SM Journal of Biology ISSN: 2573-3710

Research Article

The Impact of Seed-Borne Fungi Associated with Roasted Cashew (Anacardium Occidentale L) Nuts on Its Food Value, Mineral and Anti-Nutrient Contents and Human Health

Ibiam, O. F. A¹*, Nweke, A¹ and Kanayochukwu, U. L²

Abstract

Isolation and identification of seed-borne fungi associated with cashew nuts from source of production and market was carried out. The proximate, mineral and anti-nutrient composition of the source of production and the market samples of roasted cashew nuts were also investigated. The result of isolation of fungi associated with the nuts from source of production and the market showed that Claviceps purpurea, Aspergillus fischeri, Aspergillus carbonarius, Aspergillus flavus, Aspergillus tamrii and Aspergillus fumigatus were associated with seeds from samples from the two sources. The ash, lipid, carbohydrate and protein contents of the source sample were relatively higher, while the moisture, fibre and vitamin C content of the markets samples were relatively lower. The Sodium, Zinc, Nitrate, Nitrogen and phosphorus contents of the market samples were observed to be higher when compared with the source sample, while the phosphate, Magnesium, Calcium, Manganese and Copper contents of the source samples were higher than the market sample. The saponin and the cyanogenic glycoside content of both market and source samples was the same, while the alkaloid content of the source samples were relatively higher. The flavonoid content of the market sample was observed to be higher when compared with the source samples.

Introduction

Cashew (Anacardium occidentale L) is next to cocoa as an export crop and a major source of cash income to many small holder farmers in the Central and Northern parts of Nigeria [1,2]. The Cashew Nut Liquid (CNL), a by-product of processing cashew, is mostly composed of anacardic acids [3]. These acids have been used effectively against tooth abscesses due to their lethality to a wide range of Gram-positive bacteria [4]. The bark is scraped and soaked overnight or boiled and used as an anti-diarrhea, and the seeds when ground into powders are used as anti-venom for snake bites [4]. The nut oil is used topically as an anti-fungal agent, and for healing cracked heels [4]. Anacardic acid is used in the chemical industry for the production of cardanol, which is used for resins, coatings, and frictional materials [3].

The cashew nut is a popular snack often eaten on its own. Not only do cashews have a lower fat content than most other nuts, but approximately 75% of their fat is unsaturated fatty acids, which includes oleic acid that promotes good cardiovascular health [5]. According to [6], when it is added to a low-fat diet, it can help to reduce high triglyceride levels associated with an increased risk for heart disease, and even in diabetic patients, as triglycerides are a form in which fats are carried in the blood. It is also reported that high triglyceride levels are associated with an increased risk for heart disease. Kelly and Sabate (2006), reported that consuming nuts at least 4 times a week resulted in a 37% reduced risk of coronary heart disease compared to those who never or seldom ate nuts, and that each additional serving of nuts per week was associated with an average 8.3% reduced risk of coronary heart disease [7].

According to Ensminger and Ensminger (1986), topping your morning cereal with a quartercup of cashews will supply you with 38.0% of the daily value for copper, known for its antioxidant effects, energy production etc [8]. Calcium is necessary for strong bones, and Magnesium is also vital for healthy bones as about two-thirds of the Magnesium in the human body is found in our bone. They give bones their physical structure, while the rest is found on the surface of the bone where it is stored for the body to draw upon [9].

People who eat nuts at least twice a week are much less likely to gain weight than those who almost never eat nuts [10]. He also reported that Zinc content in nuts plays a crucial role in blood formation, and that Copper and Zinc present even in trace concentrations are important for physiological function of living tissues, and regulate many biochemical processes.

The anti-nutritional factors in the A. occidentale are Cynic Acid, Oxalate Acid, Phytatic Acid and Taninic Acid, and a daily intake of 450mg of Oxalic Acid interfered with metabolism [11]. High Oxalate levels in food may reduce the bio-availability of Calcium, and Phytic Acid intake of 4.00-9.00 mg/l00g reduces iron absorption by 4-5 fold in humans [11,12], reported that Oxalate forms insoluble complexes with Calcium, Magnesium, Zinc and Iron, interfering with the utilization of these mineral elements. The same was applicable to Phytate and Tannins with very low concentration in varieties of A. occidentale, though Tannins and Phytates are also know to affect human nutrition and metabolism, as high intake of tannic acid has been associated with carcinogenic effect in humans, poor protein utilization liver and kidney toxicity [11]. He further stated that Tannic Acid is associated with lower nutritive value of protein in foods, however, the concentration in these varieties did not exceed lethal levels; hence, the consumption of the nut will not pose any harmful effect to health. Phytic Acid intake of 4-9 mg/100g is thought to decrease Iron absorption by 4-5 folds in human [12].

The most predominantly encountered species in decreasing order of isolation from the non-disinfected nuts were Aspergillus nigar, A. restrictus, A. Flavus, A. Fumigatus, Rhizopus nigrians, R. arrhizus and Macrophomina pusillus, while A. tamari, Penicillium citrinum, A. ochraceus, Penicillium Sp; P. digitatum and Syncephalastrum sp were the less frequent isolates and were not recovered from the surface – disinfected nuts [13].

