BackgroundTo systematically develop dietary strategies based on resistant starch (RS) that modulate the human gut microbiome, detailed in vivo studies that evaluate the effects of different forms of RS on the community structure and population dynamics of the gut microbiota are necessary. The aim of the present study was to gain a community wide perspective of the effects of RS types 2 (RS2) and 4 (RS4) on the fecal microbiota in human individuals.Methods and FindingsTen human subjects consumed crackers for three weeks each containing either RS2, RS4, or native starch in a double-blind, crossover design. Multiplex sequencing of 16S rRNA tags revealed that both types of RS induced several significant compositional alterations in the fecal microbial populations, with differential effects on community structure. RS4 but not RS2 induced phylum-level changes, significantly increasing Actinobacteria and Bacteroidetes while decreasing Firmicutes. At the species level, the changes evoked by RS4 were increases in Bifidobacterium adolescentis and Parabacteroides distasonis, while RS2 significantly raised the proportions of Ruminococcus bromii and Eubacterium rectale when compared to RS4. The population shifts caused by RS4 were numerically substantial for several taxa, leading for example, to a ten-fold increase in bifidobacteria in three of the subjects, enriching them to 18–30% of the fecal microbial community. The responses to RS and their magnitudes varied between individuals, and they were reversible and tightly associated with the consumption of RS.ConclusionOur results demonstrate that RS2 and RS4 show functional differences in their effect on human fecal microbiota composition, indicating that the chemical structure of RS determines its accessibility by groups of colonic bacteria. The findings imply that specific bacterial populations could be selectively targeted by well designed functional carbohydrates, but the inter-subject variations in the response to RS indicates that such strategies might benefit from more personalized approaches.

The relationship between surface-enhanced resonance Raman scattering (SERRS) intensity and the rate of deposition during silver-island film preparation was examined, using zinc tetraphenylporphine (ZnTPP) as the adsorbate. The effect of the deposition rate on the optical properties of the films at specific wavelengths was also analyzed. The data show that the film extinction (the term extinction is used rather than absorption because the spectra have not been corrected for reflection or scattering losses) increases exponentially at 514 and 458 nm as the deposition rate is decreased. SERRS intensities also increase exponentially at these two excitation wavelengths with a decrease in the deposition rate. The optical density is linearly related to the SERRS intensity, and maximal enhancement is observed for films with the greatest extinction at these excitation wavelengths. In contrast, neither the extinction at 406 nm nor the SERRS scattering intensities resulting from excitation at this wavelength differ substantially. The surface-enhanced Raman scattering (SERS) intensity and the electronic spectra of 4,4'-bipyridine (BP) adsorbed onto silver films as a function deposition rate were also examined. The behavior of the nonresonantly enhanced BP is comparable to that of the resonantly enhanced ZnTPP samples. The effects of the surface morphology, as determined from transmission electron micrographs of the films at various deposition rates, on the corresponding electronic spectra and SERS/SERRS spectra are described.

Recombinant ovine interferon-tau (r-oIFN-tau) production by Pichia pastoris was studied using methanol as the sole carbon source during induction. The cells were grown on glycerol up to a certain cell density before induction of the AOX1 promoter by methanol for expression of the recombinant protein. Cell growth on methanol has been modeled using a substrate-feed equation, which served as the basis for an effective computer control of the process. The r-oIFN-tau concentration in the culture began to decline despite continued cell growth after 50 (+/- 6) h of induction, which was associated with an increase in proteolytic activity of the fermentation broth. A specific growth rate of 0.025 h(-1) was found to be optimal for r-oIFN-tau production. No significant improvement in r-oIFN-tau production was observed when the specific growth rate was stepped up before the critical point when r-oIFN-tau concentration started decreasing during fermentation. However, best results were obtained when the specific growth rate was stepped down from 0.025 to 0.02 h(-1) at 38 h of induction, whereby the active production period was prolonged until 70 h of induction and the broth protease activity was correspondingly reduced. The corresponding maximum protein yield was 391.7 mg x L(-1) after 70 h of fermentation. The proteolytic activity could be reduced by performing fermentations at specific growth rates of 0.025 h(-1) or below. The recombinant protein production can be performed at an optimal yield by directly controlling the methanol feed rate by a computer-controlled model. The production profile of r-oIFN-tau was found to be significantly different from other secreted and intracellular recombinant protein processes, which is an indication that recombinant protein production in Pichia pastoris needs to be optimized as individual processes following established principles.

The growth and activity of some Lactobacillus and Bifidobacterium strains are stimulated by the presence of nondigestible fructooligosaccharides (FOS), which are selectively fermented by specific intestinal bacteria. Consumption of FOS, therefore, enriches for those bacteria that possess metabolic pathways necessary for FOS metabolism. In this study, a DNA microarray consisting of 7,680 random genomic library fragments of Lactobacillus paracasei 1195 was used to examine genes involved in the utilization of FOS in this organism. Differential expression profiles between cells grown on FOS and those grown on glucose provided a basis for identifying genes specifically induced by FOS. Several of the FOS-induced genes shared sequence identity with genes encoding ␤-fructosidases and components of phosphoenolpyruvate-dependent phosphotransferase systems (PTS). These genes were organized in a putative operon, designated the fos operon, that may play an essential role in FOS utilization. The complete 7,631-bp nucleotide sequence of the putative fos operon was determined and consists of fosABCDXE genes, which encode a putative fructose/mannose PTS (FosABCDX) and a ␤-fructosidase precursor (FosE). The latter contains an N-terminal signal peptide sequence and cell wall sorting signals at the C-terminal region, suggesting its localization at the cell wall. Inactivation of the fosE gene led to impaired growth on FOS and other ␤-fructose-linked carbohydrates. Transcriptional analysis by reverse transcriptase PCR suggested that fosABCDXE was cotranscribed as a single mRNA during growth on FOS. Expression array analysis revealed that when glucose was added to FOS-grown cells, transcription of the FOS-induced genes was repressed, indicating that FOS metabolism is subject to catabolite regulation.

Many of the sauces used in frozen meals are oil-in-water emulsions that consist of fat droplets dispersed within an aqueous medium. This type of emulsion must remain physically and chemically stable throughout processing, freezing, storage, and defrosting conditions. Knowledge of the fundamental physicochemical mechanisms responsible for the stability of emulsion-based sauces is needed to design and fabricate high-quality sauces with the desired sensory attributes. This review provides an overview of the current understanding of the influence of freezing and thawing on the stability of oil-in-water emulsions. In particular, it focuses on the influence of product composition (such as emulsifiers, biopolymers, salts, and cryoprotectants), homogenization conditions, and freezing/thawing conditions on the stability of emulsions. The information contained in this review may be useful for optimizing the design of emulsion-based sauces for utilization in commercial food products.