Fat content increases the lethality of ultra-high-pressure homogenization on Listeria monocytogenes in milk

Listeria monocytogenes CCUG 15526 was inoculated at a concentration of approximately 7.0 log₁₀ cfu/mL in milk samples with 0.3, 3.6, 10, and 15% fat contents. Milk samples with 0.3 and 3.6% fat content were also inoculated with a lower load of approximately 3.0 log₁₀ cfu/mL. Inoculated milk samples were subjected to a single cycle of ultra-high-pressure homogenization (UHPH) treatment at 200, 300, and 400 MPa. Microbiological analyses were performed 2 h after the UHPH treatments and after 5, 8, and 15 d of storage at 4°C. Maximum lethality values were observed in samples treated at 400 MPa with 15 and 10% fat (7.95 and 7.46 log₁₀ cfu/mL), respectively. However, in skimmed and 3.6% fat milk samples, complete inactivation was not achieved and, during the subsequent 15 d of storage at 4°C, L. monocytogenes was able to recover and replicate until achieving initial counts. In milk samples with 10 and 15% fat, L. monocytogenes recovered to the level of initial counts only in the milk samples treated at 200 MPa but not in the milk samples treated at 300 and 400 MPa. When the load of L. monocytogenes was approximately 3.0 log₁₀ cfu/mL in milk samples with 0.3 and 3.6% fat, complete inactivation was not achieved and L. monocytogenes was able to recover and grow during the subsequent cold storage. Fat content increased the maximum temperature reached during UHPH treatment; this could have contributed to the lethal effect achieved, but the amount of fat of the milk had a stronger effect than the temperature on obtaining a higher death rate of L. monocytogenes.     

A comparative study of changes in the microbiota of apple juice treated by high hydrostatic pressure (HHP) or high pressure homogenisation (HPH)

The objective of this study was to assess the effect of High Pressure Homogenisation (HPH) compared with High Hydrostatic Pressure (HHP) on the microbiological quality of raw apple juice during storage at ideal (4 °C) and abuse (12 °C) temperatures. In the case of HPH, only low numbers of micro-organisms were detected after treatment at 300 MPa (typically between 2 and 3 log.ml⁻¹). These were identified as Streptomyces spp., and numbers did not increase during storage of the juice for 35 days, irrespective of storage temperature. In the case of HHP, the total aerobic counts were also reduced significantly (p < 0.05) after treatment for 1 min at 500 and 600 MPa and the numbers did not increase significantly during storage at 4 °C. However, during storage at 12 °C the counts did increase significantly (p < 0.05) and by day 14 counts at 500 MPa were not significantly different from the control juice. This confirms that good temperature control is important if the full benefits of HHP treatment are to be realised.Frateuria aurantia dominated the microbiota of the HHP apple juice stored at 12 °C along with low levels of Bacillus and Streptomyces spp.The HPH and HHP juices both turned brown during storage indicating that neither treatment was sufficient to inactivate polyphenol oxidase. The enzyme is known to be pressure resistant and this discolouration was controlled by a heat treatment (70 °C for 1 min) used in commercial practice and given prior to HP treatment.     

Microbiological Attributes of Turkish Butters Sold Under Market Conditions

In this study, microbiological quality of 45 butter samples sold under market conditions at Manisa (Turkey) was investigated. Total coliform, total fecal coliform, Escherichia coli and yeast and mould counts were found between < 1.0 – > 3.15 log₁₀ cfu.g^-1, < 1.0 – > 3.15 log₁₀ cfu.g^-1, < 1.0 – > 3.15 log₁₀ cfu.g^-1 and < 1.0 – > 6.62 log₁₀ cfu.g^-1 respectively. Only in one sample Salmonella was detected. Staphylococcus aureus was not detected in any of the samples. To that extent butters sold under market conditions in Manisa have high coliform, yeast and mould contamination. Received: April 29, 2008; received in revised form: May 28, 2008; accepted: June 3, 2008     

Influence of organic acid concentration on survival of Listeria monocytogenes and Escherichia coli 0157:H7 in beef carcass wash water and on model equipment surfaces

