12293-90 (Chinese). Except the measurement of respiration, six samples were measured and the average value of 6

Fig.11 and Fig. 12 show curves of the respiration rate of kiwi and the change of water-

the kiwi in the freezing storehouse at -1.3ºCand its relative humidity is 85%.

stored in the storehouse at -0.7ºC with a relative humidity of 85%.

the peach in the freezing storehouse at -1.3ºC and its relative humidity is 85%.

**3.1.3 Precooling process of peach** 

relative humidity is 85%.

slow cooling rate,B:

②rapid cooling rate, C:

24 24

*h h*

at -0.7ºC and its relative humidity is 85%.

measurements was used in the analysis.

**3.2 Experimental results and discussion 3.2.1 Experimental results and analysis of kiwi** 

0.3 C 0.7 C

**3.1.4 Measurement of respiration rate and nutrients** 

soluble vitamin C over storage time in preservation process.

24 hours.

Fig. 11. Curves of kiwi respiration v.s. storage time

Fig.12 Curves of kiwi water-soluble vitamin C v.s. storage time

From Fig.11, it can be found that the kiwi has two reparatory peaks under the traditional storage condition, while under the condition of the ice temperature, there is only one reparatory peak, and on both storage conditions, the time to show the first reparatory peak is almost the same. The main reason is that when kiwi was put into the storehouse, the stimulation of the low temperature strengthened the respiration rate to protect itself in cold environment. So there is a minor reparatory peak in both the storage conditions. As for the second reparatory peak under the traditional condition, the reason is that the kiwi belongs to breathing-type fruit, the reparatory peak is delayed under the traditional storage condition. But as the the fruit precooled at variable cooling rate and stored in ice temperature, it dosen't has the second reparatory peak .The main reason for that is in the pre-cooling process with different cooling rate, the kiwi has adapted the surrounding well and is stored in the vicinity of ice temperature.

Compared the respiration rate of the two storage conditions, it can be found that the respiratory rate decline rapidly in the vicinity of freezing point, which doesn't match the law of temperature coefficient. From the two figures, the temperature difference between these two storage conditions is only 4.3ºC, but the ratio of respiration rate is about 5, which does not meet with the common views.

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09

Fig. 15. Curves of pear acidity v.s. storage time

**3.3 Experimental results and analysis of peach** 

Fig. 16. Curves of peach respiration v.s. storage time

acidity(%)

over storage time.

0 20 40 60 80 100 120

Fig.16 to Fig.18 show the curves of the respiration rate, the total sugar and the acid of peach

3℃ -1.7℃

storage time(day)

405

#### **3.2.2 Experimental results and analysis of pear**

Fig. 13 to Fig. 15 show the curves of the respiration rate, the total sugar and the acid of pear over storage time.

From Fig.13, we can found that the pear under traditional storage condition has a reparatory peak after 70 days, which means that the pear has begun dying to death. As for the pear precooled at variable cooling rate, it has a smaller reparatory peak at the beginning of storage (ten days) at -1.7ºC and at other time the respiration maintains at a smaller value, which prolong storage time in a certain degree. The main reason for this smaller reparatory peak of the pear with different cooling rate is that when pears are just stored in the storehouse at -1.7ºC, they show a conditional stimulation reaction.

From the nutrition showed in Fig.14 and Fig.15, the pear precooled at variable cooling rate has higher sugar content and acidity, so that it can ensure a better quality.

Fig. 13. Curves of pear respiration v.s. storage time

Fig. 14. Curves of pear total sugar v.s. storage time

Fig. 13 to Fig. 15 show the curves of the respiration rate, the total sugar and the acid of pear

From Fig.13, we can found that the pear under traditional storage condition has a reparatory peak after 70 days, which means that the pear has begun dying to death. As for the pear precooled at variable cooling rate, it has a smaller reparatory peak at the beginning of storage (ten days) at -1.7ºC and at other time the respiration maintains at a smaller value, which prolong storage time in a certain degree. The main reason for this smaller reparatory peak of the pear with different cooling rate is that when pears are just stored in the

From the nutrition showed in Fig.14 and Fig.15, the pear precooled at variable cooling rate

3℃ -1.7℃

0 20 40 60 80 100 120

0 20 40 60 80 100 120

storage time(day)

3℃


storage time(day)

**3.2.2 Experimental results and analysis of pear** 

0

9 9.2 9.4 9.6 9.8 10 10.2 10.4 10.6 10.8

Fig. 14. Curves of pear total sugar v.s. storage time

total sugar(%)

Fig. 13. Curves of pear respiration v.s. storage time

5

10

respiration(CO2mg/kg.h)

15

20

25

storehouse at -1.7ºC, they show a conditional stimulation reaction.

has higher sugar content and acidity, so that it can ensure a better quality.

over storage time.

