Food waste: a potential bioresource for extraction of nutraceuticals and bioactive compounds

Abstract

Food waste, a by-product of various industrial, agricultural, household and other food sector activities, is rising continuously due to increase in such activities. Various studies have indicated that different kind of food wastes obtained from fruits, vegetables, cereal and other food processing industries can be used as potential source of bioactive compounds and nutraceuticals which has significant application in treating various ailments. Different secondary metabolites, minerals and vitamins have been extracted from food waste, using various extraction approaches. In the next few years these approaches could provide an innovative approach to increase the production of specific compounds for use as nutraceuticals or as ingredients in the design of functional foods. In this review a comprehensive study of various techniques for extraction of bioactive components citing successful research work have been discussed. Further, their efficient utilization in development of nutraceutical products, health benefits, bioprocess development and value addition of food waste resources has also been discussed.

Background

Food waste is produced in all the phases of food life cycle, i.e. during agricultural production, industrial manufacturing, processing and distribution. Up to 42% of food waste is produced by household activities, 39% losses occurring in the food manufacturing industry and 14% in food service sector (ready to eat food, catering and restaurants), while 5% is lost during distribution. Food waste is expected to rise to about 126 Mt by 2020, if any prevention policy or activities are not undertaken (Mirabella et al. 2014). It can be achieved through the extraction of high-value components such as proteins, polysaccharides, fibres, flavour compounds, and phytochemicals, which can be re-used as nutraceuticals and functional ingredients (Baiano 2014).

Attempts have been made broadly for the past few decades to develop methods and find different ways to utilise fruit and vegetable wastes therapeutically. Generally, agro-industrial wastes have been used extensively as animal feeds or fertilisers. Recent reports shows development of high value products (such as cosmetics, foods and medicines) from agro-industrial by-products (Rudra et al. 2015).

Natural bioactive compounds are being searched for the treatment and prevention of human diseases. These compounds efficiently interact with proteins, DNA, and other biological molecules to produce desired results, which can then be used for designing natural therapeutic agents (Ajikumar et al. 2008). There is growing interest of consumers towards food bioactives that provide beneficial effects to humans in terms of health promotion and disease risk reduction. Detailed information about food bioactives is required in order to obtain appropriate functional food products (Kumar 2015).

Nutraceuticals are medicinal foods that play a role in enhancing health, maintaining well being, improving immunity and thereby preventing as well as treating specific diseases. Phytochemicals have specific role and can be used in different forms, e.g. as antioxidants and have a positive effect on human health. Recently, lot of attention has been given to phytochemicals that possess cancer preventive properties (Kumar and Kumar 2015). Nowadays, there is growing trend in the food industry toward the development and manufacture of functional and nutraceutical products. This new class of food products have got huge attention in food market due to the increased consumer interest for “healthy” food. Hence, pharmaceutical and food domains have common interest to obtain new natural bioactive components which can be used as drugs, functional food ingredients, or nutraceuticals (Joana Gil-Chávez et al. 2013). Bioactives from food waste can be extracted and utilized for development of nutraceuticals and functional foods. This review describes the utilization of different extraction techniques for extraction of bioactives and nutraceuticals from food waste and their uses in prevention of chronic and lifestyle diseases.

Food waste as a source of bioactive compounds

Bioactive compounds comprise an excellent pool of molecules for the production of nutraceuticals, functional foods, and food additives (Joana Gil-Chávez et al. 2013). Fruits and vegetables represent the simplest form of functional foods because they are rich in several bioactive components. Fruits containing polyphenols and carotenoids have been shown to have antioxidant activity and diminish the risk of developing certain types of cancer (Day et al. 2009). The vegetable waste includes trimmings, peelings, stems, seeds, shells, bran and residues remaining after extraction of juice, oil, starch and sugar. The animal-derived waste includes waste from dairy processing and seafood industry. The recovered biomolecules and by-products can be used to produce functional foods in food processing or in medicinal and pharmaceutical preparations (Baiano 2014). Bioactive phytochemicals like sterols, tocopherols, carotenes, terpenes and polyphenols extracted from tomato by-products contain significant amounts of antioxidant activities. Therefore, these value adding components isolated from such waste can be used as natural antioxidants for the formulation of functional foods or can serve as additives in food products to extend their shelf-life (Kalogeropoulos et al. 2012).

