Abstract
The growing regulatory scrutiny and the emerging trends towards natural products and clean labels have led to a particular focus on food supplements’ composition, including excipients. The objective of this study is to establish a methodological approach combining conventional techniques, i.e., tapped density and flowability testers, with more objective and quantitative ones to identify alternative powder excipients that can replace conventional ones in the development of solid-dose formulations without affecting their processing, workability, and mechanical properties. In the first phase, the alternative powder excipients were characterized in terms of cohesiveness, compressibility, and flow function coefficient. We then evaluated the possibility of using selected excipient combinations to totally and/or partially replace the conventional excipients within three nutraceutical formulations. Glyceryl behenate at 1–3% w/w could be considered as a viable alternative lubricant to magnesium stearate without compromising the rheological properties of the mixtures. Fructo-oligosaccharides showed a free-flowing behavior comparable to calcium phosphate and microcrystalline cellulose, improving the flowability and compressibility of the formulations. The study of powder rheology could be advantageous to formulate new products or reformulate existing ones in a time- and money-saving way, leading to high-quality products that can appeal to consumers in terms of health-functional effectiveness.
Introduction
A significant number of pharmaceutical formulations and food supplements are presented in solid dosage form for oral use. Tablets and capsules are the preferred choices for both consumers, owing to their ease of administration, and manufacturers, due to their relative simplicity in production and their ability to ensure product stability, precise dosing, and controlled release kinetics [1]. Excipients play a crucial role in overcoming these challenges and optimizing the performance of solid dosage forms. A rational choice of excipients is essential to ensure adequate technological properties, such as powder flowability, processability, compressibility, and mechanical strength of the product, while also influencing the stability, bioavailability, and release profile of the active ingredient [2,3]. Moreover, excipients contribute to the overall product quality, impacting factors such as taste and ease of administration. According to their functionality, excipients for oral solid formulations can be divided into different categories. Common diluents and fillers include microcrystalline cellulose [4,5], calcium phosphates [6,7], and polyols such as mannitol or isomalt [8–10]. Binders are often based on cellulosic derivatives or synthetic polymers such as polyvinylpyrrolidone. Disintegrants include starches and superdisintegrants such as sodium croscarmellose [11], whereas hydroxypropyl methylcellulose is widely used for sustained-release matrices [12]. Lubricants and glidants are essential, such as magnesium stearate [13] and silicon dioxide [14]. Ancillary excipients such as sweeteners, flavors, colorants, and pH adjusters [15,16] complete the formulation when needed.
The nutritional supplement industry is experiencing rapid growth, driven by the increasing consumer interest in health and wellness [17]. Moreover, the growing emphasis on naturalness, clean labels, and sustainability [18,19] is forcing this industry to seek innovative approaches to product design and formulation that meet consumers’ expectations while adhering to stringent regulatory guidelines. Balancing regulatory compliance with product differentiation is essential for success in this industry. The focus on safety rather than efficacy, combined with diverse distribution channels, allows for greater flexibility and offers more opportunities for new product development compared to pharmaceuticals [20].
This study aimed to develop a methodological framework integrating conventional powder-characterization methods (e.g., flowability and tapped-density measurements) with advanced rheological analysis using a powder shear cell. This approach supports the incorporation of new functional excipients with enhanced health benefits, such as glyceryl behenate, tapioca maltodextrin, carob gum, oligosaccharides, and arabinogalactans, replacing traditional ones, without compromising the mechanical properties and technological performance of nutraceutical products.
