Growth of lactic acid bacteria in highly concentrated ultrafiltered skim milk retentates

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 10(9) cfu/ml.     

Cheddar Cheese from Water Reconstituted Retentates

Reconstituted creamed retentates of ultrafiltration were converted to ripened cheese by Cheddar manufacturing principles. Initially, the fresh cheeses resembled normal Cheddar but during ripening were transformed into Gouda-Swiss types with pH rising rapidly from 5.2 to approximately 6.0.Cheese composition was affected by amount of full fat retentate in reconstituted mixtures. As total milk solids increased in reconstituted retentates, cheese moisture decreased and cheese volume rose to high yields. Cheese yield efficiency showed 1.21 to 1.32 kg cheese per kg total solids. Rennet curd of higher total solids retentates formed more rapidly than normal, and curds were harder. Whey from retentate reconstituted cheeses showed relatively low ash and fat even from cheeses made with high retentate. Soluble protein in 2-mo-old cheeses held at 10° C was lower in cheese from retentates of high solids.     

Purification and Characterization of the Agglutinating Factor for Lactic Streptococci from Bovine Milk: IgM-Immunoglobulin

An agglutinating factor for lactic streptococci of very high potency was isolated from bovine milk. Crude euglobulin was fractionated further by gel filtration on Bio Gel A-50m, followed by three filiations on A-15m. The agglutinating activity against Streptococcus cremoris strain HP increased from 1/7.3 per 100 mg protein for skim milk to 1/520 per 100 mg for the crude euglobulin to 1/2830 per 100 mg after Bio Gel A-50m and 1/4100 per 100 mg after Bio Gel A-15m. Agglutinating activity of the purified agglutinin differed among strains of Streptococcus cremoris. Activity was maximum in the pH range of 6.5 to 8.5; it increased linearly with concentration of purified agglutinin. Heating for 10 min at 70 C or reduction with mercaptoethanol caused a loss of most of the agglutinating activity. Purified agglutinin was homogeneous on immunoelectrophoresis against bovine antisera and antisera against bovine milk euglobulin. The rate of acid production in heated skim milk by lactic streptococci was retarded by added purified agglutinin. Physico-chemical analyses showed purified agglutinin was homogeneous by analytical centrifugation with: molecular weight = 960,000 daltons; 11.02% of total carbohydrate, 6.09% hexoses, 3.09% hexosamines, 1.51% sialic acid, and 0.36% fucose. These properties were close to those of IgM-immunoglobulin from bovine serum and colostrum and from other species. The IgM-immunoglobulin is the component in normal milk causing agglutination of lactic streptococci.     

Cheddar Cheese from Ultrafiltered Whole Milk Retentates in Industrial Cheese Making

Transporting whole milk retentates of ultrafiltration to a distant large industrial Cheddar cheese making site resulted in 16 lots of Cheddar cheese from vats containing 2,546 to 16,360 kg of cheese milk. Whole milk retentates concentrated by ultrafiltration to 4.5:1 were added to cheese milks to give mixtures concentrated 1.2:1 and 1.3:1 with approximately 20 and 30% more protein and fat, respectively, than in unsupplemented control whole milks or unsupplemented commercial reference milks.Gross composition of Cheddar cheese made from commercial reference, control, and retentate-supplemented milk generally showed no major differences. Yield increased in cheese made from retentate-supplemented milk. Yield efficiency per kilogram total solids rose in retentate cheese over controls but not among commercial reference, control, and retentate lots based on per kilogram fat or total protein. Milk components were higher in wheys from retentate cheeses, but loss of components per kilogram cheese obtained generally showed lower values in whey from retentate cheese.General quality of retentate Cheddar cheese was equal to that of reference unsupplemented commercial cheese and higher than unsupplemented control Cheddar cheeses. It appears technically feasible to ultrafilter milk at one site, such as the farm, collecting station, or specialized center, and transport it to an industrial site for Cheddar cheese making.     

Microbiological analysis and starter culture growth in retentates.

