Research progress on fresh food fig storage and preservation technology

Research progress on fresh food fig storage and preservation technology

Fund Project: Hunan Provincial University Students Research Learning and Innovative Experiment Program Project(334)

1 Introduction

Ficus carica is a genus of figs in the family Cyprinidae, which is an excellent shrub species that contains economic value, ecological value, ornamental value and health care function. Native to the eastern Mediterranean and Asia Minor, it was introduced to China around the Han Dynasty, with a long history of cultivation and breeding, and its economic, nutritional, ecological and medicinal value has been continuously explored, especially in recent years, researchers have been increasingly in-depth study of its functional components and mechanisms. China's fig cultivation is mainly in Xinjiang, Shandong, Sichuan, Guangdong, Fujian and other places, with an annual output of about 40,000 to 50,000 tons, with great market potential. However, the storage and preservation of fig fresh fruit is an important restrictive factor affecting the further development of the fig industry, and fig fresh fruit is prone to browning of the peel, rapid aging and shrinkage, fermentation and rotting and deterioration after harvesting.

In this paper, the research on the storage and preservation technology of fresh figs in recent years is reviewed, in order to provide a reference for the efficient storage and preservation of figs.

2 Storage characteristics and influencing factors of fresh figs

2.1 Storage characteristics of freshly eaten figs

Figs belong to the respiratory leap type of fruit, but not exactly similar to the characteristics of typical breathing leap fruit such as kiwi fruit and banana", "green ripe picking, later ripe edible", and both have the characteristics of non-respiratory leap type fruit, that is, the phenomenon of fig fruit after ripening is not obvious, and it needs to be picked at a certain maturity. After picking, with the respiratory intensity of the figs, the ethylene release gradually increases, and the fruit softens, ages and decays very rapidly.

2.2 Key factors affecting fig storage

In order to better preserve, transport and process figs, the impact of changes in various indicators on the preservation of figs should be noted in the key links and factors of temperature, humidity, gas concentration and environmental clarity of fig storage after harvesting, as well as pre-harvest management and variety transformation.

2.2.1 Storage temperature

Storage temperature is the most important factor affecting the storage effect of figs, mainly affecting the respiratory effect of figs and thus affecting their postharvest state. The storage temperature of figs after harvest was high, the respiration was strong, and the loss and consumption of water and nutrients in the fruit was accelerated. The storage temperature is low, the comprehensive metabolic level decreases, and the fig has strong anti-freeze ability, and can still be stored well at 2 °C [6]. Reasonably setting the storage temperature can effectively reduce fig browning and extend the shelf life of figs.

2.2.2 Relative humidity

Relative humidity is another important factor affecting the storage effect of figs. Usually 85% to 95% is the suitable relative humidity for storing figs. In such a high humidity environment, condensation will occur on the surface of the fruit when the ambient temperature fluctuates up and down more than 1 °C. Molded water droplets will promote the multiplication of bacteria and fungi, affecting the value of the product. If the relative humidity is too low, or the ventilation frequency is too high, the peel fruit will lose water and shrink and accelerate browning, and the value of the commodity will decrease.

2.2.3 Gas concentration

The composition and concentration of various gas components in the storage environment are also directly related to the respiration of postharvest fig fruits, which has an important impact on the maintenance of postharvest commodity value of figs. Reasonable setting of the composition and concentration of gases in the storage link can effectively inhibit respiration, reduce pests and diseases and prolong the storage period. Usually O2 concentration is less than 5% when the respiration will be significantly reduced, but too low O2 concentration will cause anaerobic respiration and acetaldehyde and other substances caused by hypoxic damage, in general, in a reasonable low temperature storage environment, O2 concentration control at 5% ~ 10%, CO2 control at 12% ~ 20% can better extend the preservation period of figs.

2.2.4 Environmental Clarity

Environmental clarity is the most basic requirement for storing all kinds of fruits, and its storage clarity standards include the storage environment and the cleanliness of the fruit itself. A clean and hygienic storage environment, a complete and clean fruit body can reduce the reproduction and spread of various microorganisms, which is an important factor in reducing storage diseases.

2.2.5 Varieties and pre-harvest management

The durability of different varieties of figs is not the same, Zhang Ming [9] took the figs of three varieties of "Boji Red", "Green Skin" and "Branric" as the test material, and found that "Branric" is the most resistant variety, and the best storage temperature is 1 °C. In addition, the light, temperature, moisture, soil fertility, pest control and cultivation and pruning of figs before harvest affect the quality of the fruit, and are closely related to the growth and maturity of the fruit, mainly through the composition and integrity of the fruit epidermis, dry matter content and microbial adhesion and other factors affect the storage performance of fruits and vegetables. Huang Peng researched that using "Branrick" as a test material, the application of potassium fertilizer can improve the quality and storage of fig fruits, and it is applied to each plant every year

1.0 kg potassium chloride is preferred 2 times.

