Microbial communities in food and food production establishments have highly versatile structures based on various extrinsic factors. The information gained by large-scale microbial community analysis not only can deepen the understanding of food microbiology in general but also can lead to improvement of food production systems for increased quality and safety and extension of shelf life. This chapter reviews the most recent methods applied to microbial communities, and presents examples of some cutting-edge technologies. Molecular methods have been developing rapidly in recent years both for specific detection of single species and for screening assays that allow the species composition of a given food sample to be unraveled. Examples of those methods are 16S rRNA clone analysis, fingerprinting methods such as terminal restriction fragment length polymorphism (t-RFLP) and denaturing gradient gel electrophoresis (DGGE), tag-encoded pyrosequencing, single-nucleotide primer extension (SNuPE), and microarrays. Furthermore, flow cytometry is also addressed in the chapter, but this technique is based on single-cell analysis whereby a cell suspension is concentrated by nanofluidics and analyzed by laser technology. High-throughput analysis of microbial populations in food products and food processing environments has revealed the existence of a higher complexity in the microbial world than previously expected. The new approaches provide opportunities for further understanding of the microbial developments that are initiated during food production and storage.
Author: admin
Once considered exceptional rarities, extremophiles have become attractive objects for basic and applied research ranging from nanotechnology to biodiversity to the origins of life and even to the search for extraterrestrial life. Several novel aspects of extremophiles are covered in this book; the focus is firstly on unusual and less explored ecosystems such as marine hypersaline deeps, extreme cold, desert sands, and man-made clean rooms for spacecraft assembly. Secondly, the increasingly complex field of applications from extremophile research is treated and examples such as novel psychrophilic enzymes, compounds from halophiles, and detection strategies for potential extraterrestrial life forms are presented.
An analysis of the temporal trends for mercury in Arctic biota is
important for scientists and managers concerned with making
sound science-based policy with respect to changes in Hg in
the Arctic environment. Long-term datasets (ie, comparing
modern with historical or pre-industrial Hg concentrations)
can be used to estimate the relative importance of natural and
anthropogenic Hg inputs in modern biota and the environment,
while short-term datasets (ie, covering the past one to three
decades) illustrate how Hg concentrations have changed in
recent times and suggest likely trends in the near-term future.
In the previous AMAP assessment of Hg in the Arctic
environment (AMAP, 2005), evidence of increasing Hg
concentrations from pre-industrial or historical to more
recent times was presented for Arctic marine biota. Those
trends were shown to continue in recent (short-term) datasets,
primarily in higher-order marine biota from Canada and West
Greenland. In contrast, time series for lower-order marine biota
for Iceland and the European Arctic showed a general pattern
of recently stable or declining Hg concentrations. The reasons
for this spatial difference in trend patterns were not clear.
Data for higher-order marine biota from Europe and Iceland
were lacking as were temporal trend datasets for biota from
Russia and Finland. One of the recommendations resulting
from the previous AMAP assessment was that temporal trend
monitoring of Hg concentrations should be continued in order
to obtain longer and more statistically reliable trend analyzes.
This chapter presents an update of the information available
for both long-term and short-term trends, including a statistical
meta-analysis of recent temporal trends in Hg concentrations
in Arctic biota. The final section presents a discussion, using
case studies, of the possible mechanisms driving the temporal
trends observed.
The use of injection and brining as the first step in heavy salting of cod increases weight yields of the products through both salting and rehydration, compared to other pre-salting methods, like brining only and pickling. This is interesting since salt content of the muscle exceeds 20% NaCl, in all procedures. Therefore, the dissimilarities in yield were presumed to depend on the degree of protein denaturation and aggregation as influenced by the different salting procedures. This hypothesis was studied and confirmed with the aid of SDS – PAGE and DSC-analysis. Higher water retention of injected products was explained by stronger salting-in effects on proteins during pre-salting, reducing aggregation of muscle proteins during the dry salting step. The degree of protein aggregation during salting increased in the following order with regard to the different pre-salting methods: injection and brining <brining <pickling. These effects were still observed after rehydration. Furthermore, differences in denaturation / aggregation were assigned to both myosin and collagen.
The effects of different salt concentrations (6%, 15%, 18% and 24% NaCl (w / w)) on the conformational changes of cod muscle proteins during brine salting were examined in this study. Proteins were extracted from the brine salted samples with solutions of 1 M (5.9%) and 4 M (23.4%) NaCl and the quantity of salt soluble proteins (SSP), disulfide bond (S – S), total sulfhydryl (SH) and available SH content in the soluble fraction were determined. Increased salt concentration in cod muscle promoted protein denaturation and aggregation. The SSP and total SH content decreased, whereas the S – S bond and available SH content increased with increased salt concentration in cod muscle. Disulfide bond formation correlated (r = −0.6) with a decrease in total SH groups. Higher SSP and available SH groups of the samples at lower brine concentrations were explained by smaller concentration gradients and salt diffusion rates, resulting in stronger salting-in at early stages of the brining process. There was a significant difference in conformational changes in proteins extracted with a salt solution of 1 and 4 M, mainly due to a different degree of protein aggregation.
The aim of this study was to investigate the effects of salting and different pre-salting procedures (injection and brining versus brining only) on the microstructure and water retention of heavy salted cod products. Salting resulted in shrinkage of fiber diameter and enlargement of inter-cellular space. Water was expelled from the muscle and a higher fraction became located in the extra-cellular matrix. These changes were suggested to originate from myofibrillar protein aggregation and enzymatic degradation of the connective tissue. During rehydration, the muscle absorbed water again and the fibers swelled up to a similar cross-sectional area as in the raw muscle. However, the inter-cellular space remained larger, resulting in a higher water content of the muscle in the rehydrated stage. The effects of different salting procedures were strongest after salting. At that stage of the process, the inter-cellular space tended to be larger in the injected and brined muscle than in the brined only.
