Abstract

The objective of this study was to enhance the value of cashew kernel by evaluating the nutritional potential of their pastes and the quality of their oils. The physicochemical characteristics, nutritional properties, and quality indexes of cashew kernel pastes and oils were determined using standard analytical methods. All of the parameters studied showed a significant difference (p < 0.05). The results showed that cashew kernel pastes were slightly acidic (6.01 ± 0.02 to 6.33 ± 0.02) with a low moisture content (1.2 ± 0.09% to 2.28 ± 0.13%). The samples recorded different mean value macronutrient contents: fat (36.36 ± 7.86%), carbohydrates (50.05 ± 8.03%), protein (8.98 ± 0.57%), crude fiber (0.59 ± 0.18%), with an average energy value of 563.39 ± 37.57 kcal. The pastes were richest in vitamins C (8.67 ± 1.83 mg/100 g) and E (15.91 ± 2.97 mg/100 g) and the minerals Ca (116.44 mg/kg), K (176.39 mg/kg), and Mg (183.99 mg/kg). The mean values for the quality indexes of the oils obtained were 112.70 ± 1.17 g I/100 g, 1.46 ± 0.005, and 0.85 ± 0.21 meq O₂/kg for the iodine value, refractive index, and peroxide value, respectively. The pastes are rich in nutrients and constitute a good source of energy with high oil quality. They could be incorporated into certain diets.

1. Introduction

The cashew tree (Anacardium occidentale L.), is belonging to the Anacardiaceae family. It is native to Brazil and was introduced to India in the 16th century ¹. Cashew tree is growing at altitudes below 1,000 m in tropical regions in a wide variety of soils, though it prefers light, deep soils ².

The fruit of cashew tree is composed of a false fruit called the cashew apple and a true fruit, which is the cashew nut. The cashew apple, with its tart and sweet-and-sour flesh, is very juicy and rich in vitamin C. It is used to make fruit juice, vinegar, wine, alcohol, jams, jellies, and compotes ². Cashew nuts (kernels) are the main commercial product of this tree, which can produce an average of 200 to 300 fruits per year ³. They are composed of a shell and a kernel containing 45% fat (35% unsaturated fat), 21% protein, and numerous vitamins and minerals. Cashew nuts are used in the food industry and also in pharmaceuticals and cosmetics ².

Introduced to Côte d’Ivoire in the 1950 s for reforestation and erosion control, the tree has now become an important source of money for producers ⁴, ⁵. The cashew tree is now a major export crop for the African continent, which accounts for more than 55% of global cashew nut production ⁶. In 2020, according to estimates by the Food and Agriculture Organization of the United Nations (FAO), global production of in shell cashews amounted to 4.18 million metric tons, harvested from 7.10 million hectares, with Côte d’Ivoire, India, Vietnam, the Philippines, and Tanzania being the leading producers ⁷. West Africa has been the world’s leading cashew-producing region since 2015, with production exceeding 1,350,000 metric tons, and Côte d’Ivoire as the world’s leading producer of raw cashews ⁸.

According to the World Bank ⁹, between 2018 and 2024, the volume of locally processed nuts rose from 68,515 to more than 345,000 metric tons, representing approximately 30 percent of the national harvest.

The consumption of cashew kernels is becoming increasingly common among the population. Cashew kernels are available in various forms in stores, including dry-roasted or oil-roasted, salted or unsalted ¹⁰. However, cashew paste generally made from roasted cashew kernels is also available in the country’s supermarkets. These pastes come from small, local artisanal processing units. Several studies have highlighted the high nutrient content of cashew nut derivatives ¹¹, ¹², ¹³. However, the pastes produced from these nuts and sold on supermarket shelves have not been the subject of any studies. Their production is artisanal and unstandardized. It is important to proove their quality in order to attract consumers attention. The aim of this study is to contribute to the value addition of cashew kernels and to encourage consumer interest in cashew kernels pastes. To achieve this, the study will determine the nutritional potential of the pastes as well as the quality of the oils derived from them.

