International Journal of Food Sciences and Nutrition (1994) 45,l-3 0 Macmillan Press Ltd. 1994

Cyanide content of two Nigerian local sprouted millet cultivars

Lilian I. Salami

Department of Food Science and Technology, University of Maiduguri, Maiduguri, Nigeria

The seeds of two popular Nigerian cultivars (Gero and Maiwa) of millet grains (Penniseturn arnericanurn) used in the semi-arid region contained 1.38 f 0.3 and 1.43 +_ 0.1mg/100g of potential ionic cyanide. The grains of the same cultivars were sprouted for periods up to 96 h in the dark at 38°C. After 96h sprouting, Maiwa had a higher cyanide content (1.82 f 0.1mg/100g) than Gero (1.33 k 0.1 mg/100g), relative to the weight of ungerminated dry millet grains. The lowest cyanide values for ‘Gero’ and ‘Maiwa’ occurred after 60 h and 72 h of sprouting, respectively. The consumption of millet sprouts may not be hazardous. The levels of cyanide detected in this study are safe and fall within the acceptable safe human limits (10-20mg CN per lOOg sample or 0.5-0.8 rnglkg body weight).

Introduction

Cyanide is an anti-nutritional factor and it is reported that more than 1000 species of plants habitually consumed by man contain cyanogenic glycosides (Conn, 1973). Hyd- rocyanic acid (HCN) is released when the tissues of the plants are crushed or other- wise disrupted (Oke, 1969; Conn, 1973; Davis, 1979). Hydrocyanic acid has been incriminated in the aetiology of tropical ataxic neuropathy (Osuntokun, 1973). Once cyanide is in the body, it attacks the nervous system acting on the spinal cord and its numerous nerves. Many authors have recommended germination of grains as a means of producing a more nutritious food ingredient, especially in third world coun- tries where grains in most cases serve as staples (Wang and Fields, 1978). However, when sprouted, most of these grains, espe- cially sorghum, are reported to contain appreciable amounts of dhurrin, a cyano- genic glycoside, and the immature plants contain exceptionally high levels of cyano- gen (Gorz 1977; Conn, 1973; Panasiuk and Bills, 1984).

There is no information available on the cyanogenic properties of sprounted millet grains. The objective of this study was to

determine the cyanide content of two sprouted cultivars of milelt grains and to determine the duration of sprouting that resulted in the minimum level of cyanide. Millet is a staple food in the semi-arid regions of Nigeria characterised by an average temperature of about 32-38°C during the dry season.

Materials and methods Two varieties of millet grains (Gero and Maiwa) were obtained from a Maiduguri local market and certified by the Agricul- ture Development Programme Office. The grains were winnowed and hand sorted. To initiate germination, 50g of each millet grain variety was soaked in tap water (1:3 w/v) for 6 h at room temperature (38 f 0.3”C). A batch of each variety was stored in the freezer after being soaked and drained to serve as the control in each case. The experimental batches were kept on jute bags in a closed dark cupboard. The grains were washed every 6 h to prevent mould growth and to give enough moisture. Although fungicide might have been more appropriate to suppress fungal growth, as slight leaching

Int J

Foo

d Sc

i Nut

r D

ownl

oade

d fr

om in

form

ahea

lthca

re.c

om b

y U

B H

eide

lber

g on

11/

16/1

4Fo

r pe

rson

al u

se o

nly.

2 L. I . Salami

Table 1. Physical characterics of millet grains sprouted for 96 h

Millet Temperature Ungerminated Germinated % Sprout Average variety e C) seeds seeds germination length (cm) length (cm)

Gero 38 f 0.3 11 260 95.77 0.11-4.5 3.1 Maiwa 38 f 0 . 3 20 410 95.13 1.1-3.6 2.6

is expected by washing every 6 h, the effect of a carry-over of the fungicide on humans has not been assessed. The sprouts were harvested every 6 h , dried in an even air flow at 40°C to maintain a uniform moisture level and stored in polyethylene bags in the freezer until use. Sprouting was terminated after 96 h. At the end of the growth period, the sprouts were drained and the length and parent germination were determined in each batch. The batches were maintained at a moisture level of 10%. Linamarase was extracted from freshly harvested cassava cortex and kept frozen as recommended by Cooke (1978).

Cassava contains poisonous cyanogenic glycosides consisting mostly of linamarin and, to a much smaller extent, lotaustralin. Many strains of cassava would cause death in man and animals if consumed directly without detoxification. The breakdown of the cyanogenic glucosides is brought about by the endogenous enzyme linamarase present in the cassava roots (Okafor, 1983). This enzyme makes contact with the lina- marin when the roots are crushed. The use of linamarase in the decomposition of dhurrin in sorghum grains has been docu- mented (Panasiuk and Bills, 1984). Each 50g batch of the sprouted millet was homogenised with a blender in phosphate buffer, pH 5.5. To 40ml of the sample, 4ml of the extracted enzyme (linamarase) was added and allowed to stand for 30min at room temperature. Sodium hydroxide (10mM; 1 ml) was added to the sample and the concentration of cyanide was read using an Orion Model EATM 920 research expandable ion-selective electrode (Cole- Parmer Instrument Co., Illinois, USA) according to the manufacturer's guidelines. This sensitive electrode did not have any interference from other compounds in the extract as it was standardised prior to being

used according to the manufacturer's advice.

Results and discussion Tables 1 and 2 represent average data of triplicate runs on a dry weight basis. The optimum time for harvesting the sprouts was chosen to be 96 h, as more mature sprouts developed leaves by the 5th day and were hence less desirable in size and appearance as a food ingredient. However, at 96h of germination, both millet grain types experi- enced an upward surge in HCN levels.

