Observation of bacterial exopolysaccharide in dairy products using cryo-scanning electron microscopy

Cryo-scanning electron microscopy was used to visualize the microstructure of two types of cheese (Karish and Feta) and milk fermented with different ropy and non-ropy strains of lactic acid bacteria. Specimen frozen in liquid nitrogen slush were transferred in a frozen state and under vacuum into the preparation chamber where they were fractured, etched and coated with gold. Specimen were then transferred under vacuum onto the cold stage and imaged using scanning electron microscopy (SEM). Milk fat and exopolysaccharide (EPS) were visible in pores within the protein network. Cheese and fermented milk made with EPS-producing cultures exhibited a porous structure in which the largest pores were associated with visible EPS. A compact structure with small pores was seen in cheese and milk fermented with EPS non-producing cultures. EPS and protein appeared to be segregated in both cheese and fermented milk. EPS formed a network-like structure. Differences were observed in the microstructure of EPS between moderately ropy and highly ropy strains. A relatively long etching (sublimation) time caused EPS to appear as thin filaments similar to those seen with conventional SEM.     

Direct observation of bacterial exopolysaccharides in dairy products using confocal scanning laser microscopy

The objective of this work was to develop a methodology for direct visualization of bacterial exopolysaccharides (EPS) in fully hydrated dairy products. The new method involved staining EPS with wheat germ agglutinin labeled with Alexa fluor 488 or staining with concanavalin A 488. Samples were observed using confocal scanning laser microscopy. Distribution of EPS produced by Lactococcus lactis (CHCC 3367), a combination of Streptococcus thermophilus (CHCC 3534) and Lactobacillus delbrueckii ssp. bulgaricus (CHCC 769) and Lactobacillus delbrueckii ssp. bulgaricus RR in milk was compared in stirred and unstirred fermented milk. The EPS and proteins were observed as distinct entities, with EPS present in the protein network pores. EPS was observed in greater amounts in milk fermented by the ropy L. lactis culture than in milk fermented by the less ropy strain of S. thermophilus. Stirring the fermented milk caused aggregation of EPS into more extended structures. The more ropy the culture, the longer and larger the strands formed during stirring. The method was also applied to Feta cheese made with an EPS-producing strain of S. thermophilus. EPS was observed in the cheese as thick sheets filling pores in the protein network.     

不同胞外多糖产生特性的乳酸菌菌种对酸乳品质的影响

不同EPS产生量的两种乳酸菌，用于酸乳的生产，在4种不同菌株组合形成的发酵乳中，球、杆菌比例和乳糖消耗基本一致，但是在粘度、EPS产生、EPS的单糖组成、对乳清析出的影响，以及感官等方面，均有区别。实验结果表明，在酸乳生产中，以产EPS的德氏乳杆菌保加利亚亚种不产EPS的唾液链球菌嗜热亚种组合较好。     

Capability of exopolysaccharide-producing Lactobacillus paraplantarum BGCG11 and its non-producing isogenic strain NB1, to counteract the effect of enteropathogens upon the epithelial cell line HT29-MTX

