Creating microstructure of dehydrated fruits and vegetables with a multi-flash drying process

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1 16/4/213 Creating microstructure of dehydrated fruits and vegetales with a multi-flash drying process ESPCA/São Paulo School of Advanced Science Advances in Molecular Structuring of Food Materials João B. Laurindo Barara Porciuncula (PhD student) Marta F. Zotarelli (PhD student) Ricardo Monteiro (MS student) Creating microstructure of dehydrated fruits and vegetales with a multi-flash drying process João B. Laurindo Barara Porciuncula (PhD student) Marta F. Zotarelli (PhD student) Ricardo Monteiro (MS student) Federal University of Santa Catarina, Florianópolis-SC, Brazil Department of Chemical and Food Engineering Campus Universitário Trindade joao@enq.ufsc.r 1

2 16/4/213 What is the (old) prolem? Tropical fruits as ananas and mangoes are perishale products with significant economic importance in many countries. The development of solutions for their preservation and processing is necessary to reduce losses, otain etter products and add value to them Dehydration is one of the oldest techniques of preservation How can we choose the drying process and process variales in order to control the microstructure of dehydrated fruits and vegetales? Processes for fruits dehydration Raw fruits Selection Wash, cut Drying Visual, color, texture Solule solids ( o Brix) Texture (penetration) Creating microstructure Convective-multiflash drying Conductive-multiflash drying Solar drying Convective drying Vacuum drying Freeze-drying CMFD KMFD Microwave vacuum drying Solar drying: cheap and traditional, drying rate depends on weather conditions Convective drying: allows controlling drying rates, thermal degradation (T, t), fruits shrinkage leads to undesirale texture properties Vacuum drying: Reduces prolems of convective drying, heat sensitive foods, does not avoid shrinkage Freeze-drying: Best dehydration process for het sensitive products, minimal shrinkage, timeconsuming, energy-consuming, high cost 2

3 CMFD cycle 16/4/213 What is the Convective-multi-flash drying process (CMFD)? CMFD is a dehydration process developed for fruits and vegetales dehydration and texturization Patent application Brazil Selection and preparation of fruit samples on a stainless steel grid Insertion of the grid+samples into a jacketed container anana ( Musa sapientum L.) : slices with thickness of 5 mm, 26 o Brix mango (Mangifera indica L.) : square slices (3 mm), 8 mm thick, 12.5 o Brix Heating the samples up to 6 o C, at P atm, inside the container, using hot air (7 o C) convection, conduction, radiation 6 o C Application of vacuum pulse (P as =15 mar) for 3-5 min flash drying-and-cooling Recovery of the atmospheric pressure in the jacketed container The CMFD process doesn t use pressures higher than the atmospheric pressure CMFD Experimental device Schematic representation of the CMFD process T P 15 mars 35 m 3 /h 3

4 Log pressure, kpa 16/4/213 The KMFD process doesn t use pressures higher than the atmospheric pressure KMFD Experimental device T P PID control for the plates temperature 6 C Fruit samples 35 m 3 /h Heated plates Vacuum oven Heating + flash evaporation cycles Water evaporation at each cycle, considering flash evaporation as an adiaatic process m w cm pt ^ H v H 225kJ/kg at P 11.3kPa T Temperature ( C) Container/flash evaporation P sat (T) PatmVacuum P=113 mar V=1.6 m 3 /kg P=15 mar V=7 m 3 /kg texturization Moist sample 4

5 16/4/213 CMFD, KMFD X SIMILAR PROCESSES Puff drying The puff-drying is performed y sumitting the product partially dehydrated to pressures of 6-8 atm and high temperatures, followed y a sudden decompression to the atmospheric pressure, which creates a product with an open structure It was developed in order to dehydrate fruits and vegetales at large scale, which could e quickly reconstituted, with operating costs comparale to convective drying Pre-dehydration of the product to e sumitted to the puff-drying is essential to avoid product disintegration during the sudden decompression, (THAKUR e THAKUR, 2; LOUKA and ALLAF, 22; IGUEDJTAL et al., 27; MUJUMDAR, 27). It is used also for processes intensification (oil extraction) LOUKA and ALLAF, 22 SOME RESULTS OF BANANA AND MANGO DRYING USING THE CMFD CONVECTIVE MULTIFLASH DRYING PROCESS 5

