Ferment Maltose Research Articles

Influence of the Sugar Composition of the Added Extract on the Refermentation of Beer in Bottles

Although beer refermentation in bottles is essentially a simple process, mixing mature beer with yeast and sugar before bottling, refermentation is often difficult to control in industrial practice. This can result in variable batch-to-batch quality, especially in small-scale breweries. In this study, industrial top-fermented beers were mixed with freshly propagated yeast and fermentable extract. The extract consisted of glucose, fructose, maltose, sucrose, or one of several commercially available sugar syrups. Glucose, fructose, and sucrose were fermented at comparable rates, reaching final attenuation within two weeks. Maltose was only partially fermented or not fermented at all, depending mainly on the yeast strain used. Several factors that may affect sugar uptake were examined. Carbon dioxide pressure in the bottled beer accounted for most of the loss in the capacity of the yeast to ferment maltose, while it had only a minor influence on the uptake of glucose and fructose. This difference is probably due to the different mechanisms by which these sugars are transported into the cell. Although maltose is the main sugar in brewing wort, its use is not appropriate for bottle refermentation. The use of sugar syrups with high maltose content may lead to irreproducible or stuck fermentations. Moreover, residual extract promotes inconsistent yeast deposit stability.

Sequences in the N-terminal cytoplasmic domain of Saccharomyces cerevisiae maltose permease are required for vacuolar degradation but not glucose-induced internalization

In Saccharomyces cerevisiae, glucose addition to maltose fermenting cells causes a rapid loss of maltose transport activity and ubiquitin-mediated vacuolar proteolysis of maltose permease. GFP-tagged Mal61 maltose permease was used to explore the role of the N-terminal cytoplasmic domain in glucose-induced inactivation. In maltose-grown cells, Mal61/HA-GFP localizes to the cell surface and, surprisingly, to the vacuole. Studies of end3Delta and doa4Delta mutants indicate that a slow constitutive internalization of Mal61/HA-GFP is required for its vacuolar localization. Site-specific mutagenesis of multiple serine/threonine residues in a putative PEST sequence of the N-terminal cytoplasmic domain of maltose permease blocks glucose-induced Mal61p degradation but does not affect the rapid loss of maltose transport activity associated with glucose-induced internalization. The internalized multiple Ser/Thr mutant protein co-localizes with Snf7p in a putative late endosome or E-compartment. Further, alteration of a putative dileucine [D/EExxxLL/I] motif at residues 64-70 causes a significant defect in maltose transport activity and mislocalization to an E-compartment but appears to have little impact on glucose-induced internalization. We conclude that the N-terminal cytoplasmic domain of maltose permease is not the target of the signaling pathways leading to glucose-induced internalization of Mal61 permease but is required for its subsequent delivery to the vacuole for degradation.

Altered Patterns of Maltose and Glucose Fermentation by Brewing and Wine Yeasts Influenced by the Complexity of Nitrogen Source

Maltose and glucose fermentations by industrial brewing and wine yeasts strains were strongly affected by the structural complexity of the nitrogen source. In this study, four Saccharomyces cerevisiae strains, two brewing and two wine yeasts, were grown in a medium containing maltose or glucose supplemented with a nitrogen source varying from a single ammonium salt (ammonium sulfate) to free amino acids (casamino acids) and peptides (peptone). Diauxie was observed at low sugar concentration for brewing and wine strains, independent of nitrogen supplementation, and the type of sugar. At high sugar concentrations altered patterns of sugar fermentation were observed, and biomass accumulation and ethanol production depended on the nature of the nitrogen source and were different for brewing and wine strains. In maltose, high biomass production was observed under peptone and casamino acids for the brewing and wine strains, however efficient maltose utilization and high ethanol production was only observed in the presence of casamino acids for one brewing and one wine strain studied. Conversely, peptone and casamino acids induced higher biomass and ethanol production for the two other brewing and wine strains studied. With glucose, in general, peptone induced higher fermentation performance for all strains, and one brewing and wine strain produced the same amount of ethanol with peptone and casamino acids supplementation. Ammonium salts always induced poor yeast performance. The results described in this paper suggest that the complex nitrogen composition of the cultivation medium may create conditions resembling those responsible for inducing sluggish/stuck fermentation, and indicate that the kind and concentration of sugar, the complexity of nitrogen source and the yeast genetic background influence optimal industrial yeast fermentation performance.

