Postharvest handling effects on the quality of soybean seed, oil and lecithin | |
| Author | Uma Sangkram |
| Call Number | AIT DISS. no. PH-03-01 |
| Subject(s) | Soybean--Quality Soybean--Seeds--Quality Soy oil Lecithin |
| Note | A disse1iation submitted in partial fulfillment of the requirements for the degree of Doctor of Technical Science. |
| Publisher | Asian Institute of Technology |
| Abstract | Quality of raw soybeans directly affects the quality of processed products. Variety, environment during growth and storage, postharvest handling and processing conditions are the factors which determine quality of the bean. Most of the soybeans grown in Thailand are harvested in rainy season, therefore, immediate drying is required. However, drying with heated air results in physical damage to the beans and promotes the deterioration of the beans when the beans are stored. The objectives of this study were to investigate the properties of soybean seeds used as raw material for commercial oil production in Thailand and to study the effect of seed breakage, initial moisture content and drying on the quality of soybean seed and its products. Physical and chemical properties of commercial soybeans from both local Thai varieties and imported beans from the U.S. and Argentina were compared. The impo1ted beans had a lower percentage of foreign material, a larger seed size and a higher splitting percentage than the local soybeans of both dry and rainy season crops. The highest percentage of damaged kernels (8.5%) was found in local soybeans harvested in the rainy season. Oil content of the imported beans was higher and better in quality when measured in terms of free fatty acids (FF A) and peroxide value (PV). The values of total phospholipid content (PL) in crude oil of imported beans were also higher than the local beans. The values were approximately 2.5-3 .3% of oil weight. The acetone insoluble value (Al) of lecithins produced from the imported beans and from Thai beans harvested in dry season was approximately the same. Comparison between local beans harvested in dry and rainy seasons showed that the quality of crude oil and lecithin from dry season beans was better than those of the rainy season beans. Effects of breakage and storage were also investigated. Three fractions namely whole, half and pieces of Thai soybean of SJ. 5 variety were stored for two months at 10 and 13% moisture contents. Breakage of the beans and storage time showed significant effects on FF A and PV of crude oil. These effects were obvious in the beans at 13% moisture content, while beans at 10% moisture content still had low FF A and PV after twomonth storage. Phospholipid content in crude oil decreased during storage, especially in the first month for beans at both moisture levels. However, the decrease was greater for beans at 13% moisture content and the rate of decrease was greatest for piece beans. Gum separated from crude oil of 13 % moisture half beans after storage for two months and 13 % moisture piece beans after storage for one and two months had a paste-like character while gum from other soybeans was semi-solid. The lecithin obtained from good quality gum (semi-solid gum) was a clear, light brown color, whereas the lecithin from poor quality gum (paste-like gum) was dark brown. The quality of lecithin measured in terms of Al value was lower for damaged soybeans and decreased during storage especially for lecithin made from poor quality gum. Effects of initial moisture contents of 15, 20 and 25% and the mixing of those three levels on the quality of soybean seeds and oil were also determined. Storage of wet beans prior to drying caused an increased deterioration of the beans (measured from extracted crude oil) which was positively correlated with the higher level of moisture content and longer storage time. When wet beans were dried immediately, the different initial moisture contents caused changes in the physical properties of the beans. Percent cracking of the beans increased with the increase of initial moisture level, whereas the breakage strength of the beans determined by impact test decreased. For beans with mixed initial moisture content, a high percent cracking was displayed by beans with the greatest difference in moisture content. The quality of extracted crude oil measured after drying in terms of FF A and PV was not effected by initial moisture content while the PL content decreased with increasing initial moisture content. Two-month storage of dried beans caused FF A and PV of extracted crude oil to increase with time while PL decreased. The decrease of phospholipids was found in both hydratable (HP) and nonhydratable (NHP) forms, and this decrease was greater in the beans with higher initial moisture content. In the study of drying, the temperatures ranged from 50 to 90°C for low temperature drying and I 00 to l 40°C for high temperature drying. Combination of high temperature drying in the first-stage and low temperature drying in the second-stage (twostage drying) was also conducted. The increase in drying temperature caused an increase in soybean seed cracking and a decrease in the breakage strength of the beans. At high drying temperature of 120 and 140°C, percent seed cracking increased, but the beans were hardened and showed higher breakage strength than at 100°C drying temperature. The quality of soybean oil after drying indicated by the values of FF A, PV and PL was not effected by drying temperature but phospholipids in the form of NHP had the increasing trend with the increase in drying temperature and two-stage dried beans tended to have a greater NHP than one-stage dried beans. For the d1ying temperature higher than 80°C in one-stage drying and higher than 100°C in the first stage of two-stage drying, the protein dispersibility index value (PDI) of soybean meal was less than the minimum value for commercial soybean meal. The AI value of lecithin was also affected by drying temperature. Shade drying and one-stage drying at 80°C caused a higher AI value of lecithin. During two-month storage of dried beans at 3 5°C in the control chamber, storage time positively affected FF A and PV and negatively affected PL content of crude oil. However, it did not cause a change in the AI value of lecithin. Scanning electron microscope study of dried beans showed that both high drying temperature and long exposure time resulted in the damage of the membranes of cell organelles and the melting of lipid in the cells. In summary, the results obtained from this study could be used as the information for improving postharvest handling particularly drying and storage of soybean to maintain the quality of the bean and its related products in commercial processing. |
| 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) | Athapol Noomhom |
| Examination Committee(s) | Jindal, Vinod K.;Rakshit, Sudip K.;Ranamukhaarachchi, S.L. |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology, 2003 |