Characterization of specialized flocculent yeasts to improve sparkling wine fermentation.

AIMS: Flocculent wine yeasts were characterized for the expression of FLO1, FLO5, FLO8, AMN1 and RGA1 genes, growth kinetics and physicochemical properties of the cell surface during a 6-month sparkling wine fermentation period. METHODS AND RESULTS: The expression of FLO1, FLO5, FLO8, AMN1 and RGA1 genes was determined by RT-qPCR. The physicochemical characterization of yeast surface properties was evaluated by the microbial adhesion to solvents method. FLO5 gene was the most expressed one and a linear correlation with the flocculent degree was found. Flocculent strains were more hydrophobic than the commercial wine strain EC1118. CONCLUSIONS: Gene expressions and the ability to face secondary wine fermentation conditions were strain dependent. The importance of FLO5 gene in developing the high flocculent characteristic of wine yeasts was highlighted. Cell surface properties depended on the time of fermentation. SIGNIFICANCE AND IMPACT OF THE STUDY: Better knowledge about the expression of some genes encoding the flocculent phenotype which could be useful to select suitable starter cultures to improve sparkling wine technology was achieved. A step forward in understanding the complexity and strain-specific nature of flocculation phenotype was done.

In Lactobacillus pentosus, the olive brine adaptation genes are required for biofilm formation.

Lactobacillus pentosus is one of the few lactic acid bacteria (LAB) species capable of surviving in olive brine, and thus desirable during table olive fermentation. We have recently generated mutants of the efficient strain L. pentosus C11 by transposon mutagenesis and identified five mutants unable to survive and adapt to olive brine conditions. Since biofilm formation represents one of the main bacterial strategy to survive in stressful environments, in this study, the capacity of adhesion and formation of biofilm on olive skin was investigated for this strain and five derivative mutants which are interrupted in metabolic genes (enoA1 and gpi), and in genes of unknown function ("oba" genes). Confocal microscopy together with bacteria count revealed that the sessile state represented the prevailing L. pentosus C11 life-style during table olive fermentation. The characterization of cell surface properties showed that mutants present less hydrophobic and basic properties than the wild type (WT). In fact, their ability to adhere to both abiotic (polystyrene plates) and biotic (olive skin) surfaces was lower than that of the WT. Confocal microscopy revealed that mutants adhered sparsely to the olive skin instead of building a thin, multilayer biofilm. Moreover, RT-qPCR showed that the three genes enoA1, gpi and obaC were upregulated in the olive biofilm compared to the planktonic state. Thus enoA1, gpi and "oba" genes are necessary in L. pentosus to form an organized biofilm on the olive skin.

Diversity of food-borne Bacillus volatile compounds and influence on fungal growth.

AIMS: To evaluate the antifungal activity of the volatile organic compounds (VOCs) produced by 75 different food-borne Bacillus species against Aspergillus niger, Aspergillus flavus, Aspergillus parasiticus, Aspergillus clavatus, Fusarium oxysporum f. sp. lactucae and Moniliophthora perniciosa and to determine the VOCs responsible for the inhibition. METHODS AND RESULTS: Bacillus strains inhibited fungal growth, although with different inhibition grades, with Bacillus subtilis, Bacillus amyloliquefaciens and Bacillus cereus strains as the best antifungal VOCs producers. While M. perniciosa DM4B and F. oxysporum f.sp. lactucae MA28 were the most sensitive fungi, A. parasiticus MG51 showed the greatest resistance to Bacillus VOCs exposure. Thirty-seven compounds were detected by SPME-GC-MS analysis, although similar patterns in volatile compounds were evidenced within the species, interspecific VOCs differences determined different effects on fungal growth. Multiple partial least regression (MPLRS) and antifungal activity of the individual VOCs revealed that only propanone, 1-butanol, 3-methyl-1-butanol, acetic acid, 2-methylpropanoic acid, carbon disulphide, 3-methylbutanoic acid and ethyl acetate were responsible for mycelia inhibition of M. perniciosa DM4B and F. oxysporum f.sp. lactucae MA28. CONCLUSIONS: The antagonistic activity of the Bacillus VOCs was demonstrated, although it cannot easily be explained through the action of a single molecule, thus a holistic approach could be more appropriate to estimate the fungal growth inhibition. SIGNIFICANCE AND IMPACT OF THE STUDY: VOCs produced by Bacillus from cooked food can be considered as promising antifungal compounds useful in the control of fungal plant pathogens. This study investigates for the first time the correlation between mycelia inhibition of M. perniciosa and F. oxysporum f. sp. lactucae and the VOCs emitted by the Bacillus species.

