Researchers are doing experiments. Courtesy of the Institute of Modern Physics, Chinese Academy of Sciences
■ Reporter Tian Ruiying
Since the beginning of this year, the price of domestic papermaking raw materials has risen sharply, and the cost of chemical materials supporting papermaking has even doubled. As a long-neglected resource, how to use waste paper efficiently to create greater value has become an urgent social problem to be solved.
Recently, after more than ten years of research, Wang Shuyang's team, a researcher at the Institute of Modern Physics of the Chinese Academy of Sciences, has made new progress in the research of using waste paper fermentation to produce cellulase. The results were published in the Journal of Cleaner Production.
"Waste paper has the advantages of low price, large amount of production, wide range of sources, easy to obtain, the cost of using waste paper as a carbon source is only about 1/10 of the microcrystalline cellulose carbon source, which can not only effectively reduce the cost of cellulase fermentation, but also realize the high-value utilization of waste paper resources." Wang Shuyang said in an interview with China Science News.
There is an urgent need to find a cheap source of carbon
Cellulase is the world's third largest industrial enzyme preparation after amylase and protease, and has been widely used in bioenergy, food, papermaking, textile washing, medicine and other fields. However, the high cost of fermentation has become a "roadblock" on its industrialization road.
Similarly, the high cost of cellulase fermentation also exists in the production of silage agents.
In 2008, when Studying Sweet Sorghum Silage, Wang Shuyang's team found that the neutral washing fiber content of sweet sorghum forage was relatively high, which affected the palatability of sweet sorghum silage and the digestion and absorption of nutrients. The team found that if a certain percentage of highly active cellulase was added, the amount of fiber in sweet sorghum silage that was not easily digested and absorbed could be reduced during the silage process.
Cellulase is a substrate-inducible enzyme that requires the addition of a cellulosic carbon source to the cellulase fermentation culture to induce a large amount of synthetic secretion of cellulase proteins. At present, the carbon source used in fermentation and production of cellulase is generally microcrystalline cellulose or crop straw and other commodities.
At first, the inducible cellulosic carbon source used by the team was a purchased commercial reagent, microcrystalline cellulose, but the experiment found that although its induced fermentation enzyme production effect is better, the fermentation production cost is relatively high.
Subsequently, they selected more studied crop straw waste, including corn straw, corn cobs, sweet sorghum straw and sweet sorghum juice residue, but the effect of fermentation enzymes was not ideal. To this end, they will be alkali treated straw as a carbon source for fermentation enzymes, although the fermentation effect has improved to a certain extent, but the alkali treatment process is cumbersome, high cost, but increased the production cost of cellulase.
Through preliminary research, Wang Shuyang found that regardless of the use of commercial microcrystalline cellulose or crop straw as a fermentation carbon source, the fermentation production cost of cellulase is relatively high, and "new and most suitable and inexpensive carbon source types must be found."
With the increasing prominence of environmental pollution and ecological problems, Wang Shuyang began to think that waste paper is not only inexpensive, but also has a high content of cellulose components, which may be used as a source of fermented carbon to induce the synthesis and secretion of cellulase.
With this inspiration, she led the team into the "waste paper".
"Tattered" waste paper becomes "protagonist"
There are many types of waste paper, and the first thing researchers should do is to find the best fermentation effect from many types of waste paper. They have successively selected four types of office waste paper, napkin waste paper, magazine paper and cardboard paper, and found that cardboard paper has the best enzyme effect in the fermentation of 4 kinds of waste paper carbon source.
"Through the structural characterization of the four types of waste paper, we found that the fiber bundles on the surface of the cardboard paper were loosely cracked and rough, and only the cardboard paper in the X diffraction analysis detected the calcium carbonate component. Therefore, we speculate that this composition and structural properties of cardboard paper are more suitable for fermentation enzymes than other types of waste paper. In an interview with China Science Daily, Dong Miaoyin, a special research assistant at the Institute of Modern Physics of the Chinese Academy of Sciences, said.
In order to further improve the effect of enzyme production, the researchers have a new idea - bran, as a by-product of agricultural processing, contains a certain amount of soluble fibro-oligosaccharides, which can effectively induce the secretion of cellulase and hemicellulose, and if used as a mixed carbon source with cardboard paper, it may increase the level of fermentation enzyme production.
Experiments proved that their idea was correct. When the cardboard paper and bran are mixed and fermented as a mixed carbon source, the β-glucosidase activity can reach up to 0.80 IU/mL, which is 56.86% higher than the cardboard paper single carbon source enzyme activity; the external cut dextranase activity, filter paper enzyme activity and xylanase activity (Xyl) also have a certain improvement, of which Xyl reaches 399.74 IU/mL, which is 16.51% higher than the microcrystalline cellulose carbon source fermentation enzyme activity.
The use of waste paper as a carbon source for cellulase production, in addition to obtaining excellent fermentation efficiency, the production cost is only about 1/10 of the microcrystalline cellulose carbon source. Not only that, the whole process is produced without pretreatment by-products, simple operation, green and pollution-free.
"If crop straw is used as a source of fermented carbon, it generally requires certain pretreatment, and the strong acids and alkalis used in this process not only corrode the equipment, but also pollute the environment." In addition, the pretreatment process also produces by-products that inhibit microbial fermentation, such as furfural, acetic acid and phenolic compounds, which adversely affect the growth of cellulase production strains and the enzyme production process. Dong Miaoyin told reporters.
Featured research helps
In Wang Shuyang's view, the whole research work can achieve a surprising fermentation effect, because the Institute of Modern Physics of the Chinese Academy of Sciences has a history of nearly 40 years of special research direction - heavy ion beam irradiation mutagenesis breeding.
The Trichoderma longifolia LC-M4 enzyme-producing fermentation strain used in this study is a high-yielding cellulase mutant strain selected by heavy ion beam mutagenesis, which has excellent properties that can simultaneously express secreted cellulase and hemicellulase lines, and can simultaneously carry out the fermentation production of cellulase and hemicellulase under the induction of cellulose carbon sources.
"Due to the multi-component synergistic expression and complex metabolic regulation network characteristics of cellulase synthesis and secretion, the genetic background of enzyme-producing filamentous fungi is unclear, so that heavy ion beam irradiation mutagenesis has obvious superiority in the breeding of enzyme-producing strains." Wang Shuyang told reporters.
In fact, in this long research process, in addition to the need to overcome technical problems, it is also necessary to overcome difficulties such as shortage of personnel and tight funds.
"The investment in the circular economy is very large, and the docking and transformation of enterprises also requires a lot of capital investment, in the most difficult time, we also hesitated whether we should change directions, but thinking that this research is of great significance to the entire ecological environment and circular economy, we still resisted the pressure and persevered." Wang Shuyang sighed as he recalled.
Next, the team will further domesticate the fermentation production strain, improve its production efficiency and level in the waste paper carbon source fermentation, and further optimize the fermentation system and conditions. In addition, it will also conduct in-depth exchanges and cooperation with cellulase production enterprises and waste paper recycling enterprises, fully understand the current needs and difficulties of enterprises, optimize the existing waste paper cellulase production process, and promote the transformation and application of research results as soon as possible.
Source: China Science Daily