Making Yogurt at Home

Tangy, nutritious yogurt can be made at home with regular kitchen utensils, and often is less expensive than buying it. This NebGuide describes how

Intracellular pH Effects in Lactic Acid Bacteria

The objectives of this research were to determine the effect of lactic acid and low pH on the intracellular pH in three species of lactic acid bacteria. A pH gradient (intracellular pH minus the extracellular pH) of .9 to 1.4 pH units was achieved by several strains of lactic acid bacteria, including Streptococcus thermophilus 19258 and 573, Lactococcus lactis ssp. lactis C2, and Lactococcus lactis ssp. cremoris HP during log phase of growth in various media. A noticeable decline of the pH gradient occurred at an internal pH of 5.5 to 6.0. In late stationary phase, the pH gradient was generally reduced to .5 pH units or less. In contrast, the aciduric Lactobacillus casei 685 maintained a large pH gradient (\u3e 1.0 pH units) even when the medium pH was reduced to less than 4.0. Rapid growth of lactococci and streptococci in media containing excess lactose did not occur when the intracellular pH was reduced below a critical pH of 5.0 or at a neutral pH when proton-uncoupling agents were present

Collapse of the Proton Motive Force in \u3ci\u3eListeria monocytogenes\u3c/i\u3e Caused by a Bacteriocin Produced by \u3ci\u3ePediococcus acidilactici\u3c/i\u3e

The effect of pediocin JD, a bacteriocin produced by Pediococcus acidilactici JD1-23, on the proton motive force and proton permeability of resting whole cells of Listeria monocytogenes Scott A was determined. Control cells, treated with trypsin-inactivated bacteriocin at a pH of 5.3 to 6.1, maintained a pH gradient and a membrane potential of approximately 0.65 pH unit and 75 mV, respectively. However, these gradients were rapidly dissipated in cells after exposure to pediocin JD, even though no cell lysis had occurred. The pH gradient and membrane potential of the producer cells were also unaffected by the bacteriocin. Whole cells treated with bacteriocin were twice as permeable to protons as control cells were. The results suggest that the inhibitory action of pediocin JD against L. monocytogenes is directed at the cytoplasmic membrane and that inhibition of L. monocytogenes may be caused by the collapse of one or both of the individual components of the proton motive force

pH Homeostasis in Lactic Acid Bacteria

The ability of lactic acid bacteria to regulate their cytoplasmic or intracellular pH is one of the most important physiological requirements of the cells. Cells unable to maintain a near neutral intracellular pH during growth or storage at low extracellular pH may lose viability and cellular activity. Despite the importance of pH homeostasis in the lactic acid bacteria, however, an understanding of cytoplasmic pH regulation has only recently begun to emerge. This review describes the specific effects of low pH on lactic acid bacteria, reports recent research on the physiological role of intracellular pH as a regulator of various metabolic activities in lactic acid bacteria, and presents the means by which lactic acid bacteria defend against low intracellular pH. Particular attention is devoted to the proton-translocating ATPase, an enzyme that is largely responsible for pH homeostasis in fermentative lactic acid bacteria

Collapse of the Proton Motive Force in \u3ci\u3eListeria monocytogenes\u3c/i\u3e Caused by a Bacteriocin Produced by \u3ci\u3ePediococcus acidilactici\u3c/i\u3e

The effect of pediocin JD, a bacteriocin produced by Pediococcus acidilactici JD1-23, on the proton motive force and proton permeability of resting whole cells of Listeria monocytogenes Scott A was determined. Control cells, treated with trypsin-inactivated bacteriocin at a pH of 5.3 to 6.1, maintained a pH gradient and a membrane potential of approximately 0.65 pH unit and 75 mV, respectively. However, these gradients were rapidly dissipated in cells after exposure to pediocin JD, even though no cell lysis had occurred. The pH gradient and membrane potential of the producer cells were also unaffected by the bacteriocin. Whole cells treated with bacteriocin were twice as permeable to protons as control cells were. The results suggest that the inhibitory action of pediocin JD against L. monocytogenes is directed at the cytoplasmic membrane and that inhibition of L. monocytogenes may be caused by the collapse of one or both of the individual components of the proton motive force

