Fungal-Bacterial Mutualism: Species and Strain-Dependent Simultaneous Modulation of Branched-Chain Esters and Indole Derivatives in Fermented Sausages through Metabolite Cross-Feeding.

The precise impact of species and strain diversity on fungal-bacterial interactions and the overall community functioning has remained unclear. First, our study revealed how Debaryomyces hansenii influences diverse bacteria to accumulate key metabolites in a simulated fermented food system. For flavor, D. hansenii promoted the accumulation of branched-chain esters in Staphylococcus xylosus by promoting growth and facilitating the precursor branched-chain acids transformations but hindered the accumulation of Staphylococcus equorum. Furthermore, fungal-bacterial interactions displayed diversity among S. equorum strains. For bioactive compounds, species and strain diversity of lactic acid bacteria (LAB) also influences the production of indole derivatives. Then, we investigated specific metabolic exchanges under reciprocal interaction. Amino acids, rather than vitamins, were identified as the primary drivers of the bacterial growth promotion. Moreover, precursor transformations by D. hansenii played a significant role in branched-chain esters production. Finally, a synthetic community capable of producing high concentrations of branched-chain esters and indole derivatives was successfully constructed. These results provide valuable insights into understanding and designing synthetic communities for fermented sausages.

Selection of yeast strains in naturally fermented cured meat as promising starter cultures for fermented cured beef, a traditional fermented meat product of northern China.

BACKGROUND: Fermented meat products are meat products with a unique flavor, color, and texture as well as an extended shelf life under natural or artificially controlled conditions. Microorganisms or enzymes are used to ferment the raw meat so that it undergoes a series of biochemical and physical changes. Common fermentation strains are lactic acid bacteria, yeasts, staphylococci, molds, and so forth. Studies on the inhibitory effect of yeast fermentation strain on N-nitrosamines in fermented meat products have not been reported. Two excellent yeast starters were identified to solve the problem of nitrosamines in fermented meat products. RESULTS: Meyerozyma guilliermondii and Debaryomyces hansenii led to weak acid production, strong resistance to NaCl and NaNO2 , and high tolerance to low acidic conditions. The inoculated fermented beef exhibited decreased lightness, moisture content, water activity, pH, protein content, nitrite content, and N-nitrosamine content in comparison with the control group fermented bacon. M. guilliermondii had a better effect, reducing pH from 5.69 to 5.41, protein content from 254.24 to 221.92 g·kg-1 , nitrite content from 28.61 to 25.33 mg·kg-1 and N-nitrosamine by 18.97%, and giving the fermented beef the desired meat color, mouthfeel, odor, taste, and tissue quality. CONCLUSION: In this study, two strains of yeast fermenters that can degrade N-nitrosamine precursors were identified, which to some extent solves the problem of the high risk of generating nitrosamines such as N-nitrosodiethylamine (NDEA) by processing fermented meat products with nitrites as precursors. These two strains are likely to be used as starter cultures for fermented meat products. © 2023 Society of Chemical Industry.

Effect of selected agents for ochratoxin A biocontrol on the colour, texture and volatile profile of dry-cured fermented sausages.

BACKGROUND: Traditional dry-cured fermented sausages favour the growth of an autochthonous microbial population, which plays an important role in their sensory aspects. However, some moulds can produce mycotoxins such as ochratoxin A (OTA). The biocontrol agents (BCAs) Debaryomyces hansenii FHSCC 253H and Staphylococcus xylosus FHSCC Sx8 have been demonstrated to reduce OTA production in dry-cured meat products, but their influence in the sensory characteristics of sausages has to be tested. The aim of this study was to evaluate the effect of these BCAs on the colour, texture and volatile profile of dry-cured fermented sausages. RESULTS: D. hansenii caused few differences in the tested parameters with respect to the control batch. S. xylosus modified the texture and colour, although the values found were within the range expected for dry-cured fermented sausages 'salchichón'. Additionally, the volatile profile revealed the potential antioxidant effect of both BCAs and their ability to produce compounds associated with the ripened aroma that could increase product acceptability. CONCLUSION: The results indicate that there were no inconveniences in implementing both BCAs during the processing of dry-cured fermented sausages 'salchichón'. Moreover, D. hansenii FHSCC 253H could improve the volatile profile of this product. © 2023 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Biocontrol of ochratoxigenic Penicillium nordicum in dry-cured fermented sausages by Debaryomyces hansenii and Staphylococcus xylosus.

