Processing of cassava, residual cyanogens and mycotoxin content in traditionally processed cassava products
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Date
1998-04
Authors
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Publisher
The University of Reading
Abstract
Cassava samples from some villages in Tanzania processed by wet fermentation, solid
state fermentation and sun drying were analysed for residual cyanogens and presence of
mycotoxins. Cassava samples (bitter varieties) processed by wet and solid-
concluded that wet fermentation is very effective in reducing cyanogens in cassava. No
mycotoxins (aflatoxins ) were detected in cassava samples.
The chemical composition of these cassava samples was also determined. Wet
fermentation showed lower content of vitamin C, reducing sugars and protein compared
to samples processed by solid state fermentation and sun drying.
In another experiment, cassava flakes were produced on a drum drier using varying pre
cooking temperatures and drum speeds. Pre-cooking conditions were: no pre-cooking,
pre-cooking at 75°C for 35 minutes and 100°C for 5 minutes. The drum speeds used were 11.5 and 14.0 r.p.m. which correspond to 4.0 and 3.4 seconds drying time respectively. The flakes were analysed for vitamin C, moisture, free starch, reducing
sugars and protein content.
Pre-cooking conditions affected vitamin C, moisture and free starch content while Hmm
speed affected only the moisture content of the flakes. Prolonged pre-cooking time
caused losses in vitamin C while pre-cooking at the higher temperature increased free
starch content of the flakes. The moisture content increased with increasing drum speed.
The soluble amylose test showed that starch retrogradation occurs when cassava is cooled after the pre-cooking stage. The textural characteristics of reconstituted mash from the flakes was analysed using the
Texture Analyser, after adding emulsifiers (stearate monoglyceride, sodium caseinate
and skim milk powder). Results from Texture Profile Analysis (TPA) (adhesiveness),
tests showed that stearate monoglyceride Back extrusion and sensory evaluation
emulsifier reduces the stickiness of reconstituted cassava flakes mash. The Differential
Scanning Calorimetry (DSC) thermograms indicated the formation of an amylose
monoglyceride complex. Cassava samples with stearate monoglyceride had low water
absorption capacity and high bulk density. Also sample with stearate monoglyceride had
low viscosity according to the results from the Brabender amylograph tests.
Samples of cassava flakes and reconstituted mash with skim milk powder and sodium
caseinate were darker in colour compared to those with stearate monoglyceride
according to the results from both instrumental (Hunter Lab spectrophotometer) and
sensory tests.
Description
PhD-Thesis
Keywords
Cassava, Cyanogens, Mycotoxin, Cassava products