Measurement and control of water activity with an aluminium oxide sensor in organic two-phase reaction mixtures for enzymic catalysis

Khan, Shahnaz A.; Halling, Peter J.; Bell, George

doi:10.1016/0141-0229(90)90057-w

Cited by 23 publications

(4 citation statements)

References 15 publications

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“…To control the water activity in an enzyme reactor, a reliable method of measurement is necessary. Relative humidity sensors have limitations with regard to the stability and the measurement range in organic solvent media due to the deleterious effects of the solvent (Khan et al, 1990). However, the solvent-free systems adopted in this study mean that a relative humidity sensor can be used for online water activity control.…”

Section: Resultsmentioning

confidence: 97%

“…Since then, several methods have been proposed for a w control during ester synthesis. One method is the recirculation of headspace air through a molecular sieve column when water removal from the reaction medium is required (Cassells and Halling, 1988;Khan et al, 1990). However, in this way only the rate of water removal can be manipulated, and it is difficult to control a w in the reaction medium at a desired set point as a result of recirculation of headspace gas.…”

Section: Introductionmentioning

confidence: 99%

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Computer‐Aided Control of Water Activity for Lipase‐Catalyzed Esterification in Solvent‐Free Systems

Won

Lee

2001

Biotechnology Progress

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A computer system for on-line monitoring and control of the water activity (a(w)) in solvent-free media has been developed. The performance of this system was investigated by carrying out the lipase-catalyzed esterification of n-capric acid with n-decyl alcohol. A humidity sensor measured the relative humidity in the reactor headspace, which was then transmitted electrically to a digital computer that was used as a feedback controller. The water activity control was achieved by sparging either humidified air or dried air through the reaction medium at a flow rate determined by the digital feedback controller. The use of humid air and dry air for a(w) control made it possible to induce a larger a(w) gradient and thereby higher water transfer rate. As a result, the water activity quickly reached the desired a(w) values. We tested whether water activity in the reaction medium can be monitored by measuring relative humidity in the headspace. When the water activity in the liquid phase was determined from measurements of water content in the medium and compared to that measured directly with the humidity sensor, the a(w) in the reaction medium did not differ significantly from that in the headspace. This indicates that there is a near-equilibrium between the liquid medium and the exit air stream. Water activity was also successfully maintained close to the set point despite the massive production of water during the esterification process. Thus, the control system developed in this study is particularly useful for systems where large amounts of water are produced and where conventional methods make it difficult to control water activity as a result of a low water transfer rate. The effects that computer control of the water activity had on the reaction rate and yield were also examined. The reaction yield was significantly improved with water activity control. The conversions obtained at 28 h without and those with water activity control were 70% and 96%, respectively. In addition, from the fact that the final yields increased with decreasing a(w), computer-aided water activity control was performed with a set-point change. By controlling a(w) at 0.55 during initial reaction phase, followed by a step change of a(w) from 0.55 to 0 after 11 h of reaction, it was possible to enhance the final conversion to 100%.

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Section: Resultsmentioning

confidence: 97%

Section: Introductionmentioning

confidence: 99%

Computer‐Aided Control of Water Activity for Lipase‐Catalyzed Esterification in Solvent‐Free Systems

Won

Lee

2001

Biotechnology Progress

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“…Reakcija esterifikacije masnih kiselina i glicerola je povratna reakcija hidrolize. Zbog toga je važno da uslovi reakcije budu podešeni tako da enzimi vrše reakciju sinteze, pre nego reakciju hidrolize, odnosno neophodno je održati mali sadržaj vode i nisku aktivnost vode u sistemu [50,51]. Takođe, problem u ovoj reakciji je i slaba rastvorljivost glicerola u organskom rastvaraču.…”

