Microcalorimetric study of the growth of Streptococcus thermophilus in renneted milk (original) (raw)
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International Dairy Journal, 2013
The growth of Streptococcus thermophilus ST12 (ST12) in milk reconstituted from non-irradiated and irradiated at 10 kGy low-heat skim milk powders (RSM and irrRSM, respectively) at 40 C was monitored by microcalorimetry. Statistically significant differences of the growth patterns of ST12 in RSM and irrRSM were found. Distinctively diauxic growth curves in RSM were replaced by one-stage growth curves in irrRSM. The final pH in RSM was 5.56 while in irrRSM samples it was 4.41. The time of initiation of gel formation was about 36 min shorter; however, the gels were considerably weaker in irrRSM than in RSM. The front-face fluorescence spectra were also used to characterise the differences in acidification processes. The microcalorimetric data together with the concentrations of metabolites determined during fermentation, rheological and fluorescence measurements indicated the substantial changes in the growth of ST12 in irrRSM in comparison with RSM.
The activity of lactase (Streptococcus thermophilus) in milk and sweet whey
Food Chemistry, 1984
A ci!ivity of lactase (Streptococcus thermophilus) in milk, sweet whey and miik salts was 33, 27 and 18 %, respectively, of the activity in phosphate buffer containing a similar level of magnesium ions. The decrease is due primarily to the unfavorable ionic environment in milk products. Milk pro teins activated the enzyme only slightly in buffer (6-14 %), but seemed to ameliorate the inhibiting effect of the ionic environment in milk and whey. Activity in raw milk was 6-8 % less than in the same milk heated to 63 or 85°C for 30min.
The effect of milk heat treatment on the growth characteristics of lactic acid bacteria
Agronomy Research, 2011
The ability to growth in milk is an important feature for lactic acid bacteria (LAB) used as starters for fermented milk products. Several decades ago the results of the studies varied widely: some of them showed that LAB grew better in raw milk and others demonstrated improved growth of the bacteria in heat-treated milk (Foster et al., 1952). The effectiveness of heat treatment of milk as a tool for modifying the functional properties of protein components has been extensively documented in the literature (Raikos, 2010), but the information on the influence of heat treatment of milk on the growth of LAB is not exhaustive. Peculiarities of growth of Streptococcus thermophilus ST12 and Lactobacillus paracasei S1R1 were studied using isothermal batch microcalorimeter TAMIII. Bacterial growth was monitored in pasteurized and ultra-high temperature (UHT) treated milk with different fat content, and also in reconstituted skim milk (RSM) prepared from low-heat skim milk powder (LHSMP). Heat produced during different growth stages (Q tot , Q exp), maximal specific growth rate (μ max) and lag-phase (λ) duration were determined by processing calorimetric curves, and detailed analysis of growth of the bacteria in differently pretreated milks were carried out on the basis of these data. The results of the experiments showed that primarily heat treatment and, to a minor extent, fat content of milk influenced the growth parameters of both bacterial strains, especially Lb. paracasei, growth of which was almost completely inhibited in UHT milk
Journal of Applied Microbiology, 2004
To study the effect of different fermentation conditions and to model the effect of temperature and pH on different biokinetic parameters of bacterial growth and exopolysaccharides (EPS) production of Streptococcus thermophilus ST 111 in milk-based medium. Methods and Results: The influence of temperature and pH was studied through fermentation and modelling. Fermentations under non-pH controlled conditions with S. thermophilus ST 111 indicated that the EPS production was low in milk medium, even if additional nitrogen sources were supplemented. Under pH-controlled conditions, addition of whey protein hydrolysate to the milk medium resulted in a fivefold increase of the EPS production. This medium did not contain polysaccharides interfering with EPS isolation. Primary and secondary modelling of different fermentations revealed an optimum temperature and pH of 40°C and constant pH 6AE2, respectively, for growth in milk medium supplemented with whey protein hydrolysate. Maximum EPS production was observed in the range of 32-42°C and constant pH 5AE5-6AE6. Whereas growth and maximum EPS production were clearly influenced by temperature and pH, the specific EPS production was only affected by stress conditions (T ¼ 49°C). Conclusions: Addition of whey protein hydrolysate to milk medium resulted in an increased growth and EPS production of S. thermophilus ST 111 under pH-controlled conditions. A modelling approach allowed studying the influence of temperature and pH on the kinetics of both growth and EPS production. Significance and Impact of the Study: The use of an appropriate milk-based medium and a combined model of temperature and pH can be of practical importance for the production of yoghurt or other fermented milks as well as for process optimization of the large-scale production of starter strains to be used for their EPS production.
Journal of Food Science, 1990
ABSTRACTAcid production and growth rates were determined in pure cultures of Streptococcus thermophilus and Lactobacillus bulgaricus and cocci/ bacilli ratios in mixed cultures of both species, using milk with modified aw as culture medium. Maximal growth rates were always at aw lower than 0.992 for all strains whcn aw of milk was adjusted with glycerol, while maximal acid production rates were at aw 0.992‐0.983. Glucose had an inhibitory effect additional to that caused by lowering aw. The cocci/bacilli ratio in mixed cultures increased as aw decreased in most cases, because of the higher susceptibility of L. bulgaricus to aw decrease. The behavior of a mixed culture could not always be predicted from data of the component strains in a pure culture, showing some kind of symbiotic compatibility between species.
