Effects of o-phenylenediamine on methylglyoxal generation from monosaccharide: Comment on “correlation of methylglyoxal with acrylamide formation in fructose/asparagine Maillard reaction model system”

Methylglyoxal (MG), a reactive carbonyl compound, has recently garnered much attention because of its ability to modify proteins over time and yield advanced glycation end products (AGEs) that are thought to contribute to the development of diabetes mellitus and its complications. In a recent paper published in Food Chemistry by Yuan et al. [Yuan, Y., Zhao, G. H., Hu, X. S., Wu, J. H., Liu, J., & Chen, F. (2007a). Correlation of methylglyoxal with acrylamide formation in fructose/asparagines Maillard reaction model system. Food Chemistry, 108(3), 885–890] authors showed a high correlation between methylglyoxal formation and acrylamide formation. However, in their study, model systems of aqueous fructose/asparagines (Fru/Asn) and fructose/asparagines/o-phenylenediamine (Fru/Asn/OPD) heating at 150 °C were used. The validity of these models relies on the assumption that OPD will only serve the role of a trapping agent for MG. In this short communication, we would like to call to attention that MG can also have a strong catalytic effect in the generation of MG from fructose. Therefore, it is concluded that the concentration of MG obtained in Fru/Asn/OPD model system cannot correspond to the total amount of MG formed by Maillard reaction of Fru and Asn as claimed by Yuan et al. [Yuan, Y., Zhao, G. H., Hu, X. S., Wu, J. H., Liu, J., & Chen, F. (2007a). Correlation of methylglyoxal with acrylamide formation in fructose/asparagines Maillard reaction model system. Food Chemistry, 108(3), 885–890, Yuan, Y., Zhao, G. H., Hu X. S., Wu, J. H., Liu, J., & Chen. F. (2007b). High correlation of methylglyoxal with acrylamide formation in glucose/asparagine Maillardreaction model. European Food Research and Technology. doi:10.1007/s00217-007-0658-0].     

Enzymatic carotenoid degradation and aroma formation in nectarines (Prunus persica)

C-13 norisoprenoids such as β-ionone, 3 hydroxy-β-ionone, and 3 hydroxy-5,6-epoxy-β-ionone are important carotenoid related aroma compounds in fruits.Apart from chemical degradation (photo-oxygenation, (auto)oxidation, thermal degradation), enzymatic cleavage is an important flavor formation pathway [Enzell, C. (1985). Biodegradation of carotenoids – an important route to aroma compounds. Pure and Applied Chemistry, 57(5), 693–700; Winterhalter, P., & Rouseff, R. (Eds.). (2001). Carotenoid-derived aroma compounds. ACS symposium series 802, Washington, DC: American Chemical Society (ISBN 0-8412-3729-8)]. In nectarines, the content of carotenoid degradation products depends on the degree of maturity. In fully ripened fruit up to 40% of the aglycons are C-13 norisoprenoids [Aubert, C., Günata, Z., Ambid, C., & Baumes, R. (2003). Changes in physicochemical characteristics and volatile constituents of yellow- and white-fleshed nectarines during maturation and artificial ripening. Journal of Agriculture and Food Chemistry, 51(10), 3083–3091]. Regiospecific carotenoid cleavage enzymes have been shown to be involved in aroma formation in different plants and fruits [Bouvier, F., Suire, C., Mutterer, J., & Camara, B. (2003). Oxidative remodeling of chromoplast carotenoids: identification of the carotenoid dioxygenase CsCCD and CsZCD genes involved in crocus secondary metabolite biogenesis. Plant Cell, 15(1), 47–62; Fleischmann, P., Studer, K., & Winterhalter, P., (2002). Partial purification and kinetic characterization of a carotenoid cleavage enzyme from quince fruit (Cydonia oblonga). Journal of Agriculture and Food Chemistry, 50(6), 1677–1680; Fleischmann, P., Watanabe, N., & Winterhalter, P., (2003). Enzymatic carotenoid cleavage in star fruit (Averrhoa carambola). Phytochemistry, 63(2), 131–137; Schwartz, Qin & Zeevaart, 2001].This paper describes the isolation and partial characterization of carotenoid cleavage enzymes in nectarines, isolated from ripe skin of commercially available fruit. The enzyme is characterized by its kinetic parameters (v_max, K_m, time constant, temperature dependence, activation energy).     

