Study on differential pressure pre cooling circula
2022-10-24- Detail
Study on the differential pressure precooling circulation fresh-keeping technology of broccoli (Part 2)
2.2.3 measurement methods
broccoli includes chlorophyll, vitamin C, sugar and other nutritional components. The chlorophyll content was determined by spectrophotometry; Vitamin C content was determined with 2,6-dichloroindophenol; The sugar content was determined by hand-held electronic sugar meter. Table 2 The weightlessness of broccoli Appearance evaluation and comprehensive evaluation
date test area temperature ℃ weight loss% yellowing odor decay comprehensive evaluation 10/09 00005.010/10a
b
a
b
c
d0
0
10
10
20
202.3
2.5
3.0
3.7
1.2
6.00
0
0.2
0.2
0.20
0
0
0
0
00
0
0
0
05.0
5.0
4.8
4.8
4.8
4.810/11A
B
A
B
C
D0
0
20
20
20
202.0
3.6
3.5
5.1
3.0
9.90
0
0.2
0.3
0.2
2.30
0
0
0
0
00
0
0
0
0
05.0
5.0
4.6
4.6
3.5
2.910/12A
B
A
B
A
B
C
D0
0
10
10
20
20
20
201.7
3.6
2.0
4.3
3.2
9.7
3.0
12.60
0.1
0
0.1
2.5
4.3
4.2
5.00
0
0
0
0
0
0
0.30
0
0
0
0
0
0
05.0
5.0
4.7
4.6
2.9
Integration of universal tensile testing machine Higher requirements for efficiency 0.7
0.8
010/13a
b
a
b0
0
20
202.2
5.4
4.5
9.80
0.1
0.2
0.40
0
0
00
0
0
05.0
4.8
4.7
4.510/14a
b20
205.0
13.52.8
5.00
00
01.8
010/16a
b0
02.4
5.70.2
0.20
00
04.6
4.510/17A
B
A
B0
0
10
102.3
6.6
2.4
7.40.1
0.2
0.3
0.30
0
0
00
0
0
04.9
4.7
4.7
4.610/18A
B
A
B0
0
20
202.0
7.8
4.1
10.20.1
0.1
0.2
0.40
0
0
00
0
0
04. 9
4.8
4.8
4.610/19a
b
a
b0
0
20
202.9
9.5
4.1
15.80.1
0.2
0.7
2.80
0
0
00
0
0
04.8
4.3
4.2
2.2
III. results and analysis
1 Weight loss, appearance evaluation and comprehensive evaluation of broccoli
according to the evaluation results in Table 2, the weight loss of broccoli under differential pressure precooling, expanded polystyrene box packaging and 0 ℃ storage conditions is significantly lower than that without precooling, carton packaging, insulated vehicle transportation and sales at 20 ℃ normal temperature. The color of broccoli changes from 3. 5% after one day, two days and three days under normal temperature at 20 ℃ after harvest Tls-s (1~20) I double digital display spring tension and compression testing machine does not turn yellow to partially or completely yellow; That is to say, the broccoli circulating under the condition of normal temperature at 20 ℃ has a life span of only one day. The broccoli stored at 0 ℃ for up to ten days after precooling, and then gradually delivered from the 0 ℃ storage warehouse in stages and transported by a one-day heat preservation vehicle. The color changes of broccoli sold at 20 ℃ for one or two days are no change, almost no change, slight change and yellowing respectively; In the case of carton packaging, the color of broccoli turns yellow more obviously. Therefore, the life of broccoli without cold chain circulation conditions after differential pressure precooling is only three days. The color of broccoli stored at 0 ℃ for ten days after differential pressure precooling has only slight change. The broccoli packed in expanded polystyrene box has the best green keeping effect, and its fresh-keeping period is at least ten days. During the test, there was no peculiar smell and decay of broccoli
2. Effects of different treatment methods on the vitamin C content of broccoli
broccoli is rich in vitamin C. The content of bridging element C in the strain gauge pasted on the broccoli life support line measured just after harvest is 127mg/100g. It can be seen from Figure 2 that the vitamin C content of broccoli packed in expanded polystyrene boxes and cartons and sold at room temperature of 20 ℃ after harvest decreases rapidly. The loss of vitamin C content of broccoli began to increase gradually after one day's transportation by heat preservation truck and two days' sales at 20 ℃ normal temperature after differential pressure precooling. When circulating at 0 ℃, we can obtain higher vitamin C content. Compared with carton packaging, the loss of vitamin C content of broccoli in the former is significantly lower than that in the latter
4. Effects of different treatment methods on the sugar content of broccoli
the sugar content of broccoli is 14.6%. It can be seen from Figure 3 that the result of the change of sugar content in broccoli is similar to that of chlorophyll and vitamin C. The sugar content of broccoli sold in carton packaging under the condition of 20 ℃ normal temperature lost the most. In order to avoid affecting the accuracy of the experimental results, it is packed in polystyrene box, and the loss of broccoli sugar content circulating at 0 ℃ is less. Compared with cartons, the loss of broccoli sugar content in the former is obviously lower than that in the latter
IV. discussion
from the above test results, it can be seen that the freshness maintenance of broccoli is related to the following factors. (1) It is hysteresis precooling, and the differential pressure precooling is obviously better than no precooling. (2) The outer packaging method, expanded polystyrene box packaging is significantly better than carton packaging. (3) Temperature, the flow energy under 0 ℃ low temperature cold chain is significantly better than that without cold chain. The best fresh-keeping method of broccoli in this experiment is to rest and quickly precooling broccoli after harvest
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