Microorganisms Involved in the Fermentation Process of Panettone Sourdough Maintaining in Japan

Samples of panettone sourdoughs manufactured in an industrial bakery located in Japan were investigated. The sourdough starter called mother sponge was imported from Italy and propagated continuously in Japan. According to traditional practice in Italy, panettone sourdoughs were prepared. Microflora was composed of Yeast (106-107cfu/g) and LAB (107-108cfu/g). All the fermentation process, predominant yeasts has the feature of no maltose fermentation and no growth at 37°C. Predominant LAB fermented maltose and has requirement of Tween 80 for growth. DNA-DNA hybridization data exhibited they were Candida milleri and Lactobacillus sanfranciscensis. Furthermore L. sanfranciscensis forming L-lactate was isolated from panettone sourdough. And lactate dehydrogenases took part in isomer of lactate produced by them. It was confirmed that the native microflora of the panettone mother sponge was successfully preserved in Japan.

Petrimonas sulfuriphila gen. nov., sp. nov., a mesophilic fermentative bacterium isolated from a biodegraded oil reservoir

A mesophilic, anaerobic, fermentative bacterium, strain BN3(T), was isolated from a producing well of a biodegraded oil reservoir in Canada. Cells were Gram-negative, non-motile rods that did not form spores. The temperature range for growth was 15-40 degrees C, with optimum growth at 37-40 degrees C. The strain grew with up 4 % NaCl, with optimum growth in the absence of NaCl. Tryptone was required for growth. Yeast extract and elemental sulfur stimulated growth. Growth was also enhanced during fermentation of glucose, arabinose, galactose, maltose, mannose, rhamnose, lactose, ribose, fructose, sucrose, cellobiose, lactate, mannitol and glycerol. Acetate, hydrogen and CO(2) were produced during glucose fermentation. Elemental sulfur and nitrate were used as electron acceptors and were reduced to sulfide and ammonium, respectively. The G + C content of the genomic DNA was 40.8 mol%. Phylogenetic analyses of the 16S rRNA gene sequence indicated that the strain was a member of the phylum 'Bacteroidetes', distantly related to the genera Bacteroides and Tannerella (similarity values of less than 90 %). The chemotaxonomic data (fatty acids, polar lipids and quinones composition) also indicated that strain BN3(T) could be clearly distinguished from its closest cultivated relatives. This novel organism possesses phenotypic, chemotaxonomic and phylogenetic traits that do not allow its classification as a member of any previously described genus; therefore, it is proposed that this isolate should be described as a member of a novel species of a new genus, Petrimonas gen. nov., of which Petrimonas sulfuriphila sp. nov. is the type species. The type strain is BN3(T) (= DSM 16547(T) = JCM 12565(T)).

Production of high‐purity isomalto‐oligosaccharides syrup by the enzymatic conversion of transglucosidase and fermentation of yeast cells

