Protected application of high intensity ultrasound for food drying enhancement

The purpose of this chapter is to summarize potential applications of the highpower ultrasound technology (5 Wcm2; 20–100 kHz) in the food industry. Those applications are mainly related to the improvement in mass and energy transfer in different processes when ultrasound is applied in water or through air, e.g., reduction in dehydration; thawing and freezing times and energy costs of plant, meat, or fishbased products; increase the extraction yields of intracellular compounds with biological activity; reduction of chemical health risks such as cadmium or acrylamide; etc. The influence of some physical parameters like temperature and pressure in cavitation intensity and the potential of this technology to even inactivate microorganisms in food products and surfaces in contact with food will be discussed. Several examples of these applications will be presented, with reference to some of the industrial or pilot plant systems available in the market to be implemented in the food industry.

1 Application of High Intensity Ultrasound for Food Drying Enhancement: A review 2Abstract: Foods are usually divided into two major categories: natural foods which structure occurs 3naturally; structured foods which structure forms as a result of processing Drying alters food structure 4or even creates new food structures Food drying is an ancient practice and is one of the most popular 5preservation methods for foods around the world due to many advantages it offers High intensity 6ultrasound-assisted drying represents as a means for food dehydration without affecting the main 7characteristics and quality of the product Drying in high intensity ultrasound assistance with modern 8drying systems has great potential to accelerate drying, improve product quality, reduce investment 9and production costs This review paper provides up-to-date researches of application of high intensity 10ultrasound as pre-treatments before drying and during drying process as well as its effects on the 11quality of different dried products 12Keywords: Drying, high intensity ultrasound, pretreatment, quality 13INTRODUCTION 14In the 2009 World Summit on Food Security, it was recognized that by 2050 food production must 15increase by about 60-70%, which is 34% higher than it is today, to feed the anticipated billion people 16Therefore, agricultural production must make progress significantly from today’s levels and food 17manufacturing systems must become more efficient, use less energy, generate less waste, and produce 18food with extended shelf life Drying is hugely important technique for the food industry and offers 19feasibility for ingredient development and novel products Dried foods offer multiple benefits including: 20extended product shelf-life, reduced packaging, storage, handling and transportation costs, and extends 21the possibility of out-of-season availability and provides a wider range of products for consumers 22Ultrasound technology as an essential field of research and development in the food industry is derive 23from mechanical waves at a frequency above the threshold of human hearing (>16 kHz), and can be 24categorized into two ranges: low and high energy Low-energy (low power, low intensity) ultrasound has 25frequencies higher than 100 kHz at intensities below Wcm-2 while high-energy (high power, high26intensity) ultrasound uses intensities higher than Wcm-2 at frequencies between 20 and 500 kHz 27Normally, low intensity ultrasounds are used to characterize the properties of food materials and for 28process control Whereas , high intensity ultrasound is used to alter physical and chemical properties of 29food or to facilitate the progress of a process Other typical applications of high-intensity ultrasonic 30waves are welding, machining of brittle materials, sorting and particle motion in fluids, surface 31cleaning, atomization of liquids, medical therapy, sonochemistry, formation and processing of 32nanomaterials, etc 33The use of ultrasound in drying of food has been carried out in two ways: using ultrasound pre34treatments prior to drying and using ultrasonic drying Application of ultrasonic waves is associated 35with a cavitation phenomenon as well as alternative cycles of compressions and rarefactions of the 36material The forces involved by the sponge effect caused by ultrasonic waves can create microscopic 37channels that may ease moisture removal These microscopic channels are utilized by water molecules 38as a special pathway to diffuse toward the surface of materials, increasing its effective water diffusivity 39Water removal is influenced by both internal and external resistances The drying process has been 40intensified highly when applying ultrasound pre-treatment, followed by high intensity ultrasound41assisted (HIU) drying 42The present work centers on reviewing current scientific literatures on application of high intensity 43ultrasound (HIUS) to enhance food drying and the effects of HIUS support on physicochemical 44properties of dried food Thus, this way could function as an always ready element to meet 45simultaneously the needs of academic, food processing industry and consumers at large 46APPLICATIONS OF HIGH INTENSITY ULTRASOUND IN FOOD DRYING 47PROCESSES 48There are many high-intensity applications remarkably in food processing such as viscosity alteration, 49emulsion generation, cell disruption, aggregate dispersion, polymerization, degassing of