再生丝素蛋白溶液脱盐新工艺及其应用

为提高丝素蛋白溶液的脱盐效率,降低脱盐能耗,采用扩散渗析-电渗析集成膜分离技术对丝素蛋白溶液进行脱盐,并初步探索所得溶液的应用。研究了丝素蛋白溶液浓度质量分数和扩散渗析预脱盐率对脱盐效率和能耗的影响,同时将所得丝素蛋白溶液加入无水乙醇制备不溶性丝素蛋白粉,测定了产品氨基酸的组成并利用扫描电子显微镜对丝素蛋白粉进行表征。结果表明,最佳的脱盐技术参数为丝素蛋白溶液浓度为5%、扩散渗析预脱盐率为40%,在此工艺条件下脱盐时间缩短至9 h,能耗（动力能耗除外）为3.81×10-2 kw?h/L;产品中丝氨酸和甘氨酸含量接近50%,丝素蛋白粉末粒径较小且分布均匀。     

响应面法优化菊粉山药酸奶发酵工艺研究

以菊粉、山药粉和脱脂牛乳为原料,研究了菊粉山药酸奶的发酵工艺。以感官评分为评价指标,在单因素试验的基础上,采用响应面法进行分析,优化了菊粉、山药粉、木糖醇和发酵剂接种量,最终得出菊粉山药酸奶最佳生产工艺参数为：菊粉添加量0.8%、山药粉添加量0.5%、木糖醇添加量10%、发酵剂接种量0.5 U/L,以此条件发酵出的菊粉山药酸奶感官评分为92.66分,与预测值93.19分较一致。     

高效液相色谱-串联质谱法测定婴幼儿乳粉中甲醛残留

目的建立一种高效液相色谱-串联质谱法(high performance liquid chromatography-tandem mass spectrometry,HPLC-MS/MS)测定婴幼儿乳粉中甲醛残留量的分析方法。方法婴幼儿乳粉中的甲醛通过2,4-二硝基苯肼-乙酸钠缓冲溶液衍生得到甲醛-2,4-二硝基苯腙化合物,经过色谱柱BEH C_(18)(2.1 mm×50 mm,1.7μm)分离,以0.1%甲酸水溶液:乙腈=3:7(V:V)为流动相进行等度洗脱,柱温40℃,流速0.4 mL/min,多反应模式监测,外标法定量。结果甲醛衍生物在0.1~1000μg/L内线性关系良好且相关系数(r2)大于0.99。方法检出限和定量限分别为0.3μg/kg和1.0μg/kg,在2.5、5.0、10 mg/kg水平添加下婴幼儿乳粉中甲醛衍生物的平均加标回收率为87.9%~92.7%,相对标准偏差小于2.7%(n=6)。结论该方法具有快速简便、准确度好、灵敏度高等特点,适用于婴幼儿乳粉体系中甲醛的测定。     

高效液相色谱法测定牛奶和奶粉中的脱氢乙酸

目的建立测定牛奶和奶粉中的脱氢乙酸的高效液相色谱法(high performance liquid chromatography,HPLC)。方法样品用硫酸铜溶液和氢氧化钠溶液沉淀蛋白,其中的脱氢乙酸用10%的乙醇溶液进行提取,以甲醇+0.02 mol/L的乙酸铵溶液(用氨水调pH=8.0)作为流动相进行梯度洗脱,经Tech Mate C_(18)色谱柱(4.6 mm×250 mm,5μm)分离,在波长292 nm处进行检测。结果此方法的线性范围是1.003~100.336μg/mL,相关系数r=0.9999,以3倍信噪比计算检出限为0.1μg/m L。加标回收率为87.2%~95.3%,相对标准偏差(relative standard deviation,RSD)为1.5%~3.9%。结论此方法简便快速,准确可靠,灵敏度高,可用于牛奶和奶粉中脱氢乙酸的检测。     

微生物法与试剂盒法测定婴幼儿配方奶粉中叶酸含量的方法比较

目的比较GB 5413.16-2010与试剂盒法测定的配方乳粉质控样品的叶酸含量。方法通过国标和试剂盒法各检测10组质控样品,得到20个检测数据,从检出限和相对标准偏差(relative standard deviation,RSD)对2种方法进行方法学考察。结果国标法和试剂盒法叶酸测试结果平均值分别为231μg/100 g和228μg/100 g,RSD分别为8.36%和8.01%。2个方法测定结果的平均值偏差为1.16%,RSD值偏差为2.14%。结论国标法与试剂盒法测定婴幼儿配方奶粉中叶酸含量的结果相近,实验室可以根据自身实际情况选择适合的检测方法。     

