Passionfruit antioxidant for edible food coatings
The high antioxidant and polyphenol content in passionfruit peels shows potential as a way to preserve fresh fruits and fresh cuts of fruit in an edible food coating, according to research from the University of Johannesburg. Such a coating could be used to reduce spoilage and plastic packaging in supply chains.
The researchers extracted, micro-encapsulated, freeze-dried and powdered passionfruit (Passiflora edulis Sims) peels from an organic farm. Their analyses showed the powders have the properties needed for an edible food coating and could also be used as functional ingredients in natural food additives.
Prof Olaniyi Fawole, from the University of Johannesburg, said if you coat the product with the powder, it creates a barrier that can reduce the interference from a high oxygen atmosphere, similar to how plastic works. “Dehydration is prevented because the coating keeps the moisture on the inside.”
However, any such coating needs to have high antioxidant content to help prevent spoilage due to oxidation and should also contain antimicrobials. An edible coating should not interfere with the colour, appearance or taste of the product.
Fresh cuts of fresh fruits, which spoil even faster than whole fruit, are exposed to far more microbes and dehydration, so they could benefit even more from such a coating.
Developing the powder
The microencapsulation process used by the researchers preserved high antioxidant and polyphenol content from the passionfruit peels. This is significant, because antioxidants and other bioactive compounds are easily destroyed by industrial processes, pH, high storage temperature, oxygen, light, solvents and metal ions.
The researchers used one of three carriers for the microencapsulation: gum arabic (GA), maltodextrin (MT), or waxy starch (WS). When they measured the encapsulation efficiency (EE) of the three carriers, they found EEs from 82.64 to 87.18%. This indicates that antioxidants and polyphenols should be well preserved within the microcapsules of the coated powder particles.
Then they analysed each encapsulated powder in turn for antioxidants and polyphenol content.
Phytochemicals such as polyphenols are numerous in plants, and no single analysis can describe the antioxidant content of the powders. Instead, the researchers used two analyses to indicate to what extent the encapsulation process affected the antioxidant activity of the bioactive compounds contained in the microparticles.
The first, DPPH radical scavenging activity showed that all three carriers possessed 45.85 to 51.29 mM Trolox Equivalent (TE)/ g DM (WS).
The second, ferric reducing antioxidant power (FRAP), showed that the carriers possessed 32.30–37.47-mM TE/ g DM.
Trolox is a synthetic water-soluble antioxidant, and it has been used as a standard antioxidant for these antioxidant assays.
“The results mean that the encapsulated powders could be viable alternatives to synthetic antioxidants and can provide valuable properties such as antibrowning and anti-senescence behaviour. They also offer the additional benefit of being edible,” Fawole said.
To identify which polyphenols are present in the microencapsulated powders, the researchers ran metabolomic analyses, using liquid chromatography mass spectrometry (LC-MS).
Commercially important polyphenols preserved in the microencapsulated powders at useful levels are vanillic acid glucoside, quercetin, citric acid, gluconic acid and caffeic acid.
“An edible coating or natural food preservative may be potent, but if its raw material is not stable, it is useless. For example, if it is hygroscopic, meaning it absorbs moisture, it is not suitable for industrial scale applications,” Fawole said.
“These microencapsulated powders are non-hygroscopic, for all three carriers. If these are well-packaged, and stored cool and dry, they should last up to six months. Also, you can open up a container, use what you need, close the container, and the rest will be stable. It won’t be necessary to use the contents of an entire container in one go.”
Overall, the detailed laboratory results indicate that microencapsulated powders from passionfruit peels are suitable as an active ingredient in edible food coatings, and natural food additives, particularly for ‘naked’ fresh and cut fruits.
The findings of the research study are published in the journal Antioxidants.
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