Capillary Isoelectric Focusing—Useful Tool for Detection and Quantification of Lactic Acid Bacteria in Milk

The lactic acid bacteria (LAB), including lactobacilli and enterococci, represent an important part of normal microflora in humans. Simultaneously, they are frequently used as probiotics and in food industry for production of fermented milk products. The rapid and sensitive detection of these microorganisms is crucial for the quality control. In this study, the capillary isoelectric focusing (CIEF) was successfully used for the separation and characterization of probiotic LAB, L. paracasei sp. paracasei; L. acidifarinae; L. fermentum; L. gasseri; L. helveticus; L. plantarum; L. delbrueckii; L. salivarius; E. durans; E. faecalis; and E. faecium, according to their isoelectric points (pI). All pIs of lactobacilli and enterococci were found in the acidic part of the pH range. Subsequently, the milk samples spiked with L. rhamnosus, and E. faecium were analyzed by CIEF. The optimal adjustment of the separation conditions allowed detection and quantification of the bacteria in the sample with sufficient sensitivity. Therefore, CIEF is an efficient approach to rapid detection and separation of LAB even directly in milk products in future.     

Survival of Salmonella, Escherichia coli O157:H7, and Listeria monocytogenes on Inoculated Almonds and Pistachios Stored at -19, 4, and 24° C

The survival of Salmonella, Escherichia coli O157:H7, and Listeria monocytogenes was determined on almonds and pistachios held at typical storage temperatures. Almond kernels and inshell pistachios were inoculated with four- to six-strain cocktails of nalidixic acid-resistant Salmonella, E. coli O157:H7, or L. monocytogenes at 6 log CFU/g and then dried for 72 h. After drying, inoculated nuts were stored at -19, 4, or 24°C for up to 12 months. During the initial drying period after inoculation, levels of all pathogens declined by 1 to -log CFU/g on both almonds and pistachios. During storage, moisture content (4.8%) and water activity (0.4) of the almonds and pistachios were consistent at -19°C; increased slowly to 6% and 0.6, respectively, at 4°C; and fluctuated from 4 to 5% and 0.3 to 0.5 at 24°C, respectively. Every 1 or 2 months, levels of each pathogen were enumerated by plating; samples were enriched when levels fell below the limit of detection. No reduction in population level was observed at -19 or 4°C for either pathogen, with the exception of E. coli O157:H7-inoculated almonds stored at 4°C (decline of 0.09 log CFU/g/month). At 24°C, initial rates of decline were 0.20, 0.60, and 0.71 log CFU/g/month on almonds and 0.15, 0.35, and 0.86 log CFU/g/month on pistachios for Salmonella, E. coli O157:H7, and L. monocytogenes, respectively, but distinct tailing of the survival curves was noted for both E. coli O157:H7 and L. monocytogenes.     

Effect of chemical dips on unchilled fresh beef inoculated with E. coli, S. aureus, S. faecalis and Cl. perfringens and Stored at 30°C and 20°C

The antimicrobial effect of three chemical dips (A: potassium sorbate, 20g; sodium acetate, 5g; sodium chloride, 5g; water, 100 ml. B: potassium sorbate, 20g; sodium acetate, 5g; sodium chloride, 5g; propylene glycol, 20 ml; glycerol, 10 ml; water, 70 ml and 0·5N NaOH to pH 10. C: potassium sorbate, 10 g; sodium acetate, 10 g; sodium citrate, 10g; sodium chloride, 5g; water, 100 ml and 0·5N NaOH to pH 10) on unchilled f resh beef samples inoculated with E. coli, S. aureus, S. faecalis and Cl. perfringens and stored at 30°C and 20 °C was investigated. Treatments had produced a significant (P < 0·01) inhibitory effect on all the organisms inoculated, with a reduction of about 3 to 5 log units compared with the control. pH changes were comparable with the control at 5°C. No significant differences were found between the treatments and shelf life could be extended up to 44 h at 30°C and 68 h at 20°C whilst, in the control, visual spoilage and high bacterial counts were observed by 20h at 30°C and by 20 to 32h at 20°C. Treatment C, containing potassium sorbate at a low level (10%), was considered better than treatments A and B since potassium sorbate at higher levels had produced slight off-odours without a greater inhibitory effect.     