During the first 6 h of sprouting, there were decreases in the levels of HCN compared to levels in the seeds from which they were grown. This decrease in cyanide may be due to both leaching and the activities of endogenous enzymes. These enzymes may have been dormant in the dry

Table 2. Effect of sprouting time on the cyanide content of millet (Pennisetum americanum)

Time (h)

Maiwa Gero EICN content HCN content (mgl100g)* (mgl100g)'

0 6

12 18 24 30 36 42 48 54 60 66 72 78 84 90 96

1.43 f 0.1 0.87 f 0.3 0.79 f 0.01 0.90 f 0.2 0.04 f 0.1 0.92 f 0.1 0.82 f 0.2 0.89 f 0.0 0.72 f 0.1 0.70 f 0.1 0.75 f 0.3 0.63 f 0.3 0.54 f 0.1 0.79 f 0.1 0.94 f 0.2 1.24 f 0.1 1.82 f 0.1

1.33 f 0.01 0.79 f 0.1 0.86 f 0.3 0.86 f 0.3 0.80 f 0.21 0.74 f 0.2 0.78 f 0.1 0.79 f 0.8 0.72 f 0.2 0.67 f 0.3 0.59 f 0.1 0.82 f 0.1 0.89 f 0.01 0.94 f 0.03 0.97 f 0.01 1.06 f 0.02 1.33 f 0.1

*Expressed as mean of triplicate runs f s.d. per lOOg dry weight of ungerminated seeds.

Int J

Foo

d Sc

i Nut

r D

ownl

oade

d fr

om in

form

ahea

lthca

re.c

om b

y U

B H

eide

lber

g on

11/

16/1

4Fo

r pe

rson

al u

se o

nly.

Cyanide content of millet cultivars 3

seeds but are activated by soaking and sprouting. Soaking has been shown to reduce HCN in cassava (Abiose, 1992). This result confirms the findings of Viehoever (1940) who reported that leaching can reduce the HCN level in lima bean. The decrease could also be attributed to the activities of the endogenous enzymes inherent in sorghum seeds (Panasiuk and Bills, 1984). Thereafter, there were slight increases in HCN, although there was an overall steady decline until 72 h. This slight upward surge may be due to reduced autolytic enzyme activities. The least amount of HCN occurred after 72 h and 60 h for Maiwa and Gero, respectively. The concentration of HCN increased after these periods of sprouting. The problem of incomplete hydrolysis of the cyanogenic glucosides may have been solved by use of the added exogenous linamarase. Conn

(1972) and Panasiuk and Bills (1984) reported that the high levels of HCN in sorghum sprouts may serve as a protective mechanism for the young growing plant. Although cyanide is toxic and implicated in chronic degenerative neuropathy (Osunto- kun, 1973), the upper safe limit of total edible cyanide in food material is 10-20mg CN per lO0g (Akroyd and Dought, 1982). The total cyanide levels detected in this study fall within the acceptable safe limits. However, it is necessary to note that the frequent use of sprouted millets may have a cumulative effect. The adverse effect of cyanide may be compounded when sprouted grains are consumed with other food cyanogens such as cassava, a staple food in most parts of Africa (Panasiuk and Bills, 1984). The continued ingestion of smaller quantities may be made possible by use of added exogenous linamarase.

References Abiose SH (1992): Reports on methods of detoxifica-

tion of roots and tubers. Restrec Newsletter 1(8,9). 20-25.

Aykroyd WR & Dought J (1982): Cyanide detoxifica- tion in legumes: legumes in human nutrition. Report,

Conn EE (1973): Cyanogenic glycosides. In Toxicants occurring naturally in foods, 2nd edition, ed FM Strong, p. 302. Washington DC: National Academy of Sciences.

Cooke RD (1978): An enzymatic assay for total cyanide content of cassava (Manihot esculenta Crantz). J . Sci. Food Agric. 29, 345-352.

Davis AB & Hoseney RC (1979): Grains sorghum condensed tannins. I. Isolation, estimation and selective absorption by starch. Cereal Chem. 56,

Davis NT (1979): Anti-nutrient factors affecting

Col. 20, p. 39.

310-314.

mineral utilization. Proc Nutr Soc 38, 121-128.

Gorz HJ, Hang WL, Specht JG & Naskins FA (1977): Assay of p-hydroxygen-aldehyde as a measure of hydrocyanic acid potential in sorghum. Crop Sci. 17, 578-610.

Okafor N (1983): Processing of Nigerian indigenous fermented foods - a change for innovation. Nigerian

Oke CL (1969): Role of hydrocyanic acid in nutrition. World Rev. Nutr. Diet. 11, 170-191.

Osuntokun BO (1973): Ataxic neutropathy in Nigeria. PhD thesis, University of Ibadan, Nigeria.

Panasiuk 0 & Bills DD (1984): Cyanide content of sorghum sprouts. J . Food Sci. 49, 791-793.

Viehoever, A. (1940): Edible and poisonous beans of the lima type (P. lunatus). Thai Sci. Bull. 2 , 1-7.

Wang YYD & Fields ML (1978): Germination of corn and sorghum in the home to improve nutritive value. J . Food Sci. 43. 1113-1115.

Food J . 1(1), 32-37.

Int J

Foo

d Sc

i Nut

r D

ownl

oade

d fr

om in

form

ahea

lthca

re.c

om b

y U

B H

eide

lber

g on

11/

16/1

4Fo

r pe

rson

al u

se o

nly.