5. AN’s in tubers
• Root crops, contain small amounts of potential toxins and AN
factors such as trypsin inhibitors.
• Wild species may contain lethal levels of toxic principles and must
be correctly processed before consumption.
• Local people are developed suitable techniques for detoxifying the
roots before consumption.
6.
7. ELEPHANT FOOT YAM
• Calcium oxalate cause acridity
• Insoluble calcium oxalate is present as raphides or needle like crystals about
50-200 micro m long and about 2-4 micro m diameter
• Cause irritation
• Proteolytic enzyme
• Acridity removed by,
1. Hcl, tartaric acid, citric acid treatment
2. Cooking in water
• Amylase/ protease inhibitor impair digestion of starch
• Phenols, tannins
8. COLOCASIA
• Acridity leads to limit the use of taro as food and animal
feed
• Acridity caused by drought, poor soil, calcium oxalate
• Forceful ejection of raphides from the idioblast cell cause
acridity
• Proteolytic enzymes
9. XANTHOSOMA
• Less acridity
• Stinging effect is felt on the lips and tounge
• Strong correlation between acridity and raphides
• High content of calcium oxalate 780 mg/1oog tuber cause acridity
• Oxalate tends to precipitate Ca – Ca deficiency
• Cause oxaluria, kidney stone
Acridity removed by,
1. Slicing, grating, soaking in water
2. By addition tamarind, tender mango, curd
10. ALOCASIA
• Carcinogenic
• All parts except rhizomes contains cynogenic principle
• Young leaves contain 0.018% of HCN
• Leaves, stalks, tubers, roots contain high concentration of
oxalate
• Cause Ca deficiency, oxaluria
12. LARGER YAM & LESSER YAM
• Amylase/ protease inhibitor impair digestion of starch,
protein.
• Boiling, steaming, frying reduce the inhibitory activity
• Phenols, tannins, alkaloids cause bitterness
• Dioscorine, di-hydrodioscorine are nerve poison
• Detoxified by soaking in water
• Cell contains bundles of crystals (raphides) cause itchiness
• Reduced by slicing, boiling.
• Trypsin, chymotrypsin
13. Potato yam
• Terpinoid compounds - bitterness of bulbils
• Calcium oxalate
• Six steroids are isolated, major steroids are;
1. Diosgenin
2. Betasitosterol
3. Stigmasterol
4. Daucosterol
14. Yam bean
• Pods contain- rotenone (isoflavonoid)
• Matured seeds high in alkaloids- insecticidal property
15. MINOR YAMS
• D. dumetorum contain bitter principles - bitter yam.
• Detoxified by soaking in a vessel of salt water, in cold or hot fresh
water or in a stream.
• The bitter principle di hydrodioscorine (alkaloid ) in D. hispida. It
is water soluble alkaloids which, on ingestion, produce severe and
distressing symptoms.
• The bitter principles of D. bulbifera is 3furanoside norditerpene
called diosbulbin, cause paralysis. Extracts are used in fishing to
immobolize the fish and thus facilitate capture.
• In Indonesia an extract of D. bulbifera is used in the preparation
of arrow poison.
17. CASSAVA
• The main toxic principle is linamarin is coexists with its methyl
homologue called methyl-linamarin lotaustralin.
• Linamarin is a cyanogenic glycoside converted to toxic
hydrocyanic acid (HCN) or prussic acid when it comes into
contact with linamarase enzyme.
• HCN - volatile compound. It evaporates rapidly in the air at temp.
28˚C and dissolves readily in water. It may easily be lost during
transport, storage.
18.
19. • The range of cyanogen content of cassava tubers is 15 and
400 mg HCN/kg (fresh weight).
• The concentration of the cyanogenic glycosides increases from
the centre of the tuber outwards.
• cyanide content is higher in the cassava peel, leaves which have
10 times more cyanogens than roots
• Traditional processing and cooking methods reduce the
cyanide content
• Sun drying fresh cassava pieces for short periods is an
inefficient detoxification process.
20. • Sun drying processing techniques reduce only 60 to 70 % of the total
cyanide content
• Cyanide residues can be quite high in the dry tubers, from 30 to 100
mg/kg.
21. Sweet potato
• Sweet potato contains raffinose, responsible for flatulence.
• The level of raffinose present depends on the cultivar.
• Trypsin inhibitor
• Oxalic acid in roots and leaves. Cattle death in japan as a result of
eating mould damaged sweet potatoes.
• There is a correlation between the trypsin inhibitor and the protein
content of the sweet potato.
22. • Heating to 90°C for several minutes inactivates trypsin inhibitors.
• In response to injury, or exposure to infectious agents, or on
exposure of wounded tissue to fungal contamination, sweet potato
will produce certain metabolites, especially the furano-terpenoids
are known to be toxic cause lungs problem.
• Fungal contamination of sweet potato tubers by Ceratocystis
fimbriata and Fusarium sp. leads to the production of
ipomeamarone, a hepatoxin.
23. • Baking destroys only 40 percent of these toxins. peeling diseased
sweet potatoes from 3 to 10 mm beyond the infested area is
sufficient to remove most of the toxin.
24. Potato
• Potato contains the glycoalkaloids alpha-solanine and alpha-
chaconine concentrated mainly in the flowers and sprouts (200 to
500 mg/100 g).
• In healthy potato tubers the concentration is < 10 mg/100 g and
this can reduced by peeling. At higher concentrations – burning
and persistent irritation similar to hot pepper.
• Decomposition temperature of solanine is about 243 ˚C.
• Glycoalkaloids are inhibitors of choline esterase and cause
haemorrhagic damage to the gastrointestinal tract and retina.
25. • Solanine poisoning cause severe illness.
• Potato also contains proteinase inhibitors - defense against
insects and micro-organisms but are no problem to humans
because they are destroyed by heat.
• Lectins or haemogglutenins are also present in potato
26. REFERENCES:
1. Peter,k.v. 2007. Tuber crops. National book trust, India, 251p.
2. FAO, (www.fao.org)- Roots, tubers, plantains and bananas in human
nutrition..
3. Zhaoa,H.,Wang,R.Y., LuoMa,B.,CaiXiong,Y.,CaiQiang, S.,Ling Wang,S.,
AnLiu,S.,MinLi,F.2014. Ridge-furrow with full plastic film mulching
improves water use efficiency and tuber yields of potato in a semiarid
rainfed ecosystem.Field Crops Res.161.137–148 pp [ 28 Mar. 2014].
