Effects of Pulsed Electric Fields on Cabernet Sauvignon Grape Berries and on the Characteristics of Wines

The treatment of Cabernet Sauvignon red grapes by pulsed electric fields (PEFs) is performed prior to vinification in order to enhance the extraction of polyphenols. PEF treatments of the longest duration and of the highest energy (E?= 0.7 kV/cm, t _PEF?=?200 ms, W?=?31 Wh/kg) changed the structure of grape skins and produced a wine that was richer in tannins (34 %), while treatment of the highest strength (E?=?4 kV/cm, t _PEF?=?1 ms, W =?4 Wh/kg) altered the visual appearance of phenolic compounds in the skins and led to greater extraction of the anthocyanins (19 %). The PEF treatments caused the depolymerization of skin tannins, improving the diffusion of these decondensed tannins which are smaller. The PEF treatment of longest duration and of the highest energy had more impact on the parietal tannins and the cell walls of the skins while treatment of the highest strength modified more the vacuolar tannins. Changes in the operating parameters of the PEF treatment (E?=?0.7 to 4 kV/cm, t _PEF?=?1 to 200 ms, W?=?4 to 31 Wh/kg) did not affect alcohol content, total acidity nor volatile acidity in finished wines compared to the values of the control wine, but seemed to cause a slight increase in pH (1–2 %).     

Stimulation of Saccharomyces cerevisiae Cultures by Pulsed Electric Fields

The effects of stimulation of Saccharomyces cerevisiae cells in an aqueous suspension by pulsed electric field (PEF) with electric field strength E?=?20–2,000 V cm^?1 and effective PEF treatment time t _PEF?=?10^?5–1 s were investigated. At relatively high electric field strengths (E?>?1,000 V cm^?1) and moderate times of PEF treatment (t _PEF?>?100 μs), the extraction of ionic components from yeast was observed, which can be related to electroporation of cell membranes. Petri dishes counting revealed dependency of the colony sizes on the time of preliminary fermentation t _f and power consumption W. The “logarithmic” and “saturated” types of electrostimulation were distinguished. At “logarithmic” electrostimulation (10^?7 J mL^?1?W??1 J mL^?1), the viability of yeast cells increased with the increase of power consumption and was higher for longer fermentation (t _f ?=?24 h). However, at “saturated” electrostimulation (10^?1 J mL^?1?W?1 J mL^?1), the viability of yeast cells was noticeably higher for t _f ?=?1 h than for t _f ?=?24 h. The impact of preliminary fermentation time and PEF protocol on biological activity of cells and consumption of nutrients was also discussed.     

Pulsed electric field treatment of red wine: Inactivation of Brettanomyces and potential hazard caused by metal ion dissolution

Pulsed electric field (PEF) technology is an attractive alternative method of wine preservation by inactivating Brettanomyces bruxellensis, a major spoilage concern affecting wines worldwide. Currently, wine preservation using SO₂ can have negative effects on consumers including headaches and allergic reactions. Therefore, the objectives of this study were to investigate the effect of PEF processing conditions, B. bruxellensis yeast strain and alcohol concentration on B. bruxellensis inactivation in red wine, as well as whether PEF treatment could have a harmful effect on wine through the release of metal ions. Electric field intensity was found to have a greater impact on inactivation than specific energy, with 31, 40 and 50 kV/cm treatments resulting in B. bruxellensis D values of 181.8, 36.1 and 13.0 μs, respectively. At 50 kV/cm, a temperature rise of almost 10 °C, doubled inactivation to 3.0 log reductions (cfu/mL). Yeast strain and alcohol concentration were also shown to influence inactivation, even though cell size comparisons of the three yeasts tested proved inconclusive. Overall, PEF treatment of wine was shown to be a possible preservation alternative for the wine industry. After PEF treatment, the wine produced remained safe for human consumption, with Fe, Cr and Ni ions contents well below dangerous levels.     