Section: Esterifikacijaunclassified

Synthesis of monoacylglycerols by enzymatic methods

Bradić¹,

Ognjanović²,

Bezbradica³

et al. 2010

Hem Ind

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Monoacylglycerols are non-ionic surfactants widely used in the food industry. They are also important in cosmetic and pharmaceutical industries as drug carriers and for the consistency improvements in creams and lotions. Current process for their production is based on the glycerolysis of natural fats and oils in the presence of inorganic catalysts at temperatures higher than 220 oC. The major drawbacks of this process include high-energy consumption, low yield, and poor product quality. The use of lipases for the monoacylglycerols production offers environmental advantages and a reduction in energy consumption. Besides, the same surfactants prepared by the enzymatic synthesis may be labeled as “natural”. Recent progress in the application of highly-stable lipases in the organic solvents offers the possibility of employing various methods to the enzyme-catalyzed synthesis of monoacylglycerols, such as selective hydrolysis of fats and oils using 1,3-regiospecific lipases, the esterification of glycerol with fatty acids and the glycerolysis of fats or oils. In this review, different reaction systems such as aqueous-organic two-phase systems, microemulsions and reverse micelles systems, anhydrous organic solvents, solvent-free systems with free or immobilized lipases, as well as the use of two-phase membrane reactor systems are presented. We discuss some of the key factors, such as the control of water content, removing of the products from reaction system, and the effects of solvent on the lipase activity and selectivity, that must be addressed in order to obtain an efficient reaction system with high yields of monoacylglycerols. Engineering of the enzymatic monoacylglycerols synthesis processes requires also optimization of other factors as: molar ratio of substrates, temperature, type of lipase immobilization and supports (if any), reactor design and operating regime

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“…Έτσι π.χ. έχει διατηρηθεί σταθερή η ενεργότητα του νερού (α) με ανακύκλωση των ατμών της αντίδρασης μέσα από στήλη με ξηραντικό υλικό (Kahn et al, 1990), (β) με επαφή των ατμών της αντίδρασης με κορεσμένο διάλυμα αλάτων, βλέπε Σχήμα 2.6α (Dudal & Lortie, 1995), (γ) με ανακύκλωση διαλύματος κορεσμένων αλάτων με τη βοήθεια σωλήνας σιλικόνης που βρίσκεται σε επαφή με το διάλυμα της αντίδρασης βλέπε Σχήμα 2.6β (Wehtje et al, 1993) και (δ) με ζεύγη αλάτων που τοποθετούνται απευθείας στο μίγμα της αντίδρασης (Kvittingen et al, 1992).…”

