Recovery of carotenoids from tomato processing by-products – a review

Food Research International 65 (2014) 311–321

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Recovery of carotenoids from tomato processing by-products – a review I.F. Strati ⁎, V. Oreopoulou Laboratory of Food Chemistry & Technology, School of Chemical Engineering, National Technical University of Athens, 15780 Athens, Greece

a r t i c l e

i n f o

Article history: Received 28 June 2014 Received in revised form 20 September 2014 Accepted 26 September 2014 Available online 13 October 2014 Keywords: Tomato by-products Carotenoids Extraction methods Process parameters Lycopene

a b s t r a c t Industrial tomato processing generates large amount of low-value by-products, primarily used as livestock feed or disposed of; however, being a rich source of natural carotenoids, tomato waste can be used to produce high value-added products for food, cosmetics, or pharmaceutical applications. The objective of this review is to summarize and give an overview of the extraction methods available for the recovery of carotenoids and, especially, lycopene from tomato processing by-products. Organic solvent extraction techniques are presented and the effect of extraction conditions on carotenoids recovery is evaluated. In particular, the use of Ultrasound Assisted (UAE), Microwave Assisted (MAE), Enzyme-Assisted (EAE) and Extraction at High Pressure (HPE) for the recovery of carotenoids is assessed. Also, this review examines the efficiency of Supercritical Fluid Extraction (SFE) and in particular the effect of process parameters on carotenoid recovery from industrial tomato waste. © 2014 Elsevier Ltd. All rights reserved.

Chemical compounds studied in this article: Lycopene (PubChem CID: 446925) β-Carotene (PubChem CID: 5280489) Astaxanthin (PubChem CID: 5281224) Ethyl lactate (PubChem CID: 7344)

1. Introduction The industrial processing of fruits and vegetables generates large quantities of by-products which can be recycled or reused by food, cosmetics, and/or pharmaceutical industries and serve as a source of valuable bioactive compounds. Within all vegetables, tomato (Lycopersicon esculentum), which is consumed either as a raw fruit or as a processed product, is the second most important vegetable crop in the world and one of the most important components of the mediterranean Diet (FAOSTAT, 2005; http://faostat.fao.org). The industrial processing of tomato leads to by-products, namely tomato seeds and peels, representing 10–40% of total processed tomatoes (Al-Wandawi, Abdul-Rahman, & Al-Shaikhly, 1985). The management of tomato by-products is considered an important problem faced by tomato processing companies, as they cannot be discharged to the environment. They are used mainly for animal feed or fertilizer (Knoblich, Anderson, & Latshaw, 2005), whereas they constitute a promising source of compounds that can be used for their nutritional properties and biological potential. The bioactive phytochemicals present in industrial tomatoes and their processing by-products include tocopherols, polyphenols, carotenoids, some terpenes and sterols, as reported by Kalogeropoulos, Chiou,

⁎ Corresponding author. E-mail addresses: [email protected], [email protected] (I.F. Strati).

http://dx.doi.org/10.1016/j.foodres.2014.09.032 0963-9969/© 2014 Elsevier Ltd. All rights reserved.

Pyriochou, Peristeraki, and Karathanos (2012), and seem to be able to withstand industrial processing methods. Tomato waste is considered as an important source of natural carotenoids. According to Knoblich et al. (2005), the carotenoid content of dry tomato by-products collected from a commercial tomato processing plant amounted to 793.2 and 157.9 μg g− 1, for peel and seed by-product, respectively. However, this content may vary, depending mostly on the tomato variety and on the industrial processing methods. In a recent study (Kalogeropoulos et al., 2012) the major carotenoids found in tomato processing waste were lycopene (413.7 μg g− 1 dry weight) and β-carotene (149.8 μg g− 1 dry weight). Carotenoids are well credited with important health-promoting functions, such as provitamin A and antioxidant activity, enhancement of the immune system and reduction of the risk of degenerative diseases such as cancer, cardiovascular diseases, cataract and macular degeneration (Rodriguez-Amaya, Kimura, Godoy, & Amaya-Farfan, 2008; Van den Berg et al., 2002). Besides their biological properties, carotenoids are utilized as natural antioxidants for the formulation of functional foods or as additives in food systems to elongate their shelf-life. Lycopene and β-carotene are authorised natural pigments that can be used in the dyeing of various kinds of food products (Cadoni, De Giorgi, Medda, & Poma, 2009). The global market for carotenoids was estimated to US$ 1.07 and is projected to top US$ 1.2 billion in 2015 (Global Industry Analysts, 2011). An evidence of that trend is that many patents have been

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recently deposited worldwide on the extraction of carotenoids from natural sources (Riggi, 2010). The present review presents the extraction methods available for the recovery of carotenoids from tomato processing by-products. Conventional organic solvent extraction and its techniques are discussed and the effect of extraction conditions on carotenoids recovery is assessed through literature research. The use of Ultrasound Assisted (UAE), Microwave Assisted (MAE), Enzyme-Assisted (EAE) and Extraction at High Pressure (HPE) to enhance the extraction of carotenoids are also reviewed and critically evaluated. Finally, this review examines Supercritical Fluid Extraction (SFE), an environmentally safe technology for the recovery of carotenoids, and, especially, lycopene from industrial tomato waste. 2. Conventional organic solvent extraction Solvent extraction is the most widely used method for the recovery of bioactive compounds from a broad range of plant origin matrices. It is a unit operation with the objective of separating determined compounds from a matrix, solid or liquid, based on the principle that the solvent diffuses in the matrix and dissolves the soluble compounds. In solid–liquid extraction, the target compound should have a selective solubility in the solvent of choice compared to other components of solid matrix (Aguilera, 2003). In fact, however, this is rarely achieved and, therefore, many research studies have focused on the optimization of extraction parameters (solvent type, solvent to solid ratio, particle size, temperature, extraction time) in order to increase the recovery of valuable components from food processing by-products of plant origin (Kaur, Wani, Oberoi, & Sogi, 2008; Strati & Oreopoulou, 2011a,b). Several solvent extraction techniques exist; however, the process conditions (target compound, solvent type and temperature) determine the choice of the most appropriate one. The main solvent extraction techniques applied for the extraction of carotenoids from tomato processing by-products are Soxhlet extraction and agitation. Despite the fact that the yield of carotenoids obtained by Soxhlet extraction is generally higher than the respective one obtained by agitation, it is not preferred due to possible degradation of thermo-sensitive compounds such as carotenoids at high temperature and long extraction time applied. 2.1. Soxhlet extraction Soxhlet extraction is a general and well-established technique, which surpasses in performance other conventional extraction techniques except for, in limited field of applications, the extraction of thermolabile compounds (Luque de Castro & Garcia-Ayuso, 1998). The efficiency of this method (as also of all other extraction techniques) depends on plant characteristics and particle size, as internal diffusion may be the limiting step during extraction (Wang & Weller, 2006). The advantages of Soxhlet extraction include the continuous contact of fresh solvent with the solid matrix and the absence of a filtration step after leaching. On the other hand, the extraction time is long, large amounts of solvent are consumed, no agitation can be provided, and there is a great possibility of thermal decomposition of carotenoids, as the extraction usually occurs at the boiling point of the solvent for a long time (Luque de Castro & Garcia-Ayuso, 1998; Wang & Weller, 2006). Soxhlet extraction is mostly applied as a laboratory technique, or a micro-scale extraction technique. 2.2. Agitation, homogenization and shaking Agitation is a common method used by industries, generally applied in ground raw materials. This method involves agitating the solvent and the plant material together, and leaving them in contact for minutes to hours. After this period, a separation step to remove the solvent is necessary and the residue is usually re-extracted. Agitation involves

