Evolution of fermenting microbiota in tarhana produced under controlled technological conditions

The purpose of this study was to evaluate the evolution of lactic acid bacteria (LAB) and yeasts during the fermentation of tarhana produced with some pasteurised ingredients and carried out at 30 and 40 °C. The chemical parameters were those typical for tarhana production. Coliform bacteria were not detected during fermentation, while LAB and yeasts were in the range 10⁷-10⁸ colony forming units (CFU) g⁻¹. Plate counts showed an optimal development of both fermenting microbial groups and the differences in cell concentrations were not significant (P > 0.05). LAB were isolated during fermentation and grouped on the basis of phenotypic and polymorphic characteristics. LAB isolates were identified by a combined genetic approach consisting of 16S/23S rRNA intergenic spacer region (ITS) and partial 16S rRNA gene sequencing as Pediococcus acidilactici, Lactobacillus plantarum and Lactobacillus brevis. Hence, the pasteurisation of the vegetable ingredients, excluded wheat flour, enhanced the hygienic conditions of tarhana without influencing the normal evolution of LAB. However, the fermentation at 40 °C favoured pediococci, while the production at 30 °C was mainly characterised by lactobacilli. Yeasts, identified by the restriction fragment length polymorphism (RFLP) of the 5.8S ITS rRNA gene, were mainly represented by the species Saccharomyces cerevisiae in both productions.     

Microbiological changes and their impact on quality characteristics of red hot chilli pepper mash during natural fermentation

Production of hot sauce may require fermentation of red hot pepper mash in barrels from 2 weeks up to 3 years. The purpose of this study was to evaluate the microbiological changes and their impact on quality characteristics of red hot pepper mash during natural fermentation over a period of 18 months. Aerobic plate count (APC), lactic acid bacteria (LAB) and yeast counts, as well as changes in pH, acid content, colour and aroma of red hot pepper mash, were analysed. LAB and yeast presented a symbiotic association throughout the fermentation process. Significant pH reduction was observed, with an inverse correlation with acid content. There were minor changes in the colour of the mash. Aroma was analysed based on six volatile compounds which had a significant increase during the first 60 days of fermentation, followed by a significant reduction after 300 days.     

Optimum conditions for combined application of Leuconostoc sp. and Saccharomyces sp. to sourdough

Investigation of the optimum conditions for the combined application of Saccharomyces sp. (yeast) and Leuconostoc sp. (lactic acid bacteria, LAB) isolated in a previous study to the development of novel sourdough was carried out by response surface analysis. First, the cell growth conditions were analyzed. LAB showed good proliferation under conditions of 30–35°C, low pH, and high acidity, whereas the growth of yeast was inhibited. The growth of yeast was optimum at 25°C for 24 h. Based on these results, analysis of sourdough was carried out by varying the LAB population, temperature, and time after fixing the number of yeast. It was determined by response surface analysis that the optimal conditions for fermentation are LAB population of 10⁵ CFU/mL, temperature of 25°C, and reaction time of 24 h. From these results, the growth of LAB should be constantly maintained, and an appropriate pH that does not inhibit the growth of yeast due to the presence of generated organic acid is required to allow for the unique properties of sourdough. This study could give useful information for the development of novel sourdough.     

高产植酸酶乳酸菌及其黑豆酸面团发酵低植酸营养面包研究

从自然发酵的黑豆中筛选出一株具有高植酸酶活性的乳酸菌L-19并将其作为发酵剂制作黑豆酸面团。通过响应面分析法对黑豆酸面团的发酵工艺进行优化,探究最佳发酵条件下目标菌株的生长及产酸特性,并分析体系中多肽的分子量分布及抗营养因子含量变化,同时以感官品评的方式对黑豆酸面团面包的烘焙特性进行评价。结果表明:乳酸菌L-19经鉴定为乳酸片球菌(Pediococcus acidilactici),其胞外酶与胞内酶活性分别为1.36,0.30 U/mL。通过响应面设计确定的最优发酵条件为面团得率(DY)300、发酵温度37℃、接种量8%,黑豆基质中,目标菌株生长良好、酸化能力适中。黑豆酸面团经发酵后,体系中的多种抗营养因子得到有效降解,其中植酸降解率高达62.70%。此外,黑豆蛋白水解后释放出多种肽,其中小分子肽占比达51.47%。与对照组相比,L-19黑豆酸面团面包表现出更高的整体可接受度。因此,乳酸片球菌L-19能够有效改善黑豆酸面团面包的营养及感官品质,具有较佳的应用潜力。     

