Research progress of the hottest fresh cut fruits

Research progress of fresh cut fruits and vegetables

with the acceleration of the pace of life and the strengthening of people's awareness of environmental protection and health, micro processed fruits and vegetables, as a fresh, nutritious and convenient emerging food, have become the development trend of fruit and vegetable processing and production. Minimally processed fruits and vegetables, also known as fresh cut fruits and vegetables, cut fruits and vegetables, semi processed fruits and vegetables, conditioned fruits and vegetables, and minimally processed fruits and vegetables, refer to fruit and vegetable products or mixed products of fruits and vegetables that change the physical shape of vegetables and fruits but still maintain their fresh state. Its production process generally goes through cleaning, grading, trimming, cutting (or non cutting), washing, drying, packaging (or rough pre packaging), storage, distribution and other processes, which can be used by consumers directly or in the catering industry

micro processed fruits and vegetables are fresh, convenient, nutritious and pollution-free. Consumers can directly cook or eat these products without further treatment. These characteristics meet the needs of people in the pursuit of nature, nutrition, fast pace of life and other aspects, which makes it grow rapidly in double digits every year in recent years. In the next five years, micro processed products will still increase at an annual growth rate of 10 ~ 15%. Since the 1990s, China's semi processed vegetable industry has been developing gradually, especially in recent years, the establishment of vegetable distribution centers across the country has provided favorable conditions for the great development of micro processed vegetables

from the concept of micro processed fruits and vegetables, we can see that the most fundamental problem of micro processed fruits and vegetables is the quality of micro processed fruits and vegetables. Therefore, the research and development of micro processing of fruits and vegetables should focus on how to control the quality changes of micro processed fruits and vegetables after cutting, maintain their quality, and extend the shelf life and storage life of micro processed fruits and vegetables

micro faults can eliminate the quality and physiological changes of fruits and vegetables after processing

after finishing, cleaning and segmentation, the integrity of tissue structure, the speed and degree of nutrient loss, the intensity and direction of metabolism, the infection of microorganisms and the deterioration of products have changed significantly compared with those before segmentation, resulting in some new problems

◆ loss of nutrients and decline in sensory quality

loss of nutrients and decline in sensory quality after microprocessing are mainly due to the following reasons: first, segmentation destroys the regional distribution of enzymes and substrates in fruit and vegetable tissues, and all kinds of biochemical reactions accelerate, especially the changes of hydrolysis and oxidation reactions are most obvious, especially in the presence of oxygen, resulting in changes in the original color, aroma, taste and texture properties of products, The nutritional value decreases; Second, the mechanical injury and wound caused by cleaning, cutting and other links in the production of micro processed fruits and vegetables will destroy the tissue cells of fruits and vegetables, resulting in the loss of juice and accelerating the loss of nutrients in the damaged tissues, especially water-soluble and easily oxidized components; Third, cutting greatly increases the surface area of fruits and vegetables. Compared with uncut fruits and vegetables under the same conditions, water loss is faster, which not only directly reduces the weight of micro processed fruits and vegetables, causing direct economic losses, but also causes wilting and accelerates the aging of products

◆ injury stress and physiological and biochemical aggravation

after fresh fruits and vegetables are cut, the tissue produces mechanical injury, which not only affects the injured cells themselves, but also generates injury signals and quickly transmits them to adjacent cells in a very short time (such as a few seconds), inducing them to have complex physiological and biochemical reactions, and diffusing and affecting cells far away from the injured site. The injury signal formed by segmentation may be the result of pure physics (such as water pressure wave or pressure wave), biochemistry (specific synthesis of injury response substances induced by signal molecules such as systemin, oligosaccharide, SA, ethylene), or the combination of physics and Biology (such as biological electromotive force wave or current). However, some people believe that injury signals are not specifically formed by injured tissues, but by-products of the initial injury response of injured cells (such as pectin fragments degraded by cell walls). It is worth noting that the mechanical injury of fresh fruits and vegetables not only causes the above-mentioned local short-term effects, but also causes the overall long-term physiological effects

◆ ethylene injury and respiration

after fruit and vegetable segmentation, the ethylene release rate increases rapidly, promoting tissue maturation, softening and aging. Ethylene burst caused by cutting takes only a few minutes in some materials, but it usually takes several hours in most materials, and reaches the peak of ethylene release within 6-12 hours. Although the injury induced ethylene synthesis pathway is the same as the normal and maturity related ethylene synthesis pathway to "strengthen the layout of cutting-edge materials", the injury induced ethylene and the ethylene produced during maturity jump are relatively independent and inconsistent in time

the most obvious manifestation and feature of fruit and vegetable tissue metabolism intensification caused by segmentation is enhanced respiration. Enhanced respiration increases the material consumption of micro processed fruits and vegetables, accelerates the loss of nutrients, reduces the sensory properties of products, and shortens the shelf life and shelf life of micro processed fruits and vegetables. The amount of increased respiration is closely related to the type, variety, development stage, cutting size and smoothness of the wound of fruits and vegetables. The juice in the micro processed fruit and vegetable tissue may block the gas channel, reduce the gas diffusion rate in the tissue cells, cause the anaerobic respiration of the internal tissue, and lead to the accumulation of ethanol and acetaldehyde, which together with other volatile substances will cause the odor of the micro processed products

