Evaluation of compatibility between dried extracts of Myracrodruon urundeuva Allemão and pharmaceutical excipients by TG and DTA
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Thermoanalytical techniques have been applied in studies of herbal products. Myracrodruon urundeuva Allemão (Anacardiaceae) is a native of Brazil with medicinal properties. This study aimed to characterize the dry extracts of M. urundeuva Allemão and to assess the compatibility of extracts with pharmaceutical excipients in physical mixtures using thermogravimetry (TG) and differential thermal analysis (DTA). The TG curve of M. urundeuva dry extract (ES) showed the occurrence of four mass loss events. The most significant mass loss of extract was observed between 193.5 and 267.0 °C with a loss of 29.7%. The DTA curve showed the endothermic nature of this event with a peak at 235.8 °C (ΔH = 568.5 J g−1). This event is associated with the thermal decomposition of carbohydrates and other organic compounds present in the plant. The SEM image showed the particles of dry extract with spherical shapes, irregular sizes and rough surfaces. SEM analysis of physical mixtures showed that extract dry particles maintained their spherical morphology and appeared uniformly dispersed in the excipient particles. The TG and DTA curves showed no thermal incompatibility between the ES and the excipients lactose, cellulose and starch, but indicated a possible interaction with maltodextrin.
KeywordsMyracrodruon urundeuva Allemão Dry extract TG DTA Spray dryer SEM
The Myracrodruon urundeuva Allemão is an arboreal species of the Anacardiaceae family native to Brazil, commonly known as “aroeira-do-sertão,” “aroeira-do-cerrado” and “aroeira-preta” [1, 2]. Studies have shown antiulcer [3, 4, 5], anti-inflammatory [4, 6], antibacterial, antifungal  and neuroprotective [8, 9] properties, as well as cytotoxicity in cancer cells .
The use of dry extracts in the production of herbal medicines in the pharmaceutical industry has been employed because of their advantages over liquid extracts due to their greater stability (chemical, physical–chemical and microbiological), higher concentrations of active compounds, the ease of patterning and handling and a greater processing capacity in different dosage forms [11, 12].
Among the techniques successfully employed in the preparation of dry plant extracts, nebulization by spray dryer is highlighted. This technique produces powders with defined characteristics such as shape and particle size, and rapid evaporation of the solvent reduces the process time and risk of changes in thermolabile products such as plant extracts [13, 14, 15, 16].
Thermal analysis has been widely used as a reliable analytical tool in the physical and chemical investigation of drugs in the control of quality and development of new pharmaceutical formulations, in studies of stability and compatibility, and in possible interactions between the drug and excipients [17, 18]. These techniques have also been applied to the analysis of raw materials and plant products. A study evaluated the thermal stability and kinetics of degradation of extracts of Cissampelos sympodialis Eichi using TG . Sampaio et al.  used TG and DTA to characterize thermally dry extracts of Arrabidaea chica obtained by spray drying. Medeiros et al.  evaluated the presence of colloidal silicon dioxide and cyclodextrin during the drying of extracts of Albizia inopinata using TG, demonstrating the greater stability of the extracts with cyclodextrin. Studies with TG were used to determine the moisture and ash content of commercial samples of Paullinia cupana Kunth in coffee powder in natura. The results showed no difference between the data obtained by conventional methods compared with the TG . Costa et al. , using DSC and TG, evaluated the degree of compatibility of a lyophilized Heliotropium indicum extract with hydroxyethylcellulose, methylparaben and propylene glycol, showing that the latter two substances interacted with the extract.
This study aimed to characterize the dry extracts of M. urundeuva Allemão and to assess the compatibility of extracts with pharmaceutical excipients in physical mixtures using thermogravimetry (TG) and differential thermal analysis (DTA).
In the study, leaves of M. urundeuva Allemão collected at Caraúbas in the state of Paraiba, Brazil, were used. A voucher specimen of this species was recorded in Lauro Pires Xavier Herbarium under the registration no. NC240, and botanical identification was carried out by Professor Alecksandra Vieira de Lacerda of the Federal University of Campina Grande. The plant material was clean, oven-dried at a temperature of 50 ± 2 °C for 96 h, ground in a mechanical mill and stored in sealed plastic bag until used. The hydroethanolic extract of leaves (10 L) was obtained by the maceration of 2 kg of powdered leaves in a solution of 50:50 (v v−1) ethanol/water for 120 h.
The hydroethanolic extract of M. urundeuva Allemão was subjected to the drying process in the spray dryer model SD-05 (Lab-Plant, Huddersfield, UK). The drying conditions were inlet air temperature in the dryer of 180 °C and a feed rate of 8 mL min−1. The atomizer double pneumatic fluid nozzle with 1.2-mm opening hole operated with an air flow rate of 62 m3 h−1 and a 2.0 bar of pressure. The colloidal silicon dioxide (Henrifarma, Lot 3157052414, Brazil) was used at 10% (mass/mass) as a drying agent.
