The study, from Jilin University, aimed to produce composite edible film with carrot puree and examine how levels of the other components – namely carboxymethyl cellulose (CMC), corn starch and gelatin – affected it mechanical and barrier properties.
The team, led by Xinwei Wang, said carrots were targeted because of their nutritional value and that few products based on the vegetable had been developed.
Carrots consist mainly of water, protein cellulosic substances and pectic – and adding these components could lead to the formation of a cost-effective and biodegradable film, said the researchers.
“Obtaining films with good oxygen permeability (OP) and desirable film mechanical properties would be an indication of the possible use of carrot as an alternative source of packaging. Carrot films may have a potential to be commercial because they can be used as food or food packaging”, they added.
The Study - Barrier and mechanical properties of carrot puree films – was published in the journal Food and Bioproducts Processing.
Film components and barrier properties
The researchers noted that varying the concentration of the components altered the properties of the film.
“Generally, films made from polysaccharides, such as starches, gelatin and cellulose derivatives, are expected to be excellent oxygen barriers due to their tightly packed, and ordered hydrogen-bonded network structure, and have high tensile strength,” said the study.
A plasticizer was added after it was found the carrot films were too brittle.
The film was produced by heating corn starch in such a way to obtain ‘starch gelatinization’. CM and gelatin were added, followed by glycerol. It was homogenized and then 120ml of the deaerated solution was placed in a level square HDPE plate and put in an oven at 60C for six hours.
All films were stored in a dessicator at around 23C and relative humidity of 50 for two days.
Film thicknesses were tested using appropriate apparatus to the nearest 0.001mm.
The study found that tensile strength (TS) - the maximum stress a film can bear – and the ability to stretch (%elongation) were affected by the film components.
The addition of CMC, gelatin and particularly corn starch increased TS.
Adding CMC, corn starch and gelatin improved its stretchability initially but actually decreased it when higher levels were added.
Increasing the plasticizer levels improved elasticity but negatively impacted TS.
Water Vapour Properties (WVP)
Impeding moisture transfer is a major function of edible films, said the team.
When the gelatin content was fixed, the WVP increased as CMC and corn starch levels were raised.
When CMC and corn starch levels were fixed, WVP initially fell as gelatin content increased from 0% to 0.3%. However gelatin content between 0.3% and 0.5% caused a jump in WVP.
WVP also increased as glycerol concentrations went up.
Overall, the scientist said carrot films had intermediate water barrier properties compared to other edible films.
But carrot films were characterised as having good oxygen barriers that suggested they have the potential “to be used as a natural packaging to protect food from oxidation reactions”
Confectionery products, baked foods, nuts and others were all flagged as possible applications, as were fruit and vegetables.
“These results suggest that carrot puree films could be suitable as edible packaging for some foods or applied as a wrap on food products to provide nutrition and convenient use for consumers reducing food packaging waste,” said the research.
Barrier and mechanical properties of carrot puree films by Xinwei Wang, Xiuxiu Sun, Huan Liu, Ming Li, Zhongsu Ma published in Food and Bioproducts Processing; doi:10.1016/j.fbp.2010.03.012