Some time ago, the news of the listing of 300 tons of "Frozen Sleeping Lychee" quickly attracted widespread attention. Lychee frozen October is still as fresh as ever, and many netizens have expressed their desire to taste it.
How do you freeze a mouthful of sweetness? Can you taste lychees in all seasons?
From June 19th to 20th, sponsored by Guangdong Agricultural Technology Extension Center and South China Agricultural University, and jointly organized by Maoming Agricultural Science and Technology Extension Center and Southern Rural Daily, the lychee ultra-low temperature freeze sleep and fresh-locking technology training activity was successfully held in Maoming, Guangdong.
The scene of lychee ultra-low temperature freeze sleep locking technology training activities
Frozen lychee leverages a big industry
On April 11, 2023, General Secretary Xi Jinping inspected the lychee plantation in Baiqiao Village, Genzi Town, Gaozhou, Maoming, Guangdong, and proposed: "The lychee industry must be developed, and it will not work if the problem of preservation is not solved."
In this regard, the Guangdong Provincial Department of Agriculture and Rural Affairs immediately responded and set up a special fund of 10 million yuan for the research, promotion and application of key technologies for the storage and preservation of lychees.
Among them, 5 million yuan was invested in the R&D and industrial application of "Lychee Ultra-low Temperature Freeze Sleep Locking Technology", which was led by Professor Cao Yong of South China Agricultural University, and a number of units were organized to set up a project team to jointly tackle key problems.
"In recent years, Maoming City has conscientiously implemented the deployment requirements of the Provincial Party Committee and the Provincial Government, focused on doing a good job in the 'native products' article, promoted the project of millions of thousands of people with high standards, promoted the advantages, made up for the shortcomings, strengths and weaknesses, and made efforts from the links of lychee planting, preservation, sales, processing, logistics, and branding, and promoted the upgrading of the lychee industry in the whole chain, and achieved remarkable results." Zhang Mei, deputy director of the Maoming Municipal Bureau of Agriculture and Rural Affairs, said in her speech.
Lychees are still fresh in October, and the appearance of "frozen sleeping lychees" helps to alleviate the sharp decline in the annual output of lychees. The "tailor-made" freeze-sleeping technology for the fresh fruit industry lays a scientific and technological foundation for "lychee freedom".
Li Zhenzhu, a third-level researcher of the Science and Technology Education Department of the Guangdong Provincial Department of Agriculture and Rural Affairs, participated in the training activities and made an opening speech, he said that with the joint efforts of South China Agricultural University, the Provincial Agricultural Technology Extension Center and other units, new breakthroughs have been made in the ultra-low temperature freezing and locking technology, the shelf life of lychees has been extended, and the supply cycle of fresh fruits has been significantly extended.
In the preliminary test, the use of lychee ultra-low temperature freeze-sleep locking technology can achieve annual storage, break the "seasonality" of lychee, and achieve year-round supply.
Jiang Feng from the Rural Revitalization and Social Service Office of South China Agricultural University emphasized in his speech that he hoped that all students could make use of the advantages of new media to develop e-commerce, give full play to everyone's strength, and push "Frozen Sleeping Lychee" out on the majority of sales platforms.
"In recent years, the province's agricultural technology department has continued to make efforts in the innovation of agricultural technology promotion models, the construction of comprehensive extension service platforms, the selection of leading varieties and main technologies of lychee, and the promotion of lychee planting and preservation technology, so as to actively promote the high-quality development of the lychee industry." Luo Guowu, deputy director of the Guangdong Provincial Agricultural Technology Extension Center, said.
Lychee has huge potential and broad consumer groups in the domestic and foreign markets, and the output value of the whole litchi industry chain in Maoming City will exceed 12 billion yuan in 2023. At present, there is a certain market gap in quick-frozen lychee at home and abroad, and it has broad consumption prospects.
Technology empowers lychees to lock freshness
Lychee has a strong respiration effect, and the ripening period is generally concentrated in the high temperature and humidity season of May ~ July, and it is susceptible to microbial infection or mechanical damage after picking, resulting in quality deterioration, known as "one day color change, three days of taste change", resulting in short-term oversupply of lychee fresh fruits, insufficient annual supply, and lack of raw materials for deep processing.
According to statistics, the annual loss due to decay accounts for 20% of the total production.
How to effectively extend the life cycle of fresh fruits? Freezing is one of the ways. However, the freezing rate of traditional frozen lychee is slow, the juice loss rate is high after thawing, the color browning is fast, and the nutrient loss is large. Ultra-low temperature quick-freezing technologies such as liquid nitrogen quick-freezing have a fast freezing rate, which promotes the formation of fine and uniform ice crystals and improves the quality of frozen food.
Cao Yong, a professor at the College of Food Science and Technology of South China Agricultural University, proposed that the R&D and application promotion plan of Guangdong Province's lychee ultra-low temperature freezing and locking technology focuses on two aspects: "promoting the research of lychee ultra-low temperature freezing and locking technology" and "promoting the ultra-low temperature freezing and locking technology of lychee".
Cao Yong, a professor at the College of Food Science and Technology, South China Agricultural University
Among them, liquid nitrogen quick-freezing technology refers to the technology of freezing food by absorbing a large amount of latent heat and sensible heat through liquid nitrogen in contact with food.
