The study – published in the Journal of Food Science – reports that when crushed with water, avocado (Persea americana) seeds develop an orange colour that has potential uses as a naturally and sustainably sourced food colourant.
The researchers found that enzymatic treatment of the seeds, which are not currently commercially and represent a large waste stream, leads to the development of a stable orange colour that could provide a source of natural colours for the food processing industry.
“There is growing public and scientific interest in the development of natural alternatives to synthetic colorants in foods,” explained the researchers – led by Dr Gregory Ziegler of Pennsylvania State University, USA.
“Our data indicate that avocado seed represents a potential source of new natural colorants for use in foods,” they added.
Ziegler and his colleagues noted there is an increasing consumer demand for, and scientific interest in, new natural colorants.
“Colour plays a key role in determining the expectations and perceptions of consumers with respect to food … It is one of the most obvious characteristics of a food and, if not appealing, negatively impacts consumer acceptance,” they said.
The team added that colour is also interrelated with flavour intensity, sweetness, and salinity sensations, and may also indicate the safety of food to consumers.
“Although artificial colorants have a long history of use, and are easy to produce, stable, less expensive, and have better colouring properties than natural colorants, consumers have increasingly begun to consider synthetic colorants undesirable … Consequently, there has been increased effort to discover new natural alternatives,” wrote the researchers.
In the new study, the team examined the properties of – and the mechanism for – colour formation from avocado seed extract.
They noted that a stable orange colour is produced when avocado seeds are ground and incubated at 24 °C. Such colour production occurs rapidly, they said, noting that changes are produced at “as early as 0.5 minutes of incubation.”
Colour development was found to be dependent on the presence of the enzyme polyphenol oxidase (PPO), and prevented by heat treatment. The team revealed that colour intensified as the pH was adjusted from 2.0 to 11.0, adding that such changes were only partially reversible when pH was reduced again.
“These results suggest that the avocado seed may be a potential source of natural colorant, and that colour development is PPO-dependent,” said the researchers.
“Their application as a source of natural colorants could be of significant commercial value,” they added, noting that the seeds “represent an under-utilized waste stream.”
Ziegler and his colleagues added that the high phenolic content of the seeds may mean that the coloured extract could have additional functional attributes, “which should be explored.”
Source: Journal of Food Science