Food Suspensions Research Articles

Clearance rates of Oikopleura in cold coastal Newfoundland waters: a predictive model and its trophodynamic implications

Oikopleura vanhoeffeni inhabibng cold coastal Newfoundland waters are much larger than the extensively studied warm water species, 0. dioica; nevertheless they possess fine-meshed feeding filters capable of retaining the nanoplankton that dominate the water column throughout much of the year. Total clearance rates were determined using radioactively labelled algae presented to ~ndividuals in feeding chambers in situ over a seasonal range of ambient water temperatures and food concentrations. Stepwise multiple regression analysis indicated that oikopleurid size explained 46 % of the variance in clearance rate. An additional 10 O/o of the variation was explained by the ambient b~omass concentrations of chain-forming diatoms and of picoplankton (< 2 pm In d~amete r ) , consistent with a filter-clogging interpretation. Water temperature was not a sign~flcant vanable in the regression model and its coefficient was negative, indicating that clearing rates were highest at the near 0 C temperatures characteristic of the spring bloom, a period when bacterial activity is suppressed. Water column clearing rates attributable to Oikopleura populations were comparable to those calculated for the copepod commun~ty based on published data. The large size and c o ~ ~ s p ~ c u o u s pigmentation of 0. vanhoeffenj should make them particularly susceptible to visually feeding planktivores and they may thus constitute an important link in the food chain supporting a large commercial fishery. p-p -MARINE ECOLOGY PROGRESS SERIES Mar. Ecol. Prog. Ser. INTRODUCTION mucous house Members of the family Oikopleuridae feed within a roughly spherical mucous 'house' (Lohmann 1899) containing 2 sets of filters (Fig. 1). Sinusoidal movement of the oikopleurid's muscular tail draws water into the house through the coarse incurrent filters that exclude large particles, and then pumps the water through finer feeding filters where sieving action results in a concentrated food suspension. This suspension is then further concentrated by a mucous pharyngeal net which conveys food particles into the mouth (Deibel 1986). These animals are able to concentrate plankton too small for efficient consumption by setose-appendage feeding copepods and may constitute a key pathway of energy flow from nano and picoplankton to higher trophic levels. The phytoplankton biomass of cold coastal Newfoundland waters is dominated by small nanoincurrent filters

Ecological significance of individual variability in copepod bioenergetics

High interstage variability in body length and mass, reproductive state, and metabolic activity is characteristic of copepod populations from the Barents Sea and coastal waters in Sweden and Norway. The dry weight of a given copepodite stage, sampled at a given time from a homogeneous water mass, may vary by a factor of 4–5 between extreme individuals, protein and particularly lipid content being even more variable. Similarly, high variability in gut fullness and grazing rate within defined copepodite stages typically occurs at all times of the year, both when measured as in situ rate or experimentally determined rate, using homogeneous food suspensions. In accordance with this, maturation state (measured as length of gonads) and spawning (measured as rate of egg production over 24 h) are highly variable factors at the individual level. Since all these factors also influence the metabolic rate of the animals the respiratory rate (measured as ETS activity) of comparable individuals may vary by a factor of 5 or more. The results indicate that high individual variability in size and activity parameters is universal. This can not be explained by existing models of feeding behaviour, growth and development, and calls for new models, in which the nutritional history of the individual may play an important role.

Intermittent flow system for population toxicity studies demonstrated with Daphnia and copper.

Until the introduction of continuous-flow procedures, the physical aspects of testing the toxicity of chemicals and aqueous effluents to aquatic organisms had been of minor consideration. Today's devices ranging from pneumatic systems to electric pumps, all have some drawback or other but many of them are reduced to a minimum by the use of the proportional diluter, which is a well-established and reliable dosing apparatus. However, the Mount-Brungs diluter cannot be used for testing volatile chemicals, nor does it allow simultaneous dosing of a constant food suspension and several toxicant concentrations, which are important conditions for population toxicity studies with small invertebrates like the crustacean Daphnia magna. These restrictions are removed by the use of electric pumps, solenoids and time relays. The system described here provides for the delivery of 250 mL every 5 min to 6 h with no perceptible current-induced effects on the test organisms; it allows the automatic supply of known concentrations of food at each dilution cycle as well as the testing of volatile chemicals. In order to illustrate its usefulness in tests with Daphnia populations, the toxicity of copper was tested.

