13.2.1 Production of Cashew Gum

Cashew gum can be obtained by natural exudation or by means of incisions on the trunk and branches of the cashew tree. In Ghana, the gum exudes spontaneously from the trunk and principal branches of the trees around the middle of November, after the rainy season [9]. The dry winds, which prevail after the rainy season, cause the bark to crack, and the gum flows out, and this continues up to March when the dry season ends. The exuded gum thickens and hardens within some few days of exposure to the air, usually in the form of round or oval tears or in straight or curled cylindrical pieces of various sizes. The masses of gum are collected, either while adhering to the bark or after they fall to the ground. Generally, most cashew trees produce white gums, while a few produce amber‐colored gums. There is virtually no production of gum during the rainy season, that is, from May to August, when the trees are not under stress.

In Ghana, cashew production is concentrated in the Guinea savannah zone and in the transitional belt between the forest and the savannah zones. A study conducted on the production and yield trends of cashew gum in these two areas showed that the location of the trees had no significant effect on the production of the gum [9]. The minimum age of cashew trees for the production of the gum was 4 years, with mature trees (trees more than 10 years old) producing more gum than young trees (young trees 10 years and below). The average yield/tree for the young trees varied from 13.7 to 276.0 g and that for mature trees was from 30.1 to 1237.1 g. However, there was no significant difference between yields from mature trees and those from young trees. During the study, a very old tree which according to local farmers was 45 years in the Guinea savannah zone (Figure 13.1a), produced 7664.1, 3270.1, and 497.7 g of gum for January, May, and August, respectively, confirming that the older tree, the more gum it produces. Higher gum yields were obtained during the dry season from January to March when there was drought and the trees were under stress. In Brazil, the average production of cashew gum per tree per year is 700 g with a potential annual production of 38 000 MT [10].

Several techniques are now being used to produce gum artificially to guarantee viability and improvement of the quality of the commercial product. These techniques involve systematically controlled tapping and collection procedures. One such technique is the use of chemical stimulants in the extraction of gum from cashew tree [11]. Application of stimulants such as sulfuric acid combined with 2‐chloroethyl phosphonic acid and 5% dimethyl sulfoxide also increased gum exudation from the trees in all months following stimulant applications.

13.2.2 Chemical Structure

Cashew gum is a complex polysaccharide of high molecular mass comprising 61% galactose, 14% arabinose, 7% rhamnose, 8% glucose, 5% glucuronic acid, and 2% other sugar residues [8]. Different chemical reactions have been used to determine the structure of the gum. These include complete acid hydrolysis of cashew gum, which shows that the gum is made up of D‐galactose, L‐arabinose, D‐galacturonic acid, and L‐rhamnose [12]. Characterization of the gum showed that it contains 72%–73% galactose, 11%–14% glucose, 4.6%–5% arabinose, 3.2%–4% rhamnose, and 4.7%–6.3% glucuronic acid [10]. It is mainly composed of three types of galactan units within the core, linked by C‐1 and C‐3, C‐1 and C‐6 and C‐1, C‐3 and C‐6. The glucose is present as a side chain up to five units long. Cross‐reactions of cashew gum with different anti‐sera also confirm the presence of non‐reducing galactose units reinforced with L‐rhamnose residues. Auto‐hydrolysis of cashew gum generates a degraded gum with a molecular weight of 23 250 gmol⁻¹, which upon graded hydrolysis produces an aldobiouronic acid with an established structure of 6‐0‐ (β‐ D‐ galactopyranosyl uronic acid) ‐D‐galactose [13]. Recently, the structures of degraded and natural cashew gums have been established through methylation and Smith degradation experiments. Degraded cashew gum is a branched chain polysaccharide with a repeating unit which has a 1 → 3 linked galactan main chain [13]. This chain has galactose residues attached to it as side chains by 6 → 1 linkages. Every alternate galactose residue carries aldobiouronic acid moieties also joined by 6 → 1 linkages. The natural cashew gum differs from the degraded gum with respect to the size of the main galactan chain and in the number of auxiliary chains.