2. Materials and Methods

The biological material used for this study consisted of roasted cashew kernel pastes purchased from convenience stores and supermarkets in the city of Abidjan. A total of five brands of cashew kernels pastes, represented by one container, were selected based on their availability in stores and their production dates. Each brand, constituting a sample, was identified by a code to avoid any advertising (PC1: cashew kernel paste 1, PC2: cashew kernel paste 2, PC3: cashew kernel paste 3, PC4: cashew kernel paste 4, PC5: cashew kernel paste 5). The ingredients list mentioned for each brand was 100% cashew kernel.

Moisture and dry matter content were determined according to the NF ISO method ¹⁴. A dry porcelain crucible of mass M₀ containing a mass M₁ of sample was placed in an oven at 105°±5°C for 24 hours. The crucible was then removed, allowed to cool in a desiccator, and weighed to give mass M₂.

The moisture content (% H) was obtained using following expression:

%H = ((M0+M1) – M2) / M1 x 100 (1)

The dry matter (% DM) was obtained using following equation:

%DM = 100 – %H (2)

The pH was measured using a pH meter ¹⁵. A 10 g mass of cashew kernel paste was homogenized in 100 mL of distilled water. The filtrate was then collected after filtering the mixture through Whatman filter paper. The glass electrode of the pH meter (HANNA), previously calibrated with a pH 7 buffer and then a pH 4 buffer, was immersed in the filtrate while stirring. The pH value was read directly from the pH meter’s display.

The titratable acidity (Ta) was determined using the method described by ¹⁶. This acidity was determined by an acid-base titration. The principle involves measuring the titratable acidity with a 0.1 N sodium hydroxide (NaOH) solution in the presence of 2 to 3 drops of 2% phenolphthalein, which serves as a color indicator. The titratable acidity level was obtained in g.100 mL⁻¹ according to the following formula:

Ta = (NNaOH x VNaOH x 0.9/V) x 100 (3)

VNaOH = volume of sodium hydroxide required for titration in mL

NNaOH = normality of the sodium hydroxide solution in meq g/L

V = volume of the test sample in mL

0.9 = milliequivalent gram of lactic acid

The ash content was determined according to the method described by ¹⁵. The method involves incinerating organic matter in a muffle furnace at 550°C ± 2°C for 24 hours until white ash is obtained.

The ash content (%Ac) was determined as follows:

%Ac= ((M2-M0)/(M1-M0)) x100 (4)

M0: empty crucible mass

M1: crucible mass + dry sample

M2: crucible mass + calcined sample

The fat content was determined using the Soxhlet method ¹⁵ with hexane as the solvent. The protein content was determined using the Kjeldahl method ¹⁵. The nitrogen content was multiplied by 6.25 (the nitrogen to protein conversion factor) to determine the protein content of the sample. The total sugar and reducing sugar contents of the cashew kernel pastes were determined by spectrophotometric analysis at 490 nm and 540 nm, respectively by ¹⁷, ¹⁸ methods. The crude fiber content was determined using the Weende method ¹⁵. The total carbohydrate content of the cashew kernel paste samples was obtained by subtraction according to the method ¹⁹. It was calculated by subtracting the sum of the moisture, fat, protein, and ash contents of the various samples from 100. The energy value of the sample was calculated according to the method of ²⁰ using the following formula:

Ev (kcal) = (%C× 4) + (%F× 9) + (%P× 4) (5)

Ev: Energy value

C: Carbohydrates

F: Fat

P: protein

The vitamin A, C, and E contents were determined for each of the cashew paste samples. The method used to determine the vitamin C content of the samples was that described by ²¹, which is based on the reduction of 2,6-DCPIP (2,6-dichlorophenol-indophenol) by vitamin C. Vitamin E concentrations were determined by HPLC analysis. To determine vitamin A concentrations, the procedure first involved measuring β-carotene using the method described by ²². After extraction and centrifugation of the mixture, the optical density of the supernatant was measured at 450 nm using a spectrophotometer. For each test, the amount of β-carotene was calculated from a calibration curve with the following regression equation: OD₄₅₀ = 0.0163 Q, where R² = 0.9988. The vitamin A content of the samples was determined by dividing the β-carotene contents by 6 ²³.

Mineral content was determined using an Agilent 5800 air-argon flame ICP-OES instrument ¹⁵.