Prevalence and impact of single-strain starter cultures of lactic acid bacteria on metabolite formation in sourdough

Flavour of type II sourdoughs is influenced by the ingredients, processing conditions, and starter culture composition. It is, however, not fully clear to what extent different sourdough lactic acid bacteria (LAB) contribute to flavour. Therefore, two types of flour (rye and wheat) and different LAB starter culture strains were used to prepare sourdoughs, thereby leaving the yeast microbiota uncontrolled. All LAB starter culture strains tested were shown to be prevalent and to acidify the flour/water mixture to pH values between 3.1 and 3.9 after 24 h of fermentation. Multiple aldehydes, alcohols, ketones, and carboxylic acids were produced by the sourdough-associated microbiota throughout the fermentation period. Based on the organoleptic evaluation of breads produced with these sourdoughs, five LAB strains were selected to perform prolonged wheat and rye fermentations as to their capacity to result in an acidic (Lactobacillus fermentum IMDO 130101, Lactobacillus plantarum IMDO 130201, and Lactobacillus crustorum LMG 23699), buttermilk-like (Lactobacillus amylovorus DCE 471), or fruity flavour (Lactobacillus sakei CG1). Upon prolonged fermentation, higher metabolite concentrations were produced. For instance, L. sakei CG1 produced the highest amounts of 3-methyl-1-butanol, which was further converted into 3-methylbutyl acetate. The latter compound resulted in a fruity banana flavour after 48 h of fermentation, probably due to yeast interference. Rye fermentations resulted in sourdoughs richer in volatiles than wheat, including 3-methyl-1-butanol, 2-phenylethanol, and ethyl acetate.     

Diversity of bacteria and yeast in the naturally fermented cotton seed and rice beverage produced by Brazilian Amerindians

Microorganisms associated with the fermentation of cotton seed and rice were studied using a combination of culture-dependent and -independent methods. Samples of the cotton seed and rice beverage were collected every 8 h during the fermentation process for analysis of the microbiota present over 48 h. The lactic acid bacteria (LAB) population reached values of approximately 8.0 log cfu/mL. A total of 162 bacteria and 81 yeast isolates were identified using polyphasic methods. LAB (Lactobacillus plantarum, Lactobacillus vermiforme, Lactobacillus paracasei) were the most frequently isolated bacteria. Bacillus subtilis was present from 16 h until the end of the fermentation process. A decrease in pH value from 6.92 (0 h) to 4.76 (48 h) was observed, and the concentration of lactic acid reached 24 g/L at the end of the fermentation process. DGGE (denaturing gradient gel electrophoresis) was performed to determine the dynamics of the communities of bacteria and yeast, and the analysis revealed a predominance of LAB throughout the fermentation process. No changes were observed in the yeast community. The yeast species detected were Candida parapsilosis, Candida orthopsilosis, Clavispora lusitaniae and Rhodotorula mucilaginosa. Our studies indicate that the DGGE technique combined with a culture-dependent method is required to discern the dynamics in the fermentation of cotton seed and rice.     

Influence of technological conditions of sausage fermentation on the aminogenic activity of L. curvatus CTC273

The influence of technological factors (temperature and relative humidity of the manufacturing process and the diameter of the sausage) on the aminogenic activity of the strain Lactobacillus curvatus CTC273 was evaluated. Inoculation of sausages with L. curvatus CTC273 resulted in the accumulation of large amounts of biogenic amines (higher than 1000 mg/kg dry matter in some samples) during the manufacture of fuet and llonganissa sausages. Sausages produced via process ‘A’ (3 days at 20-23 °C and 90-95% RH followed by 20 days at 12-14 °C and 70% RH) contained significantly higher amounts (p < 0.05) of biogenic amines than those manufactured via process ‘B’ (23 days at 12-13 °C and 70-90% RH), specifically tyramine, cadaverine and phenylethylamine in llonganissa and phenylethylamine in fuet. The higher fermentation temperature and relative humidity during the fermentation stage in process ‘A’ promoted decarboxylase activity in L. curvatus CTC273 and thus favoured amine accumulation. The diameter of the sausages also influenced biogenic amine production. Higher amine levels were found (p < 0.05) in llonganissa than in fuet, regardless of the manufacturing conditions. The effect of the factors considered on the modulation of aminogenic activity is not necessarily linked to the effect of strain growth, but chiefly favouring proteolytic and decarboxylase reactions.     