13.2.3 Organoleptic Properties of Cashew Gum

Cashew gum, just like other gums, is odorless and tasteless, and it can be sorted on the basis of color and brightness. Sorting of cashew gum yielded three different grades [9], with the physical properties of grade 1 gum being glassy and transparent in form, while grades 2 and 3 were translucent. Grades 1 and 2 were whitish yellow in color, with grade 2 being more yellowish than grade 1 (Figure 13.1b). Grade 3 cashew gum was amber or brown in color (Figure 13.1c). The lower grades were generally more strongly colored than the higher grades. The color differences depend on the presence of impurities and the age of the tree that produced the gum. Milled cashew gum was also white or pale brown in color (Figure 13.1d) depending on the color of the gum nodule that was milled. Some studies have also shown cashew gum to be cream to white [14], golden brown to glassy white [15,16], or pale yellow to reddish in color [13]. They also found it to be tasteless, odorless, translucent, glassy in form, and gritty in texture. However, cashew gum, when purified by dissolving crude gum in water and precipitating it with 96% ethanol, was glassy white, tasteless, odorless, and smooth in texture [ 15, 16], but when precipitated with acetone, the purified gum was off‐white in color and turned brown on exposure to air [17].

13.2.4 Physicochemical Properties of Cashew Gum

Physicochemical properties of natural gums vary in terms of differences in tree species [18]. Gums from the same tree species but of different ages and from different soil types also differ in physicochemical properties. Some concerns have been raised on the production, processing, and use of natural gums, and these include the accurate identification of the sources of gums and their quality assurance. The use of gums in numerous industries including the food, pharmaceutical, and cosmetic industries has increased widely in these last decades [19], and this is due to the numerous interesting characteristics such as the gelling, stabilizing, and thickening functions of these polymers. These functions and the physicochemical properties of the gums are used to determine their quality and how they will perform during processing. In view of this, some works have been done on the elementary analysis of cashew gum.

Proximate analysis of cashew gum has revealed that it is mostly made up of carbohydrates with some moisture and very low amounts of protein, fat, and fiber. Lima et al. [8] reported that the gum has 7.4% moisture, 0.5% protein, 0.06% fat, 0.95% fiber, 0.95% ash, and 98.0% carbohydrate. Purification of crude cashew gum using 96% ethanol has been found to reduce chemical components of the gum [ 15,20]. However, purification increases the pH of the crude gum, making its purified form less acidic (Tables 13.1 and 13.2). Chemical components such as fat, protein, fiber, and tannins were not detected in the purified gum (Table 13.1). The absence of tannins may explain why purified cashew gum is always white in color. Tannins undergo oxidative reactions which result in the development of brown color in the crude gum. Cashew gum purified with acetone has also been reported to have reduced mineral and moisture content compared to its crude form [17].

Studies on the effect of tree maturity on cashew gum have shown that gum from the mature tree was more acidic than that from young trees [21]. The pH of cashew gum ranged from 3.80 to 4.20 (Table 13.3). The phenol content of mature tree gum was higher than that in young tree gum. However, gum from young trees had higher protein and sugar content than those from mature trees (Table 13.3). This may due to the fact that the young trees, which are actively growing, synthesize more nutrients than the mature ones [22]. Proteins are important for the emulsifying properties of gums [18]. The moisture content of cashew gum was found to be between 9.8% and 13.2%, with mature tree gum having higher moisture content, and this may be due to the fact that they produced more gum and would need a longer time to dry. The mature trees also have well‐developed root systems which have the ability to take up more water from the soil for their metabolic processes.