liquid food, 50extraction of enzymes and proteins, microorganism inactivation, cutting, improvement of freezing and 51defrosting, crystallization, filtration, pasteurization and sterilization, etc 52New drying methods such as microwave, infrared, vacuum, freeze, or combined hybrid drying are used 53increasingly more often in the industry The positive effects of these methods are aimed at a reduction 54of both the drying time and energy consumption, in particular when using non-conventional or 55combined techniques, such as ultrasound, microwave and ultrasound ,, convective-microwave drying 56and convective–infrared drying, acoustic and solar energy Hybrid drying is a very attractive and 57promising solution from the product quality point of view and for process economy There is both a 58time and energy profit due to the diversity of mechanisms providing the energy needed for moisture 59removal, the synergistic effects, the reversion of adverse thermo-diffusion effects 60The application of HIUS in food drying is a relatively new and emerging technology in food industry Its 61main purpose is to accelerate the drying process, improve product quality and ensure duration of the 62food products Hot air with HIUS support resulting in an acceleration of heat and mass transfer and 63reduction of the drying time without a significant increase in product temperature Considering the 64great importance of HIUS in food drying, many researches have applied HIUS as pretreatment (Table 1) 65and during drying (Table 2) The results obtained is successful and remarkable 66Ultrasonic Pretreatment Before Drying Process 67To improve dried product quality and accelerate the drying process with minimal cost, pretreatment 68are processes often employed before drying Pretreatment of the material prior to drying is a well69explored area, and many methods have been developed New pretreatment techniques have drawn 70the attention of researchers in improving their efficiency in food drying technology The principle of 71ultrasound application in liquid systems is based on the effects of mechanical waves which are mainly 72related to the cavitation phenomenon Cavitation is considered to be responsible for the creation of 73microscopic channels in the material, which facilitates mass transport Bubbles are produced during 74cavitation they collapse and form tiny jets directly interacting with the surface of objects in liquid This 75micro jet raises the mass and heat transfers between liquid and solid by breaking the respective 76diffusion boundary layers Acoustic energy during the interaction with the medium is converted into 77thermal energy 78Propagation Mode 79Ultrasound technology has been directly or indirectly used as a pretreatment in many drying and or 80dehydration applications which differ in their effectiveness, performance and capability There are two 81types of devices which are used as direct mode and indirect mode The directly ultrasonic probe which 82has a vibrating titanium tip in different diameters and can be immersed in the liquid near the sample 83The liquid is irradiated with an ultrasonic wave directly from the horn tip so that a high power intensity 84could be obtained The indirectly ultrasonic bath, an ultrasonic transducer is attached to the outer 85surface of the liquid container and the liquid irradiates with an ultrasonic wave from the surface of the 86liquid container Ultrasonic baths are available commercially in different tank capacities, ultrasonic 87powers or frequencies The typical acoustic amplitude in a standing wave type sonochemical reactor is 88much smaller than that in a horn-type sonochemical reactor Several researches have used ultrasonic 89bath in the pretreatment of fruits and vegetables such as apple, pineapple, guava, carrot, Malay 90apple,melon,mushrooms, cherries and strawberry, Brussels sprout Besides, some investigators tended 91to ultrasonic probe in pretreatment of apple, carrot, cauliflower, onion , mulberry leaves, sea92cucumber, guava 93Kek et al studied differences between direct and indirect application of HIUS to ultrasonic 94pretreatment using an ultrasonic probe and ultrasonic bath, respectively Indirect sonication in osmotic 95solutions contributed to high water loss and solid gain with acceptable total color change than direct 96sonication Applying ultrasound pre-osmotic treatment in 700Brix prior to hot-air drying reduced the 97drying time by 33%, increased the effective diffusivity by 35% Another work conducted directly and 98indirectly on button mushroom, cauliflower, Brussels sprouts which pH of the surrounding water of 99vegetables decreased after the ultrasound treatments with the probe and the bath (for Brussels 100sprout), the highest decrease occurring with 20 kHz probe for 10 in all samples because the probe 101is more powerful that the 40 kHz bath Staining of cauliflower, button mushroom and Brussels sprouts 102tissue surfaces performed for the damage determination showed that cavitation damage (blue spots) 103was present after the ultrasonic treatment with 20 kHz probe for min, followed by 20 kHz probe for 10410 min, while very little cavitational damage occurred on cauliflower and button mushroom but no 105cavitation on Brussels sprouts after sonication with 40 kHz bath for and 10 Most cases proved 106that theultrasonic assistance increased the efficiency of the total osmotic dehydration process From 107reports of Rodríguez et al and Cárcel et al, the higher the ultrasonic power applied, the