◆ wound healing and secondary metabolism

after tissue segmentation of fruits and vegetables, cork or/and lignin are produced and deposited in the cell wall of the injured cells, and the reaction of different fruits and vegetables is different. After tomato peel injury, the surface cells all have a corking reaction, while the injured part of citrus peel has a lignification reaction, especially on carrots, potatoes and other fruits and vegetables. The formation of cell tethering and callus periderm is affected by the condition of the tissue itself and the surrounding environmental conditions (such as temperature, humidity, gas components). The wound healing energy of the tissue can change the appearance of the micro processed products, affect the commodity properties and reduce the edible value

fruit and vegetable tissues can induce the synthesis of a series of secondary metabolites such as phenylpropane, polyketones, flavonoids, mushrooms, alkaloids, tannins, mustard oil, long-chain fatty acids and alcohols after being cut. These substances are mainly concentrated in the wound and its adjacent tissues, participating in the wound healing response and resisting the invasion of pests and diseases. Not only different kinds of fruits and vegetables, but also different varieties of the same fruit and vegetable, produce different kinds and quantities of secondary substances. The same variety with different origins also has different secondary substances induced by injury

to sum up, the injury signals produced by injury in the production of micro processed fruits and vegetables will significantly affect the metabolism of respiration, phenol and ethylene, which are interrelated in the metabolic system of fruits and vegetables

◆ microbial infection

micro processed fruits and vegetables are usually in an environment of low acidity and high water content in processing and circulation, and the wound caused by segmentation not only brings convenience to microbial infection, but also provides sufficient water and nutrition conditions for the reproduction of microorganisms after infection. The cutting process itself also increases the opportunity of microbial pollution of fruits and vegetables, Therefore, the measurement of this kind of force has come to an end. Products are very vulnerable to contamination by external microorganisms. The rapid propagation of microorganisms leads to low carbon steel: the sample is gradually flattened, which will shorten the shelf life of micro processed fruits and vegetables, but also cause product safety problems. Therefore, how to control the impact of microorganisms during and after the production of micro processed fruits and vegetables is one of the key issues that need to be seriously addressed

research status of quality maintenance of micro processed fruits and vegetables at home and abroad

◆ inhibition of browning and selection of preservatives

browning is one of the main quality problems of micro processed fruits and vegetables. Browning will affect the color of the product and seriously affect the appearance quality. Generally speaking, there are two kinds of fruit and vegetable browning reactions: enzymatic browning and non enzymatic browning. Non enzymatic browning is more complex than enzymatic browning. Enzymatic browning is the browning under the oxidation of polyphenols catalyzed by oxidase and ascorbic acid. The occurrence must be accompanied by polyphenols, polyphenol oxidase and oxygen. To prevent enzymatic Browning, these three factors must be properly controlled. The effective method is to inhibit the activity of polyphenol oxidase, such as low temperature or scalding treatment, adjusting pH value, using chelating agents (such as citric acid, EDTA), etc

◆ storage temperature

low temperature treatment can effectively slow down the activities of enzymes and microorganisms, inhibit the respiratory intensity of fruits and vegetables, reduce the speed of various biochemical reactions, delay aging and inhibit browning. The temperature coefficient Q10 of enzymatic reaction is, and the physiological and biochemical reaction decreases to 1//3 for every 10 ℃ drop in temperature. Therefore, low temperature is the key condition to ensure the quality of micro processed fruits and vegetables. Most studies believe that micro processed fruits and vegetables are more suitable for storage at ℃. In order to ensure the quality of micro processed fruits and vegetables, the temperature control in the processing place and the cold chain in the storage process are important factors for the success or failure of preservation

◆ sterilization treatment

micro processed fruits and vegetables are vulnerable to microbial infection due to man-made mechanical damage. Therefore, micro processed fruits and vegetables usually need sterilization before packaging. Common cold sterilization methods include ultraviolet sterilization, ultrasonic sterilization, ozone sterilization and irradiation sterilization. At present, the most commonly used method is to soak the aqueous solution containing chlorine and hypochlorite for a certain time before packaging for sterilization. The application of stable chlorine dioxide bactericide on micro processed mango was studied. It was found that ClO2 had a significant bactericidal effect on mango. Within a certain concentration range, the bactericidal effect increased with the increase of ClO2 bactericide concentration, but with the extension of storage period, the bactericidal effect of high concentration ClO2 decreased the fastest. Low temperature storage was helpful to maintain and enhance the bactericidal effect of ClO2. At the same time, It was found that ClO2 also had a good anti browning effect, and its anti browning effect increased with the increase of concentration

◆ cutting size and cutting method

the volume of micro processed fruits and vegetables also has a certain impact on the quality. The smaller the volume of cut fruits and vegetables, the larger the cutting area. The faster the surface water transpiration, the more serious the respiratory injury caused by it. The phenolic substances from the cutting surface are easy to be oxidized and browning, which affects the appearance quality and is not conducive to the preservation of products. The bamboo shoots were cut into pieces of different sizes and stored at 4 ℃. It was found that the water loss rate of small bamboo shoots was always higher than that of large bamboo shoots, and the comprehensive score of their quality was always lower than that of the latter, resulting in poor storage resistance

different cutting methods will also lead to the difference of wound area and nutrient loss of cut fruits, thus affecting the fresh-keeping effect of cut fruits. Different cutting methods were used to study the cut pineapple. The results showed that the storage resistance and quality maintenance of longitudinal cut pineapple were better than that of transverse cut pineapple

◆ edible coating

coating can reduce the water loss of micro processed fruits and vegetables, prevent the contact with oxygen, reduce the infection opportunities of microorganisms, prevent the volatilization of aromatic components, inhibit respiration, delay the production of ethylene, reduce the metabolic rate, so as to delay the aging and corruption of micro processed fruits and vegetables, and maintain the quality and stability of products. The membrane itself can be used as a carrier of antibacterial agents and antioxidants. Therefore, a single coating agent or several materials can be selected for compounding. At the same time, antibacterial agents, preservatives, etc. are added to the coating solution to prevent the contact between tissue enzymes and oxygen. through