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food and bioproducts processing 9 1 ( 2 0 1 3 ) 575–579

Contents lists available at ScienceDirect

Food and Bioproducts Processing

j ourna l ho me page: www.elsev ier .com/ locate / fbp

hort communication

merging technologies for the production of nutraceuticalsrom agricultural by-products: A viewpoint of opportunitiesnd challenges

haris M. Galanakis ∗

hemical Analytical Laboratories “Galanakis”, Skalidi 34, GR-73131 Chania, Greece

a b s t r a c t

Agricultural by-products were considered for many years as undervalued substrates due to their removal from food

production line and the complicated problems arise from their treatment and disposal in the environment. Nowadays,

the urgent demands for sustainability in the food and agricultural sectors led to their valorization as a source of

nutraceuticals. The latest are typically produced using conventional technologies with well-known technological and

scale-up boundaries, which reduce their efficacy and production yield. Emerging technologies promise to overcome

these problems, but is this truth? The current viewpoint is trying to answer this question by exploring the possibility

of adapting the latest technologies in the recovery downstream processing. Opportunities and challenges in the field

are also discussed with a final aim of inspiring researchers to investigate the critical parameters that prevent for the

moment the broad commercial implementation of emerging technologies in the particular application.

© 2013 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.

Keywords: Nutraceuticals; Recovery; Extraction; By-products; Emerging technologies

. Introduction

gricultural by-products are nowadays considered as a sourcef functional ingredients like antioxidants and dietary fibers

Galanakis, 2011; Patsioura et al., 2011). The latter are includedn the general term “nutraceutical”, which indicates a food-tuff (food additive or dietary supplement) providing healthenefits (Ramaa et al., 2006; Tapas et al., 2008). The renaissancef nutraceuticals from agricultural by-products is realized dueo the existence of methodologies, which allow not only theecovery, but also their reutilization inside foods. Productions principally conducted in 5 steps: macroscopic pretreatment,

acro- and micro-molecules separation, extraction, purifica-ion and nutraceuticals formation (Galanakis, 2012). Thereby,lassic processing technologies and specific methodologiesave been developed to meet the goals of each recapture step.or instance, wet milling, mechanical pressing and microfil-

ration are efficient for the macroscopic pre-treatment and the

∗ Tel.: +30 28210 93056; fax: +30 28210 88981.E-mail addresses: cgalanakis@chemlab.gr, cgalanakis@isc.tuc.grReceived 9 November 2012; Received in revised form 20 December 201

960-3085/$ – see front matter © 2013 The Institution of Chemical Engittp://dx.doi.org/10.1016/j.fbp.2013.01.004

separation of solids, fats and/or water from the waste streams(Oreopoulou and Tzia, 2007). Alcohol precipitation, isoelectricsolubilization and ultrafiltration are able to remove macro-molecules (i.e. proteins, pectin etc.) (Galanakis et al., 2010a,b;Tahergorabi et al., 2011). Solvent and supercritical fluid extrac-tion methodologies separate smaller molecules (i.e. phenolsor sugars) from the resultant substrates (Herrero et al., 2010;Galanakis et al., 2013). Likewise, resin adsorption, chromatog-raphy and nanofiltration isolate and purify target compoundsprior their encapsulation with conventional spray or freezedrying (González et al., 2008; Soto et al., 2011).

All these technologies are well documented and estab-lished, while they are generally assumed as safe due to the factthat they have been used in different sectors of food industryfor many decades. So is there any specific need for investi-gating their replacement with more modern technologies? Asnew equipment represents a challenge and each innovationunder development requires extensive testing. The latest is

2; Accepted 8 January 2013

translated into costly investments and industrial risks. Nev-ertheless, depending on the application, the answer could

neers. Published by Elsevier B.V. All rights reserved.

576 food and bioproducts processing 9 1 ( 2 0 1 3 ) 575–579

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be positive for two reasons. Firstly, conventional technologieshave also well-known technological and scale-up boundariesthat restrict the efficacy of the proposed methodologies andultimately their commercial implementation. For example,membrane processes (i.e. nanofiltration) require increasedenergy consumption, whereas others, such as chromatogra-phy, possess high operational cost. Thermal processes (i.e.concentration, spray drying) sometimes cause detrimentaleffects on the target compounds, loss of functionality due toover-heating of the food matrix and uncontrolled generationof Maillard by-products (Galanakis et al., 2010c; Mujumdar andLaw, 2010; Galanakis, 2012). Extraction solvents are not always“food friendly” and raise public awareness with regard to theirsafe utilization inside food chain. Finally, additional problemslike the production of unstable nutraceuticals (that are diffi-cult to preserve in the shelf) may arise during encapsulation oremulsification of the final product. The second reason is thatconsumers in the 21st century possess high quality organolep-tic standards, while they demand accurate delivery and rapidadsorption of the much advertised nutraceuticals inside theirbody.

