The potential of the microwave-vacuum technique in drying of probiotic and starter cultures

Transcription

1 The potential of the microwave-vacuum technique in drying of probiotic and starter cultures IDS 212, Xiamen, China 12 th November 212 Sabine Ambros, S.A.W. Bauer, Ulrich Kulozik, Petra Först Chair for and Dairy Technology Technische Universität München, Freising-Weihenstephan, Germany

2 Microbial cultures Fields of application of starter cultures and probiotics: dairy products, pastries, pickles, raw sausages probiotic foods Advantages of direct starter cultures: - no contamination by bacteriophages - reproducible product quality - little know-how and personnel expenditure Stabilization by: - freezing - drying 2

3 Motivation Current standard procedures in drying of microbial cultures: Freezedrying Spraydrying Vacuumdrying High time and energy effort Low product quality Time consuming Microwave vacuum-drying as an alternative? Process duration Energy efficiency Costs Microwavevacuum drying Process controllability Gentle processing Product quality 3

4 Quality aspects of microbial cultures Viability Metabolic activity Storage stability Handling Rehydratibility Proper dosability Logarithmus der Keimzahl Short lag-phase! Zeit Abb.6.1: Vermehrungsphasen einer Bakterienkultur: 1. Latenzphase, 2. Beschleunigungsphase, 3. exponentielle Vermehrungsphase, 4. Verzögerungsphase, 5. stationäre Phase, 6. letale Phase Aim: Maintainence of technological and biological functionality for direct inoculation without preculturing 4

5 Culture preparation/ Test set-up Drying parameters: Fermentation Harvest Drying Storage Model strain: Lactobacillus paracasei spp. paracasei (F19) 1 g cell suspension h sample =.5 cm Drying jar: Duran glass Residual water content = 6-7% Analytics: Survival rate by plate count method and flow cytometry Acidification power test ph( t ) = 4 ph ph ( t) dt + a (1+ e t t b ) ph end tend = c AUC 5

6 Microwave vacuum dryer Manufacturer: Püschner MicrowavePowerSystems, Schwanewede-Bremen, Germany Microwave power: max. 1 kw/ 2,45 MHz Integrated load cell and IR-camera Prozess visualization: online-measuring of p, m, T, P Influencing factors: - Microwave power - Pressure - Product characteristics (dielectric loss factor) P r = 2 π f E 2 ε ε P r : Relative absorbed power f: Frequency E: Electric field strength ε : Absolute dielectric constant ε : Dielectric loss factor 6

7 Drying rates Drying rate [g/ min] 3,5 3, 2,5 2, 1,5 1,,5 Moisture content [g water/ g dry matter] 4, 3,5 3, 2,5 2, 1,5 1,,5 Lb. paracasei 1 mbar,,,5, 1, 1,5 2, 2,5 3, 3,5,,5 1, 1,5 2, Moisture content [g water/ g dry matter] Time [h] Vacuum 1 W 2 W 3 W Vacuum 1 W 2 W 3 W Clear dependence of the drying rate on the microwave power input Process can be controlled via microwave energy input 7

8 Performance and replicability of drying process 4 Product temperature [ C] C, 5 mbar 35 C, 1 mbar Time [h] 8

9 Drying profiles for continuous microwave input Product moisture [g water/ g dry matter] Temperature at 1 W Temperature at 2 W Moisture at 1 W Moisture at 2 W,,5 1, 1,5 2, Drying time [h] Product temperature [ C] Drying below critical residual water content leads to detrimental product temperatures 9

10 Pulsed microwave input Pulsed energy input: Temperature regulation according to T max 4 Mikrowellenleistung [W] Eingebrachte MW-Leistung Produkttemperatur Obere und untere Temperaturgrenze Temperatur [ C] Microwave power input [W] Microwave power input Temperature Product moisture Product temperature [ C] Moisture content [%] Zeit [h] Time [h] 1

11 Influence of chamber pressure and product temperature on drying time and survival 5 Lb. paracasei 1W microwave input 6 Lb. paracasei 1W microwave input Drying time [h] Survival rate [%] C, 5 mbar 3 C, 1 mbar 35 C, 5 mbar 35 C, 1 mbar 3 C, 5 mbar 3 C, 1 mbar 35 C, 5 mbar 35 C, 1 mbar Besides microwave power input T max determines drying time High survival at low T max and low chamber pressures 11

12 Influence of chamber pressure und product temperature on acidification activity ph [ ] 6, 5,5 5, 4,5 4, 3 C, 5 mbar 3 C, 1 mbar 35 C, 5 mbar 35 C, 1 mbar Reference AreaA/ Reference [ ] 2, 1,5 1,,5 Lb. paracasei 1W microwave input 3,5, Time [h] Reference 3 C, 5 mbar 3 C, 1 mbar 35 C, 5 mbar 35 C, 1 mbar Low T max and low chamber pressures are favourable for vitality 12

13 Summary Microwave vacuum-drying of lactic acid bacteria is generally possible! Microwave enables shortening of drying time up to 9% in comparison to freeze and vacuum drying Pulsed microwave input enables gentle drying and thus high survival rates Microwave vacuum-drying has got the potential to overcome many inconveniences in the drying of lactic acid bacteria and so could replace or at least complement the established drying techniques 13