MSc

Cassava forms an important food crop in the tropical countries and are rich in starch
(20-40%) having desirable physico-chemical and functional properties. Starch and
starch derivatives form an important constituent in biodegradable film preparation
due to its renewability, abundance availability, low cost, film forming properties,
high oxygen barriers, odorless, tasteless, colourless, nontoxic, low solubility,
biodegradability etc. But films from the native cassava starch often possess poor
physico-mechanical and hydrophobic
properties. Hence modified starches by
chemical, physical and enzymatic methods offer better scope for the production of
biodegradable films which has got wide applications in the food packaging industry.
The objectives of the present study was to find out the film forming properties of
enzymatically modified cassava starch viz., liquefaction by -amylase and
debranching by pullulanase enzymes added with glycerol as plasticiser. Rheological
properties were measured in terms of the dynamic mechanical spectra of the film
forming solutions viz., storage modulus, loss modulus, phase angle and complex
viscosity. Filmogenic solutions based on -amylase was prepared with starch 5%,
glycerol 20%, amylase concentration: 100, 200 and 300 μl from the stock solution
(0.l ml amylase in 100 ml distilled water), temperature: 80, 85 and 90°C and time:
20, 30 and 40 min for gelatinization. For developing the pullulanase modified starch
based films, the starch (5%) was incubated with pullulanase at 2, 3 and 4 units
concentrations at 45, 50, 55 0C for 8, 16 and 24 h and the filmogenic solutions
added with 20% glycerol were
gelatinised at
90 0C for 20 min.
Both the
experiments were designed using response surface methodology using Box- Behnken
design. The physico-mechanical, functional hygroscopic, biodegradation and storage
studies of the films were carried out.
The dextrose equivalent of the filmogenic solutions varied between 1.6-8.4
with the amylase and 2.2-16.0 with the pullulanase treated starch. The higher values
of storage modulus, complex viscosity and low phase angle of the solution containing
153pullulanase treated starch compared to -amylase treated solutions showed that the
gel formed during gelatinization of the solution is having more solid nature in their
visco-elastic character. The films containing -amylase treated cassava starch
showed better whiteness properties.
Thickness, moisture content, tensile force,
elongation at break and swelling capacity of the films containing pullulanase treated
starch was higher than that of the films with -amylase treated starch. The higher
solubility of the -amylase based starch films helps easy degradation of the films in
the soil whereas offers poor packing ability. Pullulanase film‘s packing ability is
better owing to low permeability and solubility. Though the films with both the
modified starch is easily biodegradable, pullulalanase took 4 weeks for completely
degrade into the soil as evidenced from the soil burial test. The microbial analysis
studies showed that the soil in which -amylase treated film buried for degradation
had highest bacterial, fungal and actinomycetes population than that of the soils with
pululanase treated films. Considering various physical, mechanical and functional
properties, the pullulanase modified starch offers better scope for the production of
biodegradable packing materials.