An improved version of the Haney grazing chamber

SUMMARY An in situ grazing chamber is described which facilitates the handling of radioactive materials, improves the capture of zooplank‐ ton, and optimizes the mixing of labelled food particles into the food suspension.

LITERATURE ABSTRACTS

GENERAL PRINCIPLES: Effect of Different Tube Materials on the Steady Shear Tube Flow of Semi‐Solid Foods. M. Dervisoglu and J. L. KokiniGENERAL PRINCIPLES: Predicting and Flow Properties of Food Suspensions of Plant Origin. M. A. RaoGENERAL PRINCIPLES: Viscoelastic Properties of Semisolid Foods and Their Biopolymeric Components. J. L. Kokini and G. J. PlutchokGENERAL PRINCIPLES: Measurement and Interpretation of Rheological Properties of Foods. E. B. Bagley and D. D. ChristiansonGENERAL PRINCIPLES: Mixed Proteinaceous Emulsiflers: Review of Competitive Protein Adsorption and the Relationship of Food Colloid Stabilization. Eric DickinsonGENERAL PRINCIPLES: Viscosity Behaviour of Vicia Faba Protein Isolates and Their Acetylated Derivatives. G. Schmidt, H. Schmandke and R. SchottelGENERAL PRINCIPLES: Functional Properties of Safflower Protein Isolates: Water Absorption, Whipping and Emulsifying Characteristics. Octavio Paredes‐López and César Ordorica‐FalomirINSTRUMENTATION ∧ METHODOLOGY: Dynamic Rheological Measurements on Heat‐Induced Mymh Gels: An Evaluation of the Method's Suitability for the Filamentous Gels. Bjørg EgelandsdalINSTRUMENTATION ∧ METHODOLOGY: Extrusion Behavior of Different Soya Isolates and the Effect of Particle Size. P. R. Sheard, J. R. Mitchell and D. A. LedwardINSTRUMENTATION ∧ METHODOLOGY: Back‐Extrusion of Non‐Newtonian Fluids. J. F. Steffe and F. A. OsorioINSTRUMENTATION ∧ METHODOLOGY: Instrumentation for Rheological Measurements of Food. C. F. Shoemaker, J. I. Lewis and M. S. TamuraINSTRUMENTATION ∧ METHODOLOGY: Methods for Measurement of Rheological Changes During Thermally Induced Gelation of Proteins. D. D. HamannINSTRUMENTATION ∧ METHODOLOGY: Effect of Sample Weight and Orientation in the Shear Press Testing of Canadian Bacon. G. E. Skinner and V. N. M. RaoINSTRUMENTATION ∧ METHODOLOGY: Effects of Freeze‐Thaw Abuse on the Viscosity and Gel‐Forming Properties of Surimi from Two Species. B. Y. Kim, D. D. Hamann, T. C. Lanier and M. C. WuOBJECTIVE MEASUREMENT: Rheological and Thermal Properties of Agarose and Kappa‐Carrageenan Gels Containing Urea, Guanidine Hydrochloride or Formamide. M. Watase and K. NishinariOBJECTIVE MEASUREMENT: Comparative Studies of the Meehnnicpl Properties of Mixed Gels Formed by Kappa Carrageenan and Tarn Gum or Carob Gum. P. Cairns, V. J. Morris, M. J. Miles and G. J. BrownseyOBJECTIVE MEASUREMENT: The Precipitation of Bovine Plasma Proteins By Anionic Polysaccharides 2. Rheological Study of the Coprecipitates Obtained With Sodium Alginate and λ‐Carrageenan. M. P. Goncalves, C. M. Bourgeois, J. Lefebvre and J.