Technological Performance of the Enterocin A Producer <Emphasis Type="Italic">Enterococcus faecium</Emphasis> MMRA as a Protective Adjunct Culture to Enhance Hygienic and Sensory Attributes of Traditional Fermented Milk ‘Rayeb’

Enterococcus faecium MMRA is an enterocin A producer isolated from ‘Rayeb’, a Tunisian fermented milk drink. In this work, safety aspects and its behaviour in raw milk were investigated to assess its suitability as a protective adjunct culture. E. faecium MMRA showed interesting features such as the absence of several virulence traits, susceptibility to vancomycin and other clinically relevant antibiotics, and lack of haemolytic activity. To evaluate its performance as an adjunct culture for Rayeb, changes in the overall composition of control (non-inoculated) and experimental Rayeb (inoculated with 1%, v/v, E. faecium MMRA) were determined throughout duplicate fermentations of raw milk using microbiological, chemical, HPLC and headspace GC-MS analyses. E. faecium MMRA could multiply in raw milk and produced enterocin A. Interestingly, a higher content of volatile compounds including ethanol, diacetyl and 2-propanol was observed in the presence of this bacteriocin producer. Furthermore, this strain was capable of inhibiting the growth of Listeria monocytogenes CECT 4032 in pasteurised milk, although total killing was not achieved. Further experiments confirmed the development of resistant variants to enterocin A. On similar challenge assays, L. monocytogenes CECT 5672 growth was halted by the presence of the enterocin producer, but viability was only slightly reduced during cold storage. According to our results, E. faecium MMRA meets the criteria for an autochthonous protective adjunct culture to enhance both the hygienic and the sensory attributes of Rayeb.     

Modelling the Water Sorption Isotherms of Quinoa Seeds (<Emphasis Type="Italic">Chenopodium quinoa</Emphasis> Willd.) and Determination of Sorption Heats

Adsorption and desorption isotherms of quinoa seeds (Chenopodium quinoa Willd.) were measured using the static gravimetric method at three temperatures (20, 40 and 60 °C). Water activity ranged from 0.118 to 0.937. The moisture sorption behaviour of quinoa was temperature dependent, as indicated by a decrease in equilibrium moisture content, at all levels of a _w, with increasing temperature. Eight mathematical equations available in the literature were used to model the experimental data, namely, GAB, BET, Caurie, Henderson, Oswin, Halsey, Smith and Iglesias–Chirife. All the equations showed generally a good fit; however, the Iglesias–Chirife and Oswin equations were considered the best to predict the experimental data for both isotherms. Effect of temperature on model parameters was analysed and studied through an Arrhenius-type equation. The net isosteric heats of desorption and adsorption were determined by applying the Clausius–Clapeyron equation resulting in 69.24 kJ mol⁻¹ for desorption and 61.26 kJ mol⁻¹ for adsorption. The experimental heat data were satisfactorily modelled by Tsami’s equation.     

Recent Studies Related to Microwave Processing of Fluid Foods

Microwave heating is a convenient way to heat materials; it is considered to be a fast, clean, and easy to use technology. The use of microwaves for industrial food unit operations is the subject of research since several years ago. However, the application of microwaves depends, among other variables, on the dielectric properties of the material to be heated; otherwise, the efficiency of the process and the quality of the final product cannot be guaranteed. This paper reviews basic concepts related to microwaves and dielectric properties, and then it presents reported dielectric properties data for selected fluid foods and microwave-heating processes that have been recently studied. These processes are focused mainly on microbial inactivation, enzyme inactivation, chemical, physical, or sensory changes evaluation, or for reheating. The temperature uniformity is also discussed as a key issue for successful application of microwave heating, which is now applied by some companies.     