Psychographic measures and sensory consumer tests: When emotional experience and feeling-based judgments account for preferences

The aim of this study is to explore psychological and psychosocial individual differences in order to understand heterogeneous sensory preference clusters identified in consumer tests. We conducted two studies with 100 participants in each. Six seat car fabrics were rated on liking items. A questionnaire composed of the Affect Intensity Measure (AIM) [Larsen, R. J. (1984). Theory and measurement of affect intensity as an individual difference characteristic. Dissertation Abstracts International, 85, 2297B], the Rational-Experiential Inventory (REI), the Iowa–Netherlands Comparison Orientation Scale, (INCOM) [Gibbons, F. X., & Buunk, B. P. (1999). Individual differences in social comparison: Development of a scale of social comparison orientation. Journal of Personality and Social Psychology, 76, 129–142], and the Centrality of Visual Products Aesthetics (CVPA) [Bloch, P. H., Brunel, F. F., & Arnold, T. J. (2003). Individual differences in the centrality of visual product aesthetics: Concept and measurement. Journal of Consumer Research, 29, 551–565] was used. Two clusters of preferences were characterized by the AIM and REI measures. One group, “the velvet fabrics likers”, experienced emotions more intensely than the “non-velvet likers” who in turn, appeared to rely mostly on feelings in the judgment process. We discuss the possible influence of these psychological factors on the significance of sensory input used in the evaluation process.     

Optimization of extraction and isolation for 11S and 7S globulins of soybean seed storage protein

A new method was developed for extraction and isolation of 7S and 11S fractions from soybean seed, based on methods of Nagano et al., Thanh and Shibasaki [Nagano, T., Hirotsuka, M., & Mori, H. (1992). Dynamic viscoelastic study on the gelation of 7S globulin from soybeans. Journal of Agricultural and food chemistry 40, 941–944 and Thanh, V. H., & Shibasaki, K. (1976). Major proteins of soybean seeds. A straightforward fraction and their characterization. Journal of Agricultural and Food Chemistry 24, 1117–1121]. Optimization of the extraction and isolation of 11S and 7S globulins from soybean seed was investigated under various conditions by the Kjeldahl method and SDS-PAGE. The optimal conditions were as follows: 0.03–0.06 M Tris–HCl buffer (pH 8.5) containing 0.01 M sodium bisulfite as extract solution, extraction twice at 45 °C for 1 h, and with a 1:15 ratio (w/v) of flour:Tris–HCl. The 11S fraction was precipitated at pH 6.4, and the supernatant, after centrifugation, was adjusted to pH 5.5 to remove the insoluble intermediate fraction by further centrifugation. The supernatant obtained was then adjusted to pH 4.8 to afford the 7S fraction as a precipitate by centrifugation. With the improvements, the protein contents and purities of the isolated 11S and 7S fractions were significantly increased. The contents of all subunits of the isolated 11S and 7S fraction were markedly higher than those by Thanh and Shibasaki method, while the contents of α, β and B₃ were also significantly higher than those by Nagano et al. method.     

Predicting inactivation of Salmonella senftenberg by pulsed electric fields

Pulsed electric field inactivation of Salmonella senftenberg suspended in McIlvaine buffer of pH 7 and conductivity 2 mS/cm was investigated. In this study, square wave waveform pulses were used. After the same treatment time, inactivation of S. senftenberg depended neither on pulse width (1–15 μs) nor frequency of treatment (1–5 Hz). Survivor curves of S. senftenberg at different electric field strengths did not follow first-order kinetics. These survival curves were described by the log-logistic model proposed by Cole et al. [Cole, M. B., Davies, K. W., Munro, G., Holyoak, C. D., and Kilsby, D. C. (1993). A vitalistic model to describe the thermal inactivation of Listeria monocytogenes. Journal of Industrial Microbiology, 12, 232–239]. Comparison of measured and estimated values showed that this model accurately described the inactivation of S. senftenberg by high electric field pulses in the range of 12–28 kV/cm.     

