Spoilage Species Research Articles

Suitability of bifidobacteria and thymol as biopreservatives in extending the shelf life of fresh packed plaice fillets

The present study was aimed to evaluate the microbiological and sensory characteristics of biopreserved packed fresh plaice (Pleuronectes platessa), during storage. Fish samples were treated with a Bifidobacterium bifidum strain and thymol as preservatives, stored at different temperatures (4 and 12 degrees C) and package atmospheres (in air, under vacuum, modified atmosphere). Data about the total viable count (TVC) were used to predict the shelf life of the fish fillets as affected by the preservatives used and the storage conditions. Data obtained revealed that B. bifidum could perform an efficient synergy with thymol, in controlling the hygiene biological markers. Besides, the tested bifidobacterial species, combined with low storage temperature and anoxia/hypoxia, showed a great efficacy against the main fresh packaged fish spoilage species (Pseudomonas spp., Photobacterium phosphoreum). The studied technique could be considered effective in fresh fish spoilage control. Great interest is developing on food biopreservation, because of the ever increasing needs to protect consumers' and environment's health, and to revalorize some important food characteristics, such as naturalness and authenticity, without leaving the safety aside.

Isolation of a Hop-Sensitive Variant of Lactobacillus lindneri and Identification of Genetic Markers for Beer Spoilage Ability of Lactic Acid Bacteria

We have isolated a hop-sensitive variant of the beer spoilage bacterium Lactobacillus lindneri DSM 20692. The variant lost a plasmid carrying two contiguous open reading frames (ORF s) designated horB(L) and horC(L) that encode a putative regulator and multidrug transporter presumably belonging to the resistance-nodulation-cell division superfamily. The loss of hop resistance ability occurred with the loss of resistance to other drugs, including ethidium bromide, novobiocin, and cetyltrimethylammonium bromide. PCR and Southern blot analysis using 51 beer spoilage strains of various species of lactic acid bacteria (LAB) revealed that 49 strains possessed homologs of horB and horC. No false-positive results have been observed for nonspoilage LAB or frequently encountered brewery isolates. These features are superior to those of horA and ORF 5, previously reported genetic markers for determining the beer spoilage ability of LAB. It was further shown that the combined use of horB/horC and horA is able to detect all 51 beer spoilage strains examined in this study. Furthermore sequence comparison of horB and horC homologs identified in four different beer spoilage species indicates these homologs are 96.6 to 99.5% identical, which is not typical of distinct species. The wide and exclusive distribution of horB and horC homologs among beer spoilage LAB and their sequence identities suggest that the hop resistance ability of beer spoilage LAB has been acquired through horizontal gene transfer. These insights provide a foundation for applying trans-species genetic markers to differentiating beer spoilage LAB including previously unencountered species.

Inactivation of refrigerator biofilm bacteria for application in the food service environment

AbstractRefrigerator biofilm formation in food environments can result in spoilage and food safety problems. Biofouling of food contact surfaces are difficult to combat, and while there are significant risks involved with tolerating their presence, methods for their removal are not commonly available. In this study, biofilms were grown on plastic refrigerator trays. Cultures of mixed wild strains were started using kitchen scraps suspended in nutrient broth. Biofilms were allowed to mature with approximately 109 CFU per tray test area. Spoilage species identified included Pseudomonas putida, Sphingobacterium multivorum, Citrobacter freundii and Proteus vulgaris. A series of 39 different treatment interventions were trialed during three different biofilm test runs. Results obtained from treatments ranged from a less than 1 log10 reduction for light duty cleaning operations to over a 5 log10 reduction involving more complex treatment methods. The latter included combinations of hot soapy water (75 °C), scrubbing, treatment with high pH (12.0) cleaners followed by acetic acid (vinegar) exposure and included pre‐ and post‐treatment wiping with paper towels.

Shelf-life modelling for fresh-cut vegetables

Abstract The influence of various operations during the preparation of the ‘ready-to-use’ salads on the initial level and subsequent growth of microbial spoilage species was analyzed. The factors considered were the quality of the water used to wash the vegetables, the delay between the washing and cutting phases, and the level of active chlorine in the water used for washing. The dynamics of the processes and the effectiveness of the washing operations play the most important role in the reduction of the contamination level. Furthermore, the use of potential inhibiting ingredients, such as red chicory, and the antagonistic effect of Lactobacillus plantarum were all successful in reducing the growth of hazardous species, such as Aeromonas hydrophila . These effects were modelled on the basis of the results of the Central Composite Design (CCD) using clarified juices. From the results obtained, the inhibiting activity of red chicory was confirmed, but A. hydrophila seems to be counteracted by the presence of L. plantarum , which appears to negate the inhibiting effect of red chicory.

