A rapid chemical spot test for the detection of lactic acid as an indicator of microbial spoilage in preserved foods

A ckland , M.R. & R eeder , J.E. 1984. A rapid chemical spot test for the detection of lactic acid as an indicator of microbial spoilage in preserved foods. Journal of Applied Bacteriology 56 , 415–419.
A rapid method for the detection of lactic acid in preserved foods has been developed, based upon a chemical spot test which does not require solvent extraction or derivatisation of the lactic acid in the sample. The test can be completed within 5 min and was shown to confirm microbial spoilage detected by cultural techniques in a range of preserved foods. In addition the test was able to indicate microbial spoilage in samples where cultural techniques failed because the spoilage organisms were dead. The test may not be appropriate for products which have a naturally high lactic acid content.     

A decision support system for prediction of microbial spoilage in foods

Summary A method is developed to combine qualitative and quantitative information for the prediction of growth of microorganisms in foods. pH, water activity, temperature and oxygen availability of foods are coupled to growth characteristics of microorganisms. For that purpose, a database with characteristics of foods and a database of kinetic parameters of microorganisms are built. The first database has a tree structure, based on physical similarity of food products. This structure makes it possible to estimate information about a food product which is not listed by comparison with similar products at the same level of the tree or the level above. A method is developed to make an estimation of the microbial growth kinetics on the basis of models. This is done by introducing a growth factor, which can be calculated on the basis of readily available data from literature. Finally, qualitative knowledge is added. Since any bit of information can be changed, the system will give better predictions when more and more accurate information is added.     

A simple test for use in experiments on the occurrence and the prevention of microbial lipolytic spoilage in foods

Summary A simple model test for microbial lipolytic spoilage in foods has been developed, wherein both pH-changes in the aqueous phase and partition equilibria between lipid and aqueous phase is accounted for. The lipid phase is represented by hydrogenated coconut oil; the aqueous phase by a dextrose/yeast-extract/nutrient solution—containing 10% glycerol when testing esters of gallic acid—and the infection by 10⁴ cells/ml ofCandida lipolytica. Lipolysis is followed by titration of the free fatty acids formed. In this test butyl gallate, octyl gallate, dehydroacetic acid, sorbic acid and benzoic acid turned out to be more or less powerful inhibitors of lipolytic spoilage, whereas dodecyl gallate was found inactive.     

Development of an immunochromatographic strip test for the rapid detection of okadaic acid in shellfish sample

A rapid detection technology for okadaic acid (OA) in shellfish with one-step immunochromatographic assay using colloidal gold-labeled monoclonal antibody (Mab) probe was developed. OA is one of the diarrhetic shellfish toxins. Firstly, OA was conjugated to bovine serum albumin, and the conjugations as immunogen were injected into mice to raise the polyclonal antibody against OA. Hybridoma cells fused between spleen cells from immunized mouse and myeloma cells (Sp2/0) were prepared and injected into mice intraperitoneally at 1?×?10⁶?cells to produce monoclonal antibody in the ascitic fluid. With the monoclonal antibody against OA, the idc-ELISA assay was established to detect OA. The calibration curve for OA was linear over the concentration range of 0.31–50 ng mL^?1, and the detection limit for OA was 0.45 ng mL^?1. On that basis, paper test strips for detecting OA were prepared, and a fast detection method for okadaic acid using gold-labeled immunological assay was established. With the paper test strips, the detection limit was 6.25 ng mL^?1, and whole detection process for OA in shellfish samples needed only about 40 min.     

利用色谱法快速检测分析啤酒腐败菌的新方法

啤酒在生产过程中很容易染菌,而传统的用于啤酒腐败菌检测的方法耗时长,不能满足实际需求.由于腐败菌污染的啤酒通过色谱检测,相应组分(生物胺、有机酸和风味物质)都会有特征峰的产生,所以本研究通过建立无腐败菌污染的啤酒中各组分的标准色谱图,再使啤酒强制染菌,对其组分进行色谱分析,并与标准色谱图进行比较,从而找出各组分对应的特征峰.未来,此方法可用于实际生产线上快速检测啤酒是否发生微生物污染.     

Determining endotoxin content of ground beef by the Limulus amoebocyte lysate test as a rapid indicator of microbial quality.