higher the solid 108gain and the water loss Using of different ultrasound amplitudes causes reduction of the drying time 109and allows elimination of more water from the apple slices 110Propagation Medium 111The selection of liquid medium that is used in the ultrasonically assisted pretreatment depends on the 112desirable purpose Hence, the pH or solute concentration can induce a great influence with respect to 113the effect of acoustic energy on the food product and interaction between the solid and the 114surrounding medium The opposite mass transport occurs when an osmotic solution is used instead of 115distilled water These mass transfer processes are important factors in pretreatment because it 116influences the natural change in the taste in dried product and are used to evaluate performance of 117drying after pretreatments The common solutions for osmotic pretreatments of fruits and vegetables 118are distilled water and sugar dissolved in distilled water The self-juice of the fruit has been recently 119used in a few studies as an osmotic solution with the purpose of evaluating the effect of HIU 120application when the liquid medium and the food product are of the same nature 121If the liquid medium is distilled, water-soluble solids migrate from the fruit to the medium and water 122moves into the fruit as a result of the mass transfer exchange promoted by the solute gradient between 123the food product and the surrounding media It is worth declaring that the increase in the initial 124moisture content of treated samples is indicative of the water intake during the treatment, although 125this water might have a free character inside the fruit tissue, leading to a weak interaction with the 126solutes in the sample and easier removal during the drying process Fernandes et al conducted 127ultrasonic pre-treatment with distilled water for banana, the amount of sugars lost during the process 128was 21.3% of reducing sugars of the fruit after 30 while water gain was 11.1% Moreover, the 129overall drying time was reduced by 11%, which represents an economy of energy since air-drying is 130energy cost intensive Thus, the ultrasonic pre-treatment can be an interesting process to produce 131dried fruits with low sugar content However, the same ultrasound intensity in pre-treatment pointed 132out varying effects on different materials which some fruits gain water during exposure to ultrasound, 133whereas others show loss of water 134Concentration has been carried out using sugar solutions ranging from 25 to 70 0Brix The work 135examined the influence of ultrasonic pre-treatment prior to air drying of Malay apple Distilled water as 136the liquid medium, caused loss of soluble solids from the fruit to the liquid medium 33.4% after 60 137The results concluded that the increase in effective water diffusivity was estimated in 28.1% (5.84×1013810m2s-1) after 30 of ultrasound for the process carried out using an osmotic solution of 25°Brix 139leading to faster air drying of the fruit The exception occurred with the pre-treatment using an osmotic 140solution of 50°Bx, which reduced the water effective diffusivity (D e) to 3.98×10-10m2s-1 in 10 and 1413.74×10-10m2s-1 in 60 The reason could be due to the saturation of the surface of the fruit with 142sucrose creating an extra resistance for mass transfer Similar results was reported by Garcia-Noguera 143et al where neither higher osmotic concentrations nor extended periods in ultrasonic applications had 144resulted higher effective diffusivities in pre-treated strawberries Kek et al stated the effective diffusivity 145of ultrasound pre-osmotic treated dried guava increased 18% for the 35°Brix and 35% for the 70°Brix 146when compared with the De of hot-air dried guava When comparing with the osmo-dehydrated dried 147guava, the De of ultrasound pre-osmotic treated dried guava was 12% higher for the 35 ◦Brix and there 148was no significant difference for the 70°Brix 149 Table Application of high intensity ultrasound as pretreatment Raw material Ultrasonic Acoustically assisted pretreatment Method Medium Pretreatment device Apples (Zlatni Probe Immersing Distilled water delises) Apple Probe Immersing Distilled water (Malus Drying Method/ Drying conditions Device conditio 200 W infrared n 85°C 24 kHz dryer 400 W/L ultrasound- 45-60°C 10 assisted 1-3 m/s domestica L var Royal Gala) Apple (Granny convective Probe Smith var.) Apple (var Bath Osmotic Distilled water 2.1, 12.9 W /cm2 drier Convective 50 °C, dehydration Apple juice 25°C; Dryer m/s Immersing Citric acid 1% Distilled water 3, W /cm2 Convective 70°C 21, 35 kHz Dryer m/s 30 20,45,60 W/L Freeze dryer -55°C Idared) Barley grass Refer Tank Immersing Distilled water 20 kHz 10°C 70% water ,L 10 25-45 kHz hot air 60°C (Musculus sakei DSM 15831 65 W drying oven 0.3 m/s Semitendinosu culture,1.5%salt , 30°C s) 1.0% sugar, 30 Beef Bath Immersing ence 0.05% sodium Blackberry Probe Immersing nitrite Distilled water 85 W /cm3 hot air dryer 40–60 (Rubus glaucus 400 W °C Benth 24 kHz m/ s var Andean) 15°C, 10–30 7- 75.78 W/cm2 air-drying 50°C seaweed 750 W oven 0.3 m/s (Ascophyllum 10 hot air dryer 60°C Brown Probe nodosum) Brussels sprout Bath/Prob (Brassica e Immersing Immersing Distilled water Distilled water 0.5–43 W /cm2 20–24 kHz oleracea 18°C var 3, 10 gemmifera) Carrot (Var Bath Immersing Distilled water Flakee) 0.3 m /s 700 W Convective 40– 25 kHz drying oven 60°C; 23°C; m/s 30–60 400 W Convective 46°C; (Daucus carota 20 kHz tray dryer 4.9 