Estrogen receptor (ESR) 2 partially offsets the absence of ESR1 in gonadotropes of pituitary-specific Esr1 knockout female mice

Estrogen receptor 1 and 2 (ESR1 and 2) mediate estrogen (E) action on gonadotrope function. While much is known about the effects of ESR1 on the gonadotrope, there is still some controversy regarding the effects of ESR2. To investigate the role of ESR2 in the gonadotrope, 45-day-old female mice of two different genotypes were used: wild type (WT) and pituitary (gonadotropes and thyrotropes)-specific Esr1 knockout (KO). All mice were ovariectomized (OVX) and 15 days later injected over 3 days with 2.5 μg 17β-estradiol (E(2)), 0.2 mg of the selective ESR1 or 2 agonists, propylpyrazole triol and diarylpropionitrile, respectively, or 0.1 ml oil. The day after treatment, anterior pituitary glands were dissected out for evaluation of gonadotrope ultrastructural morphology and pituitary immunohistochemical expression of progesterone receptor (Pgr (Pr)). Blood was collected and serum LH levels were assessed. Activation of ESR1 in WT mice resulted in the following: i) uterine ballooning and vaginal cornification, ii) negative feedback on LH secretion, iii) increased number of homogeneous (functional) gonadotropes, and iv) pituitary Pgr expression (35.9±2.0% of pituitary cells). Activation of ESR1 in KO mice induced normal uterine, vaginal, and LH secretion responses, but failed to increase the number of functional gonadotropes, and induced significantly lower Pgr expression (21.0±3.0% of pituitary cells) than in WT mice. Whilst activation of ESR2 had no significant effects in WT mice, it doubled the number of functional gonadotropes exhibited by KO mice injected with oil. It is concluded that E(2) exerted its action in KO mouse gonadotropes via ESR2.     

Labor supply and the business cycle: The “bandwagon worker effect”

The relationship between labour force participation and the business cycle is a common topic in economic literature. However, few studies have examined if the cyclical sensitivity of labour force participation is influenced by social effects. In this paper, we construct a theoretical model defining a relatively new hypothesis, the bandwagon worker effect (BWE). We use spatial econometrics techniques to test the existence of the BWE in the local labour markets in Spain. Our results reveal a positive spatial dependence in the cyclical sensitivity of labour force participation that decreases as we fix a laxer neighbourhood criterion, which verifies the existence of the BWE.     

Specific effect of high-pressure treatment of milk on cheese proteolysis

The extent of primary and secondary proteolysis of cheeses made from raw (RA), pasteurized (PA, 72 degrees C, 15 s) or pressure-treated (PR, 500 MPa, 15 min, 20 degrees C) goats' milk was assessed. Modifications in cheese-making technology were introduced to obtain cheeses with the same moisture content, and thus studied per se the effect of milk treatment on cheese proteolysis.The PR milk cheese samples were differentiated from RA and PA milk cheeses by their elevated beta-lg content, and by the faster degradation of alphas1-, alphas2- and beta-CN throughout ripening. Non-significant differences were found in either pH 4.6 soluble-nitrogen or trichloracetic acid soluble-nitrogen contents of cheeses. However, the pasteurization of milk decreased the free amino acid production in cheese. The RA milk cheeses had the highest amount of proline and the lowest concentrations of serine, tyrosine, arginine and alpha-aminobutyric acid, whereas PR milk cheese showed higher levels of arginine.     

Reuterin and High Hydrostatic Pressure Treatments on the Inactivation of Listeria monocytogenes and Effect on the Characteristics of Cold-Smoked Salmon

The effect of reuterin and high hydrostatic pressure (HHP) processing at 450 MPa for 5 min on the inactivation of Listeria monocytogenes and the characteristics of cold-smoked salmon during 35 days at 4 and 10 °C were investigated. The growth rate of the pathogen was reduced by reuterin addition and a synergistic antimicrobial effect against L. monocytogenes was recorded when the biopreservative was applied in combination with HHP at 450 MPa for 5 min. This combined treatment prevented the pathogen recovery observed with individual treatments and delayed the spoilage of smoked salmon maintaining total viable counts under 3.5 log units during 35 days of storage at 4 °C. All treatments assayed induced changes in lightness (L*) and redness (a*), resulting in a brighter appearance of smoked salmon, whereas no modifications were recorded in shear strength values immediately after treatments. Moreover, reuterin and HHP treatments, individually or in combination, avoided the formation of biogenic amines during the 35 days of storage at 4 and 10 °C. The addition of reuterin in combination with HHP at 450 MPa for 5 min might be applied as a hurdle technology to improve the safety and extend the shelf life of lightly preserved seafood products, such as cold-smoked salmon.