Eighty-four samples of ground beef were placed into five half-log cycle groups based upon aerobic plate count (APC) results. Endotoxins were determined by the Limulus amoebocyte lysate test (LAL), and gram-negative viable counts were determined by a violet red bile agar overlay method. Ten samples with a log of APC of less than 5.50 had an APC mean of less than 5.24 and mean endotoxin content by the LAL of 51 ng/g. The 15 samples with APCs between a log of 5.50 and 5.99 had an APC mean of 5.79/g and an endotoxin mean of 103.8 ng/g. Twenty-eight samples had APCs between a log of 6.00 and 6.49 with a mean of 5.28/g and an endotoxin mean of 1106.4 ng/g. The 20 samples with APCs between a log of 6.50 and 7.00 had a mean of 6.77/g and an endotoxin mean of 5067.6 ng/g, while 11 samples had a log of APCs of greater than 7.00 with a mean of 7.53 and an endotoxin mean of 7,472 ng/g. Correlation of half-log cycle mean APC and violet red bile agar counts with mean endotoxin content were both highly significant, indicating that LAL-determined endotoxin content can be used to make a rapid approximation of viable plate counts. Because results can be obtained by LAL in 1 h, the finding of low levels of endotoxins can be taken to indicate low-count meat. The use of additional tests of microbial quality may be necessary when high endotoxin levels are found because the LAL detects both viable and nonviable cells.     

Determining endotoxin content of ground beef by the Limulus amoebocyte lysate test as a rapid indicator of microbial quality.

Eighty-four samples of ground beef were placed into five half-log cycle groups based upon aerobic plate count (APC) results. Endotoxins were determined by the Limulus amoebocyte lysate test (LAL), and gram-negative viable counts were determined by a violet red bile agar overlay method. Ten samples with a log of APC of less than 5.50 had an APC mean of less than 5.24 and mean endotoxin content by the LAL of 51 ng/g. The 15 samples with APCs between a log of 5.50 and 5.99 had an APC mean of 5.79/g and an endotoxin mean of 103.8 ng/g. Twenty-eight samples had APCs between a log of 6.00 and 6.49 with a mean of 5.28/g and an endotoxin mean of 1106.4 ng/g. The 20 samples with APCs between a log of 6.50 and 7.00 had a mean of 6.77/g and an endotoxin mean of 5067.6 ng/g, while 11 samples had a log of APCs of greater than 7.00 with a mean of 7.53 and an endotoxin mean of 7,472 ng/g. Correlation of half-log cycle mean APC and violet red bile agar counts with mean endotoxin content were both highly significant, indicating that LAL-determined endotoxin content can be used to make a rapid approximation of viable plate counts. Because results can be obtained by LAL in 1 h, the finding of low levels of endotoxins can be taken to indicate low-count meat. The use of additional tests of microbial quality may be necessary when high endotoxin levels are found because the LAL detects both viable and nonviable cells.     

Nucleic acid sequence based amplification for the rapid and sensitive detection of Salmonella enterica from foods

AIMS: The purpose of this study was to apply nucleic acid sequence-based amplification (NASBA) for the detection of Salmonella enterica serovar Enteritidis (S. Enteritidis) in representative foods. METHODS AND RESULTS: A previously reported primer and probe set based on mRNA sequences of the dnaK gene of Salmonella were used in this study. To test for possible food matrix inhibition and assay detection limits, 25-g samples of representative food commodities (fresh meats, poultry, fish, ready-to-eat salads and bakery products) were pre-enriched with and without S. Enteritidis inoculation. The NucliSens(R) Basic Kit, supplemented with enzymes from various other commercial sources, was used for RNA isolation, NASBA amplification and electrochemiluminescent (ECL) detection. The end point detection limit of the NASBA-ECL assay was equivalent to 101 CFU of S. Enteritidis per amplification reaction. When the assay was tested on noncontaminated foods, none of the food matrices produced false-positive results. Some of the food matrices inhibited the NASBA-ECL reaction unless the associated RNA was diluted 10-fold prior to amplification. CONCLUSIONS: For all food items tested, positive ECL signals were achieved after 18 h of pre-enrichment and subsequent NASBA at initial inoculum levels of 102 and 101 CFU per 25 g food sample. SIGNIFICANCE AND IMPACT OF THE STUDY: This rapid, semi-automated detection method has potential for use in the food, agricultural and public health sectors.     