Isolation of Alicyclobacillus and the influence of different growth parameters

Alicyclobacillus species are thermo-acidophilic, endospore-forming bacteria that are able to survive pasteurisation and have been implicated in a number of spoilage incidents involving acidic foods and beverages. The aim of this study was to compare three isolation methods used for the detection of Alicyclobacillus acidoterrestris and to investigate the influence of incubation temperature on the growth of A. acidoterrestris and A. acidocaldarius. Peach juice samples inoculated with A. acidoterrestris K47 were analysed using either the International Federation of Fruit Juice Producers (IFU) Method No. 12 (Method A), which involved spread plating onto Bacillus acidoterrestris (BAT) agar at pH 4.0; Method B, which involved pour plating using potato dextrose agar (PDA) at pH 3.7; or Method C, which made use of membrane filtration followed by incubation on K agar at pH 3.7. The performance of the three methods differed significantly, with the IFU Method No. 12 recovering the highest percentage of cells at 75.97%, followed by Method B at 66.79% and Method C at 3.43%. These findings strengthen the proposal of the IFU for the use of the IFU Method No. 12 as a standard international method for the detection of Alicyclobacillus. To investigate the effect on growth of different incubation temperatures A. acidoterrestris (three strains) and A. acidocaldarius (two strains) were incubated at either 45 °C or 25 °C. Growth at 25 °C was slower and maximum cell concentrations were lower (1 × 10⁵-10⁶ cfu/mL compared to 1 × 10⁷-10⁸ cfu/mL) than at 45 °C for A. acidoterrestris. A. acidocaldarius was unable to grow at 25 °C and cell concentrations decreased by 1-2 logs. Since a growth temperature of 25 °C could not inhibit growth of A. acidoterrestris, cooling to room temperature (20°-25 °C) is not an effective control measure for A. acidoterrestris inhibition.     

Alicyclobacillus acidoterrestris in pasteurized exotic Brazilian fruit juices: Isolation,genotypic characterization and heat resistance

In this study, the population of Alicyclobacillus spp. was estimated in pasteurized exotic Brazilian fruit juices using the most probable number (MPN) technique followed by biochemical tests. Pasteurized passion fruit (n = 57) and pineapple (n = 50) juices were taken directly from Brazilian manufacturers. While Alicyclobacillus spp. was isolated from passion fruit juice, the microorganism was not found in any pineapple juice samples. A higher incidence of Alicyclobacillus was observed in samples taken in June and July (dry months in Brazil) in comparison to the other months (March, April, May and August), and the highest Alicyclobacillus counts were recovered from these samples(>23 MNP/100 mL). Sixteen (n = 16) Alicyclobacillus strains were typed using the randomly amplified polymorphic DNA method (RAPD-PCR). RAPD-PCR revealed great genetic similarity between the passion fruit juice strains and Alicyclobacillus acidoterrestris DSM 2498. The heat resistance of three isolates was determined, and the mean D_95°  (1.7 min) and z (7.6 °C) values in the passion fruit juice were not significantly different (p > 0.05) from those obtained for the DSM 2498 strain (D_95°  = 1.5 min and z = 7.1 °C). This is the first report on the isolation of A. acidoterrestris from exotic fruit juices such as passion fruit juice. It is worth pointing out the importance of applying good agricultural practices in the field and applying controls for the fruit selection and washing steps, as well as controlling the time/temperature conditions for pasteurization so as to reduce the incidence and chances of A. acidoterrestris spoilage in these juices.     

Effect of single and combined UV-C and ultra-high pressure homogenisation treatments on inactivation of Alicyclobacillus acidoterrestris spores in apple juice

