Garbage to Glamour: Recycling Food by-products for Skin Care

There is rediscovered interest in understanding the potential for recycling industrially processed food waste to create new safe and effective products for other applications; e.g., energy, pharma, nutraceuticals and cosmetics, to name the top few.¹ An increase in food processing in the last 50 years has slowly and consistently generated a large amount of non-edible by-products, including fruit and vegetable peels, seeds and leaves. Additionally, disposing of waste water from food processing in a manner that avoids environmental pollution is a management issue.²

The idea of being able to use every part of a raw material without discarding any of its elements is not new. In 1993, Paul Hawken cited in his controversial and revolutionary book, “Ecology of Commerce,” examples of production integration in manufacturing. He described industrial hubs created around specific raw materials and their by-products to use every part of materials without waste.³

Hawken called this process industrial ecology, where “pollution is eliminated by tailoring manufacturing by-products so that they become the raw materials of subsequent processes.” Different industries developing products for diverse markets created local consortiums, where by-products were recycled in different finished goods.

In developed countries, recycling ingredients is not an option anymore; it’s an obligation. Increasing consumption is associated with limited raw material options, which pushes the sustainability print of a raw material to the edge. Indeed, if different industries were to leverage the use of a raw material, it would limit the need to source the same raw material multiple times and it would increase the sustainability of it.

As an example, the cosmetic industry could extract polyphenol-rich materials from parts of the fruit not used by the food industry. These plant ingredients provide antioxidant benefits. Companies producing apple juice that remove the apple skin and seeds could sell these materials to companies producing polyphenol-rich apple extracts for cosmetic, cosmeceutical, nutraceutical or pharma applications. In the early 2000s, research exploded in this area at different universities funded by local governments all over the world. The point is to understand and develop processing protocols to value these wasted by-product ingredients.

A recent example is the BioWaste program funded by the European Commission Department of Agriculture. This program includes projects such as Apopros and Transbio. Apopros aims to “develop eco-efficient, bio-mechanical processing solutions to enrich intermediate fractions from industrial high protein and oil-containing process residues originating from agriculture sub-products.” Transbio is focused on developing new products from the fruit and vegetable processing industry using environmentally friendly biotechnology solutions.⁴

By-products including seeds, stems, leaves and skins—not used pulp—are usually discarded. The total amount of these by-products can be as little as 3% to as high as 60% of the total plant food, e.g., in the case of artichoke.⁵ The challenge in recovering these by-products is finding the best and most environmentally friendly extraction technique possible to achieve the maximum yield without compromising the stability of the extract and its components. Analytical chemistry of the waste and procedures to valorize it would then follow.

The chemical composition of a by-product is similar to its edible parts,⁶ so it did not take long to discover that most of the discarded natural by-products have a similar, if not higher, health value than their edible processed counterparts.^7, 8 Research on the properties of by-products and their applications has been published; some is presented here. Examples of food processing waste for cosmetics is given for coffee, tomato, olive and citrus. These ingredients have significant consumption worldwide, therefore their waste has a negative impact on the environment and economy. The possibility to recycle this waste could lower this impact and increase the sustainability of these ingredients.

Coffee Waste

Coffee is one of the world's most popular drinks and it has a strong commercial value. It is only second to petroleum as the most traded commodity worldwide.⁹ The coffee industry generates a hefty amount of waste, including unused coffee beans, spent coffee grounds and silver skin/husks.⁵

Like other food waste,¹⁰ spent coffee grounds were investigated to produce energy.^{11, 12} In some cases, wet coffee processing waste is not properly disposed, causing serious environmental and health issues. Therefore, its conversion into bio-fuel would not only help the economy, but also prevent damage to the environment and reduce health problems.¹³

To investigate the use of coffee waste for medicinal and cosmetic purposes, several labs have performed analytical studies to identify the major components in unused coffee beans, spent coffee grounds and silver skin/husks. A series of healthy molecules was found, particularly phenols and polyphenols such as caffeoylquinic acids, caffeic acid and ferulic acid.^14-17 Additionally, the waste contained 15% of oil and is rich in linoleic acid^{17, 18} and phytosterols.¹⁷

Further studies have demonstrated the strong biological activity of these molecules, particularly as antioxidants.^{17, 19} Subsequently, the antioxidant properties of coffee waste extract have been assessed: in vitro, to protect against accelerated aging;²⁰ in vivo, in animal models, to protect against UVB, limit photo-aging and/or stimulate skin repair;^{21, 22} and clinically, in a finished product, to increase skin hydration.²³

Increasing consumption is associated with limited raw material options, which pushes the sustainability print of a raw material to the edge.

