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Food science

Protein enrichment of cashew wastes for animal feeds

T. L. M. Stamford, R. Vieira, N. B. Guerra, R. B. de Medeiros, and M. L. Cavalcante



The use of fruit wastes as a carbon source to produce microbial protein is advantageous from technological and economic points of view. The analytical procedures required are unsophisticated and can be used not only by feed and waste industries but also by aviculturists and co-operatives. These wastes are available free, or are sold at very low prices by food industries for ruminant feeds without additional treatment. Production costs are low, as the product is prepared in three stages: fermentation, drying, and grinding. The process can be carried out by untrained technicians.

Industrial wastes from the cashew, Anacardium occidentale, are scarce because technological procedures use the whole pseudofruit for pulpy juice. In addition, when the nuts are harvested, a substantial amount of waste is lost in the sandbanks where cashew trees are grown. According to Berk [1], the nut is also considered a waste product. The process used in our laboratory to produce the concentrated cashew juice increases the supply of this raw material however [2].

This study investigated the advantages of converting cashew wastes efficiently into protein-rich feeds for animal consumption.


Materials and methods

Assays were performed with fermented or non-fermented cashew wastes from the fruit used in the pilot plant of the Food Sciences Laboratory of the Nutrition Department of the Federal University of Pernambuco, in Recife, Brazil, for production of concentrated juices. The chemical composition of the wastes is given in table 1.

TABLE 1. Chemical composition of cashew waste (pseudofruit)

  g/100 g
Water 76.91
Protein 2.32
Ether extract 1.36
Fibre 1.46
Ash 1.07
Carbohydratesa 16.88

a. Estimated by difference.

The fibre content was measured by the Horwitz method [3]. The other determinations were performed in accordance with the analytical methods of the Adolfo Lutz Institute [4]. The material was kept in a cool chamber at 3°C during the experimental period.

The fungi used, Aspergillus niger-2228, Myrothecium verrucaria-2100, and Trichoderma viride-2596, were obtained from the culture collection of the university's Mycology Department. The strains were maintained at 5°C in a Sabouraud-agar medium and reinoculated monthly. The basic culture medium was Czapek's without saccharose, modified. In the experiments in which only partial salt was added and potassium chloride (KCl) and ferrous sulfate (FeSO4) were removed, two fermentation processes were used: submerged liquid and moist solid-state. The composition of the salt mixture was as follows: KN2PO4, 1 g; MgSO4, 0.5 g; KCl, 0.5 g; and FeSO4, 0.01 g. The last two were removed from the mixture in the experiments with only partial salt added.

In the preliminary assays for the submerged liquid fermentation process [5], 250-ml flasks were used, three for each treatment. Each flask contained 100 ml of the medium, 20 g cashew waste, and 80 ml distilled water with and without additional salt. The flasks were autoclaved at 121.5°C for 15 minutes, inoculated with a 2% spore suspension, and incubated in a shaker at 30°C at 100 rpm for 48, 72, and 96 hours. The filtered mycelia were dried in a 60°C oven with air circulation until they reached a constant weight.

With the moist solid-state fermentation method, the cashew waste was heated at 100°C under a constant steam as a culture medium for growth of A. niger and T. viride, with or without the addition of KCl and FeSO4. The waste was spread on nylon sieves in wooden frames in uniform layers 1 cm thick to allow sufficient aeration. Fungi were inoculated with the spore suspension and the trays were on open racks at room temperature, some for 48 and some for 72 hours. The material was dried in an oven with air circulation at 50°C and 55°C for 48 hours.

Total nitrogen was measured in the mycelia by the micro-Kjeldahl method [6] The crude protein content of the mycelia was calculated by the factor 6.25 x N. Amino acids were measured in a Backman auto-analyser reaction with nihydrine.

In the assays for production of non-fermented cashew flour, the wastes were spread on metal trays and dried in an oven at 45°C and 60°C, or sun dried.

The organoleptic characteristics, as well as the nutrients of the flour, were determined.

Results and discussion

The data from the preliminary assays with cashew waste using the submerged liquid fermentation process are shown in table 2. The values obtained in the waste inoculated with A. niger were the most representative, confirming previous findings with passion fruit [5] and pineapple wastes [7]. Cashew waste contained the highest protein content, 21.48%, at 72 hours of incubation when treated with only partial salt. This corresponds to a 140% increase in the protein content over that of the 60°C oven-dried waste without additional treatment, that is, 9.7 g per cent.