葡萄酒与微生物

在整个葡萄酒的酿造生产过程中 ,不同的微生物起着不同的作用 ,酿酒酵母将糖转化成酒精 ,乳酸菌会将苹果酸转化成乳酸等 ,这些是正常的发酵过程 ;而醋酸菌会使葡萄酒发生酸败 ,产膜酵母会使葡萄酒起膜浑浊 ,霉菌会影响酒的风味等 ,这些是有害微生物的作用     

Impact of Electric Pulse Treatment on Selective Extraction of Intracellular Compounds from Saccharomyces cerevisiae Yeasts

Treatments by high-voltage electrical discharges (HVED, needle-plate electrode geometry, U?=?40 kV, t _p?≈?0.5 μs) and pulsed electric field (PEF, plate–plate electrode geometry, E?=?5–40 kV/cm, t _p?≈?8.3 μs) were evaluated as tools for selective extraction of different intracellular components from the wine Saccharomyces cerevisiae (bayanus) yeasts in a 0.5% (w/w) aqueous suspension. The pulses in the form of damped oscillations and exponential decay were applied in HVED and PEF modes of treatment, respectively. The extraction efficiency results obtained using HVED and PEF techniques were compared with those for high-pressure homogenization technique. The HVED and PEF treatments always resulted in incomplete damage of yeast cells, though efficiency of HVED was higher than that of PEF. The high selectivity of extraction of ionic substances, proteins, and nucleic acids was demonstrated; e.g., electric pulse treatments at E?=?40 kV/cm and N?=?500 allowed extraction of ≈80% and ≈70% of ionic substances, ≈4% and ≈1% of proteins and ≈30% and ≈16% of nucleic acids in cases of HVED and PEF modes, respectively.     

The impact of pulsed electric fields on quality parameters of freeze-dried red beets and pineapples

The effect of pulsed electric fields (PEF) on the cell disintegration index (Zp), the freeze-drying process and the final product quality of red beet and pineapple tissue was studied. Red beets and pineapples were PEF-treated at an electric field strength of 1.07 kV/cm and specific energy inputs of 1 kJ/kg and 4 kJ/kg (PEF₁ and PEF₂, respectively). Freeze-drying was performed at a pressure of 1 mbar and heating plate temperature of 50 °C for red beet and 40 °C for pineapple. The quality of freeze-dried tissue was evaluated by the analysis of residual moisture content, macrostructure, texture, colour and rehydration properties. For freeze-dried red beets, the betalain content from extracts was studied. It could be stated that PEF pre-treatment had no significant influence on drying time reduction, however significantly improved the final quality of freeze-dried product. Moreover, the effect of PEF was strongly depending on type of plant material used.     

Acetic acid bacteria spoilage of bottled red wine -- a review

Acetic acid bacteria (AAB) are ubiquitous organisms that are well adapted to sugar and ethanol rich environments. This family of Gram-positive bacteria are well known for their ability to produce acetic acid, the main constituent in vinegar. The oxidation of ethanol through acetaldehyde to acetic acid is well understood and characterised. AAB form part of the complex natural microbial flora of grapes and wine, however their presence is less desirable than the lactic acid bacteria and yeast. Even though AAB were described by Pasteur in the 1850s, wine associated AAB are still difficult to cultivate on artificial laboratory media and until more recently, their taxonomy has not been well characterised. Wine is at most risk of spoilage during production and the presence of these strictly aerobic bacteria in grape must and during wine maturation can be controlled by eliminating, or at least limiting oxygen, an essential growth factor. However, a new risk, spoilage of wine by AAB after packaging, has only recently been reported. As wine is not always sterile filtered prior to bottling, especially red wine, it often has a small resident bacterial population (<10(3) cfu/mL), which under conducive conditions might proliferate. Bottled red wines, sealed with natural cork closures, and stored in a vertical upright position may develop spoilage by acetic acid bacteria. This spoilage is evident as a distinct deposit of bacterial biofilm in the neck of the bottle at the interface of the wine and the headspace of air, and is accompanied with vinegar, sherry, bruised apple, nutty, and solvent like off-aromas, depending on the degree of spoilage. This review focuses on the wine associated AAB species, the aroma and flavour changes in wine due to AAB metabolism, discusses the importance of oxygen ingress into the bottle and presents a hypothesis for the mechanism of spoilage of bottled red wine.     

