Abstract
In the food industry approaches for using bioengineering are investigated as alternatives to conventional chemical and physical starch modification techniques in development of starches with specific properties. Enzyme-assisted post-harvest modification is an interesting approach to this, since it
is considered a clean and energy saving technology. This thesis aimed to investigate the effect of using reaction conditions, simulating an industrial process, for enzymatic treatment of starch with branching enzyme (BE) from Rhodothermus obamensis. Thus treatements were conducted at 70°C using very high substrate concentration (30-40% dry matter (DM)) and high enzyme activity (750-2250 BE units (BEU)/g sample). Starches from various botanical sources, representing a broad range of properties, were used as substrates. The effects of the used conditions on the BE-reaction were evaluated by characterization of the obtained products and were correlated to properties of the starch substrates.
It was found that the obtained products differed depending on both the conditions used and the properties of the starch. Products of starch from certain origins completely lost their granular structure during the enzyme treatment while others were able to largely retain granular structure. All products were, though, modified with regard to chain length distribution, which indicated an increased degree of branching. Also all products showed a decrease in molecular size. The products, which remained granular, were found to show a high degree of crystallinity and had maintained a large fraction of apparent amylose (AM). This indicated that AM and crystalline AP had somehow become protected from BE during the treatment. It was demonstrated that the granular state of the product was determined by the hydration state of the starch substrate, and granular products were only obtained at low hydration of the starch. Hence, limiting hydration and gelatinization by using low-phosphate starch and high substrate oncentration was required for obtaining these products. Also high BE activity was a requirement and could partly compensate for increased starch hydration caused by either lower substrate concentration or higher phosphate content. Based on this information, a hypothetic model accounting for the observed effects was proposed. According to this model, granular stabilization ccurred as an effect of a high degree of intermolecular branching connecting larger chain segments. In case of high BE activity this transfer happened prior to hydration and phase separation. The starch substrates thereby became locked in their granular structure and blocked furher access of BE.
Transferase-based modification of starch has today almost exclusively been conducted on gelatinized starch. This study provides a new concept for transferase-based modification of starches in granular state.
is considered a clean and energy saving technology. This thesis aimed to investigate the effect of using reaction conditions, simulating an industrial process, for enzymatic treatment of starch with branching enzyme (BE) from Rhodothermus obamensis. Thus treatements were conducted at 70°C using very high substrate concentration (30-40% dry matter (DM)) and high enzyme activity (750-2250 BE units (BEU)/g sample). Starches from various botanical sources, representing a broad range of properties, were used as substrates. The effects of the used conditions on the BE-reaction were evaluated by characterization of the obtained products and were correlated to properties of the starch substrates.
It was found that the obtained products differed depending on both the conditions used and the properties of the starch. Products of starch from certain origins completely lost their granular structure during the enzyme treatment while others were able to largely retain granular structure. All products were, though, modified with regard to chain length distribution, which indicated an increased degree of branching. Also all products showed a decrease in molecular size. The products, which remained granular, were found to show a high degree of crystallinity and had maintained a large fraction of apparent amylose (AM). This indicated that AM and crystalline AP had somehow become protected from BE during the treatment. It was demonstrated that the granular state of the product was determined by the hydration state of the starch substrate, and granular products were only obtained at low hydration of the starch. Hence, limiting hydration and gelatinization by using low-phosphate starch and high substrate oncentration was required for obtaining these products. Also high BE activity was a requirement and could partly compensate for increased starch hydration caused by either lower substrate concentration or higher phosphate content. Based on this information, a hypothetic model accounting for the observed effects was proposed. According to this model, granular stabilization ccurred as an effect of a high degree of intermolecular branching connecting larger chain segments. In case of high BE activity this transfer happened prior to hydration and phase separation. The starch substrates thereby became locked in their granular structure and blocked furher access of BE.
Transferase-based modification of starch has today almost exclusively been conducted on gelatinized starch. This study provides a new concept for transferase-based modification of starches in granular state.
| Original language | English |
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| Publisher | Department of Plant and Environmental Sciences, Faculty of Science, University of Copenhagen |
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| Number of pages | 135 |
| Publication status | Published - 2013 |