Tomato Waste

About one-fourth of the world’s industrial tomato processing is for tomato paste, and peeled and unpeeled tomatoes either chopped or in purees, juices, ketchup, soups, etc.^{5, 24} From this, tomato by-products including unused pulp, skin and seeds are produced. Tomato pomace is a popular by-product rich in tomato skin and water. It represents 4% of the fruit weight.²⁴

Although apart from water the main components of tomato pomace are fibers (60% of its dry weight), pomace also contains proteins, pectins, fat, minerals and healthy antioxidants, including the carotenoid lycopene.^{25, 26} Commercially interesting ingredients such as proteins, pectins, antioxidant molecules—e.g., caffeic acid, ferulic acid, chlorogenic acids, quercetin-3-β-O-glycoside, quercetin and the aforementioned lycopene—have been recovered from the pomace through different means;^26-29 albeit with a series of challenges, especially for an unstable material such as lycopene.²⁶

Ingredients extracted from tomato waste demonstrate biological activity as antioxidants; in vitro, they also modulate cell growth and impart anti-mutagenic properties.^{29, 30} Another interesting application of protein-rich tomato waste is its fermentation into amino acids and peptides with antioxidant and anti-inflammatory activities.³¹ Investigations have identified the anti-inflammatory properties come from naringenin-chalcone in the tomato skin. This molecule also was shown to effectively reduce edema in animal models.³²

Olive Waste

The production of olive oil also generates massive amounts of waste, including olive oil mill waste water (OMWW), olive pomace and filter cake. The Mediterranean region produces 95% of the world’s olive oil. Here, OMWW alone represents more than 30 million cubic meters of waste worldwide for just two to three months of olive oil production.³³

Olive oil waste is heavily rich in polyphenols.^34, 35 In fact, during olive oil production, only 2% of the total phenols of olive fruit partition in the oil, while most phenols partition in the waste—53% in the OMWW and 45% in the solid pomace. This is due to the olive fruit phenols being more water-soluble.³⁶ Traditionally, the waste is discarded in soil or marine water, building up toxic concentrations of polyphenols from 0.1–18 g/L. Furthermore, the presence of ammonium and phosphorus in the waste also affect the bio-system, inhibiting plant and microorganism growth.^{37, 38}

The relatively low cost of phenols from olive by-products makes it worth considering recovering them from environment, which will further decrease toxic concentrations of waste. This could also sustainably stimulate economy by recovering healthy phenols and concentrating them to sell for other applications.

A complete analysis of the polyphenols recovered from olive fruit waste identified: hydroxytyrosol, tyrosol, caffeic acid, vanillic acid, verbascoside, oleuropein, ferulic acid and p-coumaric acid.³⁹ These polyphenols were studied for their biological properties, especially oleuropein and hydroxytyrosol. They are strong antioxidants^{39, 40} and their activity is often associated with the healthy benefits of the Mediterranean diet.⁴¹

Further research has proven these polyphenols to inhibit cancer cell proliferation and protect DNA from oxidative damage.⁴² A fraction isolated from olive mill waste water, containing mainly hydroxytyrosol, verbascoside and tyrosol, also completely inhibited the growth of Gram-positive and Gram-negative bacteria.⁴³ Additional studies have shown the antimicrobial potency of phenol-rich olive pomace powder,⁴⁴ suggesting the use of olive oil production by-products for natural preservation.

Finally, polyphenols from olive waste were tested on skin and showed a series of beneficial anti-aging effects, including the stimulation of collagen production, antioxidant activity and the inhibition of melanogenesis.^{45, 46} In conclusion, it is possible to recycle olive waste and its phenolic content to reduce environmental impact, while using it for applications in human health and skin care.

