Researchers find way of blocking weevils entry into cereal boxes

The overall goal of their research, published in Innovative Food Science and Emerging Technologies​ was to develop a biodegradable carrier material to control insect pests in cereal products, with propionic acid incorporated into biodegradable coatings then applied onto carton intended for packaging cereal goods.

They said propionic acid is commonly used by food industry as a preservative agent in several food products and it is known to be very effective in inhibiting Gram-negative bacteria strains and stored grain moulds.

And the compound is GRAS (Generally Recognised as Safe) approved by the US Food and Drug Administration, explained the researchers.

The scientists, based at the University of Foggia, said post-harvest insect pests cause severe quantitative and qualitative losses not only in stored raw materials but also in semi-processed and final food products, due to their capability to enter packaged goods during transportation, storage in warehouse, or at the retail stage.

Most insects, they continue, enter into finished products through openings caused by sewing, folding, or damage and not by chewing through packaging.

The method​

The authors said that in behavioural bioassays, zein and policaprolactone (PCL) paperboard coatings, used as propionic acid carriers, were tested for repellence against granary weevils.​

“The bioassay used in this study, carried out by adopting a high number of insects confined in a small space and damaged cartons imitating breakdown or poor sealed packaging, was aimed to simulate the worst field conditions for packaged cereal goods when exposed to an insect infestation,” ​they said.

The researchers explained that two different solutions were coated on each carton, corn zein and PCL, respectively, to realize mono and multilayer biodegradable systems, with cartons without any coating and cartons coated with one layer or two layers of zein or PCL solutions without active compound used as controls.

They said that invasion tests were carried out with packages aged one, two, seven or 15 days.

“Cartons were randomly and equidistantly distributed along a circumference signed around the centre of the box and located 2 cm from the side walls. The test box was closed by a lid provided with two holes (2 cm diameter) screened with fine metallic net (0.1 mm mesh) to prevent insects from escaping and allowing air circulation,”​ explained the researchers.

Tests were carried out in the dark, and the number of insects in each carton was counted after 24 hours, with the mean percentages of insect infestation in different packages analysed by Friedman two-way analysis of variance (ANOVA), they added.​

Results ​

The researchers said that their results showed that, despite the favourable conditions for insect infestation, propionic acid-loaded PCL and zein coatings significantly cut the number of insects entering cartons filled with wheat kernels in comparison to the controls.

“The mean percentage of S. granarius adults that entered 1 to 15-day aged cartons coated with the active PCL ranged from 8.2 to 13.1 and from 0.7 to 11.3, for mono and multilayer coatings, respectively,”​ said the authors.

Moreover, they noted that their results demonstrated that polymer composition influenced the repellent release, thus resulting in a different effectiveness between PCL and zein coating.

The results for the zein coating, they added, showed that the mean percentages of insect infestation in 1 to 15-day aged cartons provided with the propionic acid varied from 8.0 to 18.0 and from 4.0 to 10.7, for mono and multilayer zein systems, respectively.

The mean percentage of insect entering cartons with PCL monolayer coating did not vary significantly from 1 to 15-day aging period, said the researchers, while for the other coatings a significant increase of insect penetration in cartons was observed.

“The PCL multilayer provided better results than zein multilayer and both mono-coated packaging systems, mainly evident for the 1 and 2-day aged cartons. This indicates the better ability of PCL multilayer to retain and then slowly release propionic acid, more efficiently then zein coatings,” ​argue the scientists.

The use of propionic acid in biodegradable packaging coatings, concluded the team, could be of great interest by the bakery and cereals sector since it is a natural compound even emitted by cereal grains and it is already used as a food preservative, due to its inhibitory effects towards bacteria, moulds and fungi.

Source: Innovative Food Science and Emerging Technologies​
Published online ahead of print
Title: Propionic acid in bio-based packaging to prevent Sitophilus granarius (L.)(Coleoptera, Dryophthoridae) infestation in cereal products​
Authors: Germinara, G.S., Conte, A., Lecce, L., Di Palma, A. & Del Nobile, M.A