The mineral content of plant materials is thought to be a function of the composition of the soil on which the plants grow [23]. Cashew gum was found to have very high levels of calcium, sodium, and potassium, with calcium being predominant (Tables 13.2 and 13.3). Gum from mature trees had higher mineral content than that from young trees, and this may be due to the fact their root systems take much of the soil nutrients and store them in other parts of the plants [22]. Sodium and potassium content of the gums tend to increase from the transitional belt to the Guinea savannah zone, and this is an indication of high levels of potassium and sodium in the soils of the Guinea savannah zone. The high levels of minerals which are normally found in their ionic state may account for the acidity of cashew gum [24].

13.2.5 Rheological Properties of Cashew Gum

There are two rheological properties of particular importance to hydrocolloids: their gel and flow properties. Hydrocolloids are used to thicken and/or gel aqueous solutions in order to modify and/or control the flow properties of liquid products and the deformation properties of semisolid products [19]. They are generally used in food products at concentrations of 0.25%–0.50%, which indicates their great ability to produce viscosity and to form gels [25]. Many hydrocolloids, which include natural gums, are capable of forming gels of various strengths depending on their structure and concentration as well as on environmental factors such as ionic strength, pH, and temperature.

Cashew and acacia gums have been found to have similar rheological properties [14]. Solutions of both gums showed an increase in viscosity with concentration, but the viscosity increase was more gradual with gum arabic, indicating that cashew gum has better thickening capability. Changes in pH, temperature, and storage time affected the viscosity of both gums. However, their effects on viscosity were not significant. Dissolving xanthan gum in cashew juice produced a higher viscosity than dissolving cashew gum in cashew juice, indicating that cashew gum has less thickening capability than xanthan gum [26]. However, when the two gums were blended in cashew juice, it produced juice with a viscosity similar to that with xanthan gum. This is due to the synergistic interactions between the two gums in solution.

Addition of zinc oxide (ZnO) at concentrations of 3%, 5%, 7%, and 10% to aqueous cashew gum solution raised its pH from 4.74 to the range 6.3–6.7 and its viscosity from 4.82 to the range 5.07–8.01 mPa s [27]. This shows that zinc oxide essentially controls the acidity of the gum, thereby acting as a stabilizer and a filter agent in the gum. However, the addition of starch to the raw gum solution at the same concentrations as those used in ZnO slightly reduced the pH of the gum to the range 4.5–4.7, while the viscosity increased to the range 4.67–9.56 mPa s. The starch, therefore, acted as a binding agent. Addition of glycerine to the gum at concentrations of 3%, 5%, 7%, and 10% also decreased its pH to the range 4.2–4.5 but increased the viscosity to its highest range, 5.26–10.21 mPa s. In the presence of glycerine, the gum became more slippery, suggesting that glycerine aids the easy spread of the gum. Combinations of the additives, that is, zinc oxide and glycerine, produced pHs between 4.20 and 5.30 and viscosities between 5.20–6.78 mPa s. This indicates that combining cashew gum with additives such as zinc oxide, starch, and glycerin can improve the rheological properties of the gum.

Studies have also shown that increasing the cashew gum concentration increases the viscosity and facilitates gelation of the gum [ 15, 16,28]. The flow behavior of cashew gum showed that the gum was liquid at concentrations of 4%–12%, viscous at 16%–40%, and gel at 80% and higher, but the gel produced rapidly dissolved when heated at a temperature of 80 °C [28]. The gelation may be accounted for by enhanced interactions among the binding forces of the gum molecules [25]. The viscosity also decreased with an increase in temperature (Figure 13.2a), confirming reports that the major effect of temperature on hydrocolloids is a decrease in viscosity [19]. The change in viscosity with temperature also indicates the possible thermal decomposition of hydrocolloids during heating. However, the mechanism of thermal decomposition of gums is unknown [10]. Therefore, the use of high operating temperatures is not encouraged in processes that involve hydrocolloids such as cashew gum [19]. The average viscosity of 1% cashew gum solution at 25 °C was 10.03 mPa s, and the viscosity of gum arabic as reported by TIC Gums [29] is less than 5 mPa s at 1% solution. This, therefore, makes cashew gum a better thickening or stabilizing agent.