PROTEOMICS, 2008
Streptococcus thermophilus is a thermophilic lactic acid bacterium widely used as starter in the manufacture of dairy products in particular in yoghurt manufacture in combination with Lactobacillus delbrueckii ssp. bulgaricus. However, in spite of its massive use, the physiological state of S. thermophilus in milk has hardly been investigated. We established the first map of the cytosolic proteome of S. thermophilus LMG18311 grown in milk. It comprises 203 identified proteins corresponding to 32% of theoretical proteome. In addition, using proteomic and transcriptomic approaches, we analyzed the physiology of LMG18311 during its late stage of growth in milk (between 2h30 and 5h30). It revealed the up-regulation of (i) peptides and AA transporters and of specific AA biosynthetic pathways notably for sulfur AA and (ii) genes and proteins involved in the metabolism of various sugars. These two effects were also observed in LMG18311 grown in milk in coculture with L. bulgaricus although the effect on sugar metabolism was less pronounced. It suggests that the stimulatory effect of Lactobacillus on the Streptococcus growth is more complex than AA or peptides supply.
Brazilian Journal of Microbiology, 2006
Sensory evaluation and analysis of pH, titratable acidity and microbial counts after 1, 7, 14 and 21 days of storage of five combinations of lyophilized Bifidobacterium longum and/or Lactobacillus acidophilus added to milk fermented with Streptococcus thermophilus were studied during storage at 4ºC. The taste and acidity sensory attributes were significantly (P<0.05) perceived as the storage time increased. Favourite combinations contained, initially, Bif. longum and L. acidophilus (10 8 and 10 7 cfu/mL, respectively) and Bif. longum only (10 8 cfu/mL). These combinations did not differ significantly among them and neither from the standard fermented milk. The lowest sensory scores and highest titratable acidity values were obtained for fermented milk added of L. acidophilus (10 8 cfu/mL initial concentration). During the 21 days of storage at 4ºC the viable cell counts of: Str. thermophilus did not change. Bif. longum viable cells counts kept constant or reduced 1 logarithmic cycle and L. acidophilus reduced 1 or 2 logarithmic cycle. We did not observe inhibition of over-acidification caused by the presence of bifidobacteria or L. acidophilus.
Calorimetric assessment of microbial growth in milk as affected by different conditions
Thermochimica Acta, 2002
Milk quality assessment is of paramount importance for dairy facilities. Standard microbiological techniques are time consuming and demand for faster, accurate methods is increasing. On the other hand, inefficient temperature control to handle raw milk, due to lack of appropriate facilities, requires the search for strategies to maximize quality from the microbiological standpoint. Activation of the lactoperoxidase system (LPS) has been established as an easy and safe procedure to attain such results. Good quality milk samples were obtained in sterile containers right after milking. A test temperature of 30 • C was chosen based upon preliminary tests. Raw unpasteurized milk was incubated at 30 • C for 16 h. Microbial growth was assessed at 4 h intervals and the maximum value attained was 4.59 × 10 6 CFU ml −1 after 8 h. Simultaneously, metabolic heat rate from the same samples was measured under isothermal conditions at 30 • C. A regression equation was obtained to relate microbial growth and heat output, with a coefficient of determination of 0.99. Milk samples were divided in three equal aliquots for (a) pasteurization at 72 • C for 15 s; (b) activation of LPS, and (c) untreated control. LPS activated milk maintained good quality during 8 h, while pasteurized milk showed an initial increase in microbial population after 8 h followed by a decline possibly due to residual activity of its LPS.
Current Research in Nutrition and Food Science Journal, 2021
Fermentation serves a key role in inhibiting spoilage microorganism through acidification and production of antimicrobial compounds. The technological information on properties of Streptococcus infantarius sub sp. infantarius which is predominant in most African fermented is dairy products very little. This study was therefore carried out to determine the functionality of selected African Streptococci strains in fermented dairy products. Pasteurized milk samples from camels and cows were inoculated with different strains and a selected combination at a rate of 3% v/v and incubated at different temperatures of 25 oC, 30 oC, 37 oC, and 45 oC for 9 hours. Analysis was done after every 3 hours for pH and titratable acidity while viscosity was done after incubation and cooling of the product. The different fermented milk samples were subsequently evaluated for consumer acceptability. Milk inoculated with both African type Streptococcus thermophillus (146A8.2) and Streptococcus infantariu...
Short Communication: Growth Characteristics of Streptococcus uberis in UHT-Treated Milk
Journal of Dairy Science, 2004
Streptococcus uberis is an important environmental pathogen associated with bovine mastitis as well as with high total bacterial numbers in bulk tank milk. This study was conducted to determine whether S. uberis reproduction is likely to contribute to high bacterial numbers in bulk tank milk. Four S. uberis raw milk isolates were individually inoculated into UHT-treated milk and incubated at 4.4 or 7°C for up to 5 d to simulate appropriate cooling; at 10°C for 5 d to simulate marginally inadequate cooling; at 21 or 25°C for 7 h to simulate ambient temperatures; or at 32°C for 7 h to simulate elevated temperature conditions. None of the S. uberis isolates grew at either 4.4 or 7°C. Streptococcus uberis growth at 10°C appeared to be ribotype-specific. Although ribotype 116-520-S-1 isolates did not grow at 10°C, ribotype 116-520-S-2 isolate numbers increased up to 3.5 log 10 cfu/mL within 5 d. Generation times were calculated as 2.7 ± 0.1 h, 2.1 ± 0.1 h, and 1.0 ± 0.1 h for 116-520-S-1 isolates and 1.8 ± 0.4 h, 1.3 ± 0.3 h, and 0.8 ± 0.1 h for 116-520-S-2 isolates at 21, 25, and 32°C, respectively. Our results suggest that high numbers of S. uberis in bulk tank milk are more likely to reflect high numbers of S. uberis shed by mastitic cows, rather than multiplication of these organisms under cooling conditions required for production of Grade A milk.