Polysaccharides

Properties and Applications

Mohd Imran Ahamed, Rajender Boddula, Tariq Altalhi, Mohd Imran Ahamed, Rajender Boddula, Tariq A. Altalhi

• Publisher: Wiley-Scrivener
• Year: 2021
• ISBN:
  9781119711407
• Edition: 1
• Topic: Technik & Maschinenbau
• Subtopic: Chemie- & Biochemietechnik

This book provides the whole spectrum of polysaccharides from basic concepts to commercial market applications. Chapters cover various types of sources, classification, properties, characterization, processing, rheology and fabrication of polysaccharide-based materials and their composites and gels. The applications of polysaccharides include in cosmetics, food science, drug delivery, biomedicine, biofuel production, marine, packaging, chromatography and environmental remediation. It also reviews the fabrication of inorganic and carbon nanomaterials from polysaccharides. The book incorporates industrial applications and will fill the gap between the exploration works in the laboratory and viable applications in related ventures.

1
Natural Polysaccharides From Aloe vera L. Gel (Aloe barbadensis Miller): Processing Techniques and Analytical Methods

Silvana Teresa Lacerda Jales^1,2, Raquel de Melo Barbosa^3,4*, Girliane Regina da Silva⁵, Patricia Severino^6,7 and Tulio Flávio Accioly de Lima Moura^1,4

¹Program on Development and Technological Innovation in Medications, Federal University of Rio Grande do Norte, Natal, Brazil

²Department of Pharmaceutical Sciences, Federal University of Paraíba, João Pessoa, Brazil

³Visiting scholar at MIT Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, USA

⁴Laboratory of Drug Development, Department of Pharmacy, Federal University of Rio Grande do Norte, Natal, Brazil

⁵Department of Chemistry, Federal Rural University of Pernambuco, Recife, Brazil

⁶University of Tiradentes (Unit), Aracaju, Brazil

⁷Institute of Technology and Research (ITP), Nanomedicine and Nanotechnology Laboratory (LNMed), Aracaju, Brazil

Abstract

Aloe vera L. (Aloe barbadensis Miller) from Asphodelaceae (Liliaceae) family, is a medicinal plant frequently used in medicines, cosmetics, and food products. Seventy-five potentially active compounds have already been identified from A. vera extract, among them: enzymes, minerals, lignin, saponins, salicylic acids, amino acids, sugars, and vitamins. In this chapter, the authors highlight the mucopolysaccharide acemannan (an acetylated glucomannan), extracted from the mucilaginous gel leaves. Acemannan has a backbone of β(1–4)-linked mannose units, partially acetylated, interspersed by glucose units, and some galactose side-chains. However, several of its structural characteristics, such as degree of acetylation, presence of glucose monomers, and its molecular weight, are always quantified because they present inconsistencies and disparities. Growing conditions of the plant and harvesting period, different processes for obtaining the gel, and its derivatives, besides the many different analytical methods applied, contribute to the lack of standardization of A. vera gel and its derivatives. Therefore, this chapter aimed to present the different techniques used for processing mucilaginous gel along with the various analytic methods applied in recent years.

Keywords: Acemannan, acetylated glucomannan, Aloe vera, polysaccharides, polymer

1.1 Introduction

Aloe vera L. (Aloe barbadensis Miller) is a medicinal plant belonging to the Liliaceae family, currently defined as Asphodelaceae by the Angiosperm Phylogeny Group III System—APG III of 2009 [1]. Of the over 300 species of Aloe, A. vera is the most widely used in medicines, cosmetics and food products. Numerous therapeutic activities, including antiviral, antibacterial, radiation protection, antioxidant, anti-inflammatory, anticancer, antidiabetic, antiallergic, immunostimulant, and ultraviolet (UV) protection have been attributed to the plant, particularly to its polysaccharides [1–7].

The leaves of A. vera can be divided into two main fractions, a thick epidermis, or outer green rind, including the vascular bundles, and an inner colorless pulp called A. vera gel. The bitter yellow exudate from the cells surrounding the vascular bundles is rich in derivatives of 1,8-dihydroxyanthraquinone and its glycosides, whereas the pulp contains proteins, lipids, amino acids, vitamins, enzymes, inorganic compounds, small organic compounds, besides different carbohydrates (soluble sugar and polysaccharides) [6].

The inner most part of the leaves (leaf pulp) of A. vera contains parenchymatous cells which produce a mucilaginous liquid referred to as A. vera pulp, among other terms such as inner gel, leaf parenchyma, mucilaginous gel and/or simply A. vera gel [4]. Water is the main constituent, ranging from 98.5 to 99.5% in the fresh plant, while around 60% of the remaining solid material is made up of polysaccharides [8, 9].

Several reports have identified acemannan as the major polysaccharide in the mucilaginous gel of A. vera. It is composed of large quantities (>60%) of partially acetylated mannose units, followed by glucose (approximately 20%) and, in lower amounts, galactose (<10%) [3, 9–11]. The acetyl groups are the only ones that are not functional groups present in sugars and appear to play a fundamental role not only in terms of physicochemical properties but also in the biological activity of A. vera [12–14].

Acemannan is highly unstable and readily degraded by different physicochemical factors including high temperatures, pH changes, microbiological factors like bacterial contamination, or by enzymatic action, such as from the mannases present in the gel [15, 16]. Studies have shown that the effects of deacetylation, i.e., removal of the acetyl group, reduce the bioactivity of the polysaccharides. Thus, the acetyl group may have functional control of acemannan affecting, at least in part, its physical properties and biological activity [14].

Controlling the chemical, functional, and physical properties of A. vera during its processing remains a significant challenge. This is due to the microbial, mechanical, enzymatic, and structural changes which take place under different climatic and processing conditions [9, 17, 18]. Thus, the choice of method for obtaining the gel is an essential factor, given that A. vera gel is often sold in concentrated powder forms [19].

Given the high activity of water in A. vera gel and its major carbohydrate composition, its shelf life is only 3–4 days at room temperature, requiring the use of stabilization processes to preserve most of the active ingredients and extend its usable life. Thus, stabilization is done to reduce t...