Spinning Disc Reactors

Transcription

1 Spinning Disc Reactors A novel processing machine for the food and chemical industry Basically a rotating disc, that can be heated or cooled, is fed with one or more liquids at its centre. The liquids mix and spread over the disc and are collected at the edge. Mixing, heat transfer and mass transfer occurs on the disc

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3 SDRs and Food processing; key characteristics Ability to very rapidly heat and cool fluids, especially viscous fluids; pasteurisation, fine crystal formation. Very low delta T gives less thermal damage. Film coefficients up to 5kW/m2K, overall 1kW/m2K. Self cleaning/easy clean characteristic Enhanced mass transfer for evaporation and odour removal with less thermal damage Effective use of UV radiation (sunshine treated!) Unique combination of shear and draw gives opportunities for structure manipulation

4 And there s more Fundamentally easy to scale Surface can be catalyst coated Surface can be modified to alter residence times Precipitation and crystallisation can be carried out without scaling Non foaming Especially good at handling viscous fluids particularly in cooling heat transfer Pure plug flow; no back mixing SDRs and viscous fluids A unique ability to manage viscous fluids thanks to a combination of shear, draw and high temperatures. Feed Pipe Angular Draw Radial Shear Rotation of Disc Normal Entangled Polymer Drawn Disentangled Polymer The liquid film is drawn which tend to align and orientate long molecules Increased Area of Coverage

5 Removal of water (dissolved and as separate phase) from oil SDR Processing Cloudy moist organic around 1ppm H 2 O Clear processed organic around 25ppm H 2 O Organic heated rapidly to 2 o C Water removed with counter-current current gas flow. No spitting, no foaming Organic cooled on walls. Increased vapour pressure, water easily stripped with modest gas flow or vacuum. Exposure time short enough to avoid degrading despite temperature Result : Product is clear and dry. An example of heat and mass transfer SDR in the Food Industry; work carried out at Leeds University Mayonnaise Emulsions Ice Cream Fruit Juices

6 Mayonnaise (7% Oil) Lemon juice, vinegar, mustard, black pepper and egg yolk were mixed and passed over the reactor disc. The temperature was increased to 3, 4, 5 and 58 o C. A high viscosity and creamy mayonnaise was produced. at 25 o C at 58 o C Volume (%) Particle Size Distribution 2 Conclusion: Slowly increasing the temperature to 58 o C, could produce pasteurised, consistent, smooth and homogeneous mayonnaise Particle Size (µm) 7% oil SDR mayonaise 58 C, 4/5/5 12:32:4 SDR-mayonnaise, 3/27/5 19:14:58 Salmonella test has been confirmed negative. Comparison with Commercial Mayonnaise Hellmann s Real Mayonnaise Aver. droplet size ~ 25 µm V olum e (% ) Particle Size Distribution SDR SDR Mayonnaise Aver. droplet size ~ 7 µm Hellmann s Particle Size (µm) SDR-mayonnaise, 3/27/5 19:14:58 Hellman's mayonnaise repeat, 3/27/5 19:3:3 SDR mayonnaise is more consistent, smoother and softer than Hellmann s real mayonnaise. Microbiology tests confirmed that the mayonnaise was negative for Salmonella.

7 Multiple emulsions There are two distinct forms of simple multiple emulsion. - a water-in-oil-in-water (W/O/W) and - an oil-in-water-in-oil (O/W/O). water (W 1 ) oil (O 1 ) oil (O) water (W 2 ) water (W) oil (O 2 ) a W 1 /O/W 2 multiple emulsion an O 1 /W/O 2 multiple emulsion W/O/W multiple emulsions Stage I Primary Emulsion oil+lipophilic emulsifier (8 vol%) Jet Homogenizer Pressure 35 bar aqueous phase (2 vol%) Stage II Secondary Emulsion W+hydrophilic emulsifier aqueous phase (8 vol%) primary emulsion (W/O) average droplet size ~.5-1 µm Spinning disc reactor 8 ml/s, 2 rpm primary emulsion (2 vol%) a W/O/W multiple emulsion average droplet size ~ 2 1 µm