A method for the production of high-purity isomalto-oligosaccharides (IMO) involving the transglucosylation by transglucosidase and yeast fermentation was proposed. The starch of rice crumbs was enzymatically liquefied and saccharified, and then converted to low-purity IMO syrup by transglucosylation. The low-purity IMO produced either from rice crumbs or tapioca flour as the starch source could be effectively converted to high-purity IMO by yeast fermentation to remove the digestible sugars including glucose, maltose, and maltotriose. Both Saccharomyces carlsbergensis and Saccharomyces cerevisiae were able to ferment glucose in the IMO syrup. Cells of S. carlsbergensis harvested from the medium of malt juice were also able to ferment maltose and maltotriose. A combination of these two yeasts or S. carlsbergensis alone could be used to totally remove the digestible sugars in the IMO, coupled with the production of ethanol. The resultant high-purity IMO, including mainly isomaltose, panose, and isomaltotriose made up more than 98% w/w of the total sugars after a 3-day fermentation. When the low-purity IMO was produced from the starch of tapioca flour, 3-day fermentation under the same conditions resulted in IMO with purity lower than that from rice crumbs. For low-purity IMO from rice crumbs, fermentation with washed S. carlsbergensis cells harvested at log phase was the most effective. However, for the low-purity IMO from tapioca flour, incubation with S. cerevisiae for the first 24 h and then supplementing with an equal amount of S. carlsbergensis cells for further fermentation was the most effective approach for producing high-purity IMO.

Acidic proteome of growing and resting Lactococcus lactis metabolizing maltose

The acidic proteome of Lactococcus lactis grown anaerobically was compared for three different growth conditions: cells growing on maltose, resting cells metabolizing maltose, and cells growing on glucose. In maltose metabolizing cells several proteins were up-regulated compared with glucose metabolizing cells, however only some of the up-regulated proteins had apparent relation to maltose metabolism. Cells growing on maltose produced formate, acetate and ethanol in addition to lactate, whereas resting cells metabolizing maltose and cells growing on glucose produced only lactate. Increased levels of alcohol-acetaldehyde dehydrogenase (ADH) and phosphate acetyltransferase (PTA) in maltose-growing cells compared with glucose-growing cells coincided with formation of mixed acids in maltose-growing cells. The resting cells did not grow due to lack of an amino acid source and fermented maltose with lactate as the sole product, although ADH and PTA were present at high levels. The maltose consumption rate was approximately three times lower in resting cells than in exponentially growing cells. However, the enzyme levels in resting and growing cells metabolizing maltose were similar, which indicates that the difference in product formation in this case is due to regulation at the enzyme level. The levels of 30S ribosomal proteins S1 and S2 increased with increasing growth rate for resting cells metabolizing maltose, maltose-growing cells and glucose-growing cells. A modified form of HPr was synthesized under amino acid starvation. This is suggested to be due to alanine misincorporation for valine, which L. lactis is auxotrophic for. L. lactis conserves the protein profile to a high extent, even after prolonged amino acid starvation, so that the protein expression profile of the bacterium remains almost invariant.

Characterization of the Yeast Population Involved in the Production of a Typical Italian Bread

ABSTRACT: This work was aimed to characterize the yeast population of Ferrara bread, a baked product to which the European Community assigned the Protected Geographical Indication, and to focus the attention on the yeasts of the sourdough used for its production. In addition, the physicochemical parameters were monitored. High amounts of acetic acid were found in the sourdough (more than 3 g/kg) because of the prevalence of heterofermentative lactic acid bacteria. The major part of the yeasts were not able to ferment maltose. Candida milleri was the dominant species (as shown by random amplification of polymorphic DNA‐polymerase chain reaction analysis), but several biotypes of this species coexisted and colonized the sourdough.

Isolation of Hop-Sensitive Variants from Beer-Spoilage Lactobacillus Brevis Strains

To elucidate the mechanisms underlying the hop-resistance ability of beer-spoilage lactic acid bacteria, we attempted to isolate hop-sensitive variants from beer-spoilage Lactobacillus brevis. As a result, the repeated subcultures at 37°C were found to cause the hop resistance of six beer-spoilage L. brevis strains to be lost. In contrast to the wild-type strains, the hop-resistance ability of these variants was no longer inducible, as indicated by the inability to grow in DeMan-Rogosa-Sharpe (MRS) media supplemented with progressively higher concentrations of hop compounds. The diminished adaptability to hop compounds was comparable with that of the originally non-spoilage L. brevis strain, JCM1059T. When the variants were inoculated in beer and incubated anaerobically at 25°C, the viability of the strains was lost within one week, whereas the wild-type strains were able to grow during the same period of incubation. From these observations, it has been concluded that the variants obtained in this study lost the beer-spoilage ability. The biochemical characterization of the variants revealed narrower carbohydrate utilization profiles in some of the strains, notably with regard to the ability to ferment maltose.