Identification of critical genes for growth in olive brine by transposon mutagenesis of Lactobacillus pentosus C11.

Olive brine represents a stressful environment due to the high NaCl concentration, presence of phenolic compounds known as antimicrobials, and low availability of nutrients. Thus, only a few strains of lactic acid bacteria (LAB) are adapted to grow in and ferment table olives. To identify the mechanisms by which these few strains are able to grow in olive brine, Lactobacillus pentosus C11, a particularly resistant strain isolated from naturally fermented table olives, was mutagenized by random transposition using the P(junc)-TpaseIS1223 system (H. Licandro-Seraut, S. Brinster, M. van de Guchte, H. Scornec, E. Maguin, P. Sansonetti, J. F. Cavin, and P. Serror, Appl. Environ. Microbiol. 78:5417-5423, 2012). A library of 6,000 mutants was generated and screened for adaptation and subsequent growth in a medium, named BSM (brine screening medium), which presents the stressful conditions encountered in olive brine. Five transposition mutants impaired in growth on BSM were identified. Transposition occurred in two open reading frames and in three transcription terminators affecting stability of transcripts. Thus, several essential genes for adaptation and growth of L. pentosus C11 in olive brine were identified.

Growth and metabolites production by Penicillium brevicompactum in yoghurt.

Penicillium brevicompactum, commonly encountered in the indoor air, is known to produce a mycotoxin, mycophenolic acid (MPA). This mould has been isolated from a wide range of foods; considering that we had previously isolated this species from contaminated yoghurt, in this study we have evaluated its growth in yoghurt sweetened with sucrose, fructose and fructose added with fruit pieces. Fungal growth was evaluated monitoring CO(2) production in the headspace during yoghurt storage at 4+/-1, 8+/-1 and 10+/-1 degrees C throughout 21 days. P. brevicompactum grew well in the samples sweetened with fructose at 8 and 10 degrees C. The addition of sucrose influenced the growth negatively, particularly at 4 degrees C. Volatile Organic Compounds (VOC) and MPA production was determined at 8 degrees C in inoculated and uninoculated yoghurt, as well as in liquid malt extract. Differences in VOC profiles and in MPA production were correlated with the age of the fungus and with the growth medium. This study points out for the first time the early qualitative changes in volatile production patterns of a common indoor mould, grown in yoghurt, as well as the production of MPA during storage at refrigeration temperatures.

Genotypic and phenotypic diversity of Lactobacillus rossiae strains isolated from sourdough.

AIM: To characterize the genetic and phenotypic diversity of 33 strains of Lactobacillus rossiae. METHODS AND RESULTS: Genotypic identification was carried out by partial 16S rRNA gene sequence analysis. Genetic diversity was evaluated by RAPD-PCR analysis. Phenotypic diversity was evaluated through fermentative profile by Biolog system, proteinase and peptidase activities using synthetic substrates, and acidification capacity and amino acid profile during sourdough fermentation. The genetic analyses excluded clonal relatedness among the strains used. A large phenotypic diversity was found. It mainly concerned the capacity to use carbon sources available in sourdough during fermentation, the quotient of fermentation and the peptidase activities, especially towards proline containing synthetic substrates. The free amino acid profiles differed either for the total concentration or for the type of amino acids. With a few exceptions, proteinase activity towards wheat albumins and globulins was weak. CONCLUSIONS: Overall, no relationships between genetic and physiological analyses were found, and the strains examined showed a marked genetic and phenotypic heterogeneity. L. rossiae strains had interesting properties for application in sourdough fermentation. Although some strains combined several technological traits, the association of more strains seemed to be a requisite to get optimal sourdough characteristics. SIGNIFICANCE AND IMPACT OF THE STUDY: It represents the first characterization of the diversity within the L. rossiae species. Besides, it may represent an example of computerized analysis of genotypic and phenotypic information to select strains for improving sourdough characteristics.

