Seed Galactomannans: An Overview

Abstract

Seed galactomannans are vegetable, heterogeneous polysaccharides widely distributed in nature. Generally, they possess (1-->4)-linked D-mannopyranose (Man) main chains to which are attached (1-->6)-linked D-galactopyranosyl (Gal) units. The Man/Gal ratios differ from gum to gum, resulting in a change in structure, which, in turn, determines the various industrial applications of seed galactomannans. These materials are important in paper, textile, petroleum-drilling, pharmaceutics, food, cosmaceutics, and explosives industries. In this review, the biodiversified applicability of galactomannan gums is discussed, particularly with respect to structural aspects, properties, human consumption, and technical applications. Especially important is that the solution properties (rheological behaviour, viscosity, emulsifying tendency, etc.) of natural and chemically modified galactomannans can be tuned by interaction with other (carbohydrate-based) monomers or polymers.

Pharmaceutical use of galactomannans

“…This biopolymer constitutes the second largest group of storage polysaccharides in terms of its distribution in the plant world, and has been found as endosperm cell wall storage in the seeds of several botanical families. [3][4][5][6][7] Galactomannans consist of a (1→4)-linked α-D-mannopyranosyl backbone, substituted at O-6 by single units of β-D-galactopyranose ( Figure 1). The mannose/galactose ratio (M/G) varies from about 10 to 1, depending on the plant source.…”

“…Solubility at lower temperatures is confined to chains whose galactose content is higher than the average value for the whole gum, and indeed fractions of different M/G ratio can be obtained by dissolving at progressively higher temperatures. 6,8,9 Galactomannans are often used in different forms for human consumption. With their different physicochemical properties, they are a versatile material with many applications.…”

“…The absence of toxicity also favors their use in the textile, pharmaceutical, biomedical, cosmetics, and food industries. 6,9 They are mainly used in pharmaceutical technology and cosmetics, not as pure galactomannan but as a crude flour. Commercially sold flours are reported to contain about 85% pure galactomannan on a mass basis and make an important contribution to the hydrocolloid usage in many products.…”

“…Plant-based products are considered 'generally recognized as safe' 29 and ecologically friendly, as their production and application do not cause pollution and do not disturb the ecosystem. 6 Current international trends demand the introduction of alterna- tive sources of seed gums 30 and it is therefore important to search for alternative renewable sources, for example in the production of pharmaceutical materials. In Latin America, the number of known sources of galactomannans is small, despite the rich biodiversity of the local flora and the favorable climate for their production.…”

“…45 Over the last few decades, many reports have appeared on the composition and physiochemical properties of galactomannans from different plant sources. 6,33,[36][37][38][40][41][42][43][44][46][47][48][49][50][51][52][53][54][55][56][57][58][59] However, only guar, locust bean, tara and cassia gum are manufactured on a large scale, and these are being extensively investigated by various researchers. 5,11,12,19,21,[60][61][62][63][64][65][66] Srivastava and Kapoor 6 described, in their overview of galactomannans, chemical screening of more than 300 Indian species of water-soluble gums.…”