融合魏斯氏菌和异常威克汉姆酵母混菌发酵荞麦酸面团馒头的香气物质特征

应用分离自我国酒鬼酒曲中的融合魏斯氏菌和梅兰春酒醅中的异常威克汉姆酵母进行混菌发酵,通过测定菌株生长曲线探索两株菌的共生作用,采用固相微萃取结合气质联用(SPME-GC-MS)和气相电子鼻技术,对比混菌发酵酸面团(MBF)和单菌发酵酸面团及其荞麦馒头风味化合物的差异性。结果表明,在MBF中乳酸菌、酵母菌菌落数分别达到9.38 log CFU/g、8.51 log CFU/g,两株菌具有良好的共生关系。发酵后荞麦酸面团的主要特征风味物质为乙醇、乙酸、乙酸乙酯、乙偶姻和异戊醇。与酵母菌单菌发酵荞麦酸面团馒头相比,混菌发酵馒头中酯类物质相对含量从5.27%提高到9.53%,结合ROAV分析,混菌发酵荞麦馒头的风味强度明显高于单一乳酸发酵和单一酵母发酵,赋予馒头更浓郁的酒香和果香,感官评定证实其整体可接受度高于其他组。     

Efficiency of high hydrostatic pressure at 600 MPa against food-borne microorganisms by challenge tests on convenience meat products

The food-borne pathogens Listeria monocytogenes, Salmonella enterica, Staphylococcus aureus, Yersinia enterocolitica and Campylobacter jejuni, and the spoilage lactic acid bacteria (LAB), Escherichia coli and the yeast Debaryomyces hansenii were inoculated on slices of cooked ham, dry cured ham and marinated beef loin. During storage at 4 °C, L. monocytogenes and LAB increased up to 3.5 log units while the other species, unable to grow under refrigeration, continued at the spiking level. The application of a 600 MPa treatment effectively inactivated most of the microorganisms, the counts of which, except for LAB that increased in cooked ham and in beef loin, progressively decreased or maintained below the detection limit during the whole storage (120 days at 4 °C).     

Overview of Sourdough Technology: from Production to Marketing

Sourdough is a type of dough fermented by yeast and lactic acid bacteria (LAB) used as sponge dough in bread making. Sourdough may have four classifications according to the fermentation type and the technological process used. On sourdough type I, the fermentation of yeasts and LAB present in the flour occurs spontaneously whereas in type II, fermentation occurs after the inoculation of a starter culture. Type III is simply type II sourdough dehydrated and type IV is a mixture of type I and type II sourdough, produced on laboratory scale. With LAB’s growth during fermentation, pH decreases with subsequent hydrolysis of starch and protein, favoring the growth of yeasts. The yeast in turn, releases amino acids during autolysis, contributing to the growth of LAB. Due to this synergistic growth of LAB and yeasts, the products obtained from sourdough show more concentration of flavor, more elastic dough, and a longer shelf life than bread fermented only by yeast. Although, the benefits of this technology, using sourdough, is present just in a few countries, where it is also possible to obtain the dehydrated sourdough starters, for domestic use, in local supermarkets. Due to its fermentative process complexity, this paper presents updated information about the fabrication process of sourdough, main factors affecting this process, benefits of sourdough use for bakery products, and the varieties of dehydrated sourdough commercially available throughout the world.     

Evaluating the individual effects of temperature and salt on table olive related microorganisms

Statistical modelling techniques were used in the present study to assess the individual effects of temperature and NaCl concentration on the growth of 10 lactic acid bacteria and 6 yeast strains mostly isolated from different forms of table olive processing and belonging to the species Lactobacillus pentosus, Lactobacillus plantarum, Saccharomyces cerevisiae, Wickerhamomyces anomalus and Candida boidinii. The mathematical models obtained in synthetic laboratory media show that yeasts, except for C. boidinii, were more resistant to a high salt concentration than lactic acid bacteria, with an MIC value ranging from 163.5 (S. cerevisiae) to 166.9 g/L (W. anomalus); while for L. pentosus and L. plantarum this parameter ranged from 110.6 to 117.6 g/L, respectively. With regards to temperature, lactic acid bacteria showed a slight trend towards supporting higher temperature values than yeasts, with the exception of S. cerevisiae. The maximum temperatures for growth of L. pentosus and L. plantarum were 41.9 and 43.0 °C, respectively; while for W. anomalus and C. boidinii they were 38.2 and 36.5 °C. The optimum temperatures for growth were also higher for L. pentosus and L. plantarum (35.5 and 32.9 °C), compared to W. anomalus and C. boidinii (29.3 and 26.9 °C, respectively). Additional experiments carried out in natural olive brines confirmed previous results, showing that high NaCl concentrations clearly favoured yeast growth and that at high temperatures LAB slightly overcame yeasts. Results obtained in this paper could be useful for industry for a better control of both table olive fermentation and packaging.     