The bioactive compounds present in mango peel are phenolic compounds, carotenoids, vitamin C and dietary fibre. It has been well recognized that these compounds contribute to lower the risk of cancer, cataracts, Alzheimer’s disease and Parkinson’s disease (Ayala-Zavala et al. 2010). Wastes from wine making industry include biodegradable solids namely stems, skins, and seeds. Bioactive compounds from winery by-products have been shown to improve health promoting activities both in vitro and in vivo. These compounds act as effective agents for prevention of degenerative processes through their incorporation into functional foods, nutraceuticals, and cosmetics (Teixeira et al. 2014). These are commonly utilized for the production of pharmaceuticals and as food additives to increase the functionality of foods (Ayala-Zavala et al. 2010). Citrus is the most abundant fruit crop in the world. Its one-third of the crop is processed. Oranges, lemons, grapefruits and mandarins represent approximately 98% of the entire industrialized crop. Citrus fruits are processed, not only to obtain juice, but also, in the canning industry to produce jam and segments of mandarin.

Lemes et al. (2016) reported bioactive peptides as the new generation of biologically active regulators that can prevent oxidation and microbial degradation in foods, and might be helpful in treatment of various diseases. These can be extracted from residual waste and incorporated into value added products. Their encapsulated form may be utilized in a controlled manner for efficient use in human body. Development of suitable techniques for large-scale recovery and purification of peptides will increase their applications in pharmaceutical and food industries.

Pujol et al. (2013) investigated the chemical composition of exhausted coffee waste generated in a soluble coffee industry and found that total polyphenols and tannins represent <6 and <4% of the exhausted coffee wastes, respectively. Zuorro and Lavecchia (2012) extracted total phenolic content of 17.75 mg gallic acid equivalent GAE (gallic acid equivalents)/g from spent coffee grounds (SCG) collected from coffee bars and 21.56 mg GAE/g from coffee capsules unloaded from an automatic espresso machine. Mussatto et al. (2011) optimised the extraction of antioxidant phenolic compounds from SCG and found that extraction using 60% methanol in a solvent/solid ratio of 40 ml/g SCG, for 90 min, was the most appropriate condition to produce an extract with 16 mg GAE/g SCG of phenolic compounds having high antioxidant activity, i.e. Ferric reducing antioxidant power (FRAP) of 0.10 mM Fe(II)/g). Rebecca et al. (2014) extracted the amount of caffeine from used tea leaves of black, white, green and red tea using dichloromethane as solvent and found that caffeine content was maximum (60 mg/100 g) in green tea and minimum in red tea (3 mg/100 g). Some of the bioactive components found in different food waste residues are summarized in Table 1.

Table 1 Bioactive components in different industrial food waste residues

Extraction technologies for bioactive compounds from food waste

Bioactive components present in agro-industrial waste can be recovered using various techniques. Availability of these techniques provides an opportunity for optimal use of any of these for recovery of specific compounds. Based on literature survey, the extraction techniques for bioactive compounds are mainly based on solvent extraction (SE), supercritical fluid extraction (SFE), subcritical water extraction (SCW), use of enzymes, ultrasounds and microwaves. In the following sections, these techniques have been discussed independently in reference to recent studies.

Solvent extraction technique

In this extraction approach, the suitably sized raw material is exposed to different organic solvents, which takes up soluble components of interest and also other flavouring and colouring agents such as anthocyanins which are anti-cancerous and anti-inflammatory (Vyas et al. 2009, 2014) (Fig. 1). Samples are usually centrifuged and filtered to remove solid residue, and the extract could be used as additive, food supplement or for the preparation of functional foods (Zulkifli et al. 2012). Solvent Extraction is beneficial compared to other methods due to low processing cost and ease of operation. However, this method uses toxic solvents, requires an evaporation/concentration step for recovery, and usually calls for large amounts of solvent and extended time to be carried out. Moreover, the possibility of thermal degradation of natural bioactive components cannot be ignored due to the high temperatures of the solvents during the long times of extraction. Solvent extraction has been improved by other methods such as Soxhlet’s, ultrasound, or microwave extraction and SFE in order to obtain better yields (Szentmihályi et al. 2002).

