| 1. |
- Holt, Sylvester, et al.
(författare)
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Bioflavoring by non-conventional yeasts in sequential beer fermentations
- 2018
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Ingår i: Food Microbiology. - : Elsevier BV. - 0740-0020 .- 1095-9998. ; 72, s. 55-66
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Tidskriftsartikel (refereegranskat)abstract
- Non-conventional yeast species have great capacity for producing diverse flavor profiles in production of alcoholic beverages, but their potential for beer brewing, in particular in consecutive fermentations with Saccharomyces cerevisiae, has only poorly been explored. We have screened 17 non-conventional yeast species for production of an appealing profile of flavor esters and phenolics in the first phase of alcoholic fermentation, followed by inoculation with S. cerevisiae to complete the fermentation. For measurement of phenolic compoundsand their precursors we developed an improved and highly sensitive methodology. The results show that non-conventional yeast species possess promising potential for enhancement of desirable flavors in beer production. Notable examples are increasing isoamyl acetate (fruity, banana flavor) by application of P. kluyverii, augmenting ethyl phenolic compounds (spicy notes) with Brettanomycesspecies and enhancing 4-vinyl guaiacol (clove-like aroma) with T. delbrueckii. All Pichia strains also produced high levels of ethyl acetate (solvent-like flavor). This might be selectively counteracted by selection of an appropriate S. cerevisiae strain for the second fermentation phase, which lowers total ester profile. Hence, optimization of the process conditions and/or proper strain selection in sequentially inoculated fermentations are required to unlock the full potential for aroma improvement by the non-conventional yeast species.
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| 2. |
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| 3. |
- Makariti, I P, et al.
(författare)
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Investigating boundaries of survival, growth and expression of genes associated with stress and virulence of Listeria monocytogenes in response to acid and osmotic stress.
- 2015
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Ingår i: Food Microbiology. - : Elsevier BV. - 1095-9998 .- 0740-0020. ; 45:Pt B, s. 231-244
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Tidskriftsartikel (refereegranskat)abstract
- The objective of this study was to correlate the relative transcription of Listeria monocytogenes (strains C5, 6179) stress- (gad2, sigB) and virulence- (prfA) associated genes following habituation at twenty-five pH (4.8, 5.0, 5.2, 5.5, 6.4) and NaCl (2, 4, 6, 8, 10% w/v) combinations at 7 °C, with the survival against subsequent exposure to severe acid stress (pH 2.0 at 37 °C). Our findings pointed out the inter-strain variation governing growth inhibiting conditions (pH ≤5.0 and NaCl ≥6%), where C5 was less affected (a reduction of 2.0-3.0 log CFU/mL) than 6179 which was reduced by 4.0-6.0 log CFU/mL at the end of storage. Nevertheless, the higher the habituation at the growth permitting (pH ≥5.5; NaCl ≤4% w/v) or growth inhibiting conditions, the higher the acquired acid resistance or sensitization, respectively. At day 2, gad2 increased relative transcriptional levels are more related to elevated acid resistance, while at day 6 both gad2 transcriptional levels and upregulation of sigB were correlated to low log reductions and high DpH:2.0-values against severe acid stress. Regarding virulence, the increased transcriptional levels of prfA at day 2 were correlated to adverse pH and NaCl combinations, while prolonged stay in suboptimal conditions as well as exposure to severe acid stress resulted in general activation of the virulence regulator. Such data could definitely contribute in designing safe intervention strategies and additionally integrate -omics aspects in quantitative microbial risk assessment.
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| 4. |
- Pallin, Anton, et al.
(författare)
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Evaluation of growth, metabolism and production of potentially bioactive components during fermentation of barley with Lactobacillus reuteri
- 2016
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Ingår i: Food Microbiology. - : Elsevier BV. - 0740-0020 .- 1095-9998. ; 57, s. 159-171
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Tidskriftsartikel (refereegranskat)abstract
- Eighteen bacterial isolates from millet, buckwheat and rye flour were identified as Lactobacillus reuteri. Genomic fingerprinting (rep-PCR) revealed that they represented five strains and phylogenetic analyses using multi locus sequence analysis (MLSA) showed that all clustered with strains of rodent origin. Two strains (SU12-3 and SU18-3) from different phylogenetic clades were used in fermentations of six varieties of barley, both untreated and heat-treated (with inactivated indigenous enzymes) flour. They were compared with two probiotic strains of human origin (DSM 17938 and ATCC PTA 6475), one previously isolated sourdough strain (LTH 5531) and one strain of Lactobacillus plantarum (36E). Analyses of growth (CFU) and metabolism (1H-NMR) revealed differences at species level, with L. plantarum showing a higher capacity to assimilate nutrients without help of the cereal enzymes. Similarities were observed between L. reuteri strains isolated from sourdough, while the greatest differences between L. reuteri strains were observed between strains 6475 and 17938. Multivariate analysis of the metabolic profiles revealed clear clustering according to flour treatment, species of bacteria and barley variety and to some extent also bacterial strain. Possible bioactive compounds such as gamma-aminobutyric acid (GABA), 1,3-propanediol (sign of reuterin production) and histamine were identified and quantified. (C) 2016 Elsevier Ltd. All rights reserved.
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| 5. |
- Sternberg Lewerin, Susanna
(författare)
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Theoretical value of pre-trade testing for Salmonella in Swedish cattle herds
- 2018
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Ingår i: Food Microbiology. - : Elsevier BV. - 0740-0020 .- 1095-9998. ; 71, s. 68-72
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Tidskriftsartikel (refereegranskat)abstract
- The Swedish Salmonella control programme includes mandatory action if Salmonella is detected in a herd. The aim of this study was to assess the relative value of different strategies for pre-movement testing of cattle.Three fictitious herds were included: dairy, beef and specialised calf-fattening. The yearly risks of introducing Salmonella with and without individual serological or bulk milk testing were assessed as well as the effects of sourcing animals from low-prevalence areas or reducing the number of source herds.The initial risk was highest for the calf-fattening herd and lowest for the beef herd. For the beef and dairy herds, the yearly risk of Salmonella introduction was reduced by about 75% with individual testing. Sourcing animals from low-prevalence areas reduced the risk by > 99%. For the calf-fattening herd, the yearly risk was reduced by almost 50% by individual testing or sourcing animals from a maximum of five herds.The method was useful for illustrating effects of risk mitigation when introducing animals into a herd. Sourcing animals from low-risk areas (or herds) is more effective than single testing of individual animals or bulk milk. A comprehensive approach to reduce the risk of introducing Salmonella from source herds is justified. (C) 2017 Elsevier Ltd. All rights reserved.
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