ESTABLISHMENT OF BASELINE DATA ON THE MICROBIOTA OF MEATS

The United States Department of Agriculture's Food Safety and Inspection Service has initiated the National Microbiological Baseline Data Collection Programs to determine the prevalence and levels of selected bacteria on meat and poultry slaughtered under federal inspection. This paper reviews the methodology and results of the first completed study on samples collected from steer and heifer carcasses. Potential applications for this type of testing are discussed.     

超声波辅助提取松籽油及其脂肪酸的检测

研究超声波功率、时间、料液比以及提取次数对松籽油提取率的影响,得出最佳提取条件为超声波功率为160W,超声波处理20min,料液比为1∶7,超声波处理4次.并通过气相色谱-质谱联用法测定其中皮诺敛酸(Pinolenic acid)的含量.     

乳酸菌营养饮料稳定性的研究

探讨了蛋白酶酶解牛乳蛋白对发酵型乳酸菌饮料稳定性的影响。研究表明,加入0.0015%的胰蛋白酶,在42℃下发酵6h的酸乳,制作的乳酸菌饮料多肽和游离氨基酸的含量较高;当控制酸度在60°T,乳化稳定剂的添加量为0.5%,糖10%时,乳酸菌饮料的稳定性最佳,同时风味也较好。     

INFLUENCE OF BACTERIA ON THE CARBONYL COMPOUNDS OF GROUND PORCINE MUSCLE

Quantitative data were obtained for total carbonyls, total monocarbonyls, methyl ketones, saturated aldehydes, 2-enals and 2,4dienals from fresh, reduced surface flora (Dip) and inoculated muscle samples incubated at the optimal growth temperature of the respective bacteria. Individual monocarbonyl compounds were identified by thin-layer and gas liquid chromatography. Micrococcus cryophilus, Pseudomonas fluorescens and Staphylococcus aureus decreased total carbonyls by 57, 18 and 43%, respectively, and total monocarbonyls by 53, 20 and 33%, respectively. Pediococcus cerevisiae increased the total carbonyl and total monocarbonyl content by 70 and 71%. Concentrations of carbonyls in the control samples were directly related to temperature of incubation. Methyl ketones, saturated aldehydes, 2-enals and 2,4dienals were decreased by M. cryophilus, Ps. fluorescens and S. aureus but each monocarbonyl class was increased by P. cerevisiae.     

基因工程技术在醋酸菌改良中的应用

醋酸发酵过程乙醇脱氢酶(ADH)、乙醛脱氢酶(ALDH)酶系起着重要作用,主要影响着醋酸菌的产酸速率和耐酸性,介绍了醋酸菌的耐热机制和耐酸机制.阐述了基因dnaKJ与groESL等基因克隆技术在耐高温醋酸菌构建上的应用,醋酸耐酸因子aarA、aatA以及ADH、ALDH、辅酶Q(PQQ)和不饱和脂肪酸、顺乌头酸酶等对酸度的耐受情况,通过过量表达上述影响因子提高醋酸菌的耐酸性.展望了在国家863等项目引导下研究机构和企业加强醋酸发酵的基础研究以便于构建高活性的醋酸菌.     

THE ACTION OF NISIN ON BEER SPOILAGE LACTIC ACID BACTERIA

Within one minute of adding nisin to suspensions of Lactobacilli clumping of cells was observed. This happened with all the strains assayed, irrespective of their sensitivity or resistance to nisin. There was, however, no evidence of cell lysis. Two different assays for cell viability were used to show that the vast majority of cells of sensitive strains were killed within one minute of contact with nisin. The time needed to kill all the cells depended on the concentrations of both nisin and cells. One strain was more resistant and only 50–60% of the cells died within one minute of nisin addition . Using an ATP-bioluminescence assay it was shown that the addition of nisin to both Lactobacilli and Pediococci caused a rapid fall in intracellular ATP levels, which was reflected in a simultaneous appearance of ATP in the extracellular medium. Actively growing cells lost ATP more rapidly than did those in stationary phase. The amount of intracellular ATP lost was affected both by the concentration of nisin used and the sensitivity of the bacteria. It appears that an initial effect of nisin is to make the cell membrane ‘leaky’ as happens with many antibiotics, yeast killer factors (zymocins), colicins, and other gram-positive bacteriocins .     

DISCUSSION OF THE BINDING QUALITY OF MINCED MEATS BASED ON THEIR RHEOLOGICAL PROPERTIES BEFORE AND AFTER HEATING

Abstract Raw fish meat and three muscle groupings of cockerel meat were analyzed for total nitrogen, myofibrillar and sarcoplasmic proteins, non-protein and residual nitrogen, fat, pH, moisture and hydration capacity. Stress relaxation measurements were made on both raw and heat coagulated samples. Tensile strength measurements were made on heat coagulated samples. Using breaking energy as an index of binding, myofibrillar protein content and hydration were tentatively related to binding quality. Equilibrium modulus values offered an indication of the presence of crosslinking after heating. The rheological behavior of fish meat could be explained by a seven element model and that of cockerel meat by a five element model before heating. An analysis is presented of the mathematical treatment of rheological measurements and their relationship to binding quality and chemical composition of the tested samples.