Pulsed Electric Field treatment after malolactic fermentation of Tempranillo Rioja wines: Influence on microbial,physicochemical and sensorial quality

During wine stabilization, control of the microbial population is required in order to ensure a quality wine. Pulsed Electric Field (PEF) was applied to commercial wines in a continuous flow to reduce the amount of SO₂ added after the end of malolactic fermentation to manage microbial populations. Samples of wine from three commercial wineries of the Rioja Qualified Designation of Origin were treated with 30 mg/L SO₂, with 15 mg/L SO₂ and PEF, and only with PEF. The inactivation of the microbiota with the PEF treatment was greater than the inactivation achieved with SO₂ four days after treatment. Six months later, the lactic acid bacteria population was still viable in some of the wines. Regarding the physicochemical characterization of the wines, the PEF treatment was positive for quality because the wines had greater color intensity and lower volatile acidity. Moreover, organoleptic analysis indicated different scoring depending mainly on the characteristics of the original wine. Despite these positive results, further studies are advisable to optimize the control of lactic acid bacteria.Industrial relevanceThe application of PEF during wine stabilization after MLF can be a viable alternative for the oenological industry to reduce the SO₂ dosage used in winemaking.     

Control of Microbial Spoilage on Fresh Poultry using a Combination Potassium Sorbate/Carbon Dioxide Packaging System

The effects of potassium sorbate combined with vacuum or carbon dioxide modified atmosphere packaging on natural poultry spoilage flora were examined. Fresh chicken thighs were dipped into either 2.5% potassium sorbate solution or distilled water, adjusted to pH 6.0 and packaged on trays in Nylon/Plexar/Surlyn bags. Atmospheres of either air, vacuum or 100% C0₂ were created in the packages which were then stored at 10 ± 1°C for 10 days. Changes in aerobic plate counts, lactic acid bacteria and pseudomonads were monitored. The combination of CO₂ packaging and sorbate treatment provided the most effective inhibitory system against the poultry spoilage organisms, especially Pseudomonas species, without creating a selective environment for the growth of lactic acid bacteria and premature souring of the product. The shelf life of the sorbate/CO₂ samples was extended 3 days over the control/air samples at 10°C.     

传统黄酒淋饭酒母制作过程微生物的变化和作用

搭窝糖化期：乳酸球菌以肠球菌属、明串珠菌属、片球菌属、乳球菌属、酒球菌属等属的菌株为主，且有极少量乳酸杆菌。静止期：升酸幅度较大，酵母增殖迅速。搅拌期：酵母快速产酒精，乳酸球菌数迅速下降，乳酸杆菌数大量增加达到高峰期，醪液pH值又降至最低；是酵母、乳酸菌(乳酸球菌、乳酸杆菌)变化最剧烈的时期；此期间拟内孢霉酵母的作用已小。淋饭酒母制作过程中乳酸球菌、乳酸杆菌起到非常重要的作用，把酒药、曲、熟地上接入的酵母和乳酸杆菌顺利培养成酒母。乳酸球菌、乳酸杆菌是保障淋饭酒母制作正常进行、顺利完成的关键菌。影响淋饭酒母制作的主要因素：气温、曲、操作手法、水。淋饭酒母中主要微生物来源于酒药、曲和生产场地。淋饭酒母的作用：接种、作掺醅、冲缸、淋饭酒、家酿酒、分离酵母菌和乳酸杆菌等。(孙悟)     

Pilot scale inulin extraction from chicory roots assisted by pulsed electric fields

A pilot study for the pulsed electric fields (PEF) assisted countercurrent diffusion of inulin from chicory roots is presented. The influence of PEF parameters (electric field intensity E = 600 V cm^?1, treatment duration t_PEF = 10–50 ms) and diffusion temperature (varied between 30 and 80 °C) on soluble matter extraction kinetics, inulin content of juice, and pulp exhaustion are investigated. The draft (liquid to solid mass ratio) was fixed at 140%, similar to the industrial conditions. PEF treatment facilitates extraction of inulin at conventional diffusion temperature (70–80 °C), and diffusion temperature can even be reduced by 10–15 °C with comparable juice inulin concentration. Less energy consumption can be achieved by reducing PEF treatment duration to 10 ms, which is observed sufficient for effective extraction.     

Inactivation of wine-associated microbiota by continuous pulsed electric field treatments

Four different treatments of pulsed electric field (PEF) technology were tested in a continuous-flow system for inactivating 25 species of yeast, lactic acid bacteria and acetic acid bacteria associated with wines. Overall, the reached inactivation varied from 0.64 to 4.94 log units. Curiously, it was determined that the application of higher specific energy did not provide significant declination of yeast population, although significantly different inactivations were determined for bacteria. The inactivation of bacteria highly depended on each species and results corroborated different sensitivity of two Oenococcus oeni strains what could be related with their genetic characteristics.     

