Browsing by Author "Xu, Yi"
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Xu, Yi (2023)The literature review detailed the theoretical background for this study, identified the possibility about development of faba bean protein stabilized emulsion for food products and studied the effect of increased oil addition on the structure of emulsions. The practical work was divided into three parts emulsion analysis, emulsion gel analysis and sensory evaluation. Various research methods were applie d to support this study, including droplet size distribution , droplet charge ζ potential), texture evaluation, and rheological analysis. This study showed that oil addition increased emulsion droplet size, as well as the absolute value of ζ potential . Emulsifying activity index (EAI) and emulsion stability index (ESI) decreased with increasing oil concentration. F aba protein stabilized emulsions were better stabilized by oil addition , compared with those without oil additi on . From texture analysis of gel properties, firmness improved with increasing oil concentrations (0% 30%). In addition, rheolog ical analysis for faba yogurt samples showed that increasing oil concentrations improved the viscosity of the faba yogurt samples. T he results also illustrated that increasing oil concentrations led to increased deformation meaning the emulsion gels were more easily destroyed with increasing oil concentrations (0 30%). Oil addition resulted in higher whiteness when compared with samples without oil. Sensory evaluation by a professional panel for faba yogurt samples indicated that samples with 20% oil concentration w ere the most preferred and had the highest overall quality .
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Xu, Yi (2020)Tiivistelmä/Referat – Abstract Global warming and its coinstantaneous disturbance are intensively influencing the northern area. As a major natural disturbance in northern forest, winter moth (Operophtera brumata) and autumn moth (Epirrita autumnata) has caused wide defoliation in the mountain birch forest (Betula pubescens ssp. czerepanovii) at the subarctic area, exerting great impact on soil C stocks. Increasing temperature has promoted the vegetation expansion in the northern area and elevated the plant productivity, leading to higher C input to soil C stock. Litter decomposition may be accelerated by higher temperature, which decreases soil C storage. Moth herbivory usually increases the soil C stock in the short-term through litter and frass deposition, despite its aboveground suppression on photosynthesis. Belowground microbial community and composition shift would happen after moth outbreak, mediating the soil C turnover. However, the long-term effect of moth outbreak on soil C stock is still uncertain. This study investigated the influence of different tree status on soil C stock at subarctic mountain birch treeline forest, which went through severe moth outbreaks at 10 and 60 years ago. Living trees have observed with higher soil C stock than dead trees and treeless tundra, indicating the living tree may have a positive impact on soil C stock probably due to great aboveground photosynthesis. Living tree and its understory vegetation enhanced the soil respiration and ecosystem respiration, which would speed the C turnover, especially in the peak growing season. Dead trees were observed with slightly higher soil C stock than treeless tundra, both at 10 and 60 years’ perspectives. In contrast to direct C input provided by the living tree, the positive effect of dead tree on soil C stock is mainly due to the recalcitrant accumulation in the soil organic layer. Thus, soil C stock at the subarctic treeline after moth outbreak showed variations depending on the tree status, but overall remained as a C sink, which is good for mitigating the climate change. The mechanism behind the changes of soil C stock needs to be further investigated in future.
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