Physicochemical Properties,antioxidant And Antibacterial Activities Of Polysaccharides Sequentially Extracted From Allium Cepa L.

Onion(Allium cepa L.)is popular all over the world due to its unique flavor,abundant nutrients and various functional properties.In this study,four kind of onion polysaccharides(ACLPs)were sequentially extracted by hot buffer,chelating agent,dilute alkaline and concentrated alkaline,and obtained ACLPs were named as HBSS,CHSS,DASS and CASS,respectively.The chemical composition,physicochemical,functional properties,antioxidant and antibacterial properties of these polysaccharides were systematically studied,which results may provide a theoretical basis for their application in the development of functional foods.UV scanning spectrum and FT-IR analysis showed the characteristic absorption peaks of ACLPs were respectively appeared at 200 nm,3600–3200 cm-1 and1200–800 cm-1.Monosaccharide compositions analyzed by gas chromatography indicated that the major sugar and content were different in these ACLPs.The molecular weight of HBSS,CHSS,DASS and CASS was 7.702×103,4.690×103,4.943×103and 1.390×103k Da,respectