Browsing by Subject "LAB"

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  • Koort, Joanna; Coenye, Tom; Vandamme, Peter; Sukura, Antti; Björkroth, Johanna (Society for General Microbiology, 2004)
    Isolates 302, 334, 356, 377 and 379, detected in modified atmosphere packaged (MAP) broiler meat, together with LMG 12317T and LMG 13617, detected in dog tonsils, were analysed in a polyphasic taxonomy study including numerical analysis of ribopatterns and whole cell protein patterns, 16S rDNA sequence analysis, DNA-DNA hybridisation and determination of some phenotypic properties. The results indicated that these isolates represent a new species in the genus Enterococcus. The isolates showed classical phenotypic reactions for the genus Enterococcus with the exception of not possessing the Lancefield group D antigen. Isolates 334, LMG 12317T, and LMG 13617 showed the highest 16S rDNA sequence similarity (98.3-99.0%) with the Enterococcus pallens type strain. In the distance matrix tree based on 16S rDNA sequences, the three isolates were located in the Enterococcus avium –group with E. pallens as their closest phylogenic neighbour. Numerical analyses of whole cell protein patterns and HindIII/EcoRI ribotypes placed all seven isolates together in a single cluster separated from the E. avium group reference strains. The DNA-DNA hybridisation level between strains 334 and LMG 12317T was 93.5% confirming that they represent the same species. Low hybridisation levels (12-30%) were, on the other hand, obtained with the E. pallens and Enterococcus raffinosus type strains. The name Enterococcus hermanniensis sp. nov. is proposed, with strain LMG 12317T (=CCUG 48100 T) as the type strain.
  • Zhang, Yuetuan (Helsingin yliopisto, 2015)
    The literature review described the importance of folate enhancement to human health especially to coeliac patients with an introduction to folate analysis, pseudocereals and possible fortification methods. The aim of this study was to study the natural folate enhancement methods in pseudocereal matrix. Pseudocereal materials consisted of buckwheat, amaranth and quinoa, each of which was subjected to three different treatments: germination, fermentation and combined treatment. Total folate determination was based on an official microbiological assay method (Lactobacillus rhamnosus ATCC 7469). Germination of pseudocereals lasted for 4–5 days. Fermentation was conducted using either baking yeast Saccharomyces cerevisiae ALKO743 or LAB Streptococcus thermophilus ABM5097. All germinated whole grain pseudocereals indeed showed a significant increase in total folate content. Specifically, the increase was 5.4-fold in buckwheat, 5-fold in amaranth and 2.6-fold in quinoa. Fermentation of native pseudocereals also enhanced total folate level. As for the combined treatment, the total folate level of germinated seeds did not further significantly increase or decrease in later fermentation period. Although more studies are needed for processing real pseudocereal foods, our study showed great potential of folate enhancement using germination or fermentation.
  • Favereau, Judith; Nagatsu, Michiru (2020)
    In this paper, we critically and constructively examine the methodology of evidence-based development economics, which deploys randomized field experiments (RFEs) as its main tool. We describe the context in which this movement started, and illustrate in detail how RFEs are designed and implemented in practice, drawing on a series of experiments by Pascaline Dupas and her colleagues on the use of bednets, saving and governance in Kenya. We show that this line of experiments have evolved to address the limitation of obtaining policy-relevant insights from RFEs alone, characterized as their lack of external validity in the literature. After examining the two prominent responses by leading figures of evidence-based development economics, namely machine learning and structured speculation, we propose an alternative methodological strategy that incorporates two sub-fields, namely experimental economics and behavioral economics, to complement RFEs in investigating the data-generating process underlying the treatment effects of RFEs. This strategy highlights promising methodological developments in RFEs neither captured by the two proposals nor recognized by methodologists, and also guides how to combine different sub-fields of economics.