The use of multiplex PCR to detect and differentiate food- and beverage-associated microorganisms: a review.

Regarding food safety, rapid detection of microbial species is crucial to develop effective preventive and/or adjustment measures. Classical methods for determining the presence of certain species are time-consuming and labor-intensive, hence, molecular methods, which offer speed, sensitivity and specificity, have been developed to address this problem. Multiplex PCR (MPCR) is widely applied in the various fields of microbiology for the rapid differentiation of microbial species without compromising accuracy. This paper describes the method and reports on the state-of-the-art application of this technique to the identification of microorganisms vehiculated with foods and beverages. The identification of both pathogens and probiotics and the species important for food fermentation or deterioration will be discussed. Applications of MPCR in combination with other techniques are also reviewed. Potentials, pitfalls, limitations and future prospects are summarised.

Application of a novel polyphasic approach to study the lactobacilli composition of sourdoughs from the Abruzzo region (central Italy).

AIMS: To characterize the lactobacilli community of 20 sourdoughs using a novel polyphasic approach. METHODS AND RESULTS: A polyphasic approach, consisting of a two-step multiplex polymerase chain reaction (PCR) system, 16S rRNA gene sequence analysis and physiological features, was applied to identify 127 isolates, representing about 37% of the presumptive lactobacilli collected from sourdough samples. Multiplex PCR successfully identified 111 isolates, while 16S rRNA gene sequencing was applied for the other 16 isolates, two of which could not be associated with any previously described lactic acid bacteria (LAB) species. Strain diversity was evaluated by phenotypic and random amplified polymorphic DNA-PCR analysis. Molecular detection of Lactobacillus group species was also performed on total DNA extracted from the doughs. CONCLUSIONS: Abruzzo region sourdough lactobacilli biodiversity, reflected in both Lactobacillus species composition and strain polymorphism, is similar to that of other Italian regions and is a source of novel LAB species. SIGNIFICANCE AND IMPACT OF THE STUDY: Within culture-independent methods, multiplex PCR is a rapid tool to study the lactobacilli population of sourdoughs.

In situ activity of a bacteriocin-producing Lactococcus lactis strain. Influence on the interactions between lactic acid bacteria during sourdough fermentation.

AIMS: To biochemically characterize the bacteriocin produced by Lactococcus lactis ssp. lactis M30 and demonstrate its effect on lactic acid bacteria (LAB) during sourdough propagation. METHODS AND RESULTS: A two-peptide bacteriocin produced by L. lactis ssp. lactis M30 was purified by ion exchange, hydrophobic interaction and reversed phase chromatography. Mass spectrometry of the two peptides and sequence analysis of the ltnA2 gene showed that the bacteriocin was almost identical to lacticin 3147. During a 20-day period of sourdough propagation the stability of L. lactis M30 was demonstrated, with concomitant inhibition of the indicator strain Lactobacillus plantarum 20, as well as the non-interference with the growth of the starter strain Lact. sanfranciscensis CB1. CONCLUSIONS: In situ active bacteriocins influence the microbial consortium of sourdough LAB and can "support" the dominance of insensitive strains during sourdough fermentation. SIGNIFICANCE AND IMPACT OF THE STUDY: The in situ bacteriocinogenic activity of selected lactococci enables the persistence of insensitive Lact. sanfranciscensis strains, useful to confer good characteristics to the dough, at a higher cell concentration with respect to other LAB of the same ecosystem.

Characterization of bacteriocin-like inhibitory substances (BLIS) from sourdough lactic acid bacteria and evaluation of their in vitro and in situ activity.

