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Biomedical subjects

R T Marshall

Publications and source records attributed to R T Marshall.

At least 19 recordsLinked to original sources
PubMed2001

Natural exopolysaccharides enhance survival of lactic acid bacteria in frozen dairy desserts.

Viable lactic acid-producing bacteria in frozen dairy desserts can be a source of beta-galactosidase for persons who absorb lactose insufficiently. However, freezing kills many of the cells, causing loss of enzymatic activity. Cultures selected for high beta-galactosidase activities and high survival rates in the presence of bile were examined for survivability during freezing in reduced-fat ice cream. Encapsulated S. thermophilus strains survived better than their nonencapsulated mutants in reduced-fat ice cream after freezing and frozen storage at -29 degrees C for 16 d (28 vs. 19%). However, a small nonencapsulated strain of Lactobacillus delbrueckii sp. bulgaricus survived better than the large encapsulated strain in reduced-fat ice cream. Factors that improved survival of encapsulated S. thermophilus 1068 in ice cream were 1) harvest of cells in the late-log phase of growth at 37 degrees C rather than at 40, 42.5, or 45 degrees C; 2) overrun at 50% rather than 100%; and 3) storage at -17 degrees C rather than -23 or -29 degrees C. Survival of strain ST1068 was unaffected by 1) neutralization of acid during growth or 2) substitution of nitrogen for air in building overrun.

Animals↗
PubMed2001

Effects of milk fat, cocoa butter, or selected fat replacers on flavor volatiles of chocolate ice cream.

Selected volatile compounds of chocolate ice creams containing 0.6, 4.0, 6.0, or 9.0% milk fat or containing 2.5% milk fat, cocoa butter, or one of three fat replacers (Simplesse, Dairy Lo, or Oatrim) were analyzed by gas chromatography and gas chromatography-mass spectrometry using headspace solid-phase microextraction. The headspace concentration of most of the selected volatile compounds increased with decreasing milk fat concentration. Fat replacers generally increased the concentration of volatiles found in the headspace compared with milk fat or cocoa butter. Few differences in flavor volatiles were found between the ice cream containing milk fat and the ice cream containing cocoa butter. Among the selected volatiles, the concentration of 2,5-dimethyl-3(2-methyl propyl) pyrazine was the most highly correlated (negatively) with the concentration of milk fat, and it best discriminated among ice creams containing milk fat, cocoa butter, or one of the fat replacers.

Animals↗
PubMed2000

Effect of milk fat, cocoa butter, and whey protein fat replacers on the sensory properties of lowfat and nonfat chocolate ice cream.

Lowfat and nonfat chocolate ice creams were made with 2.5% of milk fat, cocoa butter, or one of two whey protein-based fat replacers, Dairy Lo or Simplesse. Polydextrose was added as required so that all formulations contained the same amount of total solids. Ice cream was stored at a control temperature of-30 degrees C. Hardness, viscosity, and melting rate were measured by physical methods. Trained panelists conducted descriptive sensory analyses of the samples at 0, 6, and 12 wk. Attribute ratings were analyzed by analysis o variance with least significant difference mean separation and orthogonal contrasting. Data were also analyzed by multivariate analysis of variance with canonical variate analysis. Consumer acceptance (n = 50) did not differ among the fresh ice creams (wk 0). Ice cream containing milk fat had less intense cocoa flavor and was more resistant to textural changes over time compared with the other ice creams. Simplesse was more similar to milk fat than was Dairy Lo in its effect on brown color, cocoa flavor, cocoa character, and textural stability but was less similar in terms of thickness and mouthcoating.

Analysis of Variance↗
PubMed1999

Evaluation of ruminally protected methionine and lysine or blood meal and fish meal as protein sources for lactating Holsteins.