m/s L var Nantesa) 60–70°C hot air drier 60°C Carrots Carrots Probe Probe Blanching Blanching distilled water Distilled water 10–15 0.4–1.0 Wm/L (Daucus 20 kHz carota, cv 25°C Nerac) Carrot Bath 0.3 m/s Osmotic Fructose 3, 10 320 W chamber 70°C dehydration 40, 60°Brix 38 kHz dryer 1.1 m/ s 120 75–373 W /cm2 air-drying 60°C 20 kHz oven m /s hot air dryer 60°C 30° C Cashew apple Probe Immersing Distilled water bagasse puree (Anacardium 20 C occidentale L.) Cauliflower Bath/Prob (Brassica e Immersing Distilled water 2–10 0.5–43 W /cm2 20–24 kHz 0.3 m /s oleracea var botrytis) Cherries 18°C Bath (Prunus Osmotic Glucose 3, 10 700 W chamber dehydration 60°Brix 25 kHz dryer 60°C 250C cerasus L.) Osmotic Commercial 30 0–2.5 kW convection 70°C dehydration sugar 25 kHz oven 0.06 0–70°Brix 30°C Osmotic Commercial 20–60 400 W convective 70°C dehydration sugar 20 kHz oven 0.06 Immersing 0–70°Brix Distill water 6–20 0.75-1.5 W/g microwave m/s 15 W/g 20, 35,80 kHz vacuum 20 kPa 25°C dryer 10 49-203W/in2 Low (Lepidium 40W temperature meyenii) 40kHz oven Guava Bath (Psidium guajava) Guava Probe (Psidium guajava) Lotus seed Maca Bath Bath Freeze-thaw Thermostatic air m/s 30°C 20°C, 3-12 h -20°C 25.2–117.6 W/ L Convective 60°C leaves 200C air-drying 2.5 m/s (Morus alba L) Mushrooms 5–15 480 W oven Hot air drier 50°C Mulberry Probe Bath Immersing Immersing Distilled water Distilled water (A bisporus) 35 kHz 1.5 m/s 300C Mushroom Bath/Prob (Agaricus e Immersing Distilled water hot air dryer 20–24 kHz 60°C 0.3 m /s 180C Biosporus) Onion 10–30 0.5–43 W /cm2 Probe Blanching distilled water 3, 10 0.06- 0.59 W/mL hot-air drier 60°C 20 kHz 0.3 m /s 70°C h 1-5 freeze-drier 0.04mb ar, 72h Parsley leaves 300 W microwave- 20-40° C (Petroselinum 21 kHz convective 0.7 m /s Crispum) 22°C dryer Distilled water 20 5.1 W /L air-drying 60°C Pineapple juice 25 kHz oven 0.5 m/ s 10–30 160-320 W microwave -40°C 25 kHz freeze dryer Pineapple Bath Bath Immersing Immersing (Ananas Distilled water comosus var Perola) Sea- 30°C Probe cucumbers, Osmotic Brine 20% dehydration (Stichopus japonicas) Sweet 24°C Immersing Distilled water 30 25KW/m3 air blast 65°C potatoes (cv Osmotic Sucrose 35°Bx 40kHz drying oven 1.5 m/s Hongjiu) dehydration 25°C Microwave 22W/g, 30min vacuum 90kPa Bath dryer 150 151Ultrasonic Treatment during the Drying Process 152Currently, different systems have been developed to efficiently transmit the acoustic energy from the 153emitter for the acoustically assisted convective drying There are two main ways for ultrasound devices 154assisting food drying processes: the ultrasound transducers are directly contacted into the samples 155during drying (direct contact systems); the ultrasound transducers work without direct contact 156between the vibrating element and the samples (contactless systems) Some specific ultrasonic 157transducers undertake higher intensity capacities have partially solved problems observed in the 158application of contact systems One of the most popular contactless system is the aluminum vibrating 159cylinder driven by a piezoelectric composite transducer (21.8 kHz) capable of converting the electric 160energy in vibration movement generating a high-intensity ultrasonic field inside the cylinder (75 W, 161154.3 dB) with a relative low energy consumption The HIU convective drying process permits the use 162of lower temperatures and may be useful for drying heat-sensitive materials such as fruits and 163vegetables 164Gallego-Juárez and co-workers carried out two experimental procedures by airborne ultrasound and 165ultrasonic vibration in direct contact with the vegetable Forced-air dehydration assisted by airborne 166ultrasound for acoustic intensity applied 155 dB and 163dB Comparing results between these 167intensities showed that the effect of increasing the acoustic pressure in about dB allows the 168temperature to be diminished by about 10°C with little increase in the airflow velocity Ultrasonic 169dehydration by direct coupling of the vibration, at two different powers applied by contact ultrasound, 17025 W and 50 W Influence of the ultrasonic power applied is clearly observed, the moisture is rapidly 171released by 50 W treatment D e increased significantly from 1.33×10 -9 m2/s by applying a power of 45 W 172and was even greater when the applied power reached 90 W (1.72×10-9 m2/s) on HIU drying system 173(154.3 dB) for orange peel In order to examine the influence of ultrasound on the drying process of 174olive leaves, air drying experiments were carried out (40°C and m/s) without and with ultrasound 175application (8, 16, 25 and 33 kW/m3) Samples dried without ultrasound spent 7.4 h to achieve a 176moisture content of 0.12 kg water / kg dry matter (kg W/kg dm), while samples dried with application 177of ultrasound (33 kW/m3) only 3.6 h as well as the mass transfer coefficient was increased Based on 178results the authors stated that the power of the applied ultrasound had a meaningful influence on the 179kinetics of the process, the higher the applied ultrasonic intensity, the greater De, the faster the drying 180 181Regarding the effects of the use of HIUS on D e in the drying of apples, the increase of D e was of 1.6– 1.8 182times at 18.5 kW/m3 and 2.4–2.2 times at 30.8 kW/m for temperatures between 30°C and 50°C, and 183smaller when the drying temperature was of 70°C (1.3 times at 18.5 kW/m and 1.4 times at 30.8 184kW/m3) Similarly, an experiment carried out at 40, 50, 60, 70°C with ultrasound application (21,7 kHz, 18530.8 