The researchers characterised the antimicrobial activity of several compounds isolated from the mustard seed meal – a waste product of very low value to industry, finding that the waste product contained elements that could be used as natural food preservatives.
Writing in the journal European Food Research & Technology, the Canadian team reported that treatment of the mustard seed meal enabled the isolation of the antimicrobial sinapic acid.
The team, led by Christina Engels from the University of Alberta, said the natural compound shows antibacterial effects against strains including Staphylococcus aureus, E. coli and Listeria monocytogenes, and could be used to protect against food spoilage.
Engels said the isolation of sinapic acid lends a useful function to mustard seed meal – which is the product left over after the seed is pressed for its oil.
While the oil can be used for production of biodiesel and is used for cooking oils in some markets, she explained that "the defatted seed meal left over is currently of little economic value."
"That means the mustard seed meal can be used as a source for natural food preservatives," said Engels, who added that the use of sinapic acid from mustard waste could mean greater consumer choice when it comes to choosing foods containing preservatives.
Engels and her colleagues extracted phenolic compounds from defatted Oriental mustard (Brassica juncea L.) seed meal. They revealed that sinapic acid, along with several sinapoyl conjugates, were identified.
“The crude extract and a purified phenolic fraction exhibited selective antibacterial effects against Gram-negative and Gram-positive spoilage bacteria,” said the research team.
However, after alkaline hydrolysis, only sinapic acid could be detected in the extract – which allowed the Canadian team to quantify it with an authentic reference substance.
“The release of sinapic acid after alkaline hydrolysis not only allows for the quantification using the reference substances but also facilitates the standardization of the antibacterial activity of plant extracts for use as food preservative,” they said.
They team revealed that alkaline hydrolysis released 2.66 mg of sinapic acid per gram of dry defatted mustard seed meal.
Engels and her colleagues added that the minimum concentration of the hydrolyzed extract needed for inhibition of microbes such as Bacillus subtilis, Escherichia coli, L. monocytogenes, Pseudomonas fluorescens, and S. aureus was 0.1 grams per litre.
Source: European Food Research and Technology
Volume 234, Number 3, 535-542, DOI: 10.1007/s00217-012-1669-z
“Sinapic acid derivatives in defatted Oriental mustard (Brassica juncea L.) seed meal extracts using UHPLC-DAD-ESI-MSn and identification of compounds with antibacterial activity”
Authors: C. Engels, A. Schieber, M.G. Gänzle