Research Progress on postharvest storage and prese

Advances in research on postharvest storage and preservation of strawberry fruits

strawberry belongs to the perennial evergreen herb of the strawberry genus (Fragaria L.) in the Rosaceae. With short plants, soft and juicy fruits, rich in vitamin C, iron and other minerals, it is one of the most popular fruits. However, strawberry peel is extremely thin, which is easy to be damaged and infected by microorganisms during harvest and transportation, leading to decay. Generally, the commodity value will be lost after 1 ~ 2 days of postharvest storage. In many main strawberry producing areas, due to the failure to find good measures for storage, transportation and preservation, a large number of strawberries rot, which directly affects the economic benefits of producers. Therefore, how to prolong the storage period or shelf life of strawberry fruit is an urgent problem to be solved in production. This paper summarizes the research in this area

1 storage and preservation methods of strawberries

there are many storage and preservation methods of strawberries. After years of research and practice, the commonly used methods are: low temperature storage, controlled atmosphere storage, Postharvest Heat treatment, chemical preservation and polymer coating

1.1 low temperature storage

generally speaking, the storage temperature of strawberry fruit is 0 ℃, and the relative humidity is 90% - 95%. Therefore, it is better to force ventilation and cooling in time after fruit harvest to reduce the fruit temperature to 1 ℃ and then refrigerate it. Hao Liping (1993) stored Baojiao early-growing strawberries at near freezing temperature (-0.5 ± 0.2) ℃ with relative humidity of 85% - 95%, and obtained good fresh-keeping effect [1]. In addition, due to the high CO2 resistance of strawberries, it was found that the storage time of strawberries could be prolonged after adding 10% CO2 treatment at 0 ℃ low temperature storage, which had a good preservative effect [2]

another kind of low-temperature storage is quick freezing. The quality of quick-frozen food depends on two processes, one is the cooling process, the other is the storage process. The cooling speed is fast, during which small ice crystals are generated, so that the cells are not damaged, and the loss of juice is less after thawing, which can better maintain the original appearance and freshness, but the size of ice crystals in frozen food also depends on the storage temperature. Liu Baolin et al. (1997) measured the quality of strawberries stored at -18 ℃ and -75 ℃ after quick freezing. The results are shown in Table 1 [3]

Table 1 Determination of strawberry fruit quality stored at different temperatures

project temperature/℃

-18 -75

appearance soft collapse, skin dry and full

color dark red bright, bright, fruit surface color consistent

texture meat soft rotten, hair cotton structure plump, fruit flesh solid, elastic

soup juice loss more, juice thick and red juice loss less, and light color

flavor and taste weak and sour taste, No rancidity taste

quick frozen strawberries can maintain the original quality of strawberries to the greatest extent when stored at a lower temperature, but creating a lower storage temperature requires a lot of cost. At present, scientists are committed to the research in this area, trying to add some high molecular substances to make it store at a higher temperature and maintain its original quality

1.2 controlled atmosphere storage

controlled atmosphere storage is designed on the basis of reducing the respiration rate of fruits during storage. The specific method is: remove the pest fruits and inferior fruits, gently put the selected berries into the special fruit tray or packing box, and then cover the fruit tray or packing box with polyethylene plastic film bag and seal it. Add an appropriate amount of sodium bisulfate, activated carbon or hydrated lime into the bag for controlled atmosphere storage (temperature: 0 ~ 0.5 ℃, rh:85% - 95%, o2:3% - 5%, co2:6% - 20%), which can store strawberries for more than 2 months [4, 5]. In recent years, the method of controlled atmosphere storage has been continuously improved, and the control of gas composition is more refined. It is no longer to control the proportion of O2 and CO2 in the environment at a fixed value, but to give different O2 and CO2 contents according to different storage stages, so as to meet the requirements of O2 and CO2 at different stages of fruit ripening and aging after harvest, and obtain better storage effects

1.3 Postharvest Heat Treatment

in recent years, studies at home and abroad have proved that postharvest pre storage heat treatment can delay the softening of apples and peaches, inhibit some physiological diseases, and prevent fruit decay. Heat treatment is gradually attracting people's attention, and important progress has also been made in strawberries [6 ~ 12]. After strawberry is infected with gray mold, the fruit has strong respiration, causing aging and decay. Garcia, J.M. (1996) inoculated strawberry fruits with Botrytis cinerea pers After treatment with hot water at different temperatures, it was found that higher temperatures could significantly inhibit the reproduction of Botrytis cinerea and maintain the hardness, color and original quality of the fruit. After that, people have carried out further research, identified the quality of strawberry fruits stored after heat treatment, and studied their physiological and biochemical characteristics. The results showed that heat treatment inhibited the release of ethylene, inactivated the activities of some senescence enzymes, effectively removed intracellular reactive oxygen species, delayed fruit ripening and senescence, improved fruit resistance, and significantly reduced fruit decay index [13, 14]. Therefore, heat treatment is an effective physical method to prolong the storage life

