Lactic Starter Cultures Research Articles

Starter culture production in fluidized bed reactor with a flocculent strain ofL. plantarum

A lactic starter culture of a flocculentLactobacillus plantarum was produced in a fluidized bed reactor with higher cell volumetric productivities than in a continuous stirred tank reactor. The fluidized bed reactor was operated at optimised parameters obtained in batch reactor performed with and without pH control.

Fate and Thermal Inactivation of Listeria monocytogenes in Beaker Sausage and Pepperoni

Listeria monocytogenes may survive the typical process used to produce sausage such as pepperoni and hard salami that is made from uncooked meat. Studies were done to identify heat treatments that could be applied during sausage-making to inactivate the organism to undetectable levels. Initial studies with beaker sausage revealed that heat treatments of 51.7°C for 8 h or 57.2°C for 4 h reduced L. monocytogenes counts by >2 log10 CFU/g, but for each treatment the organism was detected by enrichment in one of two samples. Heating beaker sausage to an internal temperature of 62.8°C inactivated listeriae to undetectable levels. Studies with pepperoni revealed that heating sausage at 51.7°C for 4 h after fermentation but before the drying cycle killed most L. monocytogenes, but the organism was occasionally detected in samples during drying. Heating pepperoni at 51.7°C for 4 h after the drying cycle completely inactivated L. monocytogenes in all samples. An additional study done to determine the fate of L. monocytogenes in beaker sausage made with and without lactic starter culture revealed that the organism could grow at 32.2°C in sausage batter during the fermentation period if the lactic starter culture was not added. The organism did not grow, but was reduced by about 1 to 2 log10 CFU/g during fermentation, in sausage made with lactic starter culture.

Detection of hydrogen peroxide produced by meat lactic starter cultures

Twelve strains of meat lactic starter cultures (Pediococcus spp. and Lactobacillus plantarum) were found to produce hydrogen peroxide in vitro. The (cumulative) amounts of H2O2 produced were measured through the peroxidative action of catalase on H2O2 and oxidation of added formate to CO2 by the H2O2‐catalase complex formed. There was a problem in building a calibration curve for converting values of formate oxidation into amounts of H2O2, either by adding H2O2 directly to the assay mixture or having it produced via a glucose‐glucose oxidase system.

Behavior of Listeria monocytogenes in Skim Milk during Fermentation with Mesophilic Lactic Starter Cultures

The ability of Listeria monocytogenes to grow and compete with mesophilic lactic acid bacteria was examined. Autoclaved skim milk was inoculated with 103 cells of L. monocytogenes (strain V7 or Ohio)/ml, and with 5.0, 1.0, 0.5 or 0.1% of a milk culture of either Streptococcus cremoris or Streptococcus lactis. Inoculated milks were fermented for 15 h at 21 or 30°C, followed by refrigeration at 4°C. Samples were plated on McBride Listeria Agar to enumerate L. monocytogenes and on either APT Agar or plate count agar to enumerate lactic acid bacteria. L. monocytogenes survived in all fermentations, and commonly also grew to some extent. Incubation at 30°C with 5% S. lactis as inoculum appeared to be the most inhibitory combination for strain V7, causing 100% inhibition in growth based on maximum population attained. S. cremoris at the 5.0% and 0.1% inoculum levels, was slightly less inhibitory to L. monocytogenes at 37°C, but it was slightly more inhibitory to L. monocytogenes at the 1.0% inoculum level than was S. lactis. In general, S. lactis reduced the pH of fermented milks more than did S. cremoris. The population of L. monocytogenes began to decrease before 15 h in only one test combination, which was use of a 5.0% inoculum of S. cremoris and 30°C incubation. In most instances, growth of the pathogen appeared to be completely inhibited when the pH dropped below 4.75.