6 16/4/213 Convective-multi-flash drying process CMFD Movie anana flash drying Convective-multi-flash drying process CMFD Movie mango flash drying + texturization P=15-2 mar Water oiling at approximately 15 o C 6

7 16/4/213 Convective-multi-flash drying process CMFD (anana) Evolution of the pressure in the jacketed container and fruit temperature during the CMFD process applied to anana samples Evolution of experimental moisture content of anana during the CMFD process and the estimated contriution of flashevaporation to the whole drying process Drying curve Flash-drying contriution Evolution of anana samples water activity during the processing. Water activity Convective-multi-flash drying process - CMFD P=15-2 mar aprox. 15 o C P=15-2 mar aprox.15 o C After flash evaporation (= flash cooling) heat transfer from hot air (7 C) to the fruits is improved y the high temperature difference etween hot air and cooled fruits During flash-evaporation part of the internal moisture is drained to the fruit surface and improve evaporation during the heating step (convective drying) Drying of anana CMFD is a very efficient dehydration process 6 o C 3 h 6-7 h 15 h 7

8 16/4/213 Some pictures of mango during dehydration y CMFD Pictures of mango fruits after every heating-vacuum pulse cycle CMFD cycles Pictures of mango fruits after 12 cycles of heating-vacuum pulses SEM of freeze-dried mango - 2x DEHYDRATED MANGO SEM of oven-dried mango 2x SEM of mango dehydrated y CMFD 2x 8

9 Force (N) 16/4/213 Puncture tests of dehydrated mango Dried y CMFD Jagged curves crispy foods Numer of peaks, fractal dimension Dried y hot air Strain (%) Freeze-dried SEM of freeze-dried anana- 2x DEHYDRATED BANANA SEM of oven-dried anana 2x SEM of anana dehydrated y CMFD 2x 9

10 Force (N) Força (N) 16/4/213 Puncture tests of dehydrated anana Jagged curves crispy foods Numer of peaks, fractal dimension Banana "in natura" seca por 12 CAPV Banana Liofilizada Comercial Dried y CMFD Freeze-dried Strain (%) Deformação Relativa (%) REMARKS It is possile to produce dried-and-crisp fruits using the convective-multi-flash drying process (CMFD) with texture properties that are similar to those otained with freeze-drying Product color is preserved due to the use of moderate process temperatures ( Do you want it? ) Process time of CMFD and KMFD are shorter (aout 2-3 hours at laoratory scale) than the characteristic times of freeze-drying Equipment and process are simple and use low pressures and temperatures smaller investment and energy requirements than freeze-drying 1

11 16/4/213 Can we control the microstructure of dehydrated fruits and vegetales? YES, WE CAN! How can we follow the microstructure evolution during drying? Bulk or apparent volume V ( m ma ) ( m 1 ma 1) d solvent V = apparent volume (cm³) m = sample weight in air (g) m a = support mass (g) m 1 = sample weight immersed n-heptane (g) m a1 = support weight immersed in n-heptane (g) Becker with n-heptane 11

12 16/4/213 True volume of a porous material using a gas picnometer (Sereno et al., 27) V 1 V 2 V p = true volume (cm³) Moist material = volume of the solids forming the sample structure + volume of the liquid Dry material = volume of the solids forming the fruit structure FROM THE BULK VOLUME AND THE TRUE VOLUME WE CAN DETERMINE Material porosity, V V p % 1 1 V = ulk volume (cm³) V p = true volume (cm³) Accessile porosity during drying Accessile porosity increases at each cycle of CMFD or KMFD during drying Fruits shrinking during drying S V 1 V 1 V V shrinking patterns 12

13 16/4/213 SEM- Scanning electronic microscopy Samples preparation fruit slices were removed from the dryer, frozen y liquid nitrogen and freeze-dried (It was considered that ultra rapid freezing and freeze-drying did not change significantly the fruit structure) Convective drying T = 6 C 13

14 Void spaces (%) True volume (cm³) 16/4/213 True volumes (solid + liquid) as determined with the gas porosimeter Strong shrinking True volume of dried fruits Evolution of the void spaces during drying using convective drying (moist samples) 7 6 V V p % Porosity of dried fruits (57%)

