Milk Medium Research Articles

Optimization of fermentation process to achieve bacterial cellulose on molasses medium and sugarcane juice medium

The objective of this thesis is studying the condition of fermentation using Acetobacter xylinum on molasses medium and sugarcane juice medium. Multi-objective optimization method was used to optimized the factors of fermentation process in order to achieve the highest yield of Bacterial Cellulose. The results showed that pepton: 1.0%; glucose 2.78% ; pH 4.9, tempurature 30oC in 107 hours were optimal fermentation conditions for molasses medium while pepton: 0.93% ; glucose: 3.65% ; pH 5.2; tempurature 30.5 oC in 102 hours were optimal fermentation conditions for sugarcane juice medium. These two media above can be used as new media for the culture of Acetobacter xylinum in comparision to coconut milk medium.

α-Galactosidase Activity and Oligosaccharides Utilization by Lactobacilli during Fermentation of Soy Milk

In this study, α-galactosidase activity and depletion of oligosaccharides by six standard probiotic lactobacillus cultures were evaluated under at incubation times (6, 12, 18, 24, 30 h) in soy milk medium fortified with whey protein concentrate (WPC70) at 1.5%. Reduction of stachyose was higher due to maximum production of α-galactosidase (α-gal) enzyme (133.65 U/mg) by Lactobacillus rhamnosus C6 as compared with the other Lactobacillus cultures and was highest at 30 h of incubation (3.03 mg/100 mL). The results of this study will allow selection of L. rhamnosus C6 culture in soy milk medium supplemented with whey protein concentrate (WPC70), which will enhance growth of Lactobacillus and also reduce whey separation during fermentation process. This culture also showed highest proteolytic activity (381.67 μg serine/mL) by hydrolyzing soy proteins and produce soy bioactive peptides, which have health beneficial activities. L. rhamnosus C6 strain showed maximum α-galactosidase production as well as reduction of oligosaccharides viz. raffinose, stachyose and sucrose mostly present in soy milk. However, Lactobacilus casei NCDC17 also exhibited similar activity during soy milk fermentation. WPC70 fortification enhanced bacterial growth providing nutrition to the bacteria and also increased physiological activity during fermentation in soy milk medium. These two strains can be selected for the development of functional soy foods like soy yoghurt, soy cheese, soy beverages and soy dahi.

Correlation between protein to fat ratio of milk and chemical parameters and the yield of semi-hard cheese

In order to obtain good cheese quality, the milk has to possess good physical-chemical properties and should originate from healthy cows. Since milk fat and milk protein are the main constituents of cheese, their proportion in milk is of particular importance for the product yield and quality. This paper describes studies on the protein to fat ratio of milk and the consequent influence on the chemical composition and yield of semi-hard cheese, commercially called "Montenegrin naturally dried cheese". The tests were conducted on six bulk milk samples and six cheese samples. The milk parameters were analysed by the Milkoscan 400 unit whereas chemical analysis of cheese and whey were carried out with the Milkoscan FT 120 device. The average composition of the cheeses was: 29.27% fat, 21.90% protein, 55.27% total dry matter and 0.78% sodium chloride. The mean value for the content of dry matter without fat was 26%, whereas the fat content of the cheese dry matter was 53.18%, the moisture content in cheese 44.73% and moisture content in fat-free matter 63.24%. There was a medium positive correlation between the ratio of fat to protein in milk and fat content in cheese (r = 0.60309), the ratio of fat to protein in milk and dry matter of cheese (r = 0.57103), weak positive correlation between the ratio of fat to protein in milk and cheese protein (r = 0.48067) and medium negative correlation between the ratio of fat to protein in milk and moisture content in cheese (r = -0.57103). Medium negative correlation was found between the ratio of protein to fat in milk and content of cheese fat (r = -0.56416), the ratio of protein to fat in milk and cheese protein content (r = -0.51899), the ratio of protein to fat in milk and dry matter of cheese (r = -0.53118) and medium positive correlation between the ratio of protein to fat in milk and moisture content in cheese (r = -0.53118). Ratio fat to protein in milk and the actual yield of cheese was determined as medium positive (r = 0.66459) and the ratio protein to fat in milk and the actual yield of cheese as medium negative correlation (r = -0.67807). The protein to fat ratio in milk influences the decline of fat, protein, dry matter and yield of cheese and increase moisture content in cheese.