The quality of oil was evaluated by determining their refractive index, acid value, peroxide value, and iodine value. The refractive index (IR) was determined using a refractometer according to the method described in the French standard NF T-60-212 ²⁴. First, the refractometer was calibrated with distilled water according to the manufacturer’s instructions. Next, the oil was heated to 40°C for 30 minutes before being transferred to the refractometer’s cell. Finally, the refractive index and temperature were read directly from the refractometer’s display. The tests were performed in triplicate.

The acid value was determined according to the standardized method specified in the French standard NF EN ISO 660 ²⁵. To do this, 0.5 g of oil was dissolved in a 25 mL mixture of ethanol and ether (50/50 v/v). The resulting solution was titrated with a 0.1 N alcoholic potassium hydroxide (KOH in ethanol) solution in the presence of a few drops of phenolphthalein (color indicator) until the solution turns pink. The acidity of the solvent (ethanol/ether) was neutralized before use with a 0.1 N potassium hydroxide solution. The tests were performed in triplicate for each sample.

The acid value (Av) was given by the following formula :

Av = 56.1 x V x N/m (6)

Av is expressed in mg KOH/g

V: volume of the ethanolic KOH solution in mL used to titrate the sample

N: normality of the KOH solution

M: mass of the oil test sample in grams

The peroxide value was determined in accordance with standard ²⁶. 2 g of oil were dissolved in 10 mL of chloroform in a flask. To this mixture, 15 mL of acetic acid and 1 mL of potassium iodide solution (10%, v/v) were added, respectively. The flask was capped and shaken for 1 minute, then left in the dark for 5 to 10 minutes. Next, 75 mL of distilled water were added. A few drops of starch paste (a color indicator) were added while shaking vigorously. Next, the mixture was titrated with a 0.02 N sodium thiosulfate solution until the solution was completely decolorized. At equivalence, the color change was observed. A blank test (with oil replaced by distilled water) was performed. The tests were performed in triplicate for each sample.

The peroxide value (Pv) was determined using the following formula :

Pv =(V-V0) x N x 1000/m (7)

Pv expressed in meq O₂/kg

N: concentration of the sodium thiosulfate solution used

V: volume of the sodium thiosulfate solution added to the test sample, in mL

V₀: volume of the sodium thiosulfate solution added to the blank, in mL

m: mass of the test sample of fat (oil), in grams

The iodine value was determined by titrimetry in accordance with the international standard NF EN ISO 3961 ²⁷. This method involves titrating a quantity of fat (oil) with an excess of iodine. The excess iodine was then titrated with Na₂S₂O₃ (aq) to determine the quantity of iodine that reacted (back titration or indirect titration). To this end, 0.5 g of oil was dissolved in 15 mL of chloroform (tetrachloromethane, CCl₄) in a flask, to which 20 mL of Wijs’s reagent was added. The flask was sealed, shaken gently, and then placed in the dark for 1 hour. A blank test was also prepared by replacing the sample (oil) with distilled water. After removing the flask from the dark, 10 mL of a 10% (m/v) potassium iodide (KI) solution and 150 mL of distilled water were added. Next, the released iodine was titrated with a 0.1 N sodium thiosulfate solution in the presence of a 1% (m/v) starch paste as a color indicator until complete decolorization occurs. The tests were performed in triplicate for each sample. Thus, the iodine index was calculated using the following formula:

Iv = ((V0-V) x N x 12.69) /m (8)

Iv expressed in g/100 g

V0: volume of sodium thiosulfate added to the blank test (control) in mL

V: volume of sodium thiosulfate added to the test in mL

N: molar concentration of the sodium thiosulfate solution

m: mass of oil weighed in grams

Each test was performed in triplicate. The means of the various parameters studied were determined using Excel (version 2016); analysis of variance (ANOVA) at a 5% significance level was performed using Tukey’s test with the XLSTAT software version 2021.

