Monitoring the bacterial population dynamics during fermentation of artisanal Argentinean sausages

The dynamics of the microbial community responsible for the artisanal fermentation of dry sausage produced in Argentina was investigated by using classical and molecular approaches. The combined use of RAPD analysis with primers M13, XD9, RAPD1 and RAPD2 and 16S rDNA sequencing were applied to the identification and intraspecific differentiation of 100 strains of lactobacilli and Micrococcaceae. DGGE analysis was used to monitor the dynamic changes in population after total microbial DNA was directly extracted from sausages and subjected to PCR using V3f (GC), Bact-0124f-GC and Univ-0515r primers. The sequence analysis of 16S rDNA of the dominant species was also carried out. Lactobacillus sakei and Lactobacillus plantarum were the dominant lactic acid organisms during the fermentation while Staphylococcus saprophyticus represented the dominant species of Micrococcaceae. It was demonstrated that the ripening process of Argentinean artisanal fermented sausage is driven by a limited number of Lactobacillus and Staphylococcus strains selected from environmental microbiota by the ability to best compete under the prevailing conditions of the ecological niche. The identification of dominant communities present in this artisanal fermented sausage can help in the selection of starter cultures consisting in well adapted strains to the particular production technology.     

Indoor indirect solar dryer for ceramic craft industry

We report the development of a prototype indirect solar dryer for plaster molds for the ceramic craft industry. The prototype was designed considering the reduction of the drying time against the traditional technique, working indoors and using minimal conventional energy. The indoor drying chamber has a capacity for 32 plaster molds with a total weight of 425 kg. The drying rate through day and night, drying efficiency and drying constant were of 0.54 kg-H₂O/h, 0.29±0.02% and 0.0094 h^?1, respectively. The solar energy supplied to heat the air of drying was 58% and the remaining 42% was provided by the ambient air. To meet the requirements of the moisture content of potters 5.5 days (132 hours) was needed, resulting in a reduction of two-thirds of the traditional drying time of plaster molds (21 days). The continuous rate of drying reveals the solar dryer ability to dry reasonably rapidly under indoor conditions.     

RDG System in Remote Areas with Utility or Local Feed Topology and Operation Strategy

In remote regions with availability of wind energy, a RDG （renewable distributed generation） system is an advantageous alternative to increase the provision of electrical supply. Usually, these systems are structured on the basis of a connection to an existing weak grid. When the grid is out of service, the system may operate in islanding mode, if the RDG configuration allows it, continuing the provision of energy with standard voltage and frequency values. Facing the latter situation, a wind-diesel/gas generation system is proposed, with a conversion and control strategies based on a variable speed wind turbine employing a DFIG （doubly fed induction generator）, a SC （ultracapacitor） storage system and a SG （synchronous generator） driven by a diesel/gas engine.     

Characterization of homofermentative lactobacilli isolated from kefir grains: potential use as probiotic

Considering that several health promoting properties are associated with kefir consumption and a reliable probiotic product requires a complete identification of the bacterial species, the present work evaluates several proved markers of probiotic potential of eleven isolates of homofermentative lactobacilli isolated from kefir grains and molecular identification and genotypic diversity. Using restriction analysis of amplified ribosomal DNA (ARDRA) and analysis of the 16S-23S rRNA internal spacer region we confirmed that all homofermentative lactobacilli belong to the species Lactobacillus plantarum. RAPD-PCR analysis allowed the discrimination of lactobacilli in five clusters. All isolates exhibited high resistance to bile salt. High survival after one hour of exposure to pH 2.5 was observed in Lb. plantarum CIDCA 8313, 83210, 8327 and 8338. All isolates were hydrophilic and non autoaggregative. Isolate CIDCA 8337 showed the highest percentage of adhesion among strains. All tested lactobacilli had strong inhibitory power against Salmonella typhimurium and Escherichia coli. Seven out of eleven isolates showed inhibition against Sal. enterica and five isolates were effective against Sal. gallinarum. Only CIDCA 8323 and CIDCA 8327 were able to inhibit Sal. sonnei. We did not find any correlation between the five clusters based on RAPD-PCR and the probiotic properties, suggesting that these isolates have unique characteristics.     