coupling an agitator to the vessel containing the raw material, while homogenization involves mixing the solvent and the raw material and then leaving them in contact with no further agitation, and shaking involves agitating the tank containing the solvent and the raw material (Prado, Veggi, & Meireles, 2014). The dispersion of the particles in the liquid solvent by the agitation facilitates the contact of the solid with the solvent, accelerating the process by favoring the diffusion of the extracted components and avoiding super saturation in the immediate proximity of the surface of the solid to be extracted (Naviglio et al., 2007). However, major disadvantages of this method are considered to be: i) the large consumption of organic solvents and the subsequent cleanup and concentration steps; ii) the high energy required for the solventsolute mixture separation; iii) the gradual decrease of mass transfer rate because the solvent is continuously enriched with solutes; iv) the coextraction of undesirable components; and v) the possible degradation of thermo sensitive compounds such as carotenoids (Wang & Weller, 2006), 2.3. Centrifugal extraction Centrifugation allows phase separation by the centrifuge force. In centrifugal extraction, the raw material is placed in the centrifugal vessel with solvent and submitted to centrifugation, followed by a filtration step to separate the exhausted raw material from the extract. The main drawback of this method is the necessity of an additional filtration step. Centrifugal extraction is a technique mainly used to obtain herbal extracts (Prado et al., 2014). For the recovery of carotenoids from tomato by-products, centrifugation has only been reported in combination with other techniques, such as agitation and sonication (Kassama, Shi, & Mittal, 2008; Naviglio, Pizzolongo, Ferrara, Aragòn, & Santini, 2008; Rozzi, Singh, Vierling, & Watkins, 2002).. 2.4. Effect of extraction conditions on carotenoids recovery Table 1 presents a literature review on the conventional organic solvent extraction methods for the recovery of carotenoids from tomato processing by-products. As it is observed, there is a wide variation in reported extraction yields of carotenoids, which may be attributed to factors like tomato variety, tomato processing method, kind of by-product, solvent selection, extraction techniques and parameters. 2.4.1. Effect of solvent Solvent selection is usually considered as the most important factor. As most tomato carotenoids are lipid-soluble, common organic solvents have been tested for carotenoid extraction, including hexane, acetone, ethanol, ethyl acetate, chloroform and petroleum ether, as well as mixtures of polar and nonpolar solvents in different ratios (Periago, Rincon, Aguera, & Ros, 2004; Shi, Maguiere, & Bryan, 2002; Strati & Oreopoulou, 2011a,b; Taungbodhitham, Jones, Wahlqvist, & Briggs, 1998). Solvents such as diethyl ether and tetrahydrofuran are not preferred because they may contain peroxides that react with carotenoids. The oxygenated derivatives (xanthophylls) are more soluble in hydrophilic solvents, whereas carotenes possess a more hydrophobic nature and limited solubility in water and are more soluble in nonpolar solvents. Vagi et al. (2007) compared the yields of several carotenoids by Soxhlet extraction using hexane or ethanol and found an almost ten-fold increase of the lycopene yield in hexane extract, whereas the yield of β-carotene was almost the same by using either solvent. The ethanolic extract contained mainly polar xanthophylls. A similar trend was observed in the study of Calvo, Dado, and Santa-Maria (2007) who evaluated the extraction yield by using the food grade solvents, ethanol and ethyl acetate, and found that the yield of all-translycopene in ethyl acetate extract was twenty-fold higher than the respective yield obtained in ethanol. Also, Strati and Oreopoulou (2011a) reported the following order in the yield of lycopene from

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Table 1 Conventional organic solvent extraction methods for the recovery of carotenoids from tomato processing by-products. Tomato processing by–

Extraction parameters: Method (M);

Extracted carotenoids (mg/kg raw material, unless specified

product

Solvent type (S); Solvent/Feed ratio (S/F);

otherwise; db–dry basis; wb–wet basis; nd: not detectable)

Reference

Temperature (T); Pressure (P); time (t); Particle size (D); Moisture content (H); Rotation (R); Frequency (F); Power (Pw) Freeze–dried tomato

M=agitation; S = ethanol or ethyl acetate;

Ethanol extract

Ethyl acetate extract

Calvo, Dado, and Santa–

skins

S/F = 80 (v/w); t = 5,10,20,30 and 40 min;

All–trans–lycopene (10–60 db)

All–trans–lycopene (200–1200 db)

Maria (2007)

T= 25°C, 35°C, 50°C and 60°C

cis–lycopene (2–10 db)

cis–lycopene (50–150 db)

β–carotene (41–135 db)

β–carotene (0–15.6 db)

Phytoene (10.2–39.5 db) Phytofluene (4.0–20.7 db)

Phytoene (0.6–3.1 db)

Dried tomato pomace

M = Soxhlet; S = ethanol or hexane

Ethanol extract

Hexane extract

Extraction yield

12.56 & 57.92 % (db)

3.39 & 15.33 % (db)

Polyoxy xanthophylls

2465 mg/kg

nd

Lutein

0 & 1 mg/kg

6 & 16 mg/kg

Neolutein

0 & 2 mg/kg

7 & 56 mg/kg

α–cryptoxanthin

nd

2 & 36 mg/kg

β–cryptoxanthin

0 & 19 mg/kg

19 & 28 mg/kg

lycoxanthin

0 & 17 mg/kg

10 & 164 mg/kg

cis–lycoxanthin

nd

4–33 mg/kg

Lycopene

77 & 703 mg/kg

40 & 6772 mg/kg

Neolycopene

6 & 21 mg/kg

23 mg/kg

γ–carotene

0 & 11 mg/kg

12 & 53 mg/kg

β–carotene

34 mg/kg

37 mg/kg

Vagi et al. (2007)

Sample 1: H=4.6 %, D=0.6 mm Sample 2: H=10.7 %, D= 0.3 mm

Tomato industrial waste

M = agitation; S = hexane, ethanol, ethyl

Total carotenoids* (hexane =34.5 db; acetone =51.9 db; ethanol =17.6

Strati, and Oreopoulou

(mixture of skins and

acetate, or ethyl lactate; S/F = 10 (v/w);

db; ethyl acetate =46.2 db; ethyl lactate =243.0 db)

(2011a)

seeds)

t= 3 X 30 min; T =25, 50, 70 °C

Tomato industrial waste

M = agitation; S = hexane:ethanol (1:1), hexane:acetone (1:1), or hexane:ethyl acetate (1:1); S/F = 9.1 (v/w); t= 30 min; T= 25°C; D= 0.56 mm

Total carotenoids [hexane:ethanol (1:1) = 28.1 db; hexane:acetone

Strati, and Oreopoulou (2011b)

M = Soxhlet; S = acetone:hexane (1:1, v/v); t = 6 h; D= 0.15, 0.36, 0.72 mm; H = 4.6–82.9 %

Lipid content (10.7–31.3 % oil–free db)

M= homogenization ; S= hexane/acetone/absolute alcohol/toluene mixture

Lycopene (309.6 db)

Tomato peel sand seeds

M= homogenization; S= acetone: ethanol (2:1, v/v) (3X75 mL); t=30 s

Lutein (9.9–10.5db)

Montesano, Gennari, Seccia, and Albrizio (2012)

Tomato pomace

M= agitation; S= hexane: acetone: ethanol

Lycopene (607.3 db)

Perretti et al. (2013)

(mixture of skins and seeds) Tomato industrial waste (mixture of skins and seeds) Tomato industrial waste (mixture of skins and seeds)

(1:1) = 30.5 db; hexane:ethyl acetate (1:1) = 37.5 db]

trans–lycopene (52.1–691 oil–free db)

Nobre, Palavra, Pessoa, and Mendes (2009)

cis–lycopene (0–76.3 oil–free db) β–carotene (29.6 db)

Baysal, Ersus, and Starmans (2000)

(1:1:1, v/v/v); S/F= 30; T = 50 °C; t= 60 min; H= 75% M= agitation; S= ethanol:sunflower oil (1:1, v/v); S/F= 10; T = 50 °C; t= 120 min;H= 5%