The boiling point of liquid nitrogen at atmospheric pressure is -195.8 °C, and the liquid nitrogen is in contact with food, and the temperature difference of more than 200K is used for intense heat exchange, and the maximum ice crystal formation zone is passed in the shortest time. The ice crystals formed by the moisture in the food are uniform and fine, the food damage is small, and the thawed food can basically maintain the original color, aroma and taste.
"Frozen Sleep Magic" solves the problem of freshness
The overall technical route of liquid nitrogen quick-freezing technology includes five key technologies: variety research and key technologies for color protection and brittle pretreatment, new safe and green quick-freezing medium and impregnation quick-freezing technology and equipment for lychee, key technologies and equipment for liquid nitrogen ultra-low temperature quick-freezing and fresh-locking, key technologies and equipment for lychee dormancy preservation, high-fidelity restoration, and integration and industrialization demonstration of key technologies and equipment for quality improvement of lychee.
Cao Yong emphasized that the key technologies and equipment for dormant preservation and high-fidelity reduction of lychees include the use of modern equipment and technologies such as colorimeter, texture analyzer, and low-field nuclear magnetic resonance to clarify the quality change law of frozen lychees; Optimize the ratio of cold storage materials to transportation materials, packaging box design parameters, product stacking mode, etc.; Finally, a new type of high-fidelity defrosting and reduction equipment was developed by using high-efficiency thermal conductive elements to provide a precise thawing solution for lychees.
The processing process of the whole industrial chain of frozen sleeping lychee includes various links such as "pretreatment, color protection, packaging, ultra-low temperature quick-freezing, low-temperature storage, cold chain transportation, thawing and reduction", involving a variety of key technologies such as raw material grading, fruit and vegetable color protection, food packaging, and quick-freezing preservation.
It is worth noting that Cao Yong's team has optimized and innovated the principle and process of key technologies such as "capacity freezing speed", and developed a new generation of "liquid nitrogen" quick-freezing technology and equipment.
Zhou Wuyi, a professor at the School of Materials and Energy of South China Agricultural University, said that lychee ultra-low temperature freeze sleep packaging materials must have high low temperature resistance, good mechanical properties and barrier properties.
Zhou Wuyi, a professor at the College of Materials and Energy, South China Agricultural University
Through a large number of experiments and application studies, it is shown that the sealing performance of the lychee can be greatly improved by using biaxially oriented nylon as the main material of the packaging of the lychee and polyethylene film as the surface encapsulation material, thereby significantly improving the production efficiency and storage quality of the lychee.
Internet+ helps industrial transformation
Driven by the "Internet +" strategy, the lychee industry is transforming to intelligence and informatization.
Based on automated processing equipment, Guangdong Province now has an annual output of 1,000 tons of ultra-low temperature quick-frozen lychee production line, this year's frozen lychee output reached 180 tons, covering more than 5 varieties.
The frozen storage quality of processed lychees was good, and the flavor, texture and shape of lychees did not change significantly compared with fresh fruits after one year of frozen storage, which could meet the market demand.
Wu Weibin, a professor at the College of Engineering of South China Agricultural University, pointed out that the core of the key technology and equipment of liquid nitrogen high-efficiency ultra-low temperature quick-freezing and fresh-locking lies in the temperature control of ultra-low temperature quick-freezing equipment, standardized quick-freezing process parameters and quality testing technology of lychee.
Ultra-low temperature quick-freezing equipment improves the quality and freshness of quick-frozen lychees, while also saving energy and resources. Standardized quick-freezing process parameters will provide accurate guidance for food production, improving production efficiency and consistency. The creation of a non-destructive testing model for lychee will help solve the quality problems in the process of fruit quick-freezing and improve the preservation effect of vulnerable fruits such as lychee.
Wu Weibin, a professor at the College of Engineering, South China Agricultural University
In the future, the new generation of information technology such as the Internet of Things, blockchain, cloud computing, big data, and mobile Internet will be combined with all aspects of the production of the litchi industry, so as to promote the development, transformation and upgrading of the "Internet +" modern litchi industry, realize the informatization and automation of the whole industrial chain, and smart lychee orchards and smart quick-freezing plants have become the mainstream of future development.
Mo Jinqi, the technical director of fresh lychee preservation of Guangzhou Conghua Hualong Fruit and Vegetable Preservation Company (hereinafter referred to as Hualong Company), mentioned that Hualong Company has built a cold chain collection and distribution center for the preservation and processing of lychee and other agricultural products in Conghua, Guangzhou, with an annual production capacity of more than 20,000 tons, integrating pre-cooling and storage, intelligent sorting and packaging, ultra-low temperature freeze sleep, and food deep processing.
It is understood that in 2024, Hualong Company will land a lychee ultra-low temperature freezing and fresh-locking processing center in Maoming to complete the promotion and application of technology in the main lychee producing areas.
Mo Jinqi, the technical person in charge of frozen sleeping lily of Guangzhou Conghua Hualong Fruit and Vegetable Preservation Company
About 100 representatives participated in the training course, including representatives from Guangdong Agricultural Technology Extension Center, teachers and students from South China Agricultural University, and technical representatives from Maoming Agricultural Science and Technology Extension Center. The opening ceremony was presided over by Liu Huaitao, head of Maoming Agricultural Science and Technology Extension Center.
【Author】He Xueqi
Source: Southern Rural Daily