Hurdle concept

In extending the shelf life of minimally processed foods, the hurdle concept uses a combination of suboptimal growth factors, such as (1) reduced temperature, (2) reduced pH, (3) reduced aw (4) addition of organic acids, and (5) modified atmosphere packaging (Uyttendaele, Taverniers, and Debevere, 2001). Treatment protocols that are based only on organic acid... 

McMeekin, T. A., Presser, K., Ratkowsky, D., Ross, T., Salter, M., and Tienungoon, S. 2000. Quantifying the hurdle concept by modeling the bacterial growth/no growth interface. International Journal of Food Microbiology 55 93-98. 

The hurdle concept for effective preservation of foods may inhibit outgrowth, but has been found to induce prolonged survival of Escherichia... 

Leistner (1992) has illustrated the use of the hurdle concept to design food formulations that ensure adequate shelf-life and safety of food products. Reformulation of a pet food produced a product with a higher but suitable and allowed the omission of propylene glycol from the recipe. The a was increased from 0.85 to 0.94 and the product was made more healthy, palatable and economic. 

The Steam Injection Cycle Steam injection has been used in reciprocating engines and gas turbines for a number of years. This cycle may be an answer to the present concern with pollution and higher efficiency. Corrosion problems are the major hurdle in such a system. The concept is simple and straightforward Steam is injected into the compressor discharge air and increases the mass flow rate... 

In examining the technical options for plastic waste management, chemical recycling appears to be the least developed and most difficult. In this paper, BP Chemicals sets out its analysis of the factors that will determine the choice of chemical recycling process technology. From this a process concept based on thermal cracking is developed and the hurdles to be overcome before such a process can be realised is discussed. 

The concept of inherently safer plant has been with us now for many years. But in spite of its clear potential benefits related to safety, health and the environment (SHE), as well as the costs, there has been few applications in chemical plant design. But as Kletz (1996) has written there are hurdles to be overcome. Inherently safer design requires a basic change in approach. Instead of assuming e.g. that we can keep large quantities of hazardous materials under control we have to try and remove them. Changes in belief and the corresponding actions do not come easily. 

Hydrogen can be potentially produced from renewable sources, thus enabling the intermittent and excess power generated to be stored for applications in transport, homes, and businesses, thereby making off-grid wind and solar sources economic. However, it must be noted, that commercial applications of these concepts are fairly limited at best or nonexistent at worst, and many decades of research and development may be necessary to solve the technical hurdles for application in a large-scale fashion. 

Eschenmoser [15] has recently alluded to the concepts of structure-directed synthesis and autochthonous reactivity — the propensity of certain systems to undergo reactions as a consequence of their intrinsic molecular structural factors — within the context of certain biomolecules, particularly the organic cofactor, vitamin B12. The formation of the AD ring junction in the corrin ligand had to be regarded as a major hurdle in any proposed chemical synthesis of cobyric acid (5) (Fig. 2), and hence of vitamin B12. However, driven initially by the desire to identify a dark, and therefore potentially biomimetic, variant of the photochemical... 

The concept should be presented in the form of an executive summary. As the first element of evaluation, it is a GO/NO GO criterion. This means that this section of the deliverables must be clearly commimicated for the project to even be considered. The concept is made up of five parts the vision, targeted product(s), targeted technology, targeted market(s), and the intended benefits to the customer. In contrast to the other deliverables, there are no increasing hurdles for this criterion. The concept should, however, be reassessed constantly and may change as the project moves toward commercialization. 

Many laws, generalizations, and rules are presented in the study of basic chemistry. Most students can master these. Successful smdents, however, not only know them but also know when to use each one. Word problems are the biggest hurdle for most students who do have difficulty with chemistry. The best way to leam to do word problems is to practice intensively. Review the Examples and do the Practice Problems until you feel confident that you understand the concepts and techniques involved. (Do not try to memorize solutions there are too many different ways to ask the same questions, and many similar-sounding questions are acmally quite different.) Do the Snapshot Review items at the end of each section. Do as many of the end-of-chapter problem as you possibly can to see whether you have mastered the material. 

Those higher thermal and chemical stabilities not only make inorganic membranes very suitable for separation applications, but also for reaction enhancement The duel use of an inorganic membrane as a separator as well as reactor offers great promises which along with potential hurdles to overcome will be treated in Chapters 8 through 11. The concept and related material, catalytic and engineering issues are addressed. 

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