A medium for the detection of Lancefield Group D cocci in skimmed milk powder by measurement of conductivity changes

A selective medium for the detection of Lancefield Group D cocci in skimmed milk powder by conductivity measurements was developed and evaluated using the Bactometer M123 and Malthus 128H systems. This medium promoted large changes in conductance and capacitance. The calibration curve of detection times vs concentration of Lancefield Group D cocci showed a linear correlation coefficient of 0.93 and the method gave comparable results in both conductivity instruments. Naturally contaminated samples containing c. 10(3) cfu/g of Lancefield Group D cocci gave detection times within 16-18 h which was sufficiently rapid for the medium to be used for the routine screening of skimmed milk powder.     

阪崎肠杆菌能力验证样品均匀性和稳定性的研究

目的制备出以脱脂奶粉为基质的均匀性好、稳定性强的阪崎肠杆菌(Enterobacter sakazakii)能力验证样品。方法研究奶粉基质的粒度、奶粉和菌粉的混合比例,得到阪崎肠杆菌能力验证样品的最佳均匀性条件;研究包装形式及贮存温度对样品稳定性的影响,得到阪崎肠杆菌能力验证样品的最佳稳定性条件。结果要保证样品足够均匀,奶粉最佳粒径范围为120μmD180μm,1 g菌粉最多与300 g奶粉进行混合;贮存温度对样品稳定性有较大影响,高温明显降低样品稳定性;真空包装可以显著提高样品稳定性。结论以奶粉为基质的阪崎肠杆菌能力验证样品的制备能够更准确地考查乳品微生物检验人员的检测水平,为国内微生物能力验证水平的提高奠定了基础。     

Rennet-Induced Aggregation and Curd Formation from Skimmed Milk Powders Prepared under Different Sterilizing Conditions

Heat treatment during the production of skimmed milk powder causes denaturation of proteins, thereby affecting the physicochemical properties of the skimmed milk powder. To understand the effects of heat treatment on the sensitivity of the casein micelles in skimmed milk powders, low heating type (L), normal heating type (N), high heating type (H), and super-high heating type (SH), to reaction with rennet, rennet-induced curd formation was investigated. A well-developed network structure with wide spaces was observed only in the curd derived from the solution of type L skimmed milk powder. SDS–PAGE suggested that there was no difference in the amount of glycomacropeptide generated from κ-casein in the four types of skimmed milk powder, but casein micelles in the solution of type L skimmed milk powder formed aggregates most effectively. These results are discussed with respect to the thermal denaturation of proteins in skimmed milk powder.     

Spore germination based assay for monitoring antibiotic residues in milk at dairy farm

Spore germination based assay involves the transformation of dormant spores of Bacillus stearothermophilus 953 into active vegetative cells. The inhibition of germination process specifically in presence of antibiotic residues was used as a novel approach for monitoring target contaminants in milk. The indicator organism i.e., B. stearothermophilus 953 was initially allowed to sporulate by seeding in sporulation medium and incubating at 55 °C for 18 ± 2 h. The spores exhibited a typical chain behavior as revealed through phase contrast microscopy. The minimal medium inoculated with activated spores was incubated at 64 °C for 2-3 h for germination and outgrowth in presence of specific germinant mixture containing dextrose, whey powder and skimmed milk powder added in specific ratio along with reconstituted milk as negative control and test milk samples. The change in color of the medium from purple to yellow was used as criteria for detection of antibiotic residues in milk. The efficiency of the developed assay was evaluated through a surveillance study on 228 samples of raw, pasteurized and dried milks and results were compared with AOAC approved microbial receptor assay. The presence of antibiotic level was 10.08 % at Codex maximum residual limit having false positive result only in 0.43 % of the samples. The results of the present investigation suggest that developed spore based assay can be a practical solution to dairy industry for its application at farm level, milk processing units, independent testing and R & D centres in order to comply with the legal requirements set by Codex.     

An improved growth medium for Flavobacterium psychrophilum

Supplementing cytophaga agar and broth with 0.5 g l-1 each of D(+) galactose, D(+) glucose, L-rhamnose and skimmed milk gave a dramatic improvement in the isolation of the fish pathogen Flavobacterium psychrophilum. By means of spread-plating, approximately double the number of colonies of larger size were obtained on the improved medium compared to cytophaga agar alone. In supplemented cytophaga broth, growth of Fl. psychrophilum was more rapid and generated greater biomass.     