Acid-adapted cultures of Escherichia coli O157:H7 and Listeria monocytogenes were inoculated in meat decontamination spray-washing runoff fluids in order to evaluate their survival and potential to form biofilms on stainless steel coupons. The cultures (10⁷ cfu ml⁻¹) and stainless steel coupons were exposed to mixtures of water and organic acid washings (composites of each of 2% acetic acid or lactic acid washings with water washings from meat decontamination in proportions of 1/9, 1/49, 1/99 [vol/vol]) or to water washings for up to 14 days at 15°C. E. coli O157:H7 formed biofilms and remained detectable (1.3 log cfu cm⁻²) on stainless steel for up to 4 d in the 1/9 dilution (pH 3.17–3.77) of the organic acid washings, and persisted throughout storage (14 d) in the 1/49 (pH 3.96–4.33) and 1/99 (pH 4.34–6.86) dilution of the organic acid washings. L. monocytogenes populations were unable to form detectable (<1.3 log cfu cm⁻²) biofilms in the 1/9 and 1/49 dilutions of both organic acid washings for up to 14 d; however, by day-14 in the 1/99 dilution of the washings, the pathogen was able to attach at detectable levels (2.7 to 3.4 logs). The pH effects of lower concentrations (1/49 or 1/99) of acidic washings decreased over time due to the formation of amine compounds produced by the natural meat flora, allowing resuscitation of the acid-stressed pathogen survivors. The resuscitation of acid-stressed pathogens may potentially enhance their survival and prevalence in biofilms and thus more attention should be focused on avoiding or minimizing the collection of decontamination runoff fluids on food contact equipment surfaces.     

Combination of warm water and hydrogen peroxide to reduce the numbers of Salmonella Typhimurium and Listeria innocua on field salad (Valerianella locusta)

The optimal conditions of decontamination of field salad by treatment with warm water containing hydrogen peroxide were determined with the aid of a central composite design. It was the aim to improve the hygienic status while keeping the sensory quality at the highest level possible. Two series of experiments were performed to study the effects of the following parameters: temperature (45–50 °C), H₂O₂ (1–4%) and treatment time (60–210 s). In series 1 the effect on sensory properties and reduction of total aerobic counts was investigated. To determine sensory quality, treated samples stored at 4 °C for 7 days were subjected to evaluation by 15 panelists. Overall visual quality (OVQ), color, texture and odor correlated well with product acceptability (R²=0.934, 0.946, 0.945 and 0.956, respectively), and OVQ was the most sensitive criterion. An acceptability of 75% in OVQ was chosen as the limit and an acceptance area was defined to deduce permitted conditions for decontamination. Within that area a reduction of total counts by 2.64–3.22 and 1.9–3.48 log₁₀ cfu/g was achieved after treatment and storage at 4 °C for 7 days, respectively. In series 2 field salad was inoculated with Listeria innocua and Salmonella Typhimurium and it was observed that within the area of acceptability a reduction of the numbers of the challenge organisms by 1.27–3.26 and 0.79–3.05 log₁₀ cfu/g, respectively, was achieved immediately after treatment, and by 1.64–3.09 (L. innocua) and 1.1–2.63 log₁₀ cfu/g (S. Typhimurium) after storage. The initial decontaminating effect on L. innocua and S. Typhimurium was sustained or even increased after storage, when the salad was treated below 48.9 °C for more than 68 s. Three independent experiments confirmed the reliability of the models of the count reduction of L. innocua and S. Typhimurium.     

The fate of Clostridium perfringens spores exposed to ozone and/or mild heat pretreatment on beef surfaces followed by modified atmosphere packaging

Clostridium perfringens is a natural contaminant of raw beef products that can proliferate to dangerous cell levels under conditions of temperature abuse. Spores of the bacterium were inoculated onto irradiated London broil beef at levels of 3 log₁₀ spores/g beef. Samples of beef (7.5×10.0×1.0 cm) were treated with aqueous ozone (5 ppm O₃ for 5 min), or heat (60°C for 30 min), or both and then vacuum-packaged to 2 kPa for up to 10 d storage at 37°C, 25°C, or 4°C. Storage at 37°C resulted in increases in viable counts after 1 d to over 7 log₁₀ cfu/g beef, whereas storage at 4°C prevented spore germination and growth for all treatments. At 25°C, heat-treated beef samples reached 6 log₁₀ cfu/g viable counts in 2 d and spores/vegetative cells on control or ozone-treated samples did not germinate or grow through the first day of vacuum-packaged storage. Modified atmospheres with increasing CO₂ concentration were also compared with regard to bacterial survival during beef storage at 25°C. C. perfringens spores remained dormant in control and ozone-treated beef during a 10-d storage at 25°C. Pretreatment with heat increased germination and outgrowth during storage of beef, whereas ozone treatment and no treatment controls were effective in inhibiting spore germination and outgrowth in combination with increasing CO₂ concentrations above 30% or refrigeration. These data support the avoidance of heat in the pretreatment of raw beef.     