The putative protective role of the exopolysaccharide (EPS)-producing Lactobacillus paraplantarum BGCG11, and its non-EPS-producing isogenic strain NB1, was tested upon HT29-MTX monolayers challenged with seven opportunistic pathogens. The probiotic strain Lactobacillus rhamnosus LMG18243 (GG) was used as a reference bacterium. Tested lactobacilli were able to efficiently reduce the attachment to HT29-MTX of most pathogens. Lb. paraplantarum NB1 and Lb. rhamnosus GG were more efficient reducing the adhesion of Clostridium difficile or Yersinia enterocolitica than Lb. paraplantarum BGCG11, while strain BGCG11 reduced, to a greater extent, the adhesion of Escherichia coli and Listeria monocytogenes. The detachment and cell lysis of HT29-MTX monolayers in the presence of pathogens alone and co-incubated with lactobacilli or purified EPS was followed. L. monocytogenes induced the strongest cell detachment among the seven tested pathogens and this effect was prevented by addition of purified EPS-CG11. The results suggest that this EPS could be an effective macromolecule in protection of HT29-MTX cells from the pathogen-induced lysis. Regarding innate intestinal barrier, the presence of C. difficile induced the highest IL-8 production in HT29-MTX cells and this capability was reinforced by the co-incubation with Lb. paraplantarum NB1 and Lb. rhamnosus GG. However, the increase in IL-8 production was not noticed when C. difficile was co-incubated with EPS-producing Lb. paraplantarum BGCG11 strain or its purified EPS-CG11 polymer, thus indicating that the polymer could hinder the contact of bacteria with the intestinal epithelium. The measurement of mucus secreted by HT29-MTX and the expression of muc1, muc2, muc3B and muc5AC genes in the presence of pathogens and lactobacilli suggested that all lactobacilli strains are weak “co-adjuvants” helping some pathogens to slightly increase the secretion of mucus by HT29-MTX, while purified EPS-CG11 did not induce mucus secretion. Taking altogether, Lb. paraplantarum BGCG11 could act towards the reinforcement of the innate mucosal barrier through the synthesis of a physical-protective EPS layer which could make difficult the contact of the pathogens with the epithelial cells.     

Production of exopolysaccharides by Lactobacillus and Bifidobacterium strains of human origin, and metabolic activity of the producing bacteria in milk

This work reports on the physicochemical characterization of 21 exopolysaccharides (EPS) produced by Lactobacillus and Bifidobacterium strains isolated from human intestinal microbiota, as well as the growth and metabolic activity of the EPS-producing strains in milk. The strains belong to the species Lactobacillus casei, Lactobacillus rhamnosus, Lactobacillus plantarum, Lactobacillus vaginalis, Bifidobacterium animalis, Bifidobacterium longum, and Bifidobacterium pseudocatenulatum. The molar mass distribution of EPS fractions showed 2 peaks of different sizes, which is a feature shared with some EPS from bacteria of food origin. In general, we detected an association between the EPS size distribution and the EPS-producing species, although because of the low numbers of human bacterial EPS tested, we could not conclusively establish a correlation. The main monosaccharide components of the EPS under study were glucose, galactose, and rhamnose, which are the same as those found in food polymers; however, the rhamnose and glucose ratios was generally higher than the galactose ratio in our human bacterial EPS. All EPS-producing strains were able to grow and acidify milk; most lactobacilli produced lactic acid as the main metabolite. The lactic acid-to-acetic acid ratio in bifidobacteria was 0.7, close to the theoretical ratio, indicating that the EPS-producing strains did not produce an excessive amount of acetic acid, which could adversely affect the sensory properties of fermented milks. With respect to their viscosity-intensifying ability, L. plantarum H2 and L. rhamnosus E41 and E43R were able to increase the viscosity of stirred, fermented milks to a similar extent as the EPS-producing Streptococcus thermophilus strain used as a positive control. Therefore, these human EPS-producing bacteria could be used as adjuncts in mixed cultures for the formulation of functional foods if probiotic characteristics could be demonstrated. This is the first article reporting the physicochemical characteristics of EPS isolated from human intestinal microbiota.     

A putative glucan synthase gene dps detected in exopolysaccharide-producing Pediococcus damnosus and Oenococcus oeni strains isolated from wine and cider

Some lactic acid bacteria can induce viscosity in wine, beer and cider by production of exopolysaccharides (EPS). A polymerase chain reaction (PCR) assay was previously described for the detection of ropy Pediococcus damnosus strains in wine [J. Appl. Microbiol. 90 (2001) 535]. The primers used in that study, PF5 and PF6, are investigated in addition to new primers which broaden the range of spoiling agents detectable by PCR. Primers PF1 and PF8 allow the amplification of DNA from ropy P. damnosus strains isolated from wine, as was observed with PF5 and PF6. In addition, PF1 and PF8, unlike PF5 and PF6, are able to generate an amplicon using template DNA from a ropy P. damnosus strain isolated from cider and a ropy Oenococcus oeni strain isolated from champagne. Two different ropy Lactobacillus species were also isolated, but their DNA was not amplified using primers PF1 and PF8. The new primers PF1 and PF8 were chosen from the sequence of gene dps, a putative glucan synthase gene, found across all the ropy P. damnosus strains isolated, from both wine or cider, and also in a ropy O. oeni strain. To our knowledge, this is the first time that an EPS-producing O. oeni strain is described. Glucan biosynthesis was assessed by agglutination tests done with Streptococcus pneumoniae type 37-specific antibodies, which specifically detect glucan-producing cells. The results show that there is a direct correlation between glucan production and detection of gene dps. Therefore, Dps is considered a candidate for the glucan synthase enzyme responsible for EPS production by ropy strains of P. damnosus and O. oeni.     

