Pears are rich in water, mineral elements, vitamins, etc., so they have the effects of moistening the lungs, reducing phlegm, relieving cough, reducing fever, detoxifying and alcohol poisoning, and the boron element contained in pears can prevent osteoporosis in women. However, because pears contain a lot of water and have strong respiration, they are susceptible to germs during the growth and storage process and cause post-harvest diseases. Therefore, it is difficult to keep them fresh, resulting in a serious loss of nutritional value within a short period of time and a sharp commodity value. decline. In addition, the banana, which is one of the six major commercial fruits in the world, contains carbohydrates, a small amount of protein, fat, and nutritional ingredients such as vitamins A, B1, B2, and C in its pulp. It is a typical post-ripening fruit and is transported in circulation. In the process of selling and selling, it is also very common for bananas to be sold or discarded due to rot and blackening. At present, the preservation of fruits such as pears and bananas mainly involves low-temperature storage, chemical treatment, high-voltage electrostatic field treatment, and air-conditioning preservation. These methods basically consume high energy.
Therefore, the School of Food Science and Technology of Shanghai Ocean University has developed a bio-regulated fresh-keeping bag that packs pears and bananas together. The bio-regulating membrane has one-way air permeability. On the one hand, it reduces the oxygen entering the bag, which inhibits the breathing strength of pears and bananas, and reduces energy consumption; on the other hand, the oxygen content in the bag is reduced, which not only inhibits the growth and reproduction of aerobic microorganisms Moreover, it can avoid the oxidation of vitamins and other nutrients in fruits and inhibit the effects of some enzymatic browning, thereby extending the fruit freshness period.
The significance of co-deploying pears and bananas in this study is also to explore the effect of ethylene produced by bananas on the fresh-keeping effect of pears, hoping to provide a new method of integrating freshness and sales.
I. Preparation before experiment
1.Selection of packaging materials
Table 1 Performance comparison of films
Note: ☆ —Excellent ○ —Good △ —Fair Х—Poor
It can be seen from the figure that the various indicators of the bio-regulating film are obviously better than other types of films, so the bio-regulating packaging is made using it as a substrate for packaging pears and bananas for experimental research.
2. Characteristics and uses of bio-regulated film fresh-keeping bags
Table 2 Characteristics and uses of bio-regulated film fresh-keeping bags
Note: ☆ —Excellent ○ —Good
3. The structure of bioregulatory membrane
The bio-regulating film is a three-layer composite film, and the substrate is modified polyethylene (PE), modified polyethylene terephthalate (PET), polypropylene (PP), namely modified PE / modified PET / PP. PE has heat-sealability, which is selected as the inner layer of the fresh-keeping bag, and after modification, the combination with PE is stronger. PP has high transparency and printability, and is used as the outer layer of fresh-keeping bags. The middle layer of PET, on the one hand, makes the packaging bag very strong because of its very good toughness; on the other hand, it forms a special molecular sieve after modification, which prevents oxygen from entering and blocks the nitrogen in the bag, thereby reaching the Freshness effect.
1.Materials and equipment
Main experimental raw materials: pear, banana, bio-regulation film fresh-keeping bag. Before the experiment, choose equal, non-destructive fruits of color and size.
Main instruments and equipment: FR-A400 pedal sealer; CR-400 / 410s color difference meter; electronic balance; GY-3 hardness tester; handheld sugar content meter; ultraviolet spectrometer;
The experimental process is shown in the following figure:
Figure 1 Schematic diagram of the experimental process
2.Measurement method of experimental index
(1) Sensory evaluation
The color and gloss of fruits and vegetables are the most direct methods for judging the freshness and maturity. The gradual change in the color and smell of fruits and vegetables is also a true manifestation of the decay process. Therefore, before each experiment in this study, the sensory changes of pears and bananas were observed and recorded.
(2) Weight loss rate
The harvested fruit is still a living individual and undergoes a series of metabolic activities. The evaporation of water and the consumption of nutrients are the main reasons for fruit weight loss during postharvest storage. At the same time, the loss of quality also causes the fruit to wither and deteriorate. And important causes of decay. When the water content is high, the fruits and vegetables are strong and full, bright and bright, fresh and delicious, but they are susceptible to mechanical damage and pathogen infection. After the water and fruit tissues are dehydrated, they will wither, shrink, reduce quality, and reduce the value of the product. Therefore, it is of great practical significance to determine the moisture content of fruit and vegetable tissues.