Effect of single or sequential hot water and lactic acid decontamination treatments on the survival and growth of listeria monocytogenes and spoilage microflora during aerobic storage of fresh beef at 4, 10, and 25 degrees C

The survival and growth of Listeria monocytogenes and spoilage microflora during storage of fresh beef subjected to different decontamination treatments was studied. Fresh beef inoculated with a five-strain mixture of L. monocytogenes (5.18 log CFU/cm2) was left untreated (control) or was immersed (30 s) in hot water (HW; 75 degrees C), 2% lactic acid (LA; 55 degrees C), hot water followed by lactic acid (HW-LA), or lactic acid followed by hot water (LA-HW) and then stored aerobically at 4, 10, and 25 degrees C for 25, 17, and 5 days, respectively. Initial populations of L. monocytogenes were reduced by 0.82 (HW), 1.43 (LA), 2.73 (HW-LA), and 2.68 (LA-HW) log CFU/cm2. During storage, the pathogen grew at higher rates in HW than in control samples at all storage temperatures. Acid decontamination treatments (LA. HW-LA, and LA-HW) resulted in a weaker inhibition of L. monocytogenes (P < 0.05) at 25 degrees C than at 4 and 10 degrees C. In general, the order of effectiveness of treatments was HW-LA > LA > LA-HW > HW > control at all storage temperatures tested. In untreated samples, the spoilage microflora was dominated by pseudomonads, while lactic acid bacteria, Enterobacteriaceae, and yeasts remained at lower concentrations during storage. Brochothrix thermosphacta was detected periodically in only a limited number of samples. Although decontamination with HW did not affect the above spoilage microbial profile, acid treatments shifted the predominant microflora in the direction of yeasts and gram-positive bacteria (lactic acid bacteria). Overall, the results of the present study indicate that decontamination with LA and combinations of LA and HW could limit growth of L. monocytogenes and inhibit pseudomonads, which are the main spoilage bacteria of fresh beef stored under aerobic conditions. However, to optimize the efficacy of such treatments, they must be applied in the appropriate sequence and followed by effective temperature control.     

Optimising the inactivation of grape juice spoilage organisms by pulse electric fields

The effect of some pulsed electric field (PEF) processing parameters (electric field strength, pulse frequency and treatment time), on a mixture of microorganisms (Kloeckera apiculata, Saccharomyces cerevisiae, Lactobacillus plantarum, Lactobacillus hilgardii and Gluconobacter oxydans) typically present in grape juice and wine were evaluated. An experimental design based on response surface methodology (RSM) was used and results were also compared with those of a factorially designed experiment. The relationship between the levels of inactivation of microorganisms and the energy applied to the grape juice was analysed. Yeast and bacteria were inactivated by the PEF treatments, with reductions that ranged from 2.24 to 3.94 log units. All PEF parameters affected microbial inactivation. Optimal inactivation of the mixture of spoilage microorganisms was predicted by the RSM models at 35.0 kV cm^− 1 with 303 Hz pulse width for 1 ms. Inactivation was greater for yeasts than for bacteria, as was predicted by the RSM. The maximum efficacy of the PEF treatment for inactivation of microorganisms in grape juice was observed around 1500 MJ L^− 1 for all the microorganisms investigated. The RSM could be used in the fruit juice industry to optimise the inactivation of spoilage microorganisms by PEF.     

Antimicrobial activity of nisin against Oenococcus oeni and other wine bacteria

Nisin is a bacteriocin used against food spoilage bacteria. Sulphur dioxide is a potent antioxidant as well as an antimicrobial agent widely used in the wine industry. In this study we describe the effect of these important antibacterial agents on the growth of a collection of 64 lactic acid bacteria (23 Oenococcus, 29 Lactobacillus, 3 Leuconostoc and 9 Pediococcus), 23 acetic acid bacteria and 20 yeast isolates, most of them recovered from wine. Minimal inhibitory concentrations (MIC) and minimal bactericide concentrations of nisin, potassium metabisulphite and ethanol were determined. Nisin MIC(50) values for the tested isolates were as follows: 0.024, 12.5, 200 and > or micro for oenococci, lactobacilli-pediococci-leuconostoc, acetic acid bacteria and yeasts, respectively. Synergistic effects on bacterial growth inhibition were observed, and potassium metabisulphite MIC(50) values decreased from one to three orders of dilution when it was combined with subinhibitory concentrations of nisin in the growth media. This effect was observed in all lactic acid bacteria species of our study. Significant differences in nisin sensitivity were observed between Gram-positive and Gram-negative bacteria, and between Oenococcus oeni and other species of lactic acid bacteria. It is concluded that appropriate combinations of nisin and metabisulphite could control the growth of spoilage bacteria in wine and therefore allow a decrease in the levels of sulphur dioxide currently used by the wine industry.     