AIMS: To identify and characterize bacteriocion-producing lactic acid bacteria (LAB) in sourdoughs and to compare in vitro and in situ bacteriocin activity of sourdough- and nonsourdough LAB. METHODS AND RESULTS: Production of antimicrobial compounds by 437 Lactobacillus strains isolated from 70 sourdoughs was investigated. Five strains (Lactobacillus pentosus 2MF8 and 8CF, Lb. plantarum 4DE and 3DM and Lactobacillus spp. CS1) were found to produce distinct bacteriocin-like inhibitory substances (BLIS). BLIS-producing Lactococcus lactis isolated from raw barley showed a wider inhibitory spectrum than sourdough LAB, but they did not inhibit all strains of the key sourdough bacterium Lb. sanfranciscensis. Antimicrobial production by Lb. pentosus 2MF8 and Lc. lactis M30 was also demonstrated in situ. CONCLUSIONS: BLIS production by sourdough LAB appears to occur at a low frequency, showing limited inhibitory spectrum when compared with BLIS-producing Lc. lactis. Nevertheless, they are active BLIS producers under sourdough and bread-making conditions. SIGNIFICANCE AND IMPACT OF THE STUDY: The activity of BLIS has been demonstrated in situ. It may influence the complex sourdough microflora and support the implantation and stability of selected insensitive bacteria, such as Lb. sanfranciscensis, useful to confer good characteristics to the dough.

Best approach for prostate cancer detection: a prospective study on transperineal versus transrectal six-core prostate biopsy.

OBJECTIVES: To compare the efficacy of transperineal versus transrectal six-core prostate biopsy. Transrectal sextant biopsy is the most common method for prostate cancer detection. However, the cancer detection rate with this technique is increasingly considered inadequate. Different prostate biopsy procedures, mainly based on addition of additional transrectal cores to traditional sextant biopsy, have been proposed to increase the cancer diagnosis rate. The efficacy of the transperineal approach has not yet been fully established. METHODS: In a prospective study, 107 patients with elevated prostate-specific antigen levels (greater than 4.0 ng/mL) underwent prostate biopsy with six transperineal cores, using a "fan" scheme, plus six transrectal cores, according to the sextant technique. The median prostate-specific antigen level was 8.2 ng/mL (range 4.1 to 240). RESULTS: The overall cancer detection rate was 40% (43 of 107); prostate cancer was found in 38% (41 of 107) of patients with the transperineal approach and in 32% (34 of 107) of patients with the transrectal approach. Of 43 diagnosed cancers, 41 (95%) were found with the transperineal approach and 34 (79%) with the transrectal approach (P = 0.012). No patient had low-grade cancer (Gleason score 2 to 4), 25 patients had intermediate-grade cancer (Gleason score 5 to 6), and 18 patients had high-grade cancer (Gleason score 7 to 10). CONCLUSIONS: This is the first report comparing in vivo two different approaches to prostate biopsy. Transperineal biopsy seems superior to transrectal biopsy to detect prostate cancer. Both the transperineal and the transrectal approach should be familiar to the urologist who needs to obtain an adequate cancer detection rate. Transrectal sextant biopsy cannot be considered the standard technique for prostate cancer detection.

Characterization of sourdough lactic acid bacteria based on genotypic and cell-wall protein analyses.

AIMS: To evaluate the effectiveness of two independent methods in differentiating a large population of lactic acid bacteria (LAB) isolated from wheat flours and sourdoughs and to correlate eventual differences/similarities among strains with their geographical origin and/or process parameters. METHODS AND RESULTS: One hundred fifty strains belonging to Lactobacillus spp. and Weissella spp., plus eight type strains, one for each species, and two unidentified isolates, were characterized by randomly amplified polymorphic DNA (RAPD) and SDS-PAGE of cell-wall proteins. The RAPD analysis separated the eight type strains but did not always assign all the strains of a species to the same group, while SDS-PAGE cell-wall protein profiles were species-specific. Frequently, strains isolated from sourdoughs of the same geographical origin or produced by similar raw material/process parameters showed similar RAPD and/or cell-wall profiles. CONCLUSIONS: The combined use of the RAPD and cell-wall protein analysis represents a useful tool to classify large adventitious microbial populations and to discriminate the diversity of the strains. SIGNIFICANCE AND IMPACT OF THE STUDY: This study represents a typing of a large collection of flour/sourdough LAB and provides evidence of the advantage of using two independent methods in the classification and traceability of microorganisms.