Pasteurized skim milk was concentrated by UF to 2-, 4-, and 5-fold. The retentates were evaluated for microbiological quality, heat treatments to inactivate microorganisms, and lactic acid bacterial starter culture activity. Aerobic mesophilic bacterial counts in raw milk decreased from an initial 1.4 x 10(6) to 3.9 x 10(2) cfu/ml after pasteurization. During UF, counts increased from 3.9 x 10(2) cfu/ml UF, counts increased from 3.9 x 10(2) cfu/ml in pasteurized milk to 1.4 x 10(3), 1.4 x 10(4), and 1.8 x 10(4) cfu/ml in 2-, 4- and 5-fold retentates, respectively. Psychrotrophic bacterial counts decreased from 9.9 x 10(5) cfu/ml in raw milk to 3.7 x 10(1) cfu/ml in pasteurized milk and gradually increased to 1.0 x 10(2), 2.5 x 10(2), and 1.4 x 10(3) cfu/ml in 2-, 4-, and 5-fold retentates, respectively. Thermophilic bacterial counts remained less than 10 cfu/ml in all samples. Skim milk and retentates inoculated with five starter cultures at 1% failed to decrease the pH below 4.6 in (2-, 4- and 5-fold). The 4- and 5-fold retentates inoculated with Lactococcus lactis spp. cremoris or Lactococcus lactis spp. lactis cultures were partially coagulated with pH greater than 5.6. In general, the pH of retentates remained higher than that of skim milk. Clotting of uninoculated samples was observed, and a spore-forming contaminant, tentatively characterized as Bacillus cereus and capable of clotting milk at a pH greater than 6, was isolated from the clotted samples.(ABSTRACT TRUNCATED AT 250 WORDS)     

Development of a fermented goat's milk containing probiotic bacteria

A set-type fermented milk manufactured from goat's milk was developed. Optimal curd tension was achieved by supplementation of milk with skim milk powder and whey protein concentrate (WPC). Milk was fermented employing a commercial probiotic starter culture (ABT-2), which contained Streptococcus thermophilus ST-20Y, Lactobacillus acidophilus LA-5, and Bifidobacterium BB-12. Supplementation of milk with 3% WPC reduced fermentation time by 2 h due to the increase in viable counts of S. thermophilus and Bifidobacterium by 0.3 and 0.7 log units, respectively. Addition of WPC increased the protein content (1%) as well as potassium and magnesium content (0.3 and 0.02 g kg⁻¹, respectively). Increase of the protein content led to an increase in the apparent viscosity and gel firmness of the product, and at the same time whey syneresis was reduced. As a consequence, the product received a high score for appearance, taste, aroma, texture and overall acceptance.     

Influence of milk ultrafiltration on bacteriophages of lactic acid bacteria

Bacteriophages added to whole milk were partially concentrated during ultrafiltration. At 4:1 retentate, phage had concentrated 2.4:1. Thermal destruction at 54 degrees C followed first order kinetics up to 6% protein, whereafter it deviated. When allowed to grow in retentate in the presence of appropriate host, 3.5 generations of phage appeared after 12 h at 22 degrees C compared with four generations in skim milk. In the presence of phage, lactic acid bacteria population increased to only 10(7) cfu/ml compared with 3 X 10(9) in their absence. Retentate starter prepared in the presence of phage was as active as skim milk starter prepared in the presence of phage.     

Evaluation of a Feed Preference Agent for Dairy Calves

A feed preference agent, Firanor-24², was added (0, 50, or 100 ppm) to whole milk and starter ration to determine if association of it with milk would enhance starter intake and weaning performance in dairy calves. Thirty 1-day-old Holstein calves (six males, four females per treatment) each received 1.6 kg of milk twice daily to 30 days of age and starter ration from 7 to 40 days of age. There were no differences from treatments in daily feed intake or body weight gains.In a paired comparison preference test for Firanor-24 in milk, two groups of five unnursed newborn calves were preconditioned to 0 or 100 ppm Firanor-24 in colostrum at birth and in milk twice daily for 6 days. In the 5-day test period each calf was offered a choice of milk with 0 or 100 ppm randomized in two adjoining buckets. No differences in milk preference were observed.     

Simultaneous detection and enumeration of viable lactic acid bacteria and bifidobacteria in fermented milk by using propidium monoazide and real-time PCR

This study describes a procedure that allows specific detection and enumeration of viable bacteria in four species of lactic acid bacteria (Streptococcus thermophilus, Lactobacillus delbrueckii subsp. bulgaricus, Lactobacillus casei subsp. casei and Lactobacillus acidophilus) and of Bifidobacterium lactis, mixed in fermented milk products. The procedure is based on the combined use of propidium monoazide (PMA), able to distinguish between viable and irreversibly damaged cells, with species-specific quantitative real-time PCR (RTi-PCR). Loss of viability of the species in a fermented milk through storage at 4 °C was similarly (P < 0.05) detected by PMA–RTi-PCR and selective plate counts. Furthermore, comparison of results obtained by both methods showed a Pearson linear correlation of 0.995. The enumeration of viable bacteria by PMA–RTi-PCR could be performed in 3 h, whereas enumeration by selective plate counts required three days. The procedure developed is a fast method for the identification, enumeration and discrimination of viability of lactic acid bacteria and bifidobacteria mixed in fermented milk products.     