Lycopene (258.6 db)

Dried tomato by–product (including tomato seed and a mixture of tomato peel and seed sample, 37:63 w/w)

M = Soxhlet; S = chloroform; t= 15 h; D= unground, 1.59 and 1.05 mm

Lycopene (820 db)

Tomato pomace

M = Soxhlet; S = chloroform; S/F = 125 (v/w); t = 7 h M = agitation + sonication + centrifugation; S = chloroform; S/F = 20; t = 30 min;

Lycopene (305.3 db)

Tomato seed sand skins

M = agitation + sonication + centrifugation; S = chloroform; S/F = 20; t = 30 min; H= 48.4 %

Lycopene (24.5 db)

Tomato skin, freeze– dried

M=agitation overnight; S = hexane; S/F =

Lycopene (129.9 db)

20; T = 45 °C; D = 1 mm; H =7 %

β–carotene (8.6 db)

Dried tomato skin

M=agitation; S = hexane: acetone: ethanol

Lycopene (6.39–19.80)

Kaur, Wani, Oberoi, and Sogi (2008)

Industrial tomato by– products

Machmudah et al. (2012)

β–carotene (1510 db)

Lycopene (20)

(2:1:1, v/v/v); S/F = 30 (v/w); T = 50 °C;

Huang, Li, Niu, Li, and Zhang (2008) Naviglio, Pizzolongo, Ferrara, Arago, and Santini (2008) Rozzi, Singh, Vierling, and Watkins (2002) Shi et al. (2009a)

D = 0.15 mm; t = 8 min; H=5.74% Dried tomato skins

M = Soxhlet; S = chloroform; t = 3 Χ h 21

Lycopene (1130)

Topal, Sasaki, Goto, and Hayakawa (2006)

Dried tomato skin

M = agitation + sonication + centrifugation;

Lycopene (72db)

Kassama, Shi, and Mittal (2008)

S = chloroform; S/F = 30 (v/w); T = 45 °C; t ~ 12 h; D = 0.5–1 mm; H = 3 % Tomato skin, dry

Lycopene (380 db)

Ruiz, Mangut, Gonzalez,

Tomato skin, fresh

Lycopene (1720 db)

De la Torre, and Latorre

Tomato seeds and skin, dry

Lycopene (10 db)

(2000)

Tomato seeds and skin, fresh

Lycopene (30 db)

*At 70 °C.

M = Soxhlet; S = ethanol,; t = 30 min

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dried tomato waste extracted with conventional organic solvents: acetone N ethyl acetate N hexane N ethanol. Chloroform was also used in Soxhlet extraction of dried tomato skins (Topal, Sasaki, Goto, & Hayakawa, 2006) and dried tomato by-product (Machmudah et al., 2012) with satisfying yields of lycopene. Mixtures of polar and non polar solvents (acetone/hexane, ethanol/hexane, ethyl acetate/hexane, acetone/ethanol/hexane and hexane/acetone/absolute alcohol/toluene) have also been used in Soxhlet extraction and in extraction methods by agitation (Baysal, Ersus, & Starmans, 2000; Kaur et al., 2008; Nobre, Palavra, Pessoa, & Mendes, 2009; Perretti et al., 2013; Strati & Oreopoulou, 2011a,b). In a recent approach, Perretti et al. (2013) have extracted lycopene from dried tomato pomace with a mixture of ethanol and sunflower oil (1:1, v/v) and the lycopene content of the extract was 42.73% of the total lycopene content, as obtained by traditional solvent extraction. The combination of polar solvents with the non polar hexane seems to enhance the solubilisation of the non polar carotenoids (lycopene and β-carotene). According to Strati and Oreopoulou (2011b) the use of a mixture of polar and non-polar solvents, namely ethyl acetate and hexane, proved adequate to extract non polar carotenoids (lycopene and β-carotene) in sufficient percentages (96% of total extracted carotenoids), as well as the polar lutein (4% of total extracted carotenoids). Lutein was also selectively extracted from tomato seeds and skins by using a mixture of acetone: ethanol (2:1, v/v) and a simple clean-up procedure (Montesano, Gennari, Seccia, & Albrizio, 2012). Most nonpolar solvents that have high extraction efficiency are considered to be toxic. In a growing number of countries, most of the organic solvents are banned for food products extraction, or authorized with extremely low residual concentrations (1 mg/kg in case of hexane) since they may be associated with hazardous effects (European Commission Directive 97/60/EC, 1997). Recently, ethyl lactate has been suggested as an alternative, potent solvent to extract carotenoids, mainly β-carotene and lycopene. It is an environmentally friendly solvent, produced from the fermentation of carbohydrate feedstock and it is completely biodegradable in CO2 and water. According to Strati and Oreopoulou (2011a), ethyl lactate gave the highest carotenoids yield from tomato waste (243 mg/kg dry basis), compared to acetone (52 mg/kg) or ethyl acetate (46 mg/kg). Additionally, Ishida and Chapman (2009) demonstrated the advantage of ethyl lactate in extracting both trans- and cis-lycopene isomers. 2.4.2. Solvent to feed ratio effect Solvent to feed ratio is another factor which affects the extraction of carotenoids. An equilibrium between the use of high and low solvent to feed ratios, involving a balance between high costs and solvent wastes, on the one side, and avoidance of insufficient mixing and saturation effects, on the other side, has to be found to obtain an optimized value (Pinelo, Rubilar, Jerez, Sineiro, & Nunez, 2005). Generally, large values of solvent to feed ratio are noticed in Soxhlet extraction. This fact along with the long extraction time lead to high yields of lycopene (Calvo et al., 2007; Huang, Li, Niu, Li, & Zhang, 2008). Most researchers used a high value of solvent to feed ratio, e.g. 20:1 (v/w) (Naviglio et al., 2008; Shi, Khatri, et al., 2009) or 30:1 (v/w) (Perretti et al., 2013) to obtain high extraction yields. Kaur et al. (2008) tried to optimize the extraction conditions of lycopene from dehydrated tomato waste skin and found the optimum solvent to waste ratio equal to 30:1 (v/w) (maximum lycopene yield 19.8 mg/kg). Strati and Oreopoulou (2011b), on the other hand, by using the response surface methodology to optimize extraction conditions, obtained a maximum carotenoid yield of 37.5 mg kg−1 dry waste with a solvent to waste ratio 9.1:1 (v/w). 2.4.3. Effect of temperature, extraction time and extraction steps Several studies demonstrate the effect of temperature, extraction time and number of extraction steps on the extraction yield of carotenoids. Generally, in all the extraction techniques reviewed (UAE, MAE, EAE, HPE), the increase of temperature affects positively the mass

