Lactose Caking: Influence of the Particle Size Distribution and the Water Content

AbstractIndustrially, after the crystallisation of lactose from mother liquor, the crystals are separated by centrifugation and then dried in a flash drier followed by a fluid bed drier. It is known that if the moisture content and/or particle size is not correct then lumping and caking of the lactose can occur in the flash drier causing operational problems.The aim of this study was to characterize the influence of water content and particle size distribution on the caking of lactose powders.Powders with different d50's and different water contents had their caking/clumping characteristics analyzed with a texture analyzer, a sticky plate and a blow tester to determine their cohesion. A theoretical approach looking at the capillary interactions of the liquid bridges between lactose crystals was taken from the literature to explain the results obtained.The results showed that lactose powder with a low d50 can cake easily as soon as the water content is higher than 3%. This cohesion between lactose crystals is due to liquid bridges linking them together. The number of bridges formed affects the level of cohesion: the more numerous they are, the more cohesive the lactose crystals are. Therefore, small particles cake more easily because the number of bridges in a given volume is higher than for bigger particles.It was predicted that the capillary force cannot hold together particles with d50 bigger than 400μm and that was confirmed by experiment.Finally, in order to prevent the caking of lactose powders obtained by processes such as a decanter centrifuge, the lactose crystallization step should be controlled to obtain large crystal (with d50>300μm) and/or the final water content should not be higher than 3%

Are bacterial spores activated by High Pressure treatment at 20°C ?

International audienc

The role of water in bacteria spore resistance

International audienc

La biopréservation: une stratégie d’avenir pour la conservation des aliments

N° d'article 201511121820La demande grandissante des consommateurs pour des produits alimentaires à teneur réduite en conservateurs pousse les industriels de l’agroalimentaire à rechercher des méthodes de conservation alternatives. Dans ce contexte, la bioprotection s’impose comme un procédé à fort potentiel. Cette technique consiste à inoculer sur les aliments des cultures de bactéries protectrices. Celles-ci, par l’intermédiaire de plusieurs mécanismes, vont inhiber la croissance de bactéries pathogènes et d’altération telles que Listeria monocytogenes et Salmonella. Cependant, cette technique n’a pas d’effet sur les spores bactériennes. Ainsi, l’objet central du projet de recherche ANR BlacHP vise à inactiver ces formes résistantes, notamment en combinant la biopréservation avec un procédé de traitement par hautes pressions hydrostatiques

Understanding the Effects of High Pressure on Bacterial Spores Using Synchrotron Infrared Spectroscopy

International audienceBacterial spores are extremely resistant life-forms that play an important role in food spoilage and foodborne disease. The return of spores to a vegetative cell state is a three-step process, these being activation, germination, and emergence. High-pressure (HP) processing is known to induce germination in part of the spore population and even to inactivate a high number of Bacillus spores when combined with other mild treatments such as the addition of nisin. The aim of the present work was to investigate the mechanisms involved in the sensitization of spores to nisin following HP treatment at ambient temperature or with moderate heating leading to a heterogeneous spore response. Bacillus subtilis spores were subjected to HP treatment at 500 MPa at 20 and 50°C. The physiological state of different subpopulations was characterized. Then Fourier transform infrared (FTIR) microspectroscopy coupled to a synchrotron infrared source was used to explore the heterogeneity of the biochemical signatures of the spores after the same HP treatments. Our results confirm that HP at 50°C induces the germination of a large proportion of the spore population. HP treatment at 20°C generated a subpopulation of ungerminated spores reversibly sensitized to the presence of nisin in their growth medium. Regarding infrared spectra of individual spores, spores treated by HP at 50°C and germinated spores had similar spectral signatures involving the same structural properties. However, after HP was performed at 20°C, two groups of spores were distinguished; one of these groups was clearly identified as germinated spores. The second group displayed a unique spectral signature, with shifts in the spectral bands corresponding to changes in membrane fluidity. Besides, spores spectra in the amide region could be divided into several groups close to spectral properties of dormant, germinated, or inactivated spores. The part of the spectra corresponding to α-helix and β-sheet-structures contribute mainly to the spectral variation between spores treated by HP at 20°C and other populations. These changes in the lipid and amide regions could be the signature of reversible changes linked to spore activation

Effect of high pressure on the antimicrobial activity and secondary structure of the bacteriocin nisin

