两株小球藻培养基的优化及其产EPA性能的研究

采用L18(37)正交法优化小球藻C95和小球藻C97的生长培养基,经15 L规模培养并收获小球藻;碱性乙醇法萃取游离脂肪酸,再经脲素包埋提取多不饱和脂肪酸,并用气相色谱检测二十碳五烯酸(eicosapentaenoic acid,EPA)的含量。研究结果表明:小球藻C95最优培养基(微量元素母液0.8 m L/L,维生素母液2.4 mL/L,NaH2PO4·2H2O6.0 g/L,Na2SiO3·9H2O 9.0 g/L,NaNO360.0 g/L,FeC6H5O7·5H2O 3.0 g/L);小球藻C97最优培养基(微量元素母液1.6 m L/L,维生素母液2.4 m L/L,NaH2PO4·2H2O 4.0 g/L,Na2SiO3·9H2O 11.0 g/L,NaNO380.0 g/L,FeC6H5O7·5H2O 3.0 g/L);小球藻C95和小球藻C97对数末期(分别是第4天和第5天)达到的细胞密度分别为9.53×10^7个/mL和8.91×10^7个/mL,EPA含量分别占总脂肪酸的30.2%和29.5%,小球藻C95的EPA含量要高于小球藻C97。     

加水温度和蒸制时间对莜麦面面条水分状态和质构特性的影响

本文探讨加水温度和蒸制时间对莜麦面面条水分状态和质构特性的影响,旨在找到莜麦面面条制作工艺的关键参数。利用低场核磁共振技术和食品物性仪得到面条的水分状态和质构特性参数,研究了加水温度和蒸制时间对莜麦面面条水分状态和质构特性的影响。结果表明:加水温度和蒸制时间不改变面条中水分的主要存在形式,且水分的主要存在形式是弱结合水;提高加水温度使面条中深层结合水减少并向弱结合水和自由水方向迁移。加水温度由70 ℃升高到90 ℃的过程中,自由水含量先增加后减小,A₂₃由5.14%增加到11.2%后减小至10.4%。当蒸制时间从6 min增加到10 min时,A₂₂值和A₂₃值先升高后降低,A₂₂和A₂₃最大值分别为77.85%和10.67%,且对应的蒸制时间均为9 min。当加水温度从70 ℃升高到90 ℃时,硬度、黏着性、回复性逐渐减小,弹性、黏聚性逐渐增大,咀嚼性先减小后增大。当蒸制时间从6 min升高到10 min时,硬度、黏着性、咀嚼性、回复性先增大后减小,弹性、黏聚性先减小后增大。本研究结果为莜麦面面条的规模化生产提供一定的理论依据。     

枯草芽孢杆菌Prob1822复合抗热保护剂的研究

以枯草芽孢杆菌（Bacillus subtilis）Prob1822为研究对象,以热诱激处理（55 ℃热处理10 min）稳定期菌体存活率为评价指标,通过单因素试验和响应面法研究枯草芽孢杆菌Prob1822复合抗热保护剂的组成。结果表明,单一抗热保护剂以海藻糖、蔗糖及脱脂奶粉抗热保护效果较好;利用响应面法优化复合抗热保护剂配方为海藻糖9.0%、蔗糖5.0%和脱脂奶粉6.8%。在此最优条件下,菌体存活率为（95.24±0.84）%。糖类与蛋白质联用作为复合抗热保护剂比单一保护剂抗热保护效果更好,可减轻喷雾干燥对菌体亚细胞结构及生物大分子损伤,实现枯草芽孢杆菌的抗热保护。     

纤维素酶法提取胡芦巴甾体总皂苷工艺条件的优化

以甾体皂苷元的提取率为指标,应用L9(34)正交试验设计优化了胡芦巴种子中甾体皂苷的酶法提取工艺,实验结果表明,影响酶法提取甾体皂苷的主次因素为:酶用量>提取温度>固液比>水解时间。纤维素酶处理能显著提高甾体皂苷的提取率,加酶后甾体皂苷元提取率的平均值为83.6%,而未加酶的结果则为58.4%。酶法提取新工艺能显著提高胡芦巴甾体皂苷的提取率。     