Bacteriophages of lactobacilli

Lactobacilli are members of the bacterial flora of lactic starter cultures used to generate lactic acid fermentation in a number of animal or plant products used as human or animals foods. They can be affected by phage outbreaks, which can result in faulty and depreciated products. Two groups of phages specific of Lactobacillus casei have been thoroughly studied. 1. The first group is represented by phage PL-1. This phage behaves as lytic in its usual host L. casei ATCC 27092, but can lysogenize another strain, L. casei ATCC 334. Bacterial receptors of this phage are located in a cell-wall polysaccharide and rhamnose is the main component of the receptors. Ca 2+ and adenosine triphosphate (ATP) are indispensable to ensure the injection of the phage DNA into the bacterial cell. The phage DNA is double-stranded, mostly linear, but with cohesive ends which enables it to be circularized. The vegetative growth of PL-1 proceeds according to the classical mode. Cell lysis is produced by an N-acetyl-muramidase at the end of vegetative growth. 2. The second group is represented by the temperate phage φFSW of L. casei ATCC27139. It has been shown how virulent phages originate from this temperate phage in Japanese dairy plants. The lysogenic state of φFSW can be altered either by point mutations or by the insertion of a mobile genetic element called ISL l, which comes from the bacterial chromosome. This is the first transposable element that has been described in lactobacilli. Lysogeny appears to be widespread among lactobacilli since one study showed that 27% of 148 strains studied, representing 15 species, produced phage particles after induction by mitomycin C. Similarly, 23 out of 30 strains of Lactobacillus salivarius are lysogenic and produce, after induction by mitomycin C, temperate phages, killer particles, or defective phages. Temperate phages have also been found in 10 out of 105 strains of Lactobacillus bulgaricus or Lactobacillus lactis after induction by mitomycin C. Phages so far studied of the latter 2 and closely related lactobacilli, either temperate or isolated as lytic, may be divided into 4 unrelated groups called a, b, c and d. Most of these phages are found in group a and an unquestionable relationship has already been shown between lytic phages and temperate phages that belong to this group. Lytic phage LL-H of L. lactis LL 23, isolated in Finland, is one of the most representative of those of group a and has been extensively studied on the molecular level.

Preparation of Cheddar Cheese at Elevated Temperatures

Reduction of Cheddar cheese making time was investigated by regulating the amount of lactic starter culture initially added to the milk and preparing the cheese at 37.8°C. Laboratory trials showed that in conventional cheese making at 31.1°C, an initial cell count of 107 cfu/ml was necessary to achieve a 109 cfu/g population density and desirable acidity (pH 5.3 to 5.4) at the milling stage. In the modified process, cheese curd was prepared by prewarming milk to 37.8°C and adding starter culture at 108 cfu/ml and milk coagulant (veal rennet) simultaneously. This method shortened preparation time by as much as 90min, depending on the acid production of the starter culture. Cheeses made in six trials were stored at 4.4°C for 1 yr. Ratings by an expert panel showed no significant differences in flavor, body, and texture characteristics that could be attributed to the method of preparation. On a 5-point intensity scale, increase in sharpness correlated significantly (P⩽.05) with storage time with slightly greater increase observed in the experimental cheese. No difference in sharpness was significant between samples made by conventional and experimental methods. Decline in curdiness with storage time showed similar correlations. The results suggested that reduction of make time by increasing starter culture inoculum to 108 cfu/ml and renneting at the time of setting at a higher temperature (37.8°C) improved aging characteristics of the finished cheese over the storage time studied.

An attempt to produce ras cheese by direct acidification

Ras cheese was made from cow's milk acidified with either lactic or citric acid to pH 5·8 with and without the addition of GDL to the resultant curd from each acidulant. Also, control Ras cheese was made using lactic starter culture. The cheese made from the direct acidified milk showed slightly higher moisture and salt contents compared with the control. This was associated with slightly lower fat and acid contents. Also, the cheese made by direct acidification contained lower levels of SN, NPN, AN and TVA compared with the control cheese. The direct acidified cheese was characterized by poor body, crumbly texture and weak flavour intensity. Cheese made from citric acid-acidified milk was more acceptable than that made from milk acidified with lactic acid.