Latent bioactive peptides in milk proteins: proteolytic activation and significance in dairy processing.

After a brief description of the properties of bioactive peptides, the proteolytic activation of the bioactive sequences from milk protein precursors is discussed. The ability of proteolytic enzymes from various sources, especially from lactic acid bacteria, to release bioactive peptides and the physiological and biotechnological significance of these peptides in dairy products are reviewed.

Interactions between yeasts and bacteria in the smear surface-ripened cheeses.

In the initial phase of ripening, the microflora of bacterial smear surface-ripened cheeses such as Limburger, Taleggio, Brick, Münster and Saint-Paulin and that of surface mould-ripened cheeses such as Camembert and Brie may be similar, but at the end of the ripening, bacteria such as Brevibacterium spp., Arthrobacter spp., Micrococcus spp., Corynebacterium spp. and moulds such as Penicillium camemberti are, respectively, the dominant microorganisms. Yeasts such as Candida spp., Cryptococcus spp., Debaryomyces spp., Geotrichum candidum, Pichia spp., Rhodotorula spp., Saccharomyces spp. and Yarrowia lipolytica are often and variably isolated from the smear surface-ripened cheeses. Although not dominant within the microorganisms of the smear surface-ripened cheeses, yeasts establish significant interactions with moulds and especially bacteria, including surface bacteria and lactic acid bacteria. Some aspects of the interactions between yeasts and bacteria in such type of cheeses are considered in this paper.

Microbiological and biochemical characteristics of Canestrato Pugliese cheese made from raw milk, pasteurized milk or by heating the curd in hot whey.

Canestrato Pugliese cheeses were produced from raw ewes' milk (R and R(II) cheeses), pasteurized ewes' milk (P cheese) and by heating the curd in hot whey according to a traditional protocol (T cheese). R(II) differed from R cheese mainly by having been produced from raw milk with a higher number of somatic cells, 950.000 vs. 750.000 ml(-1), respectively. Compared to P and T cheeses, R and R(II) cheeses had a higher concentration (one or two orders of magnitude) of cheese-related bacteria such as adventitious mesophilic lactobacilli, enterococci and staphylococci. At the end of ripening, all cheeses contained less than 1.0 log cfu g(-1) of total and fecal coliforms, and Escherichia coli and Staphylococcus aureus were not detected. As shown by phenotypic identification and RAPD-PCR, R cheese contained the largest number of mesophilic lactobacilli species and the greatest diversity of strains within the Lactobacillus plantarum species. Primary proteolysis did not differ appreciably among the cheeses. On the contrary, both urea-PAGE and the RP-HPLC analyses of the water-soluble N fractions showed the more complex profiles in cheeses produced by raw milks. R and R(II) cheeses had the highest values of water-soluble N/total N (ca. 30%) and the highest concentration of total free amino acids (ca. 40 mg g(-1) which approached or exceeded those reported for Italian cheeses with very high level of proteolysis during ripening. The main differences between R-R(II) and P-T cheeses were the concentrations of aspartic acid, proline, alanine, isoleucine, histidine and lysine. The water-soluble extracts of R and R(II) cheeses contained levels of amino-, imino- and di-peptidase activities, which were about twice those found in P and T cheeses. Cheeses differed slightly in the concentration of total free fatty acids that ranged between 1673 and 1651 mg kg(-1) in R and R(II) cheeses, and 1397 and 1334 mg kg(-1) in P and T cheeses. Butyric, caproic, capric, palmitic, oleic and linoleic acids were found at the highest concentrations.

Characterization of non-starter lactic acid bacteria from Italian ewe cheeses based on phenotypic, genotypic, and cell wall protein analyses.

