Novel application and industrial exploitation of winery by-products

Natural food additives

Fractions of grape by-products into food beverages have already been evaluated, as the use of grape pomace extracts as natural antioxidants, preservatives, color stabilizers and texturizers in meat products by Beres et al. (2017). Over decades, synthetic compounds such as butylated hydroxyanizole (BHA), butylated hydroxytoluene (BHT), propyl gallate (PG) and tertiary-butyl hydroquinone (TBHQ) have been widely used as phenolic antioxidant additives and food preservatives in food sector (Ramis-Ramos 2003).

However, they have been broadly studied at high doses for potential toxicities including hazard for carcinogenicity and genotoxicity. BHA acted as a tumor promoter on the rat gastric squamous epithelium and induced hyperplasia only at high doses (Williams et al. 1990), whereas BHT could be an enhancer of thyroid carcinogenesis and rat liver hyperplasia under specific conditions (Ito et al. 1985; Inai et al. 1988). Although the concern about the possible actions from chronic exposure, FDA (Food and Drugs Administration) concludes that there are no available data that BHA demonstrates a hazard to health from exposure at current levels. However, Japan is a country that has no longer allowed the use of synthetic antioxidants BHA and TBHQ in food industry.

Over the recent years and under these circumstances, interest in the substitution of the synthetic food additives by natural ones has increased. Wine-making products could offer an alternative source of natural antioxidants in the food industry and a wide range of natural additives such as tartaric acid and enocyanine (E163). Natural tartaric acid is used as a natural preservative, as an emulsifier in the bread making industry, as an acidifier in the wine making industry and as an ingredient to enrich biscuits, sweets, jams, jellies chewing gum, cocoa powder, and alcoholic drinks (Jim and Hong-Shum 2003). Enocyanine, known as E163 in the food sector, is also a natural pigment derived from the anthocyanins in grape skin. Nowadays, EFSA (European Food Safety Authority) allows the use of anthocyanins as food dyes in drinks, marmalades, candies, ice creams and pharmaceutical product. Recently, Marchiani et al. (2016) evaluate the use of grape pomace antioxidants, before or after distillation, as ingredient in cheese-making process. This study demonstrated that grape pomace powder can be a functional ingredient and be a new approach to achieve a functional cheese.

Furthermore, research on utilization of dietary fiber from grape pomace has been conducted as a potential functional ingredient seafood (Sánchez-Alonso et al. 2007a, b) to reduce rancidity on ice storage, as alternative fining agents for red wines to remove red wine tannins and in dairy products to increase the dietary fiber (Guerrero et al. 2013), as total phenolic content and to delay lipid oxidation in yoghurt and salad dressings (Tseng and Zhao 2013a, b) or in bakery products (Acun and Gül 2014). Extracts of grape pomace were also successfully incorporated into chitosan edible films (hydrophobic and hydrophilic), providing antioxidant properties and promising shelf-life extension (Ferreira et al. 2014).

Moreover, grape pomace has a potential application in wine industry. To be more precise, adding seeds from wine pomace during wine fermentation in a warm climate at a dose of 900 g seeds/150 kg grapes improved the antioxidant potential of red wines, as indicated by total phenolic content (TPC) and total flavonoid content (TFC) (Jara-Palacios et al. 2016). In an older study conducted by Pedroza et al. (2011), when dehydrated waste grape skins used as raw additives were able to release significant amounts of pigments, bioactive compounds and aromas into white wines, with similar characteristics to commercial rosé wines. Currently, Gil et al. (2018) used fibers from “Cabernet Sauvignon” (Vitis vinifera) pomace as fining agents for red wines. The authors highlighted that this type of treatment could be a good tool for winemakers to obtain cell wall material from nonfermented grapes by reusing winery wastes instead of commercially valuable fresh grapes.

Lipid oxidation protection

The findings confirm that grape pomace extracts have the potential to protect foods from oxidative damage and lipid peroxidation. Grape seed as well as vitamin E was successful in extending the shelf life of lamb meat after the 7th day of storage by reducing lipid peroxidation and meat discoloration of about 20% (Guerra-Rivas et al. 2016). Surprisingly, under refrigerated storage conditions, grape seed powder at a level of 0.1–0.2 g/Kg acted as a better antioxidant for cooked beef and pork patties, compared to oregano water extract and rosemary oleoresin (Rojas and Brewer 2007).