Alicyclobacillus acidoterrestris is a spore-forming bacterium that can survive thermal pasteurization and acidic conditions. It produces changes in the odour and flavour of fruit juices leading to economical loses. A. acidoterrestris CECT 7094 spores were inoculated in clarified and cloudy apple juices (Golden delicious var.) in the range of 5–6 log₁₀ spores/mL and submitted to different short-wave ultraviolet light (UV-C) doses (7.2–28.7 J/mL) and ultra-high pressure homogenisation (UHPH) treatments (100–300 MPa), including their combination. A. acidoterrestris could be inactivated in clarified apple juice at a level of 4.8 log₁₀ CFU/mL by a 300 MPa-UHPH treatment when the inlet temperature was 80 °C. UV-C treatments showed to be more efficient achieving a lethality of 5.5 log₁₀ CFU/mL with a dose of 21.5 J/mL at 20 °C. In cloudy apple juice (2357 NTU) UV-C treatments were less efficient with a maximum lethality of 4.07 CFU/mL after a dose of 28.7 J/mL. A previous application of UHPH contributed with UV-C to obtain higher reductions of A. acidoterrestris spores at the doses of 14.3 and 21.5 J/mL compared with UV-C single treatments. On the other hand, this previous treatment also changed the properties of particles in the matrix which apparently reduced the effectiveness of UV-C at 28.7 J/mL.     

The impact of high power ultrasound for controlling spoilage by Alicyclobacillus acidoterrestris: A population and a single spore assessment

Consumer demand for healthier, microbiologically safe and stable, higher quality and minimally processed foods has increased in the last decades, promoting the application of non-thermal process technologies. Ultrasound processing is gaining attention because of its potential for improving quality and safety while retaining product flavor, texture, color and nutrient composition. Recently, Alicyclobacillus acidoterrestris has been recognized by manufacturers and processors in the fruit industry as a new type of thermoacidophilic, endospore-forming spoilage bacterium for commercialized fruit juices that can withstand the high temperatures applied in pasteurization process and spoil them producing taint compounds. Based on the above, the present study was undertaken to investigate the separate and combined effect of ultrasound treatment operating at 26 kHz, 90 μm, 200 W for 5, 10, 15 min and heat stress (at 80 °C for 10 min) on the recovery of A. acidoterrestris spores in K broth adjusted to pH = 4.5 with 25% (w/v) citric acid at temperatures between 35 and 45 °C at population and individual spore level. At the population level, statistically significant differences in average lag time of A. acidoterrestris spores from different treatments at 35 and 45 °C have been found. After the applied ultrasound (at 100% Amplitude for 10 min) and heat shock (at 80 °C for 10 min), the average lag time of A. acidoterrestris spores at 35 °C (7.24 ± 0.34 h) and 45 °C (6.38 ± 0.18 h) has been shown to be longer compared to the control at 35 °C (5.68 ± 0.36 h) and at 45 °C (2.87 ± 0.19 h), while for this combination, the maximum specific growth rate was not significantly different from the control samples. Additionally, the findings of this study have shown that λ among individual spores was greatly variable when they were treated by ultrasound (at 100% Amplitude for 10 min) and/or thermal treatment (at 80 °C for 10 min). The application of ultrasound and thermal treatment resulted in a more pronounced effect on median lag phase duration (25.74 h) than the heat shock (11.63 h) and affected both the position and the spread of the λ distributions of A. acidoterrestris spores. This work would help to better assess and optimize the proposed combined treatments, since ultrasound and thermal treatments could work in a synergistic way on delaying the lag time of the tested bacterial spores.     

Environmental variations of trace element concentrations in Egyptian cane sugar and soil samples (Edfu factories)

Multielements, Ag, Au, Ca, Co, Cr, Cu, Fe, K, Mg, Mn, Na, Ni, Pb, Sr, and Zn were estimated in the sugar cane plant (green bagasse or cane stalks and leaves), sugar cane, raw juice, mixed juice, in syrup at the different stages of sugar production (10 stages), in sugar (grades A and B), and in soil samples collected from the immediate vicinity of the cane plant roots at surface, 30 and 60 cm depths. The measurements were undertaken on a Pye Unicam SP 1900 Recording Flame Atomic Absorption Spectrophotometer. The results obtained are within the permissible safety baseline levels and in excellent agreement with the previous work done on the sugar cane plant and on the soil of the same area (Edfu) using INAA, ICP-AES and AAS (Awadallah, R. M., Sherif, M. K., Mohamed, A. E., & Grass, F. (1984). Determination of trace elements in Egyptian cane sugar by neutron activation analysis. Inter. J. Environ. Anal. Chem., 19 (1), 41–54; Awadallah, R. M., Sherif, M. K., Mohamed, A. E., & Grass, F. (1985). Determination of trace elements in Egyptian cane sugar by neutron activation analysis. J. Radioanal. Nucl. Chem. 92 (1), 7–25; Mohamed, A. E. (1986). Determination of trace elements in sugar cane refuse by instrumental neutron activation analysis. J. Radioanal. Nucl. Chem., Letters, 107 (2), 121–128; Mohamed, A. E., Awadallah, R. M., & Hassan, A. A. (1989). Determination of trace elements in Egyptian molasses by instrumental neutron activation analysis. J. Radioanal. Nuel. Chem. Articles, 129 (2), 453–457). ©     