Potassium (K) is mainly associated with fungal membrane function, maintaining electrical potential across membranes, anion, cation and osmotic balance; Magnesium (Mg) is a cofactor for many enzymes; Iron contributes its own role in the oxygen carrying and electron carrying in the course of respiration; Zinc help in anaerobic respiration of fungi and can be seen in alcoholic fermentation, while Copper plays a crucial role in electron transport [14].

Some research has been done on the proximate and phytochemical composition of cashew nuts, as well as fungi associated with them but no information exists on the effect of fungi on the values of these proximate and phyto-chemical contents. Hence, this work is aimed at the investigating the effect of seed-borne fungi associated with roasted cashew nuts heavily consumed in the eastern part of Nigeria, and the impact on human health.

Materials and Methods

The cashew samples were collected both from the source of production where they were roasted at Nsukka Enugu State and from the market. All organic solvents and chemicals used in the analysis were obtained from the chemistry laboratory in the University of Port Harcourt, Nigeria. The reagents used were of analytical grade (BDH).

Isolation and Identification of Fungi

Cashew nuts were placed into 1% sodium hypochlorite to remove the surface saprophytes. Five seeds were placed in potato dextrose agar in Petri-dishes after they had gelled. They were incubation for 48hrs at a temperature of 25±2 ºC in an incubator. Pure cultures were made of fungal species that grew on the seeds, after the 48hrs period. This was done for seeds obtained from the source of production and from the market. Ten plates were plated per sample. Identification of the organism were done using the habit character, or spore characteristics for those whose identification were not possible through the habit character [15,16].

Proximate and Phyto-Chemical Analyses of the Nuts Form the Source of Production and the Market

The proximate and phyto-chemical analyses were done [17]. The samples used were those from the source of production of the cashew nuts and from the market.

Proximate analysis

This involves Protein, Carbohydrate, Moisture, Fibre, Ash and Lipid.

Determination of protein: 1g sample was weighed and added into a clean conical flask of 250 ml capacity. 3g digestion catalyst was added into the flask and 20 ml concentrated sulphuric acid was also added and the flask was heated to digest the content from black to sky-blue colouration. The digest was cooled to room temperature and was diluted to 100 ml with distilled water.

Distillation: 20 ml diluted digest was measured into a distillation flask and the flask was held in place on an electro-thermal heater hot plate to distillation flask and attached to a Liebig condenser connected to a receive adaptor containing 10 ml 2% boric acid indictor. 40% sodium hydroxide was injected into the digest via a syringe attach to the mono-arm steel heated until the digested became strongly alkaline. The mixture was heated to boil and distill the ammonia gas via the condenser into the receiver beaker. The colour of the boric acid changed from purple to greenish as ammonium distillate was introduced into the bone acid.

Titration: The distillate was titrated with 0.1N hydrochloric acid back to purple from greenish. The volume of Hydrochloric acid added to effect change was recorded as titre value.

Calculation

Determination of carbohydrate: 0.1g sample was weighed into 25 ml volumetric flask, and 1.3 ml 62% perchloric acid was added and shaken for a period of 20 minutes to homogenize completely. The flask was made up to 25 ml mark with distilled water and stopped. The solution formed was filtered through a glass filter paper or allowed to sediment and decanted. 1 ml of the filtrate was collected and transferred into a 10 ml volumetric flask and diluted to desired volume with distilled water. 1 ml of the working solution was pipetted into a clean test tube and 5 ml Anthrone reagent was added. 1 ml distilled water and reagent was added and mixed. The whole mixture was read at 630nm wavelength using distilled water as blank. A standard glucose of 0.1 mg/ml was also prepared and treated as the sample with Anthrone reagent. Absorbent of the standard glucose was read and the value of carbohydrate is glucose was calculated using the formula:

Determination of moisture: 1g sample was weighed into a clean dried porcelain evaporating dish. This heated in oven set at 105 °C for 6 hrs. The evaporating dish was cooled in a desiccator to room temperature, and then this was re-weighted and recorded. Weight of moisture was calculated by subtracting the weight of dried sample from the fresh.

Determination of lipid: 2g sample was inserted into a filter paper and placed into a Soxhlet extractor. The extractor was placed into a pre-weighted dried distillation flask. The solvent (Acetone) was introduced into the distilled flask via the condenser end attached to the Soxhlet extractor. The set up was held in place with retort stand and clamp. Cold water was allowed to flow into the condenser and the heated solvent was refluxed as a result. When the lipid was observably extracted completely from the sample under test, the condenser and the extractor were disconnected and the solvent was evaporated to concentrate the lipid. The flask was then dried in the air oven to constant weight and re-weighed to obtain the weight of lipid.

Determination of ash: 1g sample was weighted into a Porcelein crucible which was previously pre-heated and weighed. The crucible was inserted into a muffle furnace and regulated to a temperature of 630 °C. This was heated for 3hrs and allowed to cool to room temperature and re-weighed.

Phytochemical analysis

References

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