Viscosities of cashew gums produced by mature trees were generally lower than those produced by young trees [28]. However, gums coming from different locations and environments were not significant. There were also differences in the viscosities of cashew gum produced at different times of the year. Those produced during the rainy season had lower viscosities than those produced during the dry season (Figure 13.2b). However, the differences were not significant. Storage of the gums for six months and above slightly reduced their viscosities.

13.2.6 Toxicity and Microbial Determination of Cashew Gum

Safety continues to be a matter of great concern to the consumer. Issues of safety include hazards and risks. A hazard is a source of danger such as microbial poisoning and allergic reactions, whereas a risk is a measure of the probability and severity of harm to human health. Safety is therefore the judgment of the acceptability of risk. A substance can therefore be considered safe if its risks are judged to be acceptable. The risk of exposure to a substance can be determined by identifying a hazard and determining the dose or amount of the substance at which there is the likelihood of the hazard occurring and finally determining the quantity of the substance to which humans are or could be exposed. All substances must be safe for use before marketing and thus must undergo the risk of exposure or toxicity assessment.

Acute toxicity is a short‐term study where test organisms are exposed to a substance for a short period of time to measure the concentration that will have a significant effect on them. Data from these tests can be used to screen or rank toxicity and to assess the potential for effects in the environment. Examination of rats fed with 5–30 g kg⁻¹ body weight (b.w.) cashew gum for 30 days showed that the gum had no allergic or adverse effect on the rats. The test rats did not show any changes in movement, appetite, water intake, salivation, and urination [9]. They also did not show any symptom of diarrhea. The median lethal dose (LD₅₀) for the gum was found to be more than 30 g kg⁻¹ b.w. This indicates that the gum is not acutely toxic according to World Health Organization (WHO) Acute Hazard Rankings (Table 13.4) and also confirms that cashew gum presents no hazard for short‐period exposure. Okoye et al. [31] also determined the lethal dose (LD₅₀) of cashew gum to be more than 5000 mg kg⁻¹ in rats. Acute toxicity studies on groups of rats fed with gum arabic in their diet for six days showed normal weight gain and food efficiency for the rats [32]. A similar observation was made in another study of cashew gum. The LD₅₀ of gum arabic was in the range 8–18 g kg⁻¹ b.w. as a bolus dose [33]. These observations suggest that although natural polysaccharides such as cashew gum are non‐toxic, they are susceptible to microbial growth.

Cashew gum has been found to have a very low microbial load. Work by Okoye et al. [31] showed that coliforms and other enteric gram‐negative bacteria were absent in the gum. However, gram‐positive bacteria, Bacillus spp., were present at a level of 66 cfu g⁻¹, which was below the accepted limits of 1000 cfu g⁻¹. This may be due to the presence of anacardic acid, which has been clinically proved to have anti‐microbial properties against several microorganisms, including Escherichia coli and Helicobacter pylori [34], in the gum. Other studies showed that E. coli, Pseudomonas aeruginosa, and Staphylococcus aureus were not present in both crude and purified gums. However, Salmonella spp. was found in the crude gum but not in the purified gum. Both crude and purified gums were infected with fungi, but their growth was scanty on the purified gum plate compared to the crude gum plate, and this could be attributed to the purification process [15]. Kumar et al. [35] also reported that cashew gum was safe to use.

Microbial determination of cashew gum by Gyedu‐Akoto et al. [21] showed that the gum contained an average of 3.2 × 10³ cfu ml⁻² of total microorganisms and 465 cfu ml⁻¹ of yeasts and molds, which can easily be destroyed by heating. Cashew gum was also found to be free from coliforms, which is an indicator of the presence of disease‐causing bacteria, such as those that cause typhoid, dysentery, hepatitis A, and cholera. This indicates that cashew gum has no potential of being a health hazard to humans or animals in terms of its microbial status. Statistical analysis of data from the microbial determination of the gum showed no significant difference between gum from mature cashew tree and that from a young tree. This confirms the Walker [33] report, which says that from the toxicological point of view, differences between gums from different tree species are not significant.