Microbial growth in vacuum packaged frankfurters produced in Spain

The effects of storage temperature and time on the microflora of vacuum packed frankfurters were analysed. Total aerobic counts, lactic acid bacteria, Brochothrix thermosphacta and yeast and moulds, were determined as functions of time. Statistically significant differences were observed (P ≤0·001) amongst the counts obtained at 2 and 7°C. At the end of the controlled storage period (42 days) the sausages kept at 7°C showed signs of spoilage. The appearance of superficial slime occurred after 28 days in samples with lactic acid bacteria at counts higher than 10⁸ cfu g⁻¹. The swelling of the pack showed after 42 days in those samples which had a level higher than 5 × 10⁸ cfu g⁻¹. On the contrary, the samples kept at 2°C did not show the aforesaid spoilage signs during the period of controlled storage. Basing our conclusions on the results obtained, a period of shelf life of 28 days was established at 7°C, whilst at 2°C a minimum shelf life of 42 days was obtained.     

Evaluation of Microbial Stability,Bioactive Compounds,Physicochemical Properties,and Consumer Acceptance of Pomegranate Juice Processed in a Commercial Scale Pulsed Electric Field System

This paper investigated the feasibility for pasteurizing raw (100 %) pomegranate juice in a commercial scale pulsed electric field (PEF) processing system. The juice was processed at 35 and 38 kV/cm for 281 μs at 55 °C with a flow rate of 100 L/h. Effect of PEF processing on microbial stability, color, °Brix, pH, sediment, antioxidant activity, total phenolic content, anthocyanin, and sensory properties after the treatments and during storage at 4 °C for 12 weeks were studied and compared to those of thermally processed juice. PEF treatments significantly (p?<?0.05) inhibited the growth of total aerobic bacteria, which remained at <2.5 log colony-forming units (CFU)/ml during the 12-week storage. No yeast and mold were detected (<0.69 log CFU/ml) in the PEF-treated juices during storage up to weeks 10 and 12, which is similar to the thermally processed juice. There were no significant differences in pH and °Brix values between the PEF processed juice and unprocessed juice. PEF processing did not alter the contents of total phenolics and anthocyanin as compared to unprocessed juice. PEF processing had significantly (p?<?0.05) less impact on the color of pomegranate juice than thermal processing. PEF-treated juice had the same consumer satisfaction scores as the unprocessed juice, which were significantly (p?<?0.05) higher than thermally processed juice samples. There was no significant difference between the two PEF treatments in all results. This study demonstrated that PEF technology extended microbial shelf-life and preserved the major quality and nutritional characteristics of pomegranate juice, and hence, is technically feasible for commercialization in the juice industry.     

Alternative Pressing/Ultrafiltration Process for Sugar Beet Valorization: Impact of Pulsed Electric Field and Cossettes Preheating on the Qualitative Characteristics of Juices

Alternative process of sugar beet transformation is investigated by tuning experimental conditions. A three-step process has been set-up: (1) sugar beet cossettes pretreatment by pulsed electric field (PEF) and (or) short preheating to different temperatures; (2) extraction of juice from pre-treated cossettes by pressing; and (3) purification of the expressed juice by ultrafiltration. The PEF treatment was applied to cold (10 °C) and preheated (to 20, 50, 60, 70, and 80 °C) sugar beet cossettes with intensity of E?=?600 V cm^?1 using rectangular monopolar pulses of 100 μs during t _PEF?=?5–20 ms. Experiments were performed with cossettes of three sizes. Control experiments were done without PEF treatment using cold (10 °C) and preheated (to 20–80 °C) cossettes. PEF-treated and (or) preheated cossettes were pressed at 5 bars during 15 min. Afterward, expressed juices obtained from the PEF-treated cossettes at 20 °C and from the untreated ones at 80 °C were purified by dead-end ultrafiltration with stirring (500 rpm) at the temperature of 20 °C by using polyethersulfone membrane with MWCO of 30 kDa. Application of PEF (E?=?600 V cm^?1, t _PEF?=?10 ms, T?=?20 °C) with following pressing of cossettes at 5 bars during 15 min permits to obtain the juice yield Y?=?66,5 %, which is equivalent to that obtained from cossettes preheated to 80 °C and untreated electrically (Y?=?64 %). The energy consumption of cold PEF treatment (≈2–3 Wh/kg) is very attractive as compared to preheating at high temperatures (≈138–194 Wh/kg). Combination of thermal and electrical pretreatments leads to additional softening of sugar beet tissue and to a slightly higher (on 5–10 %) juice yield, but the electroporation of preheated cossettes is more energetically costly. The raw juice expressed from PEF-treated cossettes at 20 °C has higher purity (93.5 %) than juices expressed at 50 °C (92.9 %) and at 80 °C (92.3 %). The temperature increasing from 20 to 80 °C results in a higher juice coloration (5680 IU at 20 °C and 7820 IU at 80 °C) and leads to a higher (on about 35 %) colloids concentration in the expressed juice. The filtrate obtained from the juice expressed at 20 °C with PEF treatment has a higher purity (96 %) than the filtrate obtained from the juice expressed at 80 °C (95.3 %) and its coloration is considerably lower (330 IU versus 1930 IU). In addition, the quantity of proteins and colloids in the filtrate of juice expressed at 20 °C is lower than that in the filtrate of juice expressed at 80 °C     