Similar effects appeared when red grape extract was applied in pork burgers by Garrido et al. (2011) and when grape pomace dietary fiber was applied in minced fish muscle during frozen storage by Sánchez-Alonso et al. (2007a, b). Considering the effects of grape pomace extract on cooked and uncooked chicken meat, Selani et al. (2011) revealed antioxidant activity during frozen storage under vacuum, due to the phenolic concentration.

Antimicrobial activity against food spoilage and pathogens

As stated earlier, different components of wine pomace interact with microorganisms in food, protecting them from spoilage flora, therefore, limiting the color deterioration, acidification, slime forming bacteria and gas production. For instance, antimicrobial effects against Z. rouxii and Z. bailii were observed in apple and orange juice after application of red and white grape pomace at concentrations corresponding to 20–100 g/Kg of phenolics (Sagdic et al. 2011). Researchers, in an effort to prevent food spoilage from the growth of microorganisms (e.g. Lactobacillus spp., Pediococcus spp., Streptococcus spp., Leuconostoc spp., Aeromonas spp. and Alteromonas putrefaciens), focus on natural antimicrobial components. Particularly, grape seed extracts delayed the growth of TAMB, LAB, Pseudomonas spp. and psychrotrophic populations in pork patties (Lorenzo et al. 2014). Silvan et al. (2017) also reported epicatechin gallate and resveratrol as the most active compounds. The antimicrobial activity of grape pomace has been extensively studied and was attributed mainly to the high content of gallic acid, followed by hydroxy benzoic and vanillic acid in the grape seed extracts (Tesaki et al. 1999). They presented antimicromial effects against B. cereus, C. coli, E. coli 0157:H7, S. infantis (Katalinic et al. 2010), L. monocytogenes ATCC 7644 and S. aureus ATCC29213 (Xu et al.2016).

In a different study, Dias et al. (2018) suggested another food application for this agricultural by-product using probiotic bacteria as a bio-preservative. In that case, the whole pomace was used as source of polysaccharides which represent a dietary fiber supplementation and a possible prebiotic function which increases the probiotic population.

Additionally, some published studies also presented the capacity of wine pomace products to promote the activity of or even to protect probiotic microorganisms. A far as concerns food applications, it has been shown that the use of grape pomace enhanced L. acidophilus fermentation by stimulating lactic acid production and reduced the fermentation time (Frumento et al. 2013). A similar effect was observed by Aliakbarian et al. (2015) who enumerated higher counts of S. thermophilus and L. acidophilus after fermentation.

Protection from potential hazardous products

A serious concern regarding food processing is acrylamide and advanced glycation end products (AGEs) formation, resulting from Maillard reaction and heat-processed foods, respectively. Acrylamide is classified as “a probably carcinogenic agent to humans (2A) and dietary AGEs are known as risk factors for diabetes, renal and cardiovascular diseases. Polyphenols from skin extracts and grape seeds have been proved to block the formation of acrylamide in a simulated physiological system and during the frying of potato chip (Xu et al. 2015).

Another potential food hazard is that both nitrites and nitrates are added to meat products giving the characteristic color and also inhibit the growth of Clostridium botulinum. Successfully, grape seed was able to reduce residuals of nitrite after ripening of dry-cured sausages and to inhibit N-nitrosodimethylamine formation (Wang et al. 2015). The last has been identified as a mutagenic and a carcinogenic agent in all species examined, according to WHO (2002).

Ingredients of functional and innovative foods

Wine-making by-products could be converted to functional and novel foods due to their multifunctional characteristics. Grape pomace extract can undoubtedly be used as a functional ingredient in food and beverages adding health benefits over and above the nutritional value. Nowadays, grape pomace powder can be used in cheese-making process, enhancing cheese total phenolic content and antioxidant activity. In parallel, the addition of grape pomace powder seems to have no effect on cheese proteolysis (Marchiani et al. 2016). Consequently, dairy products such as yogurt and cheese are fortified with whole wine pomace power and/or extract in order to increase the mineral content and inhibit the lipid oxidation (Tseng and Zhao 2013a).

