Disinfection Technology for Auricularia auricula in Bag Cultivation: Problems and Countermeasures

Xianggang WANG, Yanfang LI, Fengzhi ZANG, Yuanxia MIAO, Hui WANG, Xiaoyu YIN, Chunge SHI

1. Edible Fungi Institute, Suihua University, Suihua 152061, China; 2. Animal Quarantine Station of Dunhua, Dunhua 133700, China; 3. Dunhua Mingxing Specialty Science and Technology Development Limited Company, Dunhua 133704, China; 4. Dunhua Jiangnan Agricultural Technical Extension Station, Dunhua 133700, China

Abstract This article analyzes the problems existing in disinfection technology for Auricularia auricular in bag cultivation, introduces the concept of disinfection and sterilization technology and the technical status of humidification for disinfection of A. auricular in bag cultivation, analyzes the related problems caused by this type of technology and the reasons for the problems, and puts forward solutions to the technical problems.

Key words Auricularia auricular, Cultivation, Disinfection technology, Problems and countermeasures

1 Introduction

According to incomplete statistics, the total output ofAuriculariaauricular in China was 6.273 8 million t in 2016 and 6.388 4 million t in 2017, and there is a trend of increasing year by year. At present, the production ofA.auricularis dominated by bag cultivation[1]. The huge market demand has promoted the continuous update and improvement of the cultivation technology forA.auricularindustry, but there are still many problems in the process of continuous improvement of cultivation technology. In recent years, with the development of the industry, the cultivation scale ofA.auricularhas become larger and larger, theA.auricularplants are becoming more and more beautiful, and the mechanical equipment is becoming more and more advanced, but unfortunately, there are still many problems in the core disinfection technology, and the problems are even very serious in some areas. For example, the application of the wrong disinfection technique of humidification advocated by some people in recent years is a typical case, and it has directly led to the failure of cultivation techniques. The reason for this phenomenon is that some practitioners lack relevant basic theoretical knowledge. It is also directly or indirectly related to the promotion model of theA.auricularbag cultivation technology. This article analyzes in detail the problems in the disinfection technology forA.auricularin bag cultivation and puts forward corresponding solutions to provide technical support for practitioners.

2 Status and existing problems of disinfection technology

2.1 Disinfection and sterilization technologyDisinfection refers to killing or removing some microorganisms, such as pathogenic microorganisms and trophozoites, by physical or chemical methods. Disinfection does not work for endospores or certain spores, its role is superficial and partial. Disinfection methods are divided into physical and chemical, and according to the position of action, they are also divided into surface disinfection and space disinfection. Sterilization is to kill or remove all microorganisms by physical or chemical methods. Its role is complete and thorough. General disinfection and sterilization methods are divided into physical methods and chemical methods. Physical methods include dry heat sterilization, moist heat sterilization, filter sterilization, ultraviolet sterilization,etc. Chemical sterilization is to use certain chemicals to inhibit or kill microorganisms. There are many types of applicable chemicals, such as acids, alkalis, heavy metals, phenols, alcohols, aldehydes, halogens, oxidants, reducing agents, surfactants, dyes and antibiotics[2].

2.2 Status and existing problemsThe process of disinfection and sterilization in the bag cultivation ofA.auricularmainly includes three parts: bag sterilization, inoculation and culture. For sterilization of bags, high-pressure or normal-pressure steam sterilization is used[3]. The inoculation process is mostly carried out in inoculation box or inoculation hood, of which the space is small, the sealing is good, and the effect of ultraviolet radiation and chemical fumigation is good. Most producers pay enough attention to the sterilization and inoculation process of bags, so the former two links are less prone to problems. However, the culture link is prone to problems. This is mainly due to the large space and sealing inability of culture rooms, especially for old culture rooms that have been used for many years. If the technology is used inappropriately, all the microorganisms in the cultivation bags will die.

However, in recent years, someone has proposed a disinfection technique of humidification. Specifically, the environmental space and objects to be disinfected are first sprayed with water and humidified, and then let stand under high humidity for 24 h to make the spores of harmful microorganisms on the objects in the space germinate, which are then killed or removed by chemicals, and finally, the environment space is ventilated and air-dried. This disinfection method has been promoted to manyA.auricularpractitioners through new media and other channels on the Internet, so that this wrong disinfection technology has been misleading multiple baggedA.auricularproduction areas, causing the environmental space and objects that should be disinfected to be disinfected unqualifiedly. As a result, the degree of contamination of cultivation bags has greatly increased compared with the past.

3 Problem analysis and correct methods

3.1 Problem analysisThe proponent of humidification disinfection technology believes that humidification by spraying water is conducive to germination of spores, which will be better killed or removed by chemical disinfection. The theoretical basis is the technical principle that some chemical disinfectants will increase the disinfection efficacy by 10% every time the environment doubles the humidity. According to this understanding, humidification by spraying water can induce the rapid propagation of invisible bacteria in the environment to be disinfected. It is considered that "if you want to kill microorganisms, you must make them propagate first", fantasizing about achieving the best disinfection and sterilization effect. After disinfection, the environmental space (e.g. culture room) and objects that have been disinfected are ventilated and air-dried for standby. The promotion of this technology has led to practitioners who have no professional fundamental knowledge about disinfection and sterilization to blindly believe and implement it, resulting in significant rise in pollution degree.

