Quality Changes in Market Cassava Chips Infested by Insects
T.PREM KUMAR, S.N. MOORTHY, C.BALAGOPALAN,
C.A. JAYAPRAKAS and P.RAJAMMAT
Central Tuber Crops Research Institute, Sreekariyam, Trivandrum 695 017, Kerala, India.
(28th January 1996)
Abstract : The biochemical changes occurring in dried cassava chips collected from various marketing centres in Kerala (India) due to insect infestation were studied. Araecerus fasciculatus (Degeer) was the most important pest of plain sun-dried cassava chips and Sitophilus oryzae (L.) and Rhyzopertha dominica (F.) were the important pests of parboiled chips. There was substantial reduction in starch and sugar content in fully infested plain dried chips as compared to the uninfested chips (83.5-77.9% for starch and 6.95-1.53% for sugar). Reduction in starch was more pronounced in fully infested parboiled chips (78-57%) while sugar increased nearly three fold (6.0-15.7%). Total and soluble amylase contents and reducing values were not significantly affected in plain dried chips due to infestation. Viscosity underwent only slight reduction in plain dried chips while in parboiled chips, the reduction was noticeable even at a partially infested stage. Although there was reduction in starch content due to insect infestation, starch quality did not change much in plain dried chips, indicating the possibility of using such infested chips in animal feed formulations and in the manufacture of commodity chemicals.
Keywords : cassava quality change, insect infestation, Araecerus, fasciculatus, Sitophilus oryzae, Rhyzopertha dominica.
A major constraint in the post-harvest utilization of fresh cassava is the rapid perishability of the tubers. Normally fresh cassava tubers cannot be stored without spoilage for more than 3-5 days. Unfavourable market price prevailing at the time of harvest is another problem faced by the farmers. In order to overcome these problems the conventional practice among the farmers is slicing the fresh tubers into small pieces and sun-dried white chips and parboiled chips. Plain dried chips are obtained by cutting the tubers into pieces and drying them in sunlight and parboiled chips are prepared by immersing the chips in boiling water for 10 min, draining the water and then sun-drying the chips (Balagopalan et al., 1988).
Cassava chips are vulnerable to insect infestation and as many as 21 insect species have been associated with stored chips in India (Anon., 1991). Parboiled chips have longer shelf-life than plain dried chips due to the harder nature of the former resulting from partial gelatinization of starch and subsequent binding of the gelled starch (Balagopalan et al., 1988; Rajamma et al., 1994).
The shape of plain dried chips is lost quickly due to insect infestation and they are reduced to a powdery mass; parboiled chips are riddled by adults and larvae and lose their shape and rigidity only after prolonged infestation. The powdery mass consists of excreta of adults and larvae, uneaten cassava and dead beetles.
As much as 16% weight loss in cassava chips has been reported due to insect infestation (Parker and Booth, 1979). However, information regarding the consumption of major nutrients such as starch, sugar and fibre by insect pests and the consequent quality deterioration is lacking. This paper reports the results obtained from a study on cassava chips collected from various godowns in Kerala which is the most important cassava growing state in South India.
Materials and Methods
Plain dried white chips and parboiled chips were collected from godowns at Kattakkada in the Trivandrum district and Thaliparamba in the Kasaragod district of Kerala. Plain dried chips were mostly infested by Araecerus fasciculatus and parboiled chips by Rhyzopertha dominica and Sitophilus oryzale. Intial damage in the market samples was 10% in plain dried chips and 2% in parboiled chips. Because of regional differences in the varieties of cassava cultivated, and the drying and storage practices followed, there was some heterogeneity in the market samples. Nevertheless, a uniform sampling pattern was followed in both the locations and a representative sample for collection, a representative batch of uninfested chips from both locations was dried, powdered and sieved through a 200 mesh sieve and kept for biochemical analyses. The remaining samples were stored in polythene containers in the laboratory to enable the insects to feed on the chips for 10 months. The partially infested chips were removed by hand picking, powdered in a blender and sieved using the same mesh size. Fully infested powder was sieved to remove the dead beetles and then directly used for analyses of starch, sugar and fibre contents by standard analytical procedures (A.O.A.C., 1975). Total and soluble amylase were estimated by the method of Sowbhagya and Bhattacharaya (1971) and Santhy et al. (1980), respectively. Bulk density of the samples was calculated from the weight of the known volume of the powder. Viscosity and pasting temperatures were monitored on a Brabender viscogrph using 8% concentration for plain dried chips and 15% were monitored on a Brabender viscograph using 8% concentration for plain dried chips and 15% for parboiled chips. The heating rate was 1.5°C min¯¹ for all samples. Reducing values were estimated as ferricyanide numbers (Schoch, 1964).
Results and Discussion
The starch content decreased from 83.5% in uninfested chips to 77.9% in fully infested plain dried chips, but the decrease was minimal in partially infested chips (Table 1). This reduction might have resulted from the utilization of starch by the insects plain dried samples indicating that native sugar as well as that formed through hydrolysis of starch by insect enzymes has been utilized by the insect.