Growth of Lactic Acid Bacteria in Highly Concentrated Ultrafiltered Skim Milk Potentates

Buffer capacity of ultrafiltered skim milk retentates at various protein concentrations and growth of direct set, frozen concentrated lactic starter cultures in such retentates were studied. Maximum buffering occurred at approximately pH 5.1 to 5.3. An average .48% lactic acid concentration was required to reduce the pH of plain skim milk to 4.6 compared with 1.01% for skim milk retentates concentrated 2.3:1 and 1.14% for skim milk retentate concentrated 2.6:1. Skim milk retentates concentrated 4.3:1 and 5.8:1 were unable to attain pH 4.6 even when titratable acid was greater than 1.8%.Lactic acid required to reduce pH to 4.6 for the two lower concentrated retentates (2.3:1 and 2.6:1) were 1.85 and 2.45%. Time to attain pH 4,6 was a function of the bacterial cell concentration of the cultures and the total protein level of retentates. Starter organism growth was unaffected by high total solids or ash of retentates. Growth rate and lactose metabolism decreased markedly below pH 5.2 at which point bacterial population was 109 cfu/ml.

Factors Affecting Nonenzymatic Browning of Process Cheese

Variations in manufacturing procedures and the composition of stirred-curd Cheddar cheese were investigated for effects on nonenzymatic browning in process cheese. Using a nongalactose-fermenting Streptococcus thermophilus culture as an adjunct to mesophiic lactic starter culture resulted in increased galactose concentration in cheese and intensified browning of process cheese. The correlation between galactose content in stirred-curd cheese and brown color intensity in process cheese was very high (r=.929). Higher salt-in-moisture ratios of stirred curd cheese were related to more intense brown color in process cheese. The high salt-in-moisture ratio probably reduced the catabolic activity of the lactic starter and resulted in more residual lactose and galactose in the cheese. Increasing available amino groups in stirred curd cheese by adding casein hydrolysate proved inconclusive. Faster cooling of process cheese from 80 to 37.7°C reduced intensity of brown color. Process cheese cooled very rapidly did not develop any brown color, regardless of sugar and salt contents. Browning may be controlled by regulating salt and by using strains of Streptococcus thermophilus that ferment galactose.

Examination of Strain Interaction in a Multiple-Strain Lactic Starter Culture by Streptomycin-Resistant Mutants of Lactic Streptococci

Streptomycin-resistant mutants of lactic streptococci were used to determine strain dominance and suppression in a multiple-strain Cheddar cheese starter culture composed of two Streptococcus lactis and four Streptococcus cremoris strains. This was accomplished by growing the six strains together in six separate batches of nonfat milk and substituting a different streptomycin-resistant mutant in each experiment. Samples were taken periodically and plated onto media with and without added streptomycin. In this manner, the resistant strain in each batch could be identified and counted during growth in mixed culture. Two-strain combinations were studied similarly. Both Streptococcus lactis strains significantly inhibited two of the four Streptococcus cremoris strains, and one instance of Streptococcus cremoris-Streptococcus cremoris inhibition was found. Speculation regarded a dominance pattern in this starter.

Effects of Fermentation and Its Control on the Sensory Characteristics of Conservolea Variety Green Olives

The various factors assumed to retard or even prevent the lactic acid fermentation of Conservolea variety green olives have been investigated. Of these, the sugar supplement along with the appropriate lactic starter culture supported a complete lactic acid fermentation. Acidification, particularly of starting brine, was shown to have little or no effect, whereas heat shock treatment improved the olive fermentability slightly without modifying the course of fermentation. These findings indicate that Conservolea olives do not contain phenolic compounds in concentrations inhibitory to lactic acid bacteria.