transfer process and, consequently, the extraction yield of lycopene and other carotenoids. The increase in extraction temperature generally implies: i) the increase of solvent capacity to solubilize the target compounds, ii) the increase in diffusion rates, iii) better disruption of bonds between the target compound and the matrix, iv) the decrease of solvent viscosity, and v) the decrease in surface tension. However, limiting factor for the choice of extraction temperature is the boiling point of solvents used and the need to avoid undesirable reactions such as isomerization and ⁄ or oxidation of carotenoids (Strati & Oreopoulou, 2011a). In a study evaluating the extraction yield of lycopene, β-carotene, phytoene and phytofluene from tomato peel powder at varying temperatures (25, 35, 50 and 60 °C) for different time periods, the temperature increase caused an increase in the carotenoid concentrations; however in the extractions performed with ethanol at 60 °C, the yield of (all-E)-lycopene and their (Z)-isomers was lower than at 50 °C, indicating that isomerization both with oxidative degradation occurred in the high temperature extractions with ethanol (Calvo et al., 2007). Shi, Dai, Kakuda, Mittal, and Xue (2008) found that isomerization may proceed even at 60 °C; however, they obtained an improved yield of lycopene by heating a tomato puree matrix at 100 or 120 °C. The raw material, solvent and extraction conditions seem to affect the isomerization and/or degradation of carotenoids as temperature increases. Thus, Strati and Oreopoulou (2011a) found that the increase of temperature up to 70 °C did not cause any alterations to lycopene and other carotenoids from tomato waste, while it increased the yield, compared to extraction at 25 °C. Kaur et al. (2008) showed that lycopene recovery increased with increase in extraction time and number of extraction steps. A similar trend of increase of the carotenoid recovery with the number of extractions was observed by Strati and Oreopoulou (2011a). Moreover, they found that the carotenoids extraction is controlled by diffusion phenomena and the extraction rate decreased with the extraction time to reach equilibrium at 30 min that was adequate for each extraction step. A recovery of 55–74% of total carotenoids could be achieved in a one-step extraction, while subsequent steps are necessary to increase the recovery, especially when polar solvents are used. 2.4.4. Effect of particle size and moisture content Particle size is another parameter that influences carotenoids recovery. Yield increases with particle size decrease due to the higher interfacial area contact when particles are smaller; however, too small particles can cause packing of the extraction bed, which can result in channelling effects (Sabio et al., 2003). A trend for an increase in the recovery of trans-lycopene with a decrease in the particle size (0.15–0.72 mm) was observed in some studies (Machmudah et al., 2012; Nobre et al., 2009; Vagi et al., 2007). On the other hand, Kaur et al. (2008) evidenced that the increase in particle size from 0.05 to 0.43 mm did not vary significantly the lycopene yield. Sabio et al. (2003) verified that the extraction of lycopene from tomato wastes decreased at very small particle sizes (0.08 mm). Strati and Oreopoulou (2011b) suggested, through optimization of extraction parameters with response surface methodology, that the optimized particle size for recovery of carotenoids from tomato waste was 0.56 mm. The extracted carotenoids and, especially, lycopene appear to be related to the amount of moisture present within the sample and how it interacts with the sample matrix and the solvent. Nobre et al. (2009) examined the effect of moisture content in Soxhlet extraction of fresh (82.9%) and dried to various moisture contents (58.1%, 22.8% and 4.6%) tomato industrial wastes with acetone: hexane (1:1) for 6 h. They observed that the trans-lycopene content of tomato waste dried to moisture contents of 58.1% and 22.8% was only slightly lower than that of the fresh (82.9%) material. On the other hand, the sample with the lowest moisture content of 4.6% contained the lowest amount of trans-lycopene content. According to the authors, lycopene was not degraded but was unavailable for extraction because

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in the dried samples, the lipid pillars in the plant cell elementary membrane close due to lack of water, making the membrane impermeable to the solvent. Water can act as a co-solvent for relatively polar compounds. It may also have a positive effect in the extraction process by swelling the sample matrix, thus making it easier for the solvent to penetrate and diffuse into the sample. According to Sun and Temelli (2006) however, this positive effect is compromised by water’s more negative effects on extraction efficiency. The fresh material provides higher yields of lycopene, as documented by Ruiz, Mangut, Gonzalez, De la Torre, and Latorre (2000). Moreover, the higher lycopene and other carotenoids content is located in skins, compared to seeds, and this is the reason why several researchers suggest the use of tomato skin only. 3. Ultrasound assisted extraction (UAE) The efficiency of ultrasound-assisted as an alternative to conventional solvent extraction is mainly attributed to acoustic cavitation. Acoustic cavitation is caused by the interaction between the ultrasonic waves, the liquid, and the dissolved gas and can be generated in liquids in the frequency range of 20 kHz to N1 MHz, above critical power levels. Application of an acoustic field forces a free bubble to oscillate about its equilibrium radius. During the contraction phase, the concentration of gas inside the bubble increases and gas diffuses out of the bubble. Similarly, during the expansion phase the concentration decreases, and gas diffuses into the bubble. Since the diffusion rate is proportional to the area, more gas enters during expansion than leaves during contraction; consequently, over a complete cycle, there will be a net increase in the amount of gas inside the bubble, a phenomenon called rectified diffusion. Rectified diffusion and bubble coalescence lead to the growth of the bubbles towards a resonance size range. When bubbles reach the resonance size range, they grow to a maximum size within one acoustic cycle and violently collapse, generating very high temperature conditions within the collapsing bubbles (Ashokkumar & Mason, 2007; Louisnard & Gonzalez-Garcia, 2011). The microjetting and microstreaming effects attributed to acoustic cavitation cause disintegration of solid materials and disruption of cell walls. This phenomenon involves an increase in the contact between the solvent and the cell contents, and enhances mass transfer of the cell contents from the material to the solvent In addition, as the size of the bubbles generated during acoustic cavitation are very small relative to the total liquid volume, the heat produced on bubble collapse is rapidly dissipated with minor effect in the environmental conditions (Toma, Vinatoru, Paniwnyk, & Mason, 2001; Vilkhu, Mawson, Simons, & Bates, 2008; Vinatoru, 2001). Although there is no systematic study available on the effect of solution temperature, two opposing effects of the solution temperature on the ultrasound extraction efficiency are reported. UAE may increase the extraction yield at low temperatures, since acoustic cavitation is more efficient. On the other hand, the increase of temperature results in increased mass transfer, as mentioned in 2.4.3. Apart from the temperature, other operational parameters (sample size, moisture content, particle size, solvent type, ultrasound power and frequency, sonication time and liquid to solid ratio) are crucial to achieve hjgh extraction efficiency (Chandrapala, Oliver, Kentish, & Ashokkumar, 2013). Low-frequency ultrasound (16–100 kHz) can be used for the extraction of components/substances such as hydrophilic flavonoids (anthocyanins, tannins) and hydrophobic carotenoids (lycopene, betacarotene, capsaicin, and lutein) from horticultural products such as carrot, ginger, tomato, grapes, olives, olive pomace, and capsicum and from their processing waste (Vilkhu et al., 2008). Eh and Teoh (2012) applied an optimized (with the aid of Response Surface Methodology) UAE of lycopene from tomatoes and observed that the extraction yield of all-trans-lycopene increased by 75.93%, compared to optimized conventional method of extraction and, at the same time, no degradation or isomerization of lycopene has occurred. The optimized conditions