Effect of sourdough at different concentrations on quality and shelf life of bread

The objective of this work was to study the effect of sourdough obtained with selected exopolysaccharide (EPS)-producing lactic acid bacteria (LAB) strains on the quality of bread and its shelf life. Two sourdough concentrations were used in order to ascertain the best bread composition. Fresh bread quality was studied by means of microbiological, physical, chemical and mechanical analysis, whereas physical, thermal and mechanical properties were investigated to study the product shelf life. The results showed that dough prepared with 30 g/100 g of sourdough had a negative impact on bread quality properties in the absence of EPS-producing LAB strains, whereas the opposite was observed in the presence of EPS-producing strains: bread samples at 30 g/100 g of sourdough showed higher volume, higher moisture content and better mechanical properties during storage than samples at 20 g/100 g of sourdough. Moreover, 30 g/100 g of sourdough showed a protective effect on bread staling, thus confirming the effect of sourdough concentration and the positive role of EPS on functional properties.     

Optimization of sourdough process for improved sensory profile and texture of wheat bread

The aim of the study was to determine optimum sourdough process conditions for improved flavour and texture of wheat bread. The influence of process conditions and the starter culture on the characteristics of wheat sourdough bread was established by using response surface methodology. Influence of fermentation temperature (16-32 °C), ash content of flour (0.6-1.8 g/100 g), and fermentation time (6-20 h) were considered as independent factors and their effects were studied in sourdough bread fermented with Lactobacillus plantarum, Lactobacillus brevis, Saccharomyces cerevisiae or with a combination of yeast and lactic acid bacteria. Intensity of sensory attributes, specific volume and bread hardness were considered as the main responses. Ash content of flour and fermentation time were the main factors determining the intensity of sensory attributes. The possibility to enhance intensity of overall flavour, aftertaste and roasted flavour without excessive pungent flavour and without reduced fresh flavour in wheat bread containing 20 g sourdough/100 g of wheat dough was demonstrated by choosing e.g. Lb. brevis for a starter and by utilization of high ash content of flour, long fermentation time and reduced temperature. Bread specific volume was improved 0.2-0.5 ml/g and hardness was reduced (after 4 days of storage) up to 260 g by using low ash content of flour and by optimizing fermentation time according to the microbial strain. Lactic acid fermentation had more profound influence on both desired and undesired flavour attributes, as well as textural features of bread in comparison with yeast fermentation.     

Carbohydrate metabolic conversions to lactic acid and volatile derivatives, as influenced by Lactobacillus plantarum ATCC 8014 and Lactobacillus casei ATCC 393 efficiency during in vitro and sourdough fermentation

The use of sourdough returned to be popular due to its beneficial nutritional, sensorial properties and physical features. In this study, two types of experiments aimed to evaluate comparatively the efficiency of two Lactobacillus (Lb.) strains, Lactobacillus plantarum ATCC 8014 and Lactobacilus casei ATCC 393, to metabolize different carbohydrates (glucose, fructose, maltose and sucrose) in vitro and to compare their efficiency, combined with/without Saccharomyces cerevisiae on sourdough fermentation. Their efficiency was monitored by cellular growth dynamics, pH values and metabolite production (lactic and acetic acid, volatile derivatives) determined by HPLC and GC–MS analysis. Lb. plantarum ATCC 8014 was, generally, more efficient than Lb. casei for carbohydrate consumption in vitro and release of lactic acid. Unexpected, Lb. casei was able to produce trehalose in vitro, especially when glucose and sucrose were added in media. During sourdough fermentation, Lb. plantarum had a superior growth dynamic and a dominant nonaerobic fermentation, opposite to Lb. casei. By the addition of yeast to lactobacilli after a short-time lactic fermentation, a combined nonaerobic and aerobic fermentation was noticed, reflected by a more complex mixture of volatile derivatives. In vitro, both Lb. strains produced seven volatile compounds (carbonyl derivatives), but during sourdough fermentation, especially after yeast addition, a complex mixture of alcohols, carbonyl derivatives and acetate esters were determined. Lb. strains (especially Lb. plantarum) determined a moderate volatiles production dominated by alcohols, while addition of yeast to Lb. intensified the volatiles’ production and increase the alcohols proportion against carbonyl derivatives.     

