Cashew plant, Anacaduim occidentale L. is native to Brazil. The plant is widely grown in the continents of Asia, Europe as well as Africa. In most of the African countries, especially Nigeria, the tree is grown mainly for its pseudo apple and the nuts, which are mainly consumed raw, that is, unprocessed (Ohler, 1979; Nambiar et al., 1980). Cashew is a climacteric crop, and harvesting of the nuts often takes place between January and April or May. When the cashew apples are ripe, they fall down from the tree, and the nuts are collected after detaching from the rotten apples, sun-dried on concrete floor for two days  to attain moisture content of 12%, and this is to avoid spoilage. Nigeria’s annual cashew nut production from 466,000 MT in the year 2000 to 836,500 MT in year 2012 representing 45% of cashew nuts produced in African (FAOSTAT, 2013).

The fruit of cashew tree consists mainly of the cashew nut, an embryo shaped shelled nut and the false fruit cashew apple. The composition of the shelled nut consists of 20 to 25% kernel, 20 to 25% cashew nut shell liquid (CNSL), 20% testa and 48 to 55% shell. The cashew nuts are  majorly  sold  as  export crop and few of the nuts are roasted, flavored, and sold for local consumption in different packaging materials. Embedded in the honeycomb pericarp of the nut is a viscous brown liquid- cashew nut shell liquid, CNSL, that is, phenolic in nature. It is a by-product of the cashew nut industry. The components of this liquid have been found to be Anacardic acid (71.7%), cardol (18.7%), cardanol (4.7%), novel phenol (2.7%) and an unknown minor ingredient (2.2%) (Tyman and Morris, 1967). The liquid has been identified as an important industrial raw material (Ghatge and Maldar, 1981). For example, CNSL has been recognized as a good source of unsaturated phenol, an excellent monomer for polymer production. It is a good natural alternative to petrochemically derived phenol.

The sensory and nutritional qualities of cashew kernels cannot be overemphasized. For example, cashew kernels are excellent source of proteins (20 to 24 g/100 g), carbohydrates (23 to 25 g/100 g) and fats (40 to 57 g/100 g) (Nascimento et al., 2010; Ogunwolu et al., 2009; Yang, 2009). Moreover, studies have shown that  cashew kernels have beneficial effects on health, particularly on chronic diseases such as hypertension and obesity, coronary heart disease and diabetes. However, the high content of unsaturated fatty acids of most nut kernels is one of the most determinant factor against cardiovascular disease and obesity (Mexis and Kontominas, 2009; Oliete et al., 2008; Yang, 2009; Yang et al., 2009; Aswal et al, 2012; Horáčková et al., 2015).

Formulation of value added products from cashew kernel had received much attention from various workers over the years (Sofu and Ekinci, 2007; do Espirito Santo et al., 2010; Chen et al., 2010). There is dearth of information on the use of cashew kernel milk in yoghurt formulation, and this work seeks to be addressed.

Cashew nut kernel

Cashew nuts were obtained from Ochaja Station of Cocoa Research Institute of Nigeria. The nuts were sun dried until ready for use. The proximate composition of the kernel was carried out according to standard methods of analysis (AOAC, 1990).

Cashew kernel milk preparation

Cashew kernels were removed from nuts using manual cashew kernel breaker. The kernels were dried at oven temperature of 60°C for 6 h for easy removal of testa. Cashew kernels (250 g) were soaked in 5% NaCl solution overnight. The soaked kernel was cleaned and ground to a smooth paste. The cashew kernel paste was diluted with 3 parts of water, sieved and the supernatant was sweetened with 16 g of sugar, 0.6 g of vanilla flavor, bottled and pasteurized at 78°C for 30 min and refrigerated.

Formulation of cashew milk yoghurt

To obtain cashew kernel yoghurt, the produced milk was inoculated with Streptococcus thermophilus and incubated at 45°C for 7 h to coagulate. The resulting yoghurt (Figure 1) was then stored overnight in a bath of cold water.

Microbiological analysis

Formulated cashew kernels yoghurt samples were analyzed for total Escherichia coli, Staphylococcus aureus, Salmonella spp. and Clostridium spp., according to the American Public Health Association (Downes and Ito, 2001) guidelines.

