Microbiological spoilage of mayonnaise and salad dressings

Saccharomyces bailii was isolated from two-thirds of the spoiled mayonnaise and salad dressing samples examined. Most of the rest were spoiled by Lactobacillus fructivorans. However, one sample contained large numbers of both S. bailii and L. plantarum. Two of the spoiled samples also contained small numbers of bacilli. Bacillus subtilis, B. pumilis, B. polymyxa, B. megaterium, and B. licheniformis were found in one sample and B. subtilis and B. pumilis in another. Small numbers of B. subtilis and B. licheniformis were also present in one unspoiled sample. Several media were evaluated for the isolation of L. fructivorans. S. bailii and L. fructivorans vigorously fermented glucose. The concentration of glucose in the spoiled samples ranged from 0 to 38.5 g/kg and from 1.3 to 17.8 g/kg for the unspoiled samples.     

Molecular and physiological comparison of spoilage wine yeasts

Aims

Dekkera bruxellensis and Pichia guilliermondii are contaminating yeasts in wine due to the production of phenolic aromas. Although the degradation pathway of cinnamic acids, precursors of these phenolic compounds has been described in D. bruxellensis, no such pathway has been described in P. guilliermondii.

Methods and Results

A molecular and physiological characterization of 14 D. bruxellensis and 15 P. guilliermondii phenol‐producing strains was carried out. Both p‐coumarate decarboxylase (CD) and vinyl reductase (VR) activities, responsible for the production of volatile phenols, were quantified and the production of 4‐vinylphenol and 4‐ethylphenol were measured. All D. bruxellensis and some P. guilliermondii strains showed the two enzymatic activities, whilst 11 of the 15 strains of this latter species showed only CD activity and did not produce 4‐EP in the assay conditions. Furthermore, PCR products obtained with degenerated primers showed a low homology with the sequence of the gene for a phenyl acrylic acid decarboxylase activity described in Saccharomyces cerevisiae.

Conclusions

D. bruxellensis and P. guilliermondii may share a similar metabolic pathway for the degradation of cinnamic acids.

Significance and Impact of the Study

This is the first work that analyses the CD and VR activities in P. guilliermondii, and the results suggest that within this species, there are differences in the metabolization of cinnamic acids.     

Microbial spoilage of pre-cooked potato-topped pies

The ecological succession of bacteria which developed in pre-cooked potato-topped pies stored at two different temperatures was examined. Bacillus, Streptococcus and Staphylococcus-Micrococcus spp. were the predominant organisms isolated from freshly prepared pies and those stored at 4°C and 37°C. None of these groups of bacteria caused significant biodeterioration of pies held at 4°C, but all groups grew well in pies stored at 37°C and achieved counts of ca 10⁸/g of sample. Bacillus spp. were the first group to grow, followed by Streptococcus and Staphylococcus- Micrococcus spp. Growth which occurred at 37°C did so at the expense of glucose, lactate accumulated and the pH of pie components decreased. Amylase activity detected in all pie components during storage was associated with the growth of Bacillus spp. and probably supplemented glucose already present in pies, by hydrolytic cleavage of potato, flour or binder starches. Spoilage caused by growth and activity of the bacteria isolated was not associated with visual signs of bio-deterioration, nor production of 'off' odour usually associated with spoilage of meats. These results suggest that pre-cooked potato-topped pies held at inappropriate temperatures represent a potential public health risk.     

Microbial spoilage of pre-cooked potato-topped pies

The ecological succession of bacteria which developed in pre-cooked potato-topped pies stored at two different temperatures was examined. Bacillus, Streptococcus and Staphylococcus-Micrococcus spp. were the predominant organisms isolated from freshly prepared pies and those stored at 4 degrees and 37 degrees C. None of these groups of bacteria caused significant biodeterioration of pies held at 4 degrees C, but all groups grew well in pies stored at 37 degrees C and achieved counts of ca 10(8)/g of sample. Bacillus spp. were the first group to grow, followed by Streptococcus and Staphylococcus-Micrococcus spp. Growth which occurred at 37 degrees C did so at the expense of glucose, lactate accumulated and the pH of pie components decreased. Amylase activity detected in all pie components during storage was associated with the growth of Bacillus spp. and probably supplemented glucose already present in pies, by hydrolytic cleavage of potato, flour or binder starches. Spoilage caused by growth and activity of the bacteria isolated was not associated with visual signs of biodeterioration, nor production of 'off' odour usually associated with spoilage of meats. These results suggest that pre-cooked potato-topped pies held at inappropriate temperatures represent a potential public health risk.     

Bacterial spoilage of wine and approaches to minimize it

Bacteria are part of the natural microbial ecosystem of wine and play an important role in winemaking by reducing wine acidity and contributing to aroma and flavour. Conversely, they can cause numerous unwelcome wine spoilage problems, which reduce wine quality and value. Lactic acid bacteria, especially Oenococcus oeni, contribute positively to wine sensory characters, but other species, such as Lactobacillus sp. and Pediococcus sp can produce undesirable volatile compounds. Consequences of bacterial wine spoilage include mousy taint, bitterness, geranium notes, volatile acidity, oily and slimy-texture, and overt buttery characters. Management of wine spoilage bacteria can be as simple as manipulating wine acidity or adding sulfur dioxide. However, to control the more recalcitrant bacteria, several other technologies can be explored including pulsed electric fields, ultrahigh pressure, ultrasound or UV irradiation, and natural products, including bacteriocins and lysozyme.     