Penicillium nordicum is the main ochratoxin A (OTA) producing mould in dry-cured meat products. The use of autochthonous microorganisms as protective cultures is a promising strategy to control this hazard. The aim of this work was to evaluate the effect of Debaryomyces hansenii and Staphylococcus xylosus isolated from dry-cured meat products as biocontrol agents (BCAs) against P. nordicum during the ripening of dry-cured fermented sausages. The BCAs were added to the dough, and P. nordicum were inoculated on the surface after stuffing. Then, the sausages were ripened following a traditional processing. The growth of the microorganisms was determined by plate count at the beginning and at the end of ripening. To assess the implantation of BCAs in the sausages, the yeasts and staphylococci isolated from the sausages at the end of processing were identified by sequencing the 16S and 18S rRNA respectively, and they were characterized by pulsed field gel electrophoresis (PFGE) of the chromosomal DNA. OTA was quantified by UHPLC-MS/MS. BCAs were able to colonise and develop throughout the processing. Although none of the BCAs reduced the growth of P. nordicum, a OTA decrease was observed in the sausages inoculated with D. hansenii individually or combined with S. xylosus. The drop of OTA amount was particularly marked in the portions where the casing was damaged allowing the mould to grow inside the sausages. In these areas, OTA was not detected in the inoculated batches. In conclusion, D. hansenii could be proposed as BCA individually or in combination with S. xylosus for the biocontrol of OTA hazard in dry-cured fermented sausages.

Unfolding microbiota and volatile organic compounds of Portuguese Painho de Porco Preto fermented sausages.

In the present study, bacterial and fungal diversity, as well as volatile profiles, of ready-to-eat Portuguese Painho de Porco Preto fermented sausages manufactured by two artisanal producers in the districts of Beja (producer A) and Evora (producer B) were studied. To this end, different selective growth media and a metataxonomic analysis were combined with Headspace Solid-Phase Microextraction-Gas Chromatography/Mass Spectrometry (HS-SPME-GC/MS) analysis. The results of the microbiological viable counts revealed active microbial populations of lactic acid bacteria (up to 8 Log cfu g-1), coagulase negative cocci (up to 6 Log cfu g-1), and eumycetes (up to 6 Log cfu g-1). Bacterial populations were characterized by high relative frequencies of Latilactobacillus sakei (up to 72%), together with Weissella and Staphylococcus equorum. The mycobiota was mainly dominated by Debaryomyces hansenii (up to 55% of the relative frequency) and Kurtzmaniella zeylanoides (up to 24% of the relative frequency). Unexpected species as Wickerhamomyces subpelliculosus and Zygosaccharomyces rouxii were also detected. HS-SPME-GC/MS analysis allowed to identify a complex volatile profile, showing 159 volatile organic compounds (VOCs). VOCs belonged to twelve classes, such as aldehydes, ketones and lactones, esters and acetates, alcohols, terpenoids, sulfur compounds, aliphatic hydrocarbons, aromatic hydrocarbons, nitrogen compounds, acids, furans and pyrans, and phenols. The analysis of VOCs composition provided evidence that samples from the two producers (A and B) were different, as confirmed by the Principal Component Analysis. Hence, it is likely that the raw materials used, as well as variations related with the empirical practice of the butchers, strongly influenced the final product. The results obtained in the present study represent a further advancement in the knowledge on the biodiversity and VOCs composition of Portuguese fermented sausages. To better understand the interactions occurring between the autochthonous microorganisms and the meat batter in the Painho de Porco Preto fermented sausage, microbial and VOCs dynamics must be further deepened throughout the production process.

Unravelling microbial populations and volatile organic compounds of artisan fermented liver sausages manufactured in Central Italy.