PCR method for detection and identification of Lactobacillus casei/paracasei bacteriophages in dairy products

Bacteriophage infections of starter lactic acid bacteria (LAB) pose a serious risk to the dairy industry. Nowadays, the expanding use of valuable Lactobacillus strains as probiotic starters determines an increase in the frequency of specific bacteriophage infections in dairy plants. This work describes a simple and rapid Polymerase Chain Reaction (PCR) method that detects and identifies bacteriophages infecting Lactobacillus casei/paracasei, the main bacterial species used as probiotic. Based on a highly conserved region of the NTP-binding genes belonging to the replication module of L. casei phages phiA2 and phiAT3 (the only two whose genomes are completely sequenced), a pair of primers was designed to generate a specific fragment. Furthermore, this PCR detection method proved to be a useful tool for monitoring and identifying L. casei/paracasei phages in industrial samples since specific PCR signals were obtained from phage contaminated milk (detection limit: 10(4) PFU/mL milk) and other commercial samples (fermented milks and cheese whey) that include L. casei/paracasei as probiotic starter (detection limit: 10(6) PFU/mL fermented milk). Since this method can detect the above phages in industrial samples and can be easily incorporated into dairy industry routines, it might be readily used to earmark contaminated milk for use in processes that do not involve susceptible starter organisms, or processes which involve phage-deactivating conditions.     

Physicochemical, microbiological and sensory profiles of fermented milk containing probiotic strains isolated from kefir

A two-strain starter culture containing Lactobacillus plantarum CIDCA 83114, a potential probiotic strain isolated from kefir grains, and Streptococcus thermophilus CIDCA 321 was tested for the preparation of a fermented milk product. Kluyveromyces marxianus CIDCA 8154, a yeast with immunomodulatory properties was included to formulate a three-strain starter culture. Supernatants of enterohaemorragic Escherichia coli, shiga-toxin-producing strain, along with a two-strain or a three-strain starter culture were included in the medium of Vero-cell surface cultures. The results demonstrated that these combinations of microorganisms antagonize the cytopathic action of shiga toxins. The cell concentration of Lb. plantarum did not decrease during fermentation, indicating that the viability of this strain was not affected by low pH, nor did the number of viable bacteria change during 21 days of storage in either fermented products. The number of viable yeasts increases during fermentation and storage. Trained assessors analyzed the general acceptability of fresh fermented milks and considered both acceptable. The milk fermented with the two-strain starter culture was considered acceptable after two week of storage, while the product fermented with the three-strain starter culture remained acceptable for less than one week. The main changes in sensory attributes detected by the trained panel were in sour taste, milky taste and also in fermented attributes. The correlation between different sensory attributes and acceptability indicated that the panel was positively influenced by milky attributes (taste, odour, and flavour) as well as the intensity of flavour. In conclusion, the two-strain starter culture would be the more promising alternative for inclusion of that potential probiotic lactobacillus in a fermented milk product.     

Screening of lactic acid bacteria isolates from dairy and cereal products for exopolysaccharide production and genes involved

Scanning electron microscopy (SEM) studies revealed that exposure to 4lethal alkaline stress induced statistically significant (P < 0.05) changes in mean cell length, radius and volume in Listeria monocytogenes and a derived σ^B deficient mutant. Bacterial morphology was altered at pH values above 9.0, to include single filamentous or elongated chain forms. Such filamentation and chain formation was observed in the parent strain and in the σ^B deficient strain, and in buffered and non-buffered media. Giemsa staining revealed that the filaments were multi-nucleate, with nucleoids spaced along the length of the atypical cells. In buffered media, longer alkaline exposure was associated with increases in the frequency and length of filamentation. In non-buffered medium, longer exposure was associated with gradual decline in length and the frequency of observation of filaments. Transfer of alkaline treated cells to neutral conditions was associated with the formation of septa within filaments, cell division, and a rapid return to normal morphology, i.e. within 3 h. The observed effects, and their reversibility, may be important in increasing the alkaline tolerance of this pathogen during phagocytosis within the innate human immune system response, and in adaptation/survival in food environments treated with alkali detergents and/or sanitisers. Such atypical cells may be associated with increased survival of L. monocytogenes in adverse environments and may also contribute to qualitative and quantitative underestimation of this important pathogen in food processing environments, with potential implications in public health.     