13.2.7 Modification of Cashew Gum

Natural gums are commonly used in many industries due to their availability, sustainability, biodegradability, and biosafety [36]. Although they have very good functional properties, there are challenges associated with their applications, and these include uncontrolled rates of hydration, pH‐dependent solubility, reduction in viscosity on heating and storage, and possible contamination with microorganisms. These challenges can be addressed by chemical and physical modifications of natural gums. Gums can also be modified for specific purposes. Chemical modification of gums includes acetylation, carboxymethylation, grafting, and cross‐linking with other chemicals. Carboxymethylation of cashew gum using monochloroacetic acid as the etherifying agent increased its hydrophilic capacity and solution clarity, and made it more soluble in aqueous systems [ 17,37]. Cross‐linking of cashew gum using epichlorohydrin also reduced its swelling capacity [ 17,38]. On the other hand, Abdulsamad et al. [39] reported that cross‐linking cashew gum with a mixture of citric acid and glycerol improved the swelling, water absorption, and retention capacities. Oxidation of the gum increased its solubility, water‐holding capacity, and uronic acid from 3.7% to 38% [8]. In another study, oxidation of cashew gum also increased its uronic acid from 7.2% to 36%, viscosity by 0.1 mPa s and reduced its thermal stability from 209 to 191 °C [10]. Acetylation of cashew gum with acetic anhydride increased its viscosity and swelling capacity from 20.20 to 53.4 mPa and 10.9%–45.9%, respectively [40]. Grafting of gums modifies their swelling and film‐forming properties. Cashew gum grafted with polyacrylamide using potassium persulfate as the chemical initiator and ultrasound energy produced a flocculant (CG‐g‐PAM) which had flocculation of 96% compared with the commercial flocculant Flonex‐9045 [41]. Chemically modified gums known as semisynthetic gums have been found to be stronger emulsifiers and are less likely to undergo microbial growth.

13.3.1 Cashew Gum as an Encapsulating Agent

Encapsulation is a technique used to protect active food components from harmful environmental factors such as water, light, and oxygen. It also facilitates the delivery of active food components, such as converting liquid foods into dry particulates, and making food handling processes easy. Encapsulation of materials rich in volatile compounds by spray drying presents the challenge of removing water by vaporization without loss of odor and/or flavor components. Recent investigations into the use of cashew gum as a material for microencapsulation have been conducted by a few scientists within the food industry. Cryoconcentrated coffee extracts rich in odor components were used as a substrate core to evaluate microencapsulation with cashew gum. Biochemical, structural, and sensory evaluation of the microcapsules of the coffee extracts produced compared to those produced with gum arabic showed that both products have similar aroma protection, external morphology, and size distribution, suggesting that cashew gum is a suitable alternative to gum arabic for odor microencapsulation [43]. Evaluation of cashew gum for encapsulation of fish oil compared to conventional hydrocolloids was conducted based on the properties and oxidative stability of the spray‐dried fish oil. The viscosity of emulsions produced with cashew gum was lower than that produced with gum arabic. The particle size of the microparticles produced with cashew gum was larger (29.9 μm) than those produced with the other materials. The cashew gum encapsulation efficiency reached 76%, and this was similar to that of modified starch but higher than the 60% value for gum arabic. Microparticles produced using gum arabic and cashew gums showed greater water adsorption when exposed to higher relative humidity. However, those produced using cashew gum were more hygroscopic, their encapsulation efficiency was higher, and surface oil oxidation was less pronounced [44].