Non-starter lactic acid bacteria (NSLAB) were isolated from 12 Italian ewe cheeses representing six different types of cheese, which in several cases were produced by different manufacturers. A total of 400 presumptive Lactobacillus isolates were obtained, and 123 isolates and 10 type strains were subjected to phenotypic, genetic, and cell wall protein characterization analyses. Phenotypically, the cheese isolates included 32% Lactobacillus plantarum isolates, 15% L. brevis isolates, 12% L. paracasei subsp. paracasei isolates, 9% L. curvatus isolates, 6% L. fermentum isolates, 6% L. casei subsp. casei isolates, 5% L. pentosus isolates, 3% L. casei subsp. pseudoplantarum isolates, and 1% L. rhamnosus isolates. Eleven percent of the isolates were not phenotypically identified. Although a randomly amplified polymorphic DNA (RAPD) analysis based on three primers and clustering by the unweighted pair group method with arithmetic average (UPGMA) was useful for partially differentiating the 10 type strains, it did not provide a species-specific DNA band or a combination of bands which permitted complete separation of all the species considered. In contrast, sodium dodecyl sulfate-polyacrylamide gel electrophoresis cell wall protein profiles clustered by UPGMA were species specific and resolved the NSLAB. The only exceptions were isolates phenotypically identified as L. plantarum and L. pentosus or as L. casei subsp. casei and L. paracasei subsp. paracasei, which were grouped together. Based on protein profiles, Italian ewe cheeses frequently contained four different species and 3 to 16 strains. In general, the cheeses produced from raw ewe milk contained a larger number of more diverse strains than the cheeses produced from pasteurized milk. The same cheese produced in different factories contained different species, as well as strains that belonged to the same species but grouped in different RAPD clusters.

Phenotypic and molecular identification and clustering of lactic acid bacteria and yeasts from wheat (species Triticum durum and Triticum aestivum) sourdoughs of Southern Italy.

The microflora of 25 wheat sourdoughs from the Apulia region, Southern Italy, was characterized. The sourdoughs were mainly produced from Triticum durum wheat. The number of lactic acid bacteria and yeasts ranged from ca. log 7.5 to log 9.3 colony forming units (cfu)/g and from log 5.5 to log 8.4 cfu/g, respectively. About 38% of the 317 isolates of lactic acid bacteria were identified by conventional physiological and biochemical tests. Phenotypic identification was confirmed by 16S rDNA and 16S/23S rRNA spacer region PCR. Overall, 30% of the isolates were identified as Lactobacillus sanfranciscensis, 20% as Lb. alimentarius, 14% as Lb. brevis, 12% as Leuconostoc citreum, 7% as Lb. plantarum, 6% as Lactococcus lactis subsp. lactis, 4% as Lb. fermentum and Lb. acidophilus, 2% as Weissella confusa and 1% as Lb. delbrueckii subsp. delbrueckii. Some of these species have not been previously isolated from sourdoughs. Since bakers yeast is widely used in sourdough production, Saccharomyces cerevisiae was largely found. The phenotypical relationships within the main lactic acid bacteria identified were established by using cluster analysis. A microbial map of the 25 sourdoughs was plotted showing characteristic associations among lactic acid bacteria and differences in the lactic acid bacteria species which were mainly due to the species of wheat flour, use of bakers yeast and type of bread.

Purification and characterization of novel antifungal compounds from the sourdough Lactobacillus plantarum strain 21B.