Fig. 15. Curves of pear acidity v.s. storage time

#### **3.3 Experimental results and analysis of peach**

Fig.16 to Fig.18 show the curves of the respiration rate, the total sugar and the acid of peach over storage time.

Fig. 16. Curves of peach respiration v.s. storage time

the peach feature stored with A processing after 75 days

Fig. 19. the peach feature at different storage time

effectively and extend the storage time by 30%.

**4. Effect of ice temperature storage** 

mechanism of ice-temperature storage.

cooling one make the fruits have more soluble solids.

the peach feature stored with A processing after 105 days

Compared with the color of the peach shown in Fig.19, we can find that the peach cooled by the variable cooling rate has a better appearance than that of the peach treated by the traditional method. After 75 days in storage, the stored peach in the ice temperature has little difference with the new peach in color, hardness, etc., while the peach with traditional treatment has reached to the end of shelf period. And after 105 days, the peach at ice temperature reach to the end of shelf period with low sugar concentration shown in Fig.17. Experimental results show that precooling process with variable temperature can make the fruit to adapt the low temperature environment and delay the emergence of the respiratory peak. Compared to the conventional low temperature storage, the fruit stored under the ice temperature has smaller respiratory rate, which guarantee the quality of stored fruit

As discussed in 2, the cooling rate and heating rate of fruits before and after the ice

Under normal circumstances, the organization with rapid cooling stress will take over the depth of the cooling method to keep warm, and the one with slow cooling stress will take over the way of ice frost in the cells [5-10]. Slowly and staging cooling the organization can reduce the critical lethal temperature, thus making some of the critical lethal temperature higher than the organization of plant in the zero and can be preservation for a long time at 0ºC or below zero, extend their storage period. Different heating rate after storage at icetemperature has different effects on the shelf life of fruits. The reason is the act of fruit tissue self-adaption. For the study of the reactions of kiwi and pear under the processing conditions, the experimental studies were carried out to a better understanding the

According to the difference of respiratory type, two kinds of fruits were chosen to do the ice-temperature storage research, one is pear (breathing -jump variant ), the other is kiwi(non-breathing-jump variant).After certain days, the storage temperature was increased in different warming ways. The results showed that compared with the comparison group, ice-temperature storage can maintain the nutrients in fruits better; as to the carbohydrate material, slow cooling is helpful to maintain the sugar during storage period. Icetemperature storage by slow cooling can make the fruits have higher acidity while the fast

temperature storage finally influence the storage period、shelf life and nutrition.

the peach feature stored with C processing after 75 days

407

Fig. 17. Curves of peach total sugar v.s storage time

Fig. 18. Curves of peach acidity v.s storage time

As it can be seen from Fig.16, the peach has the first reparatory peak after 45 days in traditional storage while the ones precooled at variable cooling rate does not have. Compared with the two processes with different cooling rate, the peach cooled by the slower cooling rate shown a smaller reparatory peak, but which doesn't influence the respiration rate in the whole storage time. And from Fig.17, it can be found that the total sugar always has a peak value in the storage period. And the peak value of the peach cooled by variable cooling rate was smaller than that of the peach cooled in a traditional method. Fig. 18 shows that the acidity of peach precooled at variable rate is smaller than that of the one cooled in traditional method. However, after stored 100 days, the peach cooled by variable cooling rate still had better appearance and hardness shown in Fig.19, there is a serious decline in sugar and the flavor become worse.

As it can be seen from Fig.16, the peach has the first reparatory peak after 45 days in traditional storage while the ones precooled at variable cooling rate does not have. Compared with the two processes with different cooling rate, the peach cooled by the slower cooling rate shown a smaller reparatory peak, but which doesn't influence the respiration rate in the whole storage time. And from Fig.17, it can be found that the total sugar always has a peak value in the storage period. And the peak value of the peach cooled by variable cooling rate was smaller than that of the peach cooled in a traditional method. Fig. 18 shows that the acidity of peach precooled at variable rate is smaller than that of the one cooled in traditional method. However, after stored 100 days, the peach cooled by variable cooling rate still had better appearance and hardness shown in Fig.19, there is a

Fig. 17. Curves of peach total sugar v.s storage time

Fig. 18. Curves of peach acidity v.s storage time

serious decline in sugar and the flavor become worse.