Effect of Liquid Smoke on the Growth of Lactic Acid Starter Cultures used to Manufacture Fermented Sausage

ABSTRACTFermented sausage was manufactured using a commercial lactic acid starter culture and varying levels of liquid smoke. Samples were taken during the 24 hr fermentation period and the lactic bacterial count, pH and titratable acidity determined. Final pH values, titratable acidity and lactic bacterial counts were not affected by recommended use levels of liquid smoke, although exponential growth was delayed. Growth studies in a broth medium containing liquid smoke suggest that liquid smoke has the potential for inhibiting the lactic starter cultures used to make fermented sausage.

Behavior of Staphylococcus aureus in Cheddar Cheese Made with Sodium Chloride or a Mixture of Sodium Chloride and Potassium Chloride

Stirred-curd Cheddar cheese was manufactured from milk artificially contaminated with < 1000 Staphylococcus aureus cells/ml. Lactic starter culture was added to the milk at the rate of 1.0 or 0.5% (v/v). Curds were divided and salted with either NaCl or a mixture of KCl/NaCl to achieve final salt concentrations of approximately 2.4 or 1.2%. Some portions of curd remained unsalted. Cheeses were analyzed for moisture and salt content and were stored at 4 or 10°C for 8 weeks. Bacterial counts and pH values were determined during manufacture and storage of cheeses. Unsalted cheeses had the lowest and the 2.4%-salted cheese had the highest S. aureus counts. Cheeses salted with KCI/NaCl had considerably lower S. aureus and non-S. aureus counts than did cheeses salted with NaCl. All cheeses made with 1.0% starter culture had appreciably lower counts of S. aureus than did cheeses made with 0.5% starter culture. Low levels (0.05 to 0.52 ng/g) of enterotoxin A were found in 16 of 17 samples tested with the radio immunoassay procedure. Presence of enterotoxin was not directly associated with the kind or amount of salt used to produce the cheese.

Behavior of Enteropathogenic Escherichia coli in Camembert Cheese Made From Ultrafiltered Milk

ABSTRACTSkimmilk retentates from ultrafiltration (UF) were used in combination with concentrated cream (67% milk fat) to prepare a liquid precheese mixture that with the addition of rennet, lactic starter culture and a mold spore preparation of Penicillium candidum was transformed readily into Camembert cheese upon ripening. Yield increases from the retention of soluble milk protein, closer weight control tolerances for individual cheeses and reduction in rennet in comparison to the conventional Camembert process were observed. The behavior of enteropathogenic E. coli (ECC) serotypes was demonstrated in the Camembert cheese made from UF processes. Relationships were determined in UF Camembert as to microbial type and numbers used to inoculate the precheese, and as to site of survival and growth of different EEC serotypes. Differences which were observed in the physicochemical properties between conventional and UF cheesemilk mixtures predisposed the UF Camembert cheeses to greater E. coli survival and growth than in the Camembert cheeses made conventionally.

Influence of Lactic Acid Starter Bacteria on Enteropathogenic Escherichia coli in Ultrafiltration Prepared Camembert Cheese

A combination of Streptococcus cremoris and Lactobacillus helveticus or Lactobacillus bulgaricus lactic cultures was more effective as starter than single species cultures or S. cremoris and Streptococcus diacetylactis in combination in repressing growth and eliminating survival of enteropathogenic Escherichia coli serotype 0124 in Camembert cheese manufactured from directly ultrafiltrated skim milk concentrate. The essentiality of highly active lactic starter cultures for repressing and eliminating enteropathogenic E. coli during ultrafiltration of retentates and later in precheese was demonstrated.