Inactivation and Injury of Listeria monocytogenes under Combined Effect of Pressure and Temperature in UHT Whole Milk

AbstractInactivation and injury of Listeria monocytogenes was studied under the combined effect of high pressure and temperature. Three pressure levels (400, 500 and 600 MPa) and three temperature levels (27, 43 and 60C) were chosen. In total, seven combinations were tested: (1) 400 MPa at three temperature levels; and (2) 500 and 600 MPa at 27 and 43C, i.e., the treatment times at 60C were too short (<1 s) to obtain reliable data based on machine precision. Comparison of D‐values on both media showed that (1) the D‐values of treatment condition 400 MPa, 27C and 400 MPa, 43C were significantly different (P < 0.05), and from the rest of the five pressure and temperature combinations, (2) the remaining five combinations were not significantly different from each other (P > 0.05). Injury of L. monocytogenes was evaluated in terms of log reduction value, which was obtained from nonselective and selective media. Treatment temperature played an important role on injury of L. monocytogenes specifically at lower pressure level. At 400 MPa, the injured log reduction values obtained at 27 and 43C were 2.10 and 3.46, respectively, for 15‐min treatment time, whereas at 60C, it was 4.58 for 1 min. This study showed that 6 log10 reductions could be obtained in <2 min using low pressure (400 MPa) and high temperature (60C), which would have industrial relevance in reducing the cost related to high pressure processing of food.Practical ApplicationsListeria monocytogenes is responsible for many foodborne illnesses. Because of its psychrotrophic nature, L. monocytogenes is a potential threat to milk and dairy products as it has the ability to grow under refrigeration temperatures. Inactivation of L. monocytogenes in milk under high pressure has been studied widely. However, few studies have been done to evaluate the injury of the microorganisms, which were limited to low pressure and temperature. Quantification of injured population of L. monocytogenes is important; i.e., after high pressure treatment the sublethally injured cells can recover in the milk medium during the storage period. Hence, there is a great need of quantification of injured population of L. monocytogenes in addition to the inactivation over a wide range of pressure and temperature conditions. The kinetic data on both inactivation and injury of microorganisms will help to establish the safe processing conditions for milk during high pressure and temperature treatment.

Appraisal of Conjugated Linoleic Acid Production by Probiotic Potential of Pediococcus spp. GS4

Probiotics with ability to produce conjugated linoleic acid (CLA) is considered as an additive health benefit property for its known role in colon cancer mitigation. The conversion involves the biohydrogenation of the unsaturated fatty acid into conjugated form. Probiotic strain Pediococcus spp. GS4 was efficiently able to biohydrogenate linoleic acid (LA) into its conjugated form within 48h of incubation. Quantum of CLA produced with a concentration of 121μg/ml and sustained cell viability of 8.94log cfu/ml maximally. Moreover, antibacterial effect of LA on the strain ability for biohydrogenation was examined at different concentrations and concluded to have a direct relationship between LA and amount of CLA produced. The efficiency of the strain for CLA production at different pH was also estimated and found maximum at pH 6.0 with 149μg/ml while this ability was reduced at pH 9.0 to 63μg/ml. Sesame oil, which is rich in the triacylglycerol form of LA, was also found to act as a substrate for CLA production by Pediococcus spp. GS4 with the aid of lipase-catalyzed triacylglycerol hydrolysis and amount of CLA produced was 31μg/ml at 0.2% while 150μg/ml at 1.0% of lipolysed oil in skim milk medium. Conjugated form was analyzed using UV scanning, RP-HPLC, and GC-MS. This study also focused on the alternative use of lipolysed sesame oil instead of costly LA for biohydrogenation and could be a potential source for the industrial production of CLA.

