The manufacture and some quality characteristics of kurut, a dried dairy product

This study was designed to investigate the microbiological and chemical characteristics of kurut, a dairy product obtained by drying yogurt under the sun in rural areas of Turkey. For this purpose, 50 randomly collected kurut samples from the Kars Region were analysed for determination of their microbiological and chemical characteristics. Analysis of kurut samples showed that kurut contained on average 4.52 log₁₀ cfu/g of aerobic mesophilic bacteria, 2.78 log₁₀ cfu/g of aerobic mesophyl spores, 3.60 log₁₀ cfu/g of lactic acid bacteria, 3.60 log₁₀ cfu/g of Lactococcus , 3.94 log₁₀ cfu/g of mould and yeast, 2.13 log₁₀ cfu/g of Enterobacteriaceae, l.51 log₁₀ cfu/g of sulphite-reducing clostridia, and 1.81 log₁₀ cfu/g of coagulase-positive s taphylococci . Coliform bacteria and enterococci bacteria were not detected in any of the kurut samples. Furthermore, chemical characteristics of the kurut were as follows: pH 4.2, acidity (lactic acid) 2.9, moisture 12.1%, fat 45.9% protein 25.5%, salt 6.7% and ash 10.0%. The quality characteristics of kurut presented here may help create a different perspective for new products to be produced in the dairy sector.     

The distribution of Enterobacteriaceae and some pathogenic micro-organisms in nonbranded white cheese samples sold in Ankara city

In this research, 75 samples of nonbranded white cheese, presented for sale in small markets from various regions and bazaars in Ankara, were studied. Eighty-six isolates, 71 of which are Gram-negative isolates and 15 of which are Gram-positive isolates, were obtained. These isolates were identified by using bioMérieux API20E and classical methods. Total mesophilic bacteria counts and total coliform bacteria counts were carried out for each white cheese sample. The total average mesophilic bacteria of 75 white cheese samples was 15.5 × 10⁵ cfu/g and the total average coliform bacteria were 13.6 × 10⁵ cfu/g.     

Isolation of lactic acid bacteria from Lighvan cheese, a semihard cheese made from raw sheep milk in Iran

The lactic acid bacteria contributing to Lighvan cheese ripening during the different stages of production were investigated. Isolated strains from different culture media were identified phenotypically to species and subspecies level. In total, 413 strains were isolated from raw milk, 1-day-old cheese and fully ripened cheese. The most abundant species belonged to Enterococcus faecium (87 isolates), Lactococcus lactis ssp. lactis (68 isolates), Enterococcus faecalis (55 isolates) and Lactobacillus plantarum (48 isolates). E. faecium, Lc. lactis and Lb. plantarum were the predominantly isolated strains from ripened cheese. Therefore, they may contribute considerably to the aroma and flavour development of Lighvan cheese.     

Fate of Aflatoxin M1 during Manufacture and Storage of Feta Cheese

ABSTRACT:  The effect of feta cheese manufacture on aflatoxin M₁ (AFM₁) content was studied using an enzyme immunoassay technique. Feta cheese was made from milk spiked with 1 and 2 μg AFM₁ per kilogram milk. Pasteurization at 63 °C for 30 min caused <10% destruction of AFM₁. During cheese making, the remaining AFM₁ in milk was partitioned between curd and whey with two-thirds retained in the curd and one-third going into the whey. Cheeses were then stored for 2 mo in 8%, 10%, and 12% brine solutions at 6 and 18 °C. There was a 22% to 27% reduction of AFM₁ during the first 10 d of storage, with slightly more loss as salt concentration increased and when the cheese was stored at 18 °C. Further storage caused only slight decrease in AFM₁ and after 30 d of brining there was no difference in AFM₁ content of the cheese based upon salt concentration of the brine. At 18 °C, no further losses of AFM₁ occurred after 30 d, and at 6 °C, there was continued slight decrease in AFM₁ levels until 50 d. After 60 d of brining, there was a total loss of 25% and 29% of the AFM₁ originally present for cheese brined at 6 and 18 °C, respectively. Thus, the combination of pasteurization, conversion of milk into feta cheese, and at least 50 d storage of cheese in brine caused a total loss of about 50% of the AFM₁ originally present in the raw milk.     

