Onion Waste is Nutritious, Good for the Environment

The old adage, “Waste not, want not” comes to mind with the results of a new study which reports that onion “waste,” such as the outer layers discarded during processing, are nutrient rich and could be added to other foodstuffs. Onion leftovers are nutritious, say the researchers, and this new use is also good for the environment.

Recycling onion waste is also profitable

Onions are second only to tomatoes as a horticultural crop around the world. Many cultures highly prize the vegetable as a necessary food source in various forms, from fresh to pickled, dried, chopped, powdered, jarred, and frozen.

Industrial processing of vegetables involves waste, and onions are no exception. Given that about 66 million tons of onions are produced each year, it is no surprise that “more than 500,000 tons of onion waste are produced annually in the European Union, mainly from Spain, UK and Holland,” according to the study’s authors.

Reaping a health benefit from that waste was the focus of a study led by Vanesa Benitez from the Autonomous University of Madrid, Spain, and her colleagues. They reported that the waste products from industrial processing of onions “are an interesting source of phytochemicals and natural antioxidants and their application in food, which increases their health promoting properties, is a promising field.”

Onions are a very good source of numerous phytonutrients, including flavonoids (e.g., anthocyanins, quercetin), and vitamin C, and a good source of chromium, manganese, molybdenum, vitamin B6, folate, potassium, and copper. The flavonoids tend to be more concentrated in the outer layers of the onion, so these nutrients may be “wasted” during some types of processing.

The outer layers are also a rich source of fiber, as are the bottom and top of onions. According to the study’s authors, “brown skin showed a high concentration of quercetin aglycone and calcium, and top-bottom showed high concentration of magnesium, iron, zinc and manganese.”

Overall, the authors noted that their study “showed that each waste would have a profit,” and that because different waste products offered different compositions, industry should be interested in separating them to “exploit them as source of different bioactive compounds.” Thus far, however, this advantage had not been exploited effectively.

Enhancing the nutritional value of foods is not the only advantage the authors saw in processing onion waste products. They noted that if the creation of new products from onion waste is successful, “environmental problems could be solved” as well.

SOURCES:
Benitez V et al. Plant Foods for Human Nutrition 2011; 66(1): 48-57; doi:10.1007/s11130-011-0212-x
George Mateljan Foundation