Bread making with Saccharomyces cerevisiae CEN.PK113‐5D expressing lipase A from Bacillus subtilis: leavening characterisation and aroma enhancement

Lipase A from Bacillus subtilis was expressed in the yeast Saccharomyces cerevisiae CEN.PK113‐5D strain as a cell wall‐immobilised enzyme. The recombinant yeast was used in bread making to test the effect of lipase A on the bread properties such as rheological and aromatic properties. The results were compared to the not transformed strain and the commercial baker's yeast. The recombinant strain resulted a good leavening agent comparable to the commercial baker's yeasts provided 1% sucrose was added to the dough. Whereas, during the leavening, the trend of the rheological properties (cohesivness, gumminess and rigidity) differed from the commercial and the nontransformed (NT) strains. Moreover, using of the recombinant strain enhanced total aroma which achieved in the baked product a value of 9 μg per g_product vs the 4 and 5 μg per g_product of the NT strain and the commercial baker's yeast, respectively. To our knowledge, this is the first time that a bacterial lipase is used in bread making.     

不同酵母在发酵面制品中的应用研究

为研究典型市售面用酵母发酵特性,并使其在发酵面制品(面包、馒头)中发挥最佳作用,采用均匀设计,将以发酵面制品比容和粗细气孔比为主要依据得到的感官评分为评价指标,分别获得了8种不同酵母用于发酵面制品制备的最佳工艺参数。在面包制作中,最佳工艺条件下四个品种低糖酵母组AL、BL、CL、DL感官评分为91、89、91. 5、94;四个品种高糖酵母组AH、BH、CH、DH感官评分为96、95、93、95。在馒头制作中,最佳工艺条件下四个品种低糖酵母组AL、BL、CL、DL感官评分为96、91、94.5、95.5;四个品种高糖酵母组AH、BH、CH、DH感官评分为96、98、92.5、92。该结果表明,不同品种的酵母存在质量差异,但在优化的工艺参数条件下,低糖、高糖酵母均能够制备获得质量较好的发酵面制品。同时,由于糖含量引起渗透压的变化,高糖酵母对高渗透压的耐受性较强,而低糖酵母在高渗透压下生长会受到抑制。实验中,面包相对馒头而言添加了较多糖分,因而低糖酵母应用在面包中的整体评分低于高糖酵母,应用在馒头中的整体评分与高糖酵母相当。该研究可为制备发酵面食中合理选择酵母,并发挥酵母的最佳功效提供技术参考。     

Dough-leavening by Zymomonas mobilis and Its Application to Breadmaking

Among five strains of Zymomonas mobilis strain Z6C had the highest leavening ability in doughs containing either glucose or sucrose. Z6C most efficiently leavened the dough when it contained 5% sucrose, and this leavening ability was twice as much as that of commercial compressed yeast. At the same concentrations of NaCl, the leavening ability of Z6C was reduced more than that of baker's yeast. When comparing baked goods made with yeast, those made with Z6C had similar specific volumes, but Z6C baked goods had slight acidic flavor. Chromatographic analysis of head-space gas of yeast-leavened bread showed that two chemicals appearing in Z6C leavened bread were missing.     

Reliability of Listeria monocytogenes Identification by Specific PCR Assessed by Phenotypic and Genotypic Techniques

This study evaluates the possibility of using polymerase chain reaction (PCR) for rapid identification of food-borne Listeria monocytogenes as an alternative to API Listeria system and estimates the incidence of API Listeria misidentifications in food-borne Listeria species. A total of 198 strains, 11 L. monocytogenes, 28 other Listeria species, and 159 food isolates were phenotypically and genotypically characterized by API Listeria profiles and randomly amplified polymorphic DNA (RAPD) profiles, respectively. They were also tested for PCR amplification using genus- and species-specific primers. Clustering analysis of phenotypic and genotypic data showed discrepancies in species identification of some isolates by API Listeria profiles. Their identities were confirmed by 16S rDNA sequencing, and thus, it was revealed that 33% of Listeria innocua and 19% of Listeria welshimeri were misidentified as L. monocytogenes by API Listeria profiles. Reliable identification of L. monocytogenes was obtained by LM1–LM2 specific primers which allowed PCR amplification only in reference strains and isolates previously identified as L. monocytogenes by RAPD and 16S rDNA sequence analysis. These results corroborate the suitability of specific PCR as a rapid and accurate test for the identification of L. monocytogenes, avoiding misidentification with other Listeria species commonly found in food products.     