Rapid and sensitive in situ hybridization method for detecting and identifying lactic acid bacteria in wine

A rapid and sensitivein situhybridization method, using total genomic DNA probes, can specifically detect and identify the lactic acid bacteria in wine. The total genomic DNA probes were labelled with digoxygenin (DIG) by random priming and hybridized with the genomic DNA of the bacteria to be identified. The hybrids were detected with fluorescent anti-DIG Fab-fragments or with enzyme-conjugated anti-DIG Fab-fragments. The cell wall of the Gram-positive lactic acid bacteria was made permeable with a lysozyme treatment to allow the accessibility of the probe to the target DNA and the penetration of anti-DIG antibodies which specifically bound to their antigens. The total genomic DNA probes exhibited the same specificity with dot-blot andin situhybridization. Thein situhybridization technique made possible the control of the bacterial population in wine at different stages of vinification of storage, and the identification of lactic acid bacteria which can cause wine spoilage.     

The development of bactericidal yeast strains by expressing the Pediococcus acidilactici pediocin gene (pedA) in Saccharomyces cerevisiae

The excessive use of sulphur dioxide and other chemical preservatives in wine, beer and other fermented food and beverage products to prevent the growth of unwanted microbes holds various disadvantages for the quality of the end‐products and is confronted by mounting consumer resistance. The objective of this study was to investigate the feasibility of controlling spoilage bacteria during yeast‐based fermentations by engineering bactericidal strains of Saccharomyces cerevisiae. To test this novel concept, we have successfully expressed a bacteriocin gene in yeast. The pediocin operon of Pediococcus acidilactici PAC1·0 consists of four clustered genes, namely pedA (encoding a 62 amino acid precursor of the PA‐1 pediocin), pedB (encoding an immunity factor), pedC (encoding a PA‐1 transport protein) and pedD (encoding a protein involved in the transport and processing of PA‐1). The pedA gene was inserted into a yeast expression/secretion cassette and introduced as a multicopy episomal plasmid into a laboratory strain (Y294) of S. cerevisiae. Northern blot analysis confirmed that the pedA structural gene in this construct (ADH1_P‐MFα1_S‐pedA‐ADH1_T, designated PED1), was efficiently expressed under the control of the yeast alcohol dehydrogenase I gene promoter (ADH1_P) and terminator (ADH1_T). Secretion of the PED1‐encoded pediocin PA‐1 was directed by the yeast mating pheromone α‐factor's secretion signal (MFα1_S). The presence of biologically active antimicrobial peptides produced by the yeast transformants was indicated by agar diffusion assays against sensitive indicator bacteria (e.g. Listeria monocytogenes B73). Protein analysis indicated the secreted heterologous peptide to be approximately 4·6 kDa, which conforms to the expected size. The heterologous peptide was present at relatively low levels in the yeast supernatant but pediocin activity was readily detected when intact yeast colonies were used in sensitive strain overlays. This study could lead to the development of bactericidal yeast strains where S. cerevisiae starter cultures not only conduct the fermentations in the wine, brewing and baking industries but also act as biological control agents to inhibit the growth of spoilage bacteria. Copyright © 1999 John Wiley & Sons, Ltd.