Furthermore, when Rosales-Soto et al. (2012) enriched cereal bars, pancakes and noodles with phenols from Merlot grape seed flour, they achieved a high antioxidant activity and an increased consumer acceptance. Fortification of white bread with grape seed extract (Coe and Ryan 2016) and freeze-dried skin wine pomace (Mildner Szkudlarz and Bajerska 2013) seems to reduce postprandial glycemic response, total cholesterol and LDL levels, respectively. In the fruit processing industry, apart from antioxidant activity and color stability, white grape skin extract in a model fruit juice retained the stability of probiotic strains L. rhamnosus, B. lactis and L. paracasei, during storage (Shah et al. 2010).

Finally, an improved mineral profile of meat products has been achieved after application of a new seasoning derived from wine pomace. Precisely, higher levels of potassium and calcium and lower levels of sodium were present in treated meat samples compared to the control ones (González-SanJosé et al. 2015). Nitrates and nitrites added to meat products can form nitrosamines after reaction with a secondary or tertiary amine in the body. These compounds are considered as carninogenic ones according to the IARC. Grape seed extract could lower the levels of nitrite in dry-cured sausages and the levels of nitrosamines produced (Li et al. 2013), and also could inhibit the formation of N-nitrosodimethylamine (Wang et al. 2015).

Production of enzymes and microbial proteins

Grape pomace has an incredible potential to synthesize via fermentation hydrolytic enzymes such as xylanase, exo-polygalacturonase (exo-PG) and cellulose. These enzymes are commonly used in wine cellars during clarification processes as well as in food, paper and pulp industries (Walia et al. 2017). To enhance such utility, researchers fermented a mixture of grape pomace with orange peels causing a more efficient production of pectinase and xylanase. Similar or even better results were obtained from other agroindustrial wastes (Diaz et al. 2012).

Moreover, grape pomace can be utilized as a substrate for production of microbial proteins. These may play multiple roles, serving as an alternative source of high-quality protein in livestock feed or directly as an alternative protein source for human nutrition (Matassa et al. 2016). Single cell protein (CSP) has a high proportion of essential amino acids like lysine and valine; carbohydrates; fats; vitamins and minerals or certain essential amino acids. Bioconversion of grape pomace into microbial protein could be a promising step in reducing the protein malnutrition, especially in developing countries. Nevertheless, serious limitations of SCP from bacteria, yeasts, fungi and algae should be considered to minimize health hazards.

Active ingredients in cosmetics

Consumers claim to be concerned about allergies, skin irritations and possible health risks from long-term exposure to synthetic preservatives (e.g. parabens), colorants, aromas and stabilizers making natural formulations and organic products to become central to the aging market.

Polyphenols from grape pomace due to its anti-ageing properties could be an alternative, new cost-effective source for cosmetic industry. Cosmetic products include sunscreen, face peeling with Vitis Vinifera (Grape) Seed Oil (BioAroma Natural Products, Greece), skin-care, anti-ageing eye creams, anti-ageing moisturizers, face serum to treat dark spots from Caudalié (France), day or night creams and Grape Pomace Scrub Kit (Alexandria, VA, USA). The latest contains recycled pomace (29%) that assists human skin cell repair. Grape pomace and especially grape seeds can act as a valuable agent in skin care cosmetics, with antibacterial and antifungal properties (Baydar et al. 2006). In spite of these benefits, it should be noted that heavy metals and pesticide residues may be present in winery wastes. Thus, the cosmetics industry should remove them before entering into cosmetic formulation (Soto et al. 2015).

Regarding encapsulation and delivery, plant polyphenols present significant limitations due to chemical instability, low water solubility and low bioavailability. For this reason, encapsulation into a nanoemulsion-based delivery system of resveratrol could increase the bioavailability and protect the bioactive compound from degradation (Davidov-Pardo and McClements 2015). Encapsulation and other stabilization methods have been developed in cosmetic pharmaceutical, food, and agricultural applications.

Ingredients of dietary supplements

In the USA market, many dietary supplements are based on grape seed, grape extract and red wine powder due to their antioxidant, hypoglycemic and hypolipidemic effects. Grape seed extracts have been used in Europe for therapeutic purposes for several decades. OPCs (Oligomeric Proanthocyanidins from Grape Seeds) are often prescribed by doctors in typical doses 50–200 mg/days, as a complementary medicine and not as a replacement of conventional medicine (Weseler and Bast 2017).