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for the above study were 45.6 min (total extraction time), 47.6 °C (extraction temperature) and 74.4:1 v/w (ratio of solvent to freeze-dried tomato sample). The ultrasonic frequency was 37 kHz and the solvent used was a mixture of n-hexane: ethanol: acetone (2:1:1, v/v/v). In many analytical situations, UAE is a simpler and more efficient alternative to conventional solvent extraction, and occasionally, to modern extraction techniques (e.g., microwave, supercritical fluid). The benefits of UAE for the food industry include (a) an overall enhancement of extraction yield or rate of heat-sensitive bioactive compounds by enabling lower processing temperatures; (b) the opportunity to use alternative (GRAS) solvents by improvement of their extraction performance; and (c) the reduction of processing time (the majority of material is extracted at the first 10 min). Another possibility is that simultaneous extraction and encapsulation of lipophilic materials, for example, carotenoid pigments, can be achieved with low-frequency ultrasound provided there is an appropriate protein, carbohydrate polymer, or surfactant present in the extraction solvent. (Vilkhu et al., 2008). 4. Microwave assisted extraction (MAE) MAE is based on the following principle. The moisture inside the cells evaporates by the heat generated by the microwaves, producing a high pressure on the cell wall. The pressure increase inside the cell modifies the physical properties of the biological tissues, improves the porosity of the biological matrix and, therefore, allows better penetration of extracting solvent through the matrix and improved yield of the desired compounds (Routray & Orsat, 2011). The major advantage of MAE is that the matrix is heated internally and externally without a thermal gradient, and the target compounds can be extracted efficiently and protectively using less energy and solvent volume (Gil-Chavez et al., 2013). MAE may be affected by a large variety of factors, such as power, frequency, and time of microwave application, moisture content and particle size of sample matrix, type and concentration of solvent, ratio of solid to liquid, extraction temperature, extraction pressure and number of extraction cycles (Mandal, Mohan, & Hemalatha, 2007). Within the above mentioned factors, solvent is considered to be the most critical. There are 3 main physical parameters to select the appropriate solvent: i) solubility, ii) dielectric constant, and iii) dissipation factors. Solvents with high dielectric constant, such as ‘water’ and polar solvents, can absorb high microwave energy and are usually better solvents than nonpolar ones (Wang & Weller, 2006). In addition, the dissipation factors (the efficiency with which different solvents heat up under microwave) play an important role. Despite the fact that water has a higher dielectric constant than ethanol or methanol, its dissipation factor is lower making it inefficient to heat up the moisture inside the sample matrix and to generate pressure which activates the extraction of the desired compounds. Therefore, it has been observed that the recovery of phenolic compounds is greater using solvents such as ethanol or methanol compared with water which is associated with a higher dissipation factor (Ajila et al., 2011; Simsek, Sumnu, & Sahin, 2012). MAE has been applied for the recovery of carotenoids of polar nature, i.e. astaxanthin from microalgae and from the red yeast Xanthophyllomyces dendrorhous (Choi, Kim, Park, Kim, & Chang, 2007; Pasquet et al., 2011). Zhao et al. (2006) demonstrated that both ultrasound and microwave have significant effects on the stability of (all-E)-astaxanthin. Microwave induced the conversion of (all-E)-astaxanthin to its Zforms, preferentially to (13Z)-astaxanthin, while ultrasound probably degraded this pigment into colorless compound(s). In order to prevent the degradation and oxidation of labile compounds, such as vitamin C, β-carotene, aloin A and astaxanthin, during extraction Xiaohua, Wei, Jiayue, and Gongke (2012) proposed a low temperature vacuum microwave-assisted extraction from different food samples, which

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simultaneously performed MAE in low temperature and in vacuo environment. Lianfu and Zelong (2008) applied ultrasonic and microwave assisted extraction (UMAE) in a single apparatus in order to recover lycopene from tomato paste. By this combined technique they improved significantly the recovery of lycopene in terms of extraction time and solvent volume, compared to the use of individual techniques. More specifically, the percentage of lycopene yield was 97.4% in 6.1 min and 89.4% in 29.1 min for UMAE and UAE, respectively. MAE has many advantages over conventional extraction techniques including lower environmental pollution, higher extraction efficiency and shorter extraction time. However, in order to be considered in industrial applications there are some important limitations that must be improved including i) the recovery of nonpolar compounds and ii) the modification of the chemical structure of target compounds which may alter their bioactivity and limit their application.

5. Enzyme-assisted extraction (EAE) Enzymatic treatment of the plant material may be used prior to conventional solvent extraction process. Enzymes are ideal catalysts that can assist in the extraction, modification and/or synthesis of complex bioactive compounds of natural origin. Enzyme-assisted extraction is based on the ability of enzymes to degrade the cell walls and membranes, under mild process conditions, thereby allowing the efficient extraction and release of the bioactive compounds (Gardossi et al., 2009; Pinelo, Arnous, & Meyer, 2006). This method also offers a more ecological approach as food industry and pharmaceutical companies try to find "cleaner" procedures for the extraction of bioactive constituents (Meyer, 2010). Enzymes, such as cellulases, pectinases and hemicellulases hydrolyze cell wall components and disrupt the structural integrity of the plant cell wall. Consequently, they increase cell wall permeability and thus, higher extraction yields of bioactive compounds are achieved (Puri, Sharma, & Barrow, 2012). Although enzymes normally function at an optimal temperature, they can still be used over a range of temperatures, providing flexibility for both cost and product quality. Particle size reduction of the substrate prior to enzymatic treatment provides better accessibility of the enzyme into the plant cell; therefore, the extraction yields are significantly increased (Gardossi et al., 2009). A number of studies have investigated the use of enzymes for improving the extraction of lycopene from tomato processing byproducts (Table 2). Cellulases and pectinases were employed by several researchers and the enzymatic treatment was followed by extraction with petroleum ether: acetone (1:1, v/v), hexane, ethyl acetate, acetone or mixtures of solvents (Choudhari & Ananthanarayan, 2007; Lavecchia

& Zuorro, 2008; Papaioannou & Karabelas, 2012; Ranveer, Patil, & Sahoo, 2013; Zuorro, Fidaleo, & Lavecchia, 2011). In all cases, there was an increase in extraction yield compared to the untreated samples, which varied from to 1.5- to 20-fold. These differences may be attributed to different raw material, enzyme preparation, experimental conditions and solvents used for the subsequent extraction. More specifically, a higher increase was observed when non-polar solvents, like hexane, were used because the rupture of the plant cells, renders the lycopene much more accessible to these solvents that cannot penetrate easily the wet material due to low polarity (Strati, Gogou, & Oreopoulou, 2014). Recently, the combination of two “green” techniques, namely, sonication and biocatalysis, was reported to improve the extraction of lycopene from tomato peel, generated as a by-product of the foodprocessing industry. According to the results of this study (Konwarh, Pramanik, Kalita, Mahanta, & Karak, 2012) a multifold increase in the enzyme (cellulase ‘Onozuka R-10’)-mediated extraction of lycopene was recorded under optimized sonication parameters over the nonenzymatic protocol. Furthermore, the use of sonication resulted in a decrease in the required optimal enzyme concentration and incubation period. Cuccolini, Aldini, Visai, Daglia, and Ferrari (2013) investigated the possibility of extracting lycopene from tomato waste peels using a green chemistry protocol devoid of organic solvent. Cells were lysed thanks to a combination of pH changes and hydrolytic enzymes treatments. The final concentrated product had a 20–30-fold increase in lycopene content with respect to the initial untreated peels. Enzymatic pretreatment of raw material usually results in a reduction in extraction time and solvent volume in addition to the increased yield and quality of product. However, enzyme-assisted extraction of bioactive compounds from plants has potential commercial and technical limitations (Puri et al., 2012): i. enzymes are relatively expensive for processing large quantities of raw material ii. available enzyme preparations cannot completely hydrolyze plant cell walls iii. enzyme-assisted extraction is not always feasible to be applied in industrial scale because enzymes behave differently as environmental conditions (i.e. the percentage of dissolved oxygen, the temperature and the nutrient availability) differ. However, if the above limitations can be overcome, then enzymebased extraction could provide an opportunity to not only increase extraction yields, but also to enhance product quality by enabling the use of milder processing conditions such as lower extraction temperatures.