pH Homeostasis in Lactic Acid Bacteria

The ability of lactic acid bacteria to regulate their cytoplasmic or intracellular pH is one of the most important physiological requirements of the cells. Cells unable to maintain a near neutral intracellular pH during growth or storage at low extracellular pH may lose viability and cellular activity. Despite the importance of pH homeostasis in the lactic acid bacteria, however, an understanding of cytoplasmic pH regulation has only recently begun to emerge. This review describes the specific effects of low pH on lactic acid bacteria, reports recent research on the physiological role of intracellular pH as a regulator of various metabolic activities in lactic acid bacteria, and presents the means by which lactic acid bacteria defend against low intracellular pH. Particular attention is devoted to the proton-translocating ATPase, an enzyme that is largely responsible for pH homeostasis in fermentative lactic acid bacteria

Synbiotics for Improved Human Health: Recent Developments, Challenges, and Opportunities

Research on combining pro- and prebiotics as synbiotics to enhance human and animal health has accelerated in the past 10 years, including many clinical trials that have assessed a diverse range of synbiotic formulations. In this review, we summarize these studies as well as the commercial applications of synbiotics that are available. In particular, we critically assess the claimed health benefits of synbiotic applications and the ecological and therapeutic factors to consider when designing synbiotics and discuss the implications of these concepts for future research in this field

Galactose Transport in \u3ci\u3eStreptococcus thermophilus\u3c/i\u3e

Although Streptococcus thermophilus accumulated [14C]lactose in the absence of an endogenous energy source, galactose-fermenting (Gal+) cells were unable to accumulate [14C]galactose unless an additional energy source was added to the test system. Both Gal+ and galactose-nonfermenting (Gal-) strains transported galactose when preincubated with sucrose. Accumulation was inhibited 50 or 95% when 10 niM sodium fluoride or 1.0 mM iodoacetic acid, respectively, was added to sucrose-treated cells, indicating that ATP was required for galactose transport activity. Proton-conducting ionophores also inhibited galactose uptake, although N,N\u27-dicyclohexyl carbodiimide had no effect. The results suggest that galactose transport in S. thermophilus occurs via an ATP-dependent galactose permease and that a proton motive force is involved. The galactose permease in S. thermophilus TS2b (Gal+) had a Km for galactose of 0.25 mM and a Vmax of 195 μmol of galactose accumulated per min per g (dry weight) of cells. Several structurally similar sugars inhibited galactose uptake, indicating that the galactose permease had high affinities for these sugars

Do Lactic Acid Bacteria in fermented foods persist in the gastrointestinal tract: an in vitro investigation

It is now well established that the composition of the gastrointestinal (GI) microbiota has a profound influence on intestinal and overall health. Many contemporary diseases such as type two diabetes, IBS and obesity are associated with a dysbiotic microbiota. Therefore, researchers are interested in how diet and specific dietary components can modulate the gastrointestinal microbiota and possibly repair a dysbiotic state. One approach to improve gastrointestinal health is by consuming probiotics and prebiotics or a diet rich in fermented foods containing live microbes. Fermented foods are popular because of their enhanced preservation, safety, organoleptic, functionality, and nutritional properties. These fermented foods can also contain live microorganisms that may play a role in improving gastrointestinal health. One of the challenges, however, is that the GI environment is very stable and resistant to change. This is mainly due to barriers along the GI tract (pH, bile, enzymes). Persistence of allochthonous microorganisms within the GI tract is also limited by host response such as absence of ecological niches and colonization resistance. In addition, the microbiota composition varies in every individual, making it difficult to formulate a single therapeutic solution. It may be possible to overcome these barriers and regulate a dysbiotic system through a diet rich in fermented foods and supplemented with prebiotics

United States Patent: COMPOSITION AND METHOD FOR INHIBITING PATHOGENS AND SPOILAGE ORGANISMS IN FOOD

The method of the invention uses live cells of non-fermenting and/or non-growing lactic acid bacteria to deliver bacteriocin into edible food substances to inhibit the growth of food spoilage and/or food-borne pathogenic organisms. The method of the invention may be used to inhibit growth of these organisms in raw food substances and finished food products after processing. The lactic acid bacteria within the food mixture are capable of producing bacteriocin in the desired microbial- inhibiting amounts under conditions of non-growth and non-fermentatio