  • Laurikkala, Sini (Helsingin yliopisto, 2015)
    The literature review presents general information on fungi and mycotoxins and then deals with aflatoxins, in particular aflatoxin B1 and M1, their occurrence, significance, and current methods for controlling the risk of aflatoxin. Particular emphasis was given to studies on lactic acid bacteria (LAB) in controlling the growth of aflatoxigenic molds and binding of aflatoxins. The aim of the experimental work was to assess the ability of 171 LAB isolates originating from Kenyan naturally fermented traditional milk and maize samples (1) to inhibit the growth of Aspergillus and (2) to bind aflatoxin M1 in vitro. All the LAB isolates (n=171) were screened for their antifungal activity against A. flavus by an overlay method with 100 µl LAB culture on potato dextrose agar (PDA) plate. Out of 171 LAB isolates, mold growth was reduced by 33 isolates, of which 19 isolates were confirmed to retain their activity. These 19 LAB isolates were tested against A. flavus with three different amounts of LAB culture (50 µl, 100 µl and 200 µl). Three LAB isolates performed best against A. flavus by inhibiting the growth with all the tested amounts of LAB culture. The three LAB isolates were identified as Lactobacillus plantarum first by 16S rDNA sequence analysis and later confirmed by recA derived primers and multiplex PCR assay. The ability of 171 LAB isolates to bind AFM1 from phosphate-buffered saline (PBS) in vitro was carried out. LAB isolates were incubated with an amount equivalent to 50 ng AFM1 /ml for 4 h and then centrifuged (10 000 rpm, 10 °C) for 15 min to obtain supernatant containing unbound AFM1. The amount of unbound aflatoxin was analysed by HPLC chromatography from 51 samples. Binding ability of the analyzed isolates varied from 15,4 % to 51,5 %, and six LAB isolates were shown to bind more than 42,4 % of AFM1. The results showed that all tested indigenous LAB isolated from fermented milk and maize products manufactured in Kenya had variable ability to control the growth of A. flavus and bind AFM1 in vitro. It is suggested that such LAB strains could be used for reduction of the risk of aflatoxin contamination in food and feed chains.
  • Chandrasekar Rajendran, Suresh Chander (Helsingfors universitet, 2014)
    Idli is a popular cereal-legume fermented food of Indian origin. It is steam cooked from fermented (lactic acid-yeast) batter of rice (cereal) and black gram (legume). Idli preparation process includes three major steps – soaking of rice and black gram, grounding and fermentation. The idli preparation process is laborious, as the whole procedure takes about 20 hours. Further, the fermented batter has a shelf life of 4-5 days at 4 ºC. Literature studies reveal less efforts has been taken to improve shelf life and nutritional quality of idli. The overall aim of this thesis was to improve the quality of idli batter by mild heat treatment (Objective 1) and through microbial applications (Objective 2-4). First, the fermented idli batter was mild heat (MH) treated (57, 60, 63, 66 and 70 ºC ) to reduce the high (10.5 log cfu/g) lactic acid bacteria and yeast counts for enhancing the shelf stability at refrigerated storage. MH treatment (at 70 ºC) induced the highest reduction (3.6 log cfu/g) without affecting the pasting profile of idli batter. During storage study (upto 10 days at 4 ºC) the microbial counts further decreased without change in pH.The second objective was to monitor the changes in physicochemical properties and B-vitamin (riboflavin, folate and vitamin B12) levels in idli batter fermentation on addition of starters - Lactococcus lactis N8 (SAA1) and Saccharomyces boulardii (YEA1). Fermentation profiles were recorded individually and in combination of starters. SAA1 and YEA1 were able to enhance or retain riboflavin and folate levels, but no change in vitamin B12 levels were observed during fermentation. Further, YEA1 individually and in combination with SAA1 significantly improved the idli batter volume, implying high gas production. The third objective was to produce nisin in idli batter by addition of SAA1 (nisin producer). The results highlighted SAA1 was capable of producing nisin in idli. However, the produced nisin was degraded by the activity of indigenous LAB and yeast in idli batter. The final objective of this thesis was to determine the viability of probiotic Bacillus coagulans (BAC1) spores after cooking (steaming and microwaving) and during storage (at 4 ºC) of idli batter. Microwave cooking resulted in higher reduction of BAC1 than steam cooking. However, 5.4 log cfu/g of BAC1 spores were still viable in steamed idli from the initial added amount (8.2 log cfu/g). The BAC1 spores were not stable in idli batter suggesting spore outgrowth during storage. In summary, these results present different strategies and information for future process and product developments in idli.