the peach feature stored with A processing after 75 days

the peach feature stored with A processing after 105 days

the peach feature stored with C processing after 75 days

Fig. 19. the peach feature at different storage time

Compared with the color of the peach shown in Fig.19, we can find that the peach cooled by the variable cooling rate has a better appearance than that of the peach treated by the traditional method. After 75 days in storage, the stored peach in the ice temperature has little difference with the new peach in color, hardness, etc., while the peach with traditional treatment has reached to the end of shelf period. And after 105 days, the peach at ice temperature reach to the end of shelf period with low sugar concentration shown in Fig.17. Experimental results show that precooling process with variable temperature can make the fruit to adapt the low temperature environment and delay the emergence of the respiratory peak. Compared to the conventional low temperature storage, the fruit stored under the ice temperature has smaller respiratory rate, which guarantee the quality of stored fruit effectively and extend the storage time by 30%.

### **4. Effect of ice temperature storage**

As discussed in 2, the cooling rate and heating rate of fruits before and after the ice temperature storage finally influence the storage period、shelf life and nutrition.

Under normal circumstances, the organization with rapid cooling stress will take over the depth of the cooling method to keep warm, and the one with slow cooling stress will take over the way of ice frost in the cells [5-10]. Slowly and staging cooling the organization can reduce the critical lethal temperature, thus making some of the critical lethal temperature higher than the organization of plant in the zero and can be preservation for a long time at 0ºC or below zero, extend their storage period. Different heating rate after storage at icetemperature has different effects on the shelf life of fruits. The reason is the act of fruit tissue self-adaption. For the study of the reactions of kiwi and pear under the processing conditions, the experimental studies were carried out to a better understanding the mechanism of ice-temperature storage.

According to the difference of respiratory type, two kinds of fruits were chosen to do the ice-temperature storage research, one is pear (breathing -jump variant ), the other is kiwi(non-breathing-jump variant).After certain days, the storage temperature was increased in different warming ways. The results showed that compared with the comparison group, ice-temperature storage can maintain the nutrients in fruits better; as to the carbohydrate material, slow cooling is helpful to maintain the sugar during storage period. Icetemperature storage by slow cooling can make the fruits have higher acidity while the fast cooling one make the fruits have more soluble solids.

transfered to the ice-temperature lab (the Jan 12, 2007), where the temperature of Kiwi was 5.8ºC and 4.6ºC, and the temperature of pear was 5.9ºC and 4.3ºC. In Table 1, the processes of cooling of the two fruits were shown. In order to compare to the experimental results,

The thermal treatment consists of three steps, where the first step is a cooling process in order to bring the fruit to the ice temperature, the second stage is a storage period (one month) at ice temperature and the last step is the heating step in order to warm the fruits to

> Initial Temperature

After the two fruits were cooled down, they were stored one month in the ice temperature rooms with a set temperature of -1ºC and -0.2ºC. During the third step, the fruit were moved

pear 5.7ºC

Kiwi Fast cooling (KF-S)

Pear Fast cooling (PF-S)

Kiwi Fast cooling (KF-F)

pear Fast cooling (PF-F)

Slow cooling (KS-S)

Slow cooling (PS-S)

Slow cooling (KS-F)

Slow cooling (PS-F)

Heating mode fruit Cooling mode (name)

\*Temperature rise : slow (from -1ºC to 15ºC in five days) and fast (from -0.2ºC to 15ºC in three days)

During the step 2, one month storing time, the total sugar, the acidity and the soluble solid were measured each two week, and each measurement is an average of six samples. The

From Fig. 22 it can be easily found compared with the referenced group, t the total sugar of Kiwi and pear is higher, which means that a certain thermal process is needed before the cold storage and also means that the method of the ice-temperature is better than the method of cold storage. As for the different cooling processes, the difference is not obvious.

Final Temperature Begin of cooling

Jan 16th, 2007.

16:00

End of cooling

Jan 17th, 2007

10:00

409

before the cooling, the two fruits were cooled to 5ºC and 3.5ºC.

Kiwi fast cooling (KF) 5.0ºC 0.0ºC

Pear fast cooling (PF) 5.0ºC 0.0ºC

slow cooling (KS) 3.5ºC 0.0ºC

slow cooling (KS) 3.5ºC 0.0ºC Table 1. The step 1 of thermal cooling processes of experimental materials

out of the ice temperature rooms, they were heated as shown in Table 2.

Referenced group(5.7ºC) Kiwi 5.7ºC

Table 2. The step 3 of thermal heating processes of experimental material

But for different fruits, the cooling process plays an important role.

Processing mode (name)

a temperature of 15°C.

Slow heating :

Fast heating :

**4.2 Results and discussions** 

results were shown in Figure 22 to Figure 24.

Type of fruit