Optimisation of Tetrahymena rostrata growth using food by-products as nitrogen source

The composition of media based on yeast extract and nitrogen sources for the growth of Tetrahymena rostrata was optimised by a central composite design. Dairy products promoted better growth than fish powder and starch products and improved generation time of 25% compared to previous reports. The best optimised combination was 5.7 g yeast extract/l 6.6 g skimmed milk/l which gave the fastest generation time of 122 min and a maximal population of 8.4 × 105 cells/ml. In the case of buttermilk, two optimised combinations promoted growth : to induce fast growing (130 min) 2.5 g yeast extract/l 4.4 g buttermilk/l must be chosen although to improve maximal population (9 × 105 cells/ml) 6 g yeast extract/l 10 g buttermilk/l was more advisable.     

Survival of the postharvest biocontrol yeast Candida sake CPA-1 after dehydration by spray-drying

Spray drying was evaluated as a dehydrating method to preserve the postharvest biocontrol agent Candida sake CPA-1. The effect of drying temperature, carrier, growth and rehydrating medium on the survival of the yeast was studied. Outlet temperature had more influence on the death of the cells than inlet temperature, and survival decreased with increasing temperature. Spray drying at an inlet temperature of 150°C was optimum in terms of viability, powder recovery and moisture content of the product. Use of 10% (v/v) skimmed milk as a carrier gave the highest survival and percentage of powder recovery (34-47%). Rich rehydration media were found to be better than water or phosphate buffer, with slight differences on survival. Spray-dried cells were less effective than fresh ones in controlling Penicillium expansum rot on apples. Spray drying of C. sake was not a good dehydration method as it gave low cell survival, poor recovery of product, and low efficacy.     

Freeze-drying of live attenuated Vibrio anguillarum mutant for vaccine preparation

Vibrio anguillarum MVAV6203 is a mutant strain as a candidate of live attenuated vaccine. In vaccine preparation, the freeze-drying conditions of the strain were investigated to improve the survival after freeze-drying, including the protectant, rehydration medium, freezing temperature, and initial cell concentration. Vibrio anguillarum MVAV6203 is sensitive to freeze-drying and the viability was only 0.03% in the absence of protectant. Of the tested protectants, 5% trehalose with 15% skimmed milk gave the highest viability of 34.2%. Higher cell survival was obtained by quick freezing at -80 degrees C than slow freezing at -20 degrees C. Initial cell concentration was another important factor, preferable for 1-3 x 10(10)CFU/ml. The supplementation of 10% skimmed milk in rehydration medium improved obviously freeze-drying viability. The combination of the optimal conditions achieved 51.4% cell viability after freeze-drying.     

Optimisation of initial cell concentration enhances freeze-drying tolerance of Pseudomonas chlororaphis

The freeze-drying tolerance of Pseudomonas chlororaphis, an antifungal bacterium used as biocontrol agent was investigated. P. chlororaphis is freeze-drying sensitive and the viability drops more than 3 log units in the absence of protective freeze-drying medium. Of the freeze-drying media tested, lactose, sucrose, trehalose, glutamate, sucrose with glutamate, skimmed milk, and skimmed milk with trehalose, skimmed milk gave the lowest survival (0.6+/-0.2%) and sucrose the highest (6.4+/-1.2%). Cellular accumulation of sucrose from the freeze-drying medium and the protective effect of sucrose were dependent on sucrose concentration. The effect of initial cell concentration, from 1 x 10(7) to 5 x 10(10) CFU/ml, on survival after freeze-drying was studied for carbon starved cells with sucrose as freeze-drying medium. The highest freeze-drying survival values, 15-25%, were obtained for initial cell concentrations between 1 x 10(9) and 1 x 10(10) CFU/ml. For cell concentrations outside this window more than 10 times lower survival values were observed. P. chlororaphis was cultivated to induce stress response that could confer protection against freeze-drying inactivation. Carbon starvation and, to a lesser extent, heat treatment enhanced freeze-drying tolerance. By combining optimal cell concentration, optimal sucrose concentration and carbon starvation the survival after freeze-drying was 26+/-6%.     