A study involving an attempt to completely or partially replace a conventional hydrocolloid, maltodextrin DE10 (MD10), with cashew tree gum as a drying aid agent in spray drying of cashew apple juice was conducted by De Oliveira et al. [45]. The impact of the drying aid/cashew apple juice dry weight ratio and degree of replacement of MD10 with cashew gum on the ascorbic acid retention (AAR), hygroscopicity, flowability, and water solubility of spray‐dried cashew apple juice powder was assessed, and cashew gum was shown to be a promising maltodextrin replacer and a more effective way of reducing the juice powder hygroscopicity. The adequate drying condition resulted in more than 90% of AAR and produced a powder with good flowing properties and water solubility.

13.3.2 Cashew Gum as a Coating Agent (Film‐Former)

Attempts to replace gum arabic with cashew as a coating agent in the production of chocolate pebbles, a confection, were made by Gyedu‐Akoto et al. [28], and they concluded that the optimum concentration of cashew gum solution for this purpose was 66.7% (w/v). Comparing this to the 100% (w/v) concentration of gum arabic solution normally used for pebbles production confirmed that cashew gum is a better thickening agent than gum arabic. Physicochemical analysis of pebbles with cashew gum showed that their moisture and sugar content (2.33–2.38 and 26.05–29.66, respectively) fell within the acceptable levels for chocolate pebbles [46], which are 1%–3% and 20%–30% for moisture and sugar content, respectively. Their microbial status also conformed to the internal specification of Cocoa Processing Company (a chocolate manufacturer in Ghana) for chocolate products. Their total microbial load and yeasts/molds were 3.0 × 10² and 0 cfu ml⁻¹, respectively. The total microorganisms were relatively lower for cashew‐gum‐based pebbles compared to gum‐Arabic‐based pebbles. However, they both contain no coliforms. Sensory analysis of the two products showed no significant difference.

13.3.3 Cashew Gum as a Gelling Agent

Studies on the use of cashew gum as a gelling agent in pineapple jam production and as a stabilizer in pasteurized cashew juice showed that it was possible to gel pineapple jam with cashew gum at 5%–10% concentration [47]. However, the optimum level of the gum for pineapple jam gelation was predicted to be 5% by using the response surface methodology. Visual observation of cashew juice after heat treatment showed that cashew gum had a clarifying effect on the juice instead of retaining sediments formed in suspension. The addition of cashew gum was found to cause more sedimentation in the juice, and these sediments settled after allowing the juice to stand overnight. The increase in the sedimentation may be due to the galacturonic acid component in its structure, since reports by Baker [48] state that the addition of base‐solubilized polygalacturonic acid to fruit juices yields immediate and relatively complete clarification.

13.3.4 Cashew Gum as a Clarifying Agent

Clarification of cashew juice with cashew gum at a concentration of 4.762 g l⁻¹ resulted in 78.0% clarity and reduced the total soluble solids and vitamin C contents of the juice by 6.7% and 25.8%, respectively, but did not have any effect on the total sugar content [20]. However, clarifying with gelatin at 2.349% concentration yielded 54.7% clarity and reduced the total sugar content, total soluble solids, and vitamin C content of the juice by 4.0%, 11.7%, and 26.2%, respectively, making cashew gum a better clarifier than gelatin.

A study done by Gyedu‐Akoto et al. [47] showed that the addition of different levels of cashew gum (0.00, 0.05, 0.10, 0.15, and 0.20) to cashew juice on the basis of the central composite design clarified the juice at all levels. Sensory analysis of the clarified juices showed that the addition of cashew gum caused more sedimentation than juice without the gum and also reduced the astringency of cashew juice.

13.3.5 Cashew Gum as a Fat‐Replacing Agent

Dietary fat is a nutrient needed for a healthy lifestyle. However, high fat intake is associated with increased risk for obesity, cancer, high blood cholesterol, and coronary heart diseases [49]. To help consumers moderate their dietary fat intake, advances in food science have allowed for the development of a wide variety of reduced‐fat food products. Fat replacers are also developed to duplicate the taste and texture of fats in food [50]. In an attempt to maximize the use of cashew gum, its utilization as a fat replacer in baked doughnuts was studied by Gyedu‐Akoto [51], and the results suggested that fat may be replaced by cashew gum in baked doughnuts up to 40%.