Glyceryl behenate is based on a mix of glycerol esters of behenic acid and is commonly used in film coating and sustained drug release matrix [21,22]. It is also reported as an alternative lubricant to the conventional magnesium stearate without a significant impact on tablet strength and manufacturing [23,24]. Maltodextrins are obtained from acidic or enzymatic hydrolysis of corn starch. They are used extensively in the food industry as stabilizers, as well as binders and diluents in pharmaceutical applications [25]. The tapioca maltodextrin employed in this study presents a low dextrose equivalent (DE) value, suggesting a favorable effect of this ingredient on glycemic impact. Carob gum is a galactomannan obtained from the seeds of the carob tree (Ceratonia siliqua L.) and is commonly employed as a thickening and stabilizing agent in the food industry [26]. Carob gum is also reported as a viscous, soluble dietary fiber, suitable as a supplement for weight control and the management of glucose and lipid metabolism [27,28]. Fructo-oligosaccharides and galacto-oligosaccharides (FOS and GOS) are non-digestible oligosaccharides that are composed of a small number (2–60) of fructose and galactose units, respectively. They are usually included as active ingredients in food supplements and functional foods thanks to their prebiotic activity [29–34]. Besides their healthy positive effect and low glycemic index, GOS and FOS present some interesting technical advantages, such as very good palatability, high flowability, and solubility [35]. Larch arabinogalactan is a highly branched, non-starch hemicellulose polysaccharide made from galactose and arabinose units that may compose up to 35% of the dry wood of the larch tree [36–38]. It is proposed as an active ingredient in food supplements for the wide range of biological properties, such as protection of gastrointestinal mucosa, prebiotic effect, and enhancement of immune function [39,40].
In the reformulation of existing nutraceutical products with alternative excipients, the preservation of the processability of powder mixtures, including powders’ flowability, density, and compressibility, must be considered. These properties are influenced by a large variety of different parameters, some intrinsic to powders, such as size, shape, surface roughness, and electrical charge, and others due to external environmental conditions, such as temperature, relative air humidity, pressure, moisture content, and consolidation state [41,42].
The flow properties of powders represent a critical factor to consider during the industrial processes: their measurement allows for predicting the powders’ behavior in the development phases, including handling, pouring, and compression. Poor flowability can result in issues such as uneven mixing, equipment blockages, and packaging difficulties, which also affect the quality and consistency of the final product [43].
Different instrumental techniques are employed to assess powder flow properties during the research and development stage. Traditional methods, including flowability testing, such as the measurement of the angle of repose, and the use of tapped density testers, which allow the determination of Carr’s and Hausner’s indices, offer rapid, costeffective results. However, these methods provide only qualitative insights and are prone to operator variability and a lack of reproducibility [44,45]. In contrast, rheological measurements involving the use of shear and flow cells provide more objective and reproducible quantitative data, characterizing powder flow and cohesive properties through scientifically rigorous parameters [46]. Shear cell tests, a technique introduced by A. W. Jenike to assess hopper and bin design parameters for gravity-fed materials, are a widely used method for characterizing powder flow properties [47]. This technique provides critical insights into fundamental solid properties, including cohesion, unconfined yield strength, angle of internal friction, compressibility, and wall friction. Shear cell analysis is particularly effective for characterizing powder flowability under varying consolidation states, using the material flow function and the flow coefficient (ffc) [48–51].
However, it may be less sensitive to subtle changes in free-flowing powders that could affect process performance. Furthermore, commercial shear cell instruments can face limitations when handling larger particle sizes typical of granular materials or small quantities of loosely compacted powders. This is especially challenging in fields such as pharmaceuticals, where obtaining sufficient material for testing can be difficult [52,53].
In this work, through practical case studies, we illustrate how the aforementioned instrumental techniques can be applied to characterize and compare excipients and to optimize solid dosage formulations. Nutraceutical ingredients with well-known healthpromoting effects, also characterized by potential technical features (e.g., FOS, GOS, larch arabinogalactans, glyceryl behenate, tapioca maltodextrin, and carob gum), were employed as alternative excipients for the production of food supplements in solid forms to create innovative, healthy, and functional vehicles with comparable technical performance to conventional excipients. While many conventional excipients used in solid dosage forms (e.g., microcrystalline cellulose) are plant-derived, the clean-label trend is also influenced by the perception of minimal processing and the presence of additional functional or health related properties. For this reason, these alternative excipients are increasingly attractive, as they combine natural origin with specific technological and physiological functions that align with current consumer expectations. The alternative excipients were compared with conventional diluents and lubricants commonly used in the nutraceutical industry, considering different analytical and instrumental approaches, such as flow function, wall friction, compressibility, and flowability. Once the most appropriate alternative excipients had been identified, combinations of excipients at specific concentrations and ratios were employed to reformulate three existing food supplements to verify that the technological and flow properties remained unchanged.
