ANTI-NUTRITIONAL CONSTITUENT OF COLOCASIA ESCULENTA ...
ANTI-NUTRITIONAL CONSTITUENT OF COLOCASIA ESCULENTA ... ANTI-NUTRITIONAL CONSTITUENT OF COLOCASIA ESCULENTA ...
determine fatty acid composition. Petroleum ether extracts only non-polar lipids, while methanol-chloroform extracts both non-polar and polar lipids. Iodine values are used to measure the relative degree ofuusaturation in fats. This value calculated from fatty acid composition may give a value closely related to the number of double bonds present in the fat. The standard for oleic acid was used to determine fatty acid composition ofAmadumbe by comparing the molecular weights given by each peak to relative retention times. The results showed that the investigated Amadumbe extract contained oleic acid, linolenic and linoleic acid, with linoleic acid being the most abundant. This is in agreement with studies undertaken by Hussain et al. (1984), who determined that palmitic, oleic and linoleic acids were the main fatty acids in Colocasia esculenta (L.) Schott, with linoleic acid predominating. A.4.4 Anti-nutritional factors The nutritional value ofany food product depends largely on the availability and qnality of the nutrients as well as the presence of anti-nutritional factors. Anti-nutrients are known to reduce the availability ofnutrients to animals and humans (Rackis et a11986; Gupta, 1987). The higher the concentration of the metabolites, the greater the risk they pose to the health of the consumer. During domestic processing, anti-nutrients are partly removed and their toxicity is lowered. Nevertheless, consuming large quantities of food with anti-nutrients may still result in a health risk. The screening of the two varieties of Amadumbe tubers from the three geographical areas revealed no specific pattern in the anti-nutrient levels. It was therefore decided to process only the two varieties from the local Esikhawini areas because of ease of collection. This screening was conducted to determine the efficiency of the local processing methods (boiling, frying and roasting) employed in detoxifying the anti-nutrients present in the raw materials. 71
TIA indicated that the trypsin inhibitor in Amadumbe tubers could inhibit type I trypsin from bovine pancreas. The small variation in TIA may be due to different environmenJal factors. The handling conditions, degree ofmaturity and physiological conditions all play a major role in the production ofanti-nutritional factors (Sotelo et aI., 1998). Apart from the activity ofpapain, which was not inhibited, all other proteases were inln'bited (albeit to varying degrees) by the crude Amadumbe extract. Protease inlnbitor reacts with some functional groups in the active site of the enzyme, forming an irreversible trypsin enzyme-trypsin inhibitor complex. This complex reduces trypsin in the intestines, which leads to less protein digestI'bility and ultimately canses slower animal growth (Siddhuraju and Becker, 2001). In this study, the initial enzyme inhibitor was completely inactivated during processing. It is well established that trypsin inhibitors are heat-labile (Bhandari and Kawabata, 2006; Khokhar and Cbanban, 1986). Reduction of TIA is expected to enhance the digestIbility ofproteins in processed Amadumbe tubers. The AIA shows that a-amylase inhibitors were fairly heat-stable, compared to the trypsin inhibitors in these tubers. These observations were in close agreement with reports of Liener and Kakade (1980) who observed that, despite their susceptibility to heat inactivation, amylase inln'bitors might persist through cooking temperatures. Similarly, Prathibha et aI., (1995) and Bhandari and Kawabata (2006) reported that a-amylase inhibitors from Dioscorea tubers did not show much reduction in activity, even at 100° C, and were heat stable. Lectins were present in both Amadumbe varieties from all three localities. Leetins are heat-labile (Friedman and Brandon, 2001; Liener, 1989): however, the lectins present in Amadumbe were not destroyed during the different processing procedures. Armour et aI., (1998) reported that lectin activity was relatively heat-resistant for soya bean during aqueous heat treatment Unproeessed Amadumbe tubers were shown to contain fairly low levels of phenolic compounds. The total free phenolic content in the present study was found to be higher than the values reported in sweet potato (Hnang et al., 2006) and taro in Cameroon 72
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TIA indicated that the trypsin inhibitor in Amadumbe tubers could inhibit type I trypsin<br />
from bovine pancreas. The small variation in TIA may be due to different environmenJal<br />
factors. The handling conditions, degree ofmaturity and physiological conditions all play<br />
a major role in the production ofanti-nutritional factors (Sotelo et aI., 1998). Apart from<br />
the activity ofpapain, which was not inhibited, all other proteases were inln'bited (albeit<br />
to varying degrees) by the crude Amadumbe extract. Protease inlnbitor reacts with some<br />
functional groups in the active site of the enzyme, forming an irreversible trypsin<br />
enzyme-trypsin inhibitor complex. This complex reduces trypsin in the intestines, which<br />
leads to less protein digestI'bility and ultimately canses slower animal growth (Siddhuraju<br />
and Becker, 2001). In this study, the initial enzyme inhibitor was completely inactivated<br />
during processing. It is well established that trypsin inhibitors are heat-labile (Bhandari<br />
and Kawabata, 2006; Khokhar and Cbanban, 1986). Reduction of TIA is expected to<br />
enhance the digestIbility ofproteins in processed Amadumbe tubers.<br />
The AIA shows that a-amylase inhibitors were fairly heat-stable, compared to the trypsin<br />
inhibitors in these tubers. These observations were in close agreement with reports of<br />
Liener and Kakade (1980) who observed that, despite their susceptibility to heat<br />
inactivation, amylase inln'bitors might persist through cooking temperatures. Similarly,<br />
Prathibha et aI., (1995) and Bhandari and Kawabata (2006) reported that a-amylase<br />
inhibitors from Dioscorea tubers did not show much reduction in activity, even at 100° C,<br />
and were heat stable.<br />
Lectins were present in both Amadumbe varieties from all three localities. Leetins are<br />
heat-labile (Friedman and Brandon, 2001; Liener, 1989): however, the lectins present in<br />
Amadumbe were not destroyed during the different processing procedures. Armour et aI.,<br />
(1998) reported that lectin activity was relatively heat-resistant for soya bean during<br />
aqueous heat treatment<br />
Unproeessed Amadumbe tubers were shown to contain fairly low levels of phenolic<br />
compounds. The total free phenolic content in the present study was found to be higher<br />
than the values reported in sweet potato (Hnang et al., 2006) and taro in Cameroon<br />
72
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