Mucoadhesive and antioxidant activity of low-thiosulfinate Allium extracts
The purpose of this study was to evaluate the composition, antioxidant and mucoadhesive properties of extracts of onions that are used in human nutrition: onion (Allium cepa L.), garlic (Allium sativum L.), leek (Allium porrum L.) and bear garlic (Allium ursinum L.), with reduced content of thiosulfinates, important antioxidant constituents . Extracts were prepared by blending fresh bulb or leaves of onions with aqueous or 20% ethanolic solution, pH=3, which inactivates allinase , followed by freeze-drying. Total phenols, thiosulfinates, thiols as well as sugars were determined. For investigation of antioxidant activity two tests were employed: scavenging activity for DPPH free radical and reductive power assay. Among the extracts, aqueous extracts of garlic bulbs was richest in thiosulfinates (93.7µmol/g, expressed as allicin) and thiols (48.6µmol/g, expressed as cystein). Although thiosulfinate content was greatly reduced, the extracts demonstrated notable antioxidant activity in both tests. The most active DPPH radical scavenger was the ethanolic extract of leek leaf with EC50 of 2.1mg/ml. The same extract exhibited the strongest reducing power. However, its activity was significantly lower than the activity of positive controls: butylated hydroxyanisol and ascorbic acid. In general, extracts made of leaves were stronger antioxidants than extracts made of bulbs. There was also positive correlation (r2=0,70) between antioxidant activity and thiol content in the extracts which implicates that these compounds may play an important role in overall antioxidant activity of onions. To determine mucoadhesive properties of prepared extracts tensile studies were performed and work of adhesion values were measured. The results clearly showed that all the extracts tested had mucoadhesive characteristics. The most pronounced mucoadhesive properties were determined for aqueous extract of bulbs of A. sativum and A. ursinum.
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