3 Fresh food fig storage and preservation technology

In order to maintain the quality of fresh figs and extend the shelf life, domestic and foreign scientific researchers take the fig decay and deterioration mechanism as the foundation, and carry out extensive research and discussion on their storage and preservation technology from various influencing factors, and have found a variety of effective storage and preservation technologies, which can be divided into physical preservation technology, chemical preservation technology, composite preservation technology and other new preservation technologies according to the principles of different technologies. Among them, physical preservation methods include low temperature storage, variable temperature storage, modified atmosphere preservation, etc., and chemical preservation methods include 1-methylcyclopropene treatment, calcium treatment and biological preservation method.

3.1 Physical preservation techniques

3.1.1 Low temperature storage

The most common method of fig storage and preservation is to control low temperature conditions, but the specific parameters vary according to the variety, origin, fruit ripeness and storage time. Ma Jun et al. found in a study of Artush figs produced in Xinjiang that the preservation effect of figs stored at low temperature is significantly better than that stored at room temperature. Zhang Ming found in the study that the most suitable storage temperature of "Brooke Red", "Green Skin" and "Brandrick" was 1 °C. Compared with the 0 and 2 °C control groups, the softening rate of the three types of figs stored at 1 °C was significantly lower than that of fig fruits of their own types, and the activities of catalase (CAT) and peroxidase (POD) in the 1 °C fruit were significantly higher than those of other groups. Liao Liang et al. and Tang Xia et al. found the same experimental results on the experimental materials of Xinjiang early yellow fig and "boji red" respectively, and the biochemical reaction level of figs stored at low temperature decreased significantly, which delayed the aging and decay process of fig fruits compared with the control group. Therefore, in low temperature storage that does not cause cold or frost damage to figs, the storage temperature can be reduced as much as possible.

3.1.2 Storage at variable temperature

The main techniques for storing figs at variable temperature include heat stimulation treatment and cold stimulation treatment. Heat stimulation treatment is to treat vegetables and fruits after harvest at a suitable temperature, which can passivate enzyme activity, reduce pests and diseases, promote wax synthesis, affect protein synthesis, tissue softening and respiration to delay aging, and maintain the quality of fresh figs. Ying Tiejin et al. found that figs were treated with 6% CaCl2 solution or 43 °C hot water under the same conditions (1 °C), and the fruit preservation effect was significantly better than that of calcification treatment. Ou Gaozheng et al. comprehensively compared the cold excitation treatment of ice water mixture and the heat excitation treatment of 40 °C water bath immersion, and found that heat excitation and cold excitation can significantly inhibit the rise of fig rot index and malondialdehyde content, of which the cold excitation treatment of 1.5 h has the best preservation effect. Chen Yijun's report is similar to the above experimental results, and the rot rate and preservation effect of figs after refrigeration using polyethylene film packaging and hot water treatment at 40 °C for 5 minutes are significantly better than other treatments. Similarly, Li Fang et al. studied that bleaching figs at 90 °C for 9 s can effectively destroy the peroxidase activity, and then after pre-cooling and then 60 °C quick-freezing can better preserve the organoleptic quality of figs.

3.1.3 Modified atmosphere storage

Modified atmosphere storage is a well-studied and widely promoted postharvest preservation technology of fruit, which realizes the adjustment of gas composition to the fruit storage environment through various means [19]. Under the appropriate oxygen and carbon dioxide concentration environment, the fruit can reduce the biochemical reaction as much as possible without affecting the quality of food, maintain the hardness and nutrition of the fruit, reduce nutrient consumption and the production of harmful substances. Zhao Weijun studied that at 0 °C, oxygen concentrations were best preserved at 2% to 5%, and figs had better respiratory strength, erosion index and Vc content than other oxygen concentrations. Cai Zikang's research is similar to That's, where the concentrations of CO2 (19% ±0.5%) and O2 (3% ±0.5%) in the modified atmosphere packaging can reduce weightlessness and help maintain the higher nutritional value of figs. Foreign scholars Bahar et al. [21] also found that when storing figs through different controlled atmosphere conditions, the degree of damage to stored figs decreased with the increase of environmental CO2 concentration under certain conditions. In addition, Celia et al. explored the effect of SO2 concentration on inhibiting fig rot and prolonging its shelf life by controlling the change of environmental SO2 content.

