Saccharomyces cerevisiae as a starter culture in Mycella

The potential use of Saccharomyces cerevisiae FB7 as an additional starter culture for the production of Mycella, a Danish Gorgonzola type cheese, was investigated. Two dairy productions of Mycella, each containing batches of experimental cheeses with S. cerevisiae added and reference cheeses without yeast added were carried out. For both experimental and reference cheeses, chemical analysis (pH, a(w), NaCl, water and fat content) were carried out during the ripening period, but no significant differences were found. The evolution of lactic acid bacteria was almost identical in both the experimental and reference cheeses and similar results were found for the number of yeast. S. cerevisiae FB7 was found to be predominant in the core of the experimental cheeses throughout the ripening period, while Debaryomyces hansenii dominated in the reference cheese and on the surface of the experimental cheeses. In the cheeses with S. cerevisiae FB7, an earlier sporulation and an improved growth of Penicillium roqueforti was observed compared to the reference cheeses. Furthermore, in the experimental cheese, synergistic interactions were also found in the aroma analysis, the degradation of casein and by the sensory analysis. The observed differences indicate a positive contribution to the overall quality of Mycella by S. cerevisiae FB7.     

本土酿酒酵母的筛选及其低醇葡萄酒特性研究

以天津宝坻产区的三种葡萄为原料,分别从自然发酵的葡萄汁中筛选出340株酵母菌,经生理生化,产酸、酯、尿酶、H2S,发酵能力测定及26SrRNA测序,确定4株为酿酒酵母,用于贵人香低醇白葡萄酒的酿造。以商用酵母为对照,定量分析了不同酵母所酿酒中的香气成分、氨基甲酸乙酯含量,并进行了理化指标和感官测定,发现酵母C508和G611酿造的低醇酒具有更独特的香气特点,氨基甲酸乙酯的含量较低,微生物稳定性较高,更适合低醇酒的酿造。     

本土酿酒酵母模拟条件下酿造特性的研究

对从河北省沙城和昌黎葡萄产区不同品种葡萄上筛选得到的4株本土优选野生酿酒酵母菌株(NJZSS2、NJZSC5、NJZCS9、NJZCC 17)和商业菌株(CICC1450)进行酿酒特性的比较.测定了4株酿酒酵母和对照菌株在模拟葡萄汁小瓶发酵时的CO2失重量、产酒精能力、残糖量、总酸量、甘油量、乙醛量和产H2S能力,并对其在酒精耐受性、SO2耐受性、受温度变化的影响的各方面指标进行了综合比较.结果显示,菌株NJZSS2和NJZCC 17的综合性能最佳,具有应用于我国地区特色葡萄酒生产的潜能.     

河北产区优选酿酒酵母的中试研究

将分离自河北产区的3株本土优良葡萄酒酿酒酵母菌株NJ5、N19、NJ17用于葡萄酒中试发酵,考查不同酵母菌株的发酵性能、所发酵葡萄酒的理化特征、多酚类物质含量和挥发性香气成分组成.结果表明,3株本土酿酒酵母具有良好的发酵性能,可生产具有典型地域特征的葡萄酒,有望于用于河北地区特色葡萄酒的生产.     

Surface binding of aflatoxin B1 by Saccharomyces cerevisiae strains with potential decontaminating abilities in indigenous fermented foods

Saccharomyces cerevisiae constitutes one of the most important microorganisms involved in food fermentations throughout the world. Aflatoxin B(1) binding abilities of S. cerevisiae strains isolated from indigenous fermented foods from Ghana, West Africa were tested in vitro. Results show that aflatoxin binding was strain specific with 7 strains binding 10-20%, 8 strains binding 20-40% and 3 strains binding more than 40% of the added aflatoxin B(1) when grown and incubated under standard conditions. Binding by two of the strains was further characterized. Highest binding capacity was seen with cells collected at the exponential growth phase with the strains A18 and 26.1.11 binding 53.0 and 48.8% of the total toxin respectively and the binding reduced towards the stationary phase. Aflatoxin B(1) binding increased steadily when the cells were incubated with 1 to 20 microg/ml of aflatoxin B(1). Binding was not affected by the cells grown at temperatures ranging from 20 to 37 degrees C, but was significantly reduced at 15 degrees C. Binding seems to be a physical phenomenon with cells treated at 52, 55 and 60 degrees C for 5 and 10 min or 120 degrees C for 20 min binding significantly higher quantities (more than 2-fold in 120 degrees C treated cells) of aflatoxin B(1) than their viable counterpart. Similarly, when the cells were treated with 2 M HCl for 1 h, up to 2-fold increase in binding was observed. The results obtained show that some strains of S. cerevisiae, viable or non-viable, are effective aflatoxin binders and these properties should be considered in the selection of starter cultures for relevant indigenous fermented foods where high aflatoxin level is a potential health risk.     