kW/m3) reduced the drying time by 60%, 49%, 38%, 28% respectively on drying passion fruit peel 186Other studies that HIU application increased the drying rate, however, as the drying temperature 187increases, the influence of the US application on the drying rate decreases, , 188An alternative means to hot air drying for retaining sensory, nutritional and functional properties of 189foods is low-temperature air drying (LTD) or atmospheric freeze drying (AFD) This technique could 190combine the advantages of both freeze drying (high product quality) and convective drying (low cost 191and continuous process) However, reducing the air temperature to below the product’s freezing point Peas AFD, CV 21.7 kHz 67, 68, 69, 70, 73 W 3.1, 3.2, 3.4 m/s CL Persimmons CV 20 kHz 154.3 dB -6, -3, 0, 10, 20°C 0.5, 1, 2, 4, 6, 8, 10, CO 75W 12 m/s (Rojo Brillante) Pistachios CV 21.8 kHz 150W, 300 W 40, 50°C m/s CL Potato CV 20kHZ 155 and 163 dB 25°C 1, 1.3, 1.7 m/s CL Potato (Monalisa) CV 20 kHz 6, 12, 19, 25, 31, 37 kW/m3 22, 31°C m/s CL Raspberries CV 21.8 kHz 170 dB 40°C 55°C CL Red bell peppers FD 100 W and 200 W 76-110W 0.4 m/s -30°C CO Rice CV 160 dB 46Pa _ CL Rice CV 130, 415 Hz 160 dB 22 m/s CL 415 Hz 22°C CV 25 W/ kg 3.5% RH m/s CL CV 20 kHz 45 W 200C m/s CL 20 kHz 10, 20, 30°C Fish-Clipfish Fish-Salted codfish Fish-salted cod LTD 155 dB, 20.5 kW/m3 30% RH m/s CL (Gadus morhua) Strawberry CV 21.9 kHz 30, 60 W 20, 10, 0, -10°C m/s CL 21.8 kHz 40, 50, 60, 70°C 210 ± W 55, 65,75°C CL Ultrasonic bath :55, 65,75°C 0, 6.2, 12.3, 18.5 W/m3 1, 2, m/s CL 21.8 kHz 40, 50, 60, 70, 80°C (Fragaria x ananassa Duch) Salmon and Trout VD 40 kHz Thyme CV 228 229 AFD- Atmospheric Freeze Drying, LTD- Low Temperature Drying, CV- Convective Drying, FD-Freeze Drying, VD- Vacuum 230 Drying, IFVD-infrared-vacuum, CL-contactless, CO-contact 231EFFECT OF ULTRASOUND ON QUALITY OF DRIED PRODUCT 232Rehydration capacity 233If a high rehydration capacity such as in a fruit soup or sauce is required, HIUS assistance for dried 234products are preferred The application of HIUS before or during the drying process promoted an 235increment of rehydration capacity (RC) of dried samples compared to samples dried without HIUS 236application The dried carrot cubes (AFD and HIU-AFD) at 20.5 kW/m3 were rehydrated in distilled water 237at 25°C until constant weight, the equilibrium moisture (Weq) reached by the USAFD and the AFD 238samples was 5.05 and 4.06 kg w/kg d.m respectively The same result reported strawberry samples 239dried at 600C with ultrasound application which in rehydration ratios are 5.1 at 30W and 5.0 at 60W 240while the untreated sample was 4.7 241The RC of dried mushroom, Brussel sprout and cauliflower samples were studied at 80°C in acoustically 242treated before drying using either an ultrasonic bath (0.5 W/cm 2) or an ultrasonic probe (39–43 243W/cm2) The higher RC was achieved in samples pretreated at the higher acoustic intensity (ultrasonic 244probe ) for Brussel sprout and cauliflower except mushroom The eggplant samples dried under –10°C 245and 10°C with HIU drying (157 dB), RC conducted at 30°C, authors concluded that HIUS application 246caused a faster water inlet, it did not lead to greater water absorption (no influence on Weq) during 247rehydration Ultrasound pretreatment of samples resulted in dried products of Fuji apples with greater 248rehydration ratios was 2.849 in pretreated when comparing to untreated dried sample at value 2492.332 This can be explained by the fact that broken cells offer low resistance to water flow within the 250fruit 251Color 252The color of raw and dried food has a great influence on the acceptability of consumers, due to the fact 253that quality is evaluated based on visual impression Therefore, it should be considered when designing 254a drying process In the CIE Lab uniform color space, L* indicates lightness, a* is the chromaticity on a 255green (–) and red (+) axis, and b* is the chromaticity on a blue (–) and yellow (+) axis These three 256parameters are included in the estimation of color difference ΔE to the raw sample ΔE values higher 257than 2.0 might lead to noticeable differences in the visual perception of consumers 258Dried seaweed after rehydration (acoustic assistance 7.00 - 75.78 W/cm2), all the ultrasound pretreated 259samples showed a small increase in L value compared to the control Samples treated with the lowest 260ultrasound power (7.00 W /cm2) had the highest increase in L* value from 15.99 to 37.46 which 261represents increasing lightness of samples Moreover, samples with lowest ultrasound treatment had 262lower a* and higher b* values representing increased greenness and yellowness This phenomenon can 263be explained by the fact that ultrasound causes degassing effects physical damage and membrane 264destruction of the cells, which contributes to easier elution of pigment substance from biological 265materials For HIUS pre-treatment of guavas at 35°Brix, no significant difference of total color change 266was observed between osmo-dehydrated ( ΔE= 24), ultrasound pre-osmotic treated ΔE= 25), and hot267air dried (ΔE= 24) guavas Five drying programs applied for strawberries with different application of 268microwaves and HIUS and pure convective drying as a reference test were carried out The highest 269value of total color change, i.e 29.83 ± 0.41, was observed for the samples dried in convective270microwave drying assisted with ultrasound (CVMWUD) The samples dried by convective-ultrasound 