Impact of ropy and capsular exopolysaccharide-producing strains of Lactococcus lactis subsp. cremoris on reduced-fat Cheddar cheese production and whey composition

Cheddar cheese mixed starter cultures containing exopolysaccharide (EPS)-producing strains of Lactococcus lactis subsp. cremoris (Lac. cremoris) were characterized and used for the production of reduced-fat Cheddar cheese (15% fat). The effects of ropy and capsular strains and their combination on cheese production and physical characteristics as well as composition of the resultant whey samples were investigated and compared with the impact of adding 0.2% (w/v) of lecithin, as a thickening agent, to cheese milk. Control cheese was made using EPS-non-producing Lac. cremoris. Cheeses made with capsular or ropy strains or their combination retained 3.6–4.8% more moisture and resulted in 0.29–1.19 kg/100 kg higher yield than control cheese. Lecithin also increased the moisture retention and cheese yield by 1.4% and 0.37%, respectively, over the control cheese. Lecithin addition also substantially increased viscosity, total solid content and concentrating time by ultra-filtration (UF) of the whey produced. Compared with lecithin addition, the application of EPS-producing strains increased the viscosity of the resultant whey slightly, while decreasing whey total solids, and prolonging the time required to concentrate whey samples by UF. The amount of EPS expelled in whey ranged from 31 to 53 mg L⁻¹. Retention of EPS-producing strains in cheese curd was remarkably higher than that of non-producing strains. These results indicate the capacity of EPS-producing Lac. cremoris for enhanced moisture retention in reduced-fat Cheddar cheese; these strains would be a promising alternative to commercial stabilizers.     

Application of exopolysaccharide-producing cultures in reduced-fat Cheddar cheese: composition and proteolysis

Proteolysis during ripening of reduced fat Cheddar cheeses made with different exopolysaccharide (EPS)-producing and nonproducing cultures was studied. A ropy strain of Lactococcus lactis ssp. cremoris (JFR1) and capsule-forming nonropy and moderately ropy strains of Streptococcus thermophilus were used in making reduced-fat Cheddar cheese. Commercial Cheddar starter was used in making full-fat cheese. Results showed that the actual yield of cheese made with JFR1 was higher than that of all other reduced-fat cheeses. Cheese made with JFR1 contained higher moisture, moisture in the nonfat substance, and residual coagulant activity than all other reduced-fat cheeses. Proteolysis, as determined by PAGE and the level of water-soluble nitrogen, was also higher in cheese made with JFR1 than in all other cheeses. The HPLC analysis showed a significant increase in hydrophobic peptides (causing bitterness) during storage of cheese made with JFR1. Cheese made with the capsule-forming nonropy adjunct of S. thermophilus, which contained lower moisture and moisture in the nonfat substance levels and lower chymosin activity than did cheese made with JFR1, accumulated less hydrophobic peptides. In conclusion, some EPS-producing cultures produced reduced-fat Cheddar cheese with moisture in the nonfat substance similar to that in its full-fat counterpart without the need for modifying the standard cheese-making protocol. Such cultures might accumulate hydrophobic (bitter) peptides if they do not contain the system able to hydrolyze them. For making high quality reduced-fat Cheddar cheese, EPS-producing cultures should be used in conjunction with debittering strains.     