Since grape polyphenols are regarded as natural antioxidants that play a role in human health and disease, grape seed extract has been recently considered as a powerful antioxidant food supplement. In the market, for instance, the Lamberts^® Super Strength Antioxidant Complex contains an ORAC blend from green tea, grape seed, rosemary and oregano extracts. Each tablet provides 10,000 mg ORAC units due to its high polyphenol content. A second dietary supplement promoted for cellular protection is the Solgar Grape Seed Extract 100 mg that contains phenolic compounds (95%) such as oligomeric proanthocyanidins, monomeric polyphenols (catechins, epicatechin and epigallocatechin), organic acids (citric, gallic, epigallic acid and malic acid). LifeExtension^® Resveratrol with Pterostilbene contains synergistic phytonutrients like trans-pterostilbene and quercetin to augment resveratrol’s effects. The food supplement company states that the particular combination “promotes youthful gene expression similar to calorie restricted diets, encourages healthy insulin sensitivity and mitochondrial function and supports a healthy inflammatory response”.

A recent study conducted by Sun et al. (2016) concluded that GSPE administration may protect the retina against hyperglycemic damage, possibly by ameliorating oxidative stress-mediated injury via the activation of the Nrf2 pathway.

Another potential use of grape pomace in pharmaceutical industry is as a drug delivery vehicle. Some drugs are either unstable or no soluble in water. Considering this, microemulsions of grape pomace are considered as suitable vehicle of delivery of topical antiviral, anti-inflammatory, antioxidant (tocopherol), steroidal, antibacterial, antifungal drugs and various local anesthetics. Kumar et al. (2014) achieve better drug absorption across skin compared to cream, gel or lotion. In these conditions, the pharmaceutical market would potentially receive benefit by the addition of grape pomace microemulsion as a raw ingredient and satisfy the consumers’ demand for organic, less toxic drugs.

Agriculture production (fertiliser)

The potential application of wine pomace has received high interest from agricultural organizations, since groundwater contamination from chemical fertilizers is associated with gastric and testicular cancers, birth malformations, as well as neurological, immune and endocrine dysfunctions in mice studies.

Grape pomace as a heterogeneous mixture of seeds, skins, pulp, and stalks usually cannot directly applied into the soil, because of the possible pathogens. It should be composted at first and then can be used as a soil conditioner. Low costs composts derived from winery wastes have given promising results in horticulture and modern greenhouse agriculture, alleviating stress on the environment. Grape pomace as an organic fertilizer has a certain value mainly due to low content in phosphoric acids and nitrogen. Chemical analyses of the compost based on winery waste reveal variety in different elements such as Ca, Mg, Fe, Zn and heavy metals (Pb, Ni, Cr, Cd). In this way, it could gradually replace other chemical fertilizers recovering heat and CO₂, during composting (Ferrer et al. 2001).

In strawberry cultivation, pressed grape skins (25% v/v) mixed with pumice (75% v/v) produced an average fruit yield of 306 g per plant and biomass of 97 g per plant. These values were higher than those derived from olive tree leaves compost (Manios 2004).

Animal feeding

Several works reported in the literature have used the grape seed by-product in farm animals feeding. In the last years, it is estimated that 3% of grape pomace produced is reused for animal feed (Dwyer et al. 2014; Brenes et al. 2016). For example, Taranu et al. (2017) showed that although grape seed diet did not influence the pig performance, it reduced the production of inflammatory cytokine (IL-1β, IL-8, TNF-α and IFN-γ) in the liver of pigs by suppressing the protein expression of the regulatory molecules NF-Kb and Nrf2. Moreover, administration of grape seed cakes during finishing period decreased significantly (− 9.05%, p < 0.05) the cholesterol concentration and increased lgA level (+ 49.90%, p < 0.05) in plasma. Inclusion of fermented grape pomace in the diet of finishing pigs increased the number of total PUFA in the subcutaneous fat of the animals, reduced lipid peroxidation and increased color stability of meat. Apart from studies in pigs, feeding cows with diets containing grape marc were associated with increased concentration of PUFA in milk, changes in the ruminate bacterial community composition and improved cow health (Moate et al. 2014).