Fig. 1

A schematic representation of different techniques for extraction of bioactive compounds from food wastes and their health benefits

Baysal et al. (2000) utilized ethanol for extraction of Lycopene and β-carotene from tomato pomace containing dried and crushed skins (rich in lycopene and carotenes) and seeds of the fruit along with supercritical CO₂ for resulting in recoveries of up to 50%. Gan and Latiff (2011) studied the extraction of polyphenolic compounds from Parkia speciosa pod powders using 50% acetone solution. They concluded that that 50% acetone yielded the highest content of polyphenols compared to methanol, ethanol, ethyl-acetate and hexane. Safdar et al. (2016) extracted and quantified polyphenols from kinnow (Citrus reticulate L.) peel. Maximum polyphenols were extracted with 80% methanol (32.48 mg GAE/g extract) using ultrasound assisted extraction, whereas, minimum phenolics (8.64 mg GAE/g extract) were obtained with 80% ethyl acetate through the maceration technique.

Bandar et al. (2013) found that out of the various organic solvents used in their study, ethanol was the most efficient one, producing the highest extraction yield and hexane gave the lowest yield in extracting bioactive compounds by these methods. Further they found that there was an increase in the yield of extracted compounds with increasing extraction time.

Supercritical fluid extraction

Supercritical fluid extraction is an environment friendly technology and is commonly used for extraction of bioactive compounds from natural sources such as plants, food by-products, algae and microalgae. Supercritical carbon dioxide (SC-CO₂) is an attractive alternative to organic solvents as it is non explosive, non-toxic and inexpensive. It possesses the ability to solubilise lipophilic substances, and can be removed easily from the final products (Wang and Weller 2006).

During the process of extraction, raw material is placed in an extraction container equipped with temperature and pressure controllers to maintain the required conditions. Following this, the extraction container is pressurized with the fluid by a pump. Once the fluid and dissolved compounds are transported to separators, the products are collected through a tap located in the lower part of the separators. Finally, the fluid is regenerated and cycled or released to the environment. Selection of supercritical fluids is very important for proper functioning of this process and a wide range of compounds can be used as solvents in this technique (Sihvonen et al. 1999).

Giannuzzo et al. (2003) found that SC-CO₂ modified with ethanol gave higher extraction yields of naringin (flavonoid) from citrus waste than pure SC-CO₂ at 9.5 MPa and 58.6 °C. Ashraf-Khorassani and Taylor (2004) extracted polyphenols and procyanidins from grape seeds using SFE, where, methanol was used as modifier and methanol modified CO₂ (40%) released more than 79% of catechin and epicatechin from grape seed. Liza et al. (2010) studied the feasibility of the SFE method to extract lipophilic compounds such as tocopherols, phytosterols, policosanols and free fatty acids from sorghum and the preventive role of these compounds in many diseases (skin, cardiovascular, coronary heart diseases, and cancer).

Farías-Campomanes et al. (2015) extracted polyphenols (gallic, protocatechuic, vanillic, syringic, ferulic derivatives and p-coumaric derivatives) and flavonoids (quercetin and its derivatives) from Lees generated from pisco-making process with SFE at 20 MPa and 313 K. Jung et al. (2012) carried out extraction of oil from wheat bran which is a rich source of antioxidants using SC-CO₂ and Soxhlet extraction. Pressure and temperature ranged from 10 to 30 MPa and 313.15–333.15 K, respectively during SC-CO₂ extraction. It was observed that oil obtained by SC-CO₂ extraction had higher resistance against oxidation and higher radical scavenging activity compared to hexane extracted oil. Wenzel et al. (2016) extracted phenolic compounds from black walnut (Juglans nigra) husks using SC-CO₂ with an ethanol modifier. The optimal extraction conditions were 68 °C and 20% ethanol in SC-CO₂.

Ahmadian-Kouchaksaraie and Niazmand (2017) used the SC-CO₂ for the extraction of antioxiant compounds from Crocus sativus petals at 62 °C for 47 min and 164 bar pressure. Extraction using these optimized conditions resulted in recovery of 1423 mg/100 g total phenolics, 180 mg/100 g total flavonoid and 103.4 mg/100 g total anthocyanin content. Wang and Weller (2006) described supercritical method as a significant substitute to conventional extraction methods using organic solvents for extracting biologically active compounds.

