Survival of probiotic microflora in Argentinian yoghurts during refrigerated storage

The survival of Bifidobacterium bifidum BBI and Lactobacillus acidophilus LAI in reduced-fat (liquid) and full-fat (set) yoghurts produced with two commercial lactic starter cultures (SID and SISD) was investigated. The viability of the probiotic bacteria was also assayed in milk acidified with lactic acid at different pH values. Samples were stored at 5°C for up to 4 weeks. There was a great variability in the survival ability of the probiotic cultures in the two yoghurt types. L. acidophilus LAI demonstrated, in general, a lower resistance to the yoghurt environment than B. bifidum BBI. On the other hand, the full-fat yoghurt was a more inhibitory medium than the reduced-fat one, especially for B. bifidum BBI. Regarding the lactic starters used, the results showed that the culture SISD was clearly more inhibitory for both probiotic organisms than the culture SID. The loss of cell viability in yoghurt samples was different (higher in some cases and lower in others) from that due to lactic acid only. In general, pH values of 4.5 or lower jeopardised the cell viability of the probiotic organisms in yoghurt stored at 5°C. This work shows the importance of selecting a suitable combination of probiotic strains and starter cultures when different yoghurt types are formulated.     

1H NMR characterisation of the lipid fraction and the metabolite profiles of Fossa (pit) cheese

Fossa cheese is a typical Italian cheese characterised by ripening in pits dug in tuffaceous rock. In this work, ¹H NMR spectroscopy was applied to characterise the lipid fraction and the metabolite profile of Fossa cheese produced with sheep's milk. Samples were collected before and after ripening in different pit environments. The higher levels of free amino acids (FAAs) found in samples suggest that cheeses underwent a strong proteolytic process. Differences in quantity and variety of FAAs were influenced by the two ripening environments. Diacylglycerols and butyric acid, which can be linked to lipolysis, were detected in all the samples. Longer ripened samples had higher contents of rumenic acid (18:2 cis-9, trans-11) and glycerol, and lower contents of lactate and citrate. The presence of tyramine was observed by two-dimensional NMR, while cadaverine was not detected in the samples.     

Volatile organic compound profiles of yoghurt produced from cow's milk with different somatic cell counts

The present study aimed to investigate the effect of somatic cell count (SCC) of raw cow's milk on the volatile organic compound (VOC) profiles of yoghurt. Test yoghurt samples were produced from three batches of cow's milk with low, medium and high SCC, respectively. The VOCs were determined by gas chromatography–mass spectrometry (GC–MS) analysis. A lower diacetyl and acetoin content and a higher content of 2‐heptanone, and butanoic and hexanoic acids were established in the yoghurt samples from batches with high SCC of above 1 000 000 cells/cm³. The increased SCC of cow's milk had a negative effect on the volatile organic compound profiles of yoghurt.     

A review on traditional Turkish fermented non-alcoholic beverages: Microbiota,fermentation process and quality characteristics

Shalgam juice, hardaliye, boza, ayran (yoghurt drink) and kefir are the most known traditional Turkish fermented non-alcoholic beverages. The first three are obtained from vegetables, fruits and cereals, and the last two ones are made of milk. Shalgam juice, hardaliye and ayran are produced by lactic acid fermentation. Their microbiota is mainly composed of lactic acid bacteria (LAB). Lactobacillus plantarum, Lactobacillus brevis and Lactobacillus paracasei subsp. paracasei in shalgam fermentation and L. paracasei subsp. paracasei and Lactobacillus casei subsp. pseudoplantarum in hardaliye fermentation are predominant. Ayran is traditionally prepared by mixing yoghurt with water and salt. Yoghurt starter cultures are used in industrial ayran production. On the other hand, both alcohol and lactic acid fermentation occur in boza and kefir. Boza is prepared by using a mixture of maize, wheat and rice or their flours and water. Generally previously produced boza or sourdough/yoghurt are used as starter culture which is rich in Lactobacillus spp. and yeasts. Kefir is prepared by inoculation of raw milk with kefir grains which consists of different species of yeasts, LAB, acetic acid bacteria in a protein and polysaccharide matrix. The microbiota of boza and kefir is affected from raw materials, the origin and the production methods.     