Characterization of certain bacterial strains for potential use as starter or probiotic cultures in dairy products

The present work was aimed at characterizing 12 strains of lactic acid bacteria (LAB) to obtain improved potential starter or probiotic cultures that could be used for making dairy products from ewe's milk and cow's milk. Eight strains with antimicrobial properties, isolated from ewe's milk and from cheese made from ewe's and/or cow's milk, were studied. They were identified as Enterococcus faecalis (five strains), Lactococcus lactis subsp. cremoris, Leuconostoc mesenteroides, and Lactobacillus paracasei subsp. paracasei (one strain of each species). Additionally, four strains were obtained from the American Type Culture Collection: Lactobacillus casei 393 (isolated from cheese), L. lactis subsp. lactis 11454 (origin nonspecified and a producer of nisin), and two strains isolated from human feces (L. paracasei subsp. paracasei 27092 and Lactobacillus rhamnosus 53103, antibacterial agent producer). All E. faecalis strains showed at least one virulence factor (either hemolysin or gelatinase), which emphasizes the importance of these studies in this species. Both L. lactis strains and most Lactobacillus spp. were good acidifiers in ewe's milk and cow's milk at 30°C. High β-galactosidase activity, as well as aminopeptidase activities that favor the development of desirable flavors in cheese, were detected in all Lactobacillus spp. strains. Furthermore, L. rhamnosus ATCC 53103 showed α-fucosidase activity (thought to help colonization of the intestine) and lack of α-glucosidase activity (a trait considered positive for diabetic and obese humans). This last enzymatic activity was also lacking in L. lactis ATCC 11454. L. mesenteroides was the only strain D(2)-lactic acid producer. The selection of any particular strain for probiotic or dairy cultures should be performed according to the technological and/or functional abilities needed.     

Alginate beads and apple pieces as carriers for Saccharomyces cerevisiae var. boulardii,as representative of yeast functional starter cultures

This study focused on two different carriers for Saccharomyces cerevisiae var. boulardii for its targeted release as a starter or as a probiotic: the microencapsulation into alginate beads and the immobilisation on apple pieces. Beads were studied in relation to encapsulation yield (EY), viability of cells throughout the storage, kinetic of cell release, survival under conditions that mimic the transit into the gut and in vivo application (fermentation of grape juice). Concerning the microencapsulation, EY was very high (ca. 90%), cells survived for a long period (upon to 90 days), and the beads assured cell survival and their release under conditions that mimic the gut; moreover, the capsules could be used up to ten times to start a model fermentation of grape juice. Apple pieces were a good system for the immobilisation of S. boulardii; they could be proposed successfully as a reusable carrier for a starter culture, as they assured the start of the fermentation of grape juice for at least seven times.     

Proteolytic activity of lactic acid bacteria strains and fungal biota for potential use as starter cultures in dry-cured ham

During the processing of dry-cured meat products, sarcoplasmic and myofibrillar proteins undergo proteolysis, which has a marked effect on product flavor. Microbial proteolytic activity is due to the action of mostly lactic acid bacteria (LAB) and to a lesser extent micrococci. The proteolytic capacity of molds in various meat products is of interest to meat processors in the Mediterranean area. Eleven LAB and mold strains from different commercial origins were tested for proteolytic activity against pork myosin, with a view to possible use of these strains as starter cultures for Iberian dry-cured ham. Proteolytic activity was tested by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The LAB strains with the highest proteolytic activity were Lactobacillus plantarum (L115), Pediococcus pentosaceus (Saga P TM), and Lactobacillus acidophilus (FARGO 606 TM). The best fungal candidate was Penicillium nalgiovense LEM 50I followed by Penicillium digitatum, Debaryomyces hansenii, and Penicillium chrysogenum.     

Characterization of Penicillium roqueforti strains used as cheese starter cultures by RAPD typing

Seventy-six strains of Penicillium roqueforti used as starter cultures for mould ripened blue cheeses have been analysed for their RAPD genotype by using three different primers. A comparison of the RAPD patterns within each primer group revealed that the genetic constitution of the strains was similar, as most of the strains showed very similar overall patterns. Despite these similarities with each primer, distinct RAPD genotype groups could be identified. With one of the primers, it was possible to detect two heteropolymorphic DNA regions resulting in 13 different groups. With the other two primers, three or four groups could be identified. Between the groups of the different primers marked correspondence with respect to strain distribution could be observed, indicating that the polymorphisms detected by the primers were not independent. The RAPD patterns were compared to the production of secondary metabolites. A correlation was observed between the RAPD patterns of all primers and the production of mycophenolic acid. In addition, one of the primer (ari1) was able to distinguish between P. roqueforti strains producing larger or smaller numbers of metabolites.     