Nutritionally important starch fractions in cereal based Indian food preparations

Recent research studies have invalidated the earlier assumptions regarding the rate of digestion of carbohydrates. Hence, in the present study the rate and extent of starch digestion in vitro was measured in 10 cereal-based Indian food preparations (with/without accompaniments). The selected foods included chapathi, dosa, idli, pongal, poori, ragi roti, rice roti, rice flakes upma, semolina idli and upma and the accompaniments — cooked dhal, chutney and potato palya. In view of the nutritional importance of starch, the major starch fractions viz., rapidly digestible starch, slowly digestible starch (SDS) and resistant starch as defined by Englyst [Englyst, H. N., Kingman, S. M., & Cummings, J. H. (1992). Classification and measurement of nutritionally important starch fractions. European Journal Clinical Nutrition, 46(2), 333–350] were measured, by using controlled enzymic hydrolysis with pancreatin and amyloglucosidase. In addition, rapidly available glucose (RAG) was measured and a starch digestion index was derived. Dietary fiber components (soluble and insoluble fiber) were measured by the enzymatic method [Asp, N. G., Johansson, C. G., Hallmer, H., & Siljestrom, M. (1983). Rapid enzymatic assay of insoluble and soluble dietary fiber. Journal of Agricultural Food Chemistry, 31, 476–482]. The results indicate that the course of starch hydrolysis was not only characteristic for each food but also appears to be affected by the addition of accompaniment. Also, while the correlation between RAG and SDS did not attain significance in foods with accompaniment, a significant inverse correlation (r=−0.68, P<0.05) was seen in foods without accompaniment. It is evident that starch digestibility in Indian foods is influenced by the accompaniment rather than the cereal base.     

Isolation,identification and typification of Alicyclobacillus acidoterrestris and Alicyclobacillus acidocaldarius strains from orchard soil and the fruit processing environment in South Africa

Alicyclobacillus acidoterrestris and Alicyclobacillus acidocaldarius are thermo-acidophilic, non-pathogenic, spore-forming bacteria that can survive the typical heat processing of fruit juices and concentrates. Bacterial endospores then germinate, grow and cause spoilage of acid food products. Species of Alicyclobacillus were isolated from orchard soil and a fruit concentrate production factory in South Africa. Preliminary identification of the isolates was based on morphological, biochemical and physiological properties. Identification at species level was done by PCR amplification using genus-specific primers and 16S ribosomal RNA (rRNA) gene sequencing. The majority of isolates belonged to the species A. acidoterrestris, but A. acidocaldarius was also isolated and identified. As far as we could determine, this is the first report of the isolation of A. acidoterrestris from wash water and soil outside a fruit processing plant, as well as the isolation of A. acidocaldarius from vinigar flies. The genotypic relatedness between strains of A. acidoterrestris and between strains of A. acidocaldarius was determined by RAPD-PCR. Sixteen isolates identified as A. acidoterrestris grouped into four clusters based on RAPD-PCR banding patterns, suggesting that they belong to at least four genotypic groups. Three isolateT:/PGN/ELSEVIER/YFMIC/web/00001155/s identified as A. acidocaldarius gave three unique banding patterns.     