Efeito de diferentes níveis de concentrado no período pré e pós-parto sobre a produção de leite e escore corporal de vacas leiteiras

This experiment was carried out with the objective of evaluating the effects of different levels of concentrate supplement in the pre and post-parturition periods on milk production and body score of dairy cow. 54 cows in a completely randomized design, distributed in 3 x 2 factorial arrangement, with 3 treatments, 2 periods and 9 repetitions for treatment, were used. The treatments with different levels of concentrate supplement (in dry basis) in the pre-parturition periods (PRE), were: PRE1 = 0% of the body weight (BW); PRE2 = 0.5% of the BW; PRE3 = 1.0% of the BW; and in the post-parturition (POS), were: POS1 = 1kg for each 2.5 kg of produced milk; POS2 = 1kg for each 2.0kg of produced milk and POS3 = 1kg for each 1.5kg of produced milk, above 6 kg of milk a day. The milk weight and body condition scores were evaluated every seven days. There was not significant difference among the treatments of PRE period for milk production, however, it was verified that the increase in the PRE supplementation, improved the average body condition of animals in post parturition period. In the treatments of POS period, there was positive and increasing effect with the increasing supplementation level, on milk production and medium body score of the animals. Improvement was not observed in the milk production with the increase of supplement in the PRE period, but in the POS period there was higher milk production with the increase supplement. There were not correlation among pre-parturition treatments and milk production, but there was correlation of these with body score to the parturition (r=0.66). There was correlation of supplement levels in the post parturition with medium body score (0.36) and with milk production (0.32). It can be concluded that the increasing supplement level in the pre-parturition period improves the body score but not the milk production of the animals. The increase of supplement in the post parturition period gets better so much the body score as the milk production.

HEAT-INDUCED CHANGES IN VOLATILES OF MILK AND EFFECTS OF THERMAL PROCESSING ON MICROBIAL METABOLISM OF YOGURT

Flavor and texture of yogurt are highly associated with the consumer acceptability. The volatiles in the headspace of heated milk and yogurt were analyzed to assess the effects of preheat treatment on microbial metabolism. Seventeen and 25 volatiles were found in fresh raw milk and reconstituted milk using Solid Phase Microextraction-Gas Chromatography-Mass Spectrometry, while 23 and 31 volatiles were investigated in their yogurt products, respectively. The levels of aldehydes, methyl ketones, alkanes, olefinic aldehydes and ketenes increased in liquid milk with increasing the intensity of heat treatments. Meanwhile, their levels in respective yogurt showed similar changes. 2-Pentanone, 2,3-butanedione and 2,3-pentanedione that were metabolized by starter culture organisms decreased due to increasing the intensity of heat treatments, suggesting that these heat treatments can inhibit the flavor metabolism of organisms. By analyzing the texture profile of yogurt, hardness, adhesiveness and gumminess increased with increasing the intensity of heat treatments; however, little difference was observed between the raw milk samples and the reconstituted milk samples. PRACTICAL APPLICATIONS This study demonstrated the differences in flavor impact compounds and textural properties of yogurt due to the preheat treatment and microbial metabolism. Results explain the source of volatile compounds in yogurt processing. Information on the changes in flavor as affected by heating processes would help in understanding their suitability in yogurt production. The research on flavor metabolism would shed light on the final application of some approaches to improve yogurt such as modification of milk medium, screening of the flavor-producing bacteria and the processing control of flavor production. Also, the finding could be used in the production of flavoring agent.

Research on Some Factors Influencing Acid and Exopolysaccharide Produced by Dairy Propionibacterium Strains Isolated from Traditional Homemade Turkish Cheeses

In this study, a total of 32 isolated strains and 5 reference strains of dairy propionibacteria were analyzed for acid and exopolysaccharide (EPS) production in skim milk and yeast extract-lactate broth (YEL) media in order to investigate the physiological background and preservative role of acid and EPS. The effects of final culture pH and optical density on acid and EPS production were also determined. On average, all strains produced more acid and reached lower final pH values in skim milk than in YEL medium. While the correlations obtained between the acid produced by propionibacterium strains and their final culture pH in skim milk medium were significant (P < 0.01), no correlations were found between optical density, final pH, and produced acid in YEL medium. Sixteen isolated and five reference strains of propionibacteria were tested further for the ability to produce propionic and acetic acids. On average, Propionibacterium freudenreichii subsp. shermanii and P. freudenreichii subsp. freudenreichii strains produced higher amounts of propionic and acetic acids than did Propionibacterium jensenii in YEL medium. The acid produced by these strains may be used as a preservative in the food industry for replacement or reduction of the increasing use of chemical additives. The EPS production by propionibacterium strains during growth in YEL medium was 72 to 168 mg/liter, while in skim milk it was 94 to 359 mg/liter. The monomer compositions of the EPSs formed by the six selected dairy propionibacteria strains were analyzed. The EPSs may have applications as food grade additives and viscosity-stabilizing agents.