271drying (CVUD) and CVMW30minUD, were characterized by lower discoloration, however, the best dried 272product from the color point of view was obtained after convective-ultrasound drying (ΔE = 12.23 ± 2731.22) In dried carrot slices, a significant difference in perceivable ΔE was observed for blanched hot air 274drying (BHD), ultrasound pretreatment (1500W) followed by hot air drying (UPHD )and ultrasound 275pretreatment followed by freeze drying (UPFD) samples compared to fresh samples, with no significant 276difference between BHD and UPHD Neverthless, UPFD samples showed significantly higher ΔE 277compared to UPHD and BHD samples Mothibe et al stated that, after drying at 70°C, L* values in 278ultrasonically treated apples tended to decrease with an increasing exposure time to ultrasonic waves 279(25 kHz, 200 W) This might be because ultrasound destruction of cells released enzymes responsible 280for browning to the surface, leading to a dark color 281Bantle et al performed different test series of temperature (-6°C, -3°C, 0°C, 10°C, and 20°C), drying time 282and high ultrasonic intensities in the AFD of peas The quality, as well as the color of all dried products 283did not change significantly for drying with and without ultrasonic assistance Drying experiments were 284carried out at -10, 0, 10 and 20°C on salted cod slices at m/s with air drying (AIR) combine HIUS ( 20.5 285kW/m3, 155dB) and without ultrasonic application Authors realized that AIR + US samples dried at -10 286and 0°C exhibited higher lightness and lower yellowness values in comparison to AIR samples, which 287could be interesting for the cod industry which requires products with high whiteness values 288Moreover, AIR + US samples dried at 10 and 20°C did not show significant (p < 0.05) changes in L* and 289b* coordinates compared to AIR samples In research of Kowalski et al, the raspberries were first 290subjected to pure convective drying as a reference process and then to hybrid drying as a combination 291of convective, microwave and HIUS (150.5 dB) drying methods The lowest total color change (ΔE 292=12.5) was achieved for the CVUD200W test whereas convective drying test shows the highest total 293color change, ΔE = 16.56 ± 0.67 It is necessary to point out that despite a lower value of ΔE after HIUS 294application, the obtained values are still high, since above ΔE = the observer has an impression of two 295different colors 296Vitamin Content 297Using HIU air-drying (153.3dB, 75 W; 21 kHz) of cherry tomatoes, the application of ultrasound during 298the mildest drying conditions tested (45°C and m/s) achieves the highest content of both types of the 299lipid-soluble vitamin E and the group of B vitamin, releasing the vitamins bounded to membrane, 300protein, or apoenzyme Another study examined influence of HIU air-drying on apple with the same 301ultrasonic parameters and drying conditions of cherry tomatoes , the results observed for apples 302showed a higher increase in vitamins B1+B2 and B3 and a lower increase in vitamin B6 when compared 303to tomatoes A different trend was observed for vitamin B5, which decreased during HIUS drying of 304apples but has presented a significant increase in tomatoes Degradation of vitamin B5 was observed 305(only in apple), possibly because it was presented in its free form 306Vitamin C (VC) is a very sensitive compound to processing conditions, and a non-subjective and 307relatively easy-to measure criterion of food quality It has also been reported that if VC is conveniently 308retained, other nutrients can be also well preserved Values of vitamin C retention were very high 309(≥65%), even under the most severe conditions used (ultrasound at 70°C, 60 W) on dried strawberry 310sample A combined effect of HIUS and heat was observed, since the lowest retention of vitamin C was 311found in HIU dried samples at high temperature, the highest preservation of VC was obtained after 312treatments carried out at 40 and 50°C Frías et al indicated that the ultrasound treatment significantly 313affected content of VC in all the studied conditions and both low temperature and high drying time 314(20°C, 120 min) led to the maximum vitamin retention (92%), while high temperature and short drying 315time (60°C, 75 min) brought about larger losses of VC, and a retention was 82% The effects of HIUS 316(75- 373 W/cm2) pre-treatment on air-drying conducted by Fonteles et al immersed in water, sonicated 317cashew apple bagasse showed higher VC content compared to non-sonicated sample Sonication 318increased vitamin C content due to cell disruption and release of the intracellular content 319Other reseaches reported VC reduction after convective drying of guava slices and pineapple applied by 320acoustically assisted pretreatment The ultrasound pre-osmotic treated dried guava had the lowest 321vitamin C content among all the drying methods It was 13–33% lower than hot-air dried guava, 4.1– 32217% lower than osmo-dehydrated dried guava, and 14–33% lower than commercial dried guava The 323VC reduction in the higher osmotic concentration of 70°Brix was less and this could be due to a lesser 324cavitation effect produced in viscous liquids where the natural cohesive forces acting within the liquid 325may help to reduce the destruction in soluble nutrients Pretreatments for pineapple were carried out 326using two different soaking media were distilled water and pineapple juice at 30°C The result after 327drying with acoustic assistance (23.2 