Evaluation of Listeria innocua as a suitable indicator for replacing Listeria monocytogenes during ripening of Camembert cheese

The suitability of Listeria innocua for use as an indicator for replacing Listeria monocytogenes during the cheese-making and ripening of Camembert cheese was evaluated. Pasteurized whole milk inoculated with either L. innocua or L. monocytogenes was used to make Camembert cheese, which were ripened in three stages. All cheese was ripened in three stages: room temperature (∼20 °C) and relative humidity of 60% for 36 h; 12 °C and relative humidity of 93% for 2 weeks; and 7 °C and relative humidity of 85% for 3 weeks. Results showed that population values of L. innocua and L. monocytogenes on day 1 were 7.16 and 6.11 log₁₀ CFU/g, respectively, which declined to 6.54 and 5.45 log₁₀ CFU/g, respectively, during subsequent 20 days. Thereafter, L. innocua and L. monocytogenes populations increased to 7.38 and 6.06 log₁₀ CFU/g on day 35 of ripening, respectively. During ripening, surface and interior of cheeses were analysed for populations of L. innocua and L. monocytogenes , respectively. The data were collected on day 1, 5, 10, 15, 20, 25, 30, and 35 of ripening. Generally, the growth of L. innocua and L. monocytogenes is faster in surface than in centre. Top centre, bottom centre and bottom surface locations had similar population values during ripening. There were no significant differences ( P  > 0.05) between batch and section of cheese. The ripening time and locations had significant effect ( P  < 0.05) on the survival and growth of L. innocua and L. monocytogenes . The trends of survival and growth of L. innocua and L. monocytogenes were similar. These results indicated that L. innocua can be considered as an indicator for L. monocytogenes during ripening of Camembert cheese.     

Effect of Microencapsulation on Viability of Lactobacillus acidophilus LA-5 and Bifidobacterium bifidum BB-12 During Kasar Cheese Ripening

The viability of encapsulated Lactobacillus acidophilus LA-5 and Bifidobacterium bifidum BB-12 by emulsion or extrusion techniques in Kasar cheese was investigated. The microbiological, biochemical and organoleptic properties of cheeses were assessed throughout 90-day storage. Results showed that the viability of probiotic bacteria was maintained to a great extent by microencapsulation. No difference was noted between the two encapsulation techniques with regard to bacterial counts, proteolysis and organoleptical properties of the final products. Scalding caused a drastic decline in the counts of probiotic bacteria in all cheeses. Following scalding, while the numbers of nonencapsulated probiotic bacteria decreased continuously in the control cheese, the numbers of encapsulated bacteria remained well above the threshold for a minimum probiotic effect (10⁷ cfu/g).     

Production of hard cheese from caprine milk by the use of two types of probiotic cultures as adjuncts

Hard cheeses (Kefalotyri-like) were manufactured from caprine milk with yoghurt as a starter (A), and with its partial replacement with the probiotic adjuncts Lactobacillus rhamnosus LC 705 (B) and/or Lactobacillus paracasei ssp. paracasei DC 412 (C). Both adjuncts retarded the growth of enterococci, and the environment in cheese B did not favour the recovery of lactic acid bacteria (LAB) on Rogosa agar. However, better recovery of the LAB population on M17 agar from cheeses B and C made with adjuncts was recorded early in ripening, and this was accompanied by a greater decrease in pH. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) of whole-cell protein demonstrated that cheese C, made with Lb. paracasei ssp. paracasei as adjunct, is a better vehicle for delivery of live probiotic cells (10 ⁷   cfu/g) to the gastrointestinal tract than cheese B, made with Lb. rhamnosus ; the latter did not belong to the predominant microflora of one out of the two B cheeses. Urea-PAGE electrophoresis results indicated that adjunct lactobacilli enhanced the degradation of both α _S -casein (α _S -CN) and β-casein (β-CN). In the fresh cheese, hydrolysis of α _S -CN was more rapid than β-CN, and the free amino acid content of B and C was higher than in A. Lipolysis products were also higher in B and C than in A as ripening progressed, and the organoleptic characteristics of these cheeses resulted in higher scores, in the order C > B > A. Thus, making Kefalotyri-like cheese from caprine milk with probiotic lactobacilli, particularly Lb. paracasei ssp. paracasei, as adjunct can be considered an effective way of producing a cheese with a large number of probiotic cells.     