Effect of 'ropy' strains of Lactobacillus delbrueckii ssp. bulgaricus and Streptococcus thermophilus on rheology of stirred yogurt

The TA-TX2 Texture Analyser and the Brookfield RVT Viscometer have been used to investigate the contribution of ropiness to the texture of stirred yogurts made using ropy strains of bacteria. Back extrusion and texture profile analysis, not commonly used to quantify rheological properties of semi-solid foods, have been found useful in distinguishing the contribution of exopolysaccharides to different texture attributes (Toba et al ., 1990). Thus ropiness, a characteristic which is imparted to the product as a result of fermentation with particular polysaccharide-producing strains, contributes to 'adhesiveness', while 'firmness' and 'elasticity' are likely to be influenced more by the protein matrix of the yogurt than by secretion of the polysaccharide by the ropy strains. Effects on viscosity and ability to recover viscosity after disruption were apparent, although the contribution of ropiness was not always positive. Ropy strains increased viscosity of stirred yogurts when compared to yogurt made with non-ropy cultures. But, whilst a ropy Lactobacillus delbrueckii ssp. bulgaricus (Lb r⁺) combined with a non-ropy Streptococcus thermophilus (St r⁻) produced a viscous product which recovered its viscosity well, a yogurt made by combining both ropy strains did not recover its viscosity as well as yogurt made by combining two non-ropy cultures and lost its structure more rapidly during the destructive testing. These results show therefore that inclusion of a ropy strain will not always lead to improved texture attributes, that while ropy strains may increase viscosity they may not influence 'firmness' and lend support to the view that this latter attribute is more influenced by protein–protein interactions.     

Short communication: effect of exopolysaccharide isolated from "viili" on the adhesion of probiotics and pathogens to intestinal mucus

The strong ropy character of the Scandinavian fermented milk viili is conferred by the exopolysaccharides (EPS) produced by lactococcal strains. These biopolymers can be responsible for some health benefits. We have assessed the influence of the EPS fraction isolated from commercial viili on the adhesion of some probiotics and pathogens to human intestinal mucus. Concentrations of viili EPS greater than 0.1 mg/mL promoted a decrease in adherence of Bifidobacterium lactis Bb12 and Lactobacillus rhamnosus GG and this effect was dose-dependent. However, no modifications were detected on the adhesion levels of the pathogenic strains tested at a concentration of 1 mg/mL of EPS. Results obtained in the present work should be considered in the design of new probiotic products.     

Application of ruthenium red and colloidal gold-labeled lectin for the visualization of bacterial exopolysaccharides in Cheddar cheese matrix using transmission electron microscopy

The objective of the present study was to develop a methodology for direct observation of capsular and ropy strains and their exopolysaccharides (EPS) in a Cheddar cheese matrix. Cheddar cheeses with 50% reduced fat were made from milk containing 1.7% fat using mixed starter culture containing either capsule-forming Lactococcus lactis subsp. cremoris (SMQ-461) or ropy L. lactis subsp. cremoris (JRF-1) strains. Control cheese was made using the EPS-negative L. lactis subsp. cremoris (RBL132) strain. Following cheese pressing, samples were taken from each cheese treatment and examined by transmission electron microscopy (TEM). Samples were divided into two series: the first was prepared following the conventional methods (involving fixation, post fixation, dehydration and embedding in resin) and the second with added ruthenium red at 0.15% (w/v) during the fixation, post fixation and washing procedures. Gold-labeled lectin was also used for the visualization and localization of EPS in cheese matrix. Electron micrographs showed that ruthenium red makes it possible to visualize and enhance the resolution of the EPS in a Cheddar matrix compared with the conventional method. The EPS layer of the capsular strain appeared regular and evenly distributed around the cell, whereas the cell-associated EPS layer produced by the ropy strain was longer, more irregular (having a filamentous structure) and unevenly surrounded the cell. EPS released from the ropy strain appeared to form a network-like structure located principally in whey pockets and appeared to interact with the casein matrix and fat globule membrane. Labeling EPS by lectin conjugated to colloidal gold could only be performed with conventional preparation of cheese samples and appeared to react only with the cell surface rather than with liberated EPS. Besides their ability to bind water and increase cheese yield, capsular and ropy strains used in this study appear to have potential autolytic characteristics, which may have an impact on cheese proteolysis, texture and flavor quality.     

