Starch Noodles from Edible Canna

Canna is easy to grow. It has no significant pests or diseases. The crop thrives on residual nutrients and can be grown continuously. Typically yielding 20-40 t per ha, canna is often grown without irrigation on marginal soils or on slopes where its long crop duration (10-12 months) helps prevent erosion.

Nowhere else is canna as important as in north Vietnam where, over the last 30 years, the area in canna has expanded to an estimated 20,000-30,000 ha. Canna is grown for the sole purpose of extracting starch. Wooden drum graters and simple sedimentation tanks are used to extract the starch. Canna starch has the largest known granules (30-100 mm), resulting in fast settling. The rhizomes contain 22% to 25% of dry matter and starch yields range from 12% to 16%.

The overwhelming portion of canna starch production in Vietnam is processed into transparent starch noodles ("cellophane noodles"), a luxury food of south-east Asia and traditionally made of costly mungbean starch. Good cellophane noodles are about 1 mm thick; they display high tensile strength and good transparency. Dry matter loss during prolonged cooking is less than 10%.

Starch noodles of non-canna origin are usually produced through extrusion cooking, which requires the extruded noodles to pass through a cooling water bath. By contrast, canna noodles are manufactured by a different, and previously undescribed, process involving the steam-sheeting of a starch/water dough. The resulting gel sheets are stretched and semi-dried on bamboo frames. The gel sheets are then folded and cut into straight noodles. They are finally dried to a moisture content of about 18% to 21%.

Canna noodles in Vietnam have excellent eating quality, much superior to extrusion noodles made experimentally from sweet potato and cassava starches which are widely available in southeast Asia. Special but as yet poorly understood functional properties of canna starch make it a substitute which has totally replaced expensive mungbean starch as the raw material for cellophane noodles in Vietnam. The high amylose content (25% to 30%) of canna starch as compared with other root starches has been proposed to explain the high peak viscosity observed during gelatinization, which permits the sheets to be easily handled. Canna starch also displays high gel retrogradation (recrystallization) and transparency which is critical to noodle quality.

Canna processing in Vietnam provides employment to many thousands of people in rural communities with as little as 500 m² of arable land per capita. Canna use in Vietnam shows how product development can provide new perspectives for crop utilization and stimulate demand for otherwise obsolete crops.

Fig 1. Canna production and noodle processing in Vietnam. A: Muong girl cleaning canna rhizomes (Tu Ly, Hoa Binh Province, 400 m altitude);

B: Canna market in Duong Lieu (Ha Tay Province, Red River Delta);

C: Canna starch extraction plant (Duong Lieu, Ha Tay Province);

D: Drying of canna starch (Duong Lieu, Ha Tay Province);

E: Steam-sheeting of canna starch dough (Duong Lieu, Ha Tay Province);

F: Stretching canna starch gels (Duong Lieu, Ha Tay Province);

G: Canna noodles on sale (Central Market, Hanoi). (Photographs taken November 1992, all north Vietnam).