Physicochemical and textural characteristics and volatile compounds of semihard goat cheese as affected by starter cultures

Today, cheese is valued because of its high nutritional value and unique characteristics. Improving the texture and flavor of cheese by selecting suitable starter cultures is an important way to promote the development of cheese industry. The effect of starter cultures on the physicochemical and textural properties and volatile compounds during the ripening of semihard goat cheese were investigated in this work. Different starter cultures—mesophilic (M) and thermophilic starters (T), Lactobacillus plantarum ssp. plantarum ATCC 14917 (Lp), a mix of the M and T starters (M1), and mix of the M, T, and Lp starters (M2)—were used in the production of the goat cheeses. Volatile compounds were determined by a solid-phase microextraction/gas chromatography-mass spectrometric (SPME/GC-MS) method. The results showed that the moisture content of cheeses produced with the 5 kinds of starter cultures decreased after maturation, whereas ash content increased. The pH values of goat cheeses decreased first and then increased during maturity, and the pH value of M2 cheese was the lowest among the cheeses. The hardness and chewiness of the cheeses increased with increasing maturity, whereas cohesiveness, springiness, and resilience showed the opposite tendency. The 60-d-old cheese made with Lp had the highest chewiness, cohesiveness, springiness, and resilience, whereas the 60-d-old cheese made with M2 had the highest hardness. A total of 53 volatile components were identified by SPME/GC-MS, and carboxylic acids, alcohols, ketones, and esters were the 4 major contributors to the characteristic flavors of the cheeses. Volatile components and their contents differed greatly among the produced cheeses. The M2 cheese contained the highest relative content of the main volatile compounds (90.10%), especially butanoic acid and acetoin. Through a comprehensive comparison of the results, we concluded that M2 cheese had a dense texture and milky flavor, and M2 is a potential starter culture candidate for the production of goat cheese.     

韧性胶乳水泥浆在试验评价及其水平井固井作业中的应用

长水平段大位移水平井钻井是页岩气开采和提高开采效益的关键,钻进中,因为井浅、水平段长,固井质量往往难以保证。为提高页岩气水平井固井质量,研究开发了一套韧性胶乳水泥浆体系,室内对该水泥浆体系的性能进行了评价研究。结果表明,该水泥浆不仅具有良好的稳定性和自由水控制能力,同时具有快速的静胶凝强度发展速度和较强的流体阻隔能力,表现出较强的防窜效果;另外,通过模拟射孔试验发现,该水泥浆具有较高的抗冲击韧性,这对于保证射孔压裂完井下水泥环的完整性具有重要的意义。该水泥浆体系在建页2井生产套管长水平井固井中进行了应用,封固水平段长达1050m,48h变密度测井检测结果显示,建页2井页岩气长水平段的固井质量为全优质。     

新疆1949—2019年洪水灾害调查与特征分析

洪水灾害是新疆最严重的自然灾害,调查并研究洪水灾害的特征与规律对防洪减灾有重要意义。本文通过调查新疆洪水灾害相关的年鉴、公报、简报及文献资料等,统计分析了新疆1949-2019年近71年主要洪水灾害,给出了洪水灾害的时间及地域分布规律、灾害类型特征。对洪水灾害造成的直接经济损失及占国民生产总值的比例进行了统计分析,并重点对2006年以后的受灾人口与死亡人口、直接经济损失进行了分析。结果表明,虽然洪水频次与洪灾直接经济损失有增加趋势,但因灾死亡人口及直接经济损失所占GDP比重不断减少,并趋于平稳,防洪减灾效益明显。本文研究为新疆洪水灾害风险评估、防御应对与决策支持提供了借鉴参考。     

黏性液体三次雾化的试验研究

对黏性液体进行了超音速二次雾化和基于撞击流技术的三次雾化试验,并对三次雾化的影响因素进行了分析。分析结果表明：随着进气压力和压缩空气流量增大,油雾颗粒粒径变小;随着进气压力增大,油雾浓度逐渐变小;随着韦伯数增大,粒径变化率变小。当韦伯数小于5．376时,粒径变化率大于零;当韦伯数大于5．376时,粒径变化率小于零;当韦伯数为22．81时,油雾颗粒粒径变化率绝对值最大,且喷嘴喉口直径为影响粒径变化率大小的主要因素。     

TK-208无线通信手持机功能参数及信道频率编程技术

针对无线通信组网常用的手持机TK-208VHF在使用维修中经常出现需重新编程问题，总结出了一套功能参数预置方法及信道编程技术，并提出了在编程操作实践中需注意的问题。     

The Effect of Precipitation Characteristics on Hardening Behavior in Cu–Cr–Sn Alloy with Sn Variation

Powder Metallurgy and Metal Ceramics - The influence of minor solute additions of Sn on hardening behavior and microstructure evolution of the Cu–Cr–Sn alloys has been investigated with...     