Microstructure and rheology of an acid-coagulated cheese (Karish) made with an exopolysaccharide-producing Streptococcus thermophilus strain and its exopolysaccharide non-producing genetic variant

The objective of this research was to determine the effect of exopolysaccharide (EPS) production by lactic acid bacteria on the microstructure and rheology of Karish cheese, a soft acid coagulated cheese made using skim milk. An EPS-producing strain of Streptococcus thermophilus, and its EPS non-producing genetic variant were used to make comparable batches of the cheese. EPS in cheese was visualized by cryo-SEM as a large, dense, filamentous mass. Cheese made with the EPS non-producing culture was characterized by a dense protein network with smaller pores compared to that prepared with the EPS-producing culture. High elastic and viscous moduli measured by dynamic rheology were observed for EPS negative cheese and was attributed to its dense protein network. Creep test experiments demonstrated that cheese prepared with the EPS non-producing strain was more rigid and recovered its deformation, while cheese made using the EPS producing culture was more deformable. These results indicate that EPS-producing cultures can improve the physical properties of Karish cheese by reducing undesirable rigidity.     

Assessment of potential probiotic properties of Lactobacillus spp., Lactococcus spp., and Pediococcus spp. strains isolated from kefir

In this study, the metabolic activities (in terms of quantities of the produced lactic acid, hydrogen peroxide, and exopolysaccharides) of 8 strains of Lactobacillus spp., Lactococcus spp., and Pediococcus spp., were determined. Lactic acid levels produced by strains were 8.1 to 17.4 mg/L. The L. acidophilus Z1L strain produced the maximum amount (3.18 μg/mL) of hydrogen peroxide. The exopolysaccharides (EPS) production by the strains was ranged between 173 and 378 mg/L. The susceptibility of 7 different antibiotics against these strains was also tested. All strains were found to be sensitive to ampicillin. The tolerance of the strains to low pH, their resistance to bile salts of strains, and their abilities to autoaggregate and coaggregate with Escherichia coli ATCC 11229 were also evaluated. High EPS-producing strains showed significant autoaggregation and coaggregation ability with test bacteria (P < 0.01). A correlation also was determined between EPS production and acid-bile tolerance (P < 0.05). EPS production possibly affects or is involved in acid-bile tolerance and aggregation of Lactobacillus spp., Lactococcus spp., and Pediococcus spp. strains and supports the potential of L. acidophilus Z1L strain as new probiotic.     

Application of exopolysaccharide-producing cultures in reduced-fat Cheddar cheese: texture and melting properties

Textural, melting, and sensory characteristics of reduced-fat Cheddar cheeses made with exopolysaccharide (EPS)-producing and nonproducing cultures were monitored during ripening. Hardness, gumminess, springiness, and chewiness significantly increased in the cheeses as fat content decreased. Cheese made with EPS-producing cultures was the least affected by fat reduction. No differences in hardness, springiness, and chewiness were found between young reduced fat cheese made with a ropy Lactococcus lactis ssp. cremoris [JFR1; the culture that produced reduced-fat cheese with moisture in the nonfat substance (MNFS) similar to that in its full-fat counterpart] and its full-fat counterpart. Whereas hardness of full-fat cheese and reduced-fat cheese made with JFR1 increased during ripening, a significant decrease in its value was observed in all other cheeses. After 6 mo of ripening, reduced fat cheeses made with all EPS-producing cultures maintained lower values of all texture profile analysis parameters than did those made with no EPS. Fat reduction decreased cheese meltability. However, no differences in meltability were found between the young full-fat cheese and the reduced-fat cheese made with the ropy culture JFR1. Both the aged full- and reduced-fat cheeses made with JFR1 had similar melting patterns. When heated, they both became soft and creamy without losing shape, whereas reduced-fat cheese made with no EPS ran and separated into greasy solids and liquid. No differences were detected by panelists between the textures of the full-fat cheese and reduced-fat cheese made with JFR1, both of which were less rubbery or firm, curdy, and crumbly than all other reduced-fat cheeses.     