Section: θερμοδυναμική ενεργότητα νερού (A")unclassified

Ενζυμική Εστεροποίηση Μονο- Και Πολυ- Υδρόξυ Ενώσεων

Sereti¹,

Σερέτη²

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Υγρό-υγρό (μη-αναμίξιμος με το νερό διαλύτης + νερό) 6 2.1.1.2. Υγρό-υγρό-στερεό (μη-αναμίζιμος με το νερό διαλύτης + νερό + στερεό) 7 2.1.1.3. Στερεό-υγρό (μη-αναμίξιμος με το νερό διαλύτης + στερεό) 1 2.1.1.4. Στερεό-υγρό (αναμίξιμος διαλυτής + στερεό) 8 2.1.1 Μικροετερογενή συστήματα 8 2.1.2.1. Διαλυτοποιημένα ένζυμα σε μίγμα νερού και αναμίξιμου διαλύτη 8 2.1.2.2. Ένζυμα, χημικά τροποποιημένα, διαλυμένα σε μη-αναμίξιμους διαλύτες 9 2.1.2.3. Ένζυμα διαλυμένα σε μη-αναμίξιμους διαλύτες χρησιμοποιώντας επιφανειονεργά ή συνδιαλύτες 9 2.1.3. Ειδικά συστήματα αντιδράσεων 10 2.1.3.1. Οργανογέλες ή γέλες βασισμένες σε μικρογαλακτώματα 10 2.1.3.2. Μη συνεχή συστήματα επιφανειενεργού/διαλύτη/νερού, όπως λυότροποι υγροί κρύσταλλοι και μη συνεχή μικρογαλακτώματα 11 2.1.3.3. Υπερκρίσιμα ρευστά 11 2.2. ΕΠΙΔΡΑΣΗ ΤΟΥ ΔΙΑΛΥΤΗ ΣΤΗΝ ΕΝΖΥΜΒΚΗ ΚΑΤΑΛΥΣΗ ΣΕ ΜΗ ΣΥΜΒΑΤΙΚΑ ΜΕΣΑ 11 2.2.1. Επίδραση του διαλύτη στην εξειδίκευση του ενζύμου 15 2.3. ΕΠΙΔΡΑΣΗ ΤΟΥ ΝΕΡΟΥ ΣΤΗΝ ENZYMHOE ΚΑΤΑΛΥΣΗ ΣΕ ΜΗ ΣΥΜΒΑΤΙΚΑ ΜΕΣΑ 18 2.3.1. Θερμοδυναμική ενεργότητα νερού (a w ) 2.4. ΥΠΕΡΚΡΙΣΙΜΑ ΡΕΥΣΤΑ 2.4.1. Γενικά 2.4.2. Ιδιότητες των υπερκρίσιμων ρευστών 2.4.3. Ενζυμικές αντιδράσεις σε υπερκρίσιμα ρευστά 27 2.4.4. Παράγοντες που επιδρούν στην ενζυμική ενεργότητα στο υπερκρίσιμο διοξείδιο του άνθρακα 2.4.4.1. pH 2.4.4.2. Περιεκτικότητα σε νερό 2.4.4.3. Πίεση 2.4.4.4. Θερμοκρασία IX 2.4.4.5. Φαινόμενα μεταφοράς μάζας 41 2.5. ΔΟΜΙΚΑ ΧΑΡΑΚΤΗΡΙΣΤΙΚΑ ΚΑΙ ΜΗΧΑΝΙΣΜΟΣ ΔΡΑΣΗΣ ΤΩΝ ΛΙΠΑΣΩΝ 44 2.5.1. Γενικά 44 2.5.2. Αιπάσες 44 2.5.3. Δομή των λιπασών 46 2.5.3.1. Πρωτοταγής δομή 46 2.5.3.2. Δευτεροταγής και τριτοταγής δομή 46 2.5.3.3. Το πεπτιδικό κάλυμμα και η ενεργοποίηση διεπιφάνειας 48 2.5.3.4. Εξειδίκευση των λιπασών ως προς το υπόστρωμα σε σχέση με τη δομή τους 50 2.5.4. Ο καταλυτικός μηχανισμός των λιπασών 2.5.6. Λιπάσες σε μη συμβατικά μέσα 2.5.7. Κουτινάση από Fusarium solatìi pisi 56 2.6. ΕΣΤΕΡΕΣ ΥΨΗΛΗΣ ΠΡΟΣΤΙΘΕΜΕΝΗΣ ΑΞΙΑΣ 2.6.1. Επιφανειοενεργά 2.6.1.1. Φυσικές παράμετροι που χαρακτηρίζουν τα επιφανειοενεργά μόρια 59 2.6.1.2. Επιφανειοενεργά σακχάρων 60 2.6.2. Αντιοξειδωτικά 2.6.2.1. Η δράση του ασκορβικού οξέος ως αντιοξειδωτικά 2.6.2.2. Η δράση των φαινολικών οξέων ως αντιοξειδωτικά 2

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Measurement and control of water activity with an aluminium oxide sensor in organic two-phase reaction mixtures for enzymic catalysis

Cited by 23 publications

References 15 publications

Computer‐Aided Control of Water Activity for Lipase‐Catalyzed Esterification in Solvent‐Free Systems

Computer‐Aided Control of Water Activity for Lipase‐Catalyzed Esterification in Solvent‐Free Systems

Synthesis of monoacylglycerols by enzymatic methods

Ενζυμική Εστεροποίηση Μονο- Και Πολυ- Υδρόξυ Ενώσεων

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