超高性能混凝土结构的设计方法

鉴于中国有关活性粉末混凝土RPC制品方面的国家标准《活性粉末混凝土》（GB/T 31387—2015）已于2015年颁布执行,但目前尚无活性粉末混凝土结构设计规程,结合湖南省工程建设地方标准《活性粉末混凝土结构技术规程》（简称规程）的编制,对超高性能活性粉末混凝土结构的主要设计方法进行了讨论,并介绍了《规程》主要内容及若干设计考虑,通过分别引入钢纤维影响系数β_v,β_p,β_w,β_B,并基于可靠度分析得到了RPC构件抗剪承载力、抗冲切承载力、裂缝宽度、刚度计算公式。研究结果表明:RPC轴心抗压强度及轴心抗拉初裂强度标准值分别为对应立方体抗压强度的0.7倍及0.047倍;轴心抗拉强度与纤维体积掺量、纤维形状参数相关,钢纤维对轴心抗拉强度的影响系数为0.15;RPC100~RPC180弹性模量取值在40.0~48.6 GPa之间;《规程》偏安全地不考虑受拉区活性粉末混凝土抗拉作用对抗弯承载能力的贡献。     

Qualitative and quantitative identification of adulteration of milk powder using DNA extracted with a novel method

The extraction of high-quality DNA from processed dairy products is often the crucial step in an authentication process by PCR-based methods. In this study, we optimized a novel DNA extraction method for milk powder and used the extracted DNA for identification of milk powder based on PCR analysis. The DNA quality was assessed by amplifying target sequences from mitochondrial genes, as well as by monitoring the yield, purity, and integrity of the extracted DNA. In addition, a laboratory adulteration model of milk powder was detected by PCR-based methods (PCR and real-time PCR) using primers targeting the mitochondrial 12S rRNA gene. Results showed that a sufficient amount and quality of DNA could be isolated from milk powder with this method. Both PCR and real-time PCR detection of cow milk compositions in goat milk powder further confirmed the DNA extracted with this extraction method could be widely used in addressing milk powder adulterant by a PCR-based method.     

Effects of heating on the secondary structure of proteins in milk powders using mid-infrared spectroscopy

Milk powder is an important source of protein for adults and children. Protein is very sensitive to heat, which may influence people’s usage of nutrients in milk powder. In this study, we describe the temperature-induced secondary structure of protein in milk powders. In this study, whole milk powder containing 24% protein and infant formula containing 11% protein were heated from 25 to 100°C. Attenuated total reflectance (ATR) spectra in the mid-infrared range 400–4,000 cm^?1 were used to evaluate the heat effect on the secondary structure of protein in these 2 milk powders. The spectral changes as a function of temperature were maintained by difference spectra, second-derivative spectra and Gauss curve-fitted spectra. The secondary structures of protein in the whole milk powder began to change at 70°C and in the infant formula at 50°C. The β-sheet and β-turn structures in the whole milk powder both decreased in the range of 70 to 85°C, whereas α-helix structures increased. The loss of β-sheet and β-turn may contribute to the formation of α-helix in the whole milk powder. In infant formula powder, the β-sheet structure showed a decrease and then increase, whereas the β-turn structure showed an increase and then decrease in the range of 50 to 75°C, and no change was found for α-helix structures. This implies that heating may induce the transformation from β-sheet to β-turn. Overall, whole milk powder had better temperature stability than infant formula powder, probably because of the lower content of lipid in the former than in the latter. These results help us understand the thermal stability of protein in milk powder.     

Manufacture of dry‐ and brine‐salted soft camel cheeses for the camel dairy industry

Two experiments were conducted in a camel cheese study to (i) compare camel cheese to bovine cheese made from bovine milk standardised to simulate camel milk, and (ii) describe the technology for manufacture of dry (SCC‐D) and brine‐salted soft camel cheese (SCC‐B). Comparable cheese yield (camel: 7.4 ± 0.15, cow: 7.3 ± 0.55 kg/100 kg of milk) and levels of dry matter loss in whey were observed. Clotting time was 234 s for both cheeses which were made using thermophillic starters. Cheese yield was 9.31 ± 0.64 kg/100 kg with 425.6 ± 38.2 g/kg cheese dry matter for SCC‐D and 8.22 ± 0.90 kg/100 kg with 469 ± 73.8 g/kg dry matter for SCC‐B.