New insight into the regulation of class II bacteriocin production by quorum sensing in Lactobacillus pentosus 31-1

The biosynthesis of class II bacteriocins is frequently regulated by a quorum-sensing regulatory mechanism meditated by autoinducing peptide. Here, it was preliminarily confirmed that bacteriocin production by Lactobacillus pentosus 31-1 was controlled by a quorum sensing (QS) system meditated by peptide signal molecules in the cell-free supernatant (CFS). Effects of the growth medium and inoculums size on bacteriocin producing in L. pentosus 31-1 were investigated. Bacteriocin production could be detected even when L. pentosus 31-1 was diluted 108-fold in MRS broth and incubated at 37°C for 24 h. However, by dilution of the culture 200-fold or more in skim milk medium, no bacteriocin activity could be detected after 60 h of incubation. Bacteriocin production could be switched on in these cultures after the addition of CFS from a bacteriocin-producing culture, and the active components in the CFS were shown to be peptides in nature. FII-22, one of the fractions purified from the CFS was identified as the putative inducing peptide (IP). Regulation of bacteriocin production in L. pentosus 31-1 by FII-22 was affected by the additional time and amount. The optimal induction of bacteriocin production effect was obtained by addition of 0.5 µg/ml (final concentration) FII-22 to the culture after 8 h of incubation. This study provided a novel perspective on screening for QS regulated class II bacteriocin producing lactic acid bacteria. This study may assist in a deeper understanding of how QS works on regulation of class II bacteriocin production. Key words: Quorum sensing, class II bacteriocin, Lactobacillus pentosus, inducing peptide, skim milk medium.

BACTERIAL ISOLATES OF MARINE COAST AS COMMERCIAL PRODUCER OF PROTEASE

The objective of this work was to explore and exploit the extracellular protease secreting marine microbial biodiversity of the eastern coastal region of India. Culture dependent method was applied for isolation of microbes from the marine coast of West Bengal (Digha and Mandarmani) and Andhra Pradesh (Vizag) in India. Six protease secreting isolates were screened using casein hydrolysing property as well as azocasein assay and characterized on the basis of their morphological, biochemical, physiological and 16S rDNA based molecular properties. The enzymes were used for various commercial applications at a laboratory scale. Besides milk media and Luria Bertini broth, all the isolates grew in carbon minimal salt medium with jaggeri or tamarind as the carbon source (0.3% w/v). They showed intracellular metal accumulation when grown in presence of metal salts in the medium as evident from Energy Dispersive X-ray Fluorescense Analysis (EDXRF) data. Maximum accumulation of lead was found in case of Bacillus cereus SM2. It showed equal efficiency of metal removal from solid strip at zero valent state. The isolates were also capable of complete removal of silver from exposed X-ray film after 48 hrs of incubation except for Escherichia coli SD1. Bacillus cereus SM2, isolate SD2 (closest to Bacillus pumilus) and isolate SV1 (closest to Bacillus cibi) were able to enhance the cleaning efficiency of detergent when used as additive. Use of tamarind and jaggeri as carbon source in minimal medium would make the process cost effective during large scale application. The ability to grow in a wide range of temperature and pH and accumulation of heavy metals revealed that these isolates would be potential candidates for bioremediation. Thus the marine diversity for protease production is extremely rich with immense commercial applications.

Alpha toxin specific PCR for detection of toxigenic strains of Clostridium perfringens in Poultry