New Procedure for the Detection of Lactic Acid Bacteria in Vegetables Producing Antibacterial Substances

There is an increasing interest in antibacterial-producing lactic acid bacteria (LAB) as protective cultures on ready-to-use vegetables. A new procedure for detection of active strains has been developed, which consisted of anaerobic incubation (30 °C, 2 d) of juice of ‘i ceberglettuce’ on MRS agar or lactose-bromcresol purple (LBP) agar followed by overlaying with the indicator strain in soft agar (7.5 g/L). After overnight incubation at appropriate temperature, the plates were examined for clear inhibition zone around the colonies. The developed procedure permitted the detection of active LAB in 3 d compared with several weeks for the traditional procedure. The use of LBP agar in conjunction with incubation of plates at 8 °C may give additional information about the nonacidic characteristic of antibacterial substances secreted, and also about the psychrotrophic behavior of producer strains, which could be of interest as biocontrol cultures to improve the safety of ready-to-use vegetables commonly stored under refrigeration.     

Factors affecting growth of foodborne pathogens on minimally processed apples

Escherichia coli O157:H7, Salmonella and Listeria innocua increased by more than 2 log₁₀ units over a 24 h period on fresh-cut ‘Golden Delicious’ apple plugs stored at 25 and 20 °C. L. innocua reached the same final population level at 10 °C meanwhile E. coli and Salmonella only increased 1.3 log₁₀ units after 6 days. Only L. innocua was able to grow at 5 °C. No significant differences were observed between the growth of foodborne pathogens on fresh-cut ‘Golden Delicious’, ‘Granny Smith’ and ‘Shampion’ apples stored at 25 and 5 °C. The treatment of ‘Golden Delicious’ and ‘Granny Smith’ apple plugs with the antioxidants, ascorbic acid (2%) and NatureSeal^® (6%), did not affect pathogen growth. The effect of passive modified atmosphere packaging (MAP) on the growth of E. coli, Salmonella and L. innocua on ‘Golden Delicious’ apple slices was also tested. There were no significant differences in growth of pathogens in MAP conditions compared with air packaging of ‘Golden Delicious’ apple plugs, but the growth of mesophilic and psychrotrophic microorganisms was inhibited. These results highlight the importance of avoiding contamination of fresh-cut fruit with foodborne pathogens and the maintenance of the cold chain during storage until consumption.     

Application of whey of Mozzarella di Bufala Campana fermented by lactic acid bacteria as a bread biopreservative agent

A total of nine isolated lactic acid bacteria (LAB) from tomato and sourdough with antifungal activity were employed to revaluate the whey of Mozzarella di Bufala through the fermentation process for 72 h at 37 °C. Then, the fermented whey (BWF) was characterised and used as biopreservative in bread formulation. L. plantarum TR7 and L. plantarum TR2 strains showed average lactic acid concentration in BWF of 13.8 g L⁻¹. Also, the bread volatile organic compounds (VOC) analysis showed an increase in hexanal, benzeneacetaldehyde, benzaldehyde and pyrazine tetramethyl when using BWF as ingredient. Moreover, the DPPH-inhibitory activity of bread with BWF extract also reflected a 33% rise in comparison with control bread. The application of BWF as a biopreservation agent in bread showed an increase in shelf life compared with bread with 0.3% calcium propionate and bread control for 2 and 15 days, respectively. BWF can be used as an interesting biopreservation strategy of bread.     

酸面团中的微生物群落及发酵过程中的代谢反应

酸面团在发酵面食中起着非常重要的作用,本文对酸面团中的微生物群落、发酵过程中乳酸菌的代谢途径、碳水化合物和含氮化合物的代谢、胞外多糖和挥发性物质等代谢产物进行了综述,以期为今后酸面团的综合应用提供基础。      

A comparison of the physicochemical, microbiological and aromatic composition of Traditional and Industrial Leben in Tunisia

Traditional Tunisian Leben (TL) was produced according to the traditional method. Physicochemical and microbiological characteristics and major aromatic compounds were studied and compared to industrial Leben (IL) and experimental Leben (EL). The results show a decrease in lactose content and pH value and an increase in lactic acid during spontaneous fermentation. TL and EL were characterised by higher protein, lactose and ash contents but were less fatty and acidic than IL. Lactic acid bacteria (LAB) and yeasts present in TL were responsible for lactic acid fermentation and aroma development. The LAB and yeast counts in TL were higher than that in EL and IL. Dynamic headspace extraction procedure shows the existence of four major volatile compounds: acetaldehyde, ethanol, diacetyl and acetoin in TL, IL and EL. However, TL has the most important quantity of aroma.