Some of the conditions used for the extraction, recovery and characterization of bioactive compounds from food and plants using SC-CO₂ are summarized in Table 2.

Table 2 Extraction, recovery and characterization of bioactive compounds using supercritical fluid extraction

Subcritical water extraction

Subcritical water extraction is a growing alternative technology for extraction of phenolic compounds from different foods. Subcritical water refers to water at temperature between 100 and 374 °C and a pressure which is high enough to maintain the liquid state (below the critical pressure of 22 MPa). Main advantages of SCW over conventional extraction techniques are shorter extraction time, lower solvent cost, higher quality of the extraction and environment-friendly (Herrero et al. 2006). SCW is the most promising engineering approach that offers an environmentally friendly technique for extracting various compounds from plants and algae (Zakaria and Kamal 2016).

Tunchaiyaphum et al. (2013) extracted phenolic compounds from mango peels using SCW. The amount of phenolic compounds from mango peels using SCW extraction was higher than that using Soxhlet extraction technique. Therefore, SCW extraction is an alternative green technology for phenolic compounds extraction from agricultural wastes, which substitute conventional method using organic solvents.

Rangsriwong et al. (2009) studied the use of SCW for extraction of polyphenolic compounds from Terminalia chebula Retz. fruits and it was found that the amounts of extracted gallic acid and ellagic acid increased with an increasing in subcritical water temperature up to 180 °C, while the highest amount of corilagin was recovered at 120 °C. Kim et al. (2010) extracted mangiferin, a pharmacological active component from Mahkota Dewa using subcritical water extractiont at temperatures range of 323–423 K and pressures 0.7–4.0 MPa with extraction times ranging from 1 to 7 h.

Singh and Saldaña (2011) extracted eight phenolic compounds (gallic acid, chlorogenic acid, caffeic acid, protocatechuic acid, syringic acid, p-hydroxyl benzoic acid, ferulic acid, and coumaric acid) from potato peel using subcritical water. Phenolic compounds were recovered highest (81.83 mg/100 g fresh wt.) at 180 °C and extraction time of 30 min. Chlorogenic acid (14.59 mg/100 g) and gallic acid (29.56 mg/100 g) were the main phenolic compounds obtained from potato peel at 180 °C. It was concluded that subcritical water at 160–180 °C, 6 MPa and 60 min might be a good substitute to organic solvents (such as methanol and ethanol) to obtain phenolic compounds from potato peel.

Ahmadian-Kouchaksaraie et al. (2016) investigated subcritical water extraction as a green technology for the extraction of phenolic compounds from Crocus sativus petals. The optimum conditions of extraction were of 36 ml/g (water to solid ratio) 159 °C temperature and an extraction time of 54 min. Subcritical water extraction using these optimized conditions leads to extraction of 1616 mg/100 g total phenolics, 239 mg/100 g total flavonol content and 86.05% 2,2-diphenyl-1-picrylhydrazyl (DPPH).

Ko et al. (2016) enhanced production of individual phenolic compounds by subcritical water hydrolysis in pumpkin leaves by varying temperatures from 100 to 220 °C at 20 min and also by varying reaction times from 10 to 50 min at 160 °C. Caffeic acid, p-coumaric acid, ferulic acid, and gentisic acid were the major phenolic compounds in the hydrolysate of pumpkin leaves. Mayanga-Torres et al. (2017) utilized two abundant coffee waste residues (powder and defatted cake) for extraction of total phenolic compounds using subcritical water under semi-continuous flow conditions. The highest total phenolic compounds (26.64 mg GAE/g coffee powder) was recovered at 200 °C and 22.5 MPa.

There are number of advantages of SCW extraction over traditional extraction techniques used, such as higher quality of the extracts, lower extraction times, lower costs of the extracting agent, and an environment friendly technique (Joana Gil-Chávez et al. 2013).