Behavior of Enterobacter Species and Hafnia Species in Skimmilk During Fermentation by Lactic Acid Bacteria

Enterobacter cloacae, Enterobacter aerogenes and two strains of Hafnia sp. were cultured individually in skimmilk together with Streptococcus lactis, Streptococcus cremoris or with one of two commercial lactic starter cultures. Incubation was at 21 or 32 C, and the lactic culture inoculum was 0.25, 1.0 or 2.0%. Growth of E. cloacae and E. aerogenes was markedly inhibited by S. lactis and S. cremoris at 32 C, and less so at 21 C. The commercial starter cultures were less inhibitory than the individual lactic streptococci. An increase in inoculum of lactic acid bacteria was accompanied by an increase in inhibition of Enterobacter sp., especially at 32 C. Both strains of Hafnia were inhibited more by S. lactis than by S. cremoris and the commercial starter cultures. Incubation at 32 rather than 21 C and increasing the amount of added lactic starter culture increased inhibition of Hafnia sp. All of the test coliforms were partially or completely inactivated toward the end of the 15-h incubation, provided the necessary conditions prevailed.

Behavior of Enterobacter aerogenes and Hafnia Species During the Manufacture and Ripening of Camembert Cheese

Camembert cheese was made from pasteurized milk contaminated with about 102–103 cells of Enterobacter aerogenes or Hafnia sp. The coliform bacteria were enumerated with a Most Probable Number procedure and with violet red bile agar. Numbers of viable E. aerogenes decreased rapidly during ripening at 15.5 or 10 C when cheese was made with the commercial lactic starter cultures OD or C-5. No viable E. aerogenes was detected in cheese ripened at 10 C for 3 weeks. Ripening of cheese, made with starter culture OD or C-5, for 1 week at 15.5 C was accompanied by a decrease in numbers of viable Hafnia sp. to 10/g. The number of Hafnia sp. increased markedly during 7 weeks of further ripening at 10 C to yield cheese which contained numbers in excess of 107/g when ripening was almost completed. Growth of Hafnia sp. during the storage period coincided with an increase in pH of the cheese.

Growth and Enterotoxin Production by Staphylococci in Genoa Salami

Staphylococcus aureus strains 265 and 243 which produce enterotoxins A and B, respectively, were inoculated into meat being made into Genoa salami in the amount of 103, 105, and 107, cells/g. No lactic starter culture was added. Samples were taken at different stages of processing to determine the microbial populations, percentage moisture, total acidity, pH, and enterotoxin content. Staphylococcal populations varying from about 107 to 5 × 108/g were detected during tempering of the salami. Enterotoxin A was detected in surface but not in core samples of salami inoculated with 105 and 107S. aureus 265 cells/g. However, no enterotoxin B was detected in the salami inoculated with S. aureus 243, which requires a relatively high aw for enterotoxin production. Staphylococcal counts were higher in surface samples than in core samples, attributable to the difference in oxygen, but there was no significant difference in microaerophilic lactic Kid bacteria in different portions of the salami.

New Techniques in Handling Lactic Cultures to Enhance Their Performance

Problems of dairy product manufacturing continue to emphasize the need for development of new techniques in handling lactic starter cultures. This presentation will emphasize this need by identification of problems of culture performance and also by pointing out new methods being developed to solve these problems. Six areas of culture problem will be identified: a) phage inhibition, b) instability, c) antibiotic inhibition, d) inhibition by agglutinins, e) poor bulk starter media, and f) lack in uniformity of flavor.

Incidence and properties of temperate bacteriophages induced from lactic streptococci

Sixty-three strains of lactic streptococci isolated from commercial lactic streptococcal starter cultures were examined for lysogeny by treatment with ultraviolet light or mitomycin C. After treatment with the inducing agent, all strains, whether or not they lysed, were examined for evidence of phage release by electron microscopy. Thirty-eight strains yielded intact phages or phage particles of varying morphology. All the temperate phages had isometric heads and noncontractile tails; some had collars and structurally distinctive baseplates. Indicator host strains were found for phages induced from seven different strains. Three strains that released phages spontaneously yielded titers of 10(3) to 10(4) plaque-forming units per ml. When strains that spontaneously released phages were grown in mixed culture with indicator strains, increased phage titers of 10(6) to 10(7) plaque-forming units per ml were observed. These findings indicate that lysogenic lactic streptococcal strains may serve as a reservoir for phages that attack sensitive strains in mixed- or multiple-strain lactic starter cultures.