Aim : Isolation of Clostridium perfringens from necrotic enteritis cases in poultry and confirmation by alpha toxin specific PCR Materials and methods: Robertson cooked meat medium with Brain Heart Infusion broth was used for isolation of C. perfringens from intestinal contents of necrotic enteritis suspected birds. Positive cultures from perfringens agar were further confirmed by biochemical tests and subjected to alpha toxin specific PCR. Results and Discussion: Twenty Clostridium perfringens isolates were isolated from intestinal contents of thirty five NE suspected birds. Out of the twenty isolates, fourteen were isolated from commercial broilers of 2 to 6 wk of age and six from commercial layers of 9 to 15 wk of age. Frequency of isolation of C. perfringens was more with Robertson cooked meat medium with BHI broth than thioglycollate broth alone. When positive cultures were streaked on to clostridial agar appreciable luxuriant growths were obtained and the selective streaking of these colonies on perfringens agar with supplements revealed rough and black colonies with sulphate reduction. The isolates produced rough and black colonies with sulphate reduction on perfringens agar, double zone haemolysis on sheep blood agar, stormy clot fermentation on milk medium and opalescence on egg yolk medium. The isolates were found negative for oxidase, catalase, liquefied gelatin, fermented glucose, maltose, lactose and sucrose except mannitol. All the fourteen isolates obtained from commercial broilers proved the alpha toxin producing strains of C. perfringens when they were subjected to alpha toxin specific PCR. Conclusion : This study revealed alpha toxin specific PCR is highly useful for detection of toxigenic strains of Clostridium perfringens in poultry

Sensitivity and Selectivity on Aptamer-Based Assay: The Determination of Tetracycline Residue in Bovine Milk

A competitive enzyme-linked aptamer assay (ELAA) to detect tetracycline in milk was performed by using two different aptamers individually; one is 76 mer-DNA aptamer and the other is 57 mer-RNA aptamer. The best optimum condition was obtained without monovalent ion, Na+ and also by adding no Mg2+ ion in the assay buffer, along with RT incubation. The optimized ELAA showed a good sensitivity (LOD of 2.10 × 10−8 M) with a wide dynamic range (3.16 × 10−8 M ~ 3.16 × 10−4 M). In addition, the average R.S.D. across all data points of the curve was less than 2.5% with good recoveries (~101.8%) from the milk media. Thus, this method provides a good tool to monitor tetracycline in milk from MRLs' point of view. However, this ELAA method was not superior to the ELISA method in terms of specificity. This paper describes that it does not always give better sensitivity and specificity in assays even though aptamers have several advantages over antibodies and have been known to be good binders for binding assays.

Selection of Lactic Acid Bacteria Producing Antimicrobial Strain Such the Genus Lactococcus Isolated from Algerian Raw Goat's Milk

Lactic acid bacteria are known for their ability to produce inhibitory substances against unwanted germs involved in food poisoning such as Listeria innocua. Species of lactic acid bacteria can inhibit harmful germs subject of this work. techniques confrontation on solid medium and the effect of the substance on the growth of Listeria innocua were performed. The experience was conducted bacterial antagonism in the solid medium by the method of double layer and method of wells, the whole experience was packaged in a buffered medium in order to eliminate the effect of acidity . 7 strains that isolates gave an antagonistic action against Listeria innocua. The strain of Lactococcus lactis (8b), isolated from raw goat's milk showed an anti-listeria in vitro and was selected because of its ability to inhibit as Staphylococcus aureus. With a diameter of 15mm, the action of proteolytic enzymes, trypsin, chymotrypsin is shown that the substance was protein in nature, the kinetics of growth in milk medium showed that the number of St. aureus after 24 h of incubation was reduced to 7.68 log cfu in mixed culture with strain 8b which was comparable to the control of 9.14 log cfu, which signifies that the survival rate was 3.4%, the phenotypic (biochemical and physiological) and molecular-based ADNr16Ss showed that the strain is Enterococcus faecium, duran, hirae. The sequencing results showed that Leuconostoc mesenteroides and Enterococcus faecium have summers dominant anti-Listeria species in milk samples from Algerian goat. Isolates had the potential of multiple bacteriocin production and do not have some important virulence. Importance and impact of the study: The Enterococci in milk in this region of western Algeria could be partly responsible for the safety of cheese and could be useful for the production of anti-Listeria cultures protection. The purpose of the study: Our study's main objective is the selection ,and study phenotypic and molecular lactic acid bacteria from Lactococcus genus possessing biotech traits such as the production of new inhibitory substance and the study of the interaction of Listeria innocua screw opinion and St. aureus that both methods were used, a traditional approach based on morphological and biochemical studies of different cultural characteristics and a method of direct molecular amplification of bacterial DNA using PCR / RAPD colony on having targeted DNA fragment 16S lactic acid bacteria using the two primers universal: 20F (5'AGAGTTTGATCATGGCTCAG-3 '). 1500R (5'-GGTTACCTTGTTACGACTT-3 ') and two specific primers OPA-3 (5'-AGTCAGCCAC - 3') and OPH 3 (5'-AGACGTCCAC-3 ') (Bioprobe, France).

