Effect of peracetic acid on biofilms formed by Listeria monocytogenes strains isolated from a Brazilian cheese processing plant

ABSTRACT This study aimed to investigate the effect of peracetic acid (PAA, 0.5%) on adherent cells of three strains of Listeria monocytogenes strains belonging to serotypes 4b and 1/2b that had been previously isolated from the environment of a Brazilian cheese plant. The assays were conducted using polystyrene microplates and stainless steel coupons and the adhered cells were treated with PAA for 60, 120 and 180 s. On stainless steel, biofilms were partially inactivated by PAA after 60 s and almost 100% of the cells were damaged within 180 s using epifluorescence microscopy with LIVE/DEAD® staining. On polystyrene microplates, PAA decreased (P<0.05) biofilm biomass produced by the three L. monocytogenes isolates at 60 s, when compared with controls (no PAA treatment). However, PAA did not completely eliminate L. monocytogenes cells on polystyrene microplates (decreasing 1.8-2.5 log cycles after treatment with PAA for 180 s). The correct concentration and contact time of PAA is critical for eliminating biofilms formed by L. monocytogenes on stainless steel surfaces, although further studies are needed for defining efficient PAA treatments to remove adherent cells of this pathogen on plastic polymers

In vitro ability of beer fermentation residue and yeast-based products to bind aflatoxin B1

This study aimed to verify the in vitro ability of beer fermentation residue (BFR) containing Saccharomyces cerevisiae cells and five commercial products that differed in the viability and integrity of S. cerevisiae cells to remove aflatoxin B1 (AFB1) from a citrate-phosphate buffer solution (CPBS). BFR was collected at a microbrewery and prepared by drying and milling. The commercial yeast-based products were as follows: inactive intact yeast cells from beer alcoholic fermentation, inactive intact yeast cells from sugarcane alcoholic fermentation, hydrolyzed yeast cells, yeast cell walls and active yeast cells. Adsorption assays were performed in CPBS spiked with 1.0 μg AFB1/mL at pH 3.0 and 6.0 for a contact time of 60 min at room temperature. Analysis of AFB1 in the samples was performed by high performance liquid chromatography. AFB1 adsorption by the products ranged from 45.5% to 69.4% at pH 3.0 and from 24.0% to 63.8% at pH 6.0. The higher percentages (p < 0.05) of AFB1 binding at both pH values were achieved with products containing hydrolyzed yeast cells or yeast cell walls rather than intact cells. The AFB1 binding percentages of BFR were 55.0 ± 5.0% at pH 3.0 and 49.2 ± 4.5% at pH 6.0, which was not significantly different (p > 0.05) from commercial products containing inactive intact yeast cells. The results of this trial indicate that the yeast-based products tested, especially the BFR, have potential applications in animal feeds as a suitable biological method for reducing the adverse effects of aflatoxins.

Relação entre psicrotróficos e frações de caseína do leite longa vida durante o armazenamento / Relationship between psychrotrophic and casein fractions of long life milk during storage

As bactérias psicrotróficas podem afetar a qualidade de diversos produtos lácteos. A relação entre a contagem de psicrotróficos no leite pasteurizado e as frações de caseína do leite longa vida foi avaliada. O processo ultra alta temperatura foi conduzido de acordo com a seguinte sequência: pasteurização a 72-75 ºC por 15 s, pré-aquecimento a 85º C, esterilização a 142-145 ºC por 2 s por injeção direta de vapor ao leite, remoção da água condensada, resfriamento a 70 ºC, homogeneização, resfriamento a 20 ºC, envase asséptico em embalagens cartonadas de 1L e armazenamento à temperatura ambiente por 120 dias. As contagens de psicrotróficos foram determinadas no leite pasteurizado por contagem padrão em placas. As frações de caseína (as1, as2, beta e k) foram avaliadas no leite longa vida nos dias 8 e 120 de armazenamento por cromatografia líquida de alta eficiência. Foi observado aumento na quantidade de as2-caseína e redução da as2-caseína como porcentagem da caseína total ao final do armazenamento (P<0,05). Houve correlação positiva (P<0,05) no dia 120 de armazenamento entre psicrotróficos e a fração k-caseína.

Psycrothrophic bacteria can affect the quality of several dairy products. The relationship between psycrothrophic counts in pasteurized milk and casein fractions of ultra-high-temperature (UHT) milk was evaluated. The UHT process was performed according to the following sequence: pasteurization at 72-75 oC for 15 s, pre-heating at 85 oC, sterilization at 142-145 ºC for 2 s by direct steam injection into milk, removing of the condensed water, cooling to 70 ºC, homogenization, cooling to 20 ºC, bottling aseptically in 1-L sterile carton boxes and storage at room temperature for 120 days. Psycrothrophic counts were determined in pasteurized milk by standard plate count. Casein fractions (as1, as2, beta and k) were analyzed in UHT milk on days 8 and 120 by high performance liquid chromatography. It was observed increase in quantity of as2-casein and reduction of as2-casein as a percentage of total casein at the end of storage period (P<0,05). There was a positive correlation (P<0,05) on day 120 of storage between psychrotrophic and the k-casein fraction (P<0.05).

Atividade de plasmina e plasminogênio no leite longa vida com alta e baixa contagem de células somáticas durante o armazenamento / Activity of plasmin and plasminogen in ultra high temperature milk with high and low somatic cell counts during storage

O objetivo deste estudo foi avaliar o efeito da contagem de células somáticas (CCS) do leite na atividade de plasmina e plasminogênio durante o período de armazenamento do leite longa vida integral. Os leites crus foram categorizados em grupos de CCS de baixa (342.000-487.000 células mL-1) e alta contagem (603.000-808.000 células mL-1). Dois lotes de leite longa vida em cada categoria de CCS foram analisados para determinação de plasmina e plasminogênio após 10, 30, 60, 90 e 120 dias de armazenamento em temperatura ambiente. Para a fabricação do leite longa vida, o leite cru foi submetido à pasteurização rápida seguida da esterilização industrial do leite por injeção de vapor pelo método direto e embalagem asséptica do produto. A CCS não apresentou efeitos sobre as características físico-químicas do leite cru, e nem sobre a atividade de plasmina e plasminogênio nos leites cru e longa vida, armazenados por 120 dias. Entretanto, independentemente da CCS, a atividade de plasmina e plasminogênio aumentou no leite longa vida ao longo do armazenamento, indicando a possibilidade de aumento da proteólise no produto durante sua vida de prateleira.

This study aimed to evaluate the effect of somatic cell counts (SCC) in milk on plasmin and plasminogen activities of ultra high temperature (UHT) milk during storage. Raw milks were categorized in SCC groups of low (342,000-487,000 cells mL-1) and high cells (603,000-808,000 cells mL-1). Two replicates of UHT milks within each SCC category were analyzed for plasmin and plasminogen activities after 10, 30, 60, 90 and 120 days of storage at room temperature. For manufacture of UHT milk, raw milk was pasteurized and sterilized by direct vapor injection process, followed by aseptic packaging. SCC had no effect on physical-chemical characteristics of raw milk, and on plasmin or plasminogen activities in raw and UHT milks during 120 days of storage. However, independently of the SCC in raw milk, the activity of plasmin and plasminogen increased in UHT milk during storage, hence indicating a possible increase in proteolysis in the product during its shelf-life.