The effect of supplementing goats milk with whey protein concentrate on textural properties of set-type yoghurt

Yoghurt was manufactured from goat's milk and supplemented with 30 g L^?1 of whey protein concentrate (WPC). The textural properties of the yoghurt were evaluated during the shelf‐life of the product and the textural characteristics of yoghurt made from cow's milk were used as a reference. The instrumental analyses used were the puncture test, stress relaxation test and texture profile analysis. The addition of WPC to goat's milk enhanced the textural characteristics of yoghurt. These advantageous attributes included increased firmness, hardness and adhesiveness. These attributes were quantitatively similar (P > 0.05) to those obtained from yoghurt made from cow's milk. In addition, the textural properties were maintained constant throughout the shelf‐life of the product.     

Identification and functional characterization of Lactobacillus strains isolated from milk and Gioddu,a traditional Sardinian fermented milk

Raw milk from Sardinian cows and sheep, and sheep's milk yoghurt (Gioddu), are food products that are poorly characterized in terms of the presence of mesophilic Lactobacillus strains, and may be good sources from which to isolate novel bacterial strains. Sixteen Lactobacillus strains were identified by genotypic and phenotypic methods from samples of sheep's milk (n=7), fermented sheep's milk (n=7) and one sample of cows’ milk. These strains were further characterized for the presence of functional traits useful for probiotic applications, such as resistance to simulated gastric acid, resistance to bile salts, and adhesion of two different cell lines (Caco-2 and MIM/PPK). Moreover, selected aspects correlated with safety (antimicrobial susceptibility and presence of plasmids) and ecological roles (ability to produce biofilms and bacteriocin-like substances) were tested. All but 1 of the 16 strains were unambiguously allotted to three species, L. paracasei (5 strains), L. plantarum (8 strains), and L. reuteri (2 strains). Many of the strains exhibited characteristics suggesting that they would survive in the gastrointestinal tract and also had the capability to attach to various cells. Greater variability was observed for the other traits analyzed. These data suggest that Sardinian artisan dairy products are interesting sources for the isolation of bacterial strains with characteristic and differentiated functional traits.     

The impact of supplementing goats' milk with quinoa extract on some properties of yoghurt

This study investigated the impact of supplementing goats' milk with quinoa extracts, in the range of 5, 10 and 15 g/100 g on the milk fermentation. The properties of yoghurt produced from this milk, which include viscosity, microstructure and sensory acceptability, were assessed. The supplementation of goats' milk with quinoa extracts, particularly permeate extract, reduced the fermentation time and enhanced the viability of lactic acid bacteria. Supplementation of yoghurt with increased levels of quinoa extracts increased the apparent viscosity and changed the yoghurt protein matrix. Panellists highly accepted the yoghurt that contained quinoa permeate extract.     

Effects of somatic cell counts in milk on physical and chemical characteristics of yoghurt

The quality of plain stirred yoghurt produced from whole milk with somatic cell counts (SCC) at low (147,000 cells mL⁻¹), intermediate (434,000 cells mL⁻¹) and high (1,943,000 cells mL⁻¹) levels was examined. Each milk treatment was obtained from selected cows, according to its SCC status and milk composition. Yoghurt samples were analysed on days 1, 10, 20 and 30 after production. Analyses included pH, acidity, fat, lipolysis (expressed as free fatty acids, FFA), proteolysis and apparent viscosity. Viscosity of high SCC yoghurt was higher (P<0.05) than the low SCC yoghurt on days 10, 20 and 30 of storage. High SCC yoghurt also had higher FFA content (P<0.05). SCC did not affect pH, acidity, fat content and proteolysis of the yoghurt (P>0.05). Results indicate that SCC in milk increases the lipolysis in the resulting yoghurt during storage for 30 d.     

Açai pulp addition improves fatty acid profile and probiotic viability in yoghurt

The effects of açai pulp addition and different probiotic bacteria on the fatty acid profile of stirred yoghurt were examined. Skim milk was divided into two groups: one containing açai pulp and another without the fruit. Batches were inoculated with yoghurt starter culture and divided into five groups according to probiotic addition. Counts of viable microorganisms were measured at days 1, 14 and 28 of cold storage. Fatty acid profile was determined by gas chromatography at day 1. Açai pulp favoured an increase in Lactobacillus acidophilus L10, Bifidobacterium animalis ssp. lactis Bl04 and Bifidobacterium longum Bl05 counts at the end of 4 weeks of cold storage. This study demonstrated that açai pulp addition increased monounsaturated and polyunsaturated fatty acid contents in probiotic yoghurt and enhanced the production of α-linolenic and conjugated linoleic acids during fermentation of skim milk prepared with B. animalis ssp. lactis Bl04 and B94 strains.     