8 Confocal laser scanning microscopy primary emulsifier oil phase inner aqueous phase secondary emulsifier The SDR-processed multiple emulsion Confocal microscopy confirms that indeed mono-disperse multiple emulsions were formed. Ice Cream Making Process Using SDR Water, xanthan gum, sugar, unsalted butter, lecithin, milk, double cream, skimmed milk powder Heated at 55 C Homogenisation Pasteurisation The mix was passed continuously over the disc at 85 C; 3 rpm; flow rate 6 ml/s; inlet temperature 2 C Ice Cream Base Samples were collected for micro analysis -18 hr ageing Freezing/aeration Model ice cream

9 Conventional HTST Mixing (Pre-heating to 6 C) SDR Mixing (Pre-heating to 6 C) Pasteurisation 79.5 C for 15 seconds Pasteurisation 85 C for.43 seconds Homogenisation Cooling <7.2 C Cooling <7.2 C within 15 sec Balance tank hours Ageing Typical 18 hours Freezing/aeration Freezing/aeration The commercial process for making ice cream requires separate Pasteurisation and Homogenisation stages followed by 18 hours ageing of the mixture. Microbiology of Ice Cream Challenge Testing Ice cream base was spiked with E. coli K-12. The mix was passed over the SDR and samples were collected in aseptic containers. E. coli K-12 is a weak strain and is widely used as a model organism in research. E. coli x1 3 (cfu/g) disc temperature ( o C) E. coli K-12 The samples processed at 9 C indicate that sufficient heat has been applied to achieve a reduction in microbial loading associated with a safe product.

10 Particle Size Distributions ice cream base V o lu m e (% ) SDR Particle Size Distribution Particle Size (µm) Ian's ice cream, 6/26/7 17:18:38 Zero-hour Taste panel sample (1% lecithin), 6/26/7 17:34:51 Commercial The SDR generates a stable emulsion that requires zero hours ageing to subsequently produce an ice cream product. Sensory Assessment of Ice Cream mean values h 18 h commercial smoothness stickness meltability coldness ice cream at different ageing time Model ice cream at zero-hour ageing was found to be very acceptable to the panellists.

11 Pasteurisation of Fruit Juice Prepared Fresh juice Pasteurisation Homogenisation Passed over the disc at various temperatures (75-95 C); 25 rpm; flow rate 6 ml/s; inlet temp. 5-1 C Samples were collected in aseptic containers and stored in Fridge at 5 C Microbiological analysis Microbiology of Fruit Juice (a) TVC x1 3 (cfu/g) Pasteurised Un-pasteurised Commercial Time (day) (b) coliform x1 3 (cfu/g) Pasteurised Un-pasteurised Commercial Time (day) The spinning disc reactor using a processing temperature of 9 C achieves a microbiologically safe fruit juice.

12 Sensory Assessment of Fruit Juice mean values Aroma Flavour Smoothness Thickness Colour SDR- Pasteurised UnPasteurised Commercial The results show that the SDR technology doesn t have detrimental effect on the perceived aroma, flavour and colour. The SDR pasteurised juice is preferable to the commercial sample. In Summary A controllable and scalable processor that has the potential to enhance the production of existing products and to produce unique products

13 References Akhtar, M. and Krishnan, S. S. Preparation of oil-water-oil multiple emulsions using spinning disc reactor technology, an oral presentation in the World Emulsion Congress to be held in Lyon (France) 11-13th October (). Akhtar, M. Chan, P. S. K. and Dinakaran, B. S. (). Pasteurization of carrot juice using spinning disc reactor technology, submitted to LWT April. Akhtar, M., Chan, P. S. K., and Clayton, G. (). Concentration of apple juice using spinning disc reactor technology is being considered for a patent application, University of Leeds (). Akhtar, M., Blakemore, I., Clayton, G. & Knapper, S. (29). The use of spinning disc reactor for processing ice cream base effect of ageing in making model ice cream. International Journal of Food Science and Technology, 44, Akhtar, M., Chan, P. S. K., Clayton, G., Kanjee, U. & Koutsidis, G. (29). Physical and chemical properties of dark chocolate processed using spinning disc reactor technology effects of disc temperature and residence time. Journal of Food Engineering Efficiency, 3 (1), Akhtar, M. (28). Evolution in chocolate technology. Published in Food & Beverage International, February (28) pp Akhtar, M. (28). Scientists raise the bar for greener chocolate. YORKSHIRE POST, Tuesday, 15th January, (28). Contacts Ian Henderson +44 () Mahmood Akhtar + 44 () Robert Addleman +44 ()