Forty lactating Holstein cows averaging 55 days in milk were used in a randomized block designed experiment to evaluate the effectiveness of ruminally protected Met and Lys compared with that of ruminally undegradable protein for supporting lactation. Cows were fed total mixed diets for 15 wk. Diets were formulated to be isonitrogenous with the same base ingredients resulting in base crude protein percentage of 15.5. Supplemental crude protein supplied by urea, soybean meal, or a 50:50 (wt/wt) mixture of fish and blood meal increased total dietary nitrogen to 18.0% of diet DM. Two additional diets consisted of the basal diets soybean meal and urea, which were supplemented with ruminally protected DL-Met and Lys-HCL at 10 and 25 g/d, respectively (soybean meal + amino acids (AA), urea + AA). Mean measures of dry matter intake, milk yield, milk protein percentage, and milk fat percentage were not affected by protein supplement. Milk protein yield, milk fat yield, casein yield, and casein percentage also were not affected by source of supplemental protein. Results indicate that at the level of crude protein intake relative to milk production in this experiment, the source of protein did not affect lactational performance.

Animal Nutritional Physiological Phenomena↗
PubMed1998

Sensory and physical properties of ice creams containing milk fat or fat replacers.

The purpose of this research was to determine the relative effects of milk fat, nonfat milk solids, or each of three whey protein type fat replacers on the flavor and texture attributes of vanillin-flavored ice cream. Descriptive sensory analyses disclosed that ice creams containing 4.8% of any of the fat replacers in place of milk fat had no demonstrable effect on vanillin flavor but increased the intensities of whey flavor, syrup flavor, and cooked milk flavor. Compared with each substitute, milk fat significantly reduced the syrup, whey, and cooked milk flavors and increased the fresh milk and cream flavors of the ice cream. Results emphasized the importance of fat as a flavor modifier and the importance of certain fat replacers as aids in improving texture.

Animals↗
PubMed1997

Reduced oxidation of fresh pork in the presence of exogenous hydrolases and bacteria at 2 degrees C.

Exogenous lipase and phospholipase A2 added to ground pork released free fatty acids (FFA) and reduced lipid oxidation as indicated by TBA values during storage at 2 degrees C. Bovine serum albumin (BSA) added to ground pork to bind FFA accelerated lipid oxidation. Both lipase and phospholipase-producing bacteria increased in numbers, and pseudomonads that produced lipase and phospholipase became the predominant bacteria growing in pork stored at 2 degrees C. The TBA values of ground pork, which were exposed to the growth of natural microbial flora, were reduced up to 84% during storage at 2 degrees C for 16 d. Pseudomonasfragi K1 inoculated into sterilized ground pork reduced TBA values and oxidation volatiles including saturated aldehydes, unsaturated aldehydes, alcohols and ketones.

Animals↗
PubMed1997

Antiproliferative effects of yogurt fractions obtained by membrane dialysis on cultured mammalian intestinal cells.

The consumption of yogurt has been associated with a reduced incidence of colon cancer in population groups. Bioactive peptides produced during bacterial fermentation may alter the risk of colon cancer via modification of cell proliferation in the colon. Using our previously described cell culture model system, we have isolated a yogurt fraction that decreases cell proliferation. Yogurt was fractionated using 10,000- and 500-Da membrane dialysis. When the yogurt fraction was incubated with IEC-6 or Caco-2 cells, cell division was decreased compared with control treatments, as determined by thymidine incorporation. Cell division was not inhibited in response to a similarly produced milk fraction or in response to solutions of lactic acid. The determination of cell kinetics by flow cytometry revealed a decrease in the number of cells in the initial growth phase in response to the yogurt fraction for the IEC-6 cells, but not the Caco-2 cells. Alpha-Lactalbumin inhibited cell division of both cell lines, but beta-casein did not.

Animals↗
PubMed1994

A cell culture model to identify biologically active peptides generated by bacterial hydrolysis of casein.