The aim of the present study was to obtain information on the occurrence of bacteria and eumycetes in ready-to-eat fermented liver sausages manufactured by 20 artisan producers located in the Marche Region (Italy). To this end, culture-dependent analyses and metataxonomic sequencing were carried out. Physico-chemical parameters and volatilome of the fermented liver sausages were also studied. Finally, the presence of hepatitis E virus (HEV) was also assessed via real-time-RT-(q)PCR assays. Active microbial populations mainly represented by lactic acid bacteria, enterococci, coagulase-negative cocci, and eumycetes were detected. Enterobacteriaceae, Pseudomonadaceae, and sulfite-reducing anaerobes were not detected in most of the samples. Latilactobacillus sakei dominated in all the analyzed samples, reaching abundances up to 80%. Staphylococcus xylosus and Staphylococcus equorum were also detected. Among minority bacterial taxa, Weissella spp., Leuconostoc spp., Macrococcus caseolyticus, Brochothrix thermosphacta, Staphylococcus succinus, Lactobacillus coryniformis, Lactiplantibacillus plantarum, Lactococcus garviae, Psychrobacter spp., and Carnobacterium viridans were detected. The mycobiota was mainly composed by Debaryomyces hansenii that was present in all samples at the highest frequency. Among minority fungal taxa, Aspergillus spp., Penicillium spp., Kurtzmaniella zeylanoides, Candida spp., Yamadazyma spp., Scopulariopsis spp., Yarrowia spp., and Starmerella spp. were detected. Interestingly, associations between some taxa and some physico-chemical parameters were also discovered. The absence of HEV in all the samples attested a high level of safety. Finally, most of the VOCs detected in the analyzed fermented liver sausages belonged to six classes as: terpenoids, aldehydes, ketones, alcohols, esters, and acids. Nitrogen compounds, sulfur compounds, phenols, hydrocarbons, lactones, furans, and aromatic hydrocarbons were also identified. Several significant relationships were observed between mycobiota and VOCs.

Meaty aroma notes from free amino acids and thiamine in nitrite-reduced, dry-fermented, yeast-inoculated sausages.

The contribution of free amino acids and thiamine to the production of potent meat aroma compounds in nitrite-reduced, dry-fermented sausages inoculated with a D. hansenii strain was the objective of this study. For this, three different sausage formulations were manufactured; a control and two formulations reduced by half in nitrate and nitrite and one of them inoculated with D. hansenii. Free amino acids, thiamine content and savoury volatile compounds were analysed. Eleven savoury volatile compounds were quantitated. Among them, the most potent compounds above their odour thresholds were 2-methyl-3-furanthiol, 2-acetyl-1-pyrroline, methional, dimethyl trisulfide and methyl-2-methyl-3-furyl disulfide. Their generation was affected by D. hansenii inoculation as shown by the decrease in methional and methyl 2-methyl-3-furyl disulfide content, and the increase of methionol. Nitrate and nitrite reduction did not significantly affect amino acid and thiamine contents.

Competitiveness of three biocontrol candidates against ochratoxigenic Penicillium nordicum under dry-cured meat environmental and nutritional conditions.

The environmental conditions during the ripening of dry-cured meats and their nutritional composition promote the colonisation of their surface by Penicillium spp., including P. nordicum producer of ochratoxin A (OTA). The objective of this work was to study the competitiveness of three potential biocontrol candidates (Debaryomyces hansenii FHSCC 253H, Enterococcus faecium SE920 and Penicillium chrysogenum CECT, 20922) against the ochratoxigenic P. nordicum FHSCC4 under environmental and nutritional conditions simulating the ripening of dry-cured meat products. For this, the nutritional utilisation pattern, niche overlap index (NOI), interactions by dual-culture assays and OTA production were determined. The number of carbon sources (CSs) metabolised depended on the microorganism and the interacting water activity (aw) x temperature conditions. The number of CSs utilised by both filamentous fungi was quite similar and higher than those utilised by D. hansenii and E. faecium. The yeast isolate metabolised a number of CSs much larger than the bacterium. The NOI values showed that, in general, P. nordicum nutritionally dominated E. faecium and D. hansenii regardless of the environmental conditions evaluated. The relationship between the toxigenic and non-toxigenic fungal isolates depended on the aw x temperature combinations, although in none of the conditions a dominance of P. nordicum was observed. According to the interaction assays, both D. hansenii and P. chrysogenum decreased the growth of P. nordicum. The effect of D. hansenii could be attributed to the production of some extra-cellular compounds, while the action of P. chrysogenum is likely related to nutritional competition. In addition, both P. chrysogenum and D. hansenii reduced the OTA levels produced by P. nordicum. The effect of the yeast was more pronounced decreasing the concentration of OTA at quantities lower than the limit established by the Italian legislation. Therefore, P. chrysogenum and D. hansenii can be suggested as biocontrol candidates in the manufacture of dry-cured meat products.