3. Results

Figure 1 shows the physicochemical parameters of the various cashew kernel paste samples. All of the parameters differ significantly among the samples (p < 0.05). The samples are slightly acidic, with a mean value of 6.17 ± 0.12 and values ranging from 6.01 ± 0.02 to 6.33 ± 0.02 for PC5 and PC3, respectively. The titratable acidity, which corresponds to the presence of organic acids in the sample, ranges from 6.73 ± 0.03 (g/100 mL) to 8.73 ± 0.1 (g/100 mL), with a mean value of 7.60 ± 1.03 g/100 mL. The average moisture content of the pastes is 1.70 ± 0.52%, with relatively low values ranging from 1.2 ± 0.09% for PC4 to 2.28 ± 0.13% for PC5. The dry matter content, which is directly related to the moisture content, ranges from 97.72 ± 0.13% to 98.80 ± 0.09% for PC5 and PC4, respectively, with a mean value of 98.30 ± 0.52%. The ash content averages 2.90 ± 0.25%, with a minimum of 2.55 ± 0.10% and a maximum of 3.25 ± 0.03% for PC1 and PC4, respectively.

Table 1 shows the macronutrient values in cashew kernel pastes. Analysis of variance revealed that all parameters differ significantly (p < 0.05) among all samples. Cashew pastes are significant sources of energy, with a mean value of 563.39 ± 37.57 kcal. They are higher in fat and carbohydrates, with mean values of 36.36 ±7.86% and 50.05 ± 8.03%, respectively. However, they are lower in proteins, with values ranging from 8.46 ± 0.06% to 9.77 ± 0.06% for a mean value of 8.98 ± 0.57%, and lower in fiber. The soluble sugar contents are also relatively low, with mean value of 0.63 ± 0.18 mg/L for total sugars and 0.09 ± 0.05 mg/L for reducing sugars.

The mineral content of the cashew kernel paste samples is shown in Figure 2. The quantities of minerals present vary from one sample to another, with relatively low mean concentrations of 0.02 ± 0.01 mg/kg, 21.46 ± 8.63 mg/kg, and 22.64 ± 10.18 mg/kg for copper (Cu), manganese (Mn), and phosphorus (P). The concentrations of potassium (K), calcium (Ca), iron (Fe), magnesium (Mg), and zinc (Zn) are greater than 50 mg/kg, for most samples.

Table 2 presents the different vitamin concentrations of the analyzed pastes. Analysis of variance (ANOVA) revealed that all parameters differ significantly (p < 0.05) among all samples. They are rich in vitamins E and C, with levels ranging from 12.56 ± 0.07 mg/100 g to 20.14 ± 0.06 mg/100 g and from 5.83 ± 1.44 mg/100 g to 10.83 ± 1.44 mg/100 g, respectively. As for vitamin A, it is present in lower amounts, with a mean value of 373.01 ± 183.97 μg/100 g.

The values for the different quality indexes determined are listed in Table 3. All of the parameters differ significantly among the samples (p < 0.05). The iodine value ranges from 110.99 ± 0.15 g I₂/100 g for PC2 to 114.21 ± 0.10 g I₂/100 g for PC3, with an average of 112.70 ± 1.17 g I₂/100 g. As for the acid value, the values range from 4.68 ± 0.03 mg KOH/g to 17.77 ± 0.08 mg KOH/g for PC3 and PC4, respectively, with a mean value of 10.32 ± 6.19 mg KOH. Regarding the peroxide value, the samples exhibited low values ranging from 0.57 ± 0.03 meq O₂/kg to 1.13 ± 0.03 meq O₂/kg for PC1 and PC3, respectively, with a mean value of 0.85 ± 0.21 meq O₂/kg. Relative stability was observed for the refractive index, with an average of 1.46 ±0.005.

4. Discussion

The analyzed cashew kernel paste samples had an average moisture content of 1.70%, corresponding to a high dry matter content of 98.30%. This value was both lower and higher than roasted cashew kernels studied in Nigeria (5.90%) ²⁸ and in Côte d’Ivoire (1.48 ± 0.01%) ¹³, respectively. This low moisture content could be an advantage for extended shelf life. The cashew kernel pastes were slightly acidic, with an average pH of 6.17 and an average titratable acidity of 7.60 g/100 mL. This value was lower than cashew kernel pastes studied (3.75) by ¹³. Since titratable acidity is related to the organic acids in the sample, these results suggest a higher concentration in the samples studied. The average ash content found (2.90%), indicating the presence of minerals, was roughly equal to that reported for pastes made from cashew kernels in Ethiopia ²⁹.

