Showing papers in "Milchwissenschaft-milk Science International in 1995"

Influence of temperature on the production of exopolysaccharides by thermophilic lactic acid bacteria

Abstract: The influence of the incubation temperature on the exopolysaccharide (EPS) production by L. delbrueckii ssp. bulgaricus, L. acidophilus and S. salivarius ssp. thermophilus was studied. After an incubation for 24 h, a correlation between the optimum growth temperature and that for obtaining maximum EPS production was observed. The exception was S. salivarius ssp. thermophilus which produced the highest amount of polymer at 30°C. When increasing the time of fermentation up to 72 h, a marked reduction in the EPS synthesis was observed. These results were dependent both on the temperature tested (30, 37 and 42°C) and the strain of lactic acid bacteria employed. Viscosity measurements at 72 h gave aleatory results

Physical properties of stirred-curd unsweetened yoghurts stabilised with different dairy ingredients

Abstract: Yoghurts were produced from milks standardised to 2.0% fat and fortified to 5% protein with various dairy ingredients including skim milk powder (SMP), butter milk powder (BMP), sodium caseinate (NaCn) and whey protein concentrates with protein levels of 75% (WPC 75), 60% (WPC60), 45% (WPC45) and 35% (WPC35). The susceptibility to syneresis of dairy ingredient-based yoghurts decreased in the following order. WPC35 >> NaCn > WPC45 ∼ WPC60 ∼ WPC45 > SMP > BMP. The degree of shear thinning was highest for NaCn-stabilised yoghurt and lowest for WPC35-based yoghurt. The viscosities at the end of a 25 min shearing period (at a shear rate of 116.2 s −1 ) decreased in the order. NaCn > BMP ∼ SMP ∼ WPC75 ∼ WPC60 ∼ WPC45 > gelatine >> WPC35

Tryptic and chymotryptic hydrolysis of β-lactoglobulin A, B and AB at ambient and high pressure

Abstract: The differences in enzymatic hydrolysis of β-lactoglobulin (β-lg) A, B and AB by trypsin and chymotrypsin at ambient and high pressure have been studied. At ambient pressure, native β-lg A is hydrolysed by trypsin and chymotrypsin approx. 3 times faster than β-lg B. This difference might be ascribed to the substitution of Asp 64 in β-lg A with Gly 64 in β-lg B, which is located in an elongated loop of the β-lg molecule. At higher pressures (100 MPa and 300 MPa) the genetic variant associated differences in β-lg hydrolysis rates disappeared

Exopolysaccharide production by Lactobacillus casei. I: Influence of salts

Abstract: The addition of organic and inorganic salts to the culture medium influenced the growth characteristics and the exopolysaccharide (EPS) production by Lactobacillus casei. Best results were obtained with MnSO 4 which enhanced the synthesis of EPS as well as the cell viability and the production of lactic acid. The ropy characteristic of the cultures was only observed in presence of this salt. Triammonium citrate also stimulated the EPS formation while Mg 2+ and K + salts had a positive effect on colony counts

Improved yogurt physical properties using ultrafiltration and very-high temperature heating

Abstract: Nonfat yogurt milk was prepared by either ultrafiltration of skim milk and by addition of low-heat, nonfat dry milk powder to skim milk. These fortification procedures resulted in yogurt milks with 5% total protein. The yogurt milks were heat-treated from 100° to 140°C for 4 and 16 s. The milks were also vat-heated at 82°C for 20 min. Following yogurt culture inoculation, incubation, and cooling, the yogurts were tested for gel strength and stirred viscosity after 21 d storage. Yogurt prepared from ultrafiltered skim milk had greater gel strength and stirred viscosity values than yogurt prepared with nonfat dry milk-fortified skim milk. These higher values occurred despite the lower average total solids in ultrafiltered skim milk (11.43%) than in nonfat dry milk-fortified skim milk (12.98%). Heat-treating yogurt milk at 100°. 110°, or 120°C for 4 or 16 s resulted in yogurts with significantly higher gel strength and viscosity values than yogurt milk heated to 140°C for 4 or 16 s. Preparing yogurt milk by ultrafiltration and using heat treatments between 110 and 120°C can produce a yogurt that has lower toal solids and yet has acceptable physical properties without using a stabilizer

Properties of Amasi, a natural fermented milk produced by smallholder milk producers in Zimbabwe

