Whey Protein Isolate-Xylose Maillard-Based Conjugates with Tailored Microencapsulation Capacity of Flavonoids from Yellow Onions Skins

Abstract

The objective of this study is to encapsulate flavonoids from yellow onion skins in whey protein isolates (WPI) and xylose (X), by Maillard-based conjugates, as an approach to improve the ability to entrap flavonoids and to develop powders with enhanced antioxidant activity. WPI (0.6%, w/v) was conjugated to X (0.3%, w/v) through the Maillard reaction at 90 °C for 120 min, in the presence of a flavonoid-enriched extract. Two variants of powders were obtained by freeze-drying. The glycation of WPI allowed a better encapsulation efficiency, up to 90.53 ± 0.29%, corresponding to a grafting degree of 30.38 ± 1.55%. The molecular modelling approach was used to assess the impact of X interactions with α-lactalbumin and β-lactoglobulin on the ability of these proteins to bind the main flavonoids from the yellow onion skins. The results showed that X might compete with quercetin glucosides to bind with α-lactalbumin. No interference was found in the case of β-lactoglobulin. The microstructural appearance of the powders revealed finer spherosomes in powder with WPI–X conjugates via the Maillard reaction. The powders were added to nachos, followed by a phytochemical characterization, in order to test their potential added value. An increase in antioxidant activity was observed, with no significant changes during storage.

Differences in Antioxidant Potential of Allium cepa Husk of Red, Yellow, and White Varieties

“…The European Commission determined that the transition to the CE could provide an annual economic benefit of EUR 600 billion for the manufacturing sector alone [ 1 ]. The agro-industry produces a large amount of organic waste that often ends up in landfills or is used to produce products with low added value; however, the CE concept aims at converting this waste into products with high commercial value, such as medicines, nutraceuticals, and cosmeceuticals [ 5 , 6 ]. Secondary products of the food industry often contain valuable molecules that can be used as functional ingredients in the food, cosmetics, and pharmaceutical industries [ 7 ].…”

“…Onion ( Allium cepa L. ) is the second most cultivated crop worldwide after tomatoes, with a harvest estimated to be approximately 89 million tons [ 5 , 6 ]. The huge popularity of the onion is related to its versatility.…”

“…More than 550,000 tons of bio-waste are generated during onion processing [ 5 , 6 ], which consists of peeling, slicing, and dicing, and these operations generate a large amount of waste [ 11 ]. Interest in onion waste has grown significantly in recent years, as evidenced by the increase in the number of related scientific studies in the past 2 years.…”

“…The waste biomass mainly consists of skin/peel/husk (the outermost layers), roots, tops of the bulbs, and deteriorated bulbs [ 6 , 12 ]; however, onion skin represents the main waste component in onion processing (up to 60%) [ 7 , 11 ]. Onion waste is characterized by an unpleasant taste and smell; therefore, it is not suitable for animal feeding or as organic fertilizer, and is usually sent to landfill, causing an environmental problem [ 5 , 6 , 7 ]. On the other hand, onion peel is rich in polyphenolic antioxidants—mainly quercetin and its derivatives; glucosides, which belong to the flavonoids group; and ferulic acid, gallic acid, and kaempferol, which demonstrate significant beneficial effects associated with various biological activities, including antidiabetic, antioxidant, anti-inflammatory, antitumor, antimicrobial, and enzyme-inhibitory effects [ 5 , 13 ].…”

“…Onion waste is characterized by an unpleasant taste and smell; therefore, it is not suitable for animal feeding or as organic fertilizer, and is usually sent to landfill, causing an environmental problem [ 5 , 6 , 7 ]. On the other hand, onion peel is rich in polyphenolic antioxidants—mainly quercetin and its derivatives; glucosides, which belong to the flavonoids group; and ferulic acid, gallic acid, and kaempferol, which demonstrate significant beneficial effects associated with various biological activities, including antidiabetic, antioxidant, anti-inflammatory, antitumor, antimicrobial, and enzyme-inhibitory effects [ 5 , 13 ]. Concerning onion varieties, quercetin and its derivatives, along with glucosides, are the predominant flavonols in all types of onions, regardless of the white, yellow, or red color, while anthocyanins are mainly present in red onions, wherein they make up approximately 10% of the total flavonoid content in fresh weight [ 7 , 9 ].…”