Microbial assessment and quality evaluation of ogi during spoilage

The changes during the fermentation of ogi, a cereal-based traditional lactic acid-fermented weaning food were studied up to the spoilage stage. Ogi off-odour was first noticed at the fourth day of fermentation (including 24 h steeping). Yeast isolates such as Candida valida, C. krusei, Geotrichum candidum and bacteria like Lactobacillus brevis, L. plantarum, Pediococcus pentosaceus, Bacillus subtilis, Brevibacterium linens, Br. oxydans and other two Brevibacterium spp. dominated the fermenting mash at the spoilage stage. The brevibacteria contributed most significantly to ogi off-odour. Ogi samples inoculated with lactic acid bacteria increased acidity and product acceptability over the time of fermentation. The pH, titratable acidity, dissolved hydrogen sulphide and the presence of brevibacteria appear as good indices for monitoring spoilage. Hydrogen sulphide (H₂S) levels appear to be the most useful of the parameters studied. No coliforms and clostridia were identified during spoilage.     

Biogenic amine formation by poultry-associated spoilage and pathogenic bacteria

The production of biogenic amines by 50 poultry-associated bacterial strains (25 Pseudomonas , 13 Salmonella and 12 Listeria ) was investigated on amine agar plates containing lysine, histidine, ornithine, phenylalanine, tryptophan and tyrosine. Seventy-four per cent of all the strains produced cadaverine and putrescine, while phenylethylamine, histamine, tyramine and tryptamine were produced by 72, 56, 34 and 24% of strains, respectively. Different patterns of biogenic amine production amongst the three bacterial genera tested were apparent as well as amongst strains of the same genus. This study highlighted a high incidence of biogenic amine-producing bacterial strains associated with poultry.     

Validating predictive models of food spoilage organisms

The accuracy and bias of a predictive model for the maximum specific growth rate of Pseudomonas spp. were studied by means of percentage discrepancy and bias indicators. These were calculated for observations obtained both in laboratory media and in food. When independent pseudomonad data generated in broth were compared with model predictions, the error was smaller than in the case of food. The extent to which the food structure and composition of the microflora contribute to the overall error of the model was quantified.     

Cloning of Fish Enzymes and Other Fish Protein Genes

ABSTRACT:?

Fish metabolism needs special enzymes that have maximum activity at very different conditions than their mammalian counterparts. Due to the differences in activity, these enzymes, especially cold-adapted proteases, could be used advantageously for the production of some foods. In addition to the enzymes, this review describes some other unique fish polypeptides such as antifreeze proteins, fluorescent proteins, antitumor peptides, antibiotics, and hormones, that have already been cloned and used in food processing, genetic engineering, medicine, and aquaculture. Recombinant DNA technology, which allows these biological molecules to be cloned and overexpressed in microorganisms is also described, highlighting innovative applications. The expected impact of cloning fish proteins in different fields of technology is discussed.     

Microbial spoilage of whole sheep livers.

When liver treated with antibiotics to inhibit microbial growth were held at 10 degrees C, the initial high pH (6.4) declined as lactic acid accumulated throughout the storage period of 10 days. The glycogen content also declined, but the glucose concentration in the tissues remained high. When livers were allowed to spoil at 10 degrees C, distinct but variable floras developed within the tissues, in the drip, and on the upper surface. Deep-tissue floras were composed of anaerobic and facultative organisms (Lactobacillus, Enterobacter, Aeromonas); surface floras were generally dominated by strictly aerobic organisms (Pseudomonas, Acinetobacter); drip floras contained variable proportions of organisms of all three types, but the facultatively anaerobic Enterobacter were usually present as a major component. Spoilage occurred after 4 to 6 days with the development of visible discrete colonies on the upper surface without spoilage odors being evident. Changes in tissue and drip composition due to microbial activity could be detected only when spoilage had reached an advanced stage.     

Fungal volatiles as indicators of food and feeds spoilage.

Fungal growth leads to spoilage of food and animal feeds and to formation of mycotoxins and potentially allergenic spores. Fungi produce volatile compounds, during both primary and secondary metabolism, which can be used for detection and identification. Fungal volatiles from mainly Aspergillus, Fusarium, and Penicillium have been characterized with gas chromatography, mass spectrometry, and sensory analysis. Common volatiles are 2-methyl-1-propanol, 3-methyl-1-butanol, 1-octen-3-ol, 3-octanone, 3-methylfuran, ethyl acetate, and the malodorous 2-methyl-isoborneol and geosmin. Volatile sesquiterpenes can be used for taxonomic classification and species identification in Penicillium, as well as to indicate mycotoxin formation in Fusarium and Aspergillus. Developments in sensor technology have led to the construction of "electronic noses" (volatile compound mappers). Exposure of different nonspecific sensors to volatile compounds produces characteristic electrical signals. These are collected by a computer and processed by multivariate statistical methods or in an artificial neural network (ANN). Such systems can grade cereal grain with regard to presence of molds as efficiently as sensory panels evaluating grain odor. Volatile compound mapping can also be used to predict levels of ergosterol and fungal colony-forming units in grain. Further developments should make it possible to detect individual fungal species as well as the degree of mycotoxin contamination of food and animal feeds.     

鱼

侗族传统观念认为,水无鱼则不活,而水稻和鸭子没有活水的保障也就无法生存。用侗民的话来说：”稻三天无水不死,鱼三时无水则亡。“于是侗族用稻田养鱼来确保水稻和鸭子对水的需求,以此督促农人时时重视田间水资源的管理,保证田间随时都有足够的水,如此鱼才不死,稻才不枯,鸭才不渴。为达到稻鱼鸭三丰收,水是关键,