A survey on yeast microbiota associated with an Italian traditional sweet-leavened baked good fermentation

Eighty-six yeasts were isolated from samples collected during the productive process of Colomba, an Italian traditional sweet-leavened baked good. They were characterised by phenotypic methods and rapidly identified by RAPD-PCR as Candida milleri and Saccharomyces cerevisiae. Cluster analysis of RAPD-PCR profiles indicated a considerable polymorphism among the isolates. Analysis of fermentation products and sugars revealed high amounts of acetic acid and mannitol after the sourdough fermentation. C. milleri is the dominant species in the sourdough. It is not able to ferment maltose and grows fermenting the glucose released by heterofermentative lactic acid bacteria and supply the bacteria of an electron source (fructose) which increases their cell yield and acetic acid production. This strict cooperation evidenced between lactic acid bacteria and yeasts has important technological and organoleptic consequences. The increased production of acetic acid improves the qualitative characteristics of the leavened dough and of the baked product.

Regulation of Saccharomyces cerevisiae maltose fermentation by cold temperature and CSF1

Foi estudado o efeito da baixa temperatura (10oC) na fermentacao de maltose por uma cepa de S. cerevisiae selvagem, e uma cepa csf1D mutante incapaz de transportar glicose e leucina a baixas temperaturas. A baixa temperatura afeta a cinetica da fermentacao por diminuir a velocidade de crescimento e rendimento celular final, com quase nenhum etanol produzido a partir de maltose pelas celulas selvagems a 10oC. A cepa csf1D foi incapaz de crescer em maltose a 10oC, indicando que o gene CSF1 e tambem necessario para a utilizacao de maltose a baixas temperaturas. Entretanto, o mutante tambem mostrou inibicao acentuada da fermentacao de glicose e maltose por estresse salino, indicando que CSF1 tambem estaria envolvido na regulacao de outros processos fisiologicos, incluindo a homeostase ionica.

Phenotypic and genotypic characterization of provisional serotype Shigella flexneri 1c and clonal relationships with 1a and 1b strains isolated in Bangladesh.

The serotypes of 144 strains of Shigella flexneri serotype 1 (serotypes 1a, 1b, and 1c) isolated from patients attending the Dhaka treatment center of the International Centre for Diarrhoeal Disease Research, Bangladesh, between 1997 and 2001 were serologically confirmed by using commercially available antisera and a panel of monoclonal antibodies specific for S. flexneri group and type factor antigen (MASF). Among serotype 1 isolates, the prevalence of provisional serotype S. flexneri 1c increased from 0 to 56% from 1978 to 2001 in Bangladesh. Detailed biochemical studies revealed that none of the strains of serotype 1 produced indole, while all the strains fermented mannose, mannitol, and trehalose. Twenty percent of the serotype 1c and all the serotype 1a strains fermented maltose and 53% of the serotype 1c strains and 60% of the serotype 1a strains fermented arabinose, whereas all serotype 1b strains were negative for fermentation of these sugars. Only 18% of serotype 1b strains were resistant to nalidixic acid, and most of the serotype 1c and 1b strains were resistant to ampicillin, tetracycline, and trimethoprim-sulfamethoxazole. All the strains of serotypes 1a and 1b and about 88% of the serotype 1c strains were found to be invasive by the Sereny test, had a 140-MDa plasmid, and had Congo red absorption ability. Plasmid profile analysis showed that 26% of the strains of serotype 1 contained identical patterns. Most of the serotype 1c strains (72%) had the 1.6-MDa plasmid, which was not found in either serotype 1a or 1b strains. A self-transmissible middle-range plasmid (35 to 80 MDa) was found in some strains carrying the multiple-antibiotic-resistance gene. Pulsed-field gel electrophoresis analysis yielded three types (types A, B, and C) with numerous subtypes among the serotype 1c strains, whereas serotypes 1b and 1a yielded only one type for each serotype, and those types were related to the types for serotype 1c strains. Ribotyping analysis yielded three patterns for serotype 1c strains and one pattern each for serotype 1a and 1b strains which were similar to the patterns for the serotype 1c strains. Overall analysis of the results concluded that subserotype 1c is closely related to serotypes 1a and 1b. Furthermore, the high rate of prevalence of serotype 1c necessitates the commercial production of antibody against this subserotype to allow the determination of the actual burden of shigellosis caused by provisional serotype 1c.