2. Emerging technologies: the new trend

On the other hand, the disadvantages of conventional tech-niques could be overcome using new trends, the so-calledemerging technologies. The latter promise:

(a) shortening of processing and residence times,(b) accelerated heat and mass transfer,(c) control of Maillard reactions,d) improvement of product quality,(e) enhancement of functionality,(f) protection from environmental stresses,(g) and extended preservation.

Emerging technologies are today investigated in researchlevel and in some cases applied in the food industry, but thequestions still remain: could these trends be adapted in therecovery downstream processing of nutraceuticals from agri-cultural by-products? And what are the specific challenges foreach of them in order to get accepted from the food industryand ultimately consumers? Since the production of nutraceu-ticals from by-products is itself a risk issue in food science dueto high initial capital cost and safety considerations.

The 10 most popular emerging technologies applied in thebroad field of food science are:

i. Radio-frequency drying,ii. Electro-osmotic dewatering,ii. Low temperature plasma treatment,v. High-hydrostatic pressure,v. Ultrasound-assisted extraction,i. Laser ablation,

ii. High voltage electrical discharge,ii. Pulsed electric field,x. Pulsed fluid bed agglomeration,x. Nanotechnology.

3. Challenges and opportunities

Radio-frequency drying is an accurate process that opti-mizes heat transfer compared to conventional drying with

hot air. Particularly, it evaporates the water in situ at rela-tively low temperatures (i.e. <80 ◦C) by combining mechanismsof dipole rotation and conduction effects that accelerate andheat uniformly the wet material (Piyasena et al., 2003). Radio-frequency drying promises reduction in processing time andspace as well as improvement of biomaterial quality, i.e.sweetness of apple derivatives compared to conventionalwater blanching (Manzocco et al., 2008). Radio frequencyheating presents also other advantages such as reduced floor-space production requirements as well as compatibility withautomated batch and continuous flow processing (Zhao et al.,2000). But what is the essential problem for the applicationof radio frequencies in the food industry? The answer is forsure the energy transfer from the generator to the product.Because the generator efficiency reaches maximum a 60%yield in industrial practice (Orsat and Raghavan, 2005). Sinceradio frequency drying needs a high investment cost perusable kilowatt, the major part of the emitted energy mustbe absorbed uniformly by the matrix. This is far more difficultin non-uniform mixtures like agricultural by-products of highcontent variation. In other words, each of the radio frequencyequipments needs further development in order to meet thedemands of the product-specific application.

Electro-osmotic dewatering is an alternative drying tech-nique that promises the reduction of energy consumption upto two thirds compared to traditional thermal processes. Thismethod is based on osmotic dehydration principles and theenhanced mass transfer. The latest is induced by mechani-cal pressure with electrochemical double layers formed at theparticle-water interface of colloidal aqueous suspensions. Forinstance, a 3h-process of biscuit factory sludge can lead toa conditioned sludge dry matter content of 40 g/100 g and anelectricity consumption of 0.2–0.3 kW/kg of water removed.On the other hand, an 11 h-mechanical dewatering of thesludge leads to a dry matter of only 22 g/100 g (Citeau et al.,2011). Electro-osmotic dehydration is typically used in sub-strates that are difficult to dewater (i.e. it is used to concentratefruit pieces and obtain advanced characteristics of jams) andthus it could treat ideally high-sugar fruit and vegetable by-products containing labile antioxidants and surface colorants(i.e. pressed grapes). Besides, removal of water is more chal-lenging if the material is elastic and well-grained, meaningtoo soft to treat and too thick to pump. This is a problemthat electro-osmotic dewatering should address prior indus-trial implementation.

Low temperature plasma can be described as quasineu-tral particle systems of semi-gas and semi-fluid mixtures ofhighly energetic particles (free electrons, ions and molecules).It is produced by a variety of electric discharges at differentpressure levels since vacuum is enhancing conversion of liq-uid to gaseous phase in high-moisture food products. Lowtemperature plasma has mainly been utilized for the micro-bial de-activation in foods (Knorr et al., 2011), and therebyit could be easily applied in early stages of downstreamprocessing, i.e. for the pasteurization of the initial matrix. Thistechnique is the most essential example of an effective, butexpensive emerging technology. Indeed, corresponding energyconsumption is rather low (i.e. processing of 1 tn/d biomaterialrequires only 90 kW/h × 0.065D /kW/h = 3.4D /h or 4.5$/h), butthe input feed gas cost could be extremely high, i.e. 484–6917Dor 636–9096$/h when using helium (Niemira, 2012). Thereby, itraises the following question: is there any possibility of utiliz-

ing it in industrial practice? The answer could only be positiveafter reducing the feed gas consumption and investigating the

food and bioproducts processing 9 1 ( 2 0 1 3 ) 575–579 577

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oxicological effects of generated chemical residues in the by-roduct substrate.

