Pectin is an important polysaccharide with applications in foods, Pharmaceuticals, and a number of other industries. Its importance in the food sector lies in its ability to form gel in the presence of Ca2+ ions or a solute at low pH. Although the exact mechanism of gel formation is not clear, significant progress has been made in this direction. Depending on the pectin, coordinate bonding with Ca2+ ions or hydrogen bonding and hydrophobic interactions are involved in gel formation. In low‐methoxyl pectin, gelation results from ionic linkage via calcium bridges between two carboxyl groups belonging to two different chains in close contact with each other. In high‐methoxyl pectin, the cross‐linking of pectin molecules involves a combination of hydrogen bonds and hydrophobic interactions between the molecules. A number of factors—pH, presence of other solutes, molecular size, degree of methoxylation, number and arrangement of side chains, and charge density on the molecule— influence the gelation o...

Chemistry and uses of pectin--a review.

Pectin represents a very heterogeneous biopolymer whose functionality remains largely puzzling. The link between the pectin fine structure and functional properties with relevance to plant growth and development, as well as food processing, is continually being explored. This review describes the current knowledge of pectin structure–function relationships. Key mechanisms dictating pectin structure–function relationships are discussed, including the polymer biosynthesis, cross-linking mechanisms, enzymatic and nonenzymatic conversion reactions, solubility properties, and more. Insight into the polymer structure–function relationships is highlighted by examining traditional and advanced methodologies used in pectin research. The role of pectin in modulating the quality characteristics of plant-based foods is underlined while pin-pointing some of the main challenges and perspectives. An integrated approach using the pectin structure–function relationship in the precision engineering of mechanical properties of tissue-based systems is proposed.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1541-4337.2009.00071.x

Pectins in Processed Fruits and Vegetables: Part II—Structure–Function Relationships

The discovery of catalytic ability in RNA has given fresh impetus to speculations that RNA played a critical role in the origin of life. This question must rest on the plausibility of prebiotic oligonucleotide synthesis, rather than on the properties of the final product. Many cliams have been published to support the idea that the components of RNA were readily available on the prebiotic earth. In this article, the literature cited in support of the prebiotic availability of one subunit, D-ribose, is reviewed to determine whether it justifies the claim. Polymerization of formaldehyde (the formose reaction) has been the single reaction cited for prebiotic ribose synthesis. It has been conducted with different catalysts: numerous basic substances, neutral clays and heat, and various types of radiation. Ribose has been identified (yields are uncertain, but unlikely to be greater than 1%) in reactions run with concentrated (0.15 M or greater) formaldehyde. It has been claimed in reactions run at lower concentration, but characterization has been inadequate, and experimental details have not been provided. The complex sugar mixture produced in the formose reaction is rapidly destroyed under the reaction conditions. Nitrogenous substances (needed for prebiotic base synthesis) would interfere with the formose reaction by reacting with formaldehyde, the intermediates, and sugar products in undesirable ways. The evidence that is currently available does not support the availability of ribose on the prebiotic earth, except perhaps for brief periods of time, in low concentration as part of a complex mixture, and under conditions unsuitable for nucleoside synthesis.

Prebiotic ribose synthesis: a critical analysis.

A recent synthesis of activated pyrimidine ribonucleotides under prebiotically plausible conditions relied on mixed oxygenous and nitrogenous systems chemistry. As it stands, this synthesis provides support for the involvement of RNA in the origin of life, but such support would be considerably strengthened if the sugar building blocks for the synthesis—glycolaldehyde and glyceraldehyde—could be shown to derive from one carbon feedstock molecules using similarly mixed oxygenous and nitrogenous systems chemistry. Here, we show that these sugars can be formed from hydrogen cyanide by ultraviolet irradiation in the presence of cyanometallates in a remarkable systems chemistry process. Using copper cyanide complexes, the process operates catalytically to disproportionate hydrogen cyanide, first generating the sugars and then sequestering them as simple derivatives.

http://www.chtf.stuba.sk/~szolcsanyi/education/files/Chemia%20heterocyklickych%20zlucenin/Prednaska%207/Doplnkove%20studijne%20materialy/Formose%20reaction/Prebiotic%20synthesis%20of%20simple%20sugars%20by%20photoredox%20systems%20chemistry.pdf

Prebiotic synthesis of simple sugars by photoredox systems chemistry

Glycoaldehyde phosphate aldomerizes in aq. NaOH to a product mixt. contg. the racemates of two diastereomeric tetrose 2,4-diphosphates and 8 hexose 2,4,5-triphosphates. The aldomerization of glycoaldehyde in the presence of formaldehyde is a variant of the formose reaction. It avoids the formation of complex formose product mixts., because C(2)-phosphorylated aldoses cannot undergo aldose-ketose tautomerization. This work, with its demonstration of an intrinsic kinetic preference for ribose 2,4-diphosphate and allose 2,4,5-triphosphate formation, adds a piece of factual chem. information to ongoing discussion about the origin of ribonucleic acids. [on SciFinder (R)]

/pdf/chemie-von-a-aminonitrilen-aldomerisierung-von-glycolaldehyd-2737j065hu.pdf

Chemie von a-Aminonitrilen. Aldomerisierung von Glycolaldehyd-phosphat zu racemischen Hexose-2,4,6-triphosphaten und (in Gegenwart von Formaldehyd) racemischen Pentose-2,4-diphosphaten: rac-Allose-2,4,6-triphosphat und rac-Ribose-2,4-diphosphat sind die Reaktionshauptprodukte†

Homogeneously catalyzed condensation of formaldehyde to carbohydrates: VII. An overall formose reaction model

Formose sugars from formaldehyde

The problems of the synthesis of carbohydrates from formaldehyde are examined and the catalysts and conditions of the synthesis are described. The kinetics and current ideas concerning the mechanism of this process as well as different versions of its application in the regeneration of food products in manned spacevessels are discussed. The bibliography includes 141 references.

http://iopscience.iop.org/article/10.1070/RC1980v049n06ABEH002489/pdf

The Synthesis of Carbohydrates from Formaldehyde

Homogeneously catalyzed formaldehyde condensation to carbohydrates: IV. Alkaline earth hydroxide catalysts used with glycolaldehyde co-catalyst

Chemical food synthesis research is currently in progress as part of the US-USSR Research Collaboration in Catalysis for closed loop production of glycerol as a source of carbohydrates in sustained space flight and for direct synthesis of carbohydrates. Experimental results are presented which show the feasibility of producing not only glycerol but also potentially edible sugars from formaldehyde by means of the autocatalytic formose condensation reaction. The speculative possibility of large scale food refineries producing edible carbohydrates and purifying them by chromatographic methods is considered, as well as economically growing single cell protein, using formose sugars as substrate. If protein derived from synthetically produced carbohydrate can eventually be used for animal feed, farmland can be released for human foods.

M. M. Sakharov

Papers

Homogeneously catalyzed condensation of formaldehyde to carbohydrates: VII. An overall formose reaction model

Formose sugars from formaldehyde

The Synthesis of Carbohydrates from Formaldehyde

Homogeneously catalyzed formaldehyde condensation to carbohydrates: IV. Alkaline earth hydroxide catalysts used with glycolaldehyde co-catalyst

Synthetic carbohydrates from formaldehyde