1.4 chemical preservation

the destruction of the integrity of fruit cell membrane is an important index to measure the damage and aging of fruit. The membrane damage is manifested by loss of chemical activity and increased electrolyte leakage. In addition, the senescence and browning of fruits after harvest are related to the peroxidation of cell membrane, which is initiated by reactive oxygen species. Therefore, the application of antioxidants undoubtedly plays a certain role in maintaining the integrity of the film structure and improving the fresh-keeping effect. Wang shaomei et al. Treated strawberries with tea polyphenol compound preservative [15], Zhang Yiping (1993), Dong Ming et al. (1993) treated strawberries [16, 1] with phytic acid (a natural food additive extracted from rice bran or wheat bran, which has strong complex metal ions, antioxidant and pH buffer effects), respectively, and all received certain effects. However, although phytic acid can delay the degradation of vitamin C in strawberries and maintain the content of soluble solids and organic acids in fruits, it has a weak inhibitory effect on the decay caused by mold. It should also be used in combination with other bactericidal preservatives in order to give better play to its use

grey mold is one of the important factors leading to strawberry decay. Dehydrated acetic acid is a broad-spectrum food preservative, which can effectively inhibit the growth of mold, yeast and bacteria. Soaking freshly picked strawberries in 0.25% - 0.5% dehydrated acetic acid solution for 30 s can significantly prolong their storage life [17]. 8-hydroxyquinoline is a fungicide that has been used in medicine for a long time and has been selected through network voting and expert selection. In the 1950s, it was approved by the United States for the preservation of strawberries and other fruits. Later, Hodel et al. Found that the sulfate and phosphate of 5-acetyl-8-hydroxyquinoline had better effect than that of 8-hydroxyquinoline. The pendulum quickly fell back, and the antibacterial agent also had an inhibitory effect on gray mold on fresh strawberries [4]

1.5 polymer coating

the coating can artificially form a protective structure - film, blocking the channels of water loss such as pores and pores, so as to reduce water loss. In addition, it also has the functions of preventing gas exchange inside and outside the fruit, inhibiting respiration, preventing microbial infection, and improving surface finish, so as to maintain quality and freshness. Deacetylated chitin is a high molecular weight cationic polysaccharide, which can form a semi permeable membrane, non-toxic and safe for human body. With its coating, Baojiao Zaosheng and Chunxiang stored at room temperature can be delayed for 1 ~ 2 days and rot [12]. When using, evenly coat the film agent on the surface of the washed and dried fruit, and pay attention to the thickness of the film. If it is too thick, it is easy to increase decay, and if it is too thin, the effect is poor. The antiseptic and fresh-keeping effect will be better if the corresponding bactericide is added to the coating agent

2 the development direction of strawberry storage and preservation

at present, the research on fruit and vegetable storage and preservation technology is developing by leaps and bounds. Strawberry is no exception. Its general development trend is towards safety, low consumption and efficiency

2.1 in terms of physical preservation, the combination of post harvest heat treatment and low temperature controlled atmosphere storage is a safe and effective way, but it has not reached a high degree of mechanization and automation, and people are working towards this direction

2.2 in terms of chemical preservation, the use of chemical agents will pursue high efficacy, low residue and little impact on the environment and human health. Extracting active substances from natural resources to replace synthetic chemicals has received extensive attention. The bactericidal active substances extracted from the crude extracts of plants are not only antiseptic and fresh-keeping, but also safe. China is rich in natural plants and Chinese herbal medicine resources. The development of natural, safe and effective preservatives will have great potential

in addition, with the continuous progress of biological control technology of fruit postharvest diseases, some chemical preservatives will be replaced by biological agents, which will undoubtedly be safer and more effective than chemical agents and easier to be accepted by the public

about the author: Li Chunli: male, born in 1969, graduated from the Department of Horticulture of Hebei Agricultural University in 1994, and is now a teacher of the Forestry College of Hebei Agricultural University

the author will also provide an inexhaustible driving force for the development of the extruder industry. Unit: Li Chunli, Chen Zhiling (College of forestry, Hebei Agricultural University, Baoding 071000)

Li Wei (Baoding forest products company)

reprinted from: Hebei Linguo research

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