Yield and functional properties of starch extracted from dry cassava chips | |
| Author | Gebriel, Solomon Abera Habte |
| Call Number | AIT DISS. no. PH-03-03 |
| Subject(s) | Cassava--Drying Starch |
| Note | A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Enginee1ing |
| Publisher | Asian Institute of Technology |
| Abstract | Fresh roots of cassava (Manihot esculenta Crantz) are a major raw material for starch, flour, chips and pellets production in many tropical countries. The perishable nature of the root entails continuous supply of fresh root to the factories. As cultivation is largely climate dependent the supply of fresh root fluctuates seasonally. Absence of long-term storage mechanism of fresh root has forced starch factories to operate under capacity or sustain temporary closure for up to 3 - 4 months during slack harvest. At peak harvest times supply exceeds their production capacity resulting in low root price and consequent reduced return to the growers. The idea of extracting starch from dry chips is an attempt to solve this problem. Surplus root at high season could be dried and stored to supplement the deficiency in low season. This can also alleviate a problem of lack of market for Thai dry cassava chips producers due mainly to European Union quota restrictions and trade barriers. This way all the parties involved in cassava business in countries like Thailand would benefit considerably. The overall aim of this study was to find a strategy for obtaining good quality starch from dry chips and comparing it in terms of physicochemical and functional properties with that extracted from fresh roots. Four Thai and four Ethiopian cassava varieties were investigated in this study. Starches were extracted from fresh roots and dry chips in a laboratory using a blender. Among the parameters studied were blending time, size and shape of chips, chip drying method, and chip steeping time and temperature for both dry and wet milling of the dry chips. In wet milling a blending time of 5 minutes at 3000 rpm was found to give the highest starch yield (28%) after steeping the dry chips in water at room temperature for 6 hours. Longer steeping times and higher water temperatures showed little effect on the yield. Dry milling of chips followed by steeping the flour in water for 0, 6, 12 and 18 hr at 30, 45 and 55°C led to a reduced yield (16.2 to 21.5%) as compared to wet milling. While drying rate was strongly influenced by chip size and shape (bar, slice and strip) and chip drying method (sun and oven drying), little difference prevailed as regards starch yield. Variety CMR was found to have given the highest starch yield of 27 .8 and 22.1 % by wet and dry milling respectively. All starches fulfilled the specifications set for Thai domestic market. These included starch, fiber, ash, and protein contents, and color, pH, mesh size and peak viscosity. The problem of darker color reported in earlier work with chips seemed to be overcome by peeling the root prior to drying. Evaluation of functional characteristics included pasting properties by RVA, gelatinization and retrogradation properties by DSC, swelling power, paste clarity and freeze-thaw stability. Dry-chip starches exhibited a drop in peak viscosity by up to 11.7 and 15.3% for wet and dry milling methods respectively. Pasting and peak temperatures increased by up to 4°C and gelatinization temperatures by 3°C. Swelling power, paste clarity and freeze-thaw stability decreased by up to 11, 20, and 15% respectively. The major factors responsible for the differences were presumed to be the relatively higher fiber content in dry-chip starches and annealing of the same due to exposure to heat during chip drying and to excess moisture during chip steeping.Functional properties of starches were also influenced by chip size and shape. Peak viscosity was reduced by 9.3, 16.6, and 27.8% for variety CMR and by 13.0, 18.0, and 28.9% for variety KU50 for starches derived from bar, slice, and strip shape chips respectively as compared to that of the respective fresh-root starch. Starches from slice and strip shape chips showed slightly reduced gelatinization enthalpy due to damage probably due to the high intensity of blending because of their small chip size. Swelling power and paste clarity were in the order bar > slice > strip. These differences were attributed to variation in fiber content of the starches (0.21, 0.30, 0.38% for CMR35-22-196 and 0.16, 0.25, 0.36% for KU50 respectively) arising from differences in degree of chip disintegration due to variation in chip size. Besides, the difference in size and shape led to variation in surface area to volume ratio of chips (0.46, 0.73 and 1.35 mm·1 for bar, slice and ship shape chips respectively) which had probably affected the intensity of annealing of the starches during chip drying and steeping processes. The smaller the chip size the greater the impact in both fiber content and annealing, and thus the stronger is the influence on functional properties. Functional properties of starches processed from chips dried under different conditions showed little or no difference. Yield of starches processed from dry chips stored up to 8 months at 5 and 30°C dropped by up to 2.4 and 3.9% respectively for variety KU50 and 4.7 and 5.6% respectively for CMR. Functional properties such as peak viscosity, swelling power, paste clarity and freeze-thaw stability exhibited reduction with increase in time for both storage temperatures. The changes are effects of ageing of the starches in the dry chips due to storage time and condition. In general little difference has been found in starch yield between fresh root processing and wet milling of dry chips whereas dry milling incuned considerable loss. The changes in functional properties are without severe drawback for their suitability to many applications. The high stability and resistance against heat and shear of the dry chip starches could be beneficial in many respects. Given the modem processing equipment cunently in use in starch factories it may be possible to extract starch from dry cassava chips with purity and desirable functional characteristics similar to that obtained from fresh root. Hence drying of chips and subsequent extraction of starch from such chips when done under suggested conditions could be considered as an alternative method of storage of cassava in the high season for production of good quality starch in the lean season. |
| Year | 2003 |
| Type | Dissertation |
| School | School of Environment, Resources, and Development (SERD) |
| Department | Department of Food, Agriculture and Natural Resources (Former title: Department of Food Agriculture, and BioResources (DFAB)) |
| Academic Program/FoS | Postharvest and Food Process Engineering (PH) |
| Chairperson(s) | Rakshit, Sudip K. |
| Examination Committee(s) | Jindal, Vinod K.;Athapol Noomhorm;Visvanathan, C. |
| Scholarship Donor(s) | Government of Ethiopia Agricultural Research Training Program |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology, 2003 |