α-グルコシダーゼを利用したビールの高濃度醸造 (第2報)

This paper describes the utilization of yeast that has a limited ability to ferment maltose for high gravity brewing. High gravity wort was successfully fermented with a sake yeast or a wine yeast using α-glucosidase with the yeast, regardless of the maltose assimilation capability of the yeast used. The finished beer brewed with sake yeast (K-14) in a 100-L pilot-scale batch using α-glucosidase produced a distinctive fruity flavor as found in premium quality sake (ginjyo-shu). This technique may lead to the creation of beers with new taste and aroma profiles.

The biodiversity of lactic acid bacteria in Greek traditional wheat sourdoughs is reflected in both composition and metabolite formation.

Lactic acid bacteria (LAB) were isolated from Greek traditional wheat sourdoughs manufactured without the addition of baker's yeast. Application of sodium dodecyl sulfate-polyacrylamide gel electrophoresis of total cell protein, randomly amplified polymorphic DNA-PCR, DNA-DNA hybridization, and 16S ribosomal DNA sequence analysis, in combination with physiological traits such as fructose fermentation and mannitol production, allowed us to classify the isolated bacteria into the species Lactobacillus sanfranciscensis, Lactobacillus brevis, Lactobacillus paralimentarius, and Weissella cibaria. This consortium seems to be unique for the Greek traditional wheat sourdoughs studied. Strains of the species W. cibaria have not been isolated from sourdoughs previously. No Lactobacillus pontis or Lactobacillus panis strains were found. An L. brevis-like isolate (ACA-DC 3411 t1) could not be identified properly and might be a new sourdough LAB species. In addition, fermentation capabilities associated with the LAB detected have been studied. During laboratory fermentations, all heterofermentative sourdough LAB strains produced lactic acid, acetic acid, and ethanol. Mannitol was produced from fructose that served as an additional electron acceptor. In addition to glucose, almost all of the LAB isolates fermented maltose, while fructose as the sole carbohydrate source was fermented by all sourdough LAB tested except L. sanfranciscensis. Two of the L. paralimentarius isolates tested did not ferment maltose; all strains were homofermentative. In the presence of both maltose and fructose in the medium, induction of hexokinase activity occurred in all sourdough LAB species mentioned above, explaining why no glucose accumulation was found extracellularly. No maltose phosphorylase activity was found either. These data produced a variable fermentation coefficient and a unique sourdough metabolite composition.

First Report of Pink Seed of Pea Caused by Erwinia rhapontici in the United States.

