Improving saccharification process by pre-swelling of normal maize starch granules for production of sugar and fermented chemicals

Doctor of PhilosophyDepartment of Grain Science and IndustryYong Cheng ShiPartial swelling of granules above the gelatinization temperature was investigated as a strategy to enhance the enzymatic hydrolysis of normal maize starch to glucose. Native and partially swollen starches were hydrolyzed by a granular starch hydrolyzing enzyme (GSHE). After preheated at 70 °C for 30 min, enzyme kinetics study showed a 54% reduction in the Michaelis-Menten constant value (Km), suggesting that preheating increased the affinity of GSHE for the starch granules. Moreover, 94.8% of starch (2% in H₂O, w/w) was converted to glucose after a 24 h saccharification process. This relatively low-temperature process reduced the energy required to completely destroy the starch granules. Preheating at 70 °C, which resulted in partial swelling of starch granules, induced a greater degradation of large molecules, enzymatic erosion of crystallinity and granular structure. In addition, the enzyme resistant fraction could be converted to glucose after cooking. A full conversion of normal maize starch to glucose by GSHE could be achieved. In the saccharification process with a high maize starch concentration (30% in H₂O, w/w), partial swelling starch granules would result in viscosity build-up problem. To overcome that, we used an [alpha]-amylase during heat pretreatment. The viscosity decreased greatly from 2.85×10^6 cP to 12 cP, which was preferable in later saccharification. The heat treatment with [alpha]-amylase at 70 °C partially destroyed crystalline lamellae and maize starch granule structure. By combining [alpha]-amylase in the preheating process and saccharification by GSHE, a two-step enzymatic hydrolysis process was performed. Starch granules were pre-hydrolyzed by [alpha]-amylase at 70 °C for 6 h and followed the addition of GSHE and incubation at 62 °C for 72 h. The two-step enzymatic hydrolysis was more effective than the single hydrolysis at 62 °C and increased the conversion by 25%. More than 93% of total starch could be converted to glucose and the enzyme resistant residue could be further hydrolyzed by conventional cooking method. The two-step enzymatic hydrolysis offered great advantages in the production of glucose syrups and other fermentable chemicals. To further investigate the potential utilization of partially swollen maize starch with GSHE in the production of fermented chemicals, productions of citric acid and ethanol by low-temperature fermentations were studied in both lab-scale and large pilot scale. In the production of citric acid, maize starch (18% in H₂O, w/w) was fermented at 37 °C for 67 h. The initial substrate concentration (18%) was 2% greater than the starch concentration used in the conventional cooking process. The yield of the citric acid was 88%, which was 3% higher than that of conventional cooking production. For ethanol production, maize flour (30% in H₂O, w/w) was fermented at 32 °C for 72 h. The ethanol yield was 92.6%, which was 3.5% higher than that of ethanol produced by the cooking method

A self-supported, flexible, binder-free pseudo-supercapacitor electrode material with high capacitance and cycling stability from hollow, capsular polypyrrole fibers

Flexible energy devices with high performance and long-term stability are highly promising for applications in portable electronics, but remain challenging to develop. As an electrode material for pseudo-supercapacitors, conducting polymers typically show higher energy storage ability over carbon materials and larger conductivity than transition-metal oxides. However, conducting polymer-based supercapacitors often have poor cycling stability, attributable to the structural rupture caused by the large volume contrast between doping and de-doping states, which has been the main obstacle to their practical applications. Herein, we report a simple method to prepare a flexible, binder-free, self-supported polypyrrole (PPy) supercapacitor electrode with high cycling stability through using novel, hollow PPy nanofibers with porous capsular walls as a film-forming material. The unique fiber structure and capsular walls provide the PPy film with enough free-space to adapt to volume variation during doping/de-doping, leading to super-high cycling stability (capacitance retention > 90% after 11000 charge-discharge cycles at a high current density of 10 A g-1) and high rate capability (capacitance retention ∼ 82.1% at a current density in the range of 0.25-10 A g-1)

The future adoption of community shared solar: An unlabeled choice experiment in Guangdong, China

Community shared solar (CSS) program has great potentials in contributing to the complete decarbonization of the power sectors worldwide. Few research have focused on its potential diffusion from the user perspective. This paper fills the gap by conducting a survey-based unlabeled choice experiment in the Guangdong Province, China to investigate the determinants of potential users' willingness to participate in CSS programs. We analyzed the survey data using a random parameter logit model. Our results show that users are more likely to participate in CSS programs with lower upfront payment, trialability, shorter payback period, a public utility as provider and larger impact on climate change mitigation. However, they are likely to accept longer payback period in CSS programs with higher participation rate because of the potential benefit from interpersonal communication. Users' previous knowledge of CSS programs and income will also increase their willingness to participate in CSS programs with higher upfront payment. Our results provide important implications for designing policies and business models to promote the distributive renewable energy in China

Perspectives and challenges of applying the water-food-energy nexus approach to lake eutrophication modelling

Embargo until August 4, 2023The water-food-energy (WFE) nexus is about balancing competing interests to secure the sustainability of services provided by interconnected sectors. Ignoring the interconnections could cause serious consequences. For example, eutrophication caused by overemphasizing on food production maximization could threaten water security. Worldwide eutrophication intensification is one of the most important causes of the lake water quality deteriorations. Water quality models are usually important decision making tools for policy makers. This study attempts to explore the possibilities of applying the WFE nexus concept into water quality models. We propose the most significant challenge is lack of a common modelling framework to streamline connections between up- and downstream models. As the most important water quality issue, eutrophication modeling should increase its visibility in the United Nations Sustainable Develop Goals.acceptedVersio