Evaluation of mungbean protein isolates at various levels as a substrate for microbial transglutaminase and water binding agent in pork myofibrillar protein gels

The objective of this study was to investigate the effect of mungbean protein isolate (MPI) on the potential possibility of water binding agent and as a substrate for the microbial transglutaminase (MTGase) in myofibrillar protein. Cooking loss (CL,%), gel strength (GS, gf), sodium dodecyl sulphate‐polyacrylamide gel electrophoresis (SDS‐PAGE), differential scanning calorimetry (DSC) and scanning electron microscopy (SEM) were measured. The addition of MPI reduced CL, indicating that it has a water binding capacity during cooking. The major protein band (53 kDa) of MPI appeared when MPI was mixed with MP, but it disappeared when MTGase was incorporated. MPI treatment changed the endothermic peaks as compared with those of CTL. MTGase (1%) mediated pork MP increased CL and GS (P < 0.05), and reduced peak temperatures with vanishing of endothermic intensity at 1st and 3rd peaks, suggesting the structural changes of protein gelation. In microstructures, MTGase treatment showed a finely stranded structure in MP gels, while MPI showed a conglomerated surface in MTGase‐mediated MP gels. These results indicated that MPI appears to be a water binding agent during cooking and function as a substrate for MTGase in MP gelation.     

Norwegian consumers' acceptability of boar tainted meat with different levels of androstenone or skatole as related to their androstenone sensitivity

The aim of work was to study Norwegian consumers' acceptance of pork meat with different levels of skatole and androstenone. One group of androstenone sensitive consumers (N = 46) and one group of non sensitive consumers (N = 55) participated in a home test and evaluated 11 samples with different skatole (range 0–0.35 ppm) and androstenone (range 0–9.0 ppm) levels. Liking of odour during frying and odour and flavour of the fried meat were evaluated. Results showed that the non sensitive consumers accepted all levels of androstenone in the samples. Sensitive consumers gave a significantly lower liking score for androstenone samples containing 3 ppm (and more) than the reference sample when evaluating these samples above the frying pan, but no significant difference were found between 3 ppm samples and reference samples when liking of fried meat was evaluated. This indicated that the sensitive consumers accepted 3 ppm in fried meat, but not if 3 ppm was present in the sample during the frying process. The same consumer's differentiated skatole samples with regard to flavour at 0.15 ppm. The Norwegian established practise with a threshold value of 0.21 ppm skatole is higher than the value accepted by the consumers.     

Effects of N-nitrosopyrrolidine, nitrite and pyrrolidine on tumour development in mice as related to ingestion of cured meat

The incidence of tumours in mice fed a standard chow diet and given either N-nitrosopyrrolidine (NPyr), nitrite (NO₂) or nitrite plus pyrrolidine (NO₂ + Pyr) in the drinking water for 12 months at 100mg, 1 g and 1 g plus 100mg/litre, respectively, was compared with that for a control group (C) receiving no additives. Differences between groups in weight gain and feed consumption were not significant. Group 3 (NO₂) drank less water (P < 0·05) than those in groups 1 (C) and 2 (NPyr). Water intake of mice in group 4 (NO₂ + Pyr) did not differ from that of any of the other three groups. Survival rates were: 94% (C), 80% (NPyr), 92% (NO₂) and 83% (NO₂ + Pyr); but the differences were not statistically significant. Gross examination upon autopsy revealed that the incidence of all tumours in group 2 (NPyr) was 10- to 20-fold higher than that in any other group. Histological examination confirmed that NPyr induced more (P < 0.05) malignant tumours in liver and lungs with any other treatment; otherwise there were no significant differences. Results indicated that NO₂ + Pyr (nitrite plus a secondary amine) did not increase the frequency of carcinogenic tumours in mice.     

A serological method for the detection of trypsin inhibitor in commercial soy proteins and its use in detecting soy protein addition to raw meat products

Summary Specific antiserum against Soybean Trypsin Inhibitor (SBTI) was used to demonstrate the presence of this inhibitor in commercial soy proteins, and the addition of such proteins to meat products. There was a good correlation between this method and other methods used for the demonstration of trypsin inhibitors. A commercial soy protein antiserum based on heated antigen did not react with SBTI. The possible use of this method in detecting soy protein in raw meat products is discussed.

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Zusammenfassung Unter Verwendung von spezifischem Antiserum für einen Sojatrypsin-Inhibitor (SBTI) wurde das Vorkommen dieses Inhibitors in handelsüblichen Sojaproteinen sowie der Zusatz dieser Eiweißstoffe zu Fleischprodukten nachgewiesen. Mit dieser Methode konnte eine gute Übereinstimmung mit anderen Nachweismethoden erzielt werden. Ein im Handel erhältliches, auf erhitztem Antigen basierendes Sojaprotein-Antiserum ergab mit SBTI keine Reaktion. Die Anwendungsmöglichkeit dieser Methode zum Nachweis von Sojazusatz zu rohen Fleischprodukten wird beschrieben.