‐L. DoublierOBJECTIVE MEASUREMENT: Research of Tests for pndiction and Estimation of Quantitative and Qualitative Characteristics of Wheat Gluten. J. C. Autran, B. Godon, K. Kobrehel, B. Laignelet and Y. PopenauOBJECTIVE MEASUREMENT: Comparison of Sensory and Instrumental Texture ProfUe Techniques for the Evaluation of Beef and Beef‐Soy Loaves. P. L. Brady, F. K. McKeith and M. E. HuneckeOBJECTIVE MEASUREMENT: Sensory Characteristics, Shear Values and Cooking Properties of Ground Beef Patties Extended with Iron and Zinc‐Fortified Soy Isolate, Concentrate or Flour. B. W. Berry, K. F. Leddy and C. E. BodwellOBJECTIVE MEASUREMENT: Relationships of Instrumental Textural Roperties and Muscle Fiber Types to the Sensory Properties of Beef. S. C. Seideman and L. K. TheerFACTORS AFFECTING TEXTURE: Effects of an Autolyzed Yeast on Physical and Sensory Properties of Frankfurters. L. L. parks, J. A. Carpenter and J. O. ReaganFACTORS AFFECTING TEXTURE: Quantitative Analysis of Texture Change in Cod Muscle During Frozen Storage. Y. J. KimFACTORS AFFECTING TEXTURE: Water Absorption in Cereal Grains and Its Effect on Their Rupture Stress. E. U. U. Ituen, J. P. Mittal and J. S. AdeotiFACTORS AFFECTING TEXTURE: Effect of Feed Moisture and Barrel Temperature on the Rheological Properties of Extruded Cowpea Meal. M. B. Kennedy, R. D. Phillips, V. N. M. Rao and M. S. ChinnanFACTORS AFFECTING TEXTURE: Culture Effect on Ripening Characteristics and Rheological Behavior of Cheddar Cheese. G. F. Amantea, B. J. Skura and S. NakaiFACTORS AFFECTING TEXTURE: Effects of Polysaccharide Stabilizers on the Nucleation of Ice. A. H. Muhr, J. M. V. Blanshard and S. J. SheardFACTORS AFFECTING TEXTURE: Effect of Frozen Storage on Protein Denaturation in Bovine Muscle. II. Influence on Solubility, Viscosity and Electrophoretic Behaviour of Myoilbrillor Proteins. J. R. Wagner and M. C. AnonFACTORS AFFECTING TEXTURE: Heat Treatment of Whipping Cream II Effect on Cream Plug Formation. A. Streuper and A. C. M. Van HooydonkFACTORS AFFECTING TEXTURE: Innuence of Added κ‐Casein and β‐Lactoglobulin in the Heat Coagulation Time/pH Profile of Buffalo Milk. M. K. Bhavadasan, Y. S. Rajput and N. C. GonguliFACTORS AFFECTING TEXTURE: Effect of Sweeteners/Stabilizer Interactions on the Viscosity and Freezing Point of Ice Cream Mix. S. A. Wittinger and D. E. SmithFACTORS AFFECTING TEXTURE: Functional Properties of Meal Products of the Nigerian ‘Red Skin’ Groundnut (Arachis hypogaea L.). Alfred I. IhekoronyeFACTORS AFFECTING TEXTURE: Effects of Wheat Proteins on the Viscoelastic Properties of Starch Gels. Lennart Lindahl and Ann‐Charlotte EliassonRELATIONSHIP TO STRUCTURE: Degradation in Muscle Fibreconnective Tissue Junctions in the Spotted Trevalla (Seriolella punctata) Examined by Scanning Electron Microscopy. H. Allan Bremner and Ian C. HallettRELATIONSHIP TO STRUCTURE: Biochemical Components of Wheat Flour in Connection With Cookie Quality. M. Cottenet

A REVIEW of PARTICLE BEHAVIOR IN TUBE FLOW: APPLICATIONS to ASEPTIC PROCESSING1

ABSTRACTThe design of holding tubes for continuous sterilization of foods containing large particulates depends heavily on knowledge of pipe flow behavior of food suspensions. Although directly related literature is limited, a considerable body of potentially useful literature is available on solid‐liquid flows. This critical review discusses literature on solid‐liquid flow in tubes, including capsule flow, effects on bends, radial migration phenomena, particle‐particle interactions, modeling studies and other topics which may have a bearing on particle velocities in holding tubes.

