From Field to Pharmacy: Isolation, Characterization and Tableting Behaviour of Microcrystalline Cellulose from Wheat and Corn Harvest Residues
Abstract
Introduction
The rapid growth of the world’s population is accompanied by parallel growth in crop production in order to meet escalating food needs, as well as the demand from industry and livestock farming. Global crop production has increased up to 9.5 billion tonnes, which is a 54% increase in the period 2000–2021 and is predicted to increase further in the following decades [1,2]. Growing crop production has resulted in an enormous amount of agricultural waste, so developing strategies for sustainable management of this waste is of great importance. It is estimated that around 5 billion tonnes of harvest residues (HRs) are generated annually, of which the majority is from corn (1.16 billion tonnes) and wheat (1.14 billion tonnes). Unfortunately, the majority of agricultural waste remains unused, as the costs associated with the collection, transportation and processing of agricultural waste are generally considered to exceed the value of the products obtained [3]. Usually, HRs are left on the field or burnt after harvesting, which leads to air pollution, emission of greenhouse gases and other toxic products and also negatively affects the soil microflora [4,5]. Therefore, isolating the value-added components from agricultural waste is of utmost importance to mitigate the problems caused by the accumulation and improper management of this waste.
Although the composition of HRs varies depending on the species, age of the residues and storage time [6], the main components are cellulose (30–45%), hemicellulose (20–40%) and lignin (10–25%), with smaller amounts of proteins, pectin, sugars, waxes and inorganic minerals [3]. Various value-added compounds have been isolated from wheat and corn HRs, such as cellulose or its derivatives (microcrystalline [7,8,9,10] and nanocrystalline cellulose [11,12,13]), lactic acid [14], glycoside surfactants [15], xylan sulphates [16], carboxymethyl cellulose [17], monosaccharides [18], p-hydroxycinnamic acid esters [19], silicon dioxide [20], etc., while these residues were also used as starting materials for the production of adsorbents [21] and biochar [22].
Since cellulose is the main component of HRs, much attention has been paid in recent years to the development of processes for the isolation of cellulose and products of its further processing, such as microcrystalline (MCC) and nanocrystalline cellulose (NCC), from agricultural waste. Cellulose is the most abundant polymeric compound on Earth and is attractive due to its numerous applications in the pharmaceutical, food, chemical, energy and textile industries or as a feedstock for the production of other valuable compounds [11]. Chemically, cellulose consists of glucopyranose units linked by β-1-4 glycosidic bonds in chains that are stabilized by multiple hydrogen bonds between free OH groups, resulting in a microfibrillar structure. Cellulose microfibrils form a spirally coiled scaffold consisting of crystalline phases spaced out with amorphous segments [11,23]. The main problem in the technological processes for isolating cellulose is the removal of lignin and hemicellulose, which are firmly bound to the cellulose fibrils. This usually requires harsh conditions, such as treatment with strong acids and/or bases, elevated temperatures and/or pressure, with a combination of these treatments being required in most cases [24].
MCC is purified, partially depolymerized cellulose, which is usually obtained by treating cellulose with mineral acids. The acid breaks the β-1-4 glycosidic bonds mostly in the amorphous regions of the cellulose that bind the crystalline segments, resulting in the cleavage of the long cellulose chains. MCC consists mostly of shorter crystalline segments, which remain intact after acid hydrolysis, and a small fraction of amorphous material [25,26]. Since its appearance on the market in 1964, MCC has become an indispensable starting material in the pharmaceutical, cosmetic, food and chemical industries [25,27]. The most common industrial applications of MCC include diluent, binder and adsorbent in pharmaceutical formulations, stabilizer, emulsifier, anti-caking agent and fat substitute in food, gelling agent, stabilizer and suspending agent in the beverage industry and reinforcing agent in various composite materials [28,29]. MCC also has the potential to be used as a dietary fibre in foods, which has a positive effect on the gastrointestinal tract and has potential hypolipidemic and anti-obesity effects [30]. Due to its wide availability, compatibility with most active ingredients, excellent binding properties, self-disintegration ability and low lubricant requirements, MCC is one of the most commonly used excipients in tablet formulations [25].
Wood and cotton are the main feedstocks for the production of cellulose and MCC. However, these raw materials are becoming more expensive and are only available in limited quantities due to high consumption in the furniture, textile and construction industries and the use of wood for heating [26]. This imposes the need to find alternative cheap and widely available sources for production of MCC, such as residues generated after the cultivation and processing of various agricultural crops. The properties of MCC are highly dependent on the properties of the feedstock and the production process. Characterization of obtained MCC usually involves testing of physicochemical properties such as identity, purity, particle size and shape, while material behaviour in the tableting process is rarely evaluated.
Therefore, in this study different procedures were evaluated for preparation of MCC from wheat and corn HRs. Special attention was paid to the functional characterization of the obtained MCC samples by evaluating the tableting behaviour with a dynamic powder compaction analyser.
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Materials
Wheat and corn HRs, collected from agricultural land in the vicinity of Belgrade (Resnik, Belgrade, Serbia), were used as starting materials for isolation of MCC. The following chemicals were used for the treatment of HRs: sodium hydroxide (Honeywell, Charlotte, NC, USA), hydrogen peroxide (PedrogenTM 30%, Honeywell, Charlotte, NC, USA) and hydrochloric acid (Honeywell, Charlotte, NC, USA). All chemicals used for composition analysis of HRs before and after treatment were of analytical or reagent grade.
Commercially available MCC sample (CEOLUS TM PH101, Asahi Kasei, Tokyo, Japan) was used for comparative evaluation of characteristics important in tableting process of MCC isolated from HRs.
Medarević, D.; Čežek, M.; Knežević, A.; Turković, E.; Barudžija, T.; Samardžić, S.; Maksimović, Z. From Field to Pharmacy: Isolation, Characterization and Tableting Behaviour of Microcrystalline Cellulose from Wheat and Corn Harvest Residues. Pharmaceutics 2024, 16, 1090. https://doi.org/10.3390/pharmaceutics16081090
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