Characterization of the microbiota and chemical properties of pork loins during dry aging.

Dry aging (DA) allows for the storage of meat without packaging at 0 to 3°C for several weeks. It enhances the production of pleasant flavors, tenderness, and juiciness in meat. Due to the long storage period and roles of indigenous microbiota in the maturation of several meat products, the microbiota of DA meat is of interest in terms of microbial contributions and food hygiene but has not yet been characterized in detail. This study identified the microbiota of pork loins during DA using culturing and culture-independent meta-16S rRNA gene sequencing and elucidated its characteristics. The amounts of free amino acids and profiles of aroma-active compounds were also monitored by high-performance liquid chromatography and gas chromatography, respectively. The meta-16S rRNA gene sequencing revealed that Pseudomonas spp. generally dominated the microbiota throughout DA; however, the culturing analysis showed marked changes in the species composition during DA. Acinetobacter spp. were the second most dominant bacteria before DA in the culture-independent analysis but became a minor population during DA. The cell numbers of yeasts showed an increased tendency during DA, and Debaryomyces hansenii was the only microorganism isolated from all meat samples throughout DA. Well-known foodborne pathogens were not observed in two microbiota analyses. The amounts of free amino acids were increased by DA, and the number of aroma-active compounds and their flavor dilution values markedly changed during DA. Most microbial isolates showed positive reactions with proteolytic and lipolytic activities, suggesting their contribution to tenderness and aroma production in DA meats.

Counteracting the effect of reducing nitrate/nitrite levels on dry fermented sausage aroma by Debaryomyces hansenii inoculation.

The reduction of ingoing amounts of nitrate and nitrite in dry fermented sausages was studied together with the impact of Debaryomyces hansenii inoculation on aroma generation. Three different formulations of sausages were manufactured: control (C), reduced in nitrate and nitrite ingoing amounts (R) and reduced R inoculated with D. hansenii (RY). Changes in physicochemical and microbiological parameters, volatile compounds and aroma were investigated at different drying times. Nitrite/nitrate reduction did not seem to affect microbial growth but affected their metabolic activity. Moreover, nitrite/nitrate reduction decreased lipid oxidation and generation of derived volatile compounds. Yeast inoculation limited lipid oxidation and prevented nitrite oxidation. Sausage aroma profile was positively affected by D. hansenii inoculation which contributed to the generation of potent aroma compounds like ethyl ester compounds and 3-methylbutanal. Long drying time impacted sausage aroma profile as well as yeast metabolism. Yeast inoculation counteracted the negative influence of nitrite/nitrate reduction due to its antioxidant capacity, aroma generation and hindered nitrite oxidation.

Is there any still undisclosed biodiversity in Ciauscolo salami? A new glance into the microbiota of an artisan production as revealed by high-throughput sequencing.

Ciauscolo is a fermented sausage with the Protected Geographical Indication (PGI) status. To disclose the microbial ecology of a model Ciauscolo salami manufacture during its natural fermentation, viable counting, amplicon-based sequencing and real-time PCR were applied. The volatilome during fermentation was also characterized. The results allowed previously undetected species to be discovered. The core microbiota was composed by Lactobacillus algidus, Leuconostoc carnosum, Lactobacillus sakei, Debaryomyces hansenii, Glomus hyderabadensis, Tilletiopsis washingtonensis, and Kurtzmaniella zeylanoides. Salmonella spp. and Listeria monocytogenes were absent in all the samples; moreover, multiplex real-time PCR revealed the absence of the target genes bont/A, bont/B, bont/E, bont/F, and 4gyrB (CP), encoding botulinic toxins. Volatilome, deeply depending on microbiological metabolism, was characterized by spices-derived components. Limonene, sabinene, α- and ß-pinene, 3-carene, and α-thujene were the most represented monoterpene hydrocarbons, whereas ß- and α-copaene were the most represented sesquiterpene hydrocarbons. Allyl methyl sulphide and diallyl disulphide were the major aliphatic sulphur compounds, together with diallyl sulphide and allyl methyl disulphide.