Feeding mechanism and house of the appendicularian Oikopleura vanhoeffeni

Although the feeding apparatus of oikopleurid Appendicularia has been described in general, functional details of the feeding mechanism and fluid mechanical constraints on the feeding process remain unknown. My goals were to determine the number of mucous-net layers in the feeding filter of Oikopleura vanhoeffeni collected from March 1985 to February 1986, and to describe the pathway of water flow through the filter. Marker particles (i.e. Isochrysis galbana, carmine, charcoal powder, and starch), and rhodamine dye were added to the natural food suspension to help in visualizing structure and flow. The feeding filter was composed of three layers. Water flowed into the filter through two large, lateral openings at the base of each wing, and along the open distal margins of the filter. Under hydrostatic pressure generated by the tail, water moved through the filter in a one-way bulk flow and was forced through the mucous mesh of both the dorsal and ventral layers. Thus, the feeding filter concentrated the food suspension by sieving most of the incoming water. The filter did not collect or trap food particles. Because of its function, I propose calling the feeding filter the “food concentrating filter”.

Ammonium release by zooplankton in suspensions of heat-killed algae and an evaluation of the flow-cell method

The maximum e:o.:nclion rate of ;o.,IH 4 tJQ nmnl mg dry wt h I was Jircctly measured (01 DtlphnitJ pllll'x hy measuring NH4 ,1I,:l'umulalinn in bottles containing D, pU/I'X and dense, atiating suspen sions was not ~jgniflCantly different from that obtained in the ~)(tles . lbe considerable experiment-to-experimelll variation in NH4 e:o.:cn: tion was in large part !.:nrrelated /,2 = 0.73) with the feeding rate on the algae . A large percentage of nitrogen excretion in zooplankton and other animals can result from immediate catabolism of ingested proteins (e .g. Brody. 1945; Warren and Davis. 1967: Corner el a[. , 1972: Lehman . 1980: Gardner and Scavia. 1981 : Bidigare. 1983: Roman, 1983), Thus nitrogen excretion should be measured as a function of ingestion rate of food . For herbivorous zooplankton, nitrogen excretion has never been directly measured correctly and unambiguously for zooplankton feeding in suspensions of their food . algae. because of immediate sequestering of excreted nitrogen by the algae (e.g. Takahashi and Ikeda. 1975: Lehman. 1980; Gardner and Scavia. 1981). Two promising approaches to circumvent this problem have been those of Lehman (1980) and Gardner and Scavia (1981). Potential difficulties of the Lehman (1980) method are the great labor and skill requisite for determining both algal and zooplankton nutrient kinetics and the assumptions implicit in Ihe model that describes interactions among nutrients, algae and zooplankton. In the Gardner and Seavia (1980) flow-cell method. a zooplankler is taken from its suspension of food and placed in a small (0.05 mI) flow cell, where nutrient accumulalion is measured at to-min intervals over time . Nutrient release rate in the food suspension is estimated by extrapolation back to time zero because it decreases with time after removal of the organism from food. This method would appear to be ideally suited for determining nitrogen excretion for individuals but not as useful for populations since many individuals' rates must be measured to get a population estimate. Potential artifacts in this method for some zooplankton could be (i) handling and containment effects and (ii) differing release pallerns in the presence and absence of food thai cannot be corrected by extrapolation back to time zero. As an alternative to these methods, we proposed that excretion rate could be directly determined by measuring nitrogen accumulation in bottles containing zooplankton and suspensions of heat-killed phytoplankton. In this paper we apply this approach to determine the rate of NH. excretion and its relation to feeding rate of Daphnia pulex in © IRL Press Limited . Oxford , England 341 ItA. Vanderploeg tI aI. dense. satiating conccntr:..Ilions of algae. In addition. we evaluate (he assumptions implicil in Ihe Gardner and Scavia (1'181) mClhod by comparing NH, cxerclion (If z(~>planklor in suspensions or heal-killed algae wilh Ihal of zooplanklon in Ihe flow cell afler Ihei, removal from the suspensions.