Comparison of methods for the enumeration of Clostridium perfringens spores in water

Four methods for enumerating Clostridium perfringens spores in water were evaluated: (1) the IMM (Iron Milk Medium) method (MPN); (2) the LS (Lactose Sulfite Broth) method (MPN); (3) the m-CP (membrane filtration Clostridium perfringens Agar) method (membrane filtration); and (4) the TSC (Tryptose Sulfite Cycloserine Agar) method (membrane filtration). The performance of these methods was compared with that of the DRCM (Differential Reinforced Clostridium Medium) method (MPN) as adopted by CETESB (Brazil's Environmental Sanitation Technology Company) for the analysis of C. perfringens spores in water. Statistical analysis was performed according to ISO 17994:2004 (Water Quality - Criteria for Establishing Equivalence between Microbiological Methods). The LS, m-CP, and TSC methods were considered not equivalent to the DRCM method, as they gave significantly lower results. The IMM showed inconclusive results and, according to ISO 17994:2004, analysis of a greater number of samples is needed to draw definitive conclusions comparing IMM and DRCM.

Growth and exopolysaccharide production by Streptococcus thermophilus ST1 in skim milk

To analyze the exopolysaccharide (EPS) production by Streptococcus thermophilus ST1, cultures were cultivated in 10% (w/v) reconstituted skim milk under different growth conditions including various temperatures and pHs of growth medium, supplementation of the medium with various carbon sources (glucose, lactose, sucrose, galactose and fructose) and nitrogen source (whey protein concentrate, or WPC). The results showed that most EPS production by strain ST1 was obtained at a temperature (42°C) and pH (6.5) optimal for its growth. Supplementation of the skim milk medium with either carbohydrates or WPC increased both growth and polymer formation by different extents, with sucrose being most effective among the carbon sources tested. Under the optimal cultural conditions, i.e. pH 6.5, 42°C with 2% (w/v) sucrose and 0.5% (w/v) WPC, 135.80 mg l(-1) of EPS was produced by strain ST1. The monosaccharide composition of the EPS was determined to be glucose and galactose (2:1), and the molecular mass of the EPS was 3.97 × 10(6) Da. The aqueous solution of the EPS at 1% (w/v) showed relatively high viscosity, indicating the potential of this EPS-producing S. thermophilus strain for applications in the improvement of physical properties of fermented milk products.

Effect of Galaeto-Oligosaccharide and Isomalto-Oligosaccharide on Growth of Selected Probiotics

Effect of Galaeto-oligosaccharide (GOS) and Isomalto-oligosaccharide (IMO) on growth of Lactobacillus acidophilus, Bifidobacterium longum and L. rhamnosus was studied. The addition of each substance (w/v) was 0.0%, 0.1%, 0.5%, 1.0% 1.5% and 2.0%.The methods were analyzed titratable acidity (°T), pH and enumeration that using reconstituted skim goat milk media as the control. All samples were incubated at 37 C for 18h. Results were as follows: addition of GOS has the significant inhibition on the growth of L. acidophilus and promotion on the growth of L. rhamnosus, while the effect on the growth of B. longum was not obviously. Addition of IMO could promote the growth of L. acidophilus, especially in low level. The growth of B. longum was increased with increase in IMO. While the effect on the growth of L. rhamnosus by adding IMO was inhibited and obviously in the high concentration.

New insights into the citrate metabolism of Enterococcus faecium FAIR-E 198 and its possible impact on the production of fermented dairy products

Citrate metabolism by Enterococcus faecium FAIR-E 198, an isolate from Greek Feta cheese, was studied in milk-based media compared with modified de Man–Rogosa–Sharpe (mMRS) medium. Co-metabolism of lactose and citrate was shown. The presence of fermentable lactose and glucose in mMRS medium under microaerophilic conditions increased the yield of acetate from citrate conversion but decreased the yield of acetoin compared with a fermentation in the presence of non-fermentable xylose. Under anaerobic conditions in mMRS medium, the yield of ethanol based on citrate increased and diacetyl was no longer found. In milk medium, additional nitrogen sources (e.g., casitone) were necessary to sustain co-metabolism of citrate and lactose. Addition of extra citrate to milk-based medium did not affect citrate conversion, although a lower yield of acetate was found. As citrate conversion was associated with the stationary growth phase, E. faecium FAIR-E 198 is an interesting adjunct starter culture for cheese ripening.