Microbial re-inoculation reveals differences in the leavening power of sourdough yeast strains

A method based on microbial re-inoculation, or the so-called backslopping and subsequent proofing of rye bread dough simulating commercial one-stage sourdough process, was used for the screening of the leavening capacity of sourdough yeast strains. Two yeast strains were initially tested with seven Lactobacillus strains. Thereafter, 17 yeast strains, mostly of sourdough origin, were tested with a backslopping procedure with heterofermentative Lactobacillus brevis as an acidifying lactic acid bacteria (LAB). The highest leavening capacity was found in sourdoughs containing Candida milleri, in particular when it was accompanied by obligately homofermentative Lactobacillus acidophilus or facultatively heterofermentative Lactobacillus plantarum when it acted homofermentatively. The leavening capacity of the reference strain Saccharomyces cerevisiae was about half that of C. milleri in all sourdoughs tested. The re-inoculation procedure increased the differences found in the leavening capacity of the tested yeast strains during final proofing of rye bread dough. The backslopped sourdoughs containing a heterofermentative Lactobacillus strain were more suppressive than those containing a homofermentative strain. The highest leavening capacity was found in C. milleri strains. The use of one backslopping cycle before assaying the leavening capacity of a laboratory sourdough is recommended since it helps to differentiate between yeast strains to be tested for their leavening power in the final bread dough.     

Study of the behaviour of Lactobacillus plantarum and Leuconostoc starters during a complete wheat sourdough breadmaking process

The acidification properties, metabolic activity and technological performance of four individual Lactobacillus plantarum or Leuconostoc freeze-dried starters were investigated during a complete wheat sourdough breadmaking process including 0.2 g/100 g baker's yeast. Microbiological contents (lactic acid bacteria and yeasts), acidification characteristics (pH and total titratable acidity), soluble carbohydrates (maltose, glucose and fructose) and fermentative end-products (lactic and acetic acids, ethanol) contents were evaluated during both sourdough and corresponding bread dough fermentation. Biochemical and technological analysis of the resulting bread products are also presented. Some differences among strains in acidification properties and soluble carbohydrates availability were outlined both in sourdough and bread dough. Each individual Leuconostoc or Lb. plantarum starter was able to produce a characteristic fermentation and was found to ensure the production of breads with overall satisfactory acceptance.     

Sourdough fermentation as a tool for the manufacture of low-glycemic index white wheat bread enriched in dietary fibre

Three Lactobacillus strains were selected and used together as sourdough starter. Sourdough performances were evaluated for 30 days. Three breads were manufactured: wheat sourdough bread (WSB), WSB enriched with oat and rye fibres (WSB-DF) and wheat yeasted bread (WYB) fermented with baker’s yeast alone. WSB-DF and WSB showed higher specific volume and lower firmness than WYB. Sensory analysis showed that WSB-DF and WSB were preferred due to acidulous smell, taste and aroma. Compared to WYB and WSB, WSB-DF had high level of dietary fibre (DF). WYB was used as the control to estimate the hydrolysis index (HI = 100). WSB-DF had values of HI lower than WSB (59 vs. 86%). As estimated on 20 volunteers, the value of GI for WSB-DF was ca. 41%. WSB-DF bread manufactured at industrial plant combined low-GI with physiologically significant supply of DF and high standard structure and sensory features.     