W/L) presented a lower retention of VC than their non treated 328samples, properly the time exposed to high temperature is one of the main factors towards reducing 329the loss of VC It is worth to point out that, in all dried samples, the final amount of vitamins B was 330higher when samples were sonicated and distilled water was used as soaking medium In general, the 331ultrasound effect could be seen in this study is the acoustic energy during treatment allowed a 332disruption of the chemical bounding between vitamins B and its coenzymes or nucleotides, which leads 333to a higher bioavailability after treatment 334Bioactive Compounds 335Plants produce an extraordinary diversity of phenolic and flavonol compounds that are excellent 336oxygen radical scavengers As regards antioxidant potential, in overview, ultrasound application 337involved a greater degradation of polyphenol and flavonoid contents reported that HIUS application as 338a pretreatment before drying or assistance during drying The results showed the negative effect of 339ultrasound application on convective drying operation (20 kHz, 45 W) of banana, mango and guava The 340reduction percentage of total polyphenol content (TPC) was 69 % of mango, 45% of banana , 73% of 341guava in treating 10 while was 46%, 38%, 66% respectively with conventionally convective drying 342This effect could be explained by the release of oxidative enzymes and intra-cellular compounds owing 343to sample mechanical stress linked to HIUS exposition Rodríguez et al have studied the effect of 344ultrasonically assisted apple drying without ultrasound (AIR) and using two levels of ultrasonic 345intensity : 18.5 kW/m3(AIR + US1) and 30.8 kW/m (AIR + US2) on TPC and total flavonoid content 346(TFC) At 700C, there was a significant difference among the TPC loss of AIR (19.7 ± 1.6%), AIR + US1 347(33.1 ± 2.6%) and AIR + US2 (39.1 ± 2.4%) samples, as the highest level of ultrasound intensity it was 348suggested the most deteriorative treatment, and it could be related to the cellular damage induced by 349the combination of higher drying temperature and the HIUS application For different purpose, another 350study of the same authors used HIUS assitance to improve drying of apple at low-temperature During 351HIU drying brought about an average percentage of degradation of the TPC which was significantly 352higher (40.8 ± 3.5%) than in AIR experiments (30.5 ± 3.6%) at every temperature tested It could be 353observed that in AIR + US experiments the degradation of the TFC was significantly (p < 0.05) greater 354(e.g 44.7 ± 2.1% and 34.7 ± 1.5% at -10 and 0°C, respectively) than in AIR experiments (e.g 33.9 ± 3551.8% and 24.2 ± 2.1% at -10 and 0°C, respectively) Obviously, the interaction of the two factors, 356temperature and ultrasound application, significantly influenced the TPC and TFC 357A study on effects of HIUS (21,7 kHz, 30.8 kW/m3) on TPC of passion fruit peel , AIR + US samples dried 358at the lowest temperatures tested, 40 and 50°C, presented a significantly milder polyphenol 359degradation (37 and 43% respectively) compared to the samples dried at the highest temperatures 360tested, 60 and 70°C (60 and 62% respectively) Similarly, studies carried out in mushroom, mulberry 361leaves and carrot reported that HIUS application as a pretreatment before drying produced a reduction 362of the TPC of treated samples, mostly attributed to the leakage of phenolic compounds through the 363vegetal tissue during the pretreatment Rodriguez et al used in the acoustically assisted pretreatment 364(25 kHz, 5.1 W/L) of pineapples immersing distilled water at 30°C for 10–30 A reduction of 40–60% 365of TPC was observed in sonicated samples However, after drying (60 0C), the TPC increased, and so the 366final loss was only between 10% and 25% When soaking medium was pineapple juice, leading to a 367higher amount of TPC in the samples Obviously, the higher soluble solids content in the pineapple juice 368(compared to distilled water) reduces the cavitation energy and thus degradation of organic 369compounds, leading to a higher amount of phenolic compounds in the samples The ultrasound 370treatment improved the retention of TFC and TPC in onion slices dried either by freeze drying or hot-air 371drying Comparing ultrasound treated samples, freeze dried onions had a higher retention of bioactive 372compounds than hot-air dried ones 373Carotenoids present in fresh tissue are very stable However, when those products are processed, 374carotenoids become very unstable by the action of heat, light and oxygen Carotenoids determine the 375color and the nutritional quality of many dried fruits and vegetables Convective air drying and HIU 376( 100 W/cm2 ) effects on β-carotene contents in carrots were studied Ultrasound drying caused higher 377β-carotene retention (96-98%) than convective air drying (73-90%) Both low temperature and high 378drying time (20°C, 120 min) by HIU drying system for unblanched carrots led to the maximum β 379-carotene retention (98%) Similarly, The use of HIUS (21.7 kHz, 153.3 dB) allowed the retention of 380carotenoids in the dried cherry tomatoes product when drying was carried out at a low temperature 381(45°C) and low air velocities (1 m/s), which total carotenoid relative content (percentage of fresh 382tomato content) was 55.6 without ultrasound and 102.1 with ultrasound 383It is obvious that chlorophyll a and b are major pigments in the leaves The chlorophyll content of 384parsley and