Enzyme assisted extraction

There is wide use of enzymes for extraction of bioactive components from food wastes. The main sources for extraction of antioxidants are plant tissues. Plant cell walls contain polysaccharides such as cellulose, hemicellulose, and pectins which act as barriers to the release of intracellular substances. Enzymes such as cellulase, β-glucosidase, xylanase, β-gluconase, and pectinase help to degrade cell wall structure and depolymerize plant cell wall polysaccharides, facilitating the release of linked compounds (Moore et al. 2006; Singh et al. 2016). Because of using water as a solvent instead of organic chemicals, the enzyme assisted extraction is recognized as more eco-friendly technology for extraction of bioactive compounds and oil (Puri et al. 2012).

Zuorro et al. (2011) studied the enzyme-assisted extraction of lycopene from the peel fraction of tomato processing waste and found that the recovery of lycopene could be greatly improved by the use of mixed enzyme preparations with cellulolytic and pectinolytic activities, and the comparatively low cost of commercial food-grade enzyme preparations, having possible implementation on industrial scale. Puri et al. (2012) studied the enzyme-assisted extraction of bioactive compounds stevioside from Stevia rebaudiana from plant sources particularly for food and nutraceutical purposes. Reshmitha et al. (2017) prepared lycopene rich extracts by enzyme assisted extraction of tomato peel using cellulase (20 units/g) and pectinase (30 units/g) at 50 °C for 60 min.

These studies suggested that the release of bioactive compounds from plant cells by cell disruption and extraction can be optimized using enzyme preparations either alone or in mixtures. Enzyme-assisted extraction is a promising alternative to conventional solvent-based extraction methods. It is based on the ability of enzymes to catalyze reactions, under mild processing conditions, in aqueous solutions (Gardossi et al. 2010).

Extraction using ultrasounds

Ultrasound-assisted extraction is considered as a simpler and more effective technique compared to traditional extraction methods for the extraction of bioactive compounds from natural products. Ultrasound induces a greater diffusion of solvent into cellular materials, thus improving mass transfer and also disrupts cell walls, thus facilitating the release of bioactive components. Extraction yield is greatly influenced by ultrasound frequency, depending on the nature of the plant material to be extracted (Wang et al. 2008).

Wang et al. (2011) used ultrasound-assisted extraction to extract three dibenzylbutyrolactone lignans (including tracheloside, hemislienoside, and arctiin) from Hemistepta lyrata. High-performance liquid chromatography was used for simultaneous determination of the target compounds in the corresponding extracts.

Rostagno et al. (2003) studied extraction efficiency of four isoflavone derivatives, i.e. glycitin, daidzin, genistin, and malonyl genistin from soybean with mix-stirring method using different extraction times and solvents. Use of ultrasound was found to improve the extraction yield depending on solvent use. Ghafoor et al. (2011) extracted anthocyanins and phenolic compounds from grape peel using ultrasound-assisted extraction technique. Bimakr et al. (2013) also applied the ultrasound-assisted extraction technique for the extraction of bioactive valuable compounds from winter melon (Benincasa hispida) seeds.

Piñeiro et al. (2016) optimised and validated ultrasound-assisted extraction for rapid extraction of stilbenes from grape canes. By this method, stilbenes in grape canes was extracted 10 min only using extraction temperature of 75 °C and ethanol (60%) as the extraction solvent. It was concluded that grape cane by-products were potential sources of bioactive compounds of interest for pharmaceutical and food industries.

Aguiló-Aguayo et al. (2017) studied the effect of ultrasound technology in extract of water soluble polysaccharides from dried and milled by-products generated from Agaricus bisporus. β-Glucan were obtained in amounts of 1.01 and 0.98 g/100 g dry mass in particle sizes of 355–250 and 150–125 μm, respectively, from the mushroom by-products. The highest extraction yield of 4.7% was achieved with an extraction time of 15 min, amplitude of 100 μm with 1 h of precipitation in 80% ethanol.