Repair and growth of heat- and freeze-injured Escherichia coli O157:H7 in selective enrichment broths

Two Escherichia coli O157:H7 strains, ATCC 35150 and 43894, were heat injured in a beef infusion at 53°C for 40 and 50 min, respectively (1· 5–2·0 log₁₀cfu ml⁻¹of injury) and freeze injured at −25°C for 30 days (1 log₁₀cfu ml⁻¹of injury) as determined by plating on MacConkey agar with 0·60% bile salts #3 (Mac-BS) as the selective medium and on Brain Heart Infusion agar (BHIA) as the non-selective medium. Repair of injury was measured in five selective enrichment broths [buffered peptone water supplemented with vancomycin, cefsulodin, and cefixime (BPW-VCC), modified EC broth with novobiocin (mEC+n), enterohaemorrhagic E. coli enrichment broth (EEB), double modified TSB (dmTSB), and BCM^®E. coli enrichment broth (BCM^®-EB)] versus TSB as the non-selective control broth over 3 h incubation at 37°C and 42°C. Repair was measured as the increase in cfu ml⁻¹enumerated on Mac-BS with time vs the total cfu ml⁻¹(injured and uninjured cells) enumerated on BHIA. In mEC+n, EEB, and dmTSB some death of both heat- and freeze-injured cells occurred immediately during the 3 h incubation (decrease on BHIA plates), and there was either minimal or no repair of the injured cells at both temperatures. Efficient repair of heat injury was obtained with both BPW-VCC and BCM^®-EB, but the latter produced a growth rate and final cell concentration closer to TSB. In freeze-injury repair however, BPW-VCC gave poor results while repair in BCM^®-EB was equal to TSB. Both BCM^®-EB and BPW-VCC inhibited the growth of all Gram-positive and a select number of Gram-negative bacteria tested. The ability of the selective enrichment broth BCM^®-EB to resuscitate heat- and freeze-injured E. coli O157:H7 efficiently within 3 h, warrants further testing with other types of stress in both artificially and naturally contaminated foods.     

Survival of Lactobacillus casei and functional characteristics of reduced sugar red beetroot yoghurt with natural sugar substitutes

In this study, probiotic gel fermentation and functional characteristics of reduced sugar yoghurt with red beetroot bioactive components and steviol glycosides from Stevia rebaudiana extracts as natural source of noncaloric sweeteners were investigated. A significant increase in Lactobacillus casei viability and fermented gel network and a decrease in syneresis were determined in yoghurt sweetened with steviol glycosides and high content of red beetroot bioactive components such as total phenolics, anthocyanins and total antioxidant capacity (DPPH and FRAP). The survival of L. casei was maintained within probiotic and therapeutic levels (>9 log₁₀ CFU/g), due to the possible prebiotic effect of steviol glycosides and fermentable fibres and phenolic compounds of red beetroot during 28 days of cold storage of the probiotic yoghurts. Colour properties (L*, a*, b*, ΔE*, C*, h*) and such sensory properties as smoothness, sweetness astringency were significantly affected. The highest organic acid content was found in red beetroot enriched yoghurt with stevia, while the most dominant organic acids were butyric, lactic, malic and citric. As a result, it was determined that fermented milk products, which are supported by phytochemical and steviol glycoside interactions, have adequate nutritional effects, high probiotic viability and acceptable sensory properties     

Assessment of the microbiological safety of salad vegetables and sauces from kebab take-away restaurants in the United Kingdom

The purpose of this study was to establish the microbiological safety of salad vegetables and sauces served in kebab take-away restaurants. Comparison with published microbiological guidelines revealed that 4.7% of 1213 salad vegetable samples were of unsatisfactory microbiological quality due to Escherichia coli and/or Staphylococcus aureus levels at ≥10² cfu g⁻¹. Another 0.3% of salad samples were of unacceptable quality due to S. aureus at ≥10⁴ cfu g⁻¹ (2 samples) or the presence of Salmonella Kentucky (1 sample). Cucumber was the most contaminated salad vegetable with regards to unsatisfactory levels of E. coli (6.0%) or S. aureus (4.5%). Five percent of 1208 sauce samples were of unsatisfactory microbiological quality due to E. coli, S. aureus at ≥10² cfu g⁻¹ and/or Bacillus cereus and other Bacillus spp. at ≥10⁴ cfu g⁻¹. A further 0.6% of sauce samples were of unacceptable quality due to Bacillus spp. (Bacillus subtilis, Bacillus pumilus, Bacillus licheniformis) at ≥10⁵ cfu g⁻¹ or the presence of Salmonella Agbeni (1 sample). More samples of chilli sauce (8.7%) were of unsatisfactory or unacceptable microbiological quality than any other sauce types. The results emphasize the need for good hygiene practices in kebab take-away restaurants handling these types of ready-to-eat products.     

