Some milk-associated proteins are known to be nutritionally valuable and form bioactive peptides that exhibit activity against hypertension and oxidative stress. Consumption of cheeses, such as the popular Hispanic-st...Some milk-associated proteins are known to be nutritionally valuable and form bioactive peptides that exhibit activity against hypertension and oxidative stress. Consumption of cheeses, such as the popular Hispanic-style cheese Queso Fresco (QF), may be a vehicle for delivery of these milk-associated peptides. This paper describes the effects of high-pressure processing (HPP) on the antioxidative activity (ORAC- FL value) of water-soluble proteins extracted from QF samples. QFs were manufactured according to a commercial-make procedure using pasteurized, homogenized milk, without added starter cultures. The cheese was cut into 45 × 45 × 150 mm3 blocks, double packaged in vacuum bags, and received the following HPP treatments: 200, 400, or 600 MPa for either 0, 5, 10, or 20 min, with warming to an internal temperature of either 22℃ or 40℃ prior to HPP treatment. Results show that the core temperature of the cheese during HPP directly affects the ORAC-FL value. The activities of the lower temperature cheeses are independent of time and pressure, and have a median ORAC-FL value of 27 trolox equivalents (TE). The higher temperature cheeses have higher ORAC-FL values ranging from 21.5 to 96.0 TE;the highest activity corresponded to the cheese held at 400 MPa for the longest time under pressure (20 min). The 600 MPa cheeses increase in activity with increasing time under pressure, but are less active than the control cheese. These results indicate that processing temperature and pressure are important factors in the antioxidative activity of these QF samples and further understanding of the roles of these variables may lead to the manufacture of healthier and more nutritious cheeses and dairy products.展开更多
The objective of this study was to determine the effect of environmental stresses on the cytotoxicity of Shiga toxin-producing Escherichia coli (STEC). STEC O157:H7 and six non-O157 STEC strains (O26:H11, O103:H1, O10...The objective of this study was to determine the effect of environmental stresses on the cytotoxicity of Shiga toxin-producing Escherichia coli (STEC). STEC O157:H7 and six non-O157 STEC strains (O26:H11, O103:H1, O104:H4, O111:NM, O121:NM, and O145:NM) were subjected to osmotic (aw 0.95-0.98), acid (pH 4-7), and chlorine (1-5 ppm) stresses. After stress treatments, bacterial populations, expression of virulence-associated genes, and Vero-cytotoxicity were determined. Among the strains, O145:NM survived at aw 0.97 longer than other serotypes, while O111:NM was significantly more sensitive to osmotic stress. At pH 4, O103:H1 was more resistant to the stress, while O26:H11 and O111:NM had significantly less growth. For 2 ppm chlorine stress, O26:H11, O103:H1, and O145:NM had higher populations (>3 log) than other strains. Stressed strains showed a significant increase in relative gene expression levels of stx1, stx2, and eae in O103:H1, O104:H4, and O145:NM than non-stressed control. Additionally, significantly higher Vero-cytotoxicity, as indicated by lactate dehydrogenase assay, of stressed O26:H11, O103:H1, O104:H4, and O145:NM was observed. The results suggest that the growth and cytotoxicity of selected pathogenic E. coli may be enhanced after being exposed to environmental stresses.展开更多
文摘Some milk-associated proteins are known to be nutritionally valuable and form bioactive peptides that exhibit activity against hypertension and oxidative stress. Consumption of cheeses, such as the popular Hispanic-style cheese Queso Fresco (QF), may be a vehicle for delivery of these milk-associated peptides. This paper describes the effects of high-pressure processing (HPP) on the antioxidative activity (ORAC- FL value) of water-soluble proteins extracted from QF samples. QFs were manufactured according to a commercial-make procedure using pasteurized, homogenized milk, without added starter cultures. The cheese was cut into 45 × 45 × 150 mm3 blocks, double packaged in vacuum bags, and received the following HPP treatments: 200, 400, or 600 MPa for either 0, 5, 10, or 20 min, with warming to an internal temperature of either 22℃ or 40℃ prior to HPP treatment. Results show that the core temperature of the cheese during HPP directly affects the ORAC-FL value. The activities of the lower temperature cheeses are independent of time and pressure, and have a median ORAC-FL value of 27 trolox equivalents (TE). The higher temperature cheeses have higher ORAC-FL values ranging from 21.5 to 96.0 TE;the highest activity corresponded to the cheese held at 400 MPa for the longest time under pressure (20 min). The 600 MPa cheeses increase in activity with increasing time under pressure, but are less active than the control cheese. These results indicate that processing temperature and pressure are important factors in the antioxidative activity of these QF samples and further understanding of the roles of these variables may lead to the manufacture of healthier and more nutritious cheeses and dairy products.
文摘The objective of this study was to determine the effect of environmental stresses on the cytotoxicity of Shiga toxin-producing Escherichia coli (STEC). STEC O157:H7 and six non-O157 STEC strains (O26:H11, O103:H1, O104:H4, O111:NM, O121:NM, and O145:NM) were subjected to osmotic (aw 0.95-0.98), acid (pH 4-7), and chlorine (1-5 ppm) stresses. After stress treatments, bacterial populations, expression of virulence-associated genes, and Vero-cytotoxicity were determined. Among the strains, O145:NM survived at aw 0.97 longer than other serotypes, while O111:NM was significantly more sensitive to osmotic stress. At pH 4, O103:H1 was more resistant to the stress, while O26:H11 and O111:NM had significantly less growth. For 2 ppm chlorine stress, O26:H11, O103:H1, and O145:NM had higher populations (>3 log) than other strains. Stressed strains showed a significant increase in relative gene expression levels of stx1, stx2, and eae in O103:H1, O104:H4, and O145:NM than non-stressed control. Additionally, significantly higher Vero-cytotoxicity, as indicated by lactate dehydrogenase assay, of stressed O26:H11, O103:H1, O104:H4, and O145:NM was observed. The results suggest that the growth and cytotoxicity of selected pathogenic E. coli may be enhanced after being exposed to environmental stresses.