Table 2 Use of enzymes for the extraction of carotenoids from tomato processing by-products. Tomato processing by-product

Enzyme type

Increase of lycopene yield (compared to non-enzymatic treatment)

Reference

Industrial wastes

Cellulase (Celluclast-1.5 L) and Pectinase (Pectinex Ultra SP-L) Cellulase (Citrozym CEO and Citrozym Ultra L) Pectinase (Peclyve EP and Peclyve Li) Enzyme preparation (Mixture 50:50 Pectinase and Cellulase) Combined use of Cellulase (Citrozym CEO) followed by non ionic surfactant- assisted extraction Cellulase “Onozuca R-10” and use of sonication

61% and 45% (under optimized conditions) 18-20× increase of yield with Peclyve EP and Peclyve Li 8-18× increase of yield

Choudhari and Ananthanarayan (2007)

10× increase of yield

Papaioannou and Karabelas (2012) Konwarh et al. (2012)

Cellulase (Cellulyve 50LC) Pectinase (Peclyve LI and Prolyve 1000) Cellulase and pectinase

Multifold increase in the enzyme-mediated extraction of lycopene Hydrolytic enzymes and pH changes result in 20–30-fold increase in lycopene content 5× and 7× increase of yield, respectively

Cellulase (Cellulyve AN 3500) and Pectinase (Pectinex Ultra AFP)

6× and 10× increase of total carotenoid and lycopene yield, respectively

Strati et al. (unpublished data, 2014)

Tomato peels Tomato processing waste (peel fraction) Tomato peels Tomato peels Tomato processing waste (peel fraction) Tomato processing industry waste Tomato processing industry waste

Lavecchia and Zuorro (2008) Zuorro et al. (2011)

Cuccolini et al. (2013) Ranveer et al. (2013)

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6. Extraction at high pressure (HPE) 6.1. Pressurized liquid extraction (PLE) Pressurized liquid (or solvent) extraction (PLE), also referred to as accelerated solvent extraction (ASE), use organic liquid solvents at temperatures from 50 to 200 °C and pressures from 99 to 148 atm to increase the extraction rate of compounds (Dunford, Irmak, & Jonnala, 2010). When 100% water is used as a solvent, PLE is generally called superheated water extraction, subcritical water extraction, pressurized low polarity water extraction or pressurized hot water extraction (Pronyk & Mazza, 2009). The high temperatures affect positively the extraction as explained in 2.4.3. Additionally, the high pressure applied ensures that the solvent is maintained in the liquid state at the applied temperature; it forces the liquid solvent into the pores of the matrix and enhances analyte solubility (Ramos, Kristenson, & Brinkman, 2002; Richter et al., 1996). As the temperature increases, the solvent dielectric constant decreases, consequently lowering the polarity of the solvent (Abboud & Notario, 1999). Thus, temperature could be used to match the solvent polarity to that of the compounds of interest to be recovered (Dunford et al., 2010; Miron, Plaza, Bahrim, Ibanez, & Herrero, 2010). For example, the value of the dielectric constant of water at room temperature is nearly 80; however, at 250 °C it is decreased to about 30. At these conditions, a similar value is obtained with the use of some organic solvents, like ethanol or methanol. The same occurs with the solubility parameter, which decreases, approaching the value obtained for less polar compounds (Adil, Cetin, Yener, & Bayindirli, 2007). Therefore, this environmentally friendly technique can be used for the extraction of non polar compounds, as carotenoids, and replace organic solvents. The use of PLE in the extraction of carotenoids has been investigated in different types of micro and macro algae and the process parameters affecting the extraction (solvent, temperature, pressure, extraction time) were optimized. More specifically, Jaime et al. (2010) studied the extraction of carotenoids from Haematococcus pluvialis microalga with PLE, using hexane and ethanol as extracting solvents. Plaza et al. (2010) has applied PLE with hexane, ethanol, and water, 50–200 °C for 20 min for the recovery of a number of functional compounds, including carotenoids, from algae Himanthalia elongata and microalgae Synechocystis sp. The extracts obtained with ethanol at 100 °C for 20 min contained as main carotenoids β-carotene followed by zeaxanthin. PLE was also usedin order to obtain extracts from the microalga Spirulina platensis and determine their antioxidant activity. Four different solvents (hexane, light petroleum, ethanol and water) were tested in two different extraction temperatures (115 and 170 °C) with extraction times ranging from 9 to 15 min (Herrero, Ibanez, Senorans, & Cifuentes, 2004). Other studies dealt with the optimization of PLE of carotenoids from Chlorella vulgaris (Cha et al., 2010) and Dunaliella salina microalga (Herrero, Jaime, Martin-Alvarez, Cifuentes, & Ibanez, 2006). Additionally, pressurized hot ethanol was used for the extraction of astaxanthin from shrimp waste (Quan & Turner, 2009). The advantages of PLE in comparison with conventional solvent extraction are the short extraction time, the reduced usage of solvents and the higher yields obtained. However, this method is not suitable for thermolabile compounds, as high temperatures can affect their structure and functional activity (Ajila et al., 2011). 6.2. High hydrostatic pressure extraction (HHPE) High hydrostatic pressure processing has been established as a non thermal food processing and preservation technique with reduced effects on nutritional and quality parameters of food compared to the conventional thermal processing. The application of high-pressure processing to the extraction of bioactive ingredients from natural biomaterial is an emergent technique, known as high hydrostatic pressure extraction (HHPE) (Xi et al., 2009). HHPE works at high pressure

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ranging from 100 to 800 MPa or, even more, up to 1000 MPa and low temperatures (usually up to 60 °C) and provides recoveries similar to other techniques (Zhang, Xi, & Wang, 2005). The principal parameters, which affect significantly HHPE and should be optimized, are solvent, pressure, temperature, extraction time, and the number of extraction cycles. The pressure is considered as one of the most important parameters in HHPE and is directly correlated to the solubility of bioactive ingredients (Knorr, 1993; Sanchez-Moreno, Plaza, de Ancos, & Cano, 2004). Under HHPE processes the mass transfer rates of bioactive compounds from the raw material to the solvent are increased, confirming the theory that HHPE can favour the mass transfer phenomena leading to increased mass transfer rates during the extraction processes due to changes in the diffusivity coefficient. Diffusivity coefficient changes can be mainly attributed to pressure induced changes in the plant cell membrane leading to an increased cell membranes permeability thus facilitating permeation of the extraction solvent into the tomato waste cells (Tangwonchai, Ledward, & Ames, 2000). As pressure in HHPE processes is considerably increased, differential pressure between the interior and the exterior of the cell is so high that it could also favour cell wall structure changes. In addition, denaturation of the carotenoidbinding protein induced by pressure could be also involved in the cell wall damage of tomato and, therefore, facilitate the extraction of carotenoids under HP treatment (Sánchez-Moreno, De Ancos, Plaza, Elez-Martínez, & Cano, 2009). This technology has been used successfully for the extraction of many bioactive compounds from plant materials, including carotenoids from tomato processing products. Smelt (1998) has reported that HHPE can affect membranes in vegetable cells and produce disruption of chromoplasts where carotenoids are located, inducing a better release of these compounds. Qiu, Jiang, Wang, and Gao (2006) evidenced an increase in extractable lycopene in tomato puree after processing at 500 MPa, at 20 °C for12 min, which they attributed to the fact that high pressure can rupture the tissue and thereafter favour lycopene release. Under this large differential pressure, the solvent will permeate very fast through the broken membranes into cells, and the mass transfer rate of solute or the rate of dissolution is very large. This leads to shorter processing times with HP extraction compared to conventional and consequently to a more time-effective processing technique. In another study of Xi (2006) the yield of lycopene extracted from tomato paste waste by using HHPE at 500 MPa with 75% ethanol concentration in water (1:6 g/mL solid/liquid ratio, at room temperature) for 1 min was found to be higher than that obtained by 30 min UAE, under the same conditions. Moreover, HHPE can be performed at ambient temperature (25–30 °C), that do not favour degradation of carotenoids, and especially lycopene. Recently, Strati et al. (2014) investigated the use of HHPE in extracting carotenoids, and especially lycopene, from tomato processing waste using a wide range of organic solvents and solvent mixtures and found that HHPE led to higher extraction yields (from 2 to 64% increase depending on the solvent used) compared to conventional solvent extraction process performed at ambient pressure for 30 min. Moreover, it was demonstrated that HHPE can be performed at 700 MPa using lower solvent volume at reduced processing times (10 min) without affecting the extraction yields. The advantages of HHPE compared to other extraction techniques are shorter processing times, lower solvent to feed ratios, and higher extraction yields (depending on the solvent). Additionally, this extraction technique can be operated at room temperature without any heating process, except for the temperature rise resulting from the compression (Sanchez-Moreno et al., 2004). 7. Supercritical fluid extraction (SFE) Supercritical fluid Extraction (SFE) has been described as an environmentally safe technology to recover compounds commonly extracted from natural sources, including plants, food by-products, algae,

