Selection of wild lactic acid bacteria isolated from traditional Egyptian dairy products according to production and technological criteria

The Use of Lactic Acid Bacteria Starter Culture in the Production of Nunu, a Spontaneously Fermented Milk Product in Ghana

Nunu, a spontaneously fermented yoghurt-like product, is produced and consumed in parts of West Africa. A total of 373 predominant lactic acid bacteria (LAB) previously isolated and identified from Nunu product were assessed in vitro for their technological properties (acidification, exopolysaccharides production, lipolysis, proteolysis and antimicrobial activities). Following the determination of technological properties, Lactobacillus fermentum 22-16, Lactobacillus plantarum 8-2, Lactobacillus helveticus 22-7, and Leuconostoc mesenteroides 14-11 were used as single and combined starter cultures for Nunu fermentation. Starter culture fermented Nunu samples were assessed for amino acids profile and rate of acidification and were subsequently evaluated for consumer acceptability. For acidification properties, 82%, 59%, 34%, and 20% of strains belonging to Lactobacillus helveticus, L. plantarum, L. fermentum, and Leu. mesenteriodes, respectively, demonstrated fast acidification properties. High proteolytic activity (>100 to 150 μg/mL) was observed for 50% Leu. mesenteroides, 40% L. fermentum, 41% L. helveticus, 27% L. plantarum, and 10% Ent. faecium species. In starter culture fermented Nunu samples, all amino acids determined were detected in Nunu fermented with single starters of L. plantarum and L. helveticus and combined starter of L. fermntum and L. helveticus. Consumer sensory analysis showed varying degrees of acceptability for Nunu fermented with the different starter cultures.

Identification and partial characterization of lactic acid bacteria isolated from traditional dairy products produced by herders in the western Tianshan Mountains of China

Thirty strains of lactic acid bacteria (LAB) were isolated from herders' traditional dairy products collected from Xinjiang, China. The species Lactobacillus, Lactococcus, Enterococcus, Pediococcus and Leuconostoc were identified by 16S ribosomal RNA gene sequencing analysis and conventional observation. The strains' fermentation characteristics, including milk acidification, proteolysis, autolysis, antimicrobial activity and diacetyl production, were assayed and compared. Strains NL24 and NL31 showed the highest proteolytic activity-2·75 and 2·08 mmol Phe l(-1) milk, respectively. Strains C, NL41, SW2, Z3-11, NL42 and Z2-91 had high autolytic activity. In addition, most of the wild strains produced diacetyl, half of them to high levels. This study provides a clue to LAB biodiversity in traditional dairy foods produced by herders in the western Tianshan Mountains. High-performing strains should be further evaluated for practical application in value-added fermented dairy products.

SIGNIFICANCE AND IMPACT OF THE STUDY

Our results reveal a certain variety of lactic acid bacteria (LAB) in traditional dairy products from Xinjiang. Some of the LAB strains, such as Lactobacillus rhamnosus NL24 and Lactobacillus paracasei SW2, possess excellent functional properties and have the potential for application in indigenous fermented dairy products. Performance of the newly isolated strains in cheese or yogurt manufacturing was further evaluated. Application of the high-performing strains to enrich the flavour of fermented dairy products is highly desirable and holds great commercial potential.

Characterisation of Lactobacilli from eweʼs and goatʼs milk for their further processing re-utilisation

Raw ewe's and goat's milk is a good source for isolation of wild lactobacilli which are able to bring unique processing properties in development of dairy products - cheeses or fermented dairy products. 34 strains of lactobacilli were isolated, purified and identified from fermented ewe's and goat's dairy products. These products were processed without thermal treatment and without using of any commercial starters. After preliminary selection, the final collection of 5 strains was established. The strains were identified as: Lbc. plantarum (2), Lbc. paraplantarum (1), Lbc. paracasei (1) and Lbc. johnsonii (1). Except two strains, all were able to coagulate milk. After hydrolysis of lactose in milk, two strains were able to form sensorial attractive coagulate too. All of the strains were homofermentative, they produced lactic acid but they did not produce CO2. Their ability to produce diacetyl was low. They did not show strong proteolytic activity. All strains grew at 30 °C and 37 °C, however Lbc. johnsonii much slower at 30 °C than the others. Except Lbc. johnsonii, all strains tolerated 2% concentration of NaCl and even in presence of 5% concentration of NaCl their growth was inhibited only moderately. All of characterized strains can be provisionally used as starter or starter adjuncts in dairy technology, during production of cheeses or fermented milk products from pasteurised milk. These results will be used in further processing studies of isolated strains and will be supplemented with other properties e.g. safety, probiotic and antimicrobial properties.

Technological properties of bacteriocin-producing lactic acid bacteria isolated from Pico cheese an artisanal cow's milk cheese

AIM

Evaluate technologically relevant properties from bacteriocin-producing strains to use as starter/adjunct cultures in cheese making.