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This work was supported by a grant from the Agricultural Research Council of Norway.     

Characterization of certain bacterial strains for potential use as starter or probiotic cultures in dairy products

The present work was aimed at characterizing 12 strains of lactic acid bacteria (LAB) to obtain improved potential starter or probiotic cultures that could be used for making dairy products from ewe's milk and cow's milk. Eight strains with antimicrobial properties, isolated from ewe's milk and from cheese made from ewe's and/or cow's milk, were studied. They were identified as Enterococcus faecalis (five strains), Lactococcus lactis subsp. cremoris, Leuconostoc mesenteroides, and Lactobacillus paracasei subsp. paracasei (one strain of each species). Additionally, four strains were obtained from the American Type Culture Collection: Lactobacillus casei 393 (isolated from cheese), L. lactis subsp. lactis 11454 (origin nonspecified and a producer of nisin), and two strains isolated from human feces (L. paracasei subsp. paracasei 27092 and Lactobacillus rhamnosus 53103, antibacterial agent producer). All E. faecalis strains showed at least one virulence factor (either hemolysin or gelatinase), which emphasizes the importance of these studies in this species. Both L. lactis strains and most Lactobacillus spp. were good acidifiers in ewe's milk and cow's milk at 30°C. High β-galactosidase activity, as well as aminopeptidase activities that favor the development of desirable flavors in cheese, were detected in all Lactobacillus spp. strains. Furthermore, L. rhamnosus ATCC 53103 showed α-fucosidase activity (thought to help colonization of the intestine) and lack of α-glucosidase activity (a trait considered positive for diabetic and obese humans). This last enzymatic activity was also lacking in L. lactis ATCC 11454. L. mesenteroides was the only strain D(2)-lactic acid producer. The selection of any particular strain for probiotic or dairy cultures should be performed according to the technological and/or functional abilities needed.     

Determination of quantitative food consumption levels for use in microbial risk assessments: cheddar cheese as an example

Microbial risk assessment (MRA) is becoming increasingly used in the management of food safety because it can be used to quantify risks and help rank intervention strategies. The exposure assessment components of the assessments have become complex with many aspects of the contamination, survival, and growth of a pathogen in a food being taken into consideration. Insufficient consumption data constitutes an important data gap and consequently one of many sources of uncertainty in MRA even though the effects of uncertainty are smaller than those affecting bacterial concentration in foods. Therefore, food consumption data also play an important role in exposure assessment of MRA. In the United States, there are large-scale, nationwide sets of consumption data available for use in MRA, i.e., the National Health and Nutrition Examination Survey (NHANES). Newly released dietary interview data in the NHANES 2001 to 2002 survey show that it has been redesigned and that the data were sufficiently updated from previous versions to have more value for MRAs. We propose a model that can effectively use the new data sets and be incorporated into MRAs, using as an example consumption of Cheddar cheese/American-type cheese. This model included the prevalence of food eaten as well as the amount and frequency. We determined the amount of Cheddar/American cheese consumed per day with probability distribution (e.g., lognormal distribution). These could be further determined by gender, age, pregnancy, and combination food type, which we plan to do in the future. The frequency of the range of serving numbers for Cheddar/American cheese consumed per person per day and prevalence as the proportion of a population (e.g., survey respondents) eating a certain food in a day are also presented. Unlike traditional published mean values, the results of this model provide probability distribution intakes that can be compared with mean and median intakes. This allows values in the upper percentiles to be considered for inclusion in MRAs. We believe this simulation model can be adapted with different variables applicable to different foods, pathogens, and specific health risk population groups.     

The use of video image analysis for quantitative measurement of visible fat and lean in meat: Part 4- application of image analysis measurement techniques to minced meats

The quantitative measurement of fat in minced meat by video techniques has, to date, been impractical due to the nature of the raw material and camera limitations in particle resolution. The latter have been enhanced by improving the optical system and by illuminating the meat with a limited wavelength ultraviolet light source. Problems with fat smear and drip stain, causing over- and under-estimation of fat, respectively, have been overcome by better control of mincing conditions. Tempering of the meat to between -2°C and -5°C before mincing gave the best results. The level of fat detection was unchanged for up to 20 min after mincing, but, by 2 h, the initial value had fallen by 50%. Magnifying the field of view, thus reducing the sample size measured by 50%, did not adversely affect results with 4mm-10mm diameter mince. The system could not accurately resolve mince below 4 mm. Estimation of total lipid from video data using prediction equations was in good agreement with chemical analysis (r=0·99 for 10mm mince, r=0·95 for 4 mm mince). Video image analysis (VIA) can now be effectively extended to areas of meat processing using particulate meats.     