15 Shrinking (%) 16/4/213 Shrinking (determined y immersion into heptane) dried fruits (S =65-7%) S V 1 V 1 V = ulk volume at t (cm³) V = ulk volume at t= (cm³) V = average value= 5 cm 3 Initial sample 4 hours 8 hours 2x 12 hours 15

16 16/4/213 Vacuum drying T = 6 C and P = 15mar Vacuum Drying Vacuum drying of ananas was performed using a vacuum oven (Ethick Technology, 44-DE model-sp, Brazil). Banana slices (5mm) were placed evenly in a thin single layer on the drying tray and placed inside the vacuum oven. The vacuum pressure and the drying temperature were kept constant at 15mar and 6 C. The fruits were dried for 6h to a final moisture content of,76 g/g 16

17 Void spaces (%) True volume (cm³) 16/4/213 True volumes (solid + liquid) as determined with the gas porosimeter Vacuum Drying Evolution of the void spaces during drying using vacuum drying (moist samples) 9 8 V V p % Porosity of dried fruits (7%)

18 Shrinking (%) 16/4/213 Shrinking - Vacuum Drying (determined y immersion into heptane) dried fruits (S =68%) S V 1 V 1 V = ulk volume at t (cm³) V = ulk volume at t= (cm³) V = average value= 5 cm 3 Initial sample Vacuum Drying 2 hours 4 hours 2x 6 hours 18

19 16/4/213 Initial sample Vacuum Drying 2 hours 5x 4 hours 6 hours Microwave Vacuum Drying Vacuum helps to reduce drying temperature y reducing the oiling point of water during microwave-vacuum drying. Drying rates of carrot slices (Durance, 1999) - hot air at 7 C - Freeze drying - microwave-vacuum drying 19

20 16/4/213 Microwave vacuum drying Experimental device Digital vacuum meter Vacuum pump Microwave oven/dryer 12: Trapping Vacuum chamer Turntale plate SEM - Microwave vacuum drying Microwave vacuum drying Drying time 19 min Moisture,3 g/g Bulk volume 2,46 cm³ Porosity 66% Shrinking 51% 2

21 Moisture (g/g) Moisture (g/g) Water activity (Aw) 16/4/213 Structural changes in anana samples during drying y KMFD KMFD-Conductive multi-flash drying, T = 8 C KMFD Drying curves reproduciility Conductive and flash evaporation contriutions Water activity 2,5 2, 1,5 1,,5, ,5 Before flash drying 2, 1,5 1 After flash drying 1,,5, 1,8,6,4,2 flash evaporation is important Triplicate Free water

22 Force (N) Force (N) Force (N) Force (N) Force (N) 16/4/213 Puncture tests of fruits dried y KMFD Pulse 1 aw =, Pulse 12 aw =,24 Pulse 11 aw=,353 % 1% 2% 3% 4% 5% 6% 7% Strain(%) Pulse 5 Pulse 6 Pulse 7 Pulse 8 Pulse 9 Pulse 1 Pulse 11 Pulse 12 Pictures of anana slices after each KMFD cycle Puncture tests of fruits during drying y KMFD Pulse 9 % 1% 2% 3% 4% 5% 6% 7% % 1% 2% 3% 4% 5% 6% 7% Strain(%) Strain(%) Pulse Pulse 11 % 1% 2% 3% 4% 5% 6% 7% Strain(%) Pulse Strain(%) 22

23 True volume (cm³) Void spaces (%) 16/4/213 True volumes (solid + liquid) as determined with the gas porosimeter KMFD PROCESS True volume Solid matrix + liquid True volume of dried fruits Evolution of the void spaces during drying using KMFD (moist samples) 9 8 V V p % Porosity of dried fruits (75%)

24 Shrinking (%) 16/4/213 Shrinking - KMFD PROCESS (determined y immersion into heptane) dried fruits (S =4%) S V 1 V 1 V = ulk volume at t (cm³) V = ulk volume at t= (cm³) V = average value= 5 cm 3 Structural changes in anana samples during drying KMFD Optical microscopies and SEM 24

25 16/4/213 KMFD, 2x Initial sample 1 st pulse 2 nd pulse 3 rd pulse 4 th pulse 5 th pulse 6 th pulse 7 th pulse 8 th pulse 9 th pulse 1 th pulse 11 th pulse 12 th pulse 25

