No abstract

The efficiency of different processes in reducing the cyanoglucoside (CNG) content of cassava was studied. Maximum retention of CNG (>80%) was observed in baked, fried and steamed tubers. CNG retention in sun-dried chips varied from 30-60%, the retention being governed by the chip thickness. In case of cassava boiled in water, smaller chip size and sufficient water was found to be the ideal condition for maximum CNG removal. There was 25-7570 CNG retention in this process, depending on the chip size used. The most effective method for CNG removal was by crushing fresh tuber and subsequent sun-drying, whereby >95% CNG was eliminated. The studies indicated that the mode of processing greatly influenced the CNG content of cassava foods. It was concluded that since CNG can be greatly reduced by suitable processing, it may not be a limiting factor in the utilisation of cassava for food and feed purposes.

The free proline levels and activities of ornithine aminotransferase (EC 2.6.1.13) and proline oxidase (EC 1.5.2.2), two of the enzymes involved in proline metabolism were studied during the induction of water stress in a drought susceptible (M‐4) and a drought tolerant (S‐1315) cultivar of cassava (Manihot esculenta Crantz). Water stress induced by polyethylene glycol (MW 6000, osmotic potential — 1.65 MPa) caused a ca 25‐fold increase in proline in young excised leaves of the susceptible cultivar (M‐4) while the increase was about 9‐fold in the tolerant cultivar (S‐1315). The activity of ornithine aminotransferase (OAT), a key enzyme involved in the biosynthesis of proline, was found to increase 3‐fold in water stressed leaves of M‐4 and about 2‐fold in those of S‐1315. The activity of proline oxidase, which is involved in the degradation of proline to pyrroline‐5‐carboxylate, was reduced by 50% in M‐4 and nearly 25% in S‐1315 on water stress. Comparison of the kinetic properties of OAT showed that the enzyme from water‐stressed leaves is more stable to heat inactivation compared to that of control. These results indicate that during water stress there are alterations in the metabolism of proline in cassava, and the extent of alteration varies between drought‐susceptible and ‐tolerant cultivars.

The levels of the cyanoglucoside linamarin and the activity of its major metabolising enzymes (linamarase, rhodanase and fi-cyanoalanine synthase) were studied in various tissues of the cassava plant. Leaf, stem and rind tissues contained very high levels of both linamarin and linamarase, while lower levels were observed in edible tuber. Rhodanese activity was detected only in leaf tissue. High activity of B-cyanoalanine synthase in all tissues indicated that the major pathway of cyanoglucoside turnover in cassava was by conversion to asparagine.

Alternative agricultural systems, like organic farming, that are less chemical intensive, less exploitative and environment friendly are gaining popularity. Elephant foot yam (Amorphophallus paeoniifolius (Dennst.) Nicolson) is an important starchy tuberous vegetable with high nutritive and medicinal values. Since information on the organic farming of tuberous vegetables is scanty, field experiments were conducted in this crop at the Central Tuber Crops Research Institute, India, over a 5-year period. The impact of organic, conventional, traditional and biofertilizer production systems on growth, yield, quality, soil physico-chemical properties and economics were evaluated in elephant foot yam. Our results show that organic farming favoured canopy growth, corm biomass and lowered collar rot disease. Dry matter and starch contents of organic corms were significantly higher than those of conventional corms by 7% and 13%, respectively. Organic corms had 12% higher crude protein and 21% significantly lower oxalate contents. The content of K, Ca and Mg in corms were slightly higher, by 3-7% under organic farming. After 5 years of farming, the organic plots showed significantly higher pH, by 0.77 unit, and higher organic C by 19%. The exchangeable Mg, available Cu, Mn and Fe contents were also significantly higher. Organic management lowered the bulk density by 2.3%, improved the water-holding capacity by 28.4% and the porosity of soil by 16.5%. In short, organic farming proved superior and produced 20% higher yield (57.097 t ha ). The net profit was 28% higher and an additional income of Indian Rs. 47,716 ha −1 was obtained. Thus organic farming was found to be an eco-friendly management strategy in elephant foot yam for sustainable yield of quality tubers and higher profit besides maintaining soil health. Technologies for organic production involving farmyard manure incubated with bioinoculants, green manuring, neem cake, biofertilizers and ash were also standardized.