Evaluation of buoyant density centrifugation as a sample preparation method for NASBA-ELGA detection ofCampylobacter jejuni in foods

Buoyant densities of four Campylobacter jejuni strains were in the range of 1·084–1·087 g ml⁻¹. Milk (3% fat) and chicken skin homogenates had buoyant densities beneath 1·033 g ml⁻¹. Discontinuous buoyant density centrifugation (BDC) in 40% Standard Isotonic BactXTractor medium respectively succeeded in recovering C. jejuni (5×10³–5×10⁴cfu ml⁻¹) from spiked milk (3% fat) and chicken skin. NASBA–ELGA detection of C. jejuni (5×10²–5×10³cfu ml⁻¹) in 12 different food samples using four different sample preparation methods was performed: RNA extraction by heating (filter and non-filter stomacher bag), RNA extraction by BDC (non-filter stomacher bag), RNA extraction by GuSCN–Triton-X-100 lysis and silica-purification (non-filter stomacher bag). BDC succeeded in overcoming inhibition of the amplification reaction except for one of the soft cheese samples. It was noticed that for chicken skin, chicken meat, pork, chicken sausage, turkey meat, milk (3% fat) and skimmed milk a simple heat treatment at 96°C without any additional precautions to prevent inhibition accomplished NASBA–ELGA detection of the pathogen. The use of a filter stomacher bag improved the quality of the NASBA–ELGA detection signal for beef but did not prevent inhibition of the amplification reaction in the cases of ground beef, prepared minced meat, soft cheese and hard cheese. The silica purification of RNA (which was used as a control treatment) accomplished NASBA–ELGA detection of C. jejuni for all of the latter food homogenates.     

Effects of somatic cell counts on the physicochemical and rheological properties of yoghurt made from sheep’s milk

In the present work, yoghurts were made from sheep’s milk with two different somatic cell count (SCC), at low (200 000 cells mL^?1) and high (750 000 cells mL^?1) levels. The characteristics of the final product were analysed for pH, acidity, protein, total solids, fat, syneresis, water holding capacity (WHC) and apparent viscosity. Samples were analysed on days 1, 7 and 14 after production of yoghurts. The SCC had no significant effect either on the acidity or pH of the yoghurt at 24 h (P > 0.05) but a significant effect (P < 0.05) was observed at 168 h. No effects of SCC were observed on total solids and fat content of the yoghurt after 24 and 168 h. High SCC (HSCC) yoghurt had higher protein content (P < 0.05). The yoghurt with the highest SCC had the highest level of syneresis. Viscosity of HSCC yoghurt was higher than that of the low SCC yoghurt on days 1, 7 and 14 of storage. The flow properties also showed that the low SCC yoghurt was softer than that from milk with high content in somatic cells.     

Aerobic bacterial, coliform, Escherichia coli and Staphylococcus aureus counts of raw and processed milk from selected smallholder dairy farms of Zimbabwe

A cross sectional study was conducted to enumerate total viable bacteria (TBC), coliforms, Escherichia coli and Staphylococcus aureus in raw (n = 120) and processed (n = 20) milk from individual farms from three smallholder dairy schemes of Zimbabwe between October, 2009 and February, 2010. Data on management factors were collected using a structured questionnaire. A standard pour plate technique was used to enumerate total viable bacteria, while for coliforms, E. coli and S. aureus, counts were assessed by the spread plate technique. The association of total viable bacterial counts and management factors was assessed using univariable and a linear regression model. The log₁₀ TBC for raw milk differed significantly (P < 0.05) amongst the schemes with the lowest (5.6 ± 4.7 log₁₀ cfu/ml) and highest (6.7 ± 5.8 log₁₀ cfu/ml) recorded from Marirangwe and Nharira respectively. The mean log₁₀ of TBC of processed milk (6.6 ± 6.0 log₁₀ cfu/ml) were marginally higher than those of raw milk (6.4 ± 5.6 log₁₀ cfu/ml) but not significant (P > 0.05). The coliform, E. coli and S. aureus counts for raw milk significantly differed (P < 0.05) amongst the study areas. The variation in TBC, coliforms, E. coli and S. aureus counts amongst the schemes could be attributed to differences in milking hygiene where farms with more access to training and monitoring of microbiological quality of milk had lower counts. Linear regression analysis revealed dairy scheme, delivery time and season of milking as independently associated with increased TBC of raw milk. The high TBC of raw and processed milk generally indicated low levels of milking hygienic practices, and high level of post-processing contamination, respectively. The high TBC, coliform, E. coli and S. aureus counts of both raw and processed milk may present a public health hazard. Thus, educating the farmers on general hygienic practices, quickening the delivery of milk to collection centres, or availing cooling facilities on-farm will improve the microbiological quality and safety of milk.     