26 16/4/213 KMFD, 5x Initial sample 1 st pulse 2 nd pulse 3 rd pulse 4 th pulse 5 th pulse 6 th pulse 7 th pulse 8 th pulse 9 th pulse 1 th pulse 11 th pulse 12 th pulse 26

27 Moisture (g/g) Water activity (Aw) Moisture (g/g) 16/4/213 KMFD (4 vacuum pulses) + VD Conductive multi-flash drying + vacuum drying T = 8 C Drying curves reproduciility 2,5 2, 1,5 1,,5, Triplicates Vacuum drying 15 mar Conductive and flash evaporation contriutions Water activity 2,5 2, 1,5 1,,5, 1 2 Before flash drying After flash drying 3 Vacuum drying 15 mar ,8,6,4,

28 Force (N) 16/4/213 Puncture tests of dried samples KMFD (4 vacuum pulses) + VD Only dried samples % 1% 2% 3% 4% 5% 6% 7% Strain(%) Structural changes in anana samples during KMFD + vacuum drying 28

29 Void spaces (%) True volume (cm³) 16/4/213 True volumes (solid + liquid) as determined with the gas porosimeter ( KMFD + vacuum drying ) Evolution of the void spaces during drying using KMFD + vacuum drying (moist samples) V V p % Porosity of dried fruits (87%) 29

30 Shrinking (%) 16/4/213 Shrinking (determined y immersion into heptane) KMFD + vacuum drying 4 3 dried fruits (S =25-35%) S V 1 V 1 V = ulk volume at t (cm³) V = ulk volume at t= (cm³) V = average value= 5 cm 3 KMFD + vacuum drying SEM 2x, after Freeze drying of samples frozen y liquid nitrogen 3

31 16/4/213 KMFD + vacuum drying (dehydrated sample) After 4 pulses + 65 min of vacuum drying 2x 5x SEM of anana samples dehydrated y different methods COMPARISON OF GENERAL PATTERNS 31

32 16/4/213 Some pictures of dehydrated anana US$1/kg US$7/kg Air drying Freeze-drying (retail-store) Freeze-drying (Laoratory) KMFD Conductive multi-flash drying Microwave Vacuum-drying CMFD Convective multi-flash drying Convective Drying Vacuum drying Microwave drying 5x KMFD KMFD + VD 32

33 Force (N) 16/4/213 Puncture test results for different drying processes 6 5 MICROWAVE-VACUUM DRYING 4 KMFD+VACUUM DRYING CONVECTIVE DRYING Strain (%) KMFD, CMFD, FREEZE-DRYING Gloal microstructure parameters of dehydrated anana for the different drying processes Convective drying Vacuum drying MW KMFD KMFD + VD Drying time 2 h 6 h 2 min 2 h 2 h Moisture (g/g) Bulk volume (cm³) Porosity (%) Shrinkage (%) V 1 S 1 V 5 cm 3 V 33

34 16/4/213 CONCLUDING REMARKS It is possile to control the whole pattern of dehydrated fruits (e.g., anana, mango) in order to produce dried-and-crisp fruits. CMFD and KMFD and their comination with vacuum drying are appropriate processes to reach this goal Texture properties can e similar to those otained with freezedrying (depending on the operation conditions). Shorter drying times Product color is preserved due to the use of moderate process temperatures. Vitamins retention and sensorial properties need to e investigated for each fruit Equipment and process are simple and use low pressures and temperatures smaller investment and energy requirements than freeze-drying Future studies i) What the influence of fruits ripening on the microstructure formation? ii) iii) How the steepness of pressure drop (vacuum pulses) influences the texture formation during drying of a given fruit? How to correlate sensorial texture and puncture tests of dehydrated fruits? iv) How can we comine microwave vacuum drying and vacuum pulse to produce texture during dehydration? How the microwave power (per kg of fruit mass) influences the fruit texture? v) What are the more appropriate fruits and vegetales to e dehydrated y these techniques? vi) Energy consumption, costs, scale-up. 34

35 16/4/213 THANK YOU FOR YOUR ATENTION! FEDERAL UNIVERSITY OF SANTA CATARINA BRASIL 35