Effect of carbon monoxide packaging and lactate enhancement on the color stability of beef steaks stored at 1°C for 9 days

Our objective was to assess the effects of lactate enhancement in combination with different packaging systems on beef longissimus lumborum and psoas major steak color. Strip loins and tenderloins (n = 16) were assigned to one of four injection treatments (non-injected control, water-injected control, 1.25%, and 2.5% lactate in the finished product). Steaks were individually packaged in either vacuum, high-oxygen (80% O₂/20% CO₂), or 0.4% CO (30% CO₂/69.6% N₂) and stored for either 0, 5, or 9 days at 1 °C. The L^∗ and a^∗ values of both the longissimus and psoas responded similarly to lactate, which at 2.5% darkened steaks (P < 0.05) packaged in all atmospheres and improved (P < 0.05) the redness of steaks packaged in high-oxygen. Packaging steaks in CO did not counteract the darkening effects of lactate. Nevertheless, CO improved (P < 0.05) color stability compared with high-oxygen packaging.     

Technical note: Comparison of dry matter measurements from handheld near-infrared units with oven drying at 60°C for 48 hours and other on-farm methods

This study compared dry matter (DM) predictions of 3 handheld near-infrared spectrophotometer (NIRS) units (Moisture Tracker, Digi-Star Inc., Fort Atkinson, WI) to conventional oven drying at 60°C using 2 alfalfa and 2 corn silages. In addition, on-farm DM methods [microwave, Koster tester (Koster Moisture Tester Inc., Brunswick, OH), and food dehydrator methods] were also compared. Corn and alfalfa silages (1,600 g) obtained from the University of Wisconsin Dairy Cattle Center (DCC) and the Arlington Research Station (ARS) were analyzed for DM daily for 20 d. Two NIRS calibration methods were also tested within each unit. The DM predicted from the factory-preset calibrations was NIR_f. The adjusted DM prediction was NIR_a, where the average difference between oven-dried and NIR_f determined on duplicate forage samples for 3 d before the experiment was used as a bias adjustment for all subsequent DM determinations. The average predicted DM from the 20 scans was recorded as the forage DM. The process was repeated 3 times with each NIRS unit. Two 100-g subsamples of each forage were also oven-dried for 48 h at 60°C daily in a forced-air oven. Oven DM of ARS and DCC alfalfa silages were 37.3 ± 1.1% and 48.5 ± 1.9%, respectively (mean ± standard deviation). Oven DM of ARS and DCC corn silages were 34.7 ± 1.2% and 37.4 ± 0.5%, respectively (mean ± standard deviation). Dry matter determinations from NIR_f were on average 3.5 units higher than the oven DM values. The NIR_a DM predictions were on average 1.7 DM units lower than the oven DM values. Additionally, differences among the 3 NIR_f probe results were detected (43.1, 40.7, and 41.3% DM, respectively), but all other results were similar between probes. Determinations of DM by the microwave and food dehydrator were also similar with the 60°C, 48-h oven method, whereas the Koster tester was lower than the oven. The handheld NIRS units more accurately predicted DM content of the alfalfa silage but were not as accurate with corn silages when the factory preset calibrations were corrected for bias.     

A Cassava Starch–Chitosan Edible Coating Enriched with <Emphasis Type="Italic">Lippia sidoides</Emphasis> Cham. Essential Oil and Pomegranate Peel Extract for Preservation of Italian Tomatoes (<Emphasis Type="Italic">Lycopersicon esculentum</Emphasis> Mill.) Stored at Room Temperature

The effect of edible cassava starch–chitosan coatings incorporated with rosemary pepper (Lippia sidoides Cham.) essential oil and pomegranate peel extract on the shelf-life of tomatoes during storage at 25 °C for 12 days was investigated. Sixteen formulations, containing 10 g L^?1 cassava starch and various concentrations of chitosan (5, 10, 20, 30 g L^?1), essential oil (0, 2.5, 5, 10 mL L^?1) and pomegranate peel extract (0, 5, 10, 20 mL L^?1) were prepared and applied to tomatoes. Physical–chemical and microbiological analyses were performed on days 1, 4, 8 and 12. Most of the coatings delayed the ripening of tomatoes, lowering the total soluble solids (38?44 g sucrose kg^?1) and weight loss (93?128 g kg^?1) and maintaining constant firmness compared to the uncoated tomatoes (45 g sucrose kg^?1, 175 g kg^?1) at 12 days of storage. Conversely, except red intensity (a*), which was higher for the uncoated samples, the colour parameters (L*, b*) of the coated and control tomatoes were similar at the end of storage. Uncoated and coated tomatoes showed no contamination during storage. The coatings showed potential to maintain the quality of tomatoes during storage at 25 °C for 12 days. In this context, tomatoes coated with the formulation comprising 10 g L^?1 cassava starch, 10 g L^?1 chitosan, 10 mL L^?1 essential oil and 20 mL L^?1 pomegranate peel extract showed the lowest weight loss and reduced total soluble solids content compared with uncoated ones.