METHODS AND RESULTS

Eight isolates obtained from Pico cheese produced in Azores (Portugal) were found to produce bacteriocins against Listeria monocytogenes and three isolates against Clostridium perfringens. They were identified as Lactococcus lactis and Enterococcus faecalis and submitted to technological tests: growth at different conditions of temperature and salt, acid production, proteolysis, lipolysis, coexistence, enzymatic profile and autolytic capacity. Safety evaluation was performed by evaluating haemolytic, gelatinase and DNase activity, resistance to antibiotics and the presence of virulence genes. Some isolates presented good technological features such as high autolytic activity, acid and diacetyl production. Lactococcus lactis was negative for all virulence genes tested and inhibit the growth of all Lactic acid bacteria (LAB) isolates. Enterococci were positive for the presence of some virulence genes, but none of the isolates were classified as resistant to important antibiotics.

CONCLUSIONS

The bacteriocin-producing Lc. lactis present good potential for application in food as adjunct culture in cheese production. The study also reveals good technological features for some Enterococcus isolates.

SIGNIFICANCE AND IMPACT OF THE STUDY

Bacteriocin-producing strains presented important technological properties to be exploited as new adjunct culture for the dairy industry, influencing flavour development and improve safety.

Lantibiotics biosynthesis genes and bacteriocinogenic activity of Lactobacillus spp. isolated from raw milk and cheese

Lactobacillus species are usually used as starters for the production of fermented products, and some strains are capable of producing antimicrobial substances, such as bacteriocins. Because these characteristics are highly desirable, research are continually being performed for novel Lactobacillus strains with bacteriocinogenic potential for use by food industries. The aim of this study was to characterise the bacteriocinogenic potential and activity of Lactobacillus isolates. From a lactic acid bacteria culture collection obtained from raw milk and cheese, 27 isolates were identified by 16S rDNA as Lactobacillus spp. and selected for the detection of lantibiotics biosynthesis genes, bacteriocin production, antimicrobial spectra, and ideal incubation conditions for bacteriocin production. Based on the obtained results, 21 isolates presented at least one of the three lantibiotics biosynthesis genes (lanB, lanC or lamM), and 23 isolates also produced antimicrobial substances with sensitivity to at least one proteinase, indicating their bacteriocinogenic activity. In general, the isolates had broad inhibitory activity, mainly against Listeria spp. and Staphylococcus spp. strains, and the best antimicrobial performance of the isolates occurred when they were cultivated at 25 °C for 24 or 48 h or at 35 °C for 12 h. The present study identified the bacteriocinogenic potential of Lactobacillus isolates obtained from raw milk and cheese, suggesting their potential use as biopreservatives in foods.

Technological and safety properties display biodiversity among enterococci isolated from two Egyptian cheeses, "Ras" and "Domiati"

The technological and safety properties of 35 indigenous strains of Enterococcus faecium isolated from two Egyptian cheeses were characterised in order to determine their ability for rational manufacture of diversified and typical dairy products in the Middle East. A great diversity was observed within the 35 strains on the basis of their technological properties. A statistical analysis made it possible to distribute the 35 strains of E. faecium into different groups. Three groups were identified in terms of their acidification activity, measured by the Cinac system: a group of strains that quickly acidified milk, a second that moderately acidified milk, and a last cluster that revealed weak acidification activity. On the basis of texturing properties that were evaluated using a texturometer and a viscometer, a cluster of strains produced viscous and firm gels, a second cluster included fairly viscous, firm and cohesive gels, and a last group generated slightly viscous, but firm and very cohesive gels. By considering the aroma profiles that were determined by gas chromatography coupled with mass spectrometry, four clusters were identified. One cluster displayed a high dimethyl disulfide level, a second group of strains was highly aromatic, a third cluster led to typical "lactic" products, and the last cluster made it possible to obtain low aromatic products. None of the 35 strains proved to be β-haemolytic on the basis of the characterisation of their safety properties. The resistance to 20 antibiotics was assessed by the disc diffusion method. The 35 isolates were sensitive to 12 antibiotics, and among them, one isolate was resistant to only two antibiotics (nalixidic acid and streptomycin). The resistance to eight antibiotics was strain-dependant. Finally, this study demonstrates that some indigenous strains of E. faecium displayed interesting technological properties for cheese manufacture, together with good safety characteristics. They could be useful for the manufacture of typical products in Egypt.

Technological characterization of bacteriocin producing Lactococcus lactis strains employed to control Listeria monocytogenes in cottage cheese

In recent years, there has been a particular focus on the application of antimicrobial compounds produced by lactic acid bacteria (LAB) as natural preservatives to control the growth of spoilage and pathogenic bacteria in food. Bacteriocins are antimicrobial peptides which can be added to foods in concentrated forms as food preservatives, e.g. additives, or they can be produced in situ by starters or protective cultures. In this study, twenty Lactococcus lactis bacteriocin producers previously isolated from Italian fermented foods were subjected to a variety of physical and biochemical tests in order to identify those with the greatest potential as starter cultures in cheese production. Of these, four strains isolated from cheese (one nisin Z producer, one nisin A producer and two lacticin 481 producers) which fulfilled the desired technological criteria were assessed for their ability to control Listeria monocytogenes. The subsequent application of these bacteriocinogenic strains as starter cultures in Cottage cheese established that the nisin A producing Lact. lactis 40FEL3, and to a lesser extent the lacticin 481 producers 32FL1 and 32FL3, successfully controlled the growth of the pathogen. This is the first study to directly compare the ability of nisin A, nisin Z and lacticin 481 producing strains to control listerial growth during the manufacture and storage of Cottage cheese.