Abstract: Consumption of fermented milk is part of Zimbabwe culture. In the rural areas it is common practice for the people to prepare their own fermented milks using traditional methods. Smallholder dairy farmers in the Nharira/Lancashire Farming Area produce a natural fermented milk, locally known as Amasi or Mukaka wakakodzekwa, which has mild acidity and may be consumed as a refreshing drink or with other food products. The objectives of this study were to evaluate the method of preparation and to examine some chemical, microbiological and sensory properties of 10 batches of the fermented milk. Natural milk fermentation times were variable at ambient temperatures, which ranged from 18 to 30°C. The product was partially concentrated as a result of whey removal. Amasi was found to have a mean pH of 3.98, 0.97% lactic acid, 4.57% crude protein, 5.89% fat, 16.53% total solids, 10.59% solids not fat. The products were characterized by high microbial counts: viable cell counts ranged from 8.47 to 9.98 log cfu g −1 ; lactic acid bacteria from 8.29 to 9.88 log cfu g −1 ; coliforms from 3.41 to 6.90 cfu g −1 , yeasts and moulds from < 3 TO 5.65 LOG CFU G −1 . Average sensory scores for general appearance, consistency, flavour and aroma were generally good. However, there were considerable variations in the parameters of the products analyzed

A control medhod to detect bovine milk in ewe and water buffalo cheese using immunoblotting

Abstract: A specific and sensitive procedure for the detection of bovine milk in ovine cheese is described. The procedure is based on the analysis of cheese according to the modified EEC reference method. One difference consists in the use of defatted cheese instead of separating the pH 4.6 nitrogen fraction for plasmin action. The other modification consists in the use of antisera against β- casein as primary antibodies to detect γ 2 - and γ 3 -caseins along the gel isoelectric patterns. The detection limit of bovine milk in mixtures using the immunoblotting procedure is lower than 0.5% by volume. The specificity of the procedure can be useful for an accurate control of bovine milk in ovine cheeses

Selection of bifidobacteria for use under cheese-making conditions

Abstract: Growth of dairy-related bifidobacteria in milk was determined under different conditions. In renneted milk, the bacterial population of bifidobacteria strains was almost similar to that observed in milk alone. The strains of Bifidobarterium adolescentis could not grow or survive in milk under the different conditions studied. Growth and acid-producing activity of B. breve strains were higher than those observed for other dairy-related strains of B. bifidum, B. infantis, B. longum and B. animalis. Strains of B. breve could grow in the presence of lactic acid or glucono-delta-lactone and low pH conditions. Growth and survival of dairy-related bifidobacteria in milk were also studied in the presence of mesophilic starters. High survival rates of B. longum strains indicated that they should be more suitable than other species for use under cheese-making conditions

Fouling of heat exchangers by fresh and reconstituted milk and the influence of air bubbles

Abstract: The influence of reconstitution of milk and of air bubbles in milk on fouling was studied. Reconstituted milk gave much less fouling than fresh milk, for reasons that are not yet clear. Air bubbles, which arose in the milk on heating and stuck to the stainless steel wall, appear to act as nuclei for the formation of deposit and influence the composition of the deposit through drying of the membrane of air bubbles containing caseins. High shear rates may prevent air bubbles from sticking to the wall, resulting in less fouling

Analysis of caseinomacropeptide(s) by free solution capillary electrophoresis

Abstract: Preliminary studies on the performance of free solution capillary electrophoresis in an untreated capillary for analysis of caseinomacropeptide (CMP) are presented. CMP isolated from acid casein after rennet addition and CMP occurring in rennet wheywere used. By capillary electrophoresis using phosphate and borate buffers at pH 6-9, the isolated CMP appeared as 1 main peak and 1 or more minor peaks. Use of 20 mM buffers gave migration times (t' m s) for all peaks of less than 5 min, but resolution between the peaks was poor. Use of 50 mM buffers resulted in t' m s of 10-12 min for the main CMP peak, but gave a better resolution. A 40 mM phosphate buffer, pH 8.5, was chosen to give an acceptable compromise between resolution and separation time. With this buffer, t' m s of around 8 min and 9 min were obtained for the main CMP peak and the 3 minor peaks, respectively. The first and part of the second minor peaks were shown to represent N-acetylneuraminic acid (NANA) forms of CMP. Under these conditions, the CMP in rennet whey was not separated from the whey proteins. At pH 2.5, using a 40 mM phosphate buffer, CMP migrated later and separated from the major whey components. Isolated CMP appeared as one main peak, with migration time 11 min, followed by 3 other just distinguishable peaks, the last of which was CMP containing NANA. With some adaptation, this procedure could have significant advantages when studying the kinetics of rennet coagulation, as precipitaion of the whey proteins and part of CMP is avoided

Association and dissociation of single quarter and total milk flow in dairy cows: effects of milking with and without pre-stimulation