Obtaining binary mixtures
In the study, the following pharmaceutical excipients were used: lactose monohydrate 200 mesh (Pharma shows, Lot 3367, Brazil), cellulose microcrystalline PH 102 (Purifarma, Lot C1312098, Brazil), pregelatinized starch (Henrifarma, Lot GDI0258 * 036 710/15, Brazil) and maltodextrin DE 20 (Pharma Nostra Comerc, Lot 746158, Brazil), identified as LAC, CEL, AMD and MALT, respectively. Binary mixtures were prepared by the physical mixing of the dry extract of M. urundeuva Allemão (ES) with pharmaceutical excipient in the proportion of 1:1 (mass/mass) extract/excipient.
The curves dynamic TG and DTA of nebulized extract, pharmaceutical excipients and binary mixtures were obtained using the same thermobalance model DTG-60 (Shimadzu, Kyoto, Japan) in a heating rate of 10 °C min−1 from 25 to 800 °C in an atmosphere of nitrogen with a constant flow of 100 mL min−1. The samples were placed in alumina crucible with a mass around 5.0 (± 0.5) mg. The equipment was calibrated using TG calcium oxalate monohydrate. The TG and DTA curves were analyzed by the RT-60 W program (Shimadzu).
Scanning electron microscopy (SEM)
The morphology of shape and surface characteristics of M. urundeuva dry extracts and binary mixtures was assessed using scanning electron microscopy (Hitachi TM–1000, Hiscope—New Jersey, USA) under an atmospheric vacuum of 5–10 Torr. The images were captured with a voltage acceleration of 15 kV. Samples were metallized by spraying gold and were subsequently displayed in different resolutions.
Results and discussion
The fourth step of mass loss was 13.5% and occurred between 280.5 and 372.5 °C, probably corresponding to a degradation of more stable compounds and the beginning of the formation of ashes [20, 23]. A 48.9% residue was observed, which can be attributed to the mass of the colloidal silicon dioxide, which makes up 10% of the sample added to the carboxylate residue and the ash content corresponding to the minerals in the sample.
Lactose is composed of white crystalline particles used as adjuvant pharmaceutics due to its binder and diluent action in the production of tablets and capsules. The most common commercially available lactose is α-lactose monohydrate and β-lactose . The DTA curve of lactose (Fig. 2a, b) showed two endothermic peaks in range of 118–324 °C. The first peak is related to a LAC dehydration process that occurred at 148.6 °C (ΔH = 1.1 kJ g−1) and was also observed in the TG curve with a mass loss of 4.6% (T onset = 141.1 °C; T endset = 150.1 °C) attributed to the lactose monohydrate presenting 5% stoichiometric water . The second peak showed a fusion of LAC at 219.2 °C (ΔH = 566.4 J g−1); the thermal decomposition process of the excipient then occurred, confirmed by the TG curve with two steps of mass loss, 15.2% (T onset = 236.5 °C; T endset = 252.8 °C) and 31.2% (T onset = 302.6 °C; T endset = 314.5 °C) respectively. These peaks characterized α-lactose monohydrate . In temperature range 324–800 °C, two endothermic peaks with a wide temperature range and low reproducibility were observed corresponding to the processes of lactose decomposition.
The thermal behavior of the physical mixture ES–LAC was similar to the profiles of the samples of ES and LAC individually (Fig. 2a, b). The DTA curve of the mixture showed an endothermic event between 72.4 and 80.7 °C (ΔH = 45.5 J g−1) corresponding to a loss of water and volatile components of the mixture as observed in ES and also in LAC. An endothermic peak at 147.1 °C (ΔH = 45.5 J g−1) was observed in the TG curve with a mass loss of 3.4% (T onset = 136.2 °C; T endset = 148.2 °C). Another endothermic peak was observed at 210.1 °C (ΔH = 694.2 J g−1) in the TG curve corresponding to the thermal decomposition step with a mass loss of 19.8% (T onset = 205.4 °C; T endset = 225.2 °C). Thus, the ES–LAC mixture had thermal events resulting in ES and LAC individually, indicating that there was no apparent incompatibility between the LAC and the ES.
The microcrystalline cellulose is supplied as a white crystalline powder used in pharmaceutical solid formulations as a diluent, binder, suspending agent, lubricant, disintegrant and adsorbent [27, 29]. The DTA curve of the microcrystalline cellulose PH-102 (Fig. 2c, d) showed a broad endothermic peak at 54.6 °C (ΔH = 618.3 J g−1), which corresponded to the removal of surface water of the excipient, and an endothermic peak corresponding to the thermal decomposition and depolymerization of the CEL at 343.4 °C (ΔH = 3.99 kJ g−1). The TG curve showed a loss of water of CEL with a mass loss of 2.8% (T onset = 34.0 °C; T endset = 64.0 °C) and thermal decomposition process of CEL in a single step with a mass loss of 87.6% (T onset = 324.8 °C; T endset = 355.3 °C). The results were similar to those reported in [30, 31] the literature.