Effects of growth conditions on the resistance of some pathogenic and spoilage species to high pressure homogenization.

The effects of chemico-physical growth conditions such as pH, temperature and water activity (aw) on lethal high homogenization pressure effects on Listeria monocytogenes, Staphylococcus aureus, Escherichia coli and Yarrowia lipolytica were investigated. The results, though based on standard media, emphasize the importance of food system composition and its thermal history on the high pressure tolerance of the microbial population.

Evaluation of Fourier-transform infrared spectroscopy for data capture in predictive microbiology

Chemical changes in the medium, induced by the fermentative species Lactobacillus plantarum and Lactobacillus brevis and by the enzymatic action of a proteolytic, spoilage species, Yarrowia lipolytica, were analysed using Fourier-transform i.r. spectroscopy (FTIR). Changes in the absorbance data over time could be modelled using one of the more current predictive, mathematical models of microbial growth, such as the Gompertz equation. Moreover, a linear correlation between FTIR data (expressed as absorbance of some selected peaks) and viability data (expressed as log10 c.f.u./g or ml) was observed during the fermentation process, both for L. plantarum and L. brevis.

The microbial spoilage of ‘soft’ melon ball snack under tropical conditions

Abstract19 microorganisms, mostly hazardous and spoilage species were isolated from ‘soft’ melon ball snack samples in the humid Western Nigeria. Physical biodeterioration was recorded from the 6th day of storage with the early occurring rope (slime) of Bacillus sp. found to be a faster visible objectionable indicator than the commonly used fungal growth. All the 14 isolated fungi grew though, to varying extents on the snack agar and in the melon seeds infusion medium in which they also induced significant changes in the oil (decrease) and free fatty acids (increase) contents after 10 days of incubation at 30 °C. The results implicated Rhizopus arrhizus, R. nigricans, Aspergillus flavus, A. ochraceus, A. tamarii, A. niger, Mucor fragilis and Penicillium citrinum as the major fungal deteriogens. Isolation of the coliform bacterium (Escherichia coli) suggested the need for a more hygienic handling of the snack. Addition of varying amounts of breadfruit nuts mash as adjunct to melon seeds mash in order to enhance mastication of snacks with lower moisture content was investigated. Samples prepared with 20% adjunct recorded mean acceptability rating of 178 and keepability period of 10 days while 200 and 5 days were obtained respectively for the control.

Light butter: natural microbial population and potential growth of Listeria monocytogenes and Yersinia enterocolitica

Yarrowia lipolytica, Bacillus polymyxa and Enterococcus faecium were the most frequent yeast and bacterial spoilage species associated with commercial light butter. Following inoculation and incubation at 4°C, strains of Y. enterocolitica and L. monocytogenes exhibited growth rates higher than those of the naturally occurring microflora. Listeria monocytogenes displayed a higher aptitude to proliferate in such food while the cell increment of Y. enterocolitica was limited.

Extracellular nuclease activity of fish spoilage bacteria, fish pathogens, and related species.

The production of extracellular deoxyribonuclease and ribonuclease by 23 marine and 3 dairy strains of Pseudomonas putrefaciens, 15 strains of fish-pathogenic fluorescent pseudomonads, 38 strains of fluorescent pseudomonads isolated from haddock, and 34 related organisms was determined by an agar plate method. All strains of P. putrefaciens produced both deoxyribonuclease and ribonuclease. Of the other 87 organisms examined, 26.5% produced ribonuclease and 14.5% produced deoxyribonuclease. All organisms which produced deoxyribonuclease also produced ribonuclease. Deoxyribonuclease production by P. putrefaciens is suggested as a useful criterion of identity for members of this intense fish spoilage species.

Extracellular Nuclease Activity of Fish Spoilage Bacteria, Fish Pathogens, and Related Species

The production of extracellular deoxyribonuclease and ribonuclease by 23 marine and 3 dairy strains of Pseudomonas putrefaciens, 15 strains of fish-pathogenic fluorescent pseudomonads, 38 strains of fluorescent pseudomonads isolated from haddock, and 34 related organisms was determined by an agar plate method. All strains of P. putrefaciens produced both deoxyribonuclease and ribonuclease. Of the other 87 organisms examined, 26.5% produced ribonuclease and 14.5% produced deoxyribonuclease. All organisms which produced deoxyribonuclease also produced ribonuclease. Deoxyribonuclease production by P. putrefaciens is suggested as a useful criterion of identity for members of this intense fish spoilage species.