Response of the respiratory rate of Daphnia magna to changing food conditions.

The respiratory rate of the cladoceran Daphnia magna was measured at varying concentrations of a green alga in a flow-through respirometer. Daphnids were either preconditioned to the respective food concentration or the food concentration was suddenly changed during the experiment and the response of the respiratory rate monitored. Previously starved animals were provided with food or prefed animals were deprived of food. The respiratory rate increased considerably with increasing concentrations of algae until a maximum rate was reached at a critical algal concentration corresponding to the "incipient limiting level" for feeding. The response of the respiratory rate to changing food conditions was fast, lagging only a few minutes behind the change in food. The respiratory rate of starved daphnids increased quickly when they received food, even at low concentrations. Prefed daphnids responded to the replacement of the food suspension by filtered water with reductions in their respiratory rates. A linear relationship between the assimilation rate and the respiration rate was found, indicating that the more than twofold range of the respiratory rate was due to specific dynamic action. The SDA coefficients of 0.15-0.24 found for Daphnia are consistent with values for marine zooplankton.

The Social Food-Flow Within the Colony of a Stingless Bee, Melipona Favosa (F.)

Trophallaxis in workers of stingless bees was studied in colonies of Melipo favosa with marked individuals. In the brood area of the nest all trophallactic interactions are initiated by the soliciting bee, whereas spontaneous offerings occur particularly near the nest exit. The trophallactic network within the colony does not represent an open system that leads to even distribution. The cell-provisioning bees obtain food, mainly from other bees. Since cell-provisioning is strongly age-dependent, the trophallactic benefit changes strongly according to the age of the bees. The bees that discharge on a particular day are not involved in the pollen uptake from food pots on that day. The dischargers probably obtain trophallactically a liquid food suspension with a high pollen content, which they subsequently regurgitate into the brood cells. The dischargers also perform active food solicitations with other bees immediately after they have discharged during the progress of the provisioning of a cell. For this they often depart quickly from the cell that is being filled. We assume that their withdrawal from the cell vicinity enhances their chances to meet quickly bees that are less reluctant than the other dischargers nearby to donate food to them. This behavior sometimes enables dischargers to perform subsequent regurgitations in the same cell.

Filter mesh size and food particle uptake by Daphnia.

Food size selection of four Daphnia, species (D. magna, D. hyalina, D. galeata, D. pulicaria) was investigated using spherical plastic beads as artificial food and with small bacteria. The size of the particles ranged from 0.1 to 35 μm with special emphasis to the particle diameters between 0.1 and 1 μm. In one set of experiments a mixture of differently sized particles was offered as food suspension and the selectivity of filtering was determined by comparing the size spectrum of the particles found in the gut contents with the spectrum in the food suspension. In a second series of experiments suspensions of uniformly sized particles were offered to single animals and their feeding activity was observed directly. In both types of experiments the mesh sizes of the filtering apparatus of the respective animals studied were measured after the experiments by, scanning electron microscopy. The mean sizes of the filter meshes were about 0.4-0.7 μm. In all experiments the size of the particles found in the gut or those which caused high feeding activities were larger than the smallest mesh sizes of the filters. As a consequence simple mechanical sieving provides a sufficient explanation for the mechanism of particle retention of the filtering process in Daphnia. D. magna was found to feed with high efficiency on suspended freshwater bacteria, the residual species investigated showed low filtering efficiencies when bacteria were offered as food.

Functional conflicts between feeding and gas exchange in suspension-feeding tadpoles, Xenopus laevis.

