As described in the previous sections, many polyphenols can be extracted from grape pomace, but studies on the incorporation into cosmetic formulations or pharmaceutical products are limited. Safety issues, skin permeation and efficacy delivery are concerns in the development of new cosmetic products using agro-industrial by-products (Nunes, Rodrigues, & Oliveira, 2017). However, several cell-based in vitro models, predicting the safety and toxicity of cosmetic ingredient were allowed by the European Centre for the Validation of Alternative Methods (ECVAM) (Nunes et al., 2017). Assessment of skin irritant is considered a primary procedure in evaluating hazard and classifying a substance. Therefore, the application of grape pomace as active ingredients in cosmetic formulations remains challenging, although some studies showed
the potential applications of grape pomace as anti-aging agents (Wittenauer et al., 2015).
Table 1.3 summarises the most important compounds present in grape pomace and their potential functions in topical formulations.
Table 1.3 Individual compound reported in grape pomace with cosmetic interest Compounds Chemical structurec Functiona,b
Resveratrol Anti-aging
Catechin Anti-aging
Epicatechin Anti-aging
Gallic acid Anti-aging
UV protector
Ferulic acid UV protector
Vitamin E Anti-aging
Tartaric acid Exfoliating
Depigmenting
Oleic acid Anti-aging
Moisturising agent
Linoleic acid Anti-aging
Proanthocyanidins Anti-inflammatory
Quercetin Anti-aging
Kaempferol Anti-aging
aNunes, Rodrigues, & Oliveira, (2017)
bWittenauer et al., (2015)
cRoyal Society of Chemistry, (2015)
1.2.3.1 Antioxidant and Anti-aging properties
Skin aging is a complex, progressive and inevitable biological process that can be influenced by several factors such as genetics, environmental changes, lifestyle and metabolic processes (Pimple & Badole, 2013). In normal/unstressed cells, reactive oxygen species (ROS) are being produced by the functions of mitochondria in everyday cells metabolism. These ROS have been kept in balance by the action of antioxidant enzymes found inside cells such as superoxide dismutase (SOD), catalase and peroxides (Menaa, Menaa, & Tréton, 2013). When cells become stress, this balance is interrupted.
Skin is the major organ that is directly exposed to the sunlight, hence deterioration due to environments damage is inevitable. Exposure of skin to UV radiation and environmental pollutions are examples of cells stress-induced extrinsic factor which could overwhelm the ROS leading to a change in the skin normal behaviours (Menaa et al., 2013).
Several polyphenols present in the grape pomace extract were identified as the key active ingredients against collagenase and elastase enzymes, responsible for skin aging.
Wittenauer et al., (2015)found that gallic acid showed considerable inhibition values against elastase but quercetin 3-o-glucoside and quercetin 3-o-glucoronide had more pronounced effect on the collagenase. However, resveratrol itself was found to exhibit
very low inhibitory effects against both enzymes. The study also showed that the crude grape pomace extract had a higher inhibitory activity in both enzymes suggesting synergistic interactions between polyphenols, and the enzyme could play an important role regarding the inhibition mechanism. The same observation has also been noted by Ghimeray et al., (2015) by combining several superfruit extracts which showed that the inhibition of collagenase was notably high.
Naturally occurring quercetin and kaempferol have been found to exhibit strong inhibition against collagenase in comparison to other compounds from different groups, suggesting the hydroxylation patter in the B-ring is an important determinant to the inhibitory activity (Sin & Kim, 2005). In addition, epicatechin that may be found in the grape stem also exhibited strong anti-collagenase activity by possibly binding to the Zn2+
ion within the enzyme, thus preventing it from binding with the substrate (Wahab, Rahman, Ismail, Mustafa, & Hashim, 2014).
Despite the above studies, the application of grape pomace in cosmetic is rather scarce. It is important to bear in mind that the topical effectiveness of grape polyphenols in human skin implies some considerations during formulations development.
Polyphenols (or antioxidants) may be oxidised and thus inactivated before reaching the target site and permeability across the skin remained important. Formulations cream-based, lipid soluble, or organic solvent-based can be studied to enhance the permeation of polyphenols into the skin(Nichols & Katiyar, 2010). Abla & Banga, (2013)studied the permeation of three polyphenols (catechin, resveratrol and curcumin) and a vitamin (retinol) into porcine ear skin using propylene glycol as a vehicle. It was demonstrated that 10% of the retinol was retained in the stratum corneum whereas 90%penetrated into the underlying skin. The amount of total catechin in the stratum corneum was higher than
the resveratrol one, but similar amount of polyphenols was found in the underlying skin (Abla & Banga, 2013).
1.2.3.2 Protection against UV damages
Skin is exposed daily to environmental stress. For instance, UV radiation has the ability to penetrate deeply into the skin’s epidermis and dermis layers, causing skin injuries, including the generation of ROS which after chronic exposure, can cause skin photo aging, hyper-pigmentation and also skin cancer (Soto, Falqué, & Domínguez, 2015). However, these can be prevented if a proper UV protection is used. Natural polyphenols have been proposed as an active ingredients in cosmetic formulations as sunscreens ingredients due to their similar structure with chemical UV filters, presenting the same mechanism of action (Nunes et al., 2017).
A number of studies also described the effects of polyphenols extracts on human cells and UV-irradiated cells. For example, the pre-treatment of HaCat keratinocytes with chlorogenic acid and rosemarinic acid leads to a decreased intercellular ROS formation, induced by UVB or hydrogen peroxide (Cha et al., 2014; Pérez-Sánchez et al., 2014).
Resveratrol found in grape skin and/or seed is a promising natural compound with its ability to scavenge free radicals. Topical application of resveratrol to SKH-1 hairless mice before exposure to UVB radiation resulted in the inhibition of UVB-mediates skin edema and significantly inhibited the UVB-mediated induction of cyclooxygenase enzyme activity and protein expression of ornithine decarboxylase, a well-established markers for tumor promotion (Afaq, Adhami, & Ahmad, 2003).
1.2.3 Conventional and alternative extraction technologies for polyphenols recovery