Genotypic and technological characterization of Leuconostoc isolates to be used as adjunct starters in Manchego cheese manufacture

Twenty-seven Leuconostoc (Ln.) isolates from Manchego cheese were characterized by phenotypic and genotypic methods, and their technological abilities studied in order to test their potential use as dairy starter components. While phenotypic diversity was evaluated by studying the biochemical characteristics of technological interest (i.e. acidifying and aminopeptidase activities), genotypic diversity was evidenced by using Randomly Amplified Polymorphic DNA-Polymerase Chain Reaction (RAPD-PCR). Additional technological abilities such as lipolytic, proteolytic and autolytic activities, salt and pH tolerance and production of dextran, flavour compounds and biogenic amines, were investigated. The marked differences among strains reflected the existing biodiversity in naturally fermented products. After statistically evaluating their performance, strains C0W2, belonging to Ln. lactis, and C16W5 and N2W5, belonging to Ln. mesenteroides subsp. dextranicum, revealed the best properties to be used in mixed dairy starter cultures. This study evidences the fact that natural environments can be considered as a proper source of useful strains, for the dairy industry.

Analysis of the lactic acid bacteria microflora in traditional Caucasus cow's milk cheeses

A total of 157 lactic acid bacteria (LAB) were isolated from three hand-made cheeses taken from different households in the region of the Caucasus Mountains. The cheeses were manufactured from cow's milk without the addition of a starter culture. The isolates of LAB were characterized by subjecting them to phenotypic and genotypic tests. The results of identification of LAB indicate that the examined cheeses contained 10 species, viz., Lactobacillus plantarum, Lactobacillus paraplantarum, Lactobacillus arizonensis, Lactobacillus farciminis, Lactobacillus brevis, Lactococcus lactis subsp. lactis, Leuconostoc mesenteroides subsp. mesenteroides, Leuconostoc pseudomesenteroides, Enterococcus faecium, and Enterococcus faecalis. The strains within the species L. plantarum, L. arizonensis, L. paraplantarum, L. farciminis, and L. pseudomesenteroides showed good proteolytic activity.

Inhibition of Listeria monocytogenes in dairy products using the bacteriocin-like peptide cerein 8A

The efficacy of the antimicrobial peptide cerein 8A to control the development of Listeria monocytogenes in milk and soft cheese was investigated. The addition of 160 AU ml(-1) cerein 8A to UHT milk resulted in a decrease of 3 log cycles in viable cells within the 14-day period at 4 degrees C. The viable counts of L. monocytogenes in pasteurized milk samples containing cerein 8A was lower than those observed in controls without bacteriocin. Addition of cerein 8A to Minas-type soft cheese caused a delay in the start of exponential growth phase, although similar counts were observed after day 6. When cerein 8A was used to control cheese surface contamination by L. monocytogenes, a decrease of 2 log cycles in viable counts of cerein-treated samples was observed during 30 days at 4 degrees C. This antimicrobial peptide shows potential use as a biopreservative for application in dairy products.

Screening of exopolysaccharide-producing Lactobacillus and Bifidobacterium strains isolated from the human intestinal microbiota

Using phenotypic approaches, we have detected that 17% of human intestinal Lactobacillus and Bifidobacterium strains could be exopolysaccharide (EPS) producers. However, PCR techniques showed that only 7% harbored genes related to the synthesis of heteropolysaccharides. This is the first work to screen the human intestinal ecosystem for the detection of EPS-producing strains.

Direct fermentation of potato starch wastewater to lactic acid by Rhizopus oryzae and Rhizopus arrhizus

The biochemical kinetic of direct fermentation for lactic acid production by fungal species of Rhizopus arrhizus 3,6017 and Rhizopus oryzae 2,062 was studied with respect to growth pH, temperature and substrate. The direct fermentation was characterized by starch hydrolysis, accumulation of reducing sugar, and production of lactic acid and fungal biomass. Starch hydrolysis, reducing sugar accumulation, biomass formation and lactic acid production were affected with the variations in pH, temperature, and starch source and concentration. A growth condition with starch concentration approximately 20 g/l at pH 6.0 and 30 degrees C was favourable for both starch saccharification and lactic acid fermentation, resulting in lactic acid yield of 0.87-0.97 g/g starch associated with 1.5-2.0 g/l fungal biomass produced in 36 h fermentation. R. arrhizus 3,6017 had a higher capacity to produce lactic acid, while R. oryzae 2,062 produced more fungal biomass under similar conditions.