Press Release
PNG Cassava Safe for Consumption
14th April 2005
Recent reports of some 27 children dying and more than 100 others hospitalised after eating cassava in the Philippines should not cause misgivings for our farmers and consumers. The youngsters’ deaths were alleged to have been caused by cyanide poisoning from cassava and the variety consumed was not properly cooked. This surprised many countries in the Pacific islands and parts of Asia, which produce and consume cassava as a staple food. However, more recent reports revealed that the incident was caused by a pesticide found in the cassava mixture (cake), and not the cyanide that is found naturally in the tubers.
Cassava or “tapiok” has been cultivated and consumed in PNG for many years, as in the Pacific, parts of Asia and Africa, and is used all over the world. It is an important food crop in some parts of PNG with substantial contribution to food security.
Cassava varieties found locally in farmers’ fields are safe for human consumption. These include the nine high yielding and drought tolerant cultivars the National Agricultural Research Institute (NARI) has recommended for farmer adoption. Research by the Institute indicates that PNG cassava varieties have acceptable cyanide levels and most cyanide can be destroyed by boiling or cooking.
It is true that this substance can be poisonous when cassava is eaten raw or not properly prepared. Cyanide is produced at harvest from the breakdown of a chemical - cyanogenic glucoside - found naturally in the roots or tubers of the crop.
All varieties cultivated for consumption in PNG (and the Pacific) are sweet varieties with low cyanide content. The bitter varieties with high, toxic cyanide levels are mostly found in Africa and Asia.
According to Bradbury & Holloway (1988), cassava containing less than 50mg cyanide per kilogram of fresh tuber is harmless and safe to eat. Accessions with cyanide content between 50 – 100mg per kg tuber are moderately poisonous and those with over 100mg per kg tuber are highly poisonous.
Those varieties NARI has selected and recommended for farmer adoption are low in cyanide (less than 50mg HCN per kg fresh tuber) and can be safely consumed after boiling. They include four lowlands and five highlands varieties. Those for the lowlands are L 6, L 51, L 86 and L 92 – selected from the Central and East New Britain Provinces. Varieties EHS 010, EHK 012, WBS 007, WBD 011 and EDK 007 for the highlands were selected from the Western and Eastern Highlands Provinces. These selections were based on research trials undertaken by the Institute. Cyanide content was examined at the NARI Chemistry Laboratory in Port Moresby. The laboratory results ranged from 11.7 – 15 mg and 17.5 – 25 mg (per kg fresh tuber) cyanide content at harvest for the lowlands and highlands varieties respectively. The nine recommended varieties not only have low cyanide levels, but also give high yields and are tolerant to drought.
Table 1: Selected lowlands cassava varieties and their characteristics
| Variety | Total Yield (tonnes/ha) | Protein (%DM) | Total Cyanide content (mg/kg) | Tuber Flesh Colour | Remarks |
| L 86 | 20.1 | 0.74 | 13.3 | White | Acceptable yield. Good tuber shape, size. Very good taste. |
| L 51 | 29.2 | 0.63 | 12.0 | Yellow | Good yield. Good tuber shape and size Very good taste. |
| L 6 | 28.7 | 0.76 | 11.7 | Yellow | Good yield. Tuber shape and size ok. Very good taste. |
| L 92 | 28.6 | 0.65 | 15.0 | Yellow | Yields well with acceptable tuber shape and size. Good taste. |
Table 2: Selected highlands cassava varieties and their characteristics
| Variety | Average tuber no. per plant | Total yield (t/ha) | Tuber flesh cyanide at harvest (mg/kg) | Tuber flesh protein at harvest (%) | Tuber flesh colour | Taste |
| AIYME 003 | 10 | 35.96 | 17.5 | 1.78 | White | Acceptable |
| AIYME 002 | 8 | 30.23 | 22.5 | 1.52 | White/Cream | Acceptable |
| AIYME 007 | 8 | 27.49 | 25.0 | 1.49 | White/Cream | Excellent (soft & pasty) |
| 7 | 26.9 | 25.0 | 1.52 | Yellow | Good | |
| AIYME 001 | 7 | 25.96 | 25.0 | 1.84 | White/Cream | Acceptable |
Note:
Cyanide in cassava for fresh tuber:
Less than 50 mg cyanide/kg of fresh tuber is safe/harmless
50 – 100 mg cyanide/kg is moderately poisonous
More than 100 mg cyanide/kg is highly poisonous
Other cassava varieties held by NARI at its Laloki National Germplasm Collection near Port Moresby have also been tested for cyanide. This collection (from farmer’s fields) has 77 accessions, including the nine recommended varieties. Sixty-three of these accessions have cyanide content of less than 50mg/kg tuber, 12 have between 50-100mg/kg tuber and two have more than 100mg/kg fresh tuber. These two highly poisonous varieties are L O29 and L 114. However, they are not consumed by people but are used as temporary shade trees in villages. The chemical content in such poisonous varieties can still be destroyed during food preparation.
People who are uncertain about their cassavas can soak fresh tubers in water for about three days (with water replaced daily) to remove the cyanide. This is a normal practice in Africa where bitter and poisonous varieties are cultivated.
Work by NARI has also shown that immature cassava tubers and tuber skin/peel contain more cyanide than mature tubers and the flesh. So peeling would be encouraged and care should also be taken in feeding livestock with fresh peels.
Dr Sergie Bang - Acting Director General