The Microstructure and Physicochemical Properties of Probiotic Buffalo Yoghurt During Fermentation and Storage: a Comparison with Bovine Yoghurt

The physicochemical and rheological properties of yoghurt made from unstandardised unhomogenised buffalo milk were investigated during fermentation and 28 days of storage and compared to the properties of yoghurt made from homogenised fortified bovine milk. A number of differences observed in the gel network can be linked to differences in milk composition. The microstructure of buffalo yoghurt, as assessed by confocal laser scanning microscopy (CLSM) and cryo scanning electron microscopy (cryo-SEM), was interrupted by large fat globules and featured more serum pores. These fat globules have a lower surface area and bind less protein than the homogenised fat globules in bovine milk. These microstructural differences likely lead to the higher syneresis observed for buffalo yoghurt with an increase from 17.4 % (w/w) to 19.7 % (w/w) in the weight of whey generated at days 1 and 28 of the storage. The higher concentration of total calcium in buffalo milk resulted in the release of more ionic calcium during fermentation. Gelation was also slower but the strength of the two gels was similar due to similar protein and total solids concentrations. Buffalo yoghurt was more viscous, less able to recover from deformation and less Newtonian than bovine yoghurt with a thixotropy of 3,035 Pa.s^?1 measured for buffalo yoghurt at the end of the storage, at least four times higher than the thixotropy of bovine yoghurt. While the titratable acidity, lactose consumption and changes in organic acid concentrations were similar, differences were recorded in the viability of probiotic bacteria with a lower viability of Lactobacillus acidophilus of 5.17 log (CFU/g) recorded for buffalo yoghurt at day 28 of the storage. Our results show that factors other than the total solids content and protein concentration of milk affect the structural properties of yoghurt. They also illustrate the physicochemical reasons why buffalo and bovine yoghurt are reported to have different sensory properties and provide insight into how compositional changes can be used to alter the microstructure and properties of dairy products.     

Effect of Greek-style yoghurt manufacturing processes on starter and probiotic bacteria populations during storage

This study compared viable counts of Streptococcus thermophilus (starter) and Lactobacillus helveticus R0052 (probiotic), as a function of two manufacturing processes of Greek-style (GS) yoghurt: centrifugation of a curd (GS-CF process) or ultrafiltration of milk prior to fermentation (GS-UF process). Fresh GS-UF and GS-CF yoghurts had between 3 and 7 times higher counts of Lb. helveticus R0052 and S. thermophilus than the regular stirred yoghurt (Control). Strain R0052 was three times more stable in the GS-CF yoghurt than in the Control over the 44 d storage period. The highest lactose content (44 g L⁻¹) was obtained in the Control, while 60% less was obtained in the GS-UF yoghurt; the opposite trend was observed for lactic acid and galactose. Free amino acid levels were 33% higher in the GS products. GS yoghurt can be 10 times better than traditional yoghurt to deliver probiotic bacteria, as a function of the process used.     

Viability of lactic acid microflora in different types of yoghurt

The suitability of three culture media (Skim milk agar, M17 agar and MRS agar, incubated under aerobic and anaerobic conditions) to obtain total and differential counts of yoghurt bacteria, was assayed. A total of 25 samples of different yoghurt types (set, skimmed set, drinking, and set with “dulce de leche”) obtained with the culture IA, were used. The lactic microflora viability was studied at 6°C and 12°C. Skim milk agar (aerobiosis) was the most useful medium for total and differential counts of Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus. Cell viability depended on the yoghurt type and the storage temperature. On the basis of a minimum value of 10⁷ CFU g⁻¹, the shelf life of yoghurts at 6°C was longer than 60 days, with the exception of the drinking type (45 days). At 12°C, shelf life was identical for the skimmed drinking yoghurt but lower for the other yoghurt types. Both the storage temperature and the yoghurt type should be taken into account when shelf life is specified on the basis of the lactic microflora content.     