Microwave assisted extraction

Microwave-assisted extraction (MAE) is a new extraction technique that combines microwave and traditional solvent extraction. It is an advantageous technique due to shorter extraction time, higher extraction rate, less requirement of solvent and lower cost over traditional method of extraction of compounds (Delazar et al. 2012). The main advantage of MAE over ultrasonic assisted extraction and Soxhlet extraction is that, it can be used to extract plant metabolites at a shorter time interval (Afoakwah et al. 2012). Padmapriya et al. (2012) extracted mangiferin present in Curcuma amada with the help of MAE using ethanol as a solvent. The mangiferin content was reportedly increased until 500 W, but decreased as the microwave power was increased further. An optimal mangiferin yield of 41 μg/ml was obtained from an extraction time of 15.32 s for a microwave power of 500 W. Kerem et al. (2005) extracted saponins from chickpea (Cicer arietinum) using MAE and found this method superior over Soxhlet extraction with regard to amounts of solvents required, time and energy expended. The pure chickpea saponin exhibited significant inhibitory activity against Penicillium digitatum and additional filamentous fungi (Fig. 1).

Kulkarni and Rathod (2016) extracted mangiferin from the Mangifera indica leaves by microwave assisted extraction conditions using water as a solvent. The maximum extraction yield of 55 mg/g was obtained at extraction time 5 min, solid to solvent ratio 1:20 and microwave power of 272 W. In comparison to the sequential batch extraction and Soxhlet extraction, MAE increased the yield of extraction in a short span of time and also reduced the solvent requirement as compared to the conventional methods.

Smiderle et al. (2017) studied MAE and pressurized liquid extraction (PLE) as advanced techniques to obtain polysaccharides (particularly biologically active β-glucans) from Pleurotus ostreatus and Ganoderma lucidum fruiting bodies and detected β- and α-glucans and heteropolysaccharides in all extracts. In an interesting study, Filip et al. (2017) optimized MAE by response surface methodology in order to enhance the extraction of polyphenols from basil (Ocimum basilicum L). Optimal conditions for extraction were 50% ethanol, microwave power of 442 W, and an extraction time of 15 min. Under these conditions, obtained basil liquid extract contained 4.299 g GAE/100 g of total polyphenols and 0.849 g catechin equivalents/100 g DW of total flavonoids.

Therefore, it can be concluded that microwave assisted method has many advantages compared with other methods due to its higher extraction efficiency, reduced extraction time, less labor and high extraction selectivity which makes it a favourable method in extraction of bioactive compounds (Bandar et al. 2013).

Comparative evaluation of different extraction technologies for recovery of bioactive compounds

Zhang et al. (2005), compared a number of extraction methods for the recovery of alkaloids from fruit of Macleaya cordata (Willd) R. Br. The techniques used include maceration, ultrasound-assisted extraction (UAE), MAE and percolation. The method of MAE was found to be the most effective method capable of yielding 17.10 ± 0.4 mg/g sanguinarine and 7.04 ± 0.14 mg/g chelerythrine with 5 min of extraction time. They further concluded that the alkaloid content of the fruit shell was much greater than that of seed.

Corrales et al. (2008) extracted bioactive substances from grape by-products such as anthocyanins which can be used as natural antioxidants or colouring agents. They studied the effect of heat treatment at 70 °C combined with the effect of different novel technologies such as high hydrostatic pressure (600 MPa) (HHP), ultrasonics (35 kHz) and pulsed electric fields (3 kV cm⁻¹) (PEF). After 1 h extraction, the total phenolic content of samples subjected to novel technologies was 50% higher than in the control samples. They further concluded that the application of novel technologies increased the antioxidant activity of the extracts with PEF fourfold, with HHP three-fold and with ultrasonics two-fold higher than the control extraction carried out in a water bath incubated at a temperature of 70 °C for 1 h.

Plaza et al. (2011) studied the effect of different extraction technologies on extraction of bioactive compounds of orange juice. Juice was treated by high pressure (HP) (400 MPa/40 °C/1 min), pulsed electric fields (PEF) (35 kV cm¹/750 ms) and low pasteurization (LPT) (70 ℃/30 s). They extracted various bioactive compounds such as lutein, zeaxantin, α and β-cryptoxanthin, α and β-carotene, naringenin and hesperetin from grape juice. It was concluded that HPT was the most effective treatment for extraction of bioactive components from orange juice with highest recovery of bioactive components from orange juice followed by PEF and LPT.

Drosou et al. (2015) compared the extraction yield of air dried Agiorgitico red grape pomace by-products by three different extraction methods using water, water: ethanol (1:1) and ethanol as solvents. The methods included the conventional Soxhlet extraction, MAE and ultrasound assisted extraction (UAE). They concluded that UAE water: ethanol extracts were found to be rich in phenolic compounds (up to 438,984 ppm GAE in dry extract).

