IMS USING IN-HOUSE MONOCLONAL ANTIBODY-COATED MAGNETIC BEADS ASSOCIATED TO PCR ASSAY FOR DETECTION OF SALMONELLA TYPHIMURIUM IN RAW MEATS

An immunomagnetic separation (IMS) technique and a PCR assay were developed for use in detection of Salmonella Typhimurium in meat samples. To prevent false-negative results, an internal amplification control was developed. The polymerase chain reaction (PCR) using primers specific for an omp gene sequence of Salmonella spp has shown 100% sensitivity and specificity and a detection limit of 10⁴ cfu/mL. The IMS-PCR methods using PCR immediately after IMS and using 6 h postenrichment in brain heart infusion between IMS and PCR resulted in detection limits of 10³ cfu/mL and 1–10 cfu/mL, respectively. The lowest level of S. Typhimurium that could be detected by the IMS-PCR method in the presence of natural microbiota from inoculated meat samples was 1–10 cfu/25 g. When samples were analyzed using enrichment protocols without IMS, several false-negative results were obtained.

PRACTICAL APPLICATIONS

The immunomagnetic separation-polymerase chain reaction (IMS-PCR) method developed enabled a rapid and sensitive detection of Salmonella Typhimurium in inoculated meat samples. Monoclonal antibody (Mab)-coated magnetic beads prepared in-house were efficient in concentrating and separating the bacteria from the food matrix, thus improving detection limit and avoiding false-negatives. The internal amplification control (IAC), now mandatory in PCR assays, using the same primers of the target DNA further prevented false-negative results. Therefore, the IMS-PCR method developed in this study could be used in the future by the Brazilian food industry as a substitute for the expensive imported kits for Salmonella detection in foods. We are now developing a panel of Mabs against conserved antigens of Salmonella for use in the IMS-PCR method in order to extend its applicability for detection of other serovars.     

Influence of transmembrane pressure on the separation of caprine milk oligosaccharides from protein by cross‐flow ultrafiltration

Goat milk shows similarities with human milk in terms of their oligosaccharides composition. However, the supplementation of goat milk protein in infant formulae is not allowed, which demands a previous separation of oligosaccharides from protein. The purpose of this study was to evaluate the effect of transmembrane pressure on the fractionation of oligosaccharides, protein, lactose and calcium in the diafiltration of caprine milk through a 50 kDa tubular ceramic membrane. Permeates with more than 99% of the original oligosaccharides were obtained after four diavolumes. It was seen that transmembrane pressure had a great influence on filtration time and protein transmission.     

MICROBIAL STABILIZATION OF INTERMEDIATE MOISTURE FOOD SURFACES III. EFFECTS OF SURFACE PRESERVATIVE CONCENTRATION AND SURFACE pH CONTROL ON MICROBIAL STABILITY OF AN INTERMEDIATE MOISTURE CHEESE ANALOG

Localized surface condensations affect microbial stability of intermediate moisture foods (IMF). Two surface modifications previously reported were tested for their ability to improve microbial surface stability; control of surface preservative concentration and reduced surface pH.
The effectiveness of a high surface sorbic acid concentration controlled by a zein coating was confirmed in Staphylococcus aureus S-6 surface challenge experiments under extreme testing conditions. Samples with bulk water activity (aw) of 0.88, stored at 30°C under constant 88% relative humidity (RH) remained stable for over 16 days. Uncoated controls were stable for only 2 days. Samples with bulk aw = 0.85, exposed to cycles of 12 h at85% RH and 12h at 88% RH, remained stable for more than 28 days. Uncoated controls were stable for only 3 days.
The reduced surface pH approach to microbial stability required the formulation of an IMF model with low total electrolyte concentration which was coated with a deionized mixture of λ-carrageenan and agarose. The effectiveness of the resulting 2.5 fold increase in the surface availability of the active form of sorbic acid as compared to food bulk was confirmed in a challenge test with S. aureus S-6. In a test with samples at aw = 0.88, stored at RH = 88% and 30°C, we found a stability period of about 20 days and it seems possible to increase it.     

TIME-VARIABLE RETORT TEMPERATURE PROFILES FOR CYLINDRICAL CANS: BATCH PROCESS TIME,ENERGY CONSUMPTION,and QUALITY RETENTION MODEL1

The batch retort model developed uses a heat transfer equation for heat conduction in cylindrical cans, first order kinetics for microbial inactivation, first order kinetics for quality losses and a transient energy balance to estimate steam consumption. For a given retort, lethality process and quality retention, the transient energy balance equation in the model allowed the identification of feasible time-temperature profiles reducing energy consumption, total process time or both. In the examples analyzed and depending upon product specifications, time-variable retort temperatures reduced process time by 18–55 min. These examples suggested that a change from constant to time-variable retort temperatures could increase canning capacity by 20–50%.     

MODELING OF THE GERMINATION OF SPORES FROM CLOSTRIDIUM PERFRINGENS FOOD POISONING ISOLATES

Clostridium perfringens type A isolates carrying a chromosomal gene for enterotoxin production (chromosomal c. perfringens enterotoxin [ C- cpe] strains) are frequent causative agents of food poisoning. Predictive models for their growth in meat products have been published; however, the development of germination models needs further research. In this study, the Weibull function was used to describe the germination of C- cpe food poisoning strains in phosphate and Tris–HCl buffer as affected by pH (5.8–8.5), germinant concentration (1–100 mM KCl) and germination temperature (23–60C). As indicated by estimators of model accuracy and bias, an empirical model for spore germination as a function of germination temperature only, predicted accurately the germination potential of 4 C- cpe food poisoning strains in buffer and in laboratory media in the 23–50C range.

PRACTICAL APPLICATIONS

Thermal processing models based on the inactivation of a heat-resistant spore ignore the potential germination and outgrowth of spore survivors as recommended by new food safety guidelines. Germination models for spore survivors to be used in conjunction with outgrowth models should be developed using as samples the product of interest because the bioavailability and concentration of germinants such as ions and free amino acids vary with the product and its manufacturing process. Another germination model application is in conjunction with new processing technologies such as high pressure processing (HPP). The inactivation of bacterial spores has been a major challenge to HPP process developers. Since germinated spores are sensitive to pressure, germination models would be useful to design combined strategies of food thermal treatment and HPP.     

SLIP GAIN TUNING IN INDIRECT FIELD ORIENTED CONTROL DRIVES

ABSTRACT

The paper presents a simple technique for correctly and fastly tuning the slip gain in Indirect Field Oriented Control drives. To this aim no other transducers than the tachogenerator, usually included in such drives, are needed, as the tuning operation is performed by processing the effects of a suitable test signal injected in the system. The proposed approach can be used either for on-line retuning of working drives, either for the initial tuning of new installed drives. Simulation and experimental tests show that the procedure is effective and does not Interfere with normal operations of the drive.