Prevalence, concentration, spoilage, and mitigation of Alicyclobacillus spp. in tropical and subtropical fruit juice concentrates

The presence of Alicyclobacillus in fruit juices and concentrates poses a serious problem for the juice industry. This study was undertaken to determine the (i) prevalence, concentration, and species of Alicyclobacillus in tropical and subtropical concentrates; (ii) efficacy of aqueous chlorine dioxide in reducing Alicyclobacillus spp. spores on tropical and subtropical fruit surfaces; and (iii) fate of and off-flavor production by Alicyclobacillus acidoterrestris in mango and pineapple juices. One hundred and eighty tropical and subtropical juice concentrates were screened for the presence and concentration of Alicyclobacillus spp. If found, the species of Alicyclobacillus was determined by 16S rDNA sequencing and analysis with NCI BLAST. Of these samples, 6.1% were positive for Alicyclobacillus, and nine A. acidoterrestris strains and two Alicyclobacillus acidocaldarius strains were identified. A five-strain cocktail of Alicyclobacillus spp. was inoculated onto the surface of fruits (grapefruit, guava, limes, mangoes, oranges and pineapple), which were then washed with 0, 50, or 100 ppm aqueous chlorine dioxide. Significant reductions due to chlorine dioxide were only seen on citrus fruits. A five-strain cocktail of A. acidoterrestris was inoculated into mango and pineapple juices. Microbial populations were enumerated over a 16-day period. Aroma compounds in the juice were analyzed by GC-olfactometry (GC-O) and confirmed using GC-MS. GC-O of mango juice identified previously reported medicinal/antiseptic compounds. GC-O of pineapple juice revealed an unexpected “cheese” off-aroma associated with 2-methylbutyric acid and 3-methylbutyric acid.     

Escherichia coli population heterogeneity: subpopulation dynamics at super-optimal temperatures

In the past years, we explored the dynamics of Escherichia coli K12 at super-optimal temperatures under static and dynamic temperature conditions ( [Van Derlinden et?al., 2008b], [Van Derlinden et?al., 2009] and [Van Derlinden et?al., 2010]). Disturbed sigmoid growth curves, i.e., a sequence of growth, inactivation and re-growth, were observed, especially close to the maximum growth temperature. Based on the limited set of experiments (i.e., 2 static temperatures and 2 dynamic temperature profiles), the irregular growth curves were explained by postulating the co-existence of two subpopulations: a more resistant, growing population and a temperature sensitive, inactivating population.In this study, the dynamics of the two subpopulations are studied rigorously at 11 constant temperature levels in the region between 45 °C and 46 °C, with at least five repetitions per temperature.At all temperatures, the total population follows a sequence of growth, inactivation and re-growth. The sequence of different stages in the growth curves can be explained by the two subpopulations. The first growth phase and the inactivation phase reflect the presence of the sensitive subpopulation. Hereafter, the population’s dynamics are dominated by the growth of the resistant subpopulation. Generally, cell counts are characterized by a large variability.The dynamics of the two subpopulations are carefully analyzed using a heterogeneous subpopulation type model to study the relation between the kinetic parameters of the two subpopulations and temperature, and to evaluate if the fraction d of resistant cells varies with temperature. Results indicate that the growth rate of the sensitive subpopulation decreases with increasing temperature within the range of 45-46 °C. Furthermore, results point in the direction that the duration of this initial growth phase is approximately constant, i.e., around 2 h. Possibly, the stress resistance of the cells decreases after a certain period because the metabolism is fully adapted to exponential growth. Also, the growth rate of the resistant subpopulation decreases with increasing temperature. Due to the extreme variability in the cell density data, derivation of accurate relations was not possible. From the heterogeneous model implementations, given the experimental set-up, both a constant d value and a temperature dependent d value seem plausible.     

Evolution and identification of lactic acid bacteria isolated during the ripening of Sardinian sausages

Lactic acid bacteria (LAB) were isolated during the production and the ripening of Sardinian sausage, a typical Italian dry fermented sausage. Samples were taken at different stages, and 112 strains were isolated. The isolates were characterized using the micromethod proposed by Font de Valdez et al. [Font de Valdez, G., Savoy de Giori, G., Oliver, G., & De Ruiz Holgado, A. P. (1993). Development and optimization of an expensive microsystem for the biochemical characterization of lactobacilli. Microbiologie Aliments Nutrition, 11, 215–219]. Schillinger and Lücke’s [Schillinger, U., & Lücke, F. K. (1987). Identification of lactobacilli from meat and meat products. Food Microbiology. (4), 199–208] scheme and the biochemical patterns given by Bergey’s Manual of Systematic Bacteriology [Bergey’s Manual of Systematic Bacteriology (1986). Baltimore: William and Wilkins] were used for preliminary identification. A PCR-based method was then used to confirm the results. LAB were the dominant flora during ripening. They consisted mainly of homofermentative mesophilic rods. Lactobacillus sakei (43,3%), Lactobacillus plantarum (16,6%) and Lactobacillus curvatus (13,3%) were the main isolates. The results of the biochemical identification methods agreed well with those of PCR-based identification (91% agreement).     