Beneficial effects on diarrhea appearance, immune and antioxidant response were also seen in weaned piglets after administration of grape seed proacynidins (Sehm et al. 2011; Hao et al. 2015). Furthermore, the addition of grape pomace in the broiler diets was reported to increase the immune responses and reduce the feed cost per kg of live weight (Ebrahimzadeh et al. 2018) The results of that work suggested that the inclusion of up to 10% grape pomace in diets did not adversely affect broiler chickens’ performance and improved the antioxidant and immune responses of broiler chickens.

Removal of heavy metals from industrial waste water

The conventional methods of treatment of heavy metal contamination includes chemical precipitation, chemical oxidation, ion exchange, membrane separation, reverse osmosis, electro dialysis etc. These methods are not very effective, are costly, require high energy input and often contribute to generation of toxic by-products. For these reasons, there is a necessity for environmental engineers to treat heavy metal-polluted wastewater, in a cost-effective manner. Various agricultural wastes, including grape stalks, rice husk, black gram, waste tea, Turkish coffee, walnut shell, etc., have been established as potent adsorbents for heavy metal removal (Tripathi and Ranjan 2015).

The application of grape marc is negatively correlated with concentrations of heavy metals (Cd, Cu and Ni) in soil. The process of extractability of metals is a pH- and a time-dependent procedure (Karaka 2004). Winery wastes have been assessed as an adsorbent of heavy metals, Cu, Cr and Ni from aqueous solutions. Grape stalk wastes were examined as absorbing material for Cu(II) and Ni(II) removal from aqueous solutions. Results showed that ion exchange is the most important mechanism that takes place in the sorption process with significant release of Ca²⁺, Mg²⁺, K⁺ and H⁺ from grape stalks due to the uptake of Cu(II) and Ni(II). In addition, grape stalk wastes can be reused for the decontamination of metal-containing effluents (Villaescusa et al. 2004).

Energy recovery from winery waste

Producing other products from usage of agricultural goods is a novel idea. There is an attempt to cause bioconversions and biotransformations of winery waste to high value products, since the biorefinery concept was introduced to face the global energy crisis and climate change.

Bioethanol is an alternative source of sustainable energy. Europe is one of the biggest biodiesel markets worldwide where more than 8 billion liters are consumed annually. Biodiesel achieves a reduction in CO₂ emissions and uses renewable raw materials from plant oils (cottonseed, rapeseed, soya, palm, and sunflower) and from other wastes. Grape marc, vinasses, wine lees, and winery wastewater have been used as raw materials to produce lactic acid, biofuels including ethanol, enzymes, chemical intermediates and energy through anaerobic digestion and pyrolysis process.

Following the biorefinery idea, the solid fibrous plant parts (pomace, seeds, stalks or seeds) can be used to produce high value chemicals. Solid grape wastes are fractionated by enzymatic or chemical hydrolysis producing hemicellulose, pentoses, 5-C polymers, cellulose, hexoses, 6-C polymers and lignin, phenols. These fractions will be then converted to useful chemicals such as ethanol, carboxylic acids (acetic, butyric acid acetic acid), butanol, acetone and others (Luguel et al. 2011). Nevertheless, feedstock production and processes might be costly. Factors that may affect the biorefinery concept on winery waste include harvesting, transport, handling, treatment, storage, distribution, chemicals and heat mobility (Zacharof 2017).

The production of biomass surplus and energy recovery from wine residues illustrates the most important innovation in vine-growing sector. In Australia, in 2006, the Tyrell’s Wines Company states that the value of spent grape marc as a biofuel is 10 times greater than the value from selling it for feedstock. In Canada, in 2007, Inniskillin Wines and Storm Fisher Biogas in collaboration with other company created renewable electricity from the winery’s grape by-products. From this collaboration, about 1000–2000 tonnes of by-products instead of disposal were used as a fuel and the produced methane gas was used to generate power for homes in the Niagara region (Spingo et al. 2017). The conversion of biomass into thermal and electrical energy could bring both economic and environmental benefits (Corona and Nicoletti 2010). When green technologies are developed and applied, sustainability should be properly assessed by the Life Cycle Approach. This means that green technologies should be compared with other conventional or alternative ones, considering both recovery and disposal aspects (Spingo et al. 2017).