Abstract: Milking characteristics of single quarters and of the whole udder were evaluated in 24 dairy cows with or without a 1-min manual pre-stimulation. Milk yields were not significantly different with and without stimulation. 56% of the total milk yield was obtained from the rear and 44% from the front quarters. Peak and average milk flow rates were greater with than without stimulation and in rear than in front quarters. Main and total milking time were shorter following pre-stimulation. Milk flow curves were bimodal in 51 and 45% of total and single quarters, resp., in all recorded milkings. 82 and 77%, resp., were bimodal during milking without stimulation. Single quarter milk flow curves were not generally bimodal if the total milk flow curve was bimodal. Cisternal cross section areas, estimated by ultrasound, in 49 and 51% were in front and rear quarters, resp. Higher milk flow rates in the rear quarters could not compensate the mostly higher milk yields in the rear quarters. Therefore, front quarters were often overmilked while milk was still removed from the rear quarters

Lactoperoxidase and lactoferrin: changes in post partum milk during bovine lactational disorders

Abstract: Protein concentrations of lactoperoxidase and lactoferrin in the early post partum period were directly determined from acid whey derived from bovine milk using cation-exchange chromatography. The enzymatic activity of lactoperoxidase was determined for the bovine skimmed milk in the same period: the lactoperoxidase concentration increased gradually, and the same did the enzymatic activity. From the experiments with 46 samples of early p.p. milk, it was concluded that 1 mg of lactoperoxidase is equivalent to 12.63 U of its enzymatic activity. The lactoferrin concentration declined in the same period. The protein concentration and enzymatic activity were significantly influenced by the cow's lactational disorders: the enzymatic activity and protein concentration of lactoperoxidase in colostrum rose rapidly when mastitis occurred and returned to normal after medical treatment. The protein concentration of lactoferrin also rose and fell during this period. However, the enzymatic activity of lactoperoxidase repeated the rise and fall during 8 d, and the protein concentration of lactoferrin increased again at the late colostrum period. This cow was suffering from displaced abomasum and ketosis

Whey syneresis of milk enriched with different retentate powders

Abstract: Coagulation properties, whey syneresis, and whey compositions of milk enriched to 5 and 7% of proteins with low mineral retentate powder and with standard retentate powder were compared with those determined for unenriched milk with, and without calcium chloride. The use of different rennet concentrations to coagulate milk was also studied. The addition of CaCl 2 to milk, and the use of retentate powder with different mineral content to enrich milk, modified coagulation properties, whey syneresis, whey compositions, and the retention index of different components of milk. Coagulation properties of different unenriched and enriched milks could be standardized by using different rennet concentrations. However, rennet concentration did not affect whey syneresis, nor whey composition probably because the curds were cut at equal rigidity modulus. The syneresis decreased, whereas the concentration of different components of milk increased in wheys as the protein concentration in milk increased. The use low mineral retentate powder to enrich milk did not affect the syneresis, but reduced the retention indexes of fat, ash, soluble nitrogen, and non-protein nitrogen

Quantitative determination of endopeptidase activity from lactic acid bacteria with capillary electrophoresis

Abstract: A sensitive assay based on capillary electrophoresis was developed for the quantitative determination of endopeptidase activity. Concentrations of oligopeptides (metenkephaline) were determined within 9 min or less. Using electrokinetical injection, linearity of absorbance (200 nm) was observed for 0.5 μM−2.5 mM metenkephaline, with a detection limit of approximately 1 fmol. The method was also applicable for the quantification of other peptidases, such as aminopeptidases and dipeptidylaminopeptidases. The application of the method for the determination of proteolytic activities of wild-type lactic acid bacteria and peptidase-deficient mutants is described

Effect of thermal treatment on goat milk clotting time

Abstract: The influence of the pasteurization process on the technological suitability of Murciano Granadina goat milk was evaluated. Suitability for the coagulation process has been considered by studying the influence of heat treatment on milk clotting time. Higher values for this parameter were observed in milks which had undergone low temperature long time (LTLT) treatment. Of 10 different coagulant enzymes analyzed, the most suitable for goat milk were the rennet with an intermediate concentration of chymosin and kid rennet paste

Production of mixed cultures of non-isogenic Lactococcus lactis ssp. cremoris using immobilized cells

Abstract: Mixed cultures of non-isogenic proteinase-positive (E8) and proteinase-negative (HP) strains of Lactococcus lactis ssp. cremoris containing a variety of strain ratios were prepared using either released or free cells. After 10 h of fermentation in skim milk and milk-based medium, the growth of released proteinase-positive E8 cells was higher than proteinase-negative HP resulting in an increase in the relative proportion of proteinase-positive E8. The strain ratio of the mixed culture prepared with released cells remained constant during 6-h activity test in skim milk, whereas with the mixed culture prepared with free cells, the proportion of proteinase-positive E8 decreased. Maximum specific growth rates for strain E8 and specific productivity of lactic acid were higher, and lactic acid production was lower with released cells harvested in the fermented milk-based medium compared to free cells obtained in fermented milk-based medium. The technique of cell immobilization could be used to produce active mixed starter cultures with the desired proportion of strains