Air-breathing tadpoles of Xenopus laevis (Amphibia: Anura) use buccopharyngeal surfaces for both gas exchange and capture of food particles in the water. In dense food suspensions, tadpoles decrease ventilation of the buccopharynx and increase air breathing. The lung ventilatory frequency is elevated even though the rate of oxygen consumption is at or below resting levels, suggesting that the lung hyperventilation reflects compensation for decreased buccopharyngeal respiration rather than an increased metabolic requirement. If tadpoles in hypoxic water are prevented from breathing air, they increase buccopharyngeal respiration at the expense of feeding. Aerial respiration evidently permits the buccopharyngeal surfaces to be used primarily for food entrapment.

Ecological studies of a fouling bryozoan, Bugula neritina - II. Suitable food plankton for growth of a bryozoan Bugula neritina under laboratory conditions.

Two slide glasses each bearing three to five larvae of Bugula neritina attached had been placed in a one-liter beaker holding 800m/ of filtered seawater. After the daily renewal, adequate volume (10-60m/) of the cultured plankton was supplied into the beaker to make the food suspension at a definite density. The geometric means of the zooid number per colony after ten-day's culture with various food planktons were determined to compare the dietary effect. The salinity and temperature of culture water were maintained from 33.4 to 34.3‰ and from 21 to 23°, respectively. Of 24 species examined, Rhodomonas sp. supported the best growth; all young colonies exponentially increased the zooid number, from one to 72 in ten days. The growth was almost equal to that under the best natural conditions. Oxyrrhis marina cultured in the medium enriched with yeast extract was the most suitable food next to Rhodomonas (48 zooids in ten days). When fed on Dunaliella tertiolecta and Prorocentrum obtusidens, the colonies increased the zooid number only to 18 and 12, respectively. Diatoms and armored planktons had no dietary value for the animal.

Supplementary effect of several nutrients on nutritive deficiency of baker's yeast for population growth of the rotifer Brachionus plicatilis.

The culture of the sterilized rotifer Brachionus plicatilis with washed cells of a baker's yeast revealed that the yeast had no nutritive effect on the pupulation growth of the rotifer. Nutritive quality of experimental suspensions was evaluated by two kinds of culture, one of which was individual culture in which the rotifers were cultured separately in test tubes and observed daily to obtain the survival rate and fecundity while food suspension was renewed daily. From daily counts, intrinsic rate of population increase and net reproduction rate were calculated as the indices of nutritive quality of the suspension. The other was batch culture in which teh rotifers were maintained in the food suspension without any daily treatment. After 6 or 7 days culture, the increase in individual number was counted. Out of the nutrients tested on the supplementary effect, vitamin B12 was most effective. Pollack liver oil (feed oil) and cystine were also effective in strengthening the nutritive quality of the yeast cell suspension. None of the oil spluble vitamins could substitute for the supplementary role of the feed oil.

Rapid enumeration of microorganisms in foods by the direct epifluorescent filter technique.

Filtration of "stomachered" food suspensions through nylon filters (pore size, 5 microns) removed most of the food debris without affecting the recovery of microorganisms. Two to ten milliliters of these prefiltered suspensions could be filtered in the direct epifluorescent filter technique (DEFT). The technique takes less than 30 min to complete and has a lower sensitivity of less than 60,000 microorganisms per g for all products examined. Vegetative bacterial cells, spores, fungal hyphae, and yeasts could be distinguished with the technique. For fresh meat and fish, the DEFT count of prefiltered suspensions agreed well with the plate count of unfiltered suspensions over the range of 10(4) to 10(10)/g (correlation coefficient of 0.91). For frozen meat and fish and frozen vegetables, the two counting methods had correlation coefficients of 0.87 and 0.66, respectively. The poor correlation for frozen vegetables was due to the inclusion in the DEFT count of nonviable bacteria killed by the blanching process used to inactivate enzymes. Good agreement was obtained between the prefiltered DEFT count and unfiltered plate count for cooked meats, cream doughnut, and whole peppers. Possible reasons for the poor agreement between the DEFT count and plate count for certain products are discussed.