Flavour profiles and survival of starter cultures of yoghurt produced from high-pressure homogenized milk

Volatile carbonyl compounds, organic acids and yoghurt bacteria counts were investigated in yoghurts made from ultra-high pressure homogenized milk. Yoghurts were manufactured from milk treated using ultra-high pressure homogenization at 200 or 300 MPa and at 30 °C or 40 °C, and compared with those produced from heat-treated milk with 3% added skim milk powder. To study the evolution of these parameters, samples were analysed after days 1, 14 and 28 of storage. Yoghurts from milk heat-treated or treated at 300 MPa had very similar profiles of organic acids and volatile compounds, as well as similar bacterial counts of both starter cultures. In comparison, yoghurts from milk treated at 200 MPa at either 30 °C or 40 °C gave different profiles, together with a sharp decrease in counts of lactobacilli. During storage, only slight differences in flavour compounds and yoghurt bacteria counts were detected, except in those samples from milk treated at 200 MPa.     

Composition and Distribution of Lipids of Goats’ Milk

Fresh commercial goats’ milks were examined for their lipid contents and distribution of these lipids among milk fractions. Whole milk, skim milk (produced by centrifugation at 330 and 2,000 × g), and cream were studied. Petroleum ether (free lipids) and chloroform methanol (2:1) (bound lipids) were used successively to extract the lipids from all milk fractions. Average total lipid content for five bulk milk samples was 5.0 ± 1.2%. Lipid fractions of whole milk and cream contained 97 to 99% free lipid and 1 to 3% bound lipid, respectively. Free lipid was 96.8% triglyceride, whereas bound lipids contained neutral lipid, glycolipid, and phospholipid. In this respect, goats’ milk resembled cows’ milk. However, goats’ skim milk fractions contained significantly more free lipid than did cows’ milk. This free lipid, investigated in detail by gas chromatography, was shown similar in triglyceride distribution and fatty acid content to whole goats’ milk triglyceride. Quantitative data for the triglyceride distribution in all fractions are given and differ from published data for fresh goats’ milk.     

Fermentation of beet juice by beneficial lactic acid bacteria

Red beets were evaluated as a potential substrate for the production of probiotic beet juice by four species of lactic acid bacteria (Lactobacillus acidophilus, Lactobacillus casei, Lactobacillus delbrueckii, Lactobacillus plantarum). All the lactic cultures were found capable of rapidly utilizing beet juice for cell synthesis and lactic acid production. However, L. acidophilus and L. plantarum produced a greater amount of lactic acid than other cultures and reduced the pH of fermented beet juice from an initial value of 6.3 to below 4.5 after 48 h of fermentation at 30°C. Although the lactic cultures in fermented beet juice gradually lost their viability during cold storage, the viable cell counts of these lactic acid bacteria except for L. acidophilus in the fermented beet juice still remained at 10⁶–10⁸ CFU/ml after 4 weeks of cold storage at 4°C.     

Properties of Crude Ethylester-forming Enzyme Preparations from Some Lactic Acid and Psychrotrophic Bacteria

Ester-forming enzyme preparations were obtained from 48 h cultures of Streptococcus diacetilactis ATCC 15346, S. lactis ML3, Lactobacillus No. 81 and two strains of psychrotrophic bacteria belonging to the genus Pseudomonas (Strains No. 50 and 53).Optimum pH's of the enzyme preparations of Lactobacillus No. 81 and two strains of the lactic streptococci for the production of ethylbutyrate and ethylhexanoate were 6.5 and 7.0 to 7.5, respectively. Enzymes of Strains No. 50 and 53 had their maximum activities at pH 8.0. The optimum temperature was 32 C for all strains. Enzymes were generally stable below 35 C at pH 7.0, but their activities were rapidly lost at higher temperature. When the esterases were incubated at 4 C for 24 h, Lactobacillus No. 81, the lactic streptococci (Strains ML3 and ATCC 15346), and the psychrotrophic bacteria (Strains No. 50 and 53) were most stable at pH 6.0, 7.0, and 8.0, respectively. Copper, manganese, and cobalt salts inhibited all the enzymes. The inhibitory effect of cobalt on enzyme activities of Strains ML 3, No. 50 and 53 and that of copper on Strain No. 81 were especially significant.     