Susceptibility of type 431 stainless steel to erosion-corrosion by vibratory cavitation in corrosive media

By utilizing the structural characteristics of type 431 stainless steel, which reveals a wide range of strength as well as corrosion resistance with tempering after quenching, its susceptibility to erosion-corrosion was investigated as a function of tempering temperature. Tests were conducted under a vibratory cavitation condition of 6.5 kHz with a double amplitude of 75 /gmm or of 20 kHz and 50 μm in cavitation media of 3% NaCl solution, 0.1N HCl and 0.1N H₂SO₄ at 22°C. As a preliminary investigation, the mechanical properties and corrosion resistance, in the same solutions as the cavitation media, were also determined as a function of the tempering temperature.The results indicated that the susceptibility to erosion-corrosion depended predominantly upon the mechanical strength but there were some exceptions for which attention should be paid to the corrosion resistance.     

Isolation and characterization of Listeria monocytogenes in Chinese food obtained from the central area of China

The objective of this study was to investigate the prevalence and characteristics of Listeria monocytogenes isolated from Chinese food, including frozen dumplings, flavored raw meat, roasted meat, braised meat, and a cold vegetable dish with sauce. A total of 900 food samples were collected from supermarkets, open-air markets, and delicatessens in three large cities in the central area of China to examine the presence of L. monocytogenes; 21 (2.3%) of the samples were positive for this pathogen. Among the different samples, braised meat showed the highest L. monocytogenes detection rate (4.4%). Samples obtained from delicatessens showed a much higher L. monocytogenes contamination rate (8.3%) than those from open-air markets (6.7%) or supermarkets (0%). Multilocus sequence typing (MLST) analysis indicated that the 21 bacterial isolates belonged to 12 ST subgroups. ST5 was the largest and contained 7 isolates (33.3%); it was followed by ST474, ST121 and ST9 (each containing 2 isolates [10.5%]). Antibiotic susceptibility analysis showed that the 21 L. monocytogenes isolates were thoroughly resistant to cefoxitin but highly susceptible to doxycycline and ciprofloxacin. The presence of 10 virulence genes was evaluated by PCR, which showed that inlA, inlC, inlJ, prfA, hlyA, and plcB were present in all isolates and that inlB, actA, plcA and iap were present in 71.4–90.5% of the isolates. This study provides a useful reference for risk assessment and control of L. monocytogenes contamination in Chinese food and for the treatment of clinical listeriosis.     

Antifungal activity mode of Aspergillus ochraceus by bacillomycin D and its inhibition of ochratoxin A (OTA) production in food samples

The inhibition effects of bacillomycin D on the growth of Aspergillus ochraceus and the production of ochratoxin A (OTA) in food samples were investigated. The mycelia growth and sporulation were completely inhibited by 30 μg/mL of bacillomycin D. Microscopic morphological changes such as the distortion of hyphae and the disruption of spores at 20 μg/mL of bacillomycin D were significantly observed. The use of bacillomycin D resulted in cell damage, nucleic acids and proteins divulge, and more production of reactive oxygen species (ROS), and all these factors actively contributed to the promotion of apoptosis of A. ochraceus. In addition, 90 μg/g of bacillomycin D completely inhibited the growth of A. ochraceus and the production of OTA in food samples. Our results suggested that bacillomycin D showed a significant antifungal activity against A. ochraceus that could be used as a potential natural antimicrobial to control food contamination and ensure food safety.     

Intelligent release of cinnamon oil from engineered proteoliposome via stimulation of Bacillus cereus protease

Inspired by the hydrolysis of casein by protease, a new approach to deliver antimicrobials against bacterial infections was developed in this study. As a natural antibacterial agent, cinnamon oil was encapsulated into engineered liposomes inlaid with casein. The average particle size of proteoliposomes was 615.0 nm and their entrapment efficiency (EE) was 40.0%. In this work, Bacillus cereus (B. cereus) was chosen as model bacterium. The controlled release of liposome-encapsulated cinnamon oil was realized via bacterial protease secreted from B. cereus. As a result, 99.99% of the bacteria could be efficiently inhibited in rice and wheat flour.