Viability of probiotic micro-organisms (Lactobacillus acidophilus La-5 and Bifidobacterium animalis subsp. lactis Bb-12) in ice cream

The purpose of this research was to determine the survival of two probiotic micro-organisms in ice creams (4% fat). The micro-organisms were Lactobacillus acidophilus La-5 and Bifidobacterium animalis subsp . lactis Bb-12 . To meet this objective, an ice cream mixture was formulated and subjected to three treatments. Treatment 1 was inoculated with L. acidophilus , treatment 2 with B. lactis and the third treatment was inoculated with a mixture of both bacteria inoculated in 1 : 1 proportions. The inoculation was with 4% culture for each treatment. The final products were stored at −25°C for 60 days. The ice cream inoculated with L. acidophilus had a final concentration of 2 × 10 ⁶ cfu/g and the survival rate was 87%. The treatment inoculated with B. lactis had a final concentration of 9 × 10 ⁶ cfu/g, with a logarithmic decrease of 10%. When both micro-organisms were inoculated together, the survival rate was 86%.     

Isolation and characterization of the microbial population of different South African kefir grains

Kefir, a slightly acidic fermented milk, is produced by adding lactic acid bacteria and yeasts, in the form of grains, to milk. The bacteria and yeasts present in the kefir grains are known to vary widely. Selective growth media and morphological and biochemical characteristics were used for the isolation and identification of the microbes present in the grains from eight different sources in South Africa. The kefir grains were activated in milk for only 24 h to prevent any changes in the microbial population of the grains. The microbial numbers varied between 6.4 × 10⁴ and 8.5 × 10 ⁸  cfu/g on the media selective for the bacterial species and between 1.5 × 10 ⁵ and 3.7 × 10 ⁸   cfu/g on the media selective for the yeast species. The bacterial genera that were identified included Lactobacillus , Leuconostoc and Lactococcus and the yeast genera included Zygosaccharomyces , Candida and Saccharomyces . The distribution frequencies of the microbes in the different grains were determined and most of the grains were dominated by two microbial species. No pediococci, acetic acid bacteria or propionibacteria were detected.     

Influence of Australian Native Herbs on the Maturation of Vacuum-packed Cheese

The composition, microbiology and biochemistry of semi-hard cheeses flavoured with native mint, lemon myrtle and bush tomato (BT) were compared with unflavoured (control) cheese during a 90-day period of maturation. Moisture, protein and salt levels of all cheeses were similar and did not change during maturation. However, the fat content of control cheese was significantly higher than that of the flavoured cheeses while the pH of cheese flavoured with BT was consistently lower throughout maturation. Total viable organisms, Lactobacillus and Lactococcus counts were between 10⁶ and 10⁷ colony forming units (cfu)/g cheese for all cheeses. Yeast and mould count was <10² cfu/g cheese throughout the maturation of all cheeses except in the cheese flavoured with BT which was >10³ cfu/g cheese. Biochemical indices of proteolysis and lipolysis increased with the extent of maturation in all cheeses but were most pronounced in the BT-flavoured cheese. The capillary electrophoretic profile of this cheese also indicated a more extensive hydrolysis of both α s- and β -caseins. The microbiological quality of BT appeared to have exerted a very significant influence on cheese properties.     

Proteolytic and lipolytic changes during the ripening of León raw cow's milk cheese, a Spanish traditional variety

Proteolytic and lipolytic changes were studied throughout ripening of five batches of León cow's milk cheese, a traditional variety made in the north of Spain. Total soluble nitrogen, non-protein nitrogen, oligopeptides nitrogen, amino nitrogen and ammonia nitrogen fractions increased slightly during the ripening process. The final values of these nitrogen fractions indicate that this cheese undergoes a very slight proteolysis as much in extent as in depth. This weak protein degradation is corroborated when the caseins and their degradation products were quantified by electrophoresis. β-Casein stayed practically intact throughout the ripening process and only 10% of α_s-casein became degraded. The content of total free amino acids increased progressively but in a slightly increased way during ripening, reaching final average values of 592 mg (100 g)⁻¹ of total solids. The most abundant free amino acid at the end of ripening was lysine, followed by leucine, glutamic acid, tryptophan, valine and phenylalanine. The acidity index of the fat values increased during ripening by a factor of 4.39. The final values of this parameter are in the range of those observed in other cow's milk cheeses ripened by bacteria. The content in total free fatty acids underwent an increase throughout ripening reaching final average values of 6669 ppm. The most abundant free fatty acid at the end of ripening was oleic acid followed by butyric and palmitic acids. The high content of short-chain fatty acids is outstanding, specially that of butyric acid.     