Sourdough-isolated<Emphasis Type="Italic"> Lactobacillus fermentum</Emphasis> as a potent anti-mould preservative of a traditional Iranian bread

Sourdough bread is an ancient method for making long microbial shelf life and strongly flavoured breads. Traditional sourdough bread-making has been practised for centuries in Iran. Although rural bread-making is still highly reliant on sourdough, urban bakeries usually use bakers yeast and also sodium bicarbonate instead. In this study the anti-mould preservative effects of three lactic acid bacteria isolates were investigated on one of the popular traditional Iranian bread (Lavash). Starter cultures were prepared using 20 h cultures of three sourdough-isolated strains, Lactobacillus casei, Lactobacillus plantarum and Lactobacillus fermentum. Different concentrations (0.5%, 1%, 2%, 4% and 8%) of lactobacillus starter cultures were used to prepare a variety of sourdoughs. Lavash doughs were inoculated with 20% of each lactobacilli-fermented sourdough. After a 20 h incubation at 30 °C, a decrease in pH was observed in the different lactobacilli sourdoughs. However an 8% inoculum of L. fermentum resulted in a significant decrease in pH (3.87 to 2.70). Concentrations of 2% and higher of the three lactobacilli used in Lavash sourdough delayed mould growth during storage. However this preservative effect was more significant when an 8% inoculum of L. fermentum was used. These results tend to suggest that selected strains of lactobacilli have a beneficial role in prevention of bread waste by mould spoilage, and hence could extend bread shelf life.     

Effects of several starter cultures on the anti-mold activity and sensory attributes of a traditional flat bread (Sangak) from Iran

Effects of 8 different sourdoughs and their replacement levels at 10, 20, and 30%(w/w) on the volume (of dough), crust hardness, organoleptic, and anti-mold properties of Iranian sangak bread were investigated. Saccharomyces cerevisiae, Lactobacillus plantarum, Lactobacillus acidophilus, and Leuconostoc mesenteroides were selected for the preparation of sourdough samples. The highest dough volume was achieved when sourdough (those having S. cerevisiae) was used at 30%. The highest taste scores were found with the bread sample using the above-mentioned starters at 30% sourdough replacement level. Considering the chewing, appearance, and overall quality of the new products, most of the samples maintained the favorite sensory aspects of sangak bread. Use of lactic acid bacteria and yeast strains as part of the sourdough formulation (followed by the use of sourdough in the dough formulation) resulted in improved crust properties and greater anti-mold activities.     

Physicochemical Characterization and Sensory Analysis of Yeast‐leavened and Sourdough Soy Breads

Sourdough fermentation has been shown to have numerous beneficial effects on bread quality, and nutritionally enhance soy‐supplemented bread by altering isoflavone chemical forms. Given this, the objective of this study was to compare the loaf quality and shelf life of sourdough and yeast‐leavened soy breads by various physical, thermal, and sensorial methods, and to assess the effects of fermentation by various microorganisms on isoflavone profile in dough and breads using high‐performance liquid chromatography analysis. Sourdough fermentation yielded a less extensible dough compared to yeast‐leavened soy dough (P < 0.001), and resulted in a harder bread crumb (P < 0.05) and lighter crust color (P < 0.001), compared to yeast‐leavened soy bread (Y‐B). Sensory analysis revealed a significantly higher overall liking of Y‐B compared to sourdough soy bread (SD‐B) (P < 0.001). Segmentation analysis of the cohort suggests that overall liking and bread consumption frequency may be determinants of Y‐B or SD‐B preference. SD‐B and Y‐B exhibited similar shelf‐life properties. Despite significantly different enthalpies associated with the melting of amylose‐lipid complexes, thermal analysis of the 2 soy breads stored for 10 d (ambient conditions) demonstrated no significant difference in water distribution and starch retrogradation (P < 0.05). Lastly, SD‐B was determined to have 32% of total isoflavones occurring in the aglycone form compared to 17% in Y‐B. These findings warrant further investigation of sourdough fermentation as a processing technique for quality and nutritional enhancement of soy‐based baked goods.     