13.4.1 Cashew Gum as an Excipient

One of the emerging natural excipients in the pharmaceutical industry is the cashew tree gum. Several attempts have been made to incorporate this gum into the formulation of pharmaceutical products. Investigations by Kumar et al. [35] have shown that the functionality of cashew gum in cotrimoxazole granule and tablet formulation produced the best micrometric properties compared to those formulated with three standard binders, polyvinylpyrrolidone (PVP), gelatin, and corn starch . Development of unidirectional, bilayered, buccoadhesive tablets of curcumin has shown that cashew gum can be used as a polymer in the tablets [54]. The optimum formulation per batch was found to have 20% polymer concentration, 0.1% penetration enhancer, and 40 mg backing layer (ethyl cellulose). This was compressed at 2 tons cm⁻² for 10 s. The formulated tablets were stable with respect to their physicochemical and in vitro drug release behavior over a period of 60 days at different temperatures and relative humidity. The kinetics of drug release was also found to be non‐Fickian or anomalous diffusion [54]. Studies on the binding efficacy of cashew gum in tablet formulation in comparison with standard binders, acacia gum, and polyvinylpyrrolidone (PVP K‐30) revealed that cashew gum at a concentration of 2.5% produced a paracetamol tablet of better mechanical strength and dissolution profile of a particular drug substance [55]. In this study, paracetamol granules were prepared with different concentrations of the gum as a binder by the wet granulation method. Evaluation of tablets prepared from the granules showed that formulations containing a minimum concentration of 2.5% cashew gum as binding agent showed short disintegration and fast dissolution with good physicomechanical properties.

Crude cashew gum and its modified forms were used in the formulation of a sustained release delivery system with theophylline as a model drug [17]. The modified gums used were cross‐linked cashew gum, carboxymethylated cashew gum, and carboxymethylated cross‐linked cashew gum with gum‐to‐drug ratios of 1:1 and 3:1. The optimum formulations were identified using response surface methodology. The best and most stable formulation was found to contain cross‐linked cashew gum with an epichlorohydrin‐to‐gum ratio of E/G^b = 0.15. The kinetic analysis of dissolution data showed a good fit in the Peppas equation, which confirmed an anomalous non‐Fickian release mechanism for cross‐linked cashew gum with theophylline. The mechanical and coating properties of cashew‐gum‐based films, using paracetamol as a model drug, was also investigated by Ofori‐Kwakye et al. [56]. Free films used were cashew gum, cashew gum/hydroxypropyl methylcellulose (HPMC), and cashew gum–carboxymethyl cellulose (CMC), prepared by solvent casting and glycerol as a plasticizer. The cashew gum films were smooth, uniform, and transparent, while cashew gum/HPMC and cashew gum/CMC films lacked uniformity and surface smoothness, respectively. A film coating of 7.5% (w/v) cashew gum formulation to paracetamol tablet cores enhanced the mechanical strength of the tablets. However, film‐coating the tablet cores did not significantly affect the disintegration and drug release properties of the tablets compared to the uncoated tablets. Cashew gum, when applied at 7.5% (w/v), could therefore be useful as non‐functional film coatings for conventional solid dosage forms.

Sustained release matrix tablets of diclofenac sodium formulated with xanthan gum and cashew gum together with the semisynthetic release modifier HPMC were studied by Obese in 2012 [57]. At different ratios of 100:0, 80:20, 60:40, 20:80, and 0:100 of xanthan:HPMC, xanthan:cashew, and xanthan:cashew:HPMC, the granules produced had good flow properties. All the physical characteristics of the formulated tablets using the granules fell within acceptable limits. The swelling index of the tablets containing only xanthan gum exhibited the highest swelling index followed by tablets containing xanthan and cashew gums in the ratio of 80:20. Overall drug release was found to be a complex mixture of diffusion, swelling, and erosion. The drug release profile of some of the tablets was similar to the reference drug (Voltaren Retard), with the others being slightly different from the reference drug. The results obtained showed that the gums and HPMC used individually could not sufficiently produce sustained release but when combined with various ratios produced effective sustained release [57].

