Pectins are polysaccharides present commonly in dicotyledonous and non-grass monocotyledonous plants. Depending on the source, pectins may vary in molecular size, degrees of acetylation and methylation and contents of galacturonic acid and neutral sugar residues. Therefore, pectins demonstrate versatile gelling properties and are capable of forming complexes with other natural compounds, and as a result, they are useful for designing food products. This review focuses on the structure-related mechanisms of pectin gelling and linking with other natural compounds such as cellulose, hemicellulose, ferulic acid, proteins, starch, and chitosan. For each system, optimal conditions for obtaining useful functionality for food design are described. This review strongly recommends that pectins, as a natural biocomponent, should be the focus for both the food industry and the bioeconomy since pectins are abundant in fruits and may also be extracted from cell walls in a similar way to cellulose and hemicellulose. However, due to the complexity of the pectin family and the dynamic structural changes during plant organ development, a more intensive study of their structure-related properties is necessary. Fractioning using different solvents at well-defined development stages and an in-depth study of the molecular structure and properties within each fraction and stage, is one possible way to proceed with the investigation.

This study focuses on the analysis of polysaccharide residues from the cell walls of fruits and vegetables: tomato, potato, pumpkin, carrot and celery root. An alcohol-insoluble residue was prepared from plant material by extraction using the hot ethyl alcohol method and then cell wall fractions soluble in trans-1,2-diaminocyclohexane-N,N,N′,N′-tetraacetate, sodium carbonate and alkaline solution were sequentially extracted. Infrared spectroscopy combined with Fourier transform (FT-IR) was used to evaluate differences among cell wall residues and among species after each step of sequential extraction of pectins and hemicelluloses. Additionally, pectic substances were identified using an Automated Wet Chemistry Analyser. Principal component analysis (PCA) was applied to FT-IR spectra in two regions: 1,800–1,200 cm⁻¹ and 1,200–800 cm⁻¹ in order to distinguish different components of cell wall polysaccharides. This method also allowed us the possibility of highlighting the most important wavenumbers for each type of polysaccharide: 1,740, 1,610 and 1,240 cm⁻¹ denoting pectins or 1,370 and 1,317 cm⁻¹ denoting hemicelluloses and cellulose, respectively.

Pectin is a heteropolysaccharide abundant in the cell wall of plants and is obtained mainly from fruit (citrus and apple), thus its properties are particularly prone to changes occurring during ripening process. Properties of pectin depend on the string‐like structure (conformation, stiffness) of the molecules that determines their mutual interaction and with the surrounding environment. Therefore, in this review the primary, secondary, and structures of higher levels of pectin chains are discussed in relation to external factors including crosslinking mechanisms. The review shows that the primary structure of pectin is relatively well known, however, we still know little about the conformation and properties of the more realistic systems of higher orders involving side chains, functional groups, and complexes of pectin domains. In particular, there is lack of knowledge on the influence of postharvest changes and extraction method on the primary and secondary structure of pectin that would affect conformation in a given environment and assembly to higher structural levels. Exploring the above‐mentioned issues will allow to improve our understanding of pectin functionality and will help to tailor new functionalities for the food industry based on natural but often biologically variable source. The review also demonstrates that atomic force microscopy is a very convenient and adequate tool for the evaluation of pectin conformation since it allows for the relatively straightforward stretching of the pectin molecule in order to measure the force‐extension curve which is directly related to its stiffness or flexibility.

Flavonoids are secondary metabolites commonly found in plants. They are known for their antioxidant properties, are part of the defense mechanisms of plants and are responsible for the pigmentation of fruit and flowers petals. Consumption foods rich in flavonoids in the daily diet brings a number of pro-health benefits - for example blood pressure regulation, delaying the aging process or anti-cancer effect. These compounds in synthetic or natural form are also used in pharmacy. The profile of flavonoid compounds can be quickly, accurately and easy determine in the test sample by using the infrared and Raman spectroscopy. Those methods are successfully used in the food and pharmaceutical industries. Spectroscopy methods allow us to determine the chemical structure of these compounds. This review describes and compares differences between the spectroscopic spectra of individual compounds with the chemical structure for the flavonoids subgroups: flavones, isoflavones, flavanones, flavonols and anthocyanins.

A new fractionation process was developed to achieve valorization of fruit and vegetable pomaces. The importance of the residues from fruits and vegetables is still growing; therefore; the study presents the novel route of a fractioning process for the conversion of agro-industrial biomasses, such as pomaces, into useful feedstocks with potential application in the fields of fuels, chemicals, and polymers. Hence, the biorefinery process is expected to convert them into various by-products offering a great diversity of low-cost materials. The final product of the process is the cellulose of the biofuel importance. The study presents the novel route of the fractioning process for the conversion of agro-industrial biomasses, such as pomaces, into useful feedstocks with a potential application in the fields of fuels, chemicals, and polymers. Therefore the aim of this paper was to present the novel route of the pomaces fraction and the characterization of residuals. Pomaces from apple, cucumber, carrot, and tomato were treated sequentially with water, acidic solution, alkali solution, and oxidative reagent in order to obtain fractions reach in sugars, pectic polysaccharides, hemicellulose, cellulose, and lignin. Pomaces were characterized by dry matter content, neutral detergent solubles, hemicellulose, cellulose, and lignin. Obtained fractions were characterized by the content of pectins expressed as galacturonic acid equivalent and hemicelluloses expressed as a xyloglucan equivalent. The last fraction and residue was cellulose characterized by crystallinity degree by X-ray diffractometer (XRD), microfibril diameter by atomic force microscope (AFM), and overall morphology by scanning electron microscope (SEM). The hemicelluloses content was similar in all pomaces. Moreover, all the materials were characterized by the high pectins level in extracts evaluated as galacturonic acid content. The lignins content compared with other plant biomasses was on a very low level. The cellulose fraction was the highest in cucumber pomace. The cellulose fraction was characterized by crystallinity degree, microfibril diameter, and overall morphology. Isolated cellulose had a very fine structure with relatively high crystalline index but small crystallites.