Identification of Microorganisms Associated with the Quality Improvement of Dry-Aged Beef Through Microbiome Analysis and DNA Sequencing, and Evaluation of Their Effects on Beef Quality.

The objective of this study was to isolate and identify the microorganisms, especially yeasts and molds, related to the improvement of beef quality during dry-aging of beef through microbiome analysis, and to examine the possibility of using them as starter culture strains to improve the efficiency of dry-aging beef production. Beef sirloins were dry-aged for 28 days using different wind speeds (0, 2.5, and 5 m/s) at 1 to 3 °C and 75% relative humidity, and microbial compositions were confirmed by microbiome analysis. Mold and yeast samples were plated on potato dextrose agar supplemented with 10% tartaric acid, and the isolated colonies were identified by DNA sequencing. The isolates were subjected to microbial characterization (morphological characterization, growth condition, and enzyme activity). Microbiome analysis showed that the dominant microorganisms were molds and yeasts identified as Pilaira anomala SMFM201611 and Debaryomyces hansenii SMFM201707. Pilaira anomala SMFM201611 and D. hansenii SMFM201707 were inoculated into 24 sirloins of the lowest grade. All samples were dry-aged for 0, 14, 21, and 28 days and analyzed for microbial growth, pH, shear force, ultrastructure, and flavor compounds (free amino acids and free fatty acids). Inoculation with P. anomala SMFM201611 and D. hansenii SMFM201707 improved tenderness and cause the breakdown of myofibrils by proteolysis. Both microorganisms also produced free amino acids and fatty acids through proteolytic and lipolytic activities. These results indicate that P. anomala SMFM201611 and D. hansenii SMFM201707 isolated and identified from dry-aged beef can improve the quality of low-grade beef during dry-aging. PRACTICAL APPLICATION: During dry-aging, mold and yeast improve the quality of dry-aged beef. Pilaira anomala SMFM201611 and Debaryomyces hansenii SMFM201707 isolated from dry-aged beef can improve tenderness by breaking down myofibrils. Both microorganisms improve flavor by producing free fatty acids and amino acids, and the taste and aroma characteristics of low-grade beef may be improved during the dry-aging process.

Debaryomyces hansenii Metabolism of Sulfur Amino Acids As Precursors of Volatile Sulfur Compounds of Interest in Meat Products.

The ability of Debaryomyces hansenii to produce volatile sulfur compounds from sulfur amino acids and the metabolic pathway involved have been studied in seven strains from different food origins. Our results proved that l-methionine is the main precursor for sulfur compound generation. Crucial differences in the sulfur compound profile and amino acid consumption among D. hansenii strains isolated from different food sources were observed. Strains isolated from dry pork sausages displayed the most complex sulfur compound profiles. Sulfur compound production, such as that of methional, could result from chemical reactions or yeast metabolism, while according to this study, thioester methyl thioacetate appeared to be generated by yeast metabolism. No relationship between sulfur compounds production by D. hansenii strains and the expression of genes involved in sulfur amino acid metabolism was found, except for the ATF2 gene in the L1 strain for production of methyl thioacetate. Our results suggest a complex scenario during sulfur compound production by D. hansenii.

Quantitative proteomic profiling of ochratoxin A repression in Penicillium nordicum by protective cultures.

Dry-cured meat products are usually contaminated with moulds during ripening. Although fungal development contributes to the desired sensory characteristics, some moulds, such as Penicillium nordicum are able to produce ochratoxin A (OTA) on meat products. Therefore, strategies to prevent OTA contamination in ripened meat products are required. Microorganisms isolated from these meat products can be adequate as biocontrol agents, given that no negative sensory impact is expected. The PgAFP antifungal protein-producer Penicillium chrysogenum (Pc) and Debaryomyces hansenii (Dh) have been shown to successfully inhibit toxigenic moulds. However, scarce information about the mechanism of action of these biocontrol agents on toxigenic mould inhibition is available. Comparative proteomic analysis is a powerful tool to investigate the physiological response of microorganisms to stimuli. Proteomic analysis was carried out on P. nordicum co-cultured with Pc, Dh, PgAFP, and their combinations on a dry-cured ham-based medium. Additionally, OTA production by P. nordicum in the different cultures was measured. The individual inoculation of Pc or Dh repressed OTA production by P. nordicum by 5 and 3.15 fold, respectively. A total of 2844 unique P. nordicum proteins were identified by proteomic analysis. The impact of the biocontrol agents on the proteome of P. nordicum was higher for Pc-containing cultures, followed by Dh-containing treatments. PgAFP alone had minimal impact on the proteome of P. nordicum. Proteomic analyses indicated Pc repressed P. nordicum OTA production through nutrient competition, potentially reducing glucose availability. Data also suggest that Dh and Pc inhibited P. nordicum through cell wall integrity impairment. Both Pc and Dh seem to hamper P. nordicum secondary metabolism (SM) as indicated by lower levels of MAP kinases and SM-associated proteins found in the co-inoculated P. nordicum. This work paves the way to use antifungal agents in the most efficient way to prevent OTA formation in meat products.