Reduction in starch content was minimal in partially infested parboiled chips; however, in fully infested chips, there was substantial reduction in starch content (78-57%). Although reduction in sugar content from 5.68 to 3.8% was observed in partially infested chips, the sugar content increased to 15.7% in fully infested parboiled chips. The large increase in sugar content observed (Table 1) in fully infested parboiled chips have resulted from the salivary enzymes of the two insects, S. oryzae and R. dominica. As compared with native raw starch (present in plain dried chips), gelatinized starch is acted upon easily by hydrolytic enzymes. It is also known that gelatinized starch is more readily digested (both in vitro and in vivo) than native raw starch (Moorthy and Padmaja, 1991). Although large quantities of free sugars are released, only a small proportion is consumed by the insects with the result that the residual sugar content tends to increase in the remaining powder. A high performance chromatographic analysis of the sugar profiles in insect infested cassava chips reinforces this finding and it was observed that there was a predominance of sugars such as sucrose, maltose and glucose in infested parboiled chips compared with the quantity present in uninfested chips (Padmaja et al., 1994).
Table 1. Starch, sugar and fibre contents in infested and uninfested cassava chips
|Plain Dried Chips|
|Uninfested||83.5 ± 7.6||6.95 ± 0.75||1.26 ± 0.15|
|Partially Infested||82.5 ± 6.2||2.42 ± 0.40||0.42 ± 0.05|
|Fully Infested||77.9 ± 10.7||1.53 ± 0.21||0.24 ± 0.03|
|Uninfested||78.1 ± 8.2||5.98 ± 0.72||1.8 ± 0.20|
|Partially Infested||77.1 ± 10.2||3.79 ± 0.61||1.2 ± 0.18|
|Fully Infested||56.7 ± 11.2||15.68 ± 3.22||Trace|
* Each datum is the mean of six replicates (±SD)
|Reducing Value* (Ferricyanide Number)||Bulk Density* g/ml||Total Amylase* %||Soluble Amylase* %|
|Plain Dried Chips|
|Uninfested||2.70 ± 0.35||0.49 ± 0.06||23.0 ± 4.6||12.2 ± 1.4|
|Partially Infested||1.08 ± 0.30||0.44 ± 0.03||24.2 ± 4.8||10.4 ± 1.8|
|Fully Infested||1.00 ± 0.25||0.42 ± 0.05||24.6 ± 3.4||11.7 ± 2.0|
|Uninfested||1.16 ± 0.22||0.82 ± 0.15||17.2 ± 2.5||8.4 ± 1.1|
|Partially Infested||1.72 ± 0.31||0.78 ± 0.14||16.4 ± 3.0||7.1 ± 1.0|
|Fully Infested||2.60 ± 0.41||0.45 ± 0.08||15.3 ± 1.7||11.3 ± 1.5|
* Each datum is the mean of six replicates (±SD).
The crude fibre content (Table 1) in plain dried and parboiled chips underwent reduction with insect infestation, the reduction being more pronounced in fully infested parboiled chips. The results indicate the possible utilization of crude fibre during insect feeding.
Total and soluble amylase contents did not alter significantly with insect feeding (Table 2). The reducing value expressed as ferricyanide numbers presented in Table 2 showed that while the value decreased from 2.7 to 1.0 in the case of infested plain dried chips, an increase from 1.16 to 2.6 was noticed in parboiled chips. Breakdown of starch is invariably associated with an increase in reducing values to very high levels. Such a change was not observed in the plain dried chips when infested. However, there was an increase in reducing value for parboiled chips on infestation, which may be due to the higher sugar content and other compounds excreted by the insects.
Bulk density values (Table 2) showed a slight reduction from 0.49 to 0.42 ml g¯¹ for plain dried chips when infested whereas it dropped from 0.82 to 0.45 ml g¯¹ in the case of parboiled chips. The reduction in the bulk density of parboiled chips could be attributed to insect feeding. The peak viscosity of 8% paste of plain dried chips underwent only very slight changes during infestation viscosity of 8% paste of plain dried chips underwent only very slight changes during infestation (520 BU to 490 BU) (Table 3). However, in fully infested parboiled chips, the viscosity was totally lost. It was earlier observed that reducing values of the infested parboiled chips showed little increase. The loss of viscosity in the case of infested parboiled chips can be explained by the weakening of intermolecular bonds between the starch molecules brought about by insect attack. When this starch is subjected to heat and shear in the viscograph, the granules undergo breakdown leading to loss of viscosity. The viscosity after holding for 30 min did not indicate any major breakdown in partially and fully infested white chips which confirmed that there was only very slight breakdown in granular structure in plain dried chips due to infestation. The pasting temperature as read from the viscograph curves indicated only marginal differences in the infested plain dried chips indicated only marginal differences in the infested plain dried chips.
|Peak Viscosity*(BU)||Viscosity* at 97°C||Gelatinisation Temperature °C|
|Plain Dried Chips|
|uninfested||520 ± 56||490 ± 59||69-87|
|Partially Infested||630 ± 72||620 ± 71||67-92|
|Fully Infested||490 ± 52||420 ± 62||66-85|
|Uninfested||450 ± 63||390 ± 46||55-95|
* Each datum is the mean of six replicates (±SD).
(-) No reading obtained.
The study revealed only a slight reduction in starch content in plain dried chips infested with A. fasciculatus and the breakdown in starch is minimal, indicating the possibility of using the infested chips in animal feed formulations and for the manufacture of starch-based chemicals.
Acknowlgements : The authors are grateful to the Director, Central Tuber Crops Research Institute, Trivandrum for providing facilities for carrying out the work and Dr G. Padmaja, Senior Scientist, Central Tuber Crops Research Institute, Trivandrum, for critically reading the manuscript.
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