Edible biofilm extracts based on pomegranate peeling extend the shelf life of strawberries

Edible biofilms obtained from agriculture and fishing waste and developed by researchers at the San Carlos Chemistry Institute (IQSC-OSP) at the University of Sao Paulo, Brazil, can extend the shelf life of strawberries (Fragaria x Ananassa Duch.).

In clinical testing, researchers found that in refrigerated storage for more than 12 days, film-coated fruits lose 11% weight and start contaminated with fungi over 6 to 8 days.

The results of the study conducted in collaboration with researchers from the Embrapa Instrumentation and São Carlos Federal University (UFSCAR) are published in the Journal Food Chemistry.

“The application of the coating doubled the shelf life of strawberries kept under the fridge, slowing the dehydration of the fruit, and maintaining the taste, texture and volatile compounds that give it its distinctive aroma,” says Millera Romanelli Vicente Bertero, the first author of the study, a post-sectal researcher at Embrapa Equipment.

This work began during Bertolo’s doctoral studies at IQSC-OSP under the supervision of Professor Stanislau Bogs. During their research, they developed a technique that allows 84.2% antioxidants (materials with preservative properties) to be extracted from the skins of pomegranate (Punica granatum L.) skins (Punica granatum L.) using natural deep utotectic solvents (NADES).

“Over 40% of pomegranates are made up of skin, depending on the variety, which is wasted. Our idea was to use this waste to obtain an extract rich in phenolic compounds with antioxidant and antibacterial activity,” says Bogusz.

Researchers who successfully developed an extraction method have decided to test the hypothesis that pomegranate antioxidants will be incorporated into the coating based on gelatin and chitosan.

“We chose to use chitosan extracted from the squid glia (the inner shell) through the process of deacetylation of chitin found in this mollusk, as we do not have the allergenic issues that were obtained from shrimp. And in this case we combined another polymer with another polymer to improve gelatin in this case.

Fruits that are prone to rot

Strawberries were selected as a model system to test the efficacy of biofilms. Because it is one of the highest loss rate items in Brazilian supermarkets due to its rotability and short shelf life of less than about 7 days under refrigeration.

“Strawberry is a fruit with very high respiratory activity and very low pH (acidity). Therefore, it is susceptible to microbial attacks. It is also very wet and the fruit becomes smaller.

To test this hypothesis, researchers evaluated the effects of the material on the physicochemical, microbiological, volatile profile and sensory properties of fruits over 12 days of refrigerated storage, coated strawberries with edible membranes by immersion.

The results show that the material forms a membrane on the surface of the fruit, which acts as a barrier to microorganism passage, moisture loss, and gas exchange, correcting strawberry respiration. In this way, the coating slows the metabolism of the fruit during the post-harvest period, thereby extending shelf life and maintaining the fruit’s color, hardness and bioactive compounds.

“We have discovered that this film can maintain the texture, allow for slowing contamination by microorganisms, and reduce the loss of fruit clumps, which is observed during strawberry shrinkage.

Researchers said the film also allowed it to reduce the severity of fungal damage and improve the volatile profile of the fruit. “The material allows for a 40% increase in the compounds that cause fruit aroma,” says Bertolo.

Biofilms also did not interfere with the sensory properties of fruits, such as flavor, as confirmed by sensory analysis tests conducted with undergraduate chemistry students at IQSC-OSP.

“The results of our tests showed that there was no difference in the taste, aroma, or visual characteristics of strawberries coated with the material compared to strawberries without film,” says Bertolo.

Researchers intend to file patent applications for development and license the technology to interested companies.

Economic analysis shows that coatings can cost an estimated BRL of 0.15 per fruit.

“This is a cost that consumers may be willing to pay for fruits that have a long shelf life and are longer used,” Bertolo estimates.