RESUMO
Due to the scarcity of yak milk in Tibetan areas, local herders primarily use traditional freezing methods for preservation. However, the extent of microbial contamination in raw yak milk during frozen storage and its impact on milk quality remains largely unexplored. This study analyzed the changes in bacterial populations and quality of raw yak milk stored at -18 °C for 6 months. The results indicated that, compared to fresh milk, the freshness of yak milk showed no significant change after 2 months of frozen storage (P > 0.05). After 4 months, the bacterial diversity of flora in yak milk increased significantly, with Pseudomonas and Acinetobacter emerging as the dominant psychrophilic bacteria. Correspondingly, the expression of metabolic pathways related to quality deterioration increased, with a significant increase in physicochemical indicators such as acidity, proteolysis degree, acid value and fat oxidation degree (P < 0.05). Extending the frozen storage to 6 months resulted in a slight but no significant decrease in bacterial diversity, with no significant difference in quality deterioration compared to the 4-month group (P > 0.05). Correlation analysis further revealed that Acinetobacter and Psychrobacter were significantly positively correlated with quality deterioration of frozen milk (P < 0.05). In summary, when frozen for more than 4 months, raw yak milk exhibited the highest bacterial diversity and predicted the most abundant metabolic pathways, with dominant psychrophilic bacteria massive proliferation leading to a decline in quality and safety.
RESUMO
In this study, the effects of freezing yak milk at -20 °C and -40 °C for 30, 90 and 180 days on the fermentation characteristics and storage quality of the corresponding yogurt were discussed. The results showed that, compared with that of yogurt made from fresh yak milk, the lactic acid bacteria (LAB) growth and acid production rate of the yogurt in the -20 °C group decreased at 90 d. The water-holding capacity, viscosity and hardness decreased during storage, and a sour taste was prominent, while no significant changes were observed in the -40 °C group. At 180 d of freezing, the post-acidification of the yogurt in the -20 °C and -40 °C groups increased after 21 d of storage. Compared with the -40 °C group, the -20 °C group showed a significant decrease in LAB counts, a decrease in pH value to 3.63-3.80 and poor texture and sensory quality.
RESUMO
The technology for nutrient resource utilization of agricultural residues is crucial to realizing a circular agricultural economy. The assessment model provides essential support to optimize nutrient recovery and treatment technologies. We specifically summarized research progress in the assessment framework of agricultural residues nutrient recycling technology, assessment models and evaluation indicators, data sources of models and their uncertainty analysis, and the application scale of models. We found that process mathematical models and industrial eco-logy models are the common nutrient flow assessment models. Process mathematical and industrial ecology models differed greatly in terms of the reliability of assessment results and the simulation scale. The former mainly focused at laboratory or pilot scale, with higher accuracy. The latter could achieve multi-scale simulation from microscopic to macroscopic and had higher uncertainty, due to the way its data were obtained. Finally, we provided an outlook on the research on the assessment model of agricultural residues nutrient resource utilisation technology. In order to achieve accurate assessment of waste resource utilisation technology in agricultural production systems at the regional scale, a reliable model framework and database should be established by combining process mathematical models with industrial ecology models. Meanwhile, we should carry out research on model expansion at the geographical scales of factory scale, farm scale, village scale, township scale, and regional scale.
Assuntos
Agricultura , Nutrientes , Geografia , Reciclagem , Reprodutibilidade dos Testes , TecnologiaRESUMO
In the propagation phase of a dielectric metasurface, there are two important problems. Firstly, the range of transmittance of the nanopillars for a building metasurface is usually between 60% and 100%, which reduces the metasurface's overall transmittance and affects the uniformity of the transmitted light. Secondly, the realistic phase provided by the nanopillar cannot be matched very well with the theoretical phase at each lattice location.The phase difference (between a realistic phase and theoretical phase) may reach tens of degrees. Here, we propose an interesting method to solve these problems. With this new method, a metalens is designed in this paper. The nanopillars for building the metalens have transmittance over 0.95, which increases the metalens transmittance and improves the light uniformity. In addition, with the new method, the phase differences of all elements in the metalens can also be reduced to be below 0.05°, decreasing the metalens spherical aberration dramatically. This method not only helps us to optimize the metalens but also provides a useful way for designing high-quality metasurfaces.
RESUMO
Understanding the process of nitrogen flow, emission, and utilization in rural systems is of great importance to reduce pollutant emissions caused by agricultural activities and to promote the sustainable utilization of nutrient resources. Based on the NUFER (nutrient flow in food chain, environment and resources use) model and nitrogen footprint approach, we proposed a nitrogen accounting framework for municipal-scale rural systems, and conducted a quantitative and time series-based comparative study on nitrogen flow, recycling, and footprint from the perspective of three subsystems, namely planting, animal husbandry, and rural human settlement in Shenyang from 1998 to 2018. The results showed that: 1) nitrogen utilization rates of the planting subsystem, animal husbandry subsystem, and rural human settlement subsystem were 36.1%, 59.7%, and 70.1%, respectively in 2018, with a growth rate of 15.9%, 9.1%, and 0.7% respectively compared to 1998; 2) The total polluted nitrogen footprint in Shenyang grew rapidly from 1998 to 2014, but declined from 2014 to 2018. In 2018, the total footprint of nitrogen pollution was 123.5 Gg, increasing by 21.6% compared with 1998; 3) In 2018, the unused nitrogen in the planting subsystem, animal husbandry subsystem, and rural human settlement subsystem were 129.5, 62.2, and 8.7 Gg, respectively, which were equivalent to 420.4, 202.1, and 8.7 Gg of nutrient resources from nitrogen fertilizer, respectively. In general, the nitrogen use efficiency of rural system increased gradually from the production end to the consumption end, but the temporal and spatial variation of nitrogen in rural systems need further studies.