The studies of cellulose microfibrils organization and structure and their influence on mechanical properties of cell wall during the development, ripening and storage of fruits

Title: The studies of cellulose microfibrils organization and structure and their influence on mechanical properties of cell wall during the development, ripening and storage of fruits.

UMO-2011/01/D/NZ9/02494

Leader: Monika Szymańska-Chargot

Period: 2011-2015

Financed by National Science Center Poland, Sonata Program 

The main objective of this project is to determine influence of cellulose microfibrils on the structure and mechanical properties of plant cell wall during development, ripening and also during shelf life. The first aim of the project is to measure cellulose crystallinity degree, structure and cellulose microfibrils arrangement during the fruit/vegetable ripening to answer for the question whether ripening affects crystallinity. The second, is to determine the role of pectins and hemicelluloses on the crystallinity index of cellulose and cellulose microfibrils arrangement. And the third, is to set up crystallinity degree and arrangement of cellulose microfibrils with mechanical properties of cell wall.

Plant cell walls and their constitutive polysaccharides networks are vital with regards to plant organ mechanical properties like stiffness or strength. The basic components of plant cell wall are cellulose fibrils embedded in matrix polysaccharides. The main matrix polysaccharides are pectins, hemicelluloses (mainly xyloglucan) and also other polymers like lignins. Concentrations of each polymer vary according to the origin of plants, organs and tissue. The cellulose microfibrils have crystalline core surrounded by amorphous form of cellulose. Whereas the matrix polysaccharides seem to be amorphous and do not exhibit any order. The cell wall mechanical properties, its water-binding capacity, or ability to enter in chemical reactions, which directly affect the texture of fruits and vegetables, depends on crystallinity degree of cellulose microfibrils. It is important for understanding the mechanical properties of plant materials (wood, fibres) and the texture of fruits and vegetables from consumer point of view. Currently, cellulose I the native crystalline morphotype of cellulose, is receiving an increased attention due to its potential use in bioenergy.

Plant cell walls and their constitutive polysaccharides networks are vital with regards to plant organ mechanical properties like stiffness or strength. The basic components of plant cell wall are cellulose fibrils embedded in matrix polysaccharides. The main matrix polysaccharides are pectins, hemicelluloses (mainly xyloglucan) and also other constituents like lignins, protein and phenolic compounds. The matrix polysaccharides seem to be amorphous and do not exhibit any order. Concentrations of each constituent vary according to the origin of plants, organs and tissue. Cellulose microfibrils are heterogeneous. A schematic model of cellulose microfibrils involves a high crystalline core surrounded by less crystalline region and interrupted by amorphous form of cellulose. The crystalline domains in cellulosic materials are of very limited size and are mixed with noncrystalline regions in fibrils, which predominantly determine their mechanical properties, such as tensile strength. Physico-chemical behaviour, i.e.: accessibility for chemical derivatization, swelling and water binding and also mechanical properties of cell wall, which directly influence textural properties of plant tissue depends on degree of cellulose crystallinity. It is important for understanding the mechanical and the texture properties of plant materials such as fruits and vegetables from consumer point of view. Furthermore, currently, cellulose I, the native crystalline morphotype of cellulose, is receiving an increased attention due to its potential use in bioenergy.

Concentration of cell wall non-cellulosic polysaccharides  changing during development and ripening and further during senescence of fruit. During development and ripening changes of cell wall properties are result of compounds synthesis, whereas during postharvest rather dominates degradation, i.e. opposite effect. Changing concentrations of non-cellulosic polysaccharides have a tremendous effect on mechanical properties of cell wall and also on structure and arrangement of cellulose microfibrils. Although, many years of investigations under the cell wall properties and cell wall constituents, some question still remains open:

• whether the cellulose crystallinity degree is constant during fruit development and senescence of fruit,
• whether the structure and arrangement of cellulose microfibrils are changing in time and how it influence the mechanical properties of plant cell wall,
• and the impact of non-cellulosic polysaccharides of cell wall on structure and arrangement of cellulose microfibrils.

Therefore answers to this question will help understanding the processes which are responsible for changing the cell wall properties and furthermore finding optimal conditions of fruit development, ripening and storage.

The mechanical properties of cell walls have an effect on the texture of the fruit, which is a major determinant of consumer quality of fruits and vegetables. During metabolic processes, such as adolescence or storage and processing, fruit tissues undergo changes leading to an undesirable softening of the fruit. The water content which relates to the amorphous areas of the cell wall, and the content and degree of esterification of pectin affects the flexibility of cell walls. The degree of crystallinity of cellulose (crystalline regions are stiffer tensile strength) and the arrangement of fibrils is likely to affect the mechanical properties of the cell wall and thus the external features of textures that are relevant to the consumer. This project takes the issue of understanding this phenomenon and will determine whether the microcrystalline structure and its possible changes have also affected the properties in macro scale, or the mechanics of cell walls. In this respect, the results will be relevant for further research on optimizing, also in terms of consumer appeal, the processes of growth, harvesting and storing fruit and vegetables.

Plant cell walls are also used in many industries (paper production, biofuels, production of  supplementation in food products, textile industry). There is also a starting material for the preparation of many chemicals, such as nitrocellulose, used to manufacture plastics and explosives, and cellulose acetate, which is used for making plastics and rayon. Cellulose microfibrils degree of ordering , whether or not their degree of crystallinity in cell wall also have a major impact on processing and waste management. Cellulose is extremely strong polymer that is hydrolyzed by the enzyme (cellulase) or treatment with concentrated acids (sulfuric, nitric). Chemical compounds designed to interact efficiently decomposition of cellulose in the amorphous areas, but have little access to the crystalline region. Developing optimal cellulose hydrolysis technology is to increase its efficiency and reduce of imposed costs. Therefore, research on the crystalline structure of cellulose microfibrils and their arrangement in the cell walls are also important for the optimization of processing operations.

The importance of this project is also cognitive. So far, there were few studies, addressing the changes in the structure of cellulose microfibrils during growth, maturation, and storage of fruit. 

Publications:

1. Szymanska-Chargot M., Chylinska M., Kruk B., Zdunek A. „Combining FT-IR spectroscopy and multivariate analysis for qualitative and quantitative analysis of the cell wall composition changes during apples development.” Carbohydrate Polymers, 115 (2015) 93–103.
2. Chylińska M., Szymańska-Chargot M., Zdunek A., 2014. „Imaging of polysaccharides in the tomato cell wall with Raman microspectroscopy.” Plant Methods, 10:14 (2014) 1-9.
3. Szymańska-Chargot M., Zdunek A. “Use of FT-IR spectra and PCA to the bulk characterization of cell wall residues of fruits and vegetables along a fraction process.”  Food Biophysics,  8 (2013) 29-42.
4. Szymanska-Chargot M., Adamiak A.,Zdunek A.. “Pre-harvest monitoring of apple fruits development with the use of biospeckle method.” Scientia Horticulturae 145 (2012) 23-28.