Mass cultivation of Tetrahymena thermophila yielding high cell densities and short generation times

Summary A cheap medium, composed of skimmed milk powder, yeast extract, and glucose, for mass cultivation of the protozoon Tetrahymena thermophila has been developed. Cell concentrations of 5 x 10⁶ cells/ml and unprecedented short generation times of only 1.4 h were determined in batch cultures. During the exponential phase of growth, daughter cells initiated a new cell division even before the previous division had been completed, resulting in the formation of cell chains. Addition of glucose extended the stationary phase. Using a bench-top fermentor supplied with a digital control unit the utilization of nutrient components in batch culture was monitored. Milk protein and glucose were consumed completely, but lactose only partly. Correspondence to: A. Tiedtke     

SENSORY PROFILING AND POSITIONING OF COMMERCIAL SAMPLES OF MILK POWDER

Milk powders available commercially are of different qualities. The quality deviations may be due to inherent quality of the milk which in turn is dependent on various conditions like the fat content, the processing parameters, the storage time and the packaging materials used. The various brands of milk powders have been profiled sensorily for odor and flavor and also positioned using Canonical Discriminant Analysis (CDA). The study throws light on the relative qualities of the different brands, their positive and negative points and their relative position with respect to each other. The results indicate that the various types like whole milk powder, partially skimmed milk powder, skimmed milk powder and infant milk formula cluster together into the same group but the groups are separate from each other. The dominant quality attributes for the groups are different and are discussed in relation to the directional vectors.     

响应面法优化产朊假丝酵母培养及干燥工艺

本研究旨在优化产朊假丝酵母液体培养参数及干燥保护剂配方,提高产朊假丝酵母液体培养数量,制备出高复苏率的活性干酵母。以装液量、转速、温度和培养时间为影响因素,设计单因素试验,并采用Box-Behnken试验设计及响应面分析法优化产朊假丝酵母液体培养方案。在此条件下培养酵母,以L-谷氨酸钠、乳糖、脱脂奶粉为影响因素进行单因素保护试验,并采用响应面分析法优化干燥保护剂的组合。结果表明,产朊假丝酵母最佳培养条件为装液量45 mL/250 m L,转速200 r/min,温度30℃,培养时间24 h。在此条件下,培养的产朊假丝酵母数量可以达到9.34×10~8CFU/mL;最佳保护剂组合1%L-谷氨酸钠、12%脱脂奶粉、6%乳糖,经干燥后,产朊假丝酵母复苏率达到81.9%。此时活菌数7.65×10~8CFU/g,比未加保护剂组提高了3.83倍。     

Mathematical approaches to detect low concentrations in progesterone profiles

There is a general need for higher objectivity and accuracy in describing the physiological fertility performance of dairy cows. To develop the alternative meaningful starting points for the selection of genetically superior dairy cows, this study focused on the detection of low progesterone concentrations, which are indicative of estrus events. Three mathematical approaches were used: one based on the exponentially weighted moving average control chart, and two threshold methods, which were developed in-house. Data were collected from one data set that included 97 insemination data of first-lactating Holstein dairy cows, and a second set that included 160 inseminations of primiparous and multiparous Holstein dairy cows. On the basis of these 2 data sets, and using a threshold of 1.2 ng progesterone/ml skimmed milk, the sensitivity of the 3 models was high and ranged between 100% and 93.13%, with an error rate between 4% and 22.17%. The specificity varied between 97.92% and 99.93%. The average concentration levels of true-positive–detected progesterone measures were low and ranged between 0.18 and 0.28 ng progesterone/ml skimmed milk (first data set) and 0.21 to 0.26 ng progesterone/ml skimmed milk (second data set). False-positive–detected low progesterone concentrations during estrus events were closely related to progesterone values around the 1.2 ng progesterone/ml skimmed milk threshold and the detecting rules of the control chart. Thus, we suggest that a threshold of 0.8 ng progesterone/ml skimmed milk is indicative for luteal activity in defatted foremilk. By means of the three methods used, the detection of low progesterone concentrations was possible and it can be assumed that this is a good starting point for further studies (such as interval calculation) in this area.     