Sterilization and enzyme de-activation can be conductedith high hydrostatic pressure (i.e. up to 200 MPa), too, which

s now the most developing emerging technology in foodrocessing (Boulekou et al., 2010; Mújica-Paz et al., 2011). Highydrostatic pressure offers a unique opportunity to produceon-damaged, fresh-tasting, safer and long shelf-life prod-cts. These properties could be of particular interest in thease of recovering of nutraceuticals from by-products, as theseompounds have already been over-processed and furtherhermal treatment could cause an excessive loss of their func-ionality. High pressure has recently raised interest for furthertilization since it is finding more and more specific applica-ions, i.e. gelation of sarcoplasmic proteins that provides thepportunity for their inclusion in the preparation of surimi by-roducts (Ohsima et al., 1993), modification of whey proteinoncentrates hydrophobicity, solubilization of dietary fibers,xtraction anthocyanins from grape by-products etc. So inhe future, an interesting challenge to confront could be theotentiality of applying high hydrostatic pressure similar to allressurized (i.e. microwave or solvent) extraction processes inrder to increase extraction yield of recovered nutraceuticals.he main disadvantage of both low temperature plasma andigh hydrostatic pressure applications is the high capital cost,

.e. industrial scale vessels in the second case can cost from.5 to 4 million Euro (∼0.6–5.3$). Food and bioresource com-anies must be able to make a realistic cost-benefit analysisf the potential rewards by investing in such processes andhe production scale is always a key parameter for the finalecision.

Other technologies based on accelerated mass transferould suit more properly in the field due to their directncorporation with the extraction process. The cavitationsnd disrupting properties of ultrasound waves have beensed for the enhancement of anthocyanins and beta-carotenextraction from grape seeds, citrus and pomegranate peelsGhafoor et al., 2009; Pan et al., 2012). For example, con-inuous ultrasound-assisted extraction of phenolics fromomegranate peels increased the antioxidant yield by 24%ompared to conventional liquid extraction and reduced thextraction time by 90%. Concerning these cases, one of theifficulties reported in the literature is the non-standardizedethodologies and control parameters. Thereby, the cur-

ent challenge is to establish conditions in terms of energyensity, probe types and sample volumes aiming at theechno-economical optimization prior industrial exploitationRastogi, 2011). Complicated problems (i.e. the requirementsor high air generation capacity, control and sterilization)re the major barriers to overcome prior confronting thenduced and increased extraction efficiency against the over-ll manufacturer sacrifices that should be encountered duringndustrial process development.

High voltage electric discharge is a technique, in whichiquid substrates are placed in a chamber between two elec-rodes that cause particles fragmentation by providing shortulses. This method has recently been tested in combina-ion with ultrafiltration for the recovery of nutraceuticalsrom grape seeds (Liu et al., 2011). Optimized heat and massransfer can also be induced by laser ablation, which hasuccessfully been assayed for the recovery of vegetable macro-olecular active substances and it has generated prospects

or further exploitation in extracting pectin, aroma substancesnd in obtaining edible films (Panchev et al., 2011). However,

investment and operational costs have not been demonstratedyet for this application. This is important to state for thefuture researchers since technologies like laser ablation andhigh voltage electric discharge could be too sophisticated (interms of high capital cost and energy overconsumption) fortheir application in nutraceuticals recovery from by-products,which is principally a secondary priority for the manufacturer.Other problems need to be solved are the proper electricalinsulation, accurate process control systems as well as treat-ment of non-conductive parts (i.e. fat globules) in the case ofelectrical discharges.