Stock structure of Norway lobster off southern Iceland was investigated using 12 microsatellite loci. No genetic method detected significant genetic differentiation among the sampled locations, even among Icelandic samples and an out-group from Scotland. Testing the power of resolution of microsatellite loci, the loci and sample sizes used were sufficient to detect significant genetic differentiation with confidence. The lack of genetic structure is discussed in terms of the level of gene flow, recent isolation of populations, and the statistical power of the experimental design.
The effect of rearing temperature on the growth and maturation of Arctic charr (Salvelinus alpinus) was investigated. Arctic charr juveniles were reared for 6 months (phase I, October – April, size range 20–500 g) at constant temperatures of 9, 12 and 15 ° C and according to two temperature-step groups (Tstep) ie fish transferred from 15 to 12 ° C or from 12 to 9 ° C. All the previous treatments were then reared either at 7 ° C or at 12 ° C for an additional 4 months (phase II, size range 300–1000 g) and then slaughtered in August 2008. The overall growth rate was the highest at a constant temperature of 15 ° C for the first 6 months of the trial, with the fish in this group being 44% and 78% heavier than the fish reared at a constant temperature of 12 or 9 ° C respectively. Arctic charr showed a negative response in terms of the growth rate when transferred from higher to lower temperatures, especially for groups previously reared at 15 ° C. There was a trend for higher gonadosomatic index values at the end of the experiment for groups of fish that were exposed to higher rearing temperatures during the juvenile phase ie 4.18% (± 0.79) and 7.29% (± 0.89), for the temperature groups of 12 and 15 ° C, respectively, compared with 2.49% (± 0.74) for the 9 ° C group. Our results suggest that for the production of fish> 1000 g, moderate or low temperatures (here 9 ° C) should be applied during the juvenile phase in order to reduce the negative effects arising from maturation. Farmers with access to heat sources should accordingly choose more moderate rearing temperatures during the juvenile stage, especially if the fish is to be moved down in the temperature regime during the on-growing period.
The Gram-negative fish pathogenic bacterium Aeromonas salmonicida possesses the LuxIR-type quorum sensing (QS) system, termed AsaIR. In this study the role of QS in A. salmonicida subsp. achromogenes virulence and pigment production was investigated. Five wild-type Asa strains induced the N-acyl-homoserine lactone (AHL) monitor bacteria. HPLC – HR-MS analysis identified only one type of AHL, N-butanoyl-1-homoserine lactone (C4-HSL). A knock out mutant of AsaI, constructed by allelic exchange, did not produce a detectable QS signal and its virulence in fish was significantly impaired, as LD50 of the AsaI-deficient mutant was 20-fold higher than that of the isogenic wt strain and the mean day to death of the mutant was significantly prolonged. Furthermore, the expression of two virulence factors (a toxic protease, AsaP1, and a cytotoxic factor) and a brown pigment were reduced in the mutant. AsaP1 production was inhibited by synthetic QS inhibitors (N- (propylsulfanylacetyl) -1-homoserine lactone; N- (pentylsulfanylacetyl) -1-homoserine lactone; and N- (heptylsulfanylacetyl) -1-homoserine lactone) at concentrations that did not affect bacterial growth.
It is a new finding that the AHL synthase of Aeromonas affects virulence in fish and QS has not previously been associated with A. salmonicida infections in fish. Furthermore, AsaP1 production has not previously been shown to be QS regulated. The simplicity of the A. salmonicida subsp. achromogenes LuxIR-type QS system and the observation that synthetic QSI can inhibit an important virulence factor, AsaP1, without affecting bacterial growth, makes A. salmonicida subsp. achromogenes an interesting target organism to study the effects of QS in disease development and QSI in disease control.
Eggs of a single spawning batch from wild-caught Norwegian Atlantic cod Gadus morhua were hatched and first fed on either natural zooplankton or enriched rotifers Brachionus plicatilis during the larval period. Juvenile G. morhua (initial mass 14 · 2 g) from the two first-feeding groups were then reared for 3 months under a variety of temperature (10 and 14 ° C) and salinity (15 and 32) combinations. All fish were individually tagged and microsatellite markers were used in a multiplex to trace the pedigree of all fish and body mass variation analyzed according to different environmental and genetic sources. After the termination of the laboratory trial, the fish were transferred to land-based tanks and later to sea pens and reared at ambient conditions for 26 months until they were harvested in March 2009. Growth gain from the larval and juvenile periods was persistent during the 26 months of sea pen ongrowing. The final mass of the zooplankton group was 12% higher compared to the B. plicatilis group. Similarly, rearing under a temperature of 14 ° C and salinity of 15 during the initial 3 month period during the early juvenile stage resulted in 7–13% larger size at harvesting compared to the other three temperature and salinity combinations. The study indicates that the first-feeding method and temperature and salinity manipulation explain nearly 90% of the body mass variation explained by the model. The genetic effect (measured as body mass variation within the families studied) only accounted for c. 2% during the initial rearing period, whereas it has a large effect on growth variation (30%) during the long-term rearing at ambient conditions. Sex proportion and final maturation did not differ between family groups, and no interaction between sex and family group was seen.