In March 2001, the USDA Federal Grain Inspection Service sent for analysis to USDA-ARS, Pullman, WA, 12 discolored seeds of field pea (Pisum sativum L.) from northeastern Montana. Symptoms consisted of pale pinkish brown-to-bright pink discoloration throughout the seed coat. Unlike the pink coloration resulting from application of pink pesticidal seed treatments, the coloration was permanent and could not be removed by extended washing. Ten discolored seeds were disinfested in 0.5% NaOCl for 1 to 2 min and rinsed in sterile distilled water. Five seeds were placed on malt extract agar amended with streptomycin sulfate and tetracycline hydrochloride at 50 mg per liter each, and five seeds were placed on nutrient broth yeast extract agar (NBY) (3) and incubated under ambient lab conditions. No organisms were isolated from peas on the antibiotic agar, but pale pink bacterial colonies were recovered from each of the five peas on NBY. The pink colonies were streaked for selection of single colonies, stored at 4°C, and revived for growth in shaken (120 rpm) NBY broth to optical density (OD) = 0.1 at 640 nm (≈108 CFU/ml). Three pea plants and one control plant were grown in the greenhouse until pods were sufficiently developed to be syringe-inoculated at the suture with 100 μl of bacterial culture. The experiment was repeated using a second bacterial isolate. In each experiment, pods on inoculated plants, but not the control plant, exhibited pale pinkish areas and later produced seeds discolored in shades of pink matching those from the original sample. Some symptomatic seeds were shriveled or aborted as well as discolored. Discolored seeds from the two experiments were plated to NBY and pale pinkish colonies were recovered as before, but no such colonies were recovered from the controls. Two isolates from the original sample and two recovered from the experimental inoculations were tested for anaerobic and aerobic growth using API 50 CHE and API 20 NE tests (bio Mérieux Vitek, Inc., Hazlewood, MO). Known strains of Erwinia rhapontici and E. rubrifaciens from the collection of Dennis Gross (Texas A&M University) were identically analyzed for comparison. All four isolates from pea were gram-negative, facultatively anaerobic, motile rod-shaped bacteria that produced a diffusible pink pigment on NBY. Tests indicated that these strains were E. rhapontici, because the results agreed with previously published data (1,2). Results with the known strain of E. rhapontici were congruent with those from the pea strains. The strain of E. rubrifaciens also produced a pink pigment on NBY, but unlike the other strains, it grew well at 37°C and was negative for acetoin production, nitrate reduction, esculin hydrolysis, and maltose, rhamnose, inositol, and melibiose fermentation and did not assimilate citrate aerobically. Pink seed of pea has been previously reported from Alberta, Canada (2).

Crosses between Saccharomyces cerevisiae and Saccharomyces bayanus generate fertile hybrids

Crossings between strains of Saccharomyces cerevisiae and Saccharomyces bayanus were carried out. Genetic, molecular and electrophoretic karyotyping data indicated that interspecific hybrids were obtained. The hybrid cells segregated “grande” and “petite” colonies, and the latter ranged between 20 and 50%; unlike “grande” colonies, “petite” colonies did not sporulate and did not ferment maltose. In the hybrids, the extent of sporulation varied between 10 and 20%; only very rare asci (around 10 −4) held viable ascospores. Clones from the viable ascospores sporulated and produced asci with viable ascospores able to give mating with spores from both hybrid derivatives and parental species. Fertile asci could derive from allotetraploid cells generated by endomitotic events in allodiploid cells, a mechanism that enables overcoming the species barrier between S. cerevisiae and S. bayanus.

Physiological function of the maltose operon regulator, MalR, in Lactococcus lactis

BackgroundMaltose metabolism is initiated by an ATP-dependent permease system in Lactococcus lactis. The subsequent degradation of intracellular maltose is performed by the concerted action of Pi-dependent maltose phosphorylase and β-phosphoglucomutase. In some Gram-positive bacteria, maltose metabolism is regulated by a maltose operon regulator (MalR), belonging to the LacI-GalR family of transcriptional regulators. A gene presumed to encode MalR has been found directly downstream the maltose phosphorylase-encoding gene, malP in L. lactis. The purpose of this study was to investigate the physiological role of the MalR protein in maltose metabolism in L. lactis.ResultsA L. lactis ssp. lactis mutant, TMB5004, deficient in the putative MalR protein, was physiologically characterised. The mutant was not able to ferment maltose, while its capability to grow on glucose as well as trehalose was not affected. The activity of maltose phosphorylase and β-phosphoglucomutase was not affected in the mutant. However, the specific maltose uptake rate in the wild type was, at its lowest, five times higher than in the mutant. This difference in maltose uptake increased as the maltose concentration in the assay was increased.ConclusionAccording to amino acid sequence similarities, the presumed MalR is a member of the LacI-GalR family of transcriptional regulators. Due to the suggested activating effect on maltose transport and absence of effect on the activities of maltose phosphorylase and β-phosphoglucomutase, MalR of L. lactis is considered rather as an activator than a repressor.