A simple and rapid immunochromatographic test strip for detection of white spot syndrome virus (WSSV) of shrimp

A simple strip-test kit for white spot syndrome virus (WSSV) detection was developed using monoclonal antibody W29 (against the VP28 structural protein) conjugated with colloidal gold as the detector antibody. A rabbit anti-recombinant VP28F118 (rVP28) protein antibody in combination with a W28 monoclonal antibody was used as the capture complex at the test line (T), and goat anti-mouse IgG antibody (GAM) was used as the capture antibody at the control line (C). For evidence, the ready-to-use strip was kept in a plastic case and stored in a desiccated plastic bag. A sample volume of 100 microl gill homogenate in application buffer was applied to the sample chamber at one end of the strip and allowed to flow by chromatography through the nitrocellulose membrane to the other end. In test samples containing WSSV, the virus bound to the monoclonal antibody conjugated with colloidal gold and the resulting complex was captured by the antibodies at T to give a reddish-purple band. Any unbound monoclonal antibody conjugated with colloidal gold moved across T to be captured by the GAM and formed a band at C. In samples without WSSV or with WSSV below the limit of detection of the kit, only the band at C was seen. This method was 4 times less sensitive than dot blotting, and about 2 000 000 times less sensitive than 1-step PCR. Nonetheless, it could be used to screen individual shrimp or pooled shrimp samples to confirm high levels of WSSV infection or WSSV disease outbreaks. The beneficial features of this kit are that simple, convenient and quick results can be obtained without the requirement of sophisticated tools or special skills.     

Importance of lactic acid bacteria in Asian fermented foods

Lactic acid bacteria play important roles in various fermented foods in Asia. Besides being the main component in kimchi and other fermented foods, they are used to preserve edible food materials through fermentation of other raw-materials such as rice wine/beer, rice cakes, and fish by producing organic acids to control putrefactive microorganisms and pathogens. These bacteria also provide a selective environment favoring fermentative microorganisms and produce desirable flavors in various fermented foods. This paper discusses the role of lactic acid bacteria in various non-dairy fermented food products in Asia and their nutritional and physiological functions in the Asian diet.     

DNA-decorated nanoparticles as nanosensors for rapid detection of ascorbic acid

We designed an assay for rapid detection of ascorbic acid (AA) with a DNAzyme cleaving its DNA substrate in the presence of Cu(2+) and AA. The sensor consists of two DNA strands that form a complex between each other. The 5'-end of the DNAzyme binds the substrate DNA via Watson-Crick bonding and the 3'-end binds through formation of a DNA-triplex via Hoogsteen hydrogen bonding. The substrate DNA was prepared by two different methods. In the first case the nucleic acid was modified with fluorescein/dabcyl FRET pair across the cleavage site. In the second case the nucleic acid modified with fluorescein was immobilised on gold nanoparticles. DNAzyme contains a loop forming a complex with Cu(2+) ions. The oxidation of ascorbic acid (AA) with oxygen yields hydrogen peroxide. The latter interacts with Cu(2+) to give hydroxyl radicals. They break substrate DNA in close vicinity to the copper/DNA complex to separate fluorescein from gold nanoparticles leading to the increase in fluorescence intensity. Use of substrate DNA modified with the fluorescein/dabcyl couple allowed to measure AA concentration within 3 min with the detection limit of 2.5 μM. Employment of gold nanoparticles decorated with fluorescein-modified DNA allowed to improve the detection limit of AA quantification by two orders of magnitude due to enhanced cleavage of DNA catalysed by Au clusters. Fructose, sucrose, glucose, urea, and citric acid did not interfere with our assay even at concentration of 1mM. Good selectivity allowed us to apply our rapid and sensitive assays to detection of AA in vitamin C tablets, urine and orange juice.     

A rapid coagglutination test for the detection and serogrouping of Legionellae

The applicability of coagglutination for the rapid detection and serogrouping of Legionellae has been investigated. The coagglutination reaction is carried out with the aid of self-made preparations of protein A containing staphylococci, sensitized with specific antibodies against the antigens of L. pneumophila (serogroups I to 6), L. bozemanii and L. micdadei. Preliminary heating of Legionella suspensions at 100% C for 15 min was used to prevent cross coagglutination reactions and ensure greater safety of laboratory personnel during the performance of the test. The results obtained demonstrate a high specificity of coagglutination. With the aid of the coagglutination reactions it has been shown that L. pneumophila strains isolated in Bulgaria belong to serogroup I. The coagglutination method is characterized by its rapidity, simplicity and feasibility. It is a useful and convenient means for the rapid detection and serogrouping of Legionellae.