PhD

A three phase experiment was carried out to assess the level of cyanogenic glycoside (CNC) content in seven varieties of tapioca, its removal by various processing methods and its effect on metabolism in rats and kids. The role of dietary protein and iodine in modifying the deleterious effects of cyanide was investigated. Histopathological studied on the liver, pancreas and heart were also carried out in rats.

The first phase of the study revealed that CNG content in terms of cyanide varied from 40.86 + 2.79 to 186.31 + 5.30 µg/g of fresh tuber with the lowest concentration in ‘M-4’ and higher concentrations in ‘H-165’ and ‘Karkidakkan’. Processings like boiling and sun drying lowered the CNG content by about 50 percent of the original.

In the second phase 60 male albino Wistar rats divided into six groups were given the following diet.

Group I – Protein = 15%; Tapioca = Nil, Todine = Nil.
Group II – Protein = 15% ; Tapioca = 30%, Iodine = Nil
Group III – Protein = 7.5%; Tapioca = 30%, Iodine = Nil
Group IV – protein 7.5%, Tapioca without HCN = 30%, iodine = Nil
Group V – Protein = 15%, Tapioca = 30% , Iodine = 0.17 mg/kg
Group VI – Protein = 22.5%; Tapioca = 30%, Iodine = 0.17 mg/kg

Performance of rats was evaluated by recording growth rate, feed consumption and need efficiency for a period of 12 weeks. Dry matter digestibility was also determined over a period of 24h. At the end of 10th, 11th and 12th week of the study the rat were sacrificed and endocrinological, biochemical and histopathological evaluation of blood / serum and tissues were made.

Performance of rats was poor on tapioca – based diet not supplemented with iodine (Groups II and III). Rats fed on protein deficient diet in the presence of cyanide containing tapioca were the most affected (Group III). However, there was no significant variation in the performance in Groups V and VI comapared to Group I when tapioca – based diet were supplemented with iodine . The digestibility of dry matter in six groups of rats was almost inversely related to the quanity of feed consumed.

There was significant increase in DNA and decrease in protein content of thyroid thereby increasing the DNA: protein ratio, followed by extremely low levels of thyroxine and hyperplastic of the thyroid in group III. In group II also there occurred a significant reduction in the levels of thyroxine and a resultant hypertrophy of the thyroid.

Higher levels of dietary protein and Iodine supplementation were found to play a decisive role in counteracting the inhibitory effects of cyanide and thiocyanate of tapioca origin especially on thyroid functions.

The DNA: protein ratio per unit weight of pancreatic tissue was increased in groups fed on low levels of dietary protein (Groups III and IV)

Insulin levels in different groups of rats were found to be primarily related to the levels of blood glucose. There was no significant difference in insulin-to-glucose ratio between the groups. The synthesis and release of insulin from the pancreas was not affected by cyanide present in the diet of tapioca fed groups.

Rats showed no definite pattern of response in their blood glucose levels to cyanide contained in the diet of tapioca fed groups.

There was elevation in the levels of serum total protein, cholesterol and lipid concentrations in rats fed tapioca without supplementation of iodine (Groups II and III). This may be the result of the development of hypothyroidism. However, the increase in serum total protein and lipid in Group II was not significant. The results indicated that the above parameters could be used as reliable biochemical indicators of thyroid activity.

A significant reduction in haemoglobin concentration in rats of groups II and III compared to groups I and IV reflected the deleterious effects of cyanogens on thyroid functions as well as the importance of availability of dietary protein for haemoglobin synthesis.

The hepatic cells in Group II appeared slightly swollen with occasional cells showing vacuolar changes. Pancreas showed slight oedema and occasional mild degenerative changes of exocrine cells. Also there was slight interstitial oedema in the myocardium. Intensity of pathological changes in the liver, pancreas and heart were more severe in rats fed on protein deficient, tapioca diet (group III) compared to that of group IV in the diet of which tapioca was made cyanide free. The hepatic cells in Group III showed marked diffused vacuolar changes with condensed or vesicular nuclei and occasional cell necrosis. Many pancreatic exocrine cells showed vascuolar and degenerative changes. Interstitial oedema was prominent. Inspite of these pancreatic exocrine changes, it is important to note that the islets remained almost intact in all the groups studied. Myocardium shoed interstitial oedema with swollen sarcoplasm and fragmented sarcolemma. At the same time only moderate vacuolar changes in the liver, distention of interlobular space and interstitial oedema in myocardium were observed in group IV. Since the diet of Group V and VI were supplemented with iodine, no significant cytological alterations could be seen in their organs.

In the third phase of the study thirty 2 ½ - 3 months old Alpine – Malabari kids of both sexes were divided into 3 groups. They were given the following diet.

Groups I protein = 15%; Tapioca = Nil; Iodine = Nil
Groups II protein = 15%; Tapioca = 30%, Iodine = 2 mg/kg
Groups III protein = 25%; Tapioca = 30%; Iodine = 2 mg/kg

The study included evaluation of the performance of kids and determination of certain endocrinological and biochemical parameters in their blood at fortnightly intervals for 3 months.

There was no significant effect on the performance (body weight gain, dry matter intake and feed efficiency) of kids fed on tapioca – based diet supplemented with iodine, compared to group I. However, the significant difference in body weight gain between tapioca fed groups (Groups II and III) was probably due to the difference in the relative availability of protein in their diet.

The results of the study in kids indicated that there was no significant influence of cyanogenic principles present in tapioca on the thyroxin and insulin levels when iodine was supplemented in the diet. Similarly the blood glucose, serum total protein, cholesterol, lipid and haemoglobin levels were also not influenced throughout the study.