Acid production by bifidobacteria and yoghurt bacteria during fermentation and storage of milk

Three species of bifidobacteria, namelyBifidobacterium bifidum, Bifidobacterium longumandBifidobacterium adolescentiswere used in pure culture and in combination with yoghurt bacteria (B3 and SBI cultures) for the production of fermented milks. The number of bacteria during fermentation and the level of acid produced during fermentation and storage were assessed using Rogosa's modified selective agar and high performance liquid chromatography (HPLC). It was found that during fermentation all bifidobacteria exhibited growth uncoupled from acid production. Two of the species examined produced only low levels of acids when grown individually and onlyB. adolescentisproduced appreciable amounts. In mixed cultures, the level of acid was a reflection of the combination of yoghurt culture and species ofBifidobacterium, and this, observation suggests that there is a degree of influence between the cultures. During storage, the acid concentration remained quite stable in most samples. The prevention of post-production acidification that normally occurs during storage of yoghurt can be attributed to the presence of bifidobacteria, and it could be that acetic acid has a marginally inhibitory effect on theLactobacillusandStreptococcusspp.     

Intestinal anti-inflammatory activity of goat milk and goat yoghurt in the acetic acid model of rat colitis

The intestinal anti-inflammatory effect of goat milk and goat yoghurt with addition of Lactobacillus acidophilus, with or without native bee honey, was evaluated in rats with 10% acetic acid-induced colitis. The pre-treatment with goat milk, goat yoghurt or sulfasalazine significantly improved the myeloperoxidase activity, levels of leukotriene B₄ (LTB₄), interleukin-1β (IL-1β) and tumour necrosis factor-α (TNF-α). It also promoted a significant reduction in oxidative stress that could be seen by the reduction in malondialdehyde and the increase in glutathione. The benefit of the pre-treatments was also demonstrated in the preservation of colonic cytoarchitecture and the decreased expression of cyclooxygenase-2 and inducible nitric oxide synthase. These results suggest that goat milk and goat yoghurt exert protective effects similar to those of sulfasalazine on intestinal damage induced by acetic acid and that goat milk and goat yoghurt may act as functional foods in inflammatory bowel disease.     

Identification and characterization of lactic acid bacteria isolated from traditional cone yoghurt

Cone yoghurt is a yoghurt variety produced by adding only pine cones to milk without culture in a limited area of Turkey. The present study was conducted to identify and characterize lactic flora in traditional cone yoghurt. Morphological, cultural, physiological, biochemical, and genotypic characteristics were employed to identify lactic acid bacteria isolates from cones and cone yoghurts. Streptococcus salivarius subsp. thermophilus (S. thermophilus) and Lactobacillus delbrueckii subsp. bulgaricus (L. bulgaricus) were obtained from both cones and yoghurts. Among the isolates, L. plantarum was frequently isolated except for these two bacteria (S. thermophilus and L. bulgaricus). The results indicate that the cone yoghurt has a mixed microflora contrary to the yoghurt produced by the addition of a starter culture and S. thermophilus, and L. bulgaricus in cone yoghurt originates from the pine cones.     

Investigating probiotic yoghurt to reduce an aflatoxin B1 biomarker among school children in eastern Kenya: Preliminary study

Aflatoxin exposure remains a health problem in developing countries. The mean concentration of aflatoxin B1 in maize meal samples from eastern Kenya of 17.4 ppb verified that the food was contaminated. A probiotic yoghurt was created containing aflatoxin B1 binding Streptococcus thermophilus, Lactobacillus rhamnosus GR-1 and Weissella cibaria NN20 isolated from fermented kimere, a dough food product made from millet. Forty primary school children, with maize being a regular part of their diet, were randomly assigned to consume 200 mL yoghurt or control milk daily for 7 days, followed by a 7 day washout and another 7 day treatment. After both 7 day treatment periods, aflatoxin metabolite 1 concentration in urine samples was significantly lower than baseline in the probiotic group (P > 0.01), but increased in the milk group. The findings were confirmed using liquid chromatography-mass spectrometry (LC–MS). This suggests that locally produced probiotic yoghurt may reduce aflatoxin poisoning in Kenyan children.     