Low pressure CO2 storage of raw milk: microbiological effects

The effects of holding raw milk under carbon dioxide pressures of 68 to 689 kPa at temperatures of 5, 6.1, 10, and 20°C on the indigenous microbiota were investigated. These pressure-temperature combinations did not cause precipitation of proteins from the milk. Standard plate counts from treated milks demonstrated significantly lower growth rate compared with untreated controls at all temperatures, and in some cases, the treatment was microcidal. Raw milk treated with CO₂ and held at 6.1°C for 4 d exhibited reduced bacterial growth rates at pressures of 68, 172, 344, and 516 kPa; and at 689 kPa, demonstrated a significant loss of viability in standard plate count assays. The 689-kPa treatment also reduced gram-negative bacteria and total Lactobacillus spp. The time required for raw milk treated at 689 kPa and held at 4°C to reach 4.30 log₁₀ cfu/mL increased by 4 d compared with untreated controls. Total coliform counts in the treated milk were maintained at 1.95 log₁₀ cfu/mL by d 9 of treatment, whereas counts in the control significantly increased to 2.61 log₁₀ cfu/mL by d 4 and 2.89 log₁₀ cfu/mL by d 9. At d 8, Escherichia coli counts had not significantly changed in treated milk, but significantly increased in the control milk. Thermoduric bacteria counts after 8 d were 1.32 log₁₀ cfu/mL in treated milk and 1.98 log₁₀ cfu/mL in control milk. These data indicated that holding raw milk at low CO₂ pressure reduces bacterial growth rates without causing milk protein precipitation. Combining low CO₂ pressure and refrigeration would improve the microbiological quality and safety of raw milk and may be an effective strategy for shipping raw single strength or concentrated milk over long distances.     

Potential of high pressure homogenization in the control and enhancement of proteolytic and fermentative activities of some Lactobacillus species

Different species of Lactobacillus involved in dairy product fermentation and ripening were considered in order to study the effect of high pressure homogenization (HPH) on: (i) fermentation kinetics of HPH treated cells inoculated in milk; (ii) metabolic profiles; (iii) release of intracellular proteolytic enzymes; and (iv) enhance of the activity of extracellular or cellular wall located proteolytic enzymes. The HPH treatments applied were 50, 100, 150 MPa, 2 cycles at 50 and at 100 MPa. The viability loss did not exceed 1.3 log cfu/ml after the higher treatments applied. The electrophoretic profiles of α- or β-casein incubated with the different cell free filtrates shown that HPH positively affected the proteolytic activity of some strains. Moreover, HPH affected the acidification rates of the milk inoculated with the processed cells and the primary metabolism of some strains. Regarding volatile compounds, ethanol, acetoin and 2-methyl butyric acid were subjected to the major changes when the inoculum had been processed.     

Fate of Staphylococcus aureus in cheese treated by ultrahigh pressure homogenization and high hydrostatic pressure