In vitro evaluation of physiological probiotic properties of different lactic acid bacteria strains of dairy and human origin

Eleven lactic acid bacteria strains of importance to the dairy industry were subjected to in vitro analyses to determine their probiotic potential. Seven strains were isolated from ewe’s and cow’s milk (Enterococcus faecalis – five –, Lactococcus lactis and Lactobacillus paracasei). Four were obtained from American Type Culture Collection (ATCC), isolated from cheese (Lactobacillus casei 393), human feces (L. paracasei 27092 and Lactobacillus rhamnosus 53103) and used in cheese making (L. lactis 54104). Although none of the strains was able to degrade mucin, all E. faecalis showed, at least, one transferable antibiotic resistance, which excluded them as candidates for addition to foods. Of the remaining six safe strains, L. lactis strains were more tolerant to low pH than Lactobacillus spp.; all were tolerant to pancreatin and bile salts and showed antibacterial activity. The highest level of adhesion to Caco-2 cells was observed with L. lactis 660, even higher than L. rhamnosus ATCC 53103 (recognized probiotic and used as control). The physiological probiotic properties of these strains, mainly isolated from dairy sources, are interesting in view of their use in cheese productions as starter and non starter cultures. The five LAB safe strains studied may have potential as novel probiotics in the dairy foods.     

Factors influencing autoaggregation and aggregation of Lactobacillus delbrueckii subsp. bulgaricus isolated from handmade yogurt

Of 26 Lactobacillus delbrueckii subsp. bulgaricus strains isolated from yogurt, strains B2 and 22, which produce low levels (28 and 21 mg liter(-1), respectively) of extracellular polysaccharides (EPSs), and strains B3 and G12, which produce high EPS levels (211 and 175 mg liter(-1), respectively), were selected for further study. The two high EPS-producing strains showed a significant autoaggregation and coaggregation ability with Escherichia coli ATCC 11230 (P < 0.05). Moreover, the effect of bile was evaluated on autoaggregation and hydrophobicity. Autoaggregation and hydrophobicity of these L. delbrueckii subsp. bulgaricus strains decreased after treatment with bile. Only the high EPS-producing L. delbrueckii subsp. bulgaricus strain B3 showed greater autoaggregation (80%) and hydrophobicity (86%) than the other strains after bile treatment. When these strains were assessed for the inhibition of E. coli ATCC 11230 in coculture, L. delbrueckii subsp. bulgaricus B3 completely inhibited E. coli during 24 and 48 h of incubation. This investigation showed that a high EPS production and coaggregation ability may be important in the selection of probiotic strains.     

Functional foods as carriers for SYNBIO®, a probiotic bacteria combination

The popularity of functional foods continues to increase as consumers desire flavorful foods that will fulfil their health needs. Among these foods, probiotics may exert positive effects on the composition of gut microbiota and overall health. However, in order to be beneficial, the bacterial cultures have to remain live and active at the time of consumption. The aim of this study was to develop new probiotic food products, such as seasoned cheeses, salami, chocolate and ice-cream with a final probiotic concentration of approximately 10?CFU/daily dose of Lactobacillus rhamnosus IMC 501? and Lactobacillus paracasei IMC 502? mixed 1:1 (SYNBIO?). The survival and viability of probiotics were determined during the foods shelf-life. The values of viable probiotic bacteria of all dairy and non-dairy foods were between 10? and 10?CFU/g of food at the end of the shelf-life and for some of them the values were maintained even after the expiry date. Based on the results of the current study, all the dairy ("Caciotta" cheese, "Pecorino" cheese, "Büscion" Swiss cheese and "Fiordilatte" ice-cream) and non-dairy ("Ciauscolo" salami, Larded salami, Swiss small salami, milk chocolate, dark chocolate, organic jam and chocolate mousse) food products studied would be excellent vehicles to deliver the probiotic health effects because of the high viability of probiotics during the shelf-life of foods and in some cases even after their expiry date.     