Jayathunge et al. (2017), investigated the influence of moderate intensity pulsed electric field pre-processing on increasing the lycopene bioaccessibility of tomato fruit, and the combined effect of blanching, ultrasonic and high intensity pulsed electric field processing on further enhancement of the lycopene bioaccessibility after juicing. They concluded that only the treatment of blanching followed by high intensity pulsed electric field showed a significant release of trans-(4.01 ± 0.48) and cis-(5.04 ± 0.26 lg/g) Lycopene. They further concluded that processing of pre-blanched juice using high intensity pulsed electric field, derived from pre-processed tomato was the most excellent approach to achieve the highest nutritive value.

Kehili et al. (2017) extracted lycopene and carotene as oleoresin from a Tunisian industrial tomato peels by-product using supercritical CO₂ and solvent extraction using hexane, ethyl acetate and ethanol. Supercritical CO₂ extraction resulted in a lycopene extraction of 728.98 mg/kg of dry tomato peels under processing conditions of 400 bar, 80 °C and 4 g CO₂/min for 105 min. Solvent extraction of lycopene using overnight maceration with hexane, ethyl acetate and ethanol yielded 608.94 ± 10.05 mg/kg, 320.35 and 284.53 mg/kg of dry tomato peels, respectively. They further concluded that SC-CO₂ extraction method resulted in a higher lycopene production as compared to solvent extraction under the above mentioned processing conditions.

Espinosa-Pardo et al. (2017) extracted total phenolic contents (TPC) from the pomace generated in the industrial processing of orange (Citrus sinensis) juice in Brazil by SFE method. Process was carried out at pressures of 15, 25 and 35 MPa and temperatures of 40, 50 and 60°C, using pure ethanol and ethanol: water (9:1 v/v) as co-solvents. They observed that high pressures improved the recovery of TPC (18–21.8 mg GAE/g dry extract) from pomace. They further observed that the use of ethanol 90% as co-solvent enhanced the extraction of antioxidant compounds. Finally, it was concluded that biotransformation process improved the TPC and provided extracts with higher antioxidant activities.

Some of the methods, optimum conditions and yield of some bioactive compounds from different food wastes are summarized in Table 3.

Table 3 Comparative evaluation of different extraction techniques for extraction of bioactive compounds

Use of bioactive compounds as nutraceuticals and functional foods for human health

Being health related compounds, bioactive compounds are known to lower the risk of developing various diseases like cancer, alzheimer, cataracts and parkinson, among others. These beneficial effects have been attributed mainly to their antioxidant and radical scavenging activities which can delay or inhibit the oxidation of DNA, proteins and lipids. Indeed, these compounds have also shown antimicrobial effects, playing an important role in fruits’ protection against pathogenic agents, penetrating the cell membrane of microorganisms, causing lysis (Ayala-Zavala and González-Aguilar 2011).

An imbalance between the production of reactive oxygen species (ROS), and their eradication by defensive mechanisms in our body creates oxidative stress. Antioxidant systems of our body detoxify the reactive intermediates and results in reduction of oxidative stress (Al-Dalaen and Al-Qtaitat 2014). ROS can be divided into free radicals and non-radicals. Molecules containing one or more unpaired electrons are called free radicals whereas non-radical forms are created when two free radicals share their unpaired electrons. The three major ROS of physiological importance are superoxide anion (O₂ ⁻.), hydroxyl radical (.OH), and hydrogen peroxide (H₂O₂) (Birben et al. 2012). There should be interaction between free radicals, antioxidants and co-factors for maintaining health and prevention from aging and age-related diseases. Oxidative stress caused by free radicals is balanced by the endogenous antioxidant systems of our body which get strengthened by the intake of exogenous antioxidants with an input from co-factors. Production of free radicals in excess of the defensive effects of antioxidants and some co-factors causes oxidative damage which gets accumulated during life cycle resulting in aging, and chronic diseases such as cancer, cardiovascular diseases, neurodegenerative disorders, and other life style diseases (Rahman 2007).