Effect of wild strains used as starter cultures and adjunct cultures on the volatile compounds of the Pecorino Siciliano cheese

The effect of six wild strains on the volatile profile of the PS cheese was investigated and compared to that generated from industrial starters generally used to produce PS cheese. All cheeses were subjected to microbiological, physicochemical, and volatile compounds analyses. The DGGE of the 16S rDNA analysis was also applied. The volatile compounds generated during ripening were studied through the SPME and the GC-MS methods. No difference was detected between the experimental and control cheeses throughout chemical and microbiological analyses, while the DGGE results showed the presence of Streptococcus thermophilus in all cheeses, and the dominance of Enterococcus durans, Lactobacillus rhamnosus, and Lactobacillus casei in most of the experimental cheeses. Moreover, the presence of Lactococcus lactis species as in the control and in the experimental P2 and P4 cheeses was also revealed. The SPME results showed more pronounced volatile compounds in the experimental cheese samples than in the control ones.     

Reserved carbohydrates of different Saccharomyces cerevisiae strains

Three Saccharomyces strains were compared with commercial pressed yeast using the following criteria: rate of growth, crude protein, percentage of trehalose and glycogen, mannan plus glucan. Results proved that Sacch. cerevisiae 14 had better characteristic aspects than the other tested organisms. Its biomass reached 567 mg dried cells/100 ml culture, with the specific growth rate of 0.026. As a function of 120 h of incubation, Sacch. cerevisiae 14 showed the highest trehalose and glycogen, mannan plus glucan content being 21.1 mg/ 100 mg dried cells. On the other hand, the highest growth densities were obtained at 81 mg of O₂/(600 ml culture. min). Thus, the highest trehalose and glycogen, mannan plus glucan contents were obtained at 81 mg O₂/(600 ml medium. min) and 189 mg O₂/(600 ml medium. min)     

Identification of potential probiotic starter cultures for Scandinavian-type fermented sausages

Potential probiotic cultures suitable as starter cultures for the Scandinavian-type fermented sausages were identified among strains well-adapted to fermented meats as well as strains originating from a culture collection. From 15 different fermented meat products, 22 strains were isolated as dominant non-starter lactic acid bacteria (NSLAB). The isolates were identified by RAPD, API and sequence analysis of 16S rRNA and showed to be five strains of Lactobacillus sakei, five strains of Lactobacillus farciminis, five strains belonging to the group of Lactobacillus plantarum/pentosus, four strains of Lactobacillus alimentarius, two strains of Lactobacillus brevis and one strain of Lactobacillus versmoldensis. Heterofermentative strains as well as strains not growing at 37 degrees C and not lowering pH below 5.1 in a meat model were excluded leaving 9 strains for further studies. These strains together with 19 strains from a culture collection were evaluated by in vitro methods including survival upon exposure to pH 2.5 or 0.3% oxgall and adhesion to the human colon adenocarcinoma cell line Caco-2 as well as antimicrobial activity against potential pathogens. Strains that fulfilled all the probiotic criteria and showed to be fast acid producers in a meat model included three strains belonging to the group of Lb. plantarum/pentosus (MF1291, MF1298, MF1300) which originated from the dominant NSLAB of fermented meat products. MF1291 and MF 1298 were further identified as Lb. plantarum and MF1300 as Lb. pentosus. The three strains were all successfully applied as starter cultures for the production of fermented sausage. The viable count at the end of the processing period reached high cell numbers (4.7x10(7)-2.9x10(8) cfu/g) and pH of the sausages decreased to pH 4.8-4.9 without any flavour deviation compared to sausage fermented by a commercial meat starter culture.     

Characterization of natural isolates of Lactobacillus strains to be used as starter cultures in dairy fermentation

The technological relevant characteristics of five homofermentative lactobacilli strains, isolated from natural fermented hard cheeses, were studied. Isolates CRL 581 and CRL 654, from Argentinian artesanal hard cheeses, and isolates CRL 1177, CRL 1178, and CRL 1179, from Italian Grana cheeses, were identified as Lactobacillus delbrueckii subsp. lactis and Lactobacillus helveticus, respectively, by physiological and biochemical tests, SDS-PAGE of whole-cell proteins and sequencing of the variable (V1) region of the 16S ribosomal DNA. All strains showed high levels of beta-galactosidase activity. However, proteolytic activity varied widely among isolates. Strains CRL 581, CRL 654, and CRL 1177 hydrolyzed alpha- and beta-caseins and were able to coagulate reconstituted skim milk in less than 16 h at 42 degrees C. According to the substrate specificity, these proteinases have a caseinolytic activity comparable to that of the P(III)-type of lactococcal proteinases. No strains produced inhibitor substances (bacteriocin) and all were insensitive to attack by 14 L. helveticus- and L. delbrueckii subsp. lactis-specific bacteriophages.     

