Bile salt biotransformations by human intestinal bacteria.

Complementary approaches were employed to characterize transitional episodes in Pseudomonas aeruginosa biofilm development using direct observation and whole-cell protein analysis. Microscopy and in situ reporter gene analysis were used to directly observe changes in biofilm physiology and to act as signposts to standardize protein collection for two-dimensional electrophoretic analysis and protein identification in chemostat and continuous-culture biofilm-grown populations. Using these approaches, we characterized five stages of biofilm development: (i) reversible attachment, (ii) irreversible attachment, (iii) maturation-1, (iv) maturation-2, and (v) dispersion. Biofilm cells were shown to change regulation of motility, alginate production, and quorum sensing during the process of development. The average difference in detectable protein regulation between each of the five stages of development was 35% (approximately 525 proteins). When planktonic cells were compared with maturation-2 stage biofilm cells, more than 800 proteins were shown to have a sixfold or greater change in expression level (over 50% of the proteome). This difference was higher than when planktonic P. aeruginosa were compared with planktonic cultures of Pseudomonas putida. Las quorum sensing was shown to play no role in early biofilm development but was important in later stages. Biofilm cells in the dispersion stage were more similar to planktonic bacteria than to maturation-2 stage bacteria. These results demonstrate that P. aeruginosa displays multiple phenotypes during biofilm development and that knowledge of stage-specific physiology may be important in detecting and controlling biofilm growth.

Pseudomonas aeruginosa Displays Multiple Phenotypes during Development as a Biofilm

Gram-positive bacteria possess a myriad of acid resistance systems that can help them to overcome the challenge posed by different acidic environments. In this review the most common mechanisms are described: i.e., the use of proton pumps, the protection or repair of macromolecules, cell membrane changes, production of alkali, induction of pathways by transcriptional regulators, alteration of metabolism, and the role of cell density and cell signaling. We also discuss the reponses of Listeria monocytogenes, Rhodococcus, Mycobacterium, Clostridium perfringens, Staphylococcus aureus, Bacillus cereus, oral streptococci, and lactic acid bacteria to acidic environments and outline ways in which this knowledge has been or may be used to either aid or prevent bacterial survival in low-pH environments.

Surviving the Acid Test: Responses of Gram-Positive Bacteria to Low pH

Encapsulation involves the incorporation of food ingredients, enzymes, cells or other materials in small capsules. Applications for this technique have increased in the food industry since the encapsulated materials can be protected from moisture, heat or other extreme conditions, thus enhancing their stability and maintaining viability. Encapsulation in foods is also utilized to mask odours or tastes. Various techniques are employed to form the capsules, including spray drying, spray chilling or spray cooling, extrusion coating, fluidized bed coating, liposome entrapment, coacervation, inclusion complexation, centrifugal extrusion and rotational suspension separation. Each of these techniques is discussed in this review. A wide variety of foods is encapsulated--flavouring agents, acids bases, artificial sweeteners, colourants, preservatives, leavening agents, antioxidants, agents with undesirable flavours, odours and nutrients, among others. The use of encapsulation for sweeteners such as aspartame and flavours in chewing gum is well known. Fats, starches, dextrins, alginates, protein and lipid materials can be employed as encapsulating materials. Various methods exist to release the ingredients from the capsules. Release can be site-specific, stage-specific or signalled by changes in pH, temperature, irradiation or osmotic shock. In the food industry, the most common method is by solvent-activated release. The addition of water to dry beverages or cake mixes is an example. Liposomes have been applied in cheese-making, and its use in the preparation of food emulsions such as spreads, margarine and mayonnaise is a developing area. Most recent developments include the encapsulation of foods in the areas of controlled release, carrier materials, preparation methods and sweetener immobilization. New markets are being developed and current research is underway to reduce the high production costs and lack of food-grade materials.