Free radicals generated in the body during normal metabolic functions affect the vital cellular structures and functions resulting in various degenerative diseases. These free radicals are deactivated by antioxidant enzymes that catalyze oxidation/reduction reactions and serve as redox biomarkers in various human diseases along with controlling the redox state of functional proteins. Redox regulators with antioxidant properties related to active intermediates, cell organelles, and the neighbouring environments are involved in diseases related to redox imbalance including neurodegenerative diseases, aging cancer, ischemia/reperfusion injury and other lifestyle diseases (Yang and Lee 2015).

Nutraceuticals are usually consumed in pharmaceutical preparations such as pills, capsules, tablets, powder, and vials (Espín et al. 2007). Núñez Selles et al. (2016) reportred that Mangiferin (1,3,6,7-tetrahydroxyxanthone-C2-β-d-glucoside), a natural bioactive xanthonoid found in many plant species such as mango tree (Mangifera indica L) has attracted the attention of research groups around the World for cancer treatment. Single administration of mangiferin or in combination with known anticancer chemicals has shown the potential benefits of this molecule in brain, lung, cervix, breast and prostate cancers, and leukemia besides its antioxidant and anti-inflammatory properties.

Meat industry by-products such as brains, nervous systems and spinal cords are a source of cholesterol, which after extraction are used for the synthesis of vitamin D3 (Ejike and Emmanuel 2009). Chávez-Santoscoy et al. (2016) studied the the health promoting benefits of flavonoids and saponins from black bean seed coats. The effect of adding flavonoids and saponins from black bean seed coat to whole wheat bread formulation was resulted in retention of more than 90% of added flavonoids and saponins, and 80% of anthocyanins in bread after baking. Use of such breads rich in these health promoting compounds might have significant health consequences.

In the production of rolled oats, phenolic compounds derived from natural sources such as benzoin, catechin, chlorogenic acid, and ferulic acid, mixed with the other ingredients prior to extrusion might obtain products more resistant to oxidation (retardation of hexanal formation). Although processing resulted in a 24–26% reduction of the amount of the phenolic compounds added (Viscidi et al. 2004). Lozano-Sánchez et al. (2017) reported that olive by-product, so called “pâté,” generated during a modern two-phase centrifugal processing technique can be used as a natural source of bioactive compounds. It was characterized by the presence of hydroxytyrosol, β-hydroxyverbascoside, oleoside derivative, luteolin etc., as potential ingredients for nutraceuticals preparations or feed industry.

Conclusion and future prospects

As an indication, various reports of diverse array of bioactive compounds from specific food residues and availability of highly sensitive measurement tools provide a great opportunity to quantify metabolites in different range of food waste materials. Based on higher quantity of specific bioactive components, a food waste by-product could be utilized for its extraction using any of approaches discussed above. Utility of extraction methods is evident based on various reports and supercritical fluid extraction technology was proved to be very useful. A suitable extraction method could be adopted based on outcome of optimization process. Development of a bioprocess with better efficiency of bioactive component recovery will not only add value to the food waste but also be useful in reducing cost of formulated products and decreasing the use of synthetic chemicals in such formulations. With increasing setup of food processing industries and post harvest losses of fruits and vegetables, the increasing amount of food and agriculture waste is available and its utilization as a source of bioactive compounds will increase the financial status of farmers and decrease the burden of waste management. Improvement in extraction technology with lesser or no use of solvent will be of great significance towards a sustainable bioprocess.

Moreover, in India, the discarded portion of industrial waste is very high and it creates a serious waste disposal problem. Organic wastes generated from industries are hazardous to the environment and can be used as a potential bioresource for extraction of bioactive components. The present review ascertains how the use of different technologies can result into the extraction of bioactive compounds which can be used as nutraceuticals and dietary supplements. The replacement of environmentally troublesome organic solvents in such extraction techniques, with green and safe solvents such as CO₂, ethanol, and water is the main objective of this review. Steps should be taken to help build a more rational use of our natural resources. A detailed economic analysis of these extraction techniques will help setting up commercial units, thereby establishing a commercial use for such residues. This will help in complete utilization of the industrial waste thereby providing extra compensation to the industries by sale of residues and will also help in eradicating environmental pollution caused by the poor dumping of industrial food waste.