International audienceEffect of high pressure (HP) treatment on the antimicrobial properties and the structure of nisin was evaluated. Nisin solutions at pH 2.8 or 6.1 were treated by HP at 500 MPa – 10 min – 20 °C and their antimicrobial potency was determined. It appeared that HP clearly impacted the antimicrobial activity of nisin, with respective activity loss of 22.5% and 49.9% at pH 2.8 and 6.1. Structural analysis of nisin by circular dichroism and Fourier transform-infrared spectroscopies revealed that the decrease of nisin antimicrobial activity was likely due to the unfolding of the protein induced by HP. A loss of nisin β-turns structure, particularly significant at neutral pH, was linked to the drastic drop in antimicrobial activity, as these structures are implicated in the nisin interaction with the bacterial membrane.Industrial relevanceThe combination of nisin and high pressure (HP) can be use at an industrial scale to inactivate bacteria. Nisin is allowed as a food additive (E234) and can be added at a final concentration ranging from 120 to 500 IU/g, depending on the product. In this work, we showed that HP can induce a significant reduction of nisin activity (-22.5% at pH 2.8 and -49.9% at pH 6.1). Therefore, this activity loss could be taken into account to manage the final nisin concentration in HP-treated food products

Inhibitory effect of high hydrostatic pressure, nisin, and moderate heating on the inactivation of Paenibacillus sp. and Terribacillus aidingensis spores isolated from UHT milk

International audienceThe sensitivity of Paenibacillus sp. and Terribacillus aidingensis spores to combined action of HP, nisin and moderate heating were investigated for the first time. The results showed that the effect of HP on spores varies with pressure level, treatment temperature, spore species and presence of nisin. T. aidingensis spores were more resistant than Paenibacillus sp., whatever the treatment applied. The inactivation rates of both spore species did not exceed 2.7log (CFU/mL) after HP treatment at 600 MPa/50°C/10 min. However, a high synergistic effect of nisin and HP was observed after a treatment at 500 MPa/10 min/50°C with addition of nisin during HP and into the recovery medium, leading to 6log (CFU/mL) and 4log (CFU/mL) reduction for Paenibacillus and Terribacillus spores, respectively. Finally, the fraction of germinated spores by HP was measured and the results showed that germination induction is not the only underlying mechanisms of nisin sensitization by HP

Are bacterial spores activated by High Pressure treatment at 20°C ?

International audienc

High pressure sensitization of heat-resistant and pathogenic foodborne spores to nisin

International audienceToday, there is no effective non-thermal method to inactivate unwanted bacterial spores in foods. High-Pressure (HP) process has been shown to act synergistically with moderate heating and the bacteriocin nisin to inactivate spores but the mechanisms have not been elucidated. The purpose of the present work was to investigate in depth the synergy of HP and nisin on various foodborne spore species and to bring new elements of understandings.For this purpose, spores of Bacillus pumilus, B. sporothermodurans, B. licheniformis, B. weihenstephanensis, and Clostridium sp. were suspended in MES buffer, in skim milk or in a liquid medium simulating cooked ham brine and treated by HP at 500 MPa for 10 min at 50 °C or 20 °C. Nisin (20 or 50 IU/mL) was added at three different points during treatment: during HP, during and or in the plating medium of enumeration. In the latter two cases, a high synergy was observed with the inhibition of the spores of Bacillus spp. The evaluation of the germinated fraction of Bacillus spp. spores after HP revealed that this synergy was likely due to the action of nisin on HP-sensitized spores, rather than on HP-germinated spores. Thus, the combination of nisin and HP can lead to Bacillus spp. spore inhibition at 20 °C. And Nisin can act on HP-treated spores, even if they are not germinated.This paper provides new information about the inhibition of spores by the combination of HP and nisin. The high synergy observed at low temperature has not been reported yet and could allow food preservation without the use of any thermal process

Biopréservation et hautes pressions : des outils pour la maîtrise des dangers microbiologiques dans les aliments

L’utilisation d’additifs conservateurs est souvent nécessaire pour assurer la sécurité microbiologique des produits carnés réfrigérés faiblement acides. Le projet ANR BLac HP (2014-2019) a étudié une nouvelle stratégie de stabilisation des produits carnés réfrigérés pour assurer le contrôle des flores indésirables à la fois végétatives et sporulées. Grâce à une approche pluridisciplinaire, les travaux ont montré que la combinaison de la biopréservation par des bactéries lactiques et d’un traitement hautes pressions permettait d’assurer la qualité microbiologique de dés de jambon cuits à teneur réduite en nitrite pendant toute leur durée de vie. Le traitement permet de plus une qualité sensorielle optimale sans impact environnemental supplémentaire par rapport au procédé conventionnel. Mots-clés: spores, jambon, nitrites