Microbiological,chemical and sensory aspects of bread supplemented with different percentages of the culinary mushroom Pleurotus eryngii in powder form

Pleurotus eryngii (DC.) Quél. powder was used in bread production. Three dough trials (0, 5 and 10% of mushroom) were obtained with commercial baker's yeast. P. eryngii powder was first tested against several yeast species; 10% P. eryngii trial was characterised by the highest pH and total titratable acidity. P. eryngii did not influence negatively the fermentation process, since all trials reached yeast levels of 10⁸ CFU g⁻¹. Mushroom powder decreased bread height and softness, increased crust redness and crumb void fraction and cell density and, although the breads were scored diverse, the overall assessment was comparable. The final breads provided higher concentrations of thiamin, riboflavin and pantothenic acid than control breads and, mostly importantly, supplied biotin, cobalamin and cholecalciferol generally absent in wheat bread. P. eryngii can be cultivated on food residues. Thus, its inclusion in functional bread production represents an optimal strategy for the valorisation of food processing by-products.     

Characterization and quantification of folates produced by yeast strains isolated from kefir granules

For the first time to our knowledge, distribution and content of individual folate forms in kefir yeast strains were investigated. This was done using a validated method based on reversed-phase high performance liquid chromatography (HPLC) with fluorescence and diode array (DAD) detection. Eight kefir yeast strains, belonging to different Candida and Saccharomyces species, were isolated from Russian kefir granules. They were grown in synthetic media at standardized conditions before analysis. The average folate content for these yeast strains was 10,780±550 μg/100 g dry matter. In all yeast strains tested, the most abundant folate forms as percentages were 5-methyltetrahydrofolate (43–59%), and 5-formyltetrahydrofolate (23–38%), whereas tetrahydrafolate occurred in a lesser proportion (19–23%).     

A new simplified AFLP method for wine yeast strain typing

A simplified method of AFLP (Amplified Fragment Length Polymorphisms) is presented for typing yeast present during wine fermentations. The changes introduced allowed analysis by gel electrophoresis and considerably reduced the need for equipment. Another remarkable improvement was the use of non-labelled primers which reduces the cost of the analysis. This method was applied to reference strains from culture collection to test the reliability of the technique. A total of 180 colonies isolated from a spontaneous fermentation were typed into eleven different strains of Hanseniaspora uvarum, six of Hanseniaspora vineae, four of Candida zemplinina, and eleven of Saccharomyces cerevisiae. This method is suitable for typing yeast strains for routine grape and wine ecology analysis.     

Evaluation of Image Analysis Tools for Characterization of Sweet Bread Crumb Structure

Many approaches to evaluate bread crumb features by applying free or at least not too expensive image analysis (IA) software have been published; however, the described procedures showed noticeable differences. The aim of this work was to compare different image scanning resolutions and thresholding techniques to quantify sweet bread crumb features (cell density, mean cell area, shape factor) and their relation with fractal dimension. Two sets of experiments were carried out, one to determine the effect of scanning resolution and thersholding method and the other to validate the previous results by evaluating breads with different crumb structures. Nine different scanning resolutions (75, 100, 150, 200, 300, 355, 435, 515, 555 dpi) and two segmentation procedures (Otsu and Manual) were tested. Three different types of commercial sweet breads and a yeasted sweet bread added with different concentrations (six, 12%) of Chia flour (Salvia hispanica) were evaluated. Results showed that the percentage of particles with areas between 0.1 and 4.0 mm² remained almost constant when using 350 dpi or larger resolution values, while the smallest particles (<0.1 mm²) increased their proportion up to 87% at the highest scanning resolution for both thresholding methods. IA was useful to detect crumb structure differences among commercial breads and breads added with Chia flour as obtained from cell density (154 ± 4.6–246 ± 2.5) and mean cell area (0.81 ± 0.02–0.7 ± 0.03) results. However, the number of selected objects to calculate these parameters produced different results. The addition of 6% of Chia flour did not affect the bread crumb features, while at the largest proportion more and smaller pores were obtained. Fractal texture was useful to evaluate bread crumb structure, as it not depends on the number of particles detected.     