We evaluated the influence of ultrahigh pressure homogenization (UHPH) treatment applied to milk containing Staphylococcus aureus CECT 976 before cheese making, and the benefit of applying a further high hydrostatic pressure (HHP) treatment to cheese. The evolution of Staph. aureus counts during 30 d of storage at 8°C and the formation of staphylococcal enterotoxins were also assessed. Milk containing approximately 7.3 log₁₀ cfu/mL of Staph. aureus was pressurized using a 2-valve UHPH machine, applying 330 and 30 MPa at the primary and the secondary homogenizing valves, respectively. Milk inlet temperatures (T_in) of 6 and 20°C were assayed. Milk was used to elaborate soft-curd cheeses (UHPH cheese), some of which were additionally submitted to 10-min HHP treatments of 400 MPa at 20°C (UHPH+HHP cheese). Counts of Staph. aureus were measured on d 1 (24 h after manufacture or immediately after HHP treatment) and after 2, 15, and 30 d of ripening at 8°C. Counts of control cheeses not pressure-treated were approximately 8.5 log₁₀ cfu/g showing no significant decreases during storage. In cheeses made from UHPH treated milk at T_in of 6°C, counts of Staph. aureus were 5.0 ± 0.3 log₁₀ cfu/g at d 1; they decreased significantly to 2.8 ± 0.2 log₁₀ cfu/g on d 15, and were below the detection limit (1 log₁₀ cfu/g) after 30 d of storage. The use of an additional HHP treatment had a synergistic effect, increasing reductions up to 7.0 ± 0.3 log₁₀ cfu/g from d 1. However, for both UHPH and UHPH+HHP cheeses in the 6°C T_in samples, viable Staph. aureus cells were still recovered. For samples of the 20°C T_in group, complete inactivation of Staph. aureus was reached after 15 d of storage for both UHPH and UHPH+HHP cheese. Staphylococcal enterotoxins were found in controls but not in UHPH or UHPH+HHP treated samples. This study shows a new approach for significantly improving cheese safety by means of using UHPH or its combination with HHP.     

Physicochemical properties of probiotic frozen yoghurt made from camel milk

The purpose of this research was to determine and compare the physicochemical properties of probiotic frozen yoghurts made from camel and cow milks. The results showed that the viscosity of frozen yoghurt made from camel milk was significantly higher (P < 0.05) than that from cow milk. Less fat was destabilised in frozen yoghurt made from camel milk. The frozen yoghurt made from camel milk required more time for melting than that from cow milk. Flavour scores of the frozen yoghurt made from camel milk constituents were significantly lower (P < 0.05) than those made from cow milk.     

Microbiological Attributes of Turkish Butters Sold Under Market Conditions

In this study, microbiological quality of 45 butter samples sold under market conditions at Manisa (Turkey) was investigated. Total coliform, total fecal coliform, Escherichia coli and yeast and mould counts were found between < 1.0 – > 3.15 log₁₀ cfu.g^-1, < 1.0 – > 3.15 log₁₀ cfu.g^-1, < 1.0 – > 3.15 log₁₀ cfu.g^-1 and < 1.0 – > 6.62 log₁₀ cfu.g^-1 respectively. Only in one sample Salmonella was detected. Staphylococcus aureus was not detected in any of the samples. To that extent butters sold under market conditions in Manisa have high coliform, yeast and mould contamination.     

Ascospore inactivation and germination by high pressure processing is affected by ascospore age

The effects of age on high pressure resistance of the ascospores of heat resistant moulds Byssochlamys fulva, B. nivea, Neosartorya fischeri and N. spinosa were determined. Ascospores were harvested from cultures grown for 3–15 weeks at 30 °C on malt extract agar. Following filtration and determination of concentration, the ascospores were subjected to high pressure processing (HPP) at 600 MPa for 10 min in 0.1 M citrate phosphate buffer (pH 4 and 6) and mango puree (pH 5). The results supported our hypothesis that age (maturity) affects high pressure resistance of ascospores of heat resistant moulds. A reduction of log₁₀ 2.5 cfu mL^− 1 was achieved for three week old ascospores ofB. nivea whereas for nine week old ascospores only a half log reduction was achieved. Similar results were observed for B. nivea and N. fischeri. The HPP treatment caused activation of ascospores of N. spinosa, with older ascospores showing increased activation.

Industrial relevance

The observation of activation of some ascospores by HPP, indicates that HPP alone is insufficient for elimination of these problematic spoilage microorganisms. HPP would need to be combined with other hurdles in order to produce high quality pressure-treated shelf-stable fruit products.     

Bacillus and Paenibacillus species associated with extended shelf life milk during processing and storage

Characterisation of spore formers associated with extended shelf life milk was performed by analysing the bacteriological quality of milk samples collected at various processing stages and during storage. Isolates were identified with MALDI‐TOF‐MS. Milk had spore counts <2 log₁₀ cfu/mL and 4 log₁₀ cfu/mL during processing and storage, respectively. Bacillus pumilus dominated the bacterial population. Bacterial species were inoculated into sterile milk for a shelf life study, and the population change was observed over 42 days at 7 °C. Although the extended shelf life milk process was effective in reducing bacterial counts and species diversity, the presence of Bacillus cereus shows a potential safety problem in extended shelf life milk.