This kind of technical theory is wrong. The specific reasons are as follows. (i) The disinfection work of baggedA.auricularproduction process is different from the disinfection in the wet environment of aquaculture farms. The production process of baggedA.auricularmust always be kept in a ventilated and dry environment in order to effectively inhibit the growth and reproduction of miscellaneous bacteria, and to ensure that the bags are not contaminated by miscellaneous bacteria. Actually, drying itself is a broad-spectrum effective disinfection method. Water is an essential component of the composition and metabolism of microbial cells. Drying can dehydrate microbial cells, so that metabolism is hindered. In short, drying can effectively inhibit the reproduction of microorganisms such as miscellaneous bacteria. (ii) There are tens of millions of microorganisms and other harmful microorganisms on the environmental space and objects to be disinfected. They have an amazing reproduction speed during the humidification process and are difficult to control. While re-germinating and breeding, new dormant spores will be produced. After the humidification, although the disinfection effect of chemical agent is enhanced, at the same time, the proliferation of bacteria to be disinfected is soared. Subsequent chemical disinfection and ventilation drying cannot completely offset the proliferation of harmful bacteria. Moreover, after humidification by artificial water spray, the interior of objects in the space and the places that are not in contact with fungicide are moistened, and they will become a "paradise" for the growth and reproduction of harmful microorganisms such as bacteria. Thus, the difficulty of subsequent disinfection work is increased, and in order to achieve desired disinfection effect, the action time needs to be extended or the concentration of disinfectant needs to be increased. However, practitioners often do not realize this. They still operate disinfection according to usual time and concentration, resulting in incomplete disinfection and a serious hidden danger in bag pollution. (iii) Some people advocate humidification disinfection because they lack professional knowledge in microbiology, do not understand the principles of microbial disinfection and the laws of microbial reproduction and lack knowledge base of collaborative disinfection and sterilization. Since the disinfectant will increase the disinfection efficacy in a high-humidity environment, and high temperature and humidity can accelerate the germination speed of spores, they simply consider that best disinfection effect will be achieved after humidification by spraying water.

3.2 Correct disinfection methodThe environmental space and objects (usually culture room) to be disinfected should be ventilated and air-dried first to inhibit the proliferation of miscellaneous bacteria and minimizes the number of miscellaneous bacteria in the environment to be disinfected, thereby reducing the pressure of subsequent disinfection. After the disinfection, the culture room will be not ventilated any more before use to prevent the introduction of new bacteria with wind to achieve the purpose of disinfection. Second, after ventilating and drying, there is no need to spray water to increase humidity. For old culture rooms or areas that really need to be humidified for disinfection, liquid spray disinfection and aerosol disinfection are combined to coordinate comprehensive disinfection treatment. This process need not be simply understood as sterilizing the spores after humidifying the environment to be disinfected for 24 h. Instead, after liquid disinfectant is sprayed for 24 h, aerosol disinfectant is used for secondary supplementary disinfection. By the way, the technical requirements that some aerosol disinfectants can increase the disinfection effect in a humid environment are met. The purpose of liquid spray disinfection is disinfection and sterilization, and it is never intended to moisturize the environment. Excessive humidification will destroy the foundation of dry disinfection. Consequently, long-term disinfection effect cannot be achieved, and the effect of secondary aerosol disinfection is also weakened[4].

4 Countermeasures

First of all, the relevant competent departments of the industry should take measures to increase the scientific popularization of bag cultivation technology forA.auricular, and hire industry experts to actively popularize the basic disinfection and sterilization technical measures forA.auricularcultivation through new online media and other platforms. For the emerged new technologies and methods, experts in the industry need to be hired to discuss, appraise and verify. The technologies and experiences that have been proved to be effective will be widely publicized by industry authorities through various channels, making them easy for the majority of practitioners to accept. Second,A.auricularindustry research technicians should solicit opinions from multiple parties and conduct adequate theoretical research and practical verification before proposing or contacting a technical measure. They must not practice directly the content from book that is considered very practical without thinking it over and testing by practice. After proved to be effective by multiple parties, the technology will be disseminated to ordinary practitioners. Unnecessary human losses caused by being too blind must be avoided. Finally, general practitioners ofA.auricularindustry should strengthen the learning of basic theoretical knowledge, understand and master the basic knowledge of disinfection and sterilization, consult with industry technicians and experts through various channels such as online new media, and listen to many opinions. They only can listen to other new technologies, new methods, opinions and suggestions after mastering the basic principles. In addition, they can’t blindly believe others’ opinions. Instead, they should combine basic principles and multi-party opinions to get the correct technical route that suits themselves.

5 Conclusions

As the most critical link in the production of baggedA.auricular, disinfection technology is related to the success of production. But in recent years, the wrong practice of humidification disinfection technique has led to the proliferation of bacteria in the working environment. Due to the lack of attention to the dry disinfection technology and chemical disinfectant’s inability to maintain the disinfection effect for cultivation bags, the contamination chance of cultivation bags in an unqualified environment by miscellaneous bacterial increases significantly[5]. According to incomplete statistics, only in Heilongjiang Province, from winter of 2018 to spring of 2019, the number of bags cultivated due to the misleading of humidification disinfection technique reached more than 400 million, and the direct economic losses caused amounted to more than 800 million yuan, severely dampening the enthusiasm for the development of baggedA.auricularindustry in Heilongjiang Province. Even, some practitioners misled by the technology have been in debt. The currentA.auricularbag cultivation industry is different from the previous courtyard economy. Once technical error breaks out, the national economy and people’s livelihood will be directly affected. Practitioners of theA.auricularindustry should be warned, and be cautious for technological innovation to avoid falling into technical misunderstandings, thereby maintaining the healthy development of the industry.

The combination of theory and practice is of course important, but if the theoretical level and reserve of science and technology of practitioners can’t go beyond the knowledge blind spots and technology traps in the industry and if they blindly worship and spread the so-called empirical techniques before distinguishing true and false, the development of the industry will be actually misled. Technology should be supplemented by experience, and the scientific knowledge and related scientific technology of bag cultivation ofA.auricularshould be propagated actively to effectively control and predict the development of the industry, guide fungus growers and guide the industry towards a healthy development.