On the other hand, pulsed electric fields can also drill theagricultural by-products’ matrix by inducing critical electricalpotential across the cell membranes. Following the afore-mentioned example of phenols recovery from pomegranatepeel, pulsed ultrasound assisted extraction was shown toprovide again similar antioxidant yield, but 50% energy sav-ing compared to conventional ultrasound-assisted extraction(Pan et al., 2012). Indeed, the application of pulsed electricfield with an energy input of 10 KJ/Kg can lead to 30–35%higher yield of anthocyanin monoglucosides recovery fromgrape pomace compared to conventional liquid extraction(Töpfl, 2006). Likewise, the corresponding energy consump-tion is lower compared to mechanical (20–40 kJ/kg), enzymatic(60–100 kJ/kg) or high voltage electrical discharge treatments(80 kJ/kg) (Vorobiev and Lebovka, 2010; Boussetta et al., 2011).Similar conclusion was denoted by comparing the extractionof phenols from grape skin: 20 and 120 kJ/kg for pulsed electricfield and high voltage electrical discharge treatments, respec-tively (Boussetta et al., 2009). Besides, the latest technologyhas been referred to need even more energy during scale upin order to obtain equivalent phenols yield (Boussetta et al.,2012). Nevertheless, both of them seem to fit better in thedownstream processing of nutraceuticals recovery more thanfood preservation applications, where the energy consump-tion could reach even 1000 kJ/kg (Vorobiev and Lebovka, 2010).

Pulsed electric field technology differentiated over the lastyears as it has been assayed not only for the extraction ofnutraceuticals, but also for their structural modification, i.e.in whey protein isolate (Xiang et al., 2011). It has been usedfor the encapsulation of biomaterials and nutraceuticals, too,by intensifying as well as accelerating fluid bed de-wateringand agglomeration of red pepper slices and instant soy pro-tein isolate, respectively (Ade-Omowaye et al., 2001; Dacanaland Menegalli, 2010). Accelerated agglomeration is needed inorder to avoid an additional drying step that leads to increasedenergy consumption. What is important to state is that thisemerging technology could be applied in more than one recov-ery stages of the production line resulting eventually in costreduction. However, there is a clear need for the developmentof cost-effective impulse generation systems with sufficientelectrical field strength, power as well as repetition rate. Inthe same time, they should produce a restricted amount ofelectrochemical reactions, for instance, by applying shorterpulses or replacing stainless steel with carbon electrodes(Töpfl, 2006). The latest modification would be helpful in orderto avoid contamination of by-products matrix from electrodeheavy metals. Besides, a combination of pulsed electric fieldand heat treatment could lead to lower maximum tempera-ture used and less energy consumption.

Apart from pulsed electric field agglomeration, modernencapsulation is considered in terms of forming nano-

materials such as nanoemulsions. The production of multi-phase colloidal droplets of 10–100 nm ensures the physical

578 food and bioproducts processing 9 1 ( 2 0 1 3 ) 575–579

stability and increased bioavailability of the final product (Choiet al., 2011). A typical example includes the droplet (up to200 nm) emulsification of grape marc extract. Nanoemulsionspreparation has been enhanced using ultrasounds, too. Thelatest provides energy efficiency and superiority in terms ofthe droplet size compared to classical roto-stator dispersions(Kentish et al., 2008). However, the major disadvantage ofnanoemulsions preparations concerns the safety of the finalproduct. For example, the cells membrane permeability ofnano-materials and their effect on biological matrices stillremain uninvestigated and conclude an interesting field tostudy. Another important parameter is the cost since scal-ing up of higher (or even low) energy approaches used forthe production of nanoemulsions is still very expensive dueto the proportional high pressures needed to process largervolumes (Silva et al., 2012). Such costs should be reduced bytechnical optimization or simplification of the nanoemulsionsproduction.

As it has been referred above, toxicological problems occuralso with regard to the pulse electric fields application and thepotential release of heavy metals in the substrate. Althoughthe implications of electrochemical reactions and corrosionare well known in other fields, very little information existsabout the occurrence of related problems during bioresourceprocessing with these systems. The impact on food matri-ces is also unknown for other advanced techniques such aslow temperature plasma. In other words, there is a clear chal-lenge for future research to ensure consumer acceptance andfinally clarify legislative situation. The latter issue is difficultto address since there are two complex considerations: Oneoriginates to the commercialization of novel processing tech-niques that require product conformity proof to conventionalprocesses. The other is related to the certification and approvalof nutraceuticals health benefits, especially in spite of agricul-tural by-products recovery.

4. Conclusion

Despite the fact that it seems that we are far away fromthis point, the market and consumers demand for tailored-made processes and products, respectively, will lead foodmanufacturers to adapt sooner or later the aforementionedtechnologies. This would probably happen even for the by-products treatment, which is a ramification of the agriculturaland related food industry. Further research on the field wouldsupply technical feedback to reduce capital and operation cost,and set up minimal processing. Safety assessments, appli-cation route, flavor and taste impact as well as consumeracceptance are the challenges that should be addressed nextin order to take the emerging technologies closer to a com-mercial breakthrough in the field.

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