mulberry leaves were examined as a quality parameter by Sledz et al and Tao.et al 385respectively For mulberry leaves, ultrasound pretreatment was carried out at 25.2–117.6 W/L for 5– 38615 in using distilled water After drying at 60°C, the chlorophyll content of the untreated sample 387was 2.4 g/g, and treatment promoted a slight increment of 9% in treated samples For parsley leave, it 388could be emphasized that the highest chlorophyll resistance was achieved when drying at 100W and 38930°C was preceded by sonication(0.29 W/g) and equalled 89.5% with respect to the fresh parsley 390leaves 391Microstructure 392In order to analyze the impact of the drying treatments without and with ultrasound application on the 393internal structure of samples, a microstructural analysis was performed by obtaining SEM micrographs, 394cryo-SEM or light microscopy In most cases, the application of ultrasound led to a more intense effect 395on the sample structure Eggplant, orange and lemon peels exhibited the high porosity, considering the 396same acoustic energy applied during the drying, the mechanical compressions and expansions 397produced by ultrasound could be more intense in these high-porous products than the low-porous 398products Garcia-Perez et al wanted to evaluate the effect of HIUS (21.7 kHz, 154.3 dB) on the drying 399(40°C, 1m/s ) of orange peel when acoustic application (AIR+US–90 W) produced an even more intense 400disruption of the albedo cells than in the dried samples without ultrasound ( AIR samples) Ortuno et al 401noted that, the application of HIUS (154.3 dB) led to a more intense effect on the orange peel 402structure, this seemed to be more compressed and large intercellular air spaces were found, creating a 403highly porous material that facilitate water mobility Similarly, regarding to the ultrasound application 404(18.5-37.0 W/L)during the convective drying of eggplant which HIUS assisted led to the waxy 405compound spreading over the epidermis The effects on the endocarp of the ultrasonically assisted 406dried samples (AIR + US) were, in overall terms, less important than in AIR samples, but this was 407dependent on the ultrasonic power applied, the higher the acoustic intensity used, the more intense 408were the compressions and expansions produced by the ultrasound and the more marked the effect on 409the internal microstructure When applying HIUS on low-porosity products such as cassava or potato 410change in the microstructure was less affected by ultrasound induced cell disruption Micrographs of 411the treated apple cylinders revealed strong cell disruption at the surface and still visible effects of the 412ultrasound treatment in 800 μm distance from the sonicated surface Potato samples showed 413superficial cell damage as well, but micrographs taken at 800 μm distance from the sonicated surface 414resembled the untreated cell tissue 415The ultrasonic pre-treatment (25 kHz, 60W, 30 min) prior to air drying on dehydration of Malay 416apple[22], the cells did not present many differences when compared with untreated Malay apple cells 417No breakdown of cells was observed when the fruit was immersed in an osmotic solution of 25°Bx , 418whereas the fruit immersed in an osmotic solution of 50°Bx, the cells present several breakdown 419points and the intercellular spaces are much broader than when the fruit is immersed in distilled water 420and in osmotic solution of 25°Bx 421CONCLUSIONS 422HIUS application in food drying have been carried out by researchers as a pretreatment before drying 423or during the drying process applied in many fruits, vegetables and other foods Ultrasound causes of 424intensifying mass and heat transfer can be used in many operations, the investigation of the effect of 425HIUS application on the different quality parameters of the dried food product depends on lots of 426aspects The higher retention values reported is not only to the different products being dried, but also 427to the different drying systems used which processing conditions such as ultrasound characteristics 428(frequency, intensity, power, etc.), drying method (convective,infrared, microwave, freeze-drying, etc.) 429and drying condition ( temperature, air velocity, relative humidity of the drying agent,etc.), osmotic 430solution in HIU drying system The optimization of the use of HIUS technology in food drying 431processing demands technologists to make more efforts for covering a wide variety of products and to 432take this 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World Academy of Science, Engineering and Technology International Journal of 640 Biotechnology and Bioengineering, 2015 9(10): p 1307-6892 64194 Schössler, K., T Thomas, and D Knorr, Modification of cell structure and mass transfer in potato tissue by 642 contact ultrasound Food Research International, 2012 49(1): p 425-431 643 ... 45simultaneously the needs of academic, food processing industry and consumers at large 46APPLICATIONS OF HIGH INTENSITY ULTRASOUND IN FOOD DRYING 47PROCESSES 48There are many high- intensity applications remarkably... 32nanomaterials, etc 33The use of ultrasound in drying of food has been carried out in two ways: using ultrasound pre34treatments prior to drying and using ultrasonic drying Application of ultrasonic waves... control Whereas , high intensity ultrasound is used to alter physical and chemical properties of 2 9food or to facilitate the progress of a process Other typical applications of high- intensity ultrasonic