The DTA curve of the ES–CEL mixture showed three endothermal events equivalent to the three steps of mass loss in a TG curve (Fig. 2c, d). The first event occurred between 40.2 and 95.1 °C (ΔH = 327.5 J g−1), and the TG curve showed mass loss of 2.3% (T onset = 48.5 °C; T endset = 79 °C), corresponding to a loss of water and volatile components ES (as noted in ES and also in the CEL). The second peak occurred at 229.3 °C (ΔH = 218.9 J g−1), and the TG curve showed a mass loss of 16.6% (T onset = 207.7 °C; T endset = 235.6 °C), corresponding to a degradation of ES as noted. The third peak occurred at 360.5 °C (ΔH = 1.1 kJ g−1), and the TG curve showed a mass loss of 32.7% (T onset = 339.1 °C; T endset = 368.2 °C), corresponding to a degradation of CEL as noted. Thus, the thermal profiles of the curves of TG and DTA of ES–CEL mixture can be considered a superposition of TG and DTA curves of the samples of ES and CEL individually, indicating an absence of incompatibility of the extract with this excipient.
The starch is a semicrystalline biopolymer used as a binder, diluent and disintegrant for solid dosage forms . The DTA curve of AMD showed two endothermic peaks (Fig. 2e, f). The first at 74.0 °C (ΔH = 832 J g−1) corresponded to dehydration and gelatinization of the excipient with mass loss in a TG curve of 4.2% (T onset = 52.2 °C; T endset = 94.4 °C) and the second at 320.1 °C (ΔH = 3.99 kJ g−1), corresponding to the elimination of polyhydroxy groups accompanied by depolymerization and decomposition of the starch in the TG curve with a mass loss of 73.8% (T onset = 301.7 °C; T endset = 329.2 °C) .
There was no evidence of interaction of ES with AMD since the TG and DTA curves of the mixture can be regarded as a superposition of the curves individual of ES and AMD. The DTA curve of the mixture showed an endothermic peak at 72.2 °C (ΔH = 409.6 J g−1), attributed to the dehydration of the sample as occurred in ES and AMD, and an endothermic peak at 226.5 °C (ΔH = 265.4 J g−1), corresponding to a degradation of ES. An endothermic event was also observed between 327 °C and 271.6 (ΔH = 314.8 J g−1), corresponding to the degradation of AMD.
The DTA curve of MALT excipient (Fig. 2g, h) showed the first endothermic event between 43.9 and 147.6 °C (ΔH = 1.1 kJ g−1), and the TG curve showed a mass loss of 4.6% (T onset = 46.5 °C and T endset = 112.6 °C), corresponding to a loss of water and the glass transition carrier . The second event occurred between 225.3 and 275.1 °C (ΔH = 482.4 J g−1), and the TG curve showed a mass loss of 11.3% (T onset = 247.2 °C; T endset = 278.6 °C), corresponding to the dextrinization of the MALT [33, 35, 36]. The third endothermic event showed a peak at 318.5 °C (ΔH = 4.1 kJ g−1), and the TG curve showed a mass loss of 37.5% (T onset = 292.7 °C; T endset = 320.9 °C), corresponding to the decomposition and depolymerization of the MALT. An exothermic event was observed between 506.9 and 519.1 °C (ΔH = 3.3 kJ g−1), which may be related to gaseous products such as carbon dioxide and carbon monoxide resulting from the final processes of degradation of MALT .
The DTA curve of the mixture ES–MALT (Fig. 2g, h) showed that there were three endothermic events. The first event occurred between 66.6 and 101.8 °C (ΔH = 269 J g−1) in the TG curve, corresponding to a mass loss of 4.8% (T onset = 65.2 °C; T endset = 95.1 °C). This event is related to a loss of volatiles, and dehydrating the mixture was observed in the sample of ES and also in excipient. The other endothermic events corresponded in the TG curve to two steps of mass loss of mixture, the first of 15.6% (T onset = 202.4 °C; T endset = 224.6 °C) and the second of 36.3% (T onset = 283.8 °C; T endset = 322.9 °C), corresponding to the overlapping of the degradation of ES and MALT. The most intense endothermic and exothermic peaks were observed in the DTA curve; a MALT sample was not observed in the mixture, indicating a possible interaction between ES and MALT.
Scanning electron microscopy (SEM)
The thermal study of ES showed a defined thermal behavior with four stages of mass loss with proper reproducibility and can be applied in the characterization of standardized dry extracts.
The TG and DTA curves showed no thermal incompatibility between the ES and the excipients lactose, cellulose and starch, but indicated a possible interaction with maltodextrin. SEM images of dry extract showed spherical shapes with irregular sizes and rough surfaces and, physical mixtures showed that dry extract appeared uniformly dispersed in the excipient particles studied. Thus, the characterization of the dried extracts of M. urundeuva by TG, DTA and SEM provided important data that can be used as a quality control parameter and as a tool for the selection of excipients in product preformulation studies using this plant.
The authors acknowledge the fellowships received from Conselho Nacional de Pesquisa (CNPq).
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