Inoculation with a terroir selected Debaryomyces hansenii strain changes physico-chemical characteristics of Iberian cured pork loin.

Debaryomyces hansenii Lr1, previously isolated from naturally fermented cured pork loin ("lomo embuchado"), was used to inoculate Iberian pork loin under four different conditions. In all cases, specifically inoculated D. hansenii yeasts grew on the surface of the product and affected its physico-chemical and sensory characteristics. Inoculated pork loin kept higher water activity and pH and possessed lower sodium content than control samples at the end of the 90 days ripening period. Moreover, inoculation with Lr1 yeast did not change the general profile of fatty acids but modified the levels of volatile and aroma compounds by decreasing aldehydes and increasing esters and alcohol compounds. Principal Component Analysis (PCA) of the different physico-chemical parameters that were determined showed a clear separation between the samples indicating that they were different. A tendency in consumers acceptance to prefer cured pork loin specifically inoculated with the higher amounts of yeasts used in this study was observed.

Impact of a selected Debaryomyces hansenii strain's inoculation on the quality of Sardinian fermented sausages.

Dominant yeast species in Salsiccia Sarda, a traditional fermented sausage produced in Sardinia (Italy), were evaluated through the monitoring three typical production processes. Six different species were identified by molecular techniques, but Debaryomyces (D.) hansenii proved to be dominant. A D. hansenii strain was selected according to its technological features and used in three experimental sausage productions at farm scale with the aim to evaluate its antifungal effect. In all cases, two batches were inoculated with a previously selected autochthonous starter cultures (Lactobacillus plantarum and Staphylococcus xylosus), whereas two batches were left to spontaneous fermentation. D. hansenii was inoculated on the sausages surface by brushing after the sausages drying, by immersion in a yeast suspension after the stuffing, or, alternatively, casings were dipped in a yeast suspension before the dough stuffing. Microbial counts in the sausages core did not appear to be affected by D. hansenii application, while outcomes obtained for casings appeared soundly diversified. Brushing on the sausages surface at the onset of fermentation proved to be the best approach to treat sausages. Yeast inoculation exerted a noteworthy anti-mould effect, independently of the mode of application and, on the other hand, did not affect the overall quality and typical features of the product.

Biocontrol of aflatoxigenic Aspergillus parasiticus by native Debaryomyces hansenii in dry-cured meat products.

Dry-cured meat products, such as dry-cured ham or dry-fermented sausages, are characterized by their particular ripening process, where a mould population grows on their surface. Some of these moulds are hazardous to the consumers because of their ability to produce mycotoxins including aflatoxins (AFs). The use of native yeasts could be considered a potential strategy for controlling the presence of AFs in dry-cured meat products. The aim of this work was to evaluate the antagonistic activity of two native Debaryomyces hansenii strains on the relative growth rate and the AFs production in Aspergillus parasiticus. Both D. hansenii strains significantly reduced the growth rates of A. parasiticus when grown in a meat-model system at different water activity (aw) conditions. The presence of D. hansenii strains caused a stimulation of AFs production by A. parasiticus at 0.99 aw. However, at 0.92 aw the yeasts significantly reduced the AFs concentration in the meat-model system. The relative expression levels of the aflR and aflS genes involved in the AFs biosynthetic pathway were also repressed at 0.92 aw in the presence of both D. hansenii strains. These satisfactory results were confirmed in dry-cured ham and dry-fermented sausage slices inoculated with A. parasiticus, since both D. hansenii strains significantly reduced AFs amounts in these matrices. Therefore, both tested D. hansenii strains could be proposed as biocontrol agents within a HACCP framework to minimize the hazard associated with the presence of AFs in dry-cured meat products.