The weight loss rate is calculated as: weight loss rate (%) = (W0-Wi) / W0 × 100;
In the formula: W0 is the average weight of single fruit before storage (g); Wi is the average weight of single fruit after storage on day i (g)
(3) Color difference
The technical indicators of color are more and more important, especially in the processing of agricultural products. In the color indicator, the increase of a * value and b * value indicates that the green color of the fruit fades and the yellow color increases. The degree of color change directly reflects the quality of the product. Pros and cons, product color characteristics also seriously affect people's consumer psychology. Measure the color of the fresh cut surface of pear and banana with a color difference meter, and use △ E to indicate the change of the total color difference. Automatically compare the color difference between the sample and the tested fruits and vegetables. After outputting CIEL, a, and b groups of data and color comparison, Record △ E, △ L, △ a, △ b four sets of color difference data to provide a reference scheme for color matching. According to the data displayed by the colorimeter, the following analysis is performed: △ E The total color difference; △ E = [△ L + △ a + △ b]; △ L = L sample — L standard (lightness difference); △ a = a.
(4) Total number of colonies
Almost ubiquitous microorganisms are another important factor that prevents fruits and vegetables from being stored for too long. Among them, rot-causing bacteria are the main reason for the fruit to rot after harvest and cause the fruit to spoil during storage and transportation. According to the national standard GB4789.2-2010 national food safety standard -Food microbiological inspection-determination of the total number of colonies, the number of total colonies in the sample is determined.
Results and discussion
In order to measure the indicators more accurately, each of the experimental group and the blank group took three identical samples 1, samples 2, and 3 to obtain three data, and the three data were finally averaged to obtain experimental data.
1.Sensory evaluation of pears and bananas
We performed sensory evaluations on the color, smell, and texture of pears and bananas. The assessors were eight packaging students in the class. They were all familiar with the flavors of pears and bananas and liked fruits. The sensory evaluation of samples of pear / banana with bio-regulated film fresh-keeping bag is shown in the table below.
Table 3 Sensory evaluation of samples of pear / banana with bio-regulation film
Figure 3 Bananas and pears in the experimental and control groups
From Table 3 and Figure 3, it can be clearly seen that the pears and bananas in the bio-air-conditioning fresh-keeping bag of the experimental group have significant fresh-keeping effects in terms of color and appearance.
2. Changes in moisture content of pears and bananas
The following table shows the moisture change of the samples of pear / banana with bio-regulation film fresh-keeping bag during the experiment.
Table 4 Changes in moisture content of pears / bananas packaged with bio-regulated film
From the table we can see that the moisture content of pears and bananas has decreased over time. Overall, the average weightlessness of pear / banana with bio-regulated film fresh-keeping bags was 1.14%, while the average weightlessness of unpackaged pears and bananas were 7.38% and 13.87%, respectively. It can be seen that the use of bio-adjustable film preservation bags can reduce the water loss of pears / bananas.
3.Pear and banana color change
The color difference meter is used to measure the fresh cut surface of pear and banana. The change of total color difference is expressed by △ E. The larger the value, the more serious the color change of the fruit. The recorded data are as follows:
As can be seen from the table above, the total color difference increases with time, but the total color difference of the pear / banana with bio-regulation film preservation bag changes little.
4. Changes in the total number of pear and banana colonies
The table below is the change of the total number of colonies of pears and bananas with bio-regulated film preservation bags during the experiment.
Table 11 Changes in the total number of colonies in pears / bananas with bio-regulated film
According to the data in the table above, untreated bananas and pears rapidly multiplied microorganisms in the natural environment, and produced a large number of bacteria. The total number of colonies detected exceeded the standard seriously, and the total number of colonies did not meet the national standard. Compared with the control group, the total number of pear and banana colonies in the experimental group was smaller. It can be seen that the freshness of pears and bananas was improved after being packaged in the fresh-keeping bag with bio-regulated film.
Fourth, the conclusion
The above experimental research has reached the following conclusions:
1. The pear / banana partner bio-regulation film can inhibit the change of weight loss rate. The experiment shows that the average pear weight of the blank group is 8.79%, the banana is 12.72%, and the total weight loss rate of the pear and banana in the experimental group is 5.2%;
2. The pear / banana partner bio-regulation film also has a certain effect on the color difference, the blank group pear 11.2, the banana 11.49, the experimental group pear 11.2, the banana 9.35, and the pear 10.67;
3. The pear / banana partner bioregulatory membrane significantly inhibited the growth and reproduction of bacteria. The blank group was banana 7.3 × 105 CFU / g, pear 7.1 × 104 CFU / g, and the experimental group was 1.1 × 104 CFU / g and pear 1.2 ×. 104 CFU / g.
To sum up the data, it can be concluded that the pear / banana combination with the biological adjustment bag can extend the freshness period of pears and bananas, and the freshness retention effect of the pears in the freshness bag is more obvious. If this fresh-keeping packaging method is put into practical use, it will form a new food collocation sales model that changes the public's consumption habits, and it is also a packaging exploration that will be beneficial to businesses and consumers. In addition, research on complementary packaging technology for fruits and vegetables and the establishment of an effective packaging technology system for storage and preservation of fruits and vegetables will help improve the quality of our fruits and vegetables and enhance the competitiveness of exported fruits and vegetables, with huge economic and social benefits.