Changes in the microbiological and chemical characteristics of an artisanal, low-fat cheese made from raw ovine milk during ripening

Changes in the microbial flora of batzos cheese made from raw ovine milk were studied during ripening. Lactic acid bacteria and Enterobacteriaceae were the predominant groups of micro-organisms. Cheeses manufactured in summer had higher microbial counts than those made in spring, with the exception of staphylococci. Nevertheless, Enterobacteriaceae and coliforms decreased more rapidly in cheese made in summer and counts at the end of storage were lower than those in spring cheese.
Enterococci predominated in the ripened curd of cheese made in spring, whereas lactobacilli were the most abundant lactic acid bacteria in cheese made in summer. Enterococcus faecium was the predominant species in spring, and Lactobacillus paracasei ssp. paracasei predominated in cheese made in summer. The pH of the cheeses was > 5.0 throughout ripening, and NaCl-in-moisture content (> 8.0%) permitted the growth and survival of salt-tolerant micro-organisms. α_s1-Casein degraded at a faster rate than β-casein; both caseins were hydrolysed more rapidly in spring than in summer. The free amino acid content became higher in summer cheese (566.24–3460.25 µg/g of glycine equivalent) than in spring cheese because of the progress of ripening. Moreover, the milk fat of the cheese was degraded more in the summer than in the spring. The results suggest that there could be advantages to using starter cultures and improving the level of hygiene during milk and cheese production in order to eliminate undesirable micro-organisms and standardize cheese quality.     

Effect of milk centrifugation and incorporation of high heat-treated centrifugate on the microbial composition and levels of volatile organic compounds of Maasdam cheese

Centrifugation is a common milk pretreatment method for removal of Clostridium spores which, on germination, can produce high levels of butyric acid and gas, resulting in rancid, gassy cheese. The aim of this study was to determine the effect of centrifugation of milk, as well as incorporation of high heat-treated centrifugate into cheese milk, on the microbial and volatile profile of Maasdam cheese. To facilitate this, 16S rRNA amplicon sequencing in combination with a selective media-based approach were used to study the microbial composition of cheese during maturation, and volatile organic compounds within the cheese matrix were analyzed by HPLC and solid-phase microextraction coupled with gas chromatography–mass spectrometry. Both culture-based and molecular approaches revealed major differences in microbial populations within the cheese matrix before and after warm room ripening. During warm room ripening, an increase in counts of propionic acid bacteria (by ～10^1.5 cfu) and nonstarter lactic acid bacteria (by ～10⁸ cfu) and a decrease in the counts of Lactobacillus helveticus (by ～10^2.5 cfu) were observed. Lactococcus species dominated the curd population throughout ripening, followed by Lactobacillus, Propionibacterium, and Leuconostoc, and the relative abundance of these accounted for more than 99% of the total genera, as revealed by high-throughput sequencing. Among subdominant microflora, the overall relative abundance of Clostridium sensu stricto was lower in cheeses made from centrifuged milk than control cheeses, which coincided with lower levels of butyric acid. Centrifugation as well as incorporation of high heat-treated centrifugate into cheese milk seemed to have little effect on the volatile profile of Maasdam cheese, except for butyric acid levels. Overall, this study suggests that centrifugation of milk before cheesemaking is a suitable method for controlling undesirable butyric acid fermentation without significantly altering the levels of other volatile organic compounds of Maasdam cheese.     

