| Author | Rahman, S. M. Mahfuzur |
| Call Number | AIT Diss. no.BP-00-03 |
| Subject(s) | Sweet potatoes--Varieties
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| Note | A dissertation in partial fulfillment of the requirements for the degree of Doctor of Engineering, School of Environment, Resources and Development |
| Publisher | Asian Institute of Technology |
| Series Statement | Dissertation ; no. BP-00-03 |
| Abstract | Sweet potato is a low priced and abundant commodity which has a tremendous potential for an industrial raw material. However, limited information is available on the extractability and physical, chemical, rheological and organoleptic of sweet potato starch required by the target markets. A practical and cheap method for the assay of starch content in sweet potato roots is measurement of reducing sugars according to the DNS method. The treatment of roots with 20 ml of 2N hydrochloric acid for 2.5 hours was found to be optimum. Starch content in the roots harvested in the dry season for CIP 14-1 (23.4%) PIS 106-35 (29.3%) and PIS 129.3 (28.7%) varieties. Higher dry matter of sweet potato roots indicated the higher starch content. There was an inverse relationship between starch content and extractability. Increased blending time for 3 minutes expectedly increased the starch release from the roots. Sedimentation was found more to be a function of time (optimum 5.25 hours). It was shown that extractability could be increased by rasping. Blending to obtain a rasping effect of 85% was found to be the best in trading off between starch extraction and power requirement. The addition of enzymes was also found to increase the extraction of starch considerably even at lower levels of rasping. The highest yield was 2.75 times (22.2%) the control using the cytolase enzyme at 0.1% (v/w) level and mixing the slurry during incubation. The hydrocyclone was found to work effectively for the separation of sweet potato starch and can be scaled up to industrial levels. It increased the dry mass from about 5% to 35%. The volume that goes from the feed to the overflow was as high as 70% This would allow the reuse of the water for washing and other such purposes. The efficiency was high (85%). The system could also be used to obtain high purity starch. This was evident from the experiments with 94% pure starch resulting 96.3% starch in single stage of separation. The hydrocyclone was found to work effectively for the separation of sweet potato starch and can be scaled up to industrial levels. It increased the dry mass from about 5% to 35%. The volume that goes from the feed to the overflow was as 70%. This would allow the reuse of the water for washing and other such purposes. The efficiency was high (85%). The system could also be used to obtain high purity starch. This was evident from the experiments with 94% pure starch resulting 96.3% starch in single stage of separation. Rapid viscometric analysis (RVA) and Brabender analysis indicated that the viscous properties of the starch from different varieties of sweet potato were different. The range of peak viscosity was from 2306 cp (for Thai local variety) to 4069 cp South African variety. While the addition of sugars (lactose, sucrose, glucose, chitin and chitosan) could cause a small increase of viscosity of the gels, soya oil could reduce the viscosity, probably due to a coating formed on the granule. Peak viscosity decreased to about 50% on addition of 10% soya oil to sweet potato starch (PIS 115-1). Carboxy-methyl-cellulose (CMC) addition, of CMC even in small quantities, was seen to bring about large changes in the viscosity. Peak viscosity increased more than two fold when only 1% of CMC was added. There was a good correlation between the results obtained from the two instruments, the RVA and Brabender for peak and final viscosity measurements. The correlation coefficient obtained were 0.93 for peak and 0.91 for final viscosity for the varieties of sweet potato starch tested. The Differential scanning calorimeter (DSC) was used to study the energy changes during the gelling process and to determine the energy required to bring about energy changes in larger scale gelation processes. The PIS 115-1 variety of sweet potato gave a sharp enthalpy peak at 82'c and was used to study the interactive effect of this starch with additives. In the study of texture properties of sweet potato gels, a gel holder and a gel sizing device have been designed and fabricated in order to get gels of uniform size and smooth surface. This was necessary in order to get reproducible results. With the help of the designed gel holding device the negative force on the gel during the return of the plunger gave the correct adhesive force of the gels. The results of the texture profile analysis indicated that sweet potato gels produced have much higher hardness (154 g for PIS 115-1) than the gel produced with commercial cassava starch (13g of penetration force). The latter had a flow property and the hardness was difficult to measure. It world be possible to get desirable textural properties with the help of additives such as sugars. The Dynamic Mechanical Analysis (DMA) gave a comparison of the storage moduli, loss moduli and loss factor of the various starch gels studied. All measurements were made under conditions of a frequency scan indicating the sweet potato has good characteristics as compared to other starch samples The loss factors values for gels from sweet potato (<1) indicated that these gels were more elastic than viscous. |
| Year | 2000 |
| Corresponding Series Added Entry | Asian Institute of Technology. Dissertation ; no. BP-00-03 |
| 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 | Bioprocess Technology (BP) |
| Chairperson(s) | Rakshit, Sudip K.; |
| Examination Committee(s) | Stevens, Willem F.;Athapol Noomhorm;Ramachandran, K.B.; |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology, 2000 |