Corynebacterium freneyi sp. nov., alpha-glucosidase-positive strains related to Corynebacterium xerosis.

Three coryneform strains from clinical specimens were studied. They belonged to the genus Corynebacterium, since they had type IV cell walls containing corynemycolic acids. They had phenotypic characteristics that included alpha-glucosidase, pyrazinamidase and alkaline phosphatase activities and fermentation of glucose, ribose, maltose and sucrose. These are the characteristics of Corynebacterium xerosis. Since this species is very rare in human pathology, the strains were studied in more detail by comparing the 16S-23S intergenic spacers, rDNA sequences and levels of DNA similarity of these three strains and those of the reference strains C. xerosis ATCC 373T and Corynebacterium amycolatum CIP 103452T. According to DNA-DNA hybridization data, the three novel strains are members of the same species (level of DNA similarity >72%). Phylogenetic analysis revealed that these strains are closely related to C. xerosis and C. amycolatum, but DNA-relatedness experiments showed clearly that they constitute a distinct new species, with levels of DNA relatedness of less than 23% to C. xerosis ATCC 373T and less than 5% to C. amycolatum CIP 103452T. Two other alpha-glucosidase-positive strains presenting the same biochemical characteristics were included in the study and proved to be C. amycolatum. This new species can be differentiated from C. xerosis and C. amycolatum strains by carbon source utilization, intergenic spacer region length profiles and some biochemical characteristics such as glucose fermentation at 42 degrees C and growth at 20 degrees C. The name Corynebacterium freneyi sp. nov. is proposed with the type strain ISPB 6695110T (= CIP 106767T = DSM 44506T).

Effect of different cultivation conditions on Lactobacillus manihotivorans OND32 T, an amylolytic lactobacillus isolated from sour starch cassava fermentation

Study of the cassava sour starch fermentation has led to the isolation of a new homofermentative amylolytic lactic acid bacterium, Lactobacillus manihotivorans OND32 T, whose nutritional requirements have been investigated in this work. The main effect of deleting one of the substrate components of the MRS-starch medium was to reduce the amylase production. When starch fermentation with nitrogen as a gas phase was compared to fermentation under aerobic conditions, both growth and amylase production were reduced whereas lactic acid formation was not affected. Addition of carbon dioxide (≥20% v/v) to the nitrogen gas phase restored growth and amylase production. The amylase production was high with starch, maltose or cellobiose contrary to glucose, fructose and sucrose. During mixed fermentation of glucose and maltose, a diauxic growth was observed. The maltose consumption and the amylase production started after the glucose depletion. The presence of maltose altered the carbon assimilation from glucose, whereas the energetic pathway was not affected. It is concluded that the elimination of soluble sugars by the wet extraction of starch during the processing of cassava, together with the expected in situ CO 2 production, are conditions favouring the growth and the amylase synthesis. However, these are likely to be limited by the low nitrogen content in cassava.

Comparison of fermentative capacities of industrial baking and wild-type yeasts of the species Saccharomyces cerevisiae in different sugar media.

To compare the fermentative capacity of wild and domesticated isolates of the genus Saccharomyces. The fermentative capacity of yeasts from a variety of wild and domesticated sources was tested in synthetic dough media that mimic major bread dough types. Domesticated yeast strains were found to have better maltose-utilizing capacity than wild yeast strains. The capacity to ferment sugars under high osmotic stress was randomly distributed amongst wild and baking strains of Saccharomyces. The domestication of bakers' yeast has enhanced the ability of yeasts to ferment maltose, without a similar impact on the fermentative capacity under high osmotic conditions. This study, combined with molecular studies of both wild and domesticated yeast, showed that domestication of bakers' yeast has resulted in improved maltose utilization, apparently via the duplication and mutation of the MAL genes.