Pomegranate peel-based biofilm increases shelf life of strawberries

An edible biofilm, obtained from residues from agriculture and the fishing industry and developed by researchers at the São Carlos Institute of Chemistry at the University of São Paulo (IQSC-USP), allows the shelf life of strawberries to be increased (Fragaria x ananassa Duch).

In laboratory tests, the researchers found that, over 12 days of storage under refrigeration, the fruits coated with the film showed 11% less weight loss and took between 6 and 8 days to begin to become contaminated by fungi compared to four days of fruit not covered with the material.

The results of the work, carried out with support from FAPESP and in collaboration with researchers from Embrapa Instrumentação and the Federal University of São Carlos (UFSCar), were described in an article published in Food Chemistry magazine.

“Through the application of the coating, it was possible to double the shelf life of strawberries kept under refrigeration and delay the dehydration of the fruits, while preserving the flavor, texture and volatile compounds, which give the fruit the characteristic aroma,” Mirella Romanelli Vicente Bertolo, postdoctoral fellow at Embrapa Instrumentação and first author of the study, told Agência FAPESP.

The work began during Bertolo’s doctorate at IQSC-USP, under the guidance of professor Stanislau Bogusz Junior .

During the research, they managed to develop a technique that allows, through the use of natural deep eutectic solvents (NADES, its acronym in English), to extract from pomegranate peel (Punica granatum L.) 84.2% more antioxidants — substances that have preservative properties.

“More than 40% of the pomegranate, depending on the variety, is made up of peel, which is wasted. Our idea was to take advantage of this residue to obtain extracts rich in phenolic compounds, with antioxidant and antimicrobial activities”, says Bogusz.

With the success of developing the extraction method, the researchers decided to test the hypothesis of incorporating pomegranate antioxidants into coatings based on gelatin and chitosan — a polymer (natural polysaccharide) found in the skeletons of crustaceans, such as shrimp —, to develop a protective film for fruits.

“We chose to use chitosan extracted from gladius [conchas internas] from squid through a process of deacetylation of the chitin found in this mollusk because it does not present the allergenicity problem like that obtained from shrimp. And we combined this material with another polymer, in this case, gelatin, with the aim of improving its mechanical properties”, explains Bogusz.

Highly perishable fruit

Strawberries were chosen as a model system to test the effectiveness of biofilm because they are one of the items with the highest loss rates in Brazilian markets, due to their perishability and short shelf life, of approximately less than seven days under refrigeration.

“Strawberry is a fruit that has very high respiratory activity and pH [acidez] very low. Therefore, it is very susceptible to attack by microorganisms. Furthermore, it is very humid and the fruits are small. Based on this, we raised the hypothesis that if the material we developed worked, it would be efficient in any other fruit”, says Bogusz.

To test this hypothesis, the researchers coated strawberries with the edible film through immersion and evaluated the effects of the material on the physical-chemical, microbiological, volatile profile and sensory characteristics of the fruits over 12 days of refrigerated storage.

The results indicated that the material forms a film on the surface of the fruit that acts as a barrier to the passage of microorganisms, moisture loss and gas exchange, modifying the strawberry’s respiration. In this way, the coating slows down the fruit’s metabolism during the post-harvest period and, consequently, increases its shelf life, preserving the fruit’s color, firmness and bioactive compounds.

“We found that the film allowed us to maintain the texture, delay contamination by microorganisms and reduce the loss of fruit mass, which is observed when strawberries wilt. This happens very commonly in uncoated fruits because they lose water easily and become dehydrated”, says Bertolo.

According to the researcher, the film also made it possible to reduce the severity of fungal lesions and improve the volatile profile of the fruits. “The material made it possible to preserve 40% more of these compounds that are responsible for the fruit’s aroma,” says Bertolo.

The biofilm also did not interfere with the sensory characteristics of the fruit, such as flavor, as confirmed through sensory analysis tests carried out with undergraduate chemistry students at IQSC-USP.

“The results of the tests showed that they did not identify any differences in the taste, aroma and visual characteristics of strawberries coated with the material compared to strawberries without the skin” says Bertolo.

The researchers filed a patent application for the formulation, after which they intend to license the technology to interested companies.

Economic analyzes indicated that the coating could have an estimated cost of approximately R$0.15 per fruit.

“This is a cost that consumers may be willing to pay for a fruit with a longer shelf life and greater use”, estimates Bertolo.

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This content was originally published in Pomegranate peel-based biofilm increases the shelf life of strawberries on the CNN Brasil website.

Source: CNN Brasil