Compositional profile of ovine milk with a high somatic cell count: A metabolomics approach

Ovine milk (Sarda breed) with high somatic cell count (SCC) (>1 × 10⁶ cell mL⁻¹) was compared with similar milk of low SCC (<150 × 10³ cell mL⁻¹) using a metabolomics approach, whereby the metabolite profile of milk was studied by gas chromatography coupled to mass spectrometry. Discriminant analysis indicated that high SCC milk samples have metabolite profiles from those of low SCC samples. Malic acid, ribitol, glucose and medium-short chain fatty acids were up-regulated in milk with high SCC, while stearic acid, oleic acid, scyllo-inositol, glutamine, threonine, and glycine were down-regulated. These differences may be related to metabolite release by somatic cells, inflammation status, altered permeability of the udder tight junctions, and changes in milk osmotic equilibrium. Moreover, high SCC milk samples showed higher levels of proteins, casein and fat, lower concentrations of lactose and urea, and a different fatty acid profile from that of low SCC milk.     

Quality of plain yoghurt made from refrigerated and CO2-treated milk

The suitability of milk preserved by refrigeration and CO₂ addition for the manufacture of plain yoghurt was evaluated using two commercial strains of Lactobacillus delbrueckii ssp. bulgaricus and Streptococcus thermophilus. Yoghurts manufactured, after milk pasteurisation, from refrigerated CO₂-treated samples (pH 6.15) were compared with two different controls made from pasteurised milk, either fresh or refrigerated. The multiplication and acidification capacity of the starter as well as the evolution of organic acids were not affected by the previous refrigeration and CO₂-treatment of raw milk nor by the residual CO₂ present in pasteurised milk. However, refrigeration enhanced the production of ethanol and diacetyl. No differences on sensory properties were detected through the cold storage between yoghurts made from CO₂-treated milk and those made from refrigerated control milk. It was concluded that refrigerated milk acidified with CO₂ could be satisfactorily used in the manufacture of yoghurt.     

Comparison of six commercial DNA extraction kits for detection of Brucella neotomae in Mexican and Central American-style cheese and other milk products

Raw or inadequately pasteurized milk from infected animals and cheese made with such milk are a frequent vehicle for human brucellosis infection. Also, biological terrorism is a concern with certain Brucella spp. Due to matrix-associated real-time polymerase chain reaction (qPCR) inhibitors, robust sample preparations are crucial. We compared six commercial nucleic acid extraction kits using nine Mexican and Central American-style soft cheeses or creams and three liquid milk products inoculated with Brucella neotomae, a surrogate for pathogenic Brucella spp. Kits were evaluated by purity and quantity of DNA as determined by qPCR Ct values, reproducibility across cheese and milk types, and cost. At 10⁷ CFU/g in four different cheeses, Qiagen statistically outperformed all other kits. When two cheese styles were inoculated at dual levels, Qiagen and High Pure kit extracted samples at 1.5 × 10⁵ CFU/g produced average Ct values of 34–39, while PrepSEQ and MagMAX kit extracted samples exhibited higher or no Ct values. High Pure and Qiagen kits excelled also with liquid milk products. Considering matrices, inoculation levels, and kits evaluated, High Pure and Qiagen products produced Brucella DNA of high quality and quantity indicated by the lowest Ct values and were the least expensive.     

Evaluation of the antihypertensive angiotensin-converting enzyme inhibitory (ACE-I) activity and other probiotic properties of lactic acid bacteria isolated from traditional Greek dairy products

The technological and probiotic potential of lactic acid bacteria isolated from artisanal Greek yoghurt and fermented milks were evaluated. Fifty-three strains were identified by rep-PCR and 16S rDNA sequencing to belong to different Lactobacillus or Enterococcus spp., as well as to Streptococcus thermophilus and Lactococcus lactis. Several strains exhibited promising technological and probiotic properties. Among them, we focused on the production of bioactive peptides with angiotensin-converting enzyme inhibitory (ACE-I) activity during milk fermentation. The majority of strains produced ACE-I peptides when grown in skimmed milk. ACE-I peptides were sometimes sequestered in the original fermented milk sample, but were released and detected following high performance liquid chromatography (HPLC) purification. Mass spectrometry analysis of major peptide peaks in HPLC fractions with ACE-I activity revealed that they derived from the N- or C-terminal of the isracidin peptide region of α_S1-casein and two internal peptide fragments, one from β-casein and one from κ-casein.