/pdf/encapsulation-in-the-food-industry-a-review-5fceoudsmh.pdf

Encapsulation in the food industry: a review

▪ Abstract Bacteria produce and secrete lipases, which can catalyze both the hydrolysis and the synthesis of long-chain acylglycerols. These reactions usually proceed with high regioselectivity and enantioselectivity, and, therefore, lipases have become very important stereoselective biocatalysts used in organic chemistry. High-level production of these biocatalysts requires the understanding of the mechanisms underlying gene expression, folding, and secretion. Transcription of lipase genes may be regulated by quorum sensing and two-component systems; secretion can proceed either via the Sec-dependent general secretory pathway or via ABC transporters. In addition, some lipases need folding catalysts such as the lipase-specific foldases and disulfide-bond–forming proteins to achieve a secretion-competent conformation. Three-dimensional structures of bacterial lipases were solved to understand the catalytic mechanism of lipase reactions. Structural characteristics include an α/β hydrolase fold, a catalytic ...

/pdf/bacterial-biocatalysts-molecular-biology-three-dimensional-2e7iu4n7n9.pdf

Bacterial Biocatalysts: Molecular Biology, Three-Dimensional Structures, and Biotechnological Applications of Lipases

Effects of Lactobacilli and an acidophilic fungus on the production performance and immune responses in broiler chickens.

The natural biopolymer chitin and its deacetylated product chitosan are found abundantly in nature as structural building blocks and are used in all sectors of human activities like materials science, nutrition, health care, and energy Far from being fully recognized, these polymers are able to open opportunities for completely novel applications due to their exceptional properties which an economic value is intrinsically entrapped On a commercial scale, chitosan is mainly obtained from crustacean shells rather than from the fungal and insect sources Significant efforts have been devoted to commercialize chitosan extracted from fungal and insect sources to completely replace crustacean-derived chitosan However, the traditional chitin extraction processes are laden with many disadvantages The present review discusses the potential bioextraction of chitosan from fungal, insect, and crustacean as well as its superior physico-chemical properties The different aspects of fungal, insects, and crustacean chitosan extraction methods and various parameters having an effect on the yield of chitin and chitosan are discussed in detail In addition, this review also deals with essential attributes of chitosan for high value-added applications in different fields and highlighted new perspectives on the production of chitin and deacetylated chitosan from different sources with the concomitant reduction of the environmental impact

Current Status and New Perspectives on Chitin and Chitosan as Functional Biopolymers

Volatile compounds were isolated from Cheddar cheese headspace by purge and trap extraction, enriched by cryofocusing, and analyzed by multidimensional GC equipped with odor port and by GC/MS. In total, 5 aldehydes, 6 ketones, 8 alcohols, 3 esters, 11 hydrocarbons, 3 halides, and 3 sulfur compounds were positively identified. Ethanol, 2,3-butanedione, and 3-hydroxy-2-butanone were the major components isolated in cheese headspace. The paper describes the aroma characteristics of some of these volatiles and their impact on the overall Cheddar flavor. Esters, aldehydes, methyl ketones, and sulfur compounds had direct impact on Cheddar aroma by virtue of their characteristic aroma. On the other hand, alcohols and hydrocarbons formed the major portion of the GC profile but contributed little to the aroma

Analysis of Odor-Active Volatiles in Cheddar Cheese Headspace by Multidimensional GC/MS/Sniffing

Hurdle technology: A novel approach for enhanced food quality and safety – A review

The use of probiotics as food components combats not only cardiovascular diseases but also many gastrointestinal tract disorders. Their health benefits along with their increased global market have interested scientists for better formulation and appropriate administration to the consumers. However, the lack of clear elucidation of their cholesterol-lowering mechanisms has complicated their proper dosage and administration to the beneficiaries. In this review, proposed mechanisms of cholesterol reduction such as deconjugation of bile via bile salt hydrolase activity, binding of cholesterol to probiotic cellular surface and incorporation into their cell membrane, production of SCFAs from oligosaccharides, coprecipitation of cholesterol with deconjugated bile, and cholesterol conversion to coprostanol have been discussed. Also, hypocholesterolemic effects on human- and animal-trial results, commonly used probiotics and synbiotics with effect on serum cholesterol regulation, types of bile salt hydrolase genes, and substrate specificities have been discussed.

Byong H. Lee

Papers

Effects of Lactobacilli and an acidophilic fungus on the production performance and immune responses in broiler chickens.

Current Status and New Perspectives on Chitin and Chitosan as Functional Biopolymers

Analysis of Odor-Active Volatiles in Cheddar Cheese Headspace by Multidimensional GC/MS/Sniffing

Hurdle technology: A novel approach for enhanced food quality and safety – A review

The perspective on cholesterol‐lowering mechanisms of probiotics