Potential of yeasts isolated from dry-cured ham to control ochratoxin A production in meat models.

The environmental conditions reached during the ripening of dry-cured meat products favour the proliferation of moulds on their surface. Some of these moulds are hazardous to consumers because of their ability to produce ochratoxin A (OTA). Biocontrol using Debaryomyces hansenii could be a suitable strategy to prevent the growth of ochratoxigenic moulds and OTA accumulation in dry-cured meat products. The aim of this work was to evaluate the ability of two strains of D. hansenii to control the growth and OTA production of Penicillium verrucosum in a meat model under water activities (aw) values commonly reached during the dry-cured meat product ripening. The presence of D. hansenii strains triggered a lengthening of the lag phase and a decrease of the growth rate of P. verrucosum in meat-based media at 0.97 and 0.92 aw. Both D. hansenii strains significantly reduced OTA production (between 85.16 and 92.63%) by P. verrucosum in the meat-based medium at 0.92 aw. Neither absorption nor detoxification of OTA by D. hansenii strains seems to be involved. However, a repression of the expression of the non-ribosomal peptide synthetase (otanpsPN) gene linked to the OTA biosynthetic pathway was observed in the presence of D. hansenii. To confirm the protective role of D. hansenii strains, they were inoculated together with P. verrucosum Pv45 in dry-fermented sausage and dry-cured ham slices. Although P. verrucosum Pv45 counts were not affected by the presence of D. hansenii in both meat matrices, a reduction of OTA amount was observed. Therefore, the effect of D. hansenii strains on OTA accumulation should be attributed to a reduction at transcriptional level. Consequently, native D. hansenii can be useful as biocontrol agent in dry-cured meat products for preventing the hazard associated with the presence of OTA.

Lipolysis and aroma generation as mechanisms involved in masking boar taint in sodium reduced fermented sausages inoculated with Debaryomyces hansenii yeast.

BACKGROUND: The use of boar back fat for processing of fermented sausages may cause the presence of abnormal odours. In dry-cured products, ripening time is essential to develop the sensory characteristics. Yeast has been proposed as an alternative to mask boar taint odour through its metabolic activity but it is necessary to elucidate which mechanisms are involved. The aim is to study the effect of Debaryomyces hansenii inoculation on the lipolysis process and generation of aroma compounds in fermented sausages manufactured with boar back fat at two different ripening times. RESULTS: D. hansenii inoculated sausages had a higher degree of lipolysis as demonstrated by higher content of free fatty acids, ester compounds and branched aldehydes which contribute the fruity odour. The increase in lipolysis produced by D. hansenii inoculation was not followed by an increase in oxidation during processing possibly due to the metabolic activity of yeast. The effect of back fat type was scarcely appreciated whereas ripening time had a stronger effect on sausage. Boar sausages were characterised by a lower polyunsaturated fatty acid profile and lesser lipolysis than gilt sausages. CONCLUSION: Yeast inoculation with D. hansenii and long ripening time were appropriate strategies to limit the perception of boar taint in dry fermented sausages. © 2017 Society of Chemical Industry.

Screening of Debaryomyces hansenii Strains for Flavor Production under a Reduced Concentration of Nitrifying Preservatives Used in Meat Products.

A total of 15 Debaryomyces hansenii strains from different food origins were genetically characterized and tested on a culture medium resembling the composition of fermented sausages but different concentrations of nitrifying preservatives. Genetic typing of the D. hansenii strains revealed two levels of discrimination: isolation source or strain specific. Different abilities to proliferate on culture media containing different concentrations of nitrate and nitrite, as sole nitrogen sources and in the presence of amino acids, were observed within D. hansenii strains. Overall metabolism of amino acids and generation of aroma compounds were related to the strain origin of isolation. The best producers of branched aldehydes and ethyl ester compounds were strains isolated from pork sausages. Strains from cheese and llama sausages were good producers of ester compounds and branched alcohols, while vegetable strains produced mainly acid compounds. Nitrate and nitrite reduction affected in different ways the production of volatiles by D. hansenii.