Viability of probiotic micro-organisms (Lactobacillus casei Shirota and Bifidobacterium animalis subspp. lactis) in a milk-based dessert with cranberry sauce

The objective of this study was to evaluate the survival of two probiotic micro-organisms, Lactobacillus casei Shirota and Bifidobacterium animalis subspp . lactis , in a milk-based dessert (2.7% fat) with cranberry sauce added. B. lactis had a final concentration of 1.99 × 10⁶ cfu/g after 21 days of study, with a logarithmic decrease of 8.87%. On other hand, L. casei Shirota had a final concentration of 2.05 × 10⁷ cfu/g at the end of the same period, a logarithmic decrease of 8.41%. Statistical analysis showed that significant differences existed between both micro-organisms and over various storage times, the more viable micro-organism being L. casei Shirota , which decreased less than one logarithmic cycle after 21 days.     

Detection of aflatoxin M1 in milk and dairy products consumed in Adana, Turkey

A total of 70 dairy products consisting of 20 sterilized milk, 10 butter, 20 white cheese and 20 Kashar cheese samples were analysed for aflatoxin M₁ (AFM₁) by enzyme-linked immunosorbent assay (ELISA). The detection limit was 5 ng/L for milk and 25 ng/kg for butter, white cheese and Kashar cheese. Of the 70 dairy products analysed, AFM₁ in 49 samples (70%) was found to range from 10 to 388 ng/kg. Moreover, AFM₁ levels in three samples of milk, two samples of butter, one sample of white cheese and one sample of Kashar cheese were found to be higher than the Turkish legal limits.     

Modeling the Growth Characteristics of Listeria monocytogenes and Native Microflora in Smoked Salmon

ABSTRACT:  Smoked salmon contaminated with Listeria monocytogenes has been implicated in foodborne listeriosis. The objectives of this study were to model the growth characteristics and examine the growth relationship of L. monocytogenes and native microflora in smoked salmon. Smoked salmon samples with a native microflora count of 2.9 log₁₀ CFU/g were inoculated with a 6-strain mixture of L. monocytogenes to levels of log₁₀ 1.6 and log₁₀ 2.8 CFU/g, and stored at 4, 8, 12, and 16 °C. Growth characteristics (lag phase duration [LPD, h], growth rate [GR, log₁₀ CFU/h], and maximum population density [MPD, log₁₀ CFU/g]) of L. monocytogenes and native microflora were determined. At 4 to 16 °C, the LPD, GR, and MPD were 254 to 35 h, 0.0109 to 0.0538 log₁₀ CFU/h, and 4.9 to 6.9 log₁₀ CFU/g for L. monocytogenes , respectively, and were 257 to 29 h, 0.0102 to 0.0565 log₁₀ CFU/h, and 8.5 to 8.8 log₁₀ CFU/g for native microflora. The growth characteristics of L. monocytogenes or the native microflora were not significantly different ( P > 0.05), regardless the initial levels of L. monocytogenes . Mathematical equations were developed to describe the LPD, GR, and MPD of L. monocytogenes and native microflora as a function of storage temperature. The growth relationship between L. monocytogenes and native microflora was modeled and showed that the LPD and GR of L. monocytogenes were similar to those of native microflora. These models can be used to estimate the growth characteristics of L. monocytogenes in smoked salmon, and thereby enhance the microbiological safety of the product.     

Shelf life of Turkish whey cheese (Lor) under modified atmosphere packaging

In this study, the shelf life of Lor cheese stored under different atmosphere compositions was assessed and compared. Lor cheeses were held in four different atmospheres containing: vacuum packaging (VP), 40% CO₂/60% N₂, 60% CO₂/40% N₂ and 70% CO₂/30% N₂ (modified atmosphere packaging). Control cheeses were stored in air. All cheese samples were kept in the refrigerator at 4°C for 45 days and investigated for physicochemical, microbiological and sensory properties. The acidity index value was significantly higher ( P  < 0.05) in the control and vacuum packaged samples than in those stored for the same period under CO₂. Microbiological results showed that modified atmosphere packaging delayed microbial growth compared with air and VP samples. Of the three modified atmospheres, gas mixtures 60% and 70% CO₂ were the most effective for inhibition of growth of micro-organisms. Sensory evaluation (odour and taste) results showed that Lor cheese packaged under modified atmosphere packaging (60% CO₂/40% N₂ and 70% CO₂/30% N₂ ) retained good characteristics for 45 days of storage, while vacuum and control samples were sensorily unacceptable after 10 days of storage.     