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and microalgae, among others. Main advantages of this technique are considered the high selectivity, short times of extraction, increased pollution prevention, and the use of nontoxic organic solvents (Wang & Weller, 2006). SFE is based on selected properties of the fluids, such as density, diffusivity, dielectric constant, and viscosity, and exploits the solvation power of the fluids at pressure and temperature above its critical value, in order to extract or separate components of a sample. Under these conditions, a fluid is between gas and liquid state because the density of a supercritical fluid (SF) is similar to that of liquid and its viscosity is similar to that of a gas. Therefore, the SFs have improved mass transport properties compared to liquid solvents (Herrero, Cifuentes, & Ibanez, 2006). Many compounds can be used as SFs (ethylene, methane, nitrogen, xenon, or fluorocarbons), however, the CO2 has been widely used, especially regarding food or natural products, due to the low critical temperature (31.10 °C) and low critical pressure (73.76 bar), which has advantages in the conservation of thermo labile substances (Machado, Pereira, Nunes, Padilha, & Umsza-Guez, 2013). Supercritical carbon dioxide (SC-CO2) is an attractive alternative to organic solvents because it is non explosive, non toxic, inexpensive and possesses the ability to solubilize lipophilic substances, and can be easily removed from the final products (Sahena et al., 2009). In addition, it is environmentally friendly and “generally recognized as safe” (GRAS) by FDA (U.S. Food and Drug Administration) and EFSA (European Food Safety Authority). Nobre et al. (2012) extracted all-E-lycopene from tomato industrial wastes (mixture of skins and seeds) by supercritical ethane. Supercritical ethane and the near critical mixture of ethane and propane showed to be better solvents than supercritical CO2, leading to a faster extraction and a higher recovery of the carotenoid. Due to its low polarity, CO2 is less effective in extracting highly polar compounds from their matrices. For this reason, the addition of a solubility enhancer, called co-solvent or modifier, can alter the characteristics of the process, and thus favour the extraction of polar compounds. Co-solvents or modifiers include hexane, methanol, ethanol, isopropanol, acetonitrile, and dichloromethane, among others. However, ethanol is recommended as a co-solvent in SFE because of its lower toxicity and miscibility in CO2 (Gil-Chavez et al., 2013). The majority of the research studies in SFE for the recovery of carotenoids have focused on tomato products and industrial tomato by-products, as they constitute a good source of lycopene, and, to a lower extent, of β-carotene. A list of SFE studies and the process parameters concerning the recovery of lycopene from tomato processing by-

products is presented in Table 3. The effect of processing parameters is discussed below. 7.1. Effect of temperature The results reported in Table 3 indicate that increasing the temperature of the extraction by SC–CO2 results in higher yields of lycopene. Extraction temperature varies within a wide range of 55-100 °C; however, a particularly important issue to take into consideration is the isomerization and degradation of lycopene at elevated temperatures. When extracting trans-lycopene from tomato industrial waste using SC–CO2, Nobre et al. (2009) found that the recovery of trans-lycopene increased from 40% to 93% when the extraction temperature was increased from 40 to 60 °C. However, with further increase to 80 °C, the recovery of trans-lycopene decreased. This was attributed to isomerization of trans-lycopene. Similarly, Shi, Khatri, et al. (2009) observed that at extraction temperatures of 80 °C and above, there was a decline in the solubility curve of lycopene in SC–CO2, which was attributed to thermally-induced lycopene degradation. According to Yi, Shi, Xue, Jiang, and Li (2009), although an elevation of extraction temperature would increase lycopene yields, the instability of lycopene at high temperatures would cause the compound to undergo degradation and isomerization. Reverchon and De Marco (2006) suggested that the extraction temperature for thermo labile compounds should be between 35 and 60 °C, which is the vicinity of the critical point of carbon dioxide and still as low as possible to avoid degradation of the compound. 7.2. Effect of pressure and extraction time The effects of pressure on the SC–CO2 extraction of lycopene from plant matrices seem to be similar to the effects of temperature. The majority of the literature that has been surveyed indicates that an increase in the extraction pressure of the supercritical carbon dioxide leads to an increase in the amount of lycopene extracted (Huang et al., 2008; Nobre et al., 2009; Rozzi et al., 2002; Yi et al., 2009). Pressure values ranging between 200 and 450 bar produce optimum results depending on other process parameters, especially the extraction temperature, and/ or the type and features of the product. For lycopene recovery through SC–CO2 the pressure varies between 300 and 400 bar; however, especially 400 bar was set out as the optimum process pressure with extraction temperatures ranging between 40 °C and 100 °C (Huang et al., 2008; Topal et al., 2006; Yi et al., 2009).

Table 3 SFE studies and the process parameters concerning the recovery of lycopene from tomato processing by-products. Tomato processing byproduct

Extraction conditions Pressure (bar)

Flow rate (kg C02/h)

Time/temperature

Particle size

Co-solvent or Modifier

Tomato paste waste Tomato seeds and skins

300 300 344.7

4 4 2.5 mL/min

2 h/55 °C 2 h/65 °C 3.33 h/86 °C

b3 mm b3 mm -

5% ethanol 5% ethanol -

Tomato industrial wastes

300

0.792

80 °C

345 μm

5% ethanol

Tomato waste skins Industrial tomato products Tomato waste skins

400 460 450

2.5 mL/min 2.0 mL/min 3.5 L/min

6.5 h/100 °C n.d./80 °C 0.5 h/62 °C

0.3–0.6 mm 0.5–1.0 mm

14% ethanol

Tomato pomace

400

0.7 L/min

1.8 h/57 °C

-

16% ethanol

Tomato industrial waste

300

0.59 g/min

5 h/60 °C

0.36 mm

-

Tomato waste skins

350

3.5 L/min

n.d./75 °C

1.0 mm

Tomato waste skin Tomato by-product (37:63 w/w skins:seeds)

400 400

1.5 mL/min 2.0–4.0 mL/min

1.5 h/100 °C 2.5 h/90 °C

1.0 mm 1.05 mm

10% ethanol and 10% olive oil -

Recovery (%) or yield (μg/g raw material)

Reference

Lycopene (54%) β-carotene (50%) All-trans lycopene (61.0% or 7.19 μg/g) Lycopene (88%); β-carotene (80%) Lycopene (1.18 mg/g) Lycopene (90.1%) All-trans-lycopene (33%) Lycopene (93% or 0.28 mg/g) All-trans-lycopene (93%) Lycopene (73%)

Baysal et al. (2000)

Lycopene (31.25 μg/g) Lycopene (56%)

Rozzi et al. (2002) Sabio et al. (2003) Topal et al. (2006) Vagi et al. (2007) Kassama et al. (2008) Huang et al. (2008) Nobre et al. (2009) Shi, Yi, et al. (2009) Yi et al. (2009) Machmudah et al. (2012)