Relationship of Protease Activity to Shelf-Life of Skim and Whole Milk

This study was to investigate causes of a possible difference in shelf-life of pasteurized skim milk and whole milk. Samples of skim and whole milk were obtained the day of processing, in 235 ml containers, from commercial dairies throughout South Carolina. They were stored at 4.5°C for 0,4,8,10,12,14, and 16 days; 7°C for 0,4,6,8,10, and 12 days; and 10°C for 0,1,2,3,4,5, and 6 days. On each sampling day milks were tested for coliform count, psychrotrophic count, flavor score, and relative protease activity. The shelf-life of skim milk was significantly less than that of whole milk when both were stored at 4.5°C and 7°C, but not at 10 C. Bacteria counts were not significantly different; thus, they were of no predictive value as anticipated changes in flavor score. Relationship between flavor score and relative protease activity of skim and whole milk was linear. Also, relative protease activity was significantly higher in skim milk as compared to whole milk stored at 4.5 and 7° C. Therefore, a higher protease activity in skim milk may account partially for its decreased shelf-life.     

Antagonism between Listeria monocytogenes and lactococci during fermentation of products from ultrafiltered skim milk.

Tyndallized samples of unfiltered skim milk and retentate (concentrated fivefold or twofold by volume) and permeate from UF skim milk were inoculated with 5.5 x 10(3) to 1.5 x 10(5) cfu/ml of Listeria monocytogenes strains California or V7 together with 4 x 10(7) to 2.3 x 10(8) cfu/ml of mesophilic lactic acid bacteria. Numbers of L. monocytogenes (McBride Listeria agar) and lactic acid bacteria (all purpose Tween agar) were determined after 0, 6, 12, 24, 30, and 36 h of incubation at 30 degrees C. Lactic acid bacteria significantly inhibited or inactivated L. monocytogenes in all three products. Inactivation was greater in permeate (6.77 orders of magnitude) than in unfiltered skim milk (3.67 orders of magnitude) or in retentate (4.21 orders of magnitude). Degree of inactivation in retentate was related to the extent of concentration. Inactivation was not complete, and L. monocytogenes survived in these products during fermentation for up to 36 h. When fermented products were refrigerated (4 degrees C), L. monocytogenes survived for 4 to 6 wk in skim milk, 3 to 5 wk in retentate, and 1 wk in permeate. At refrigeration temperature, length of survival was dependent on type of product and strain of the pathogen.     

Influence of addition of raffinose family oligosaccharides on probiotic survival in fermented milk during refrigerated storage

The influence of the addition of raffinose family oligosaccharides (RFOs) extracted from lupin seeds on the survival of Bifidobacterium lactis Bb-12 and Lactobacillus acidophilus La-5 in fermented milk during 21 days of storage in refrigerated conditions was studied. For this purpose, viability and metabolic activity (expressed as pH, lactic and acetic acid production and utilization of soluble carbohydrates) of probiotic bacteria were determined. Retention of viability of B. lactis Bb-12 and L. acidophilus La-5 was greater in fermented milk with RFOs. The pH of probiotic fermented milk at 21 days of storage was lower (4.27) compared with probiotic fermented milk with RFOs (4.37). The highest levels of lactic and acetic acid were produced in probiotic fermented milk without RFOs compared with probiotic fermented milk with RFOs during storage at 4 °C. Soluble carbohydrates were utilised in fermented milk with and without RFOs, respectively, for maintaining B. lactis Bb-12 and L. acidophilus populations during refrigerated storage. In conclusion, all these experiments provide convincing evidence that RFOs have beneficial effects on the survival of these probiotic cultures in dairy products. As a result, such stored dairy products containing both probiotics and prebiotics have synergistic actions in the promotion of health.     

