Current views on fungal chitin/chitosan, human chitinases, food preservation, glucans, pectins and inulin: A tribute to Henri Braconnot, precursor of the carbohydrate polymers science, on the chitin bicentennial

doi:10.1016/j.carbpol.2011.09.063

Carbohydrate Polymers

Volume 87, Issue 2, 15 January 2012, Pages 995-1012

https://doi.org/10.1016/j.carbpol.2011.09.063 Get rights and content

Abstract

Two hundred years ago, Henri Braconnot described a polysaccharide containing a substantial percent of nitrogen, later to be called chitin: that discovery stemmed from investigations on the composition of edible mushrooms and their nutritional value. The present interdisciplinary article reviews the major research topics explored by Braconnot, and assesses their importance in the light of our most advanced knowledge. Thus, the value of fungi, seafoods and insects is described in connection with the significance of the presence of chitin itself in foods, and chitinases in the human digestive system. The capacity of chitin/chitosan to depress the development of microbial pathogens, is discussed in terms of crop protection and food preservation. Other topics cherished by Braconnot, such as the isolation of pectin from a large number of plants, and inulin from the Helianthus tubers, are presented in up-to-date terms. Acids isolated from plants at that early time, led to enormous scientific advancements, in particular the glyoxylic acid and levulinic acid used for the preparation of soluble chitosan derivatives that paved the way to a number of applications. An opportunity to trace the origins of the carbohydrate polymers science, and to appreciate the European scientific heritage.

Highlights

► Bicentennial of chitin, first carbohydrate polymer discovered. ► Food chitin digested by human chitinases enhances immune defenses. ► Chitosan protects crops against microbial attack and spoilage. ► Plant extracts reacted with chitosan yield valuable products. ► Braconnot's work is still pivotal for sustainable green solutions.

Introduction

This review article intends to revisit the major research topics to which Henri Braconnot devoted his scientific life, on the occasion of the bicentennial of his discovery of chitin in edible fungi. He was always attracted by the alimentary aspects of botany, and his research was most often aimed at alleviating food shortages, not to say famine, that the majority of the French population had to face. Concisely, we present here the current views on the title points to underline the durable validity of Braconnot's interests, experimental approaches and results. The problems faced 200 years ago still persist for the majority of the exceedingly large world's population, notwithstanding the technological advances made. A glimpse back to 1811 would give us an opportunity to appreciate the immense spiritual resources of the western Countries that, in the context of the American and French revolutions, elaborated new scientific interests, methodologies and communication ways. For this Journal, the chitin bicentennial is also an opportunity for tracing the roots of the carbohydrate polymers science.

Section snippets

The precursor of the carbohydrate polymer science

Henri Braconnot (1780–1855) laid the foundations of the carbohydrate polymer science: after the discovery of chitin, the first polysaccharide described 30 years earlier than cellulose, he continued with his idea of extracting sugars from edible fungi such as Agaricus bisporus, and remarkably extracted inulin from the tubers of Heliantus tuberosus. He also studied pectins of various origins, and isolated pure sugars after chemical hydrolysis of straw, wood and cotton; likewise, he isolated

The occurrence of chitin in edible and filamentous fungi

The most recent description of chitin in living organisms is the one by Muzzarelli (2011). As Fig. 1 shows, the repeating structural unit of chitin is the dimer of GlcNAc. Chitin is the characteristic component of the taxonomical groups Zygo-, Asco-, Basidio- and Deuteromycetes.

The worldwide production of mushrooms was updated by the Food and Agriculture Organization of the United Nations in 2009. China is the largest producer (>1.5 million metric tons in 2007, with an increment of 65% in 10

Human chitinases in nutrition and metabolism

Chitinases hydrolyze the β1–4 bonds of the chitin chain down to the N-acetyl-d-glucosamine dimer (Jollès & Muzzarelli, 1999). This is an extraordinary performance because the substrate chitin in most instances is an insoluble and crystalline solid that assumes a large variety of forms depending on the role of the living tissue, an example being the one in Fig. 2.

These enzymes are highly preserved through species and kingdoms (Boot et al., 2001, Gianfrancesco and Musumeci, 2004) and exert

Crop protection and food preservation

The tremendous increase in crop yields associated with the green revolution has been made possible in part by the utilization of chemicals for pest control. However, concerns over the impact of pesticides on human health and the environment has led to new pesticide registration procedures, that have prohibited a number of synthetic pesticides, including the chitin synthesis inhibitors that posed a real threat to the environment (Muzzarelli, 1986). Among new natural pesticides, chitosan is not

Pectins

Braconnot described for the first time the occurrence of an acid universally present in all vegetables. He detected this acid in carrots, apples, pears, grains and onions, and noted its gelling characteristics. Hence he coined the term pectic acid (“acide pectique”), from the Greek word πήκτίζ for coagulum. The title of this article is of impressive clarity: “Research on a novel acid universally present in all plants” (Braconnot, 1825a). He described its properties in another publication where

Plant aldehydoacids, ketoacids and phenols

When chitosan is dissolved in diluted glyoxylic acid, CHO·COOH, it undergoes spontaneously the Schiff reaction leading to the aldimine; the latter, upon hydrogenation with borohydride, NaBH₄, yields N-carboxymethyl chitosan, otherwise called glycine glucan, that combines in itself the backbone of chitin and the functionality of glycine, i.e. the two major compounds discovered by Braconnot (Muzzarelli, Tanfani, Emanuelli, & Mariotti, 1982).

Conclusion

Well, we are back from our journey to the past. We dreamed to have met Henri Braconnot in his Botanical Garden for an exciting exchange of views, and to have been admitted to his laboratory, where he used to work alone, to the point that he had no disciples. Actually he did not even get married. Even though he attended courses of chemistry, natural history and pharmacy in Strasbourg and Paris whenever possible because of recurrent military obligations, he was never concerned about getting an

Acknowledgments

The preparation of this article was a spontaneous and independent initiative of the authors, and was not financially supported. Thanks are due to Prof. M. Boulangé, former President of the University of Nancy, France, who made available copies of original documents; to Dr. Marilena Falcone, Central Library, Polytechnic University, Ancona, Italy, for assistance in handling the bibliographic information, to Mrs. Maria Weckx for assistance in the preparation of the manuscript, and to Dr. Monica