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Materials
In Table 1, the ingredients used in this work are reported, with the values of particle size declared by the suppliers in the technical data sheet. The selection of alternative excipients was based on technological suitability (as diluents, binders, or glidants), natural origin, safety considerations, functional and health-related properties, and economic feasibility. Almost all excipients employed were food-grade ingredients in compliance with the requirements established by Codex Alimentarius, Food Chemicals Codex (FCC) and Regulation (EU) No 231/2012, except for carboxymethyl cellulose and mannitol, which are pharmaceutical grade ingredients, in compliance with the current monographs in the European (Ph.Eur.), US (USP-NF) and British (BP) pharmacopeias.
Table 1. Particle size (µm) of each ingredient employed for conventional and alternative powder
mixture formulation.
| Code | Ingredient | Supplier | Function | Particle Size |
|---|---|---|---|---|
| MC | Microcrystalline cellulose | Roquette (Lestrem, France) | Conventional excipient | Residue on 250 µm (8% max) Residue on 75 µm (45% min) Residue less than 5 µm (10% max) |
| M | Mannitol | Roquette (Lestrem, France) | Conventional excipient | >500 µm (10% max) >315 µm (25% max) >40 µm (60% min) |
| CMC | Carboxymethyl cellulose | Roquette (Lestrem, France) | Conventional excipient | Retained on 75 µm (10% max) |
| CP | Dicalcium phosphate 2-hydrat | Budenheim, (Budenheim, Germany) | Conventional excipient | <45 µm (5%) >150 µm (40–80%) >425 µm (1%) |
| I | Isomalt | Beneo (Mannhein, Germany) | Conventional excipient | >500 µm max 5% >250 µm 20–70% <63 µm max 15% |
| HPC | Hydroxypropylcellulose | Ashland Industries (Milano, Italy) | Conventional excipient | Through 149 µm (75%) Through 177 µm (90%) Through 250 µm (99.5%) |
| MS | Magnesium stearate | Peter Greven (Euskirchen, Germany) | Conventional excipient | Sieve residue at 74 µm (1%) |
| S1 | Silicon dioxide | WR Grace & Co. (Columbia, MD, USA). | Conventional excipient | 2–4.5 µm |
| S2 | Silicon dioxide | Evonik (Hanau-Wolfgang, Germany) | Conventional excipient | 320 µm (75%) |
| FOS | FOS | Cosucra (Pecq, Belgium) | Alternative excipient | <500 µm |
| GOS | GOS | NFBC (Yunfu city, Guangdong Province, China) | Alternative excipient | <500 µm |
| AG | Larch arabinogalactans | Lonza (Basel, Switzerland) | Alternative excipient | Not more than 20% through 420 µm |
| MD | Tapioca maltodextrins | Ingredion (Manchester, UK) | Alternative excipient | <500 µm |
| LBG | Carob gum | Faravelli SpA (Milano, Italy). | Alternative excipient | <500 µm |
| GB | Glyceril dibehenate | Gattefossè (Saint-Priest Cedex, France) | Alternative lubricant | 50 µm (average value) |
| Lipophilic vitamin | BASF (Ludwigshafen am Rhein, Germany) | Active (product 1) | 100% through 841 µm ≥90% through 420 µm ≤15% through 149 µm |
|
| Hydrophilic vitamin | Vivatis Pharma Italia (Varese, Italy). | Active (product 2) | ≥95% through 177 µm | |
| Botanical dry extract complex from Quebracho and Chestnut | Vivatis Pharma Italia (Varese, Italy). | Active (product 3) | Min. 90% through 125 µm |
Tafuro, G.; Faggian, M.; Soppelsa, P.; Baracchini, S.; Casanova, E.; Francescato, S.; Baratto, G.; Dall’Acqua, S.; Santomaso, A.C.; Semenzato, A. Mechanical Properties and Powder Rheology of Conventional and Innovative Excipients for Food Supplements in Solid Form. Powders 2025, 4, 32. https://doi.org/10.3390/powders4040032
Read also our introduction article on Introduction to Capsules in Nutraceuticals here:
