Waste from red grapes, which are generally discarded after winemaking, can be widely used by the food industry as a source of anthocyanins (pigments that give grapes their red or purple color) in various products. This was highlighted by doctoral research from the Faculty of Food Engineering (FEA), which demonstrated in waste these compounds possessing functional characteristics for human health, due to their extraordinary antioxidant capacity. 

They presented equal or even higher amounts of anthocyanins in samples of red cultivars than in red fruits such as blackberries and blueberries, according to study author Milene Teixeira Barcia. White grape residues, despite not containing anthocyanins, presented other phenolic compounds, responsible for the antioxidant properties of foods and which act in the prevention of cardiovascular problems and aging.

This significant finding, especially in samples of red grape by-products, would in itself bring gains when added to foods such as breakfast cereal, biscuits, jellies (to add color) or even to isolate some specific compounds that may have pharmacological effects.

Milene's suggestion is that this residue also be added to yogurts (based on red fruits), ice creams, dehydrated soups (including to add color), cookies, breads and a multitude of products.

The doctoral student herself began researching a breakfast cereal using this by-product of the wine industry. The idea, at this stage, is to carry out acceptance tests. “This is a small step, but we intend that, by publicizing this, perhaps we will get other researchers interested in using the waste for new applications”, emphasizes Helena Teixeira Godoy, research advisor. 

“One step was to obtain these residues from the winery, which still have a high amount of water (in the case of skins, seeds and lees) immediately after vinification”, reports Milene. Then it was necessary to prove its antioxidant capacity and, after, the separation of the compounds of interest.

Helena Godoy emphasizes that this research certainly has important social value because it values ​​the work of rural people. “The product he is working with is 100% usable and can even be integrated into school meals.”

Surplus

Milene realized that the leftover fruit was a problem for the industrial sector, particularly what to do to dispose of the volume of pomace generated (the sum of grape skins and seeds extracted during wine processing). 

Until recently, producers tried to use these residues as fertilizers, although they did not have an ideal composition for this use. Some of them even used it as roughage in feed. It turns out that ethanol residues, during production, were still present, and the animals were affected by consumption.

The production of grappa, an alcoholic drink made from grape pomace, is modest. It started with a view to combating waste by sourcing leftovers from wineries. The bark is used to be fermented and distilled. “As we have pinga as part of the sugarcane distillate, it is possible to make distillate grappa from grape skins, which have the characteristics of pinga for human consumption”, comments the advisor. 

In Rio Grande do Sul, where there is a greater volume of bark and a culture of wine industries, a lot of grappa is produced. In the State of São Paulo, what is mostly made is cachaça from sugar cane, as people are not used to drinking grappa. 

With the data obtained by Milene, it was noted that this residue could indeed contain substances valuable to health, such as anthocyanins, widely distributed in the skin of red fruits. Several studies pointed to this potential.

The scholar's intention was then to transform the leftovers into a by-product with high added value and social importance, because a discarded substance was being reused to try to recover the anthocyanins. 

For the tests, Milene chose some varieties of table grapes and fine grapes, evaluating the residue after making the wine. 

She studied, in addition to anthocyanins, other groups of phenolics that also have pharmacological properties, such as resveratrol, a polyphenol that is present in the seeds, skin of red grapes and red wine, and which is mentioned in the literature for heart problems.

It was already said that this was a compound with functional properties, due to its action against free radicals formed in the body or even in food. “In fact, all phenolic compounds have the peculiarity of being antioxidant substances, and they have been in fashion for around 20 years. That’s why many researchers are scrutinizing them”, guarantees the professor.

Techniques

The first treatment, says Milene, included drying the samples to make them more stable during storage for a longer period, in order to be applied to some food.

Three types of drying were developed to analyze their performance. A very interesting, but expensive, technique was freeze-drying (in which food is dehydrated and subjected to low temperatures without losing the properties of the original product, such as nutritional values).

Another technique was traditional drying, whose temperature is 50º C, and another still was atomization, which promotes the drying of only the liquid residue, in the case of sludge. The shells do not go through this method.

In this last technique, the product had similar quantities to the lyophilized one, with the advantage of being a cheaper and more viable process, with the advantage of keeping the compounds stable and avoiding losses. This technique involves the same processing that powdered milk undergoes. “So we discovered the best type of drying to preserve the phenolic compounds in the sludge – the atomization technique”, reveals the researcher.

The expectation is that people will better understand the potential of these wastes so that they can be processed or adopted as a source of specific compounds, such as resveratrol and anthocyanins.

Helena Godoy highlights that red fruits are being introduced into the Brazilian diet, who were previously not used to seeing raspberries, currants and blueberries on the market. “Today they have a loyal consumer who recognizes their features.”

Milene developed a product based on waste that would otherwise be thrown away. Part of what is in the grape goes into the wine and part goes into this residue, which is the product of interest. “Many foods can be produced because the peel and dregs were transformed into a powdered product”, explains the doctoral student, who also completed a sandwich doctorate at the Universidad Castilla-La Mancha, in Spain, under the co-supervision of professor Isidro Hermosín Gutiérrez.

The research advisor emphasizes that this study does not end with these findings. “The results, associated with state-of-the-art techniques, show that there is a lot to learn, a lot to study and a lot to discover.”

Fine grapes

Grape production in the State of São Paulo is around 177 thousand tons per year, of which 50% goes to grape processing (60% for wine processing and 50% for juice). The volume of waste generated is currently around tons. 

Wine production has been increasing and, as a result, the volume of data available in Brazil on the use of this waste is now becoming more significant. 

The news is that the State of São Paulo is starting to plant fine grapes, despite its tradition of table grapes. The policy of stimulating consumption and production of wine to gain domestic and foreign markets also continues. 

São Paulo emerges as the second wine-producing state in Brazil, behind Rio Grande do Sul. Santa Catarina appears in third place.

Publication

Thesis: “Study of phenolic compounds and antioxidant capacity of by-products of the winemaking process”
Author: Milene Teixeira Barcia
Advisor: Helena Teixeira Godoy
Unity: Faculty of Food Engineering (FEA)