Reduced-fat Cheddar cheese from a mixture of cream and liquid milk protein concentrate

Reduced-fat Cheddar cheese (RFC) was manufactured from standardized milk (casein/fat, C/F ˜ 1.8), obtained by (1) mixing whole milk (WM) and skim milk (SM) (control) or (2) mixing liquid milk protein concentrate (LMPC) and 35% fat cream (experimental). The percentage yield, total solid (TS) and fat recoveries in the experimental RFC were 22.0, 63.0 and 89.5 compared to 9.0, 50.7 and 87.0 in the control RFC, respectively. The average % moisture, fat, protein, salt and lactose were 40.7, 15.3, 32.8, 1.4 and 0.07%, respectively, in the experimental cheese and 39.3, 15.4, 33.0, 1.3 and 0.10%, respectively, in the control cheese. No growth of nonstarter lactic acid bacteria (NSLAB) was detected in the control or the experimental cheeses up to 3 months of ripening. After 6 months of ripening, the experimental cheese had 10⁷ cfu NSLAB/g compared to 10⁶ cfu/g in the control. The control cheese had higher levels of water-soluble nitrogen (WSN) and total free amino acids after 6 months of ripening than the experimental cheese. Sensory analysis showed that the experimental cheeses had lower intensities of milk fat and fruity flavours and decreased bitterness but higher intensities of sulphur and brothy flavours than in the control cheese. The experimental cheeses were less mature compared to the control after 270 days of ripening. It can be concluded from the results of this study that LMPC can be used in the manufacture of RFC to improve yield, and fat and TS recovery. However, proteolysis in cheese made with LMPC and cream is slower than that made with WM and SM.     

Microbial flora of technological interest in raw ovine milk during 6°C storage

Changes in the microbial flora of ovine milk of medium hygienic quality (initial mean total plate count 3.3  ×  10⁵ cfu/mL) were studied throughout refrigerated storage at 6°C. Total plate counts after 48 h of refrigerated storage (mean count 4.6  ×  10⁵ cfu/mL) were under the current standards in the European Union (EU) for raw ovine milk to be used for cheesemaking after heat treatment. However, after 96 h, mean total plate counts (1.6  ×  10⁷ cfu/mL) were above the standards. Lactococci were found at levels higher than Pseudomonas spp. in milk freshly drawn (54.5% and 3.5% of total plate count, respectively) and after 96 h at 6°C (47.9% and 33.9% of total plate count, respectively). Lactobacilli, enterococci, coliforms and thermodurics were found at values lower than lactococci and Pseudomonas spp., before and after refrigerated storage ( ≤  0.08% of the total plate count). A significant growth ( P  < 0.001) was detected for mesophiles, Pseudomonas spp. and lactococci after 96 h of refrigeration at 6°C; however, thermodurics, coliforms, lactobacilli and enterococci, showed no significant increase ( P  > 0.05). Presumptive Escherichia coli (β-glucuronidase-positive) underwent a decrease throughout storage at 6°C.     

Microbiological characterization of artisanal Raschera PDO cheese: analysis of its indigenous lactic acid bacteria

The aim of this research was to study the bacterial populations involved in the production of artisanal Raschera PDO cheese (Italian Maritime Alps, northwest Italy) in order to collect preliminary knowledge on indigenous lactic acid bacteria (LAB). A total of 21 samples of Raschera PDO cheese, collected from six dairy farms located in the production area, were submitted to microbiological analysis. LAB were randomly isolated from M17 agar, MRS agar and KAA plates and identified by combining PCR 16S-23S rRNA gene spacer analysis, species-specific primers and 16S rRNA gene sequencing. Biodiversity of Lactococcus lactis subsp. lactis isolates was investigated by RAPD-PCR. LAB microflora showed the highest count values among all microbial groups targeted. They reached counts of 10(9) colony forming unit (cfu)/g in cheese samples after 3 days of salting and 15 days of ripening. Yeast population also showed considerable count values, while enterococci and coagulase-negative cocci (CNC) did not overcome 10(7)cfu/g. L. lactis subsp. lactis was the species most frequently isolated from Raschera PDO samples at all different production stages while in aged cheeses Lactobacillus paracasei was frequently isolated. RAPD-PCR highlighted that isolates of L. lactis subsp. lactis isolated from Raschera PDO were highly homogeneous.