Growth and exopolysaccharide production by Lactobacillus fermentum F6 in skim milk

Growth and exopolysaccharide (EPS) production by Lactobacillus fermentum F6 isolated from traditional dairy products in Inner Mongolia of China were studied when the strain was grown in 10% (w/v) reconstituted skim milk under different culture conditions. The results showed that culturing of L. fermentum F6 at a temperature (37°C) and pH (6.5) optimal for growth was also favorable for EPS production. Supplementation in 10% (w/v) skim milk with different carbon sources (glucose, lactose, galactose and fructose) increased EPS production; glucose being more effective than other sugars. Supplementation with whey protein concentrate (WPC) at 0.5% (w/v) resulted in about two-fold increase in EPS production. A maximum of 44.49 mg/l of EPS was produced by L. fermentum F6 in the skim milk medium supplemented with 2% (w/v) glucose and 0.5% (w/v) WPC at 37°C and at initial pH 6.5. Monosaccharide analysis showed that the EPS of L. fermentum F6 was composed of glucose and galactose in a molar ratio of 4:3. The molecular mass of the EPS was determined to be 3.54 × 106 Da. A 1% (w/v) aqueous solution of the EPS showed relatively high viscosity, indicating the potential of this EPS to be used as a viscosifying agent in food products. Key words : Lactic acid bacteria, Lactobacillus fermentum, exopolysaccharides.

Screening and regulation of alkaline extracellular protease and ribonuclease production of Yarrowia lipolytica strains isolated and identified from different cheeses in Turkey

In this research, 43 yeast strains were isolated from different types of cheese in Turkey and these isolates were identified with both phenotypic tests and genotypic tests with 5.8S ITS-PCR. Also, the sequence of PCR fragments obtained from ITS-PCR was analyzed by DNA sequencing. In the results of the phenotypic tests, 9 of 43 isolates were identified as Yarrowia lipolytica. After the phenotypic identification, all the isolates were identified with ITS-PCR and 13 were identified as Y. lipolytica. Yarrowia lipolytica secretes several hydrolytic enzymes including alkaline and acid proteases, lipases, a ribonuclease, and phosphotases. In this paper, the effect of carbon and nitrogen sources and pH on production of AEP and RNase were examined for our identified strains of Y. lipolytica. The best production of AEP were found in skim milk medium with pH 7.0 by TEM YL 5 and Y. lipolytica CBS 6124 type strain. An extra carbon source (glucose) reduced AEP production at all the pH studied. Glutamine which is a nitrogen source did not affect AEP production. In contrast to AEP production, glucose increased RNase production at all the pH studied.

Growth and exopolysaccharide production by Streptococcus thermophilus ST1 in skim milk

To analyze the exopolysaccharide (EPS) production by Streptococcus thermophilus ST1, cultures were cultivated in 10% (w/v) reconstituted skim milk under different growth conditions including various temperatures and pHs of growth medium, supplementation of the medium with various carbon sources (glucose, lactose, sucrose, galactose and fructose) and nitrogen source (whey protein concentrate, or WPC). The results showed that most EPS production by strain ST1 was obtained at a temperature (42°C) and pH (6.5) optimal for its growth. Supplementation of the skim milk medium with either carbohydrates or WPC increased both growth and polymer formation by different extents, with sucrose being most effective among the carbon sources tested. Under the optimal cultural conditions, i.e. pH 6.5, 42°C with 2% (w/v) sucrose and 0.5% (w/v) WPC, 135.80 mg l-1 of EPS was produced by strain ST1. The monosaccharide composition of the EPS was determined to be glucose and galactose (2:1), and the molecular mass of the EPS was 3.97 × 106 Da. The aqueous solution of the EPS at 1% (w/v) showed relatively high viscosity, indicating the potential of this EPS-producing S. thermophilus strain for applications in the improvement of physical properties of fermented milk products.