蜂粮中Lactobacillus kunkeei的益生特性研究

蜂粮是植物花粉、蜂蜜和蜜蜂唾液的发酵混合物,是营养丰富的天然食材。作者从蜂粮中分离到61株乳酸杆菌,经16S rRNA基因测序,鉴定为Lactobacillus kunkeei。首先,用邻苯二甲醛法对61株L.kunkeei进行胆固醇去除能力检测,其中5株菌胆固醇去除能力均大于15%,菌株B35对胆固醇的去除率达到(29.07±1.30)%。随后,对这5株L.kunkeei进行酸耐受性、胆盐耐受性、抗生素耐药性及抑菌等益生特性进行研究。耐酸实验和耐胆盐实验结果表明,5株L.kunkeei均具有良好的耐酸性和胆盐耐受性。药敏试验结果表明,5株L.kunkeei对4种临床常用抗生素(红霉素、克林霉素、庆大霉素、万古霉素)均敏感。通过琼脂扩散法抑菌实验,发现5株L.kunkeei对大肠埃希氏菌、金黄色葡萄球菌均有一定的抑菌作用。B35菌株的细胞黏附性能良好,对Caco-2细胞的黏附率达到3.32%。从蜂粮中分离到5株具有良好益生特性的菌株,其中菌株B35的益生特性最佳,为益生菌的开发与利用提供了新的菌种资源。     

Bread Dough and Baker's Yeast: An Uplifting Synergy

Yeast‐mediated dough fermentation is an important phase in the bread making process. The fermentative performance of yeast cells during fermentation is of critical importance for final bread quality, since yeast cells produce CO₂ and other metabolites that have an influence on dough rheology and bread texture, volume, and taste. Different factors affect the fermentative performance of yeast cells during dough fermentation, including dough ingredients, fermentation conditions, the type of yeast strain used and yeast pregrowth conditions. Bread dough is a complex matrix that contains several ingredients that can affect the fermentation rate of yeast cells. Although the individual effects of sugar availability and salt level on the leavening ability of yeast have been studied extensively, a comprehensive overview of the relationship between bread dough constituents, fermentation conditions and yeast functionality is still lacking. Moreover, the dough environment is highly variable as several types of dough like lean, sweet or frozen doughs are currently produced by commercial bread producers. For optimal fermentation rates in different types of dough, the use of appropriate yeast strains with specific phenotypic traits is required. Therefore, many researchers have focused on the improvement of yeast strains for optimal fermentation in different types of dough like lean, sweet or frozen dough. Against this background, this review summarizes the current knowledge on the interaction between bread dough and baker's yeast and how to improve this interaction, thereby providing a useful background for further research concerning the functionality of yeast in bread dough.     

Effect of a single oral administration of Lactobacillus plantarum DSMZ 8862/8866 before and at the time point of weaning on intestinal microbial communities in piglets

The aim of this study was to evaluate whether a single administration of two strains of Lactobacillus plantarum (DSMZ 8862 and 8866) either before or at the time point of weaning can influence the intestinal microbiota of piglets. A total of 176 piglets were allocated into five groups: control (LP0), administration of 5 × 10⁹ or 5 × 10¹⁰ cfu at day 25 of life (LP1, LP2) and administration of 5 × 10⁹ or 5 × 10¹⁰ cfu at day 28 of life (LP3, LP4). Piglets were weaned on day 28 of life. On day 25 (LP1, LP2), 28 (LP0, LP3, LP4), 33 (all groups) and 39 (all groups) of life, 10–13 animals of each group were killed and genomic DNA was extracted from small and large intestinal contents. Denaturing gradient gel electrophoresis demonstrated that administration of L. plantarum had a significant effect in GIT microbial communities as revealed by the Simpson's index of diversity and cluster analysis based on the Dice similarity index; this effect was more pronounced in groups LP3 and LP4. A treatment dependent presence of Clostridium glycolicum-like, Lactobacillus sobrius-like, Eubacterium rectale-like and Roseburia faecalis-like phylotypes was observed. The results show that the administration of L. plantarum at the point of weaning can influence gastrointestinal microbiota in weaning piglets which may have positive results on gastrointestinal health.     