TABLE 2. Protein biomass production from fungi grown in cashew waste using submerged liquid fermentation

Treatment and micro-organism

72-hour fermentation

96-hour fermentation

Dry Total Added Dry Total Added
matter protein protein matter protein protein
(g) (%) (%) g (%) ( % )
Waste + H2O            
A. niger 2.74 17.93 100.78 2.63 15.96 78.72
M. verrucaria 3.69 12.80 43.33 2.36 19.06 113.43
T viride 2.94 16.05 79.73 2.90 16.75 87.55
Waste + complete salts            
A. niger 2.90 20.18 125.97 2.98 20.93 134.37
M verrucaria 4.21 15.93 78.38 2.69 16.91 89.36
T. viride 3.06 17.34 94.17 2.98 17.62 97.31
Waste with no KCl and            
FeSO4 added to medium            
A. niger 2.91 21.48 140.53 2.97 20.99 135.05
M. verrucaria 4.78 15.68 75.58 2.55 17.60 97.08
T. viride 3.61 17.41 94.96 4.22 17.31 93.84

Cashew waste has 8.93 g protein per 100 g dry matter.

TABLE 3. Chemical composition of cashew waste submitted to different drying processes

  Water (g% ) Ash (g% ) Protein (g% ) Fibre (g% ) Ether extract (g% ) Carbo hydrates (g%)
Oven-dried (45°C) 12 01 2.34 11.62 10.32 6.79 56.92
Oven-dried (60°C) 6.17 1.76 9.70 9.12 4.88 68.37
Sun-dried 5.35 1.6 12.66 5.3 12.89 62.21

Fermentation of fruit and vegetable wastes can be inhibited by some cellular constituents such as fats, waxes, and long-chain fatty acids, as well as by other micro-organisms or their flora [8]. Using the moist solid-state fermentation process in pineapple waste, the growth of the A. niger was inhibited by yeast (Saccharomyces bailli Lindner) [7].

Similar inhibition was detected in the cashew waste submitted to this process. To avoid this effect, the waste underwent a thermal treatment (steam bath) before the fungi were inoculated. The values obtained using moist solid-state fermentation were not representative. Regardless of the treatment used, the addition of complete and/or incomplete salts to the waste did not change its protein content. Sugar conversion did not reach its expected level: it was the same as or lower than that of the flour obtained from oven-dried and sun-dried wastes (table 3). A comparative study of the chemical composition of flours obtained from these wastes by different treatments, without fermentation, showed that the sun-dried product was rich in protein and lipids and poor in fibre. The highest protein contents were obtained using submerged liquid fermentation methods, but sun drying is preferred with cashew wastes from the technical and economic points of view because it does not require sophisticated equipment.

TABLE 4. Cashew waste treated by the moist solid fermentation process for 72 hours

Micro-organism and treatment Wet weight (g) Dry weight (g) Water (%) Protein (%) Fibre (%)
A. niger          
Waste + H2O 200 54 11.41 10.80 8.70
Waste with no KCl and          
FeSO4 added to medium 200 54 8.64 10.80 10.66
Waste + complete salts 200 54 8.52 11.06 10.68
T. viride          
Waste + H2O 200 43 11.51 10.40 9.53
Waste with no KCl and          
FeSO4 added to medium 200 43 13.75 10.18 9.22
Waste + complete salts 200 42 11.89 10.45 8.25

The organoleptic characteristics of the sun-dried flour were as follows: texture, thin powder; colour. yellow; flavour, caramel; and odour, that of the cashew.

The aminogram and the chemical score of the flour were determined. Methionine, tyrosine, and valine were the limiting amino acids: 50.9%, 28.4%, and 25.6% respectively. The other amino acids had higher values than those of the pattern. This is of special interest for aviculturists as lysine is a limiting amino acid in poultry diets.

TABLE 5. Amino acid composition of sun-dried cashew flour



Cashew flour

Amino acid (mg%) A: E ratio Amino acid (mg%) A: E ratio Chemical score (%)
Leucine 8.8 172 8.04 233 135.4
Lysine 6.4 125 6.35 184 147.2
Phenylalanine 5.8 114 4.02 166 145.6
Tyrosine 4.2 81 2.00 58 71.6
1/2 cystine 2.4 46 - - -
Methionine 3. I 61 I .05 30 49.1
Threonine 5. I 91 4.19 121 132.9
Tryptophan I .6 21 - - -
Valine 7.3   3.64 105 74.4


From these data, it may be concluded that submerged liquid fermentation was more efficient for producing single cell protein than moist solid-state fermentation when the waste was inoculated with A. niger for 72 hours. Sun-drying was the most adequate treatment for cashew waste flour. Methionine, tyrosine, and valine were the limiting amino acids of the flour, and contents of the other amino acids, especially lysine, were relatively high. Given the chemical composition and organoleptic characteristics of the sun-dried flour. this product can be used for animal consumption.



This paper was translated into English by L. N Pedrosa, Department of Nutrition, Centre of Health Sciences, Federal University of Pernambuco.