Characteristics of carbonated fermented milk and survival of probiotic bacteria

The carbonation of pasteurised milk was evaluated as a method for improving bacterial viability in fermented milk added with probiotic bacteria (Lactobacillus acidophilus and/or Bifidobacterium bifidum). The behaviour of microorganisms during fermentation and cold storage, and the biochemical and sensory properties of the products were assessed. In AT (Streptococcus thermophilus/L. acidophilus) and ABT (S. thermophilus/L. acidophilus/B. bifidum) products, the fermentation times to decrease the pH to 5 were significantly lowered when CO₂ or lactic acid was added to milk. The higher acidity levels of carbonated (as a result of production of carbonic acid) and lactic acidified samples enhanced growth and metabolic activity of the starter during fermentation and was the reason for this reduction in incubation time. Cell counts of S. thermophilus, L. acidophilus and B. bifidum gradually decreased through the cold storage of carbonated and non-acidified fermented milk, although the counts were always higher than 10⁶ viable cells g⁻¹. The CO₂ did not exert any influence on the viability of S. thermophilus and L. acidophilus in AT fermented milk stored at 4°C but the presence of B. bifidum and CO₂ in ABT-type products was associated with lower viability of L. acidophilus during the refrigerated storage. The higher acetate concentrations of ABT products made with non-acidified milk as compared with the carbonated products could have contributed to major survival of L. acidophilus in the former. The use of milk acidified with CO₂ had no detrimental effects on the sensory properties of ABT fermented milk. Therefore, we concluded that the carbonation of pasteurised milk prior to the starter addition could be satisfactorily used to reduce the manufacture time of fermented milk.     

Applicability of heat-stable deoxyribonuclease assay for assessment of staphylococcal growth and the likely presence of enterotoxin in cheese

The relationships between growth of Staphylococcus aureus and production of deoxyribonuclease and enterotoxin A in cheese were evaluated. Conditions of cheese manufacture, such as the nature of milk used (heated or raw), type of lactic starter, and degree of starter activity, influenced deoxyribonuclease production. There was a close correlation between the S. aureus population and deoxyribonuclease content (correlation .88 in Cheddar and Colby cheeses for normal or inhibited starter, and .85 in Brick cheese for normal starter). Conditions which affected deoxyribonuclease production also had a similar influence on production of enterotoxin A. Detection of the former is especially useful in cheeses which may have had a partial starter failure not detected by the usual criteria of starter activity such as the titratable acidity of whey or the final pH of cheese. While the viable S. aureus population declined during aging, both deoxyribonuclease and enterotoxin A persisted for an extended time (3 yr at 4.4 C) in cheese of normal or inhibited starter.     

Fractionation of pasteurized skim milk proteins by dynamic filtration

This paper describes a two-stage process for separating milk proteins from pasteurized skim milk in three fractions: casein micelles, β-Lactoglobulin (β-Lg) and other large whey proteins, and α-Lactalbumin (α-La). Casein micelles were extracted in the retentate of a microfiltration using rotating ceramic disk membranes. α-La and β-Lg transmissions remained between 0.8 and 0.98. Their yields in permeate reached 81% for α-La and 76.6% for β-Lg at a VRR of 5.4. The separation between β-Lg and α-La was carried out by UF using a rotating disk module equipped with a 50 kDa PES circular membrane. Permeate fluxes were very high, remaining above 340 L h^?1 m^?2 at VRR = 5 and 40 °C. α-La transmission remained generally between 0.2 and 0.13 giving yields from 28% to 34%. β-Lg rejection was above 0.94, giving a maximum selectivity of 4.2. These data confirm the potential of dynamic membrane filtration for separating α-La and β-Lg proteins from skim milk.     

Microbiological and chemical changes during the manufacture of Kefir made from cows’ milk,using a commercial starter culture

The counts of total aerobic mesophilic bacteria, lactic acid bacteria (in three different culture media, M17 agar, MSE agar, and Rogosa agar) and yeasts, and some biochemical parameters (levels of lactose, glucose, galactose, L(+)- and D(−)-lactic acids, ethanol, titratable acidity and pH) were determined during 196 h of fermentation in five batches of Kefir made from cows’ milk using a commercial starter culture. Lactococcus spp. predominated during the first 48 h of fermentation (∼8 log₁₀ cfu g⁻¹); Lactobacillus spp. became the predominant species after 48 h (∼8.5 log₁₀ cfu g⁻¹). During the first 24 h of fermentation, the lactose content decreased from a mean value of 4.92% (w/w) to 4.02% (w/w); the concentration of L(+)-lactic acid increased from 0.01% to 0.76% (w/w) and the pH decreased to 4.24 over the same period. After 24 h of fermentation, the changes in the levels of lactose and L(+)-lactic acid, and in pH, occurred more slowly. Neither glucose nor galactose were detected during fermentation. The production of ethanol was limited, reaching a mean final value of 0.018% (w/w).