Technological characterization and survival of the exopolysaccharide-producing strain Lactobacillus delbrueckii subsp. lactis 193 and its bile-resistant derivative 193+ in simulated gastric and intestinal juices

The capacity of lactic acid bacteria to produce exopolysaccharides (EPS) conferring microorganisms a ropy phenotype could be an interesting feature from a technological point of view. Progressive adaptation to bile salts might render some lactobacilli able to overcome physiological gut barriers but could also modify functional properties of the strain, including the production of EPS. In this work some technological properties and the survival ability in simulated gastrointestinal conditions of Lactobacillus delbrueckii subsp. lactis 193, and Lb. delbrueckii subsp. lactis 193+, a strain with stable bile-resistant phenotype derived thereof, were characterized in milk in order to know whether the acquisition of resistance to bile could modify some characteristics of the microorganism. Both strains were able to grow and acidify milk similarly; however the production of ethanol increased at the expense of the aroma compound acetaldehyde in milk fermented by the strain 193+, with respect to milk fermented by the strain 193. Both microorganisms produced a heteropolysaccharide composed of glucose and galactose, and were able to increase the viscosity of fermented milks. In spite of the higher production yield of EPS by the bile-resistant strain 193+, it displayed a lower ability to increase viscosity than Lb. delbrueckii subsp. lactis 193. Milk increased survival in simulated gastric juice; the presence of bile improved adhesion to the intestinal cell line HT29-MTX in both strains. However, the acquisition of a stable resistance phenotype did not improve survival in simulated gastric and intestinal conditions or the adhesion to the intestinal cell line HT29-MTX. Thus, Lb. delbrueckii subsp. lactis 193 presents suitable technological properties for the manufacture of fermented dairy products; the acquisition of a stable bile-resistant phenotype modified some properties of the microorganism. This suggests that the possible use of bile-resistant derivative strains should be carefully evaluated in each specific application considering the influence that the acquisition of a stable bile-resistant phenotype could have in survival ability in gastric and intestinal conditions and in technological properties.     

Cyclodextrin-based carbohydrate clusters by amide bond formation

Per-6-amino-2,3-dimethyl-ß-cyclodextrin was prepared very efficiently as its hydrochloride salt from native ß-cyclodextrin in four steps and 89% overall yield. O-Acetyl-protected ß-D-thioglucose and ß-D-thiolactose derivatives, containing short spacer arms terminated with carboxylic acid functions, were prepared by the BF₃·OEt₂-catalyzed thioglycosylation of ß-D-glucose pentaacetate and ß-lactose octaacetate with 3-mercaptopropionic acid, respectively. Utilizing amide bond formation as the key step, these thio-ß-D-glucosyl and lactosyl derivatives were coupled to per-6-amino-2,3-dimethyl-ß-cyclodextrin to afford, after deprotection, perfunctionalized ß-cyclodextrin-based clusters containing seven thio-ß-D-glucosyl and seven ß-lactosyl appendages, respectively. Molecular modeling of both these ß-cyclodextrin-based clusters revealed the glucose and lactose clusters to be approximately 23 Å and 27 Å in diameter, respectively, and approximately 19 Å in height in both cases. The association constants for the complexation of the anti-inflammatory drug naproxen by ß-cyclodextrin, per-2,3-dimethyl-ß-cyclodextrin, and the lactose cluster of ß-cyclodextrin in 0.01 M phosphate buffered saline solution (pH 7.4) were found by UV-vis spectrophotometric titration to be 374 ± 75 M⁻¹, 351 ± 70 M⁻¹, and 165 ± 33 M⁻¹, respectively.     

Hydrotropic properties of some short-chain alkylbenzene- and alkylnaphthalene sulfonates

Alkylbenzene sulfonates based on toluene, xylene and cumene, and alkylnaphthalene sulfonates act as hydrotropes in surfactant systems. One measure of hydrotropicity is the amount of hydrotrope required to clear a cloudy detergent formulation; some hydrotropes are more effective than others, depending on the surfactant formulation. Another measure is the modification of the viscosity of surfactant formulations; the change in the viscosity depends on the amount and type of hydrotrope used and on the specific formulation involved. Additionally, alkylnaphthalene sulfonate hydrotropes change the solubility of nonionic surfactants in water, and both types of hydrotrope raise the cloud point of nonionic surfactant solutions; however, the naphthalene-based hydrotropes are more efficient. Ross-Miles foam test data are used to compare the foam characteristics of different alkylnaphthalene sulfonates. A critical micelle concentration (CMC) was determined for the alkylnaphthalene sulfonates, but although alkylbenzene sulfonates do show some surface activity, a CMC could not be found for these materials. Presented as a poster session at the AOCS Annual Meeting & Expo, May 1997, Seattle, Washington, and at Soaps, Detergents, and Oleochemicals: An AOCS International Conference, October 1997, Fort Lauderdale, Florida.     

Interval based MINLP superstructure synthesis of heat exchanger networks for multi-period operations

The interval based MINLP superstructure (IBMS) presented by Isafiade and Fraser (2008) is applied to the design of heat exchanger networks which can handle multiple period of operations. In multi-period operations, parameters such as supply temperature, target temperature and the flowrates of streams can vary over a specified range. In this paper the IBMS is formulated for multi-period operations involving unequal period durations. In order to ensure that each exchanger connecting the same pair of streams in two or more periods is able to transfer heat in such streams for all the periods, the maximum area per period approach of Verheyen and Zhang (2006) is used in the objective function. This method helps to simplify the model. The new method is applied to three examples from the literature.     

An engineering process for the verification of real-time systems

The complete verification of the timing properties of a large critical system cannot be undertaken in a single step or with a single method. In this paper we present a process that links together a number of techniques and approaches that cover all stages of development from requirements analysis to code testing. The key elements of the process are: a constrained form of timed automata that uses delay and deadline to define temporal behaviour, notions of rely and guarantee to cover temporal dependencies, model checking for design verification, SPARK and Ravenscar restrictions for programming, and scheduling and response time analysis for asserting implementation compliance. Extended examples of the use of the process are given.     

Testing the Schedulability of Synchronous Traffic for the Timed Token Medium Access Control Protocol

One of the key issues related to guaranteeing synchronous message deadlines in a timed token network (such as fiber distributed data interface) where the timed token medium access control protocol is used is the schedulability test of synchronous traffic (i.e., testing whether or not all synchronous messages can be transmitted before their deadlines, under a given setting of network parameters). Much work has been done on how to assign network parameters appropriately in order to guarantee timely transmission of synchronous traffic. As a result quite a few synchronous bandwidth allocation schemes and some good guidelines on selection of the target token rotation time have been proposed. In contrast, limited research has been conducted on how to effectively test whether or not given network parameters can guarantee timely transmission of all synchronous messages (of a considered synchronous message set) before their deadlines. The previous testing methods for synchronous message schedulability only provide a sufficient (but not necessary) test and therefore fail to always keep effective for any synchronous message set considered. In this paper, we propose two testing methods for determining the schedulability of a synchronous message set with message deadlines no longer than periods. The proposed tests perform better than any previous test in the sense that they are both sufficient and necessary. Some numerical examples are given to compare different testing methods, all of which have demonstrated the superiority of the proposed tests to other existing testing methods.