The determination of macronutrient contents revealed heterogeneity in the composition of the different samples. The average fat content found was lower than the kernel pastes studied by ³⁰ and ³¹. According to ³², the lower fat content may be related to the roasting conditions of the kernels. The carbohydrate content was the highest in nearly all samples, with an average of 50.05 ± 8.03%, which was significantly higher than peanut pastes solded in Ouagadougou ³³ and Côte d’Ivoire ¹³. The average protein content observed in this study was lower than that reported by ³⁴. This would suggest that proteins were denaturated due to heat during the roasting of the kernels ¹². The crude fiber content was low compared to that obtained by ³⁰. This could be explained by the complete removal of the skins from the almonds prior to grinding. Indeed, according to ¹¹, the skins are removed from roasted almonds to prevent their astringency and the tingling sensation they would cause in the mouth. The low soluble sugar contents could be explained by limited degradation of polysaccharides during the heat treatment of cashew kernels. The results show that cashew kernel pastes were high energy (mean energy value = 563.39 kcal). It could therefore be incorporated into certain diets.

Cashew kernel pastes contained various minerals and vitamins in varying amounts. These micronutrients play an essential role in the body’s physiological functioning. The high levels of calcium (Ca), magnesium (Mg), and potassium (K) could be a benefit of these pastes. Indeed, calcium is necessary for the strengthening of bones and teeth ³⁵. Magnesium is important in the synthesis of carbohydrates, lipids, nucleic acids, and proteins, as well as in other functions within various organs of the cardiovascular and neuromuscular systems ³⁶. The average magnesium content of cashew pastes (183.99 mg/kg) could meet the needs of adults, which range from 5 to 7 mg/kg/day ¹³. The average copper content (0.017 mg/kg) was below the toxicity threshold defined by the WHO ³⁷. The cashew kernel paste samples contained vitamins A, C, and E in varying rates. These levels were higher than those found by ³¹ and ³⁸ in their studies.

The iodine value reflects the degree of unsaturation of fats ³⁹, which indicates the presence of unsaturated fatty acids. The average value found (112.70 ± 1.17 g I/100 g) was lower than that of sesame, soybean, and sunflower oils ⁴⁰. However, it was higher than the values reported by ⁴¹ for cashew kernel oil (41.30 g I/100 g) and palm oil (20.70 g I/100 g). This would suggest that the oils studied were rich in unsaturated fatty acids. The peroxide value, on the other hand, indicates the degree of oxidation of the oils. The oils studied had an average peroxide value of 0.85 ± 0.21 meq O₂/kg, which was well below the maximum value (10 meq O₂/kg) accepted for edible oils ⁴². The acid value is related to the presence of free fatty acids in the sample. It also indicates the degree of lipid deterioration. The average value obtained (10.32 mg KOH/g) was lower than that reported by ²⁸. The refractive index indicates the purity of the oil and is proportional to the molecular weight of the fatty acids as well as their degree of unsaturation ⁴³. The average value obtained (1.46 ± 0.005) fell within the range established by ⁴⁰.

5. Conclusion

The objective of this study was to contribute to the promotion of commercially available cashew kernel pastes by evaluating their nutritional potential. Analysis of the physicochemical characteristics showed that the pastes were slightly acidic (6.17 ± 0.12) with a low moisture content (1.70 ± 0.52%), which would be advantageous for a long shelf life. The pastes were good sources of macronutrients and energy (563.39 kcal). They could therefore be incorporated into certain diets. They contain various minerals (calcium, magnesium, potassium, iron, manganese, zinc) and vitamins (A, C, E) necessary for the proper functioning of the body and the prevention of certain diseases. Analysis of the oil quality would suggest that they were pure (1.46 ± 0.005), rich in unsaturated fatty acids (112.70 ± 1.17 g I/100 g) and had not undergone oxidation (0.85 ± 0.21 meq O₂/kg). Regular consumption of cashew kernel pastes would be beneficial for consumers.

ACKNOWLEDGEMENTS

The authors would like to express their sincere thanks to the laboratory's (Laboratoire des Procédés Industriels de Synthèses de l'Environnement et des Energies Nouvelles) technical staff for their support during the analyses.

References