Physical properties of ice cream containing milk protein concentrates

Two milk protein concentrates (MPC, 56 and 85%) were studied as substitutes for 20 and 50% of the protein content in ice cream mix. The basic mix formula had 12% fat, 11% nonfat milk solids, 15% sweetener, and 0.3% stabilizer/emulsifier blend. Protein levels remained constant, and total solids were compensated for in MPC mixes by the addition of polydextrose. Physical properties investigated included apparent viscosity, fat globule size, melting rate, shape retention, and freezing behavior using differential scanning calorimetry. Milk protein concentrate formulations had higher mix viscosity, larger amount of fat destabilization, narrower ice melting curves, and greater shape retention compared with the control. Milk protein concentrates did not offer significant modifications of ice cream physical properties on a constant protein basis when substituted for up to 50% of the protein supplied by nonfat dry milk. Milk protein concentrates may offer ice cream manufacturers an alternative source of milk solids non-fat, especially in mixes reduced in lactose or fat, where higher milk solids nonfat are needed to compensate other losses of total solids.     

The influences of carcass weight and depot on the fatty acid composition of fats of suckling Manchego lambs

The effects of carcass weight (<5.5 kg, 5.5–6.5 kg, ⩾6.5 kg) of Manchego suckling lambs, type of fat depot of the leg (subcutaneous, intermuscular and intramuscular) and muscle (m. longissimus dorsi (LD) or m. quadriceps femoris (QF)) on the fatty acid composition were studied. Carcass fatness increased with increasing carcass weight. However, few differences in fatty acid proportion were observed between the three carcass weight groups. The lightest carcasses had lower proportions of myristic (C14:0) and palmitoleic (C16:1) acid and higher proportions of stearic (C18:0) acid, desirable fatty acids (DFA) (C18:0 + total unsaturated fatty acid (TUFA)) and a greater nutritive value ((C18:0 + C18:1)/C16:0). The fatty acid composition of subcutaneous and intermuscular fat depots of the leg were similar, whereas the intramuscular fat depot was different from both of these, since it had a lower proportion of saturated fatty acids (SFA), a greater proportion of TUFA, higher PUFA/SFA and n − 6/n − 3 ratios, and greater DFA and nutritive values. The intramuscular fat of the LD was more saturated than QF, higher SFA, and had lower value of PUFA/SFA ratio and DFA. These results indicated that the intramuscular fat quality of the leg was better than subcutaneous and intermuscular fat depots and also that intramuscular fat displayed better attributes of quality (lower SFA, higher TUFA, and greater PUFA/SFA ratio and DFA as well) than intramuscular fat of the LD from the consumer health standpoint. Despite carcass weight affected carcass fatness, it did not seem to influence the proportions of saturated or polyunsaturated fatty acids. For this reason, carcass weight probably had little effect on the organoleptic characteristics of the meat.     

A comparison of various rheological properties for modelling the kinetics of thermal softening of potato tissue (c.v. Monalisa) by water cooking and pressure steaming

The kinetics which can be used to describe thermal softening of potato tissue by water cooking and pressure steaming were established and the temperature dependence of rheological and textural properties, using six different instrumental objective methods as firmness indicators, was determined within the temperature range of 100–122 °C. In water cooking at 100 °C and in steaming at 100, 112 and 117 °C, the thermal softening was best expressed by one simple pseudo first-order kinetic mechanism, which was considered to be the response to the changes in the pectic material in the cell wall and interlamellar region. Tension energy was the best rheological property for establishing the kinetics of softening of potato by water cooking, whereas maximum shear force was the best method of representing the tissue softening by steaming, using first-order models. Steaming at 122 °C caused overcooking of the tissue, even for short times. At this high temperature, rheological parameters (compression, tension and creep compliance) and textural properties from Texture Profile Analysis (TPA) fitted second-order models. When second-order models were used, the Arrhenius equation was significant for chewiness, indicating that this textural property can be useful for detecting overcooking caused by prolonged pressure steaming in the experimental temperature range.