Bread crumb quality assessment: a plural physical approach

The aim of this study was the assessment of pan bread crumb quality attributes of commercial samples using a plural physical approach to better match consumer awareness. Static (texture profile analysis, firmness AACC and relaxation test) and dynamic (innovative oscillatory test) deformation techniques, image analysis, sensory analysis and colour measurements (colorimeter and Photoshop system) were used for white/whole commercial pan bread quality evaluation over 10 days of storage. Static (k ₁, k ₂, cohesiveness, springiness, hardness, chewiness and resilience) and dynamic (stress) bread crumb rheological properties were correlated illustrating that both techniques can be useful in evaluating crumb physical characteristics. In addition, sensory perceiveness with regard to softness and overall acceptability exhibited dependence with either dynamic stress or static firmness. Despite the fact that empirical measurements are closely linked to macroscopic features whilst dynamic tests are strongly linked to molecular characteristics, the obtained results support that both techniques are complementary since derived instrumental parameters are related to some sensory attributes. As data achieved using the proposed novel approaches might be better linked to the consumer awareness than those obtained from classical analyses, the obtained results are promising for a proper bread crumb quality assessment.     

Microbiological evaluation and molecular characterization of bifidobacteria strains in commercial fermented milks

The aim of this study was to evaluate the presence of Bifidobacterium animalis subsp. lactis in commercial dairy products using different molecular techniques. We analyzed the microbiological composition of 13 commercial fermented milks available in the Spanish market. Thirteen strains of genus Bifidobacterium were isolated from these products and were identified by genus-specific PCR, by fluorescence in situ hybridization (FISH), by multiplex PCR and amplified ribosomal DNA restriction analysis (ARDRA). The same sets of strains were typed by randomly amplified polymorphic DNA (RAPD) analysis and by amplified fragment length polymorphism technique (AFLP). All strains were identified as B. animalis subsp. lactis using ARDRA and multiplex PCR techniques. Similarity between strains was evaluated based on RAPD and AFLP profiles. The isolated strains showed similar profiles by using these techniques, revealing the reduced genetic variability existing among commercial strains, and all these profiles were reproducible in repeated analysis. ARDRA and multiplex PCR are techniques that allow differentiation of the bifidobacteria at genus and species level, but do not indicate if they are different strains, for which reason the RAPD technique is very useful. All bifidobacteria isolated from commercial fermented milks in Spain belong to the same species B. animalis subsp. lactis. Our results demonstrate the necessity to control the presence of bifidobacteria in commercial fermented milks, not only at species level but also at strain level. Multiplex PCR and RAPDs are the most suitable, rapid and precise techniques to identify all bifidobacteria contained in fermented milk products at genus-, species-, and strain levels.     

Yeasts isolated from New Zealand vineyards and wineries

Background and Aims: The yeast flora from a range of New Zealand commercial wineries was surveyed to estimate the incidence of yeast species in grape juice. Methods and Results: Molecular analysis of the internal transcribed spacer region was performed for 1279 yeast colonies isolated from 17 different fresh grape juices sampled in eight New Zealand wineries between 2003 and 2009. The 17 juices contained at least 25 different species of yeast from nine genera. Microsatellite fingerprinting of Saccharomyces cerevisiae showed that some strains were identical to known commercial yeast varieties, but we also found evidence for local populations of S. cerevisiae common to individual wineries or regions. Five genotypes from Central Otago, New Zealand, were very closely related to a single sequenced strain derived from Chile, which in turn is related to European wine isolates. Conclusions: The yeast flora found in New Zealand grape juices is broadly similar to that found in wineries elsewhere around the world. Genotyping of S. cerevisiae suggests recent dispersal of both commercial and non-commercial yeast strains from Europe to New Zealand. Significance of the Study: These data are consistent with two human-mediated modes for the international dispersal of S. cerevisiae: one via the escape of strains traded commercially, and another via long distance dispersal of non-commercial strains.