Effect of Pre-Filtration and Enzyme Treatment on Membrane Filtration of Foods

Effects of prefiltration and enzyme and surfactant treatments on the filterability of foods were examined. The clarification of food suspensions, using a fine wire cloth prefilter, did not affect microbial recovery from the 87 food samples examined. One hundred and nine foods were clarified by prefiltration and then tested for their filterability through a 0.45-μ Hydrophobic Grid Membrane Filter; 68 could be filtered without any additional treatment. Of the remaining 41 foods. 39 were rendered filterable with an appropriate enzyme or surfactant treatment. The application of these procedures greatly enhances the practicality of membrane filtration for microbiological analysis of foods.

Rapid Enumeration and Identification of Stressed Fecal Coliforms

A rapid (72 h) method for enumeration and subsequent identification of fecal coliforms is described. The procedure consists of plating a food suspension in an agar-repair medium (trypticase soy agar pour plates preincubated at 35 C for 2 h, then overlaid with violet red bile agar) incubated at 45.5 C. Fecal coliforms can be enumerated within 24 h and then confirmed as Escherichia coli within 48 h by subculturing typical colonies to an 1M ViC agar plate. Feasibility and applicability of the procedure were demonstrated by comparing the efficiency of recovery of both stressed and non-stressed cells on the agar repair medium with conventional agar and liquid most-probable-number media.

Food selectivity of the rotifer Brachionus plicatilis feeding on phytoplankton

Food selectivity was examined in amictic female rotifers, Brachionus plicatilis, fed Chlamydomonas sp. and Olisthodiscus sp. Filtering and ingestion rates of the rotifers in a single food suspension were higher with Chlamydomonas sp. than with Olisthodiscus sp. In every mixture of two food species, the apparent filtering rate on Chlamydomonas sp. was much higher than that on Olisthodiscus sp. Total filtering rate and apparent filtering rate in food suspensions containing Chlamydomonas sp. decreased with increasing cell concentration of Chlamydomonas sp. Total and apparent filtering rates were calculated from the decrease in total food concentration as well as from decreases in concentrations of each of the two food algae, respectively. B. plicatilis ingested Olisthodiscus sp. at an extremely low constant rate in all mixtures. The degree of food selectivity of the rotifers fed Chlamydomonas sp. (i.e., selective filtration) from the mixture of two food algae decreased with increasing cell concentration of Chlamydomonas sp. Filtering and ingestion rates of rotifers fed senescent Chlamydomonas sp. were relatively lower than those fed Chlamydomonas sp. in the exponential phase. This indicates that Brachionus plicatilis displays selectivity in regard to condition of cells as well as type of food.

Recovery of Clostridium perfringens, Staphylococcus aureus and Molds From Foods By The Stomacher: Effect of Fat Content, Surfactant Concentration, and Blending Time

A Colworth “Stomacher 400” was compared with an Osterizer blender for preparing food suspensions for microbiological analysis. For most foods there was no significant difference in counts produced by the two methods. For foods containing high concentrations of fat (e.g. more than 20%) the Stomacher gave a slightly lower recovery, but addition of 1.0% Tween 80 to the diluent restored the recovery efficiency. The Stomacher was less lethal than the Osterizer to Staphylococcus aureus, Streptococcus fecalis and Escherichia coli Use of the Stomacher results in considerable time and cost savings, through elimination of washing and resterilizing operations.

MEASUREMENT OF FLOW PROPERTIES OF FOOD SUSPENSIONS WITH A MIXER

Abstract. Flow properties of selected food suspensions (tomato puree, apple sauce, and apple pulp) were studied with a mixer. Power law constants for the suspensions were determined by employing an approximate method based on power correlations for mixers in the laminar flow regime. The studied suspensions cannot be characterized with narrow gap viscometers because of the size and segregation of the particles (formation of a dilute phase next to the rotor).