  1. Berk Z. Production of feed as an objective for bioconversion systems. In: Bioconversion of organic residues FOR rural communities. Tokyo, Japan: United Nations University, 1979:23-25.
  2. Vieira R, Woolfe ML, Pires EMF, Woolfe JA, Guerra NB. Produção de suco concentrado de caju. Ciência Tecnologia de Alimentos 1982;2(2):222-232.
  3. de Horwitz W. Official methods of analysis of the Association of Analytical Chemists. 10th ed. Washington, DC: AOAC, 1970.
  4. Instituto Adolfo Lutz. Normas analíticas do Instituto Adolfo Lutz. Vol. 1. São Paulo, Brazil: Instituto Adolfo Lutz.
  5. Stanton R. Bioconversion of fruit and vegetable wastes. In: Bioconversion of organic residues for rural communities. Tokyo, Japan: United Nations University, 1979: 120-121.
  6. Unichron aminoacid analyser, instruction manual. Palo Alto, Calif, USA: Bechman.
  7. Guerra NB, Stamford TLM, de Medeiros RB, de Freitas CP, Maia SR, Cavalcante ML. Protein enrichment of pineapple waste for animal feeds. Food Nutr Bull 1986;8(1):77-80.
  8. Stamford TLM, de F. Fernandes Z, Cavalcante ML, Freitas P, Guerra NB. Ração animal a partir de resíduos de frutos fermentados. Parte 1: Maracujá. Boletim da Sociedade Brasilieira de Ciência a Tecnologia de Alimentos 1983;17:107-117.

Milling high-tannin and low-tannin varieties of sorghum

A. M. M. Youssef, Y. G. Moharram, E. K. Moustafa H. Bolling, and A. Elbaya


Editor's note

While this paper does not contribute new information concerning the milling of sorghum, the technique discussed is judged to be of interest where traditional hand pounding methods are too time-consuming



Sorghum is one of the important food cereal grains in Africa and Asia. Its two major disadvantages are problems of nutrient uptake (presence of anti-nutritional polyphenols and tannin) and the need to grind the grain to make sorghum Hour. In recent years research has started to replace hand processing with pilot plant machines for sorghum milling [1-4]. Different milling machines such as a barley pearler, an abrasive mill, and a Bühler mill, in addition to various tempering conditions. have been tried to improve the milling quality of sorghum.

According to one group [5] the maximum yield of low-fat sorghum flour was obtained after eight hours of tempering. In our study two methods were used to mill high- and low-tannin sorghum grains: a single-step and a two-step process. In the latter. the grain was dehulled before milling. The study also determined the optimum conditions for tempering and dehulling the grain, and the effect of troth milling techniques in reducing tannins and improving the nutritional quality of the flour obtained.


Materials and methods

The names, sources, and properties of the varieties of sorghum (Sorghum vulgare) used in this study are shown in table 1.

TABLE 1. Sources and properties of the sorghum varieties used in the study

Variety Source Properties
BR Lippische Hauptgenossenschaft, Detmold, FRG (summer 1983) Bird-resistant, high in tannin (2.9% as catechin); length 3.2 mm. width 2.7 mm, particle size index (PSI) 70.9%; brown thick pericarp, yellow endosperm and testa layer
Giza 15 Ministry of Agriculture, Cairo, Egypt (summer 1984) Low in tannin (0.19% as catechin); length 4.3 mm, width 3 mm, PSI 66.2%; yellow thin pericarp, white endosperm. free from testa
NES 1007 Ministry of Agriculture, Cairo, Egypt (summer 1984) Low in tannin (0.25% as catechin); length 4 mm, width 2.9 mm, PSI 69.2%; yellowish brown thin pericarp, yellow endosperm, free from testa

Technological methods


Clean, whole sorghum grains were mixed with a computed amount of water to raise the moisture content to 12% 14%. 16% and 18% using a wheat-tempering laboratory mixer, type DKM 20. After 18 hours conditioning at 20°C-22°C, the grain was dehulled and milled.

Single-step milling process

The tempered grains were milled using Bühler automatic laboratory mill type 220 [1]. The milled fractions were weighed, and the percentages of flour I, flour II, shorts I, shorts II, and bran were calculated from the initial grain weight.

Two-step milling process

The tempered grain was dehulled for one, three, and five minutes using a vertical shelling machine, type 270 (F. H Schulle GmBH). The dehulled products were sieved and the percentage of dehulled grain was measured.

The dehulled grain was milled using a Bühler mill, and the percentages of the mill fractions obtained were calculated from the initial grain, weight.

Analytical methods

Moisture, ether extract. protein, starch, ash, and crude fibre contents were determined as described elsewhere [6]. Tannin content was estimated according to the method of Price et al. [7] and calculated as catechin equivalent. The automatic recording amino acid analyser (Kontron, Anocomp 500) was used to determine amino acids in sorghum grain before and after dehulling.


Results and discussion

Single-step milling process

Table 2 illustrates the effect of the degree of tempering on the yield of mill fractions and the content of polyphenols. The data show that increasing the degree of tempering from 12% to 16% was associated with a decrease in the yield of flour I and its polyphenol content and an increase in the yield of bran, shorts II, and flour II fractions.


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