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The increase in the recovery of lycopene at higher extraction pressures is mainly due to the increase in the density of SC–CO2 when pressure is increased. At higher densities, the dissolution of a solute into SC–CO2 is enhanced due to greater interaction between the solute and the supercritical fluid (Yi et al., 2009). Some studies have found that while increasing the pressure leads to an increase in the recovery of lycopene, beyond an optimum point further increase in pressure led to a decrease in the yield of lycopene. For example, Rozzi et al. (2002) found that when the extraction temperature and pressure were elevated to 86 °C and 344.7 bar, the lycopene recovery reached a maximum. Further increases in pressure beyond this point led to decrease in lycopene recovery. Similarly, Topal et al. (2006) found that increasing the pressure from 200 to 400 bar resulted in a gradual increase in lycopene recovery, but further increases in pressure from 400 to 500 bar did not improve the recovery. The extraction time ranges between 0.5 and 6.5 h, while it was found that this parameter is strongly related to the type of equipment and the flow rate of CO2. 7.3. Effect of CO2 flow rate Similarly to temperature and pressure, the effect of increasing the flow rate of SC–CO2 leads to higher yields of lycopene. Further increase of the flow rate beyond an optimum point however, leads to lower lycopene yields. Topal et al. (2006) tested SC–CO2 flow rates ranging from 1.5 to 4.5 mL/min and found the highest lycopene yield at a flow rate of 2.5 mL/min, whereas Rozzi et al. (2002) found that as the flow rate was increased from 2.5 to 15 mL/min, the yield of lycopene decreased, with the highest lycopene yield of 61% obtained at 2.5 mL/min and recoveries of less than 8% when flow rates were greater than 10 mL/min. In another study of Nobre et al. (2009) the highest amount of translycopene, 93%, was extracted at a flow rate value of 0.59 g/min. The decrease in the extraction of lycopene yields with an increase in flow rate of SC–CO2 can be attributed to channeling effects. When the SC–CO2 flow rate is increased, it flows through the sample at high velocities and instead of diffusing through the sample matrix, it flows around the sample through channels, thus limiting the contact necessary for extraction of lycopene (Nobre et al., 2009). 7.4. Effect of co-solvent or modifier The use of co-solvents or modifiers has been applied in order to increase the solvent power of SC–CO2. Co-solvents are added to the SC–CO2 stream as it flows into the extraction cell, while modifiers are added directly to the sample or mixed with the sample before extraction occurs. Various optimum values of co-solvent concentration were reported; however, the general opinion is that an increase in the concentration of the co-solvent or modifier increases the yield. Ethanol is the most commonly used co-solvent with its usage rate ranging between 5.0% and 16.0% (w/w). Baysal et al. (2000) compared the supercritical extraction of lycopene from tomato paste waste with ethanol as a co-solvent and found that the best lycopene yields (55% recovery) were obtained using 5% ethanol as co-solvent, as compared to 25% lycopene recovery in the absence of a co-solvent. The effect of the addition of ethanol, water and olive oil as different co-solvents on the yield of lycopene extracted from tomato paste waste was investigated by Shi, Yi, et al. (2009). They found that, for all three co-solvents, the extraction yield of lycopene increased when the co-solvent was increased from 5% (w/w) to 15% (w/w). Under the same conditions and co-solvent levels, the degree to which the co-solvents improved the extraction efficiency of lycopene presented the following order: olive oil N ethanol N water. Using vegetable oils as co-solvents, the lycopene is solubilised in the vegetable oil, which is extracted as well. Such lycopene-enriched-edible oil products can be used in a variety of food and nutraceutical products.

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7.5. Effect of particle size The amount of lycopene obtained by SC–CO2 extraction is also affected by the particle size of the sample. Various sample particle sizes ranging from 0.30-1.0 mm were utilized in the SC–CO2 extraction of lycopene. Similarly to conventional solvent extraction, a smaller sample particle size results in greater extraction of lycopene. This is due to higher surface to volume ratio, resulting in more solute being available for contact and interaction with SC–CO2 (Baysal et al., 2000). While most of the literature reports that reducing the sample particle size results in increased extraction lycopene by SC–CO2, extremely small particle size can have a negative effect on lycopene recovery due to very compact packing of particles in the extraction chamber (Reverchon & De Marco, 2006). 8. Conclusions It can be concluded that the recovery of carotenoids from tomato processing by-products depends on the extraction method applied and its operation parameters, which should be optimized in order to maximize the extraction yield. Among other solvents, ethyl lactate presented very good results and should be further examined, as a potential, environment friendly solvent. UAE seems a promising technique, compared to conventional solvent extraction, while further research to optimize conditions is needed. Pre-treatment with enzymes may improve the extraction yields and could be used, especially when wet raw material is available. HHPE and SFE need high investments; HHPE is efficient at low temperatures and extraction times and can reduce the volumes of solvent, whereas SFE is an environmentally safe technology. Therefore, as many food plants have already installed the relevant equipment, these techniques may be alternative solutions in the near future. References Abboud, J. L. M., & Notario, R. (1999). Critical compilation of scales of solvent parameters. Part I. Pure, non-hydrogen bond donor solvents. Pure and Applied Chemistry, 71(4), 645–718. Adil, I., Cetin, H., Yener, M., & Bayindirli, A. (2007). Subcritical (carbon dioxide + ethanol) extraction of polyphenols from apple and peach pomaces, and determination of the antioxidant activities of the extracts. Journal of Supercritical Fluids, 43(1), 55–63. Aguilera, J. M. (2003). Solid–liquid extraction. In C. Tzia, & G. Liadakis (Eds.), Extraction optimization in food engineering. New York: CRC Press (Chapter 2). Ajila, C. M., Brar, S. K., Verma, M., Tyagi, R. D., Godbout, S., & Valero, J. R. (2011). Extraction and analysis of polyphenols: recent trends. Critical Reviews in Biotechnology, 31(3), 227–249. Al-Wandawi, H., Abdul-Rahman, M., & Al-Shaikhly, K. (1985). Tomato processing wastes as essential raw material sources. Journal of Agricultural and Food Chemistry, 33, 804–807. Ashokkumar, M., & Mason, T. (2007). Sonochemistry. In Kirk-Othmer Encyclopedia of Chemical Technology. New York: John Wiley & Sons. Baysal, T., Ersus, S., & Starmans, D. A. J. (2000). Supercritical CO2 extraction of b-carotene and lycopene from tomato paste waste. Journal of Agricultural and Food Chemistry, 48, 5507–5511. Cadoni, E., De Giorgi, R., Medda, E., & Poma, G. (2009). Supercritical CO2 extraction of lycopene and b carotene from ripe tomatoes. Dyes and Pigments, 44, 27–32. Calvo, M. M., Dado, D., & Santa-Maria, G. (2007). Influence of extraction with ethanol or ethyl acetate on the yield of lycopene, β-carotene, phytoene and phytofluene from tomato peel powder. European Food Research and Technology, 224, 567–571. Cha, K. H., Lee, H. J., Koo, S. Y., Song, D. G., Lee, D. U., & Pan, C. H. (2010). Optimization of pressurized liquid extraction of carotenoids and chlorophylls from chlorella vulgaris. Journal of Agricultural and Food Chemistry, 58(2), 793–797. Chandrapala, J., Oliver, C. M., Kentish, S., & Ashokkumar, M. (2013). Use of power ultrasound to improve extraction and modify phase transitions in food processing. Food Reviews International, 29, 67–91. Choi, S. K., Kim, J. H., Park, Y. S., Kim, Y. J., & Chang, H. I. (2007). An efficient method for the extraction of astaxanthin from the red yeast Xanthophyllomyces dendrorhous. Journal of Microbiology and Biotechnology, 17(5), 847–852. Choudhari, S. M., & Ananthanarayan, L. (2007). Enzyme aided extraction of lycopene from tomato tissues. Food Chemistry, 102, 77–81. Cuccolini, S., Aldini, A., Visai, L., Daglia, M., & Ferrari, D. (2013). Environmentally friendly lycopene purification from tomato peel waste: enzymatic assisted aqueous extraction. Journal of Agricultural and Food Chemistry, 61, 1646–1651. Dunford, N., Irmak, S., & Jonnala, R. (2010). Pressurized solvent extraction of policosanol from wheat straw, germ and bran. Food Chemistry, 119(3), 1246–1249. Eh, A. L. -S., & Teoh, S. -G. (2012). Novel modified ultrasonication technique for the extraction of lycopene from tomatoes. Ultrasonics Sonochemistry, 19, 151–159.

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