Attachment of Escherichia coli O157:H7 grown in tryptic soy broth and nutrient broth to apple and lettuce surfaces as related to cell hydrophobicity, surface charge, and capsule production

This study investigated the effect of growth in tryptic soy broth (TSB) and nutrient broth (NB) on the ability Escherichia coli O157:H7 to attach to lettuce and apple surfaces. In addition, cell surface hydrophobicity, charge and capsule production were determined on cells grown in these media. Cells grown in NB attached less to lettuce and apple surfaces than did those grown in TSB. TSB, but not NB, supported capsule production by E. coli O157:H7. Cells grown in TSB were more hydrophilic than those grown in NB. No difference was found in the electrokinetic properties of cells grown in these media. Electrostatic and hydrophobic interactions and surface proteins did not appear to play an important role in the attachment of E. coli O157:H7 to these surfaces. Of the factors studied, only capsule production was associated with attachment ability.     

The use of immuno-magnetic separation (IMS) as a tool in a sample preparation method for direct detection of L. monocytogenes in cheese

A sample preparation procedure was developed for direct detection of L. monocytogenes in cheese. The sample preparation protocol consisted of a 10-fold dilution and homogenization, a centrifugation step to precipitate large food particles, passage of the supernatant over a sieve and through a separatory funnel to further eliminate food particles and fat, a centrifugation step to recover the bacterial pellet and finally enzymatic digestion of the suspension to degrade the remaining small food particles. Recovery of L. monocytogenes was confirmed by plating on Oxford medium and confirmation of suspected colonies. This protocol enabled direct detection (without prior enrichment) of low numbers of L. monocytogenes (0.5-1.5 cfu/g cheese) from different types of cheese. The performance of Dynabeads Anti-Listeria (Dynal, Oslo, Norway) for selective recovery of L. monocytogenes and their applicability in the above mentioned procedure for direct detection of low numbers of L. monocytogenes from cheese was evaluated. IMS could not separate and recover L. monocytogenes from the food particles in the concentrated suspension. The use of IMS after a 24 h enrichment procedure (as recommended by the manufacturer) allowed for the detection of low numbers of L. monocytogenes (< 10 cfu/g). However, experiments in broth cultures showed that although the detection limit of IMS with Dynabeads Anti-Listeria was 40-100 cfu/ml, the ratio of L. monocytogenes to non-Listeria flora was not increased. Thus, selective enrichment or concentration of L. monocytogenes was not obtained.     

Method for the direct observation and quantification of survival of bacteria attached to negatively or positively charged surfaces in an aqueous medium

The risk of groundwater contamination by microbial pathogens is linked to their survival in the subsurface. Although there is a large body of literature on the inactivation behavior of suspended (planktonic) microorganisms, little is known about the inactivation of bacteria when attached to sand grain surfaces in groundwater aquifers. The main goal of this study was to develop a fluorescence-based experimental technique for evaluating the extent of inactivation over time of bacteria adhered onto a surface in an aqueous environment. Key features of the developed technique are as follows: (i) attached cells do not need to be removed from the surface of interest for quantification, (ii) bacterial inactivation can be examined in real-time for prolonged time periods, and (iii) the system remains undisturbed (i.e., the aqueous environment is unchanged) during the assay. A negatively or positively charged substrate (i.e., bare or coated glass slide) was mounted in a parallel-plate flow cell, bacteria were allowed to attach onto the substrate, and the loss of bacterial membrane integrity and respiratory activity were investigated as a function of time by fluorescence microscopy using Live/Dead BacLight and BacLight RedoxSensor CTC (5-cyano-2,3-ditolyl tetrazolium chloride) viability assays. These two different measures of bacterial inactivation result in comparable trends in bacterial inactivation, confirming the validity of the experimental technique. The results of this work show that the developed technique is sensitive enough to distinguish between the inactivation kinetics of different representative bacteria attached to either a negatively charged (bare glass) surface or a positively charged (coated glass) surface. Hence, the technique can be used to characterize bacterial inactivation kinetics when attached to environmentally relevant surfaces over a broad range of groundwater chemistries.     

Physical properties of native and thermally treated European woods as potential alternative to Indian rosewood for the use in classical guitars

Untreated and thermally modified woods of cherry, service tree, pear and plum were investigated as potential substitutions for Indian rosewood in guitar making. Acoustic properties such as dynamic modulus of elasticity, dynamic shear modulus in LR-plane and loss coefficient as an indicator for damping were determined by means of experimental modal analysis and the mechanical properties by means of static bending and hardness test. The swelling behavior was also investigated. The results suggest that cherry and service tree could be used as alternative back and side material and plum and service tree may also be used for fingerboards. Thermal modifications at 160 °C for 8 h improve swelling behavior, mechanical properties, but damping was slightly increased for cherry and pear. No significant change of Brinell hardness was observed owing to thermal modification.