13.4.2 Pharmacological Studies on Cashew Gum

Pharmacology is the study of the effect of drugs on the body. In this case, cashew gum is used as a drug in the control of diseases and not as an excipient. Cashew gum has been exploited by locals since ancient times for multiple applications, including the treatment of diarrheal diseases. Studies have shown that cashew gum administered orally to rats with castor‐oil‐induced diarrhea at 30, 60, and 90 mg kg⁻¹ body weight (b.w.) had a significant antidiarrheal effect on the rats at all levels of dosage [58]. It also inhibited the total amount of stool and diarrheal stools. The 60 mg kg⁻¹ dose of cashew gum exhibited excellent antidiarrheal activity, reduced the severity of diarrhea in rats, and decreased the volume of castor‐oil‐ and PGE2‐induced intestinal fluid secretion (enteropooling) significantly. In addition, similar to loperamide, a standard drug with a dose of 5 mg kg⁻¹ b.w., cashew gum treatment reduced the distance traveled by a charcoal meal in the 30‐minutes gastrointestinal (GI) transit model by interacting with opioid receptors. In cholera toxin‐induced secretory diarrhea, the 60 mg kg⁻¹ dose of cashew gum significantly inhibited the intestinal fluid secretion and decreased chloride ion loss using cholera toxin‐treated isolated loops model of live mice. This was done by competitively binding to cholera toxin‐GM1 receptors in the mice. The antidiarrheal activity might be explained by the capacity of cashew gum to inhibit gastrointestinal motility, thereby reducing the accumulation of intestinal fluid and the secretion of water and chloride ions in the lumen of the intestine.

The use of cashew gum in the reduction of blood pressure in spontaneously hypertensive rats was studied by Mothe et al. [59]. The blood pressure of rats fed with cashew gum was reduced by 20%. There was also a 4% decrease in the ratio of the left ventricular mass and heart mass of the rats treated with the gum. This indicates that cashew gum could help retard hypertrophy in the rats. Tannins, anacardic acid, and Cardol, which are known to be the active ingredients in the cashew fruit for its medicinal properties, may also be present in the gum [36]. The long‐term use of non‐steroidal anti‐inflammatory drugs is associated with gastrointestinal (GI) lesion formation. A study on the protective activity of cashew gum on naproxen (NAP)‐induced GI damage was therefore conducted by Carvalho et al. [60] using male Wistar rats. Results showed that pretreatment with cashew gum reduced the macroscopic and microscopic damage induced by the NAP. Cashew gum significantly attenuated NAP‐induced alterations in myeloperoxidase, glutathione, and malondialdehyde levels. Furthermore, cashew gum returned adherent gastric mucus levels to normal values. These results suggest that cashew gum has a protective effect against GI damage via mechanisms that involve the inhibition of inflammation and increasing the amount of adherent mucus in the mucosa.

Cashew gum combined with water‐soluble β‐galactose and other oligosaccharides as well as proteins exhibited a high inhibitory activity of 88% against an implanted sarcoma 180, a solid tumor in mice [61]. In other words, cashew gum can be used for the prevention of cancer, and/or as an adjuvant with cancer chemotherapy drugs, after the removal of a malignant tumor. More investigation should be done with cashew gum as there is a great need for clinical study in neoplasia treatments for humans.

Other uses of cashew gum such as the construction of a kind of chromatographic matrix (hydrogel) have become a useful tool for modern biotechnology in underdeveloped countries [8]. It has been found to be an efficient method for the detection and elucidation of galactose‐specific lectins. Sarubbo et al. [62] have also studied the partitioning of two proteins, bovine serum albumin (BSA) and trypsin, in an aqueous polyethylene glycol (PEG)–cashew gum system and found the system to be very effective.