3.1.4 Ozone preservation

Ozone, also known as superoxide, has strong bacteriostatic and bactericidal capacity, is a new, efficient and environmentally friendly fungicide, in catering, medical and other industries have a wide range of use value. Therefore, the use of ozone in the storage and preservation of fruits and vegetables can also achieve the effect of maintaining product quality, reducing decay and prolonging the storage period. Yan Yuan et al. found that the use of ozone treatment before refrigeration of figs can inhibit the rot rate of fruit and maintain the rate of good fruit, but the single use of ozone treatment will reduce the Vc content of the fruit after refrigeration. Xiaona Zhang studied that an ozone concentration of 12.84 mg/m3 was most conducive to fig storage and preservation during the storage period of figs 25 days. Yang Qingrui innovatively used ozone ice film to store fresh figs, which better achieved the purpose of uniform preservation of figs, and compared with the control group, the fruit weightlessness rate and decay rate decreased significantly, while better controlling the respiratory rate, inhibiting the release of ethylene, and delaying the decline of various antioxidant enzyme activities. In addition, Jiang Jiawei et al. studied the effects of different frequencies of ozone treatment on the refrigeration and preservation of figs, and speculated that its optimal effect was related to the selection of ozone time points.

3.1.5 Film preservation

Film preservation can construct a barrier that separates food from the outside environment to protect food from external microbes, dust and air. Slip YanWen et al. [29] studied the use of commercially available polyethylene film packaging fresh figs can moderately extend the shelf life of figs. Foreign researchers Villalobos et al. studied the effect of polyethylene films with different sizes of pores on the preservation of fresh figs, under the same conditions, the pore size of 100 μm, 3 / cm 3 polyethylene film can effectively reduce the weight loss of fresh figs and delay the time of fungal contamination, while having no effect on the aroma of fresh figs themselves.

3.2 Chemical preservation technology

3.2.1 Calcium treatment and chlorine treatment

Calcium is closely related to the internal structure and changes of fruits and vegetables, and the calcium treatment of fruits and vegetables after harvesting can improve the internal calcium content of fruits and vegetables, increase the hardness of fruits and vegetables, inhibit respiration and ethylene production, and achieve a certain effect of prolonging the storage period of fruits and vegetables. Calcium treatment has been used for the storage and preservation of fruits such as peach fruits, apples and jujube fruits, and has achieved considerable preservation effects. Immersion of postharvest figs in 6% calcium chloride solution for 15 min can reduce the intensity of respiration, delay the emergence of peak ethylene concentrations and alleviate fruit softening during storage. Peng Huang studied the combined effects of calcium and naphthaleneacetic acid on the storage quality of figs, and found that the treated fig fruit had the best storage effect when 1.0% calcium chloride was treated with 30 mg/mL naphthaleneacetic acid. Zhang Dongmei et al. studied that the chlorine treatment of the fig fruit after harvest can also achieve the effect of maintaining the hardness of the fig, reducing the weight loss rate and soluble solids content of the fig, so as to improve its storage quality, and found that the effect of 80 mg/L chlorine dioxide treatment is the best. In addition, foreign scholars Irfan et al. have studied from the microbial point of view that 4% calcium chloride treatment pretreatment of fresh figs can effectively inhibit the growth of well-nourished bacteria, yeast and mold, and prolong the shelf life of figs after harvest.

3.2.2 1-Methylcyclopropene treatment

1-Methylcyclopropylene (1-methylcyclopropylene, 1-MCP) is an ethylene inhibitor and is safe and non-toxic at appropriate concentrations. The use of 1-MCP technology for fruit and vegetable preservation has received extensive research attention from researchers at home and abroad this year, and it has been found that its mechanism mainly protects the tissue structure of fruits and vegetables by inhibiting fruit and vegetable respiration and inhibiting ethylene binding to receptors. Wang Lei et al. studied that the peak of ethylene release was delayed by 5 days compared with the control group after 24 h of 1-MCP soaking treatment of figs using 1.5 μL/L, which delayed the aging process of figs and increased storage time. Han Lu et al. studied similarly to Wang Lei, and also had the best storage effect on figs under 1-MCP treatment of 1.5 μL/L. Zhang Xiaona [26] Also treated figs with various concentrations of 1-MCP, and the hardness, decay rate and activity of various antioxidant enzymes were detected, and the optimal effect concentration was consistent with the above experiments. Foreign scholars Freiman et al. [49] also studied the effect of 1-MCP on the preservation of fig fruits, and the post-harvest maturation rate of figs treated with 1-MCP before harvesting was significantly reduced, which greatly prolonged the shelf life of figs and reduced the softening rate and corruption rate.