Effects of exopolysaccharide-producing cultures on the viscoelastic properties of reduced-fat Cheddar cheese

The objective was to study the influence of different exopolysaccharide (EPS)-producing and nonproducing lactic cultures on the viscoelastic properties of reduced-fat Cheddar cheese. Changes in the viscoelastic properties were followed over a ripening period of 6 mo. Results showed that the elastic, viscous, and complex moduli were higher in reduced-fat cheeses made with EPS-nonproducing cultures than in full-fat cheese. No differences in the viscoelastic properties were found between young reduced-fat cheese made with a ropy strain of Lactococcus lactis ssp. cremoris (JFR1) and its full-fat counterpart. Interestingly, the changes in viscoelastic moduli in both full-fat cheese and reduced-fat cheese made with JFR1 during ripening followed the same pattern. Whereas the moduli increased during the first month of ripening in those 2 cheeses, a dramatic decrease was observed in all other cheeses. Slopes of the viscoelastic moduli as a function of frequency were lower in the full-fat than in reduced-fat cheeses. The creep test showed that fresh reduced-fat cheese made with JFR1 was less rigid and more deformable than that made with EPS-nonproducing cultures. The creep and recovery properties of young reduced-fat cheese made with JFR1 and the full-fat type were similar. No differences were found in the viscoelastic properties between reduced-fat cheese made with no EPS and those made with EPS-producing adjunct cultures of Streptococcus thermophilus. After 6 mo of ripening, cheeses made with EPS-producing cultures maintained lower elastic and viscous moduli than did those made with no EPS.     

益生菌对契达干酪成熟过程中抗氧化性变化的影响

为确定益生菌对契达干酪抗氧化性变化的影响,在菌株具备良好耐酸、耐盐性,适用于干酪生产前提下,以水解性和抗氧化性为指标,分别筛选出水解能力和抗氧化能力较强的菌株,并将其添加到契达干酪中,不添加益生菌的干酪为空白组,对干酪成熟过程中活菌数和抗氧化性进行分析。结果表明,9?株益生菌中,瑞士乳杆菌（Lactobacillus helveticus）1.0612和鼠李糖乳杆菌（Lactobacillus rhamnosus）1.0911分别具有较强的水解能力和抗氧化能力。在成熟过程中,添加L. helveticus 1.0612和L. rhamnosus 1.0911的两组干酪活菌数无显著差异,但均显著高于空白组。3?组干酪抗氧化能力均先升高再降低、最后趋于平缓,1,1-二苯基-2-三硝基苯肼（1,1-diphenyl-2-picrylhydrazyl,DPPH）自由基和羟自由基清除能力均在第4个月达到最大,还原能力在第5个月达到最大,且添加水解能力强的L. helveticus 1.0612干酪各项抗氧化能力的最大值（DPPH自由基、羟自由基清除能力和还原能力分别为51.05%、49.97%、0.66）均显著高于添加L. rhamnosus 1.0911的干酪（47.30%、46.19%、0.56）（P＜0.05）。因此,在契达干酪中添加水解能力较强的菌株,相比于添加本身具有良好抗氧化活性的菌株,可能会加剧干酪的蛋白水解,生成具有抗氧化能力的短肽和氨基酸,从而提高干酪的抗氧化活性。     

Characterization of a Panela cheese with added probiotics and fava bean starch

Of 20 Lactobacillus and 8 Bifidobacterium species examined, only Bifidobacterium breve ATCC 15700 was able to ferment starch from fava beans. Bifidobacterium breve ATCC 15700 and Lactobacillus rhamnosus GG ATCC 53103 were selected as probiotics for use in fresh-style Panela cheese. Two types of fresh cheese (with and without 3% fava bean starch) were manufactured with 3 combinations of probiotics: L. rhamnosus GG only, B. breve only, or both L. rhamnosus GG and B. breve. During 4 wk of storage at 4°C, the addition of fava bean starch to the cheese was not found to cause significant differences in the viability of either probiotic strain. However, the microstructure and texture of Panela cheese were altered, resulting in a much softer product. A sensory panel showed that the presence of added fava bean starch in Panela cheese was less desirable to consumers, whereas probiotic supplementation had no effect on perceived taste or appearance. Panela cheese could be a suitable food for inclusion of probiotic bacteria.