Detection method for polygalacturonase-producing strains of Saccharomyces cerevisiae

In the presence of glycerol or ethanol, SCPP (a strain of Saccharomyces cerevisiae that expresses pectinolytic activity) is capable of utilizing galacturonic acid or pectins for growth purposes. We now establish a relationship between the pectinolytic power of various strains of S. cerevisiae and their ability to grow on a pectin/glycerol-based medium. This property is further exploited for the detection of polygalacturonase-producing strains of S. cerevisiae.     

In vitro screening of probiotic properties of Saccharomyces cerevisiae var. boulardii and food-borne Saccharomyces cerevisiae strains

The probiotic potential of 18 Saccharomyces cerevisiae strains used for production of foods or beverages or isolated from such, and eight strains of Saccharomyces cerevisiae var. boulardii, was investigated. All strains included were able to withstand pH 2.5 and 0.3% Oxgall. Adhesion to the nontumorigenic porcine jejunal epithelial cell line (IPEC-J2) was investigated by incorporation of 3H-methionine into the yeast cells and use of liquid scintillation counting. Only few of the food-borne S. cerevisiae strains exhibited noteworthy adhesiveness with the strongest levels of adhesion (13.6-16.8%) recorded for two isolates from blue veined cheeses. Merely 25% of the S. cerevisiae var. boulardii strains displayed good adhesive properties (16.2-28.0%). The expression of the proinflammatory cytokine IL-1alpha decreased strikingly in IPEC-J2 cells exposed to a Shiga-like toxin 2e producing Escherichia coli strain when the cells were pre- and coincubated with S. cerevisiae var. boulardii even though this yeast strain was low adhesive (5.4%), suggesting that adhesion is not a mandatory prerequisite for such a probiotic effect. A strain of S. cerevisiae isolated from West African sorghum beer exerted similar effects hence indicating that food-borne strains of S. cerevisiae may possess probiotic properties in spite of low adhesiveness.     

The fermentation performance of nine strains of Saccharomyces cerevisiae in batch and fed-batch cultures in dilute-acid wood hydrolysate

Large differences in colony forming capacity, ethanol production and inhibitor conversion were noted between nine different strains of Saccharomyces cerevisiae in anaerobic batch and fed-batch cultures on dilute acid wood hydrolysate. S. cerevisiae ATCC 96581 was able to metabolize all added glucose and mannose in fed-batch experiments. The choice of production strain will have a significant effect on the performance of a hydrolysate-based ethanol production plant.     

Effect of dilution rate and nutrients addition on the fermentative capability and synthesis of aromatic compounds of two indigenous strains of Saccharomyces cerevisiae in continuous cultures fed with Agave tequilana juice

Knowledge of physiological behavior of indigenous tequila yeast used in fermentation process is still limited. Yeasts have significant impact on the productivity fermentation process as well as the sensorial characteristics of the alcoholic beverage. For these reasons a better knowledge of the physiological and metabolic features of these yeasts is required. The effects of dilution rate, nitrogen and phosphorus source addition and micro-aeration on growth, fermentation and synthesis of volatile compounds of two native Saccharomyces cerevisiae strains, cultured in continuous fed with Agave tequilana juice were studied. For S1 and S2 strains, maximal concentrations of biomass, ethanol, consumed sugars, alcohols and esters were obtained at 0.04 h⁻¹. Those concentrations quickly decreased as D increased. For S. cerevisiae S1 cultures (at D = 0.08 h⁻¹) supplemented with ammonium phosphate (AP) from 1 to 4 g/L, concentrations of residual sugars decreased from 29.42 to 17.60 g/L and ethanol increased from 29.63 to 40.08 g/L, respectively. The S1 culture supplemented with AP was then micro-aerated from 0 to 0.02 vvm, improving all the kinetics parameters: biomass, ethanol and glycerol concentrations increased from 5.66, 40.08 and 3.11 g/L to 8.04, 45.91 and 4.88 g/L; residual sugars decreased from 17.67 g/L to 4.48 g/L; and rates of productions of biomass and ethanol, and consumption of sugars increased from 0.45, 3.21 and 7.33 g/L·h to 0.64, 3.67 and 8.38 g/L·h, respectively. Concentrations of volatile compounds were also influenced by the micro-aeration rate. Ester and alcohol concentrations were higher, in none aerated and in aerated cultures respectively.