Consumption of fermented dairy foods has been linked to reduced incidence of colon cancer in population groups. Recently, biologically active compounds have been isolated from these products. Bacterial proteinases, produced by dairy starter cultures, generate a variety of peptides from casein. Some of these casein-derived peptides are likely to alter intestinal cell kinetics. Effects on colon cell kinetics because of the presence of casein-derived peptides may be a mechanism through which fermented dairy foods reduce the risk of colon cancer. We have used two intestinal cell lines (IEC-6 cells, derived from normal rat intestine, and Caco-2 cells, derived from human colon adenocarcinoma) to identify casein peptides that affect intestinal cell kinetics. Cell culture media containing casein were inoculated with three commercial starter cultures and incubated for 4, 8, or 24 h. The bacteria-conditioned media were then filter-sterilized and incubated with the intestinal cells for 6 or 24 h. Rates of [3H]thymidine incorporation and cell cycle kinetics determined by flow cytometry were affected by the culture-modified media in both cell lines. The IEC-6 cells tended to reduce, and Caco-2 cells to increase, rates of cell division after exposure to the media. Intestinal cell response varied among the starter cultures. The results support the use of intestinal cell cultures to identify casein peptides generated by dairy starter cultures, which affect intestinal cell kinetics.

Adenocarcinoma↗
PubMed1993

Improving survival of culture bacteria in frozen desserts by microentrapment.

Lactobacillus bulgaricus cells were entrapped in beads of calcium alginate and evaluated for their ability to survive freezing processes. Cells survived freezing (without agitation) in ice milk mix much better than in distilled water, and more entrapped cells survived than did cells that were not entrapped. Glycerol and mannitol were cryoprotective, but glucose was not, when each was added (6%) separately to the beads. Entrapment protected the lactobacilli in batch frozen and continuously frozen ice milk mixes. The percentage of survival for entrapped and unentrapped cells in continuously frozen ice milk approximated 90 and 40%, respectively. Lactobacilli survived better in beads with mean diameters > 30 microns than in those averaging 15 microns. Addition of entrapped lactobacilli had no measurable effect on the sensory characteristics of the ice milk.

Alginates↗
PubMed1981

Unique response to heat of extracellular protease of Pseudomonas fluorescens M5.

Eight proteases selected from 38 cultures of psychrotrophic bacteria were subjected to heat stability tests. Cell-free filtrates of the broth in which the cultures were grown individually were heated to 40, 50, 60, and 70 degree C for 0, 15, 30, and 60 min. Six of the filtrates were less than 50% inactivated by heating at 40 degree C for 60 min, whereas the enzyme of Pseudomonas fluorescens M5 was inactivated completely by this treatment. Of the five most proteolytic cultures tested, including P. fluorescens M5, losses in protease activity ranged from 9 to 34% on heating at 70 degree C for 60 min. Purified M5 protease retained at least 75% of its activity over the pH range of 4.5 to 7.5. Electrophoresis of active M5 protease from four chromatographed fractions revealed two bands in each with approximate molecular weights of 35,000 and 45,000. Heating at 40 degree C did not alter mobility of either band. Reasons for lability at 40 degree C but stability at 50, 60, and 70 degree C are discussed. Complexation with casein, observed with another protease, was not a possible explanation for stability at 40 degree C.

Animals↗
PubMed1976

Lecithin agar for detection of microbial phospholipases.

Lecithin agar was developed on which phospholipase C produced turbid zones and phospholipase A produced clear zones. Reactions on lecithin agar agreed 74% of the time with reactions in egg yolk broth. On lecithin agar, interpretation was easier, phospholipase A was detectable, and opaque zones were visible 1 or 2 days earlier than on egg yolk agar. All constituents of the medium can be autoclaved.

Agar↗
PubMed1976

Incidence and identification of phospholipase C-producing bacteria in fresh and spoiled homogenized milk.

Bacteria which produced phospholipase C were isolated from 13 of 34 fresh and 15 of 35 spoiled samples of homogenized milk. No single off flavor was assigned consistently to samples with phospholipase producers, but 75% of them were bitter. Pseudomonads constituted 62% of the isolates. Other phospholipase C-producing genera and their numbers were Acinetobacter, two; Alcaligenes, three; Bacillus, two; Citrobacter, one; Enterobacter, three; and Flavobacterium, two. Two unidentified yeasts also were isolated.

