12 January - 20 June 2016

Use of onion skin waste for biosugar and quercetin production

17 June 2015

Millions of tonnes of kitchen and household bio-waste are produced every month. This waste then goes either into landfill or is exported to third world countries. Due to the harm on wildlife ecosystems, there is a desire to construct new processes in order to treat waste to manufacture bio-fuel. The use of waste products to create energy is highly productive and renewable, as well as easy to transport and store. 

According to South Korean researchers writing in the Journal Food Chemistry, world onion production has increased 25% over the last 10 years, making it the second largest horticultural crop worldwide. Consequently, at least 500,000 tonnes of onion skin waste is discarded within Europe every year, which is valuable from a biofuel perspective. The skin layers of onions contain large concentrations of fibre and phenolic compounds such as the flavonoid quercetin. Due to its potential medicinal properties, extraction methods to obtain quercetin from onion skin waste have been explored. 

The research found that to obtain the highest yield of glucose an addition of cellulase, pectinase and xylanase increased the natural yield of onion glucose from 3.5 to 4.01mg /mL in their test systems. This is due to the fact that the xylanolytic and pectinolytic enzymes opened up the surface area of the onion skin and then cellulase can access the cellulose for hydrolysis. After complete enzymatic hydrolysis, the remaining solid residues were used to extract quercetin. It was concluded the most efficient way to ascertain the highest production of quercetin from onion skin waste, was via enzymatic hydrolysis monitored thin-layer chromatography. Through this technique, quercetin yield increased 1.61-fold and 90% of the available quercetin was recovered. These results indicate that enzymatic hydrolysis is highly efficient for recovering valuable biosugar and quercetin from onion waste, and is potentially useful for obtaining value-added products from agricultural waste.

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