Sourdough lactic acid bacteria were selected for antifungal activity by a conidial germination assay. The 10-fold-concentrated culture filtrate of Lactobacillus plantarum 21B grown in wheat flour hydrolysate almost completely inhibited Eurotium repens IBT18000, Eurotium rubrum FTDC3228, Penicillium corylophilum IBT6978, Penicillium roqueforti IBT18687, Penicillium expansum IDM/FS2, Endomyces fibuliger IBT605 and IDM3812, Aspergillus niger FTDC3227 and IDM1, Aspergillus flavus FTDC3226, Monilia sitophila IDM/FS5, and Fusarium graminearum IDM623. The nonconcentrated culture filtrate of L. plantarum 21B grown in whole wheat flour hydrolysate had similar inhibitory activity. The activity was fungicidal. Calcium propionate at 3 mg ml(-1) was not effective under the same assay conditions, while sodium benzoate caused inhibition similar to L. plantarum 21B. After extraction with ethyl acetate, preparative silica gel thin-layer chromatography, and chromatographic and spectroscopic analyses, novel antifungal compounds such as phenyllactic and 4-hydroxy-phenyllactic acids were identified in the culture filtrate of L. plantarum 21B. Phenyllactic acid was contained at the highest concentration in the bacterial culture filtrate and had the highest activity. It inhibited all the fungi tested at a concentration of 50 mg ml(-1) except for P. roqueforti IBT18687 and P. corylophilum IBT6978 (inhibitory concentration, 166 mg ml(-1)). L. plantarum 20B, which showed high antimold activity, was also selected. Preliminary studies showed that phenyllactic and 4-hydroxy-phenyllactic acids were also contained in the bacterial culture filtrate of strain 20B. Growth of A. niger FTDC3227 occurred after 2 days in breads started with Saccharomyces cerevisiae 141 alone or with S. cerevisiae and Lactobacillus brevis 1D, an unselected but acidifying lactic acid bacterium, while the onset of fungal growth was delayed for 7 days in bread started with S. cerevisiae and selected L. plantarum 21B.

Combined effect of sourdough lactic acid bacteria and additives on bread firmness and staling.

The effect of various sourdoughs and additives on bread firmness and staling was studied. Compared to the bread produced with Saccharomyces cerevisiae 141, the chemical acidification of dough fermented by S. cerevisiae 141 or the use of sourdoughs increased the volume of the breads. Only sourdough fermentation was effective in delaying starch retrogradation. The effect depended on the level of acidification and on the lactic acid bacteria strain. The effect of sourdough made of S. cerevisiae 141-Lactobacillus sanfranciscensis 57-Lactobacillus plantarum 13 was improved when fungal alpha-amylase or amylolytic strains such as L. amylovorus CNBL1008 or engineered L. sanfranciscensis CB1 Amy were added. When pentosans or pentosans, endoxylanase enzyme, and L. hilgardii S32 were added to the same sourdough, a greater delay of the bread firmness and staling was found. When pentosans were in part hydrolyzed by the endoxylanase enzyme, the bread also had the highest titratable acidity, due to the fermentation of pentoses by L. hilgardii S32. The addition of the bacterial protease to the sourdough increased the bread firmness and staling.

Arabinose fermentation by Lactobacillus plantarum in sourdough with added pentosans and alphaalpha-L-arabinofuranosidase: a tool to increase the production of acetic acid.

Sixty-five strains of obligately and facultatively heterofermentative sourdough lactic acid bacteria were screened for their capacity to grow optimally in the presence of arabinose, ribose and xylose as carbon sources. Lactobacillus alimentarius 15F, Lact. brevis 10A, Lact. fermentum 1F and Lact. plantarum 20B showed higher growth rate, cell yield, acidification rate and production of acetic acid when some pentoses instead of maltose were added to the SDB medium. Lactobacillus plantarum 20B used arabinose also in a synthetic medium where complex growth factors such as yeast extract were omitted. Other Lact. plantarum strains did not show the same property. Pentosan extract was treated with alpha-L-arabinofuranosidase from Aspergillus niger or endo-xylanase from Bacillus subtilis to produce hydrolysates containing mainly arabinose and xylose, respectively. In particular, the hydrolysate containing arabinose substantiated the growth and the production of lactic acid and, especially, of acetic acid by Lact. plantarum 20B. Sourdough fermentation by Lact. plantarum 20B with addition of pentosan extract and alpha-L-arabinofuranosidase increased the acidification rate, titratable acidity and acetic acid content compared with traditional sourdough. A facultatively heterofermentative strain, Lact. plantarum 20B, also produced a sourdough with an optimal fermentation quotient.