Acinetobacter↗
PubMed1975

Effects of cadmium on the growth and uptake of cadmium by microorganisms.

Six species of microorganisms, Escherichia coli, Bacillus cereus, Lactobacillus acidophilus, Staphylococcus aureus, Streptococcus faecalis and Actinomyces niger, were grown under suitable conditions in appropriate media. Cadmium chloride was added to provide 0, 5, 10, 20, 40, and 80 mug of Cd per ml. At 40 and 80 mug of Cd per ml, E. coli and B. cereus grew well and the other species were repressed. Cd uptake patterns differed significantly among the species tested. The significance of these data with respect to Cd in food chains is discussed.

Aspergillus↗
PubMed1975

Composition of cottontail rabbit milk from stomachs of young and directly from gland.

Milk samples were from stomachs of 27 nursing cottontail rabbits (Sylvilagus floridanus) within 5 min after cessation of nursing. Four milk samples were directly from mammary glands by hand milking aided by tranquilizer and oxytocin. Means and standard errors for 27 stomach samples for total solids, fat, protein, lactose, and ash were 33.6 +/- .8%, 13.9 +/- 1.7%, 14.6 +/- .5%, 2.22 +/- .05%, and 2.06 +/- .07%. Those values of 4 samples directly from the gland were 35.2 +/- .4%, 14.4 +/- .4%, 15.8 +/- .6%, 2.67 +/- .26%, and 2.07 +/- .06%. Fatty acid compositions were similar for the groups, except linoleic acid was 30.0% of fatty acids from stomach milk and 24.7% in milk obtained directly. Differences between sampling methods in palmitoleate, stearate, and oleate may have been from differences in season of sampling. Minerals were more concentrated in milk obtained directly, except potassium. Differences between milks of domesticated and cottontail rabbits are discussed.

Animals↗
PubMed1973

Effects of homologous bacteriophage on growth of Pseudomonas fragi WY in milk.

Pseudomonas fragi strain WY and its homologous bacteriophage were added in varying concentrations to sterile skim milk which was stored at 7 C for 72 hr. When the initial concentration of the bacterial host was 100,000/ml, addition of as few as 10 plaque-forming units per ml of bacteriophage resulted in significantly lower counts in treated skim milk than in the controls which contained no phage. There was no significant effect, however, when the phage input was 1 in 10 ml and the bacterial count was 1,000 or 100,00/ml. No differences in bacterial counts occurred even when the phage concentration was 1,000/ml if the initial bacterial concentration was only 1,000/ml.

Animals↗
PubMed1973

Characterization of a heat-stable protease of Pseudomonas fluorescens P26.

A heat-stable, extracellular proteolytic enzyme was isolated from Pseudomonas fluorescens P26. Brain heart infusion broth (Fisher Scientific Co.), pH 7.5, and incubation at 21 C provided the optimal conditions for bacterial growth for enzyme production. The organism had a D value of 2.6 min at 62.8 C (145 F). The enzyme, however, was quite heat-stable, requiring 15 hr at 62.8 C, 8 hr at 71.4 C, and 9 min at 121 C for complete inactivation. Milk, whey, and casein each had a protective effect on the enzyme against heat inactivation. Purification was accomplished by growth of organisms in broth, centrifugation, sterilization by filtration, ammonium sulfate precipitation (55% saturation), dialysis (against six changes of water), and protein separation by passage through a Sephadex G-100 column. Ultracentrifugation revealed a single band with a sedimentation coefficient of 1.51 which suggested a molecular weight of approximately 23,000. As little as 0.2 unit of the purified enzyme caused detectable flavor defects during 30 days of storage at 4 C, and the Hull test for liberation of tyrosine compared favorably in sensitivity with the sensory method in milk.

Amino Acids↗