  • Navarro, Andrea (Helsingin yliopisto, 2017)
    Mold spoilage is the main cause of bread spoilage. The fungal species that mostly contaminate bakery products belong to the genera Penicillium, Eurotium, Aspergillus, Monilia, Endocymes, Cladosporium, Fusarium, Neurospora and Rhizopus. The aims of the experimental work were: (1) to screen LAB strains previously isolated from bakery and sourdough environment for their antifungal properties and to be used as starters for sourdough with antifungal activity, and (2) to evaluate sourdough effects on the shelf life of white wheat bread, without affecting the textural properties. Three methods were used to determine the antifungal activity of the isolates. First, the mechanism of fungal inhibition was investigated by an agar diffusion assay with P. paneum and P. albocoremium as indicators. The inhibitory activity toward bakery-related fungi was tested with the radial growth rate of fungi measured after seven days with six indicator molds. The isolates L. pentosus/plantarum J42 and L. mesenteroides I21 were tested in the baking trials, which were conducted in the pilot plant. Physicochemical analysis and microbiological observation were performed on bread slices and loaves produced with 30% sourdough, packed and stored in polyethylene plastic bags under natural conditions at a room temperature of ~ 24 ºC in the pilot plant. The water-soluble extracts from L. pentosus/plantarum, L. mesenteroides, P. pentosaceus and W. confusa had the highest inhibition activity. L. plantarum, W. confusa, L. pseudomesenteroides/mesenteroides and L. mindensis/crustorum had low activity toward the indicator molds. Minor inhibitory effect was observed toward P. albocoremium. Overall, the highest antifungal activity toward the indicator molds was shown by L. mesenteroides I21 strain. The pH values of the water-soluble extract and the sourdough did not seem to influence the fungistatic effect observed of the selected strains toward the molds. Addition of sourdough caused no changes in the physical properties of bread. Sourdough breads had less mycelial coverage relative to the control bread. In the conditions of this study, sourdough addition was beneficial to decrease mold contamination in bread.
  • Salako, Hikmot (Helsingin yliopisto, 2022)
    The use of sourdough has numerous benefits, including improvement of the sensory attributes of baked bread in terms of flavour, texture, volume, enhanced nutritional value and extended shelf life of bread. To achieve the desired sourdough performance and bread with optimal quality and improved flavour, it is essential to understand how the starter cultures behave in specific conditions. In a previous part of this research, the metabolic traits of lactic acid bacteria starters and yeast from the food company S.P.C. (S. Korea) were studied. This thesis aimed to explore the pro-technological properties of the selected starter associations of bacteria/yeast, i.e., Lactiplantibacillus plantarum + Fructilactibacillus sanfransciscensis + Saccharomyces cerevisiae (PSY) and Latilactobacillus curvatus + Levilactobacillus brevis + Saccharomyces cerevisiae (CBY). Consequently, analysis of acidification, proteolysis analysis (including free amino acids), and volatile compound profile were done. PSY and CBY grew at the expected cell density. pH of the sourdoughs fermented by PSY decreased along the same line and slower than that of CBY over the course of 24 h. PSY sourdough had the highest TTA value (11.12 ± 0.03 ml) and organic acid production (148.6 ± 2.4 mmol/kg and 25.1 ± 1.5 mmol/kg) than CBY sourdough TTA value (9.01 ± 0.11 ml) and organic acid production (110.6 ± 1.6 mmol/kg and 20.2 ± 0.9 mmol/kg). This shows PSY as having a relatively high capacity for producing acids during sourdough fermentation among the two associations. After assessing their proteolysis capabilities, PSY sourdough had a presumptively higher peptide content while CBY produced the highest free amino acid content (i.e., Orn having a potential repercussion on bread flavour). Several volatile compounds belonging to different chemical classes, such as acids, aldehydes, ketones, alcohols, esters, and other compounds, were produced by PSY and CBY. In PCA, the control sourdough had a distinctive volatile profile from PSY and CBY. Both PSY and CBY show much correlation with about 4% variation. Ethanol, acetic acid, benzene ethanol, 2(3H)-furanone, dihydro-5-pentyl showed their strongest influence on both sourdoughs as they are found in high amount. Finally, during sourdough fermentation, the associations performed in a desired way, and they showed differences in acidity and content of free amino acids that might have a strong influence on bread flavour. Less differences were observed in the volatile profile compounds of the two associations. Proper sensory analysis and consumer test (by the company) will be the most revealing of the differences observed in this experimental study.