Germination and inactivation of Bacillus coagulans and Alicyclobacillus acidoterrestris spores by high hydrostatic pressure treatment in buffer and tomato sauce

Acidothermophilic bacteria like Alicyclobacillus acidoterrestris and Bacillus coagulans can cause spoilage of heat-processed acidic foods because they form spores with very high heat resistance and can grow at low pH. The objective of this work was to study the germination and inactivation of A. acidoterrestris and B. coagulans spores by high hydrostatic pressure (HP) treatment at temperatures up to 60 °C and both at low and neutral pH. In a first experiment, spores suspended in buffers at pH 4.0, 5.0 and 7.0 were processed for 10 min at different pressures (100-800 MPa) at 40 °C. None of these treatments caused any significant inactivation, except perhaps at 800 MPa in pH 4.0 buffer where close to 1 log inactivation of B. coagulans was observed. Spore germination up to about 2 log was observed for both bacteria but occurred mainly in a low pressure window (100-300 MPa) for A. acidoterrestris and only in a high pressure window (600-800 MPa) for B. coagulans. In addition, low pH suppressed germination in A. acidoterrestris, but stimulated it in B. coagulans. In a second series of experiments, spores were treated in tomato sauce of pH 4.2 and 5.0 at 100 - 800 MPa at 25, 40 and 60 °C for 10 min. At 40 °C, results for B. coagulans were similar as in buffer. For A. acidoterrestris, germination levels in tomato sauce were generally higher than in buffer, and showed little difference at low and high pressure. Remarkably, the pH dependence of A. acidoterrestris spore germination was reversed in tomato sauce, with more germination at the lowest pH. Furthermore, HP treatments in the pH 4.2 sauce caused between 1 and 1.5 log inactivation of A. acidoterrestris. Germination of spores in the high pressure window was strongly temperature dependent, whereas germination of A. acidoterrestris in the low pressure window showed little temperature dependence. When HP treatment was conducted at 60 °C, most of the germinated spores were also inactivated. For the pH 4.2 tomato sauce, this resulted in up to 3.5 and 2.0 log inactivation for A. acidoterrestris and B. coagulans respectively. We conclude that HP treatment can induce germination and inactivation of spores from thermoacidophilic bacteria in acidic foods, and may thus be useful to reduce spoilage of such foods caused by these bacteria.     

Improvement of a solid phase extraction method for separation of animal muscle phospholipid classes

The solid phase extraction (SPE) method used by Banni et al. (2001) [Banni, S., Carta, G., Angioni, E., Muru, E., Scanu, P., Melis, M. P., et al. (2001). Distribution of conjugated linoleic acid and metabolites in different lipid fraction in the rat liver. Journal of Lipid Research, 42, 1056–1061] for fractionation of liver phospholipids (PLs) into phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylserine (PS) and phosphatidylinositol (PI) was modified to improve its separation efficiency. A mixture of PL standards, containing PC, PE, PS and PI, was separated into individual classes by using aminopropyl minicolumns, following the method of Banni et al. (2001). The obtained eluted fractions were further analysed by thin layer chromatography (TLC) and PL classes were identified. TLC revealed the co-elution of PC and PE, that of PE with PS and no elution of PI. The SPE method was subsequently modified in order to obtain a correct PL fractionation into PC, PE, PS and PI. The principal modifications consisted of increased solvent volumes for PC, PE and PS elution, and a different solvent mixture to allow PI elution. The effectiveness of the modified SPE method was checked by TLC, using both standards and muscle samples, showing a correct elution of PC, PE, PS and PI.