建设有特色的国家工科物理教学基地

以转变教育思想为先导 ,对工科物理教学提出“科学素质教育和基础知识教育并举”的新观念 ,并以此指导基地的教改实践 ;大幅更新教学内容 ,构建现代化的大学物理教学体系 ;突出培养学生的实践能力 ,形成多层次、开放式的实验教学模式 ;全面应用信息技术 ,改革传统的教学手段和教学方式 ;重视营造学术氛围 ,打造一流的知识创新平台。通过整体优化改革 ,初步形成了中南大学国家工科物理教学基地的建设模式与特色。     

去皮鲜甘蔗的护色保鲜包装研究

通过不同浓度的盐、糖、酸溶液和不同的包装材料对去皮甘蔗进行保鲜处理,常温下贮藏,观察不同处理方法对去皮甘蔗腐坏变红的影响,再根据单因素实验和正交试验来确定最佳保鲜方案。实验结果表明:当盐溶液的质量分数为0.4%,糖溶液的质量分数为0.3%,酸溶液的质量分数为0.1%,包装材料为PP/PE或PVDC/PE时,对去皮鲜甘蔗进行保鲜处理的效果相对最好。     

Active Packaging Films from Ethylene Vinyl Alcohol Copolymer and Clove Essential Oil as Shelf Life Extenders for Grass Carp Slice

Active packaging provides a way to prevent the food putrefaction effectively . Various studies provide information on the actual preservation effect of active packaging or the migration of active agents from active films into various food stimulants separately. However, there is little related data available regarding the combined analysis of release and preservation effect. In this work, we examined the properties of active food packaging films successfully produced by extrusion of ethylene vinyl alcohol copolymer (EVOH) films with clove essential oil (C). The characterization of mechanical, thermal and barrier properties of the packaging polymers film showed that the addition of clove essential oil did not decrease their properties and C as plasticizer improved process fluidity of EVOH resin. The release of C from film to various food stimulants was measured by using HPLC, and Fickian diffusion models were used to fit the data with appropriate equation. The effects of E/C (ethylene vinyl alcohol copolymer/clove essential oil) films on quality assessment of Grass Carp slice based on sensory analysis and biochemical indices during refrigerated storage (4 ± 1°C) were examined over the period of 10 days. Total volatile basic nitrogen (TVB‐N), total viable counts, pH, TBA, water holding capacity (WHC) and texture properties were evaluated. The results indicated that the active film containing 3% clove essential oil had different release parameters in four food stimulants and it could effectively maintain the fish freshness and extend the shelf life to 7–8 days during cold storage compared with control group, which was only 4 days. Copyright © 2016 John Wiley & Sons, Ltd.     

Sliding Mode Observer Controller Design for a Two Dimensional Aeroelastic System with Gust Load

The aim of this paper is to develop state estimation and sliding mode control schemes for the vibration suppression of an underactuated wing aeroelastic system in the presence of a gust load disturbance. Ignoring structural elastic deformation and using the concentrated elastic system (spring) to simulate the overall elastic deformation, this aeroelastic model consists of a straight wing and spring system, describing flap and pitch freedoms. The corresponding dynamic motion equation is established using the Lagrange method, and the gust is modeled as a typical “1‐cosine” gust. The aerodynamic lift and moment on the wing are computed by strip theory. The open loop system exhibits the limit cycle oscillations (LCOs) at a certain freestream velocity. The objective is to design a control system for suppressing the LCOs. For the purpose of control, a single trailing‐edge control surface is used. It is assumed that only the pitch angle is measured and the remaining state variables needed for full state feedback are estimated by the designed observer. Then an integral sliding surface is put forward on the estimation space; a new continuous reaching law is proposed to reduce the chattering phenomena. The finite‐time reachability of the predesigned sliding surface is proved and guaranteed by the designed sliding mode control law. The sufficient condition for the asymptotic stability of the closed‐loop system composed of the sliding mode dynamics and the error dynamical system is derived in terms of linear matrix inequality (LMI). The effectiveness of the proposed strategy is finally demonstrated by simulation results.