3.3 Biological preservation methods

Biological preservatives are extracted substances from animal and plant sources that can be used for food antibacterial preservation in recent years. Chitosan is a cationic polysaccharide that is widely present in many crustaceans, has good antibacterial properties, biocompatibility and safety, and has been widely studied in recent years and applied to food, medicine and agriculture. Li Yuanhui used chitosan treatment to coat the figs of "Boji Red" and found that it could delay the decline of fig hardness, sugar content and Vc content, reduce fruit rot, delay the emergence of respiratory peaks and ethylene release peaks, extend their storage period and screen out the most suitable chitosan treatment concentration of 2.5%. The study of Meng Xianfang et al. also found that fig coating treatment can effectively prevent the increase in fig weight loss rate, which helps to maintain the stability of fig quality during storage. Similar to the study of Ma Xiaojing et al. Wang Guowu et al., the use of 1.5% chitosan for the "Branric" variety can effectively extend the storage period of figs. It can be found that there are certain differences in the tissue structure, skin thickness and ripening of the pulp of different types of figs, and the optimal chitosan treatment concentration needs to be analyzed on a case-by-case basis in production.

In addition, many plant extracts also exhibit the function of preservative preservation and prolonging the storage period of fruits and vegetables. Zhang Heliang et al. studied the difference between the storage effect of figs at different concentrations of their own leaf alcohol extracts under the storage conditions of 4 °C, and found that 5% of fig leaf alcohol extracts can effectively reduce fig weightlessness, rot rate and soluble solids content, and prolong the storage period of figs. Tripathi et al. studied that the essential oil extracted from ginger coated the grapes after harvesting, and the time of gray mold disease in grape berries was delayed by 10 days compared with the control group, and the skin of figs was equally soft and fragile as grapes, which was prone to fungal diseases such as gray mold, and the application of ginger extract in the preservation of fresh figs deserved in-depth research and attention. At the same time, Ji Xiaolei et al. have combined willow leaves, bitter mustard seeds, bitter beans and ginger extract flax gum to carry out a comparative experiment of coating film preservation of fig fresh fruits, and found that the coating film made of 0.1% flax gum + 0.05% ginger extract at room temperature has the best preservation effect. In addition, Zhao Guihong's research on phytic acid, cloves and schisandra extracts are all conducive to the storage and preservation of figs.

3.4 Composite preservation technology

The mixed preservation technology is a further exploration and attempt of fig preservation technology, Ye Wenbin [58] research, the use of fenugreek gum and Chinese herbal pattern party as the membrane matrix, with CaCl, glycerin, citric acid as the membrane additives to make an edible composite film for figs at room temperature (25 ~ 28 °C) storage and preservation, the 6 d after the film group good fruit rate is significantly higher than the untreated control group, and the best membrane composition ratio parameters were obtained experimentally. Slip Yanwen et al. studied that the preservation effect of polyvinyl alcohol film combined with glutamine invertase modified soybean protein on figs is better than that of commercially available ordinary polyethylene films. Foreign scholars Such as Maríadel have studied that polyethylene films combined with defatted soybean meal extracts have storage fig characteristics that are superior to ordinary polyethylene films.

3.5 Other preservation techniques

Nanomaterials technology is a major breakthrough in material technology, which also has obvious advantages in the field of fresh fruit and vegetable preservation. Cai Zikang's study determined that nanopackaging materials with nanoparticle content of 10% Ag, 5% TiO2, 2.5% ZnO and 5% kaolin had the best effect on the weightlessness and decay rate of figs. Kong et al. study storing figs in nanoscale foggy environments can also reduce fruit weight loss and decay, and avoid the weight loss and cold damage caused by traditional cold storage methods.

4 Conclusions and outlook

Physical preservation methods and chemical preservation methods have their own advantages, and suitable preservation technology can be selected according to actual production conditions and product characteristics. According to the storage characteristics and post-harvest physiological characteristics of figs, combined with physical and chemical preservation technology, the development of environmentally friendly comprehensive preservation technology with simple operation, low cost, long storage time and no harm to fruit quality will be a promising development direction for improving fig storage technology.

In addition, the postharvest physiological aging, flavonoid degradation, inclusion decline and antioxidant system regulation mechanism of figs need to be explored, and the effects of different storage preservation technologies on the quality of fresh fig fruits also need to be studied in depth, which will lay a foundation for exploring new fig preservation technologies. At the same time, due to the strong regionality and seasonality of fig planting and harvesting, how to adapt to market requirements to combine fig static preservation technology and dynamic logistics and transportation will be the key issue to promote the development of the fig industry.