Comparison of methods for the recovery and detection of low levels of injured Salmonella in ice cream and milk powder

This study compared the ability of four rapid methods and a standard cultural method to detect low levels of heat-injured cells of Salmonella typhimurium in ice cream and skimmed milk powder. The detection of Salmonella in samples contaminated with low levels (< 10 cfu 25 g-1) was significantly greater with the novel broth method than with the other methods (P 10 cfu 25 g-1, there was no significant difference between the methods except for the novel broth method and a dipstick-based immunoassay (P 相似文献   

A NOTE ON THE USE OF DEHYDRATED MILK AGAR FOR BACTERIAL COUNTS ON RAW AND DRIED MILKS

SUMMARY: The bacterial colony count of raw milk and of milk powder using milk agar prepared from a proprietary brand of the dehydrated medium has been compared with that obtained using the fresh medium prepared in the laboratory.
No significant difference was found in 17 milks which were examined using the roll-tube technique and 8 replicates/medium but in a second series of 32 milks the plate count (3 replicates/medium) was significantly lower on the reconstituted than on the fresh medium.
Some milk powders gave a much lower plate count on the reconstituted medium, due to the inability of the latter to support adequate growth of Streptococcus thermophilus.     

Immunomagnetic separation as an alternative to enrichment broths for Salmonella detection

One hundred and twenty foodstuffs were tested for the enrichment of Salmonella species by immunoseparation. The foodstuffs covered six groups: raw chicken, prawns, skimmed milk powder, herbs and spices, cocoa powder and animal feed. Half of the food samples were spiked with one Salmonella species: Salm. ealing, Salm. enteritidis, Salm. give, Salm. typhimurium or Salm. virchow . Comparison of Salmonella recovery with standard methods (selenite cystine broth, tetrathionate broth and Rappaport-Vassiliadis broth) was carried out. Immunoseparation gave similar numbers of true positives to the standard enrichment methods in a short time period. Only immunoseparation isolated Salmonella species from spiked garlic granules demonstrating the possible recovery of sublethally injured cells.     

A simple plate assay for detection of group A streptococcus proteinase

A simple plate assay based upon the digestion of skim milk contained within Columbia agar base medium has been found to be a sensitive and reproducible method for detection of proteinase production by individual surface grown colonies of group A streptococci. Use of this medium enabled demonstration of proteinase activity by 24-h aerobic cultures, 79% of 72 group A streptococcus M prototype strains being proteinase positive. None of 40 ‘viridans’ streptococcus strains were positive on this medium and of 18 representative strains of different Lancefield serogroups, only the group P streptococcus had proteinase activity similar to that of the group A streptococci. This same medium can also be used for the detection of preformed proteinase present in liquid preparations by a well diffusion assay.     

Confirmatory identification of group D streptococci by slide co-agglutination

Group D streptococci were identified by slide co-agglutination and the results obtained were compared with conventional methods for the presumptive (bile esculin medium, salt tolerance) and confirmatory (Lancefield precipitin test, latex agglutination) identification of these bacteria. Of 137 clinical specimens examined, the co-agglutination procedure showed a 100% specificity and a 96.5–100% sensitivity (depending on the method of testing) in the identification of group D streptococci. The slide co-agglutination test was easy to perform and interpret and offers a valuable alternative to other less rapid techniques for the confirmatory identification of group D streptococci.     

Determination of the structure and molecular weights of the exopolysaccharide produced by Lactobacillus acidophilus 5e2 when grown on different carbon feeds

Lactobacillus acidophilus 5e2 when grown on skimmed milk, skimmed milk supplemented with sodium formate and skimmed milk supplemented with glucose secretes a branched heteropolysaccharide having a weight average molecular weight less than 450 kDa. The exopolysaccharide has a heptasaccharide repeat unit and is composed of D-glucose, D-galactose and N-acetyl-D-glucosamine in the molar ratio 3:3:1. Using chemical techniques and 1D and 2D-NMR spectroscopy the polysaccharide has been shown to possess the following repeat unit structure:     

Improvement of fed batch mass culture for γ linolenic biosynthesis by Tetrahymena rostrata (protozoa)

Summary Despite the general high sensitivity of protozoa to shearing effects,Tetrahymena rostrata was cultivated using a controlled fed batch fermentor; the feeding medium contained 15 % skimmed milk. With an unchanged growth rate, final cell concentration (14.10⁵ cell/ml) was 4 times higher than in simple batch culture. -Linolenic acid (16 % of the total fatty acids) reached 0.5 gr/l medium.