Sensory analyses

A 9-point hedonic scale was used to measure the sensory qualities, that is, colour, aroma, mouth feel/texture, taste and overall acceptability of the product (Larmand, 1977). Ten member in-trained panelists that are used to yoghurt taste were employed to ascertain or detect any difference between the cashew milk yoghurt and the locally purchased commercialized products. These samples were coded differently and served to the panelists with a glass of water and were instructed to rinse their mouth in between the tasting period. The scale of preference ranges from 9 representing like extremely to 1 representing dislike extremely.

Statistical analysis

The results obtained were subjected to analysis of variance (ANOVA). Mean comparisons were carried out between the two yoghurt samples by Turkeys multiple range test and by Statistical Programs for Social Sciences (SPSS, 1992).

Physicochemical analysis

Table 1 presents results of the proximate composition of cashew nut flour. The mean moisture value of cashew kernel was 6.92 ± 0.2%, dry weight. This is a little below the value for some legumes ranging between 7 and 11%. The low moisture content helps to reduce microbiological deterioration. The ash content obtained for this study indicates that it is low and may not be suitable for animal feed. Results from the study shows that cashew kernel contains appreciable amount of crude fat (47%) and this makes it a potential and economically viable vegetable oil. Fat is important in diet because it promotes fat soluble vitamin absorption (Bogert et al., 1994; Champagne et al, 2010; Lee and Lucey, 2010; Shahnawaz et al., 2013). It is a high energy nutrient and does not add to the bulk of the diet.

Proximate composition of yoghurt

Table 2 shows the nutritional composition of commercially sold yoghurt as compared to that of cashew kernel milk. A pH value of 4.10 was obtained for commercial yoghurt as compared to 4.20 for cashew kernel yoghurt. This obtained result could be a reflection of the souring activity of lactic and this also explain the high titratable acidity (%), 0.5 to 0.55 obtained. Reed (1982) noted in his work that good quality yoghurt should have pH of 4.15 and TA (% lactic acid) of 0.5. The values obtained in this work are similar to these stated values. From the result, the calorific value of the cashew kernel yoghurt (133.06 KJ) was higher than that of the commercial yoghurt (112.01KJ). This means that cashew yoghurt can be taken as both proteinous and energy food.

Milk pasteurization (75°C) was done to modify milk protein to enhance proper viscosity and gelatinization of the product. This is in agreement with the work of Reed (1982). This also resulted in uniformity and smoothness in body texture of the yoghurt samples as indicated in Table 2.

Microbiological assay

The bacteriological quality of cashew kernel yoghurt samples and that of the commercial yoghurt samples is depicted in Table 3. Results revealed that total count of the samples is 1 x 10⁶ cfu/g, while specific count of E. coli, S. aureus, Salmonella spp. and Clostridium spp. were negative for both samples. This showed that the total counts as shown in table were because of the cultures used to ferment the yoghurt, thereby resulting in the production of lactic acid, which is lethal to some organisms. Lactic acid bacteria also produce hydrogen peroxide, diacetyl and bacteriosis as antimicrobial substances which create hostile environment for food-borne pathogen and spoilage organisms, and therefore are able to suppress the multiplication of pathogenic and putrefying bacteria. It is believed that pasteurization temperature of 75°C for 30 min would have effectively destroyed any microbes present in the milk samples coupled with the low pH values (Chumchuere and Robinson, 1999; Rodriguez et al., 2010). In addition, the traditional starter cultures used in cashew kernel yoghurt production contain substantial quantities of beta-D-galactosidase enzyme and consumption of cashew kernel  yoghurt  may assist in alleviating the symptoms of lactose maladsorption. The cashew kernel yoghurt was therefore considered safe microbiologically.

Sensory characteristics

The results of the organoleptic appraisal performed on all the yoghurts are shown in Table 4. The results indicates that panelist find it difficult to differentiate them from one another. The products have milky color with semi-solid texture and the taste was slightly sour. However, there was a significant difference at P> 0.05 for mouth feel. The overall acceptability showed that the yoghurt samples were acceptable but does not show any significant difference at P< 0.05.

This study shows that yoghurt can be produced from a vegetable source especially for the vegetarians. This indicates that it is possible to produce good quality yoghurt that is well acceptable for human consumption using cashew kernel. It was also shown that there were no differences in the taste and flavor of yoghurts studied and this makes the product more enjoyable and pleasurable. Thus, cashew kernel yoghurt due to its content and viscosity can delay gastric emptying and can be of an immense benefit for people who are lactose intolerant.

The authors have not declared any conflict of interests.