Citrus Waste

Citrus production worldwide totaled 135 million tons in 2013. This included mandarin, lemon/lime and grapefruit, representing 28.6, 15.1 and 8.4 million tons, respectively.⁴⁷ The edible part represents around 44% of this total; the remaining, non-edible 66% consists mainly of peel.⁵ The waste therefore represents a considerable volume, and being mostly solid, it is difficult to eliminate or recycle so it is used mostly as cattle food.

Recent investigations have attempted to use citrus waste peel as a possible biofuel, after its decomposition at high temperatures.⁴⁸ Researchers in Florida also have developed systems to recover several by-products from the same citrus peel; this waste can be fermented to produce ethanol with essential oil D-limonene obtained as the co-product.⁴⁹

Citrus waste including peel, molasses, seeds and leaves have been found to contain flavonoids, carotenoids, phenolic compounds, vitamin E, phytosterols and essential oils.^50-54 Many of these components have strong antioxidant activities,^53-55 along with other biological properties. Peel extract, for example, has shown immune-stimulating activity in T lymphocytes.⁵⁵ And compared with other peel extracts, citrus also has the strongest antimicrobial activity, especially against Gram-negative bacteria.⁵⁶ This suggests using citrus peel extract as a preservative.

Additionally, several studies have shown the capacity of citrus waste to protect or inhibit a series of mechanisms in skin models. In particular, an orange peel extract rich in flavonoids protected skin cells from UV-induced inflammation.⁵⁷ Also, citrus waste-derived nobiletin inhibited MMP-9 activity in human dermal fibroblasts.⁵⁸

Researchers in Korea assessed mandarin peel waste from juice processing and found it exhibited antioxidant, anti-melanogenesis and anti-inflammatory activities.⁵⁹ The same researchers evaluated extract from a waste-derived citrus pressed cake and found that it blocked specific melanogenesis pathways.⁶⁰ Citrus peel extracts have also shown anti-elastase and anti-collagenase activity in vitro, suggesting applications for anti-aging skin care.⁶¹

Further, animal models have shown significant anti-inflammatory effects in murine dermal inflammation and wound-healing by the orange-peel derived terpene d-Limonene and its metabolite perillyl alcohol.⁶² In conclusion, citrus waste derivatives are promising ingredients for skin care, protection and repair products.

A common approach to neutralizing toxic compounds that also transforms food waste into useful compounds, e.g., polysaccharides and phenolic compounds, is to incubate them with microorganisms.

Pros and Cons of Recycled Skin Care

A lack of resources and the need for sustainable processes is becoming today’s reality more and more. And the technology is available to eliminate waste derived from industrially processed food to reduce its environmental impact and recycle valuable materials. But the reality is, this comes at a cost.

The waste must be collected and processed from its final use, then treated, transformed and/or extracted. And in the cases of coffee and olive, the waste obtained after processing can contain toxic compounds derived from oxidation; such as phytosterol-oxidized products (POP) from coffee silverskins¹⁷ or olive pruning residues (OPR) from olive processing.⁶³ These waste derivatives would need to be neutralized or eliminated before recycling the waste for human applications. One common approach to neutralizing toxic compounds—which also transforms food waste into useful compounds such as polysaccharides and phenolic compounds—is to incubate them with microorganisms.^{63, 64}

The bioactive compounds also must be extracted and concentrated, and to do so, some techniques require specific equipment, which can be costly.⁶⁵ Although recent investigations have highlighted a cost advantage of extracting bioactive compounds from processed food waste,⁶⁶ it is important to assess the same cost for the cosmetic industry, especially considering the need for pure molecules or concentrated bio-active fractions.

It is worth noting that in this review, the ingredients identified for skin applications have mostly included phenolic compounds. However, other compounds from food processing waste include polysaccharides such as cellulose, pectins, oligosaccharides, etc.^{67, 68} These entities also exhibit antioxidant activity^{68, 69} and can function as prebiotics for skin care applications.^{69, 70}

In conclusion, waste from food processing is rich in healthy compounds that can be recovered and used into cosmetic formulations for a series of skin benefits. Recycling this waste would be a more sustainable approach to using raw materials, reducing the costs of disposal and reducing environmental impact, while bringing added value to the cosmetics industry.

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