Addition of liposome-encapsulated enzymes SP446 and flavourzyme to low at (10% fat) Gouda-type cheese

Abstract: The enzymes SP446 and Flavourzyme encapsulated in dehydrated/rehydrated (DRV) liposomes were added to a low fat Gouda-type cheese (20% fat/dry matter). The addition of SP446 to the cheese increased the moisture content and the amount of pH 4.6 soluble nitrogen in the cheese. By sensory profiling the cheese with added SP446 was considered to have a less firm texture than cheese without such addition. Flavourzyme lost much of its enzyme-activity during encapsulation. Although very small quantities of active Flavourzyme were added to the cheese, the influence on the amount of some volatile flavour compounds was significant

Development of an empirical model to predict the freezing point of ice cream mix

Abstract: One hundred an ten batches of ice cream mix, representing a wide range of composition, were manufactured. The initial freezing point of the mixes was determined using an osmometer, and these data were then related to mix composition using a quadratic mixture model. The predictive ability of the model was subsequently assessed, and it was determined that this prediction equation was a reliable alternative to the other prediction methods presently in the literature

On the transfer of gamma-linolenic acid into milk fat and its possible elongation to arachidonic acid by cows

Abstract: The long-chain polyunsaturated fatty acids, dihomo-γ-linolenic acid and arachidonic acid are important for the development of newborn infants, but the content in cow milk ― as part of infant formulas ― is low and seems not to increase even if the cow milk is enriched with the precurser linoleic acid. Therefore, it was investigated if an increased supply of the mammary gland with γ-linolenic acid would increase the content of the actual long chain fatty acids. Microencapsulated primrose oil was infused in a cow by means of a duodenal fistel in increasing amounts during 18 d The content of γ-linolenic, dihomo-γ-linolenic and arachidonic acid in the milk increased with increased infusion of primrose oil. Approximately one third of the infused γ-linolenic acid was recovered in the milk whereas one tenth was recovered as the metabolite dihomo-γ-linolenic acid and nearly one tenth as arachidonic acid. This indicates that supplying the cow with γ-linolenic acid instead of linoleic acid protected from rumen biohydrogenation may be a way to increase the important fatty acids dihomo-γ-linolenic and arachidonic acid in milk

Determination of surface hydrophobicity of milk proteins. Comparison between a new detergent binding method and hydrophobic interaction-FPLC

Abstract: A previously published method for the determination of the surface hydrophobicity of proteins using BIO-RAD protein assay combined with Tween 80 was adopted to various milk proteins. The relative retention times obtained by HI-FPLC at Phenyl-Superose for casein and whey protein were compared with results of the proposed method and expanded by the average hydrophobicity calculated according to BIGELOW. Detergent binding showed good correlation with calculated average hydrophobicities for all milk proteins, whereas HI-FPLC results were found to be accurate only for caseins. The relative order of hydrophobicity for single caseins was pH dependent. In contrast, HI-FPLC was found to be not selective for separation of whey proteins according to their hydrophobicity, but selective for the solubility characteristics related from the used buffer system. Evidence is given that this proposed method can be easily performed, is highly reliable and adaptable to a rapid quantitative differentiation between hydrophobic and hydrophilic areas on protein surfaces

Feasibility of continuous yogurt processing

Abstract: This study confirmed the feasibility of continuous yogurt processing. Five pilot scale models were established to incubate 10001 batch of yogurt. The optimum pipeline included stainless steel pipes at 80 mm diameter and a rotary pump. A pH sensor, a line heat source probe, and a gate valve were selected as the measuring and regulating elements of the control system. The flow-and-hold and partial-flow-and-hold models allowed fast flow rate (8.3 l/s), but required high pump power (15 to 25 kW). The 3 continuous models: diversion, feedback, and flow control, required less power (65 to 76 W), but the flow rate was slow (0.069 l/s)

Effect of ripening on the microbiological profile of high quality raw milk for cheese-making

Abstract: Eleven samples of milk from 6 farms were kept in the laboratory at 4°C for 24 h. Starter was then added and they were ripened. Lactococcus was not the major microorganism in all the ripened samples; there was a significant development of wild strains (p < 0.05), and Pseudomonas was the dominant flora in 4 of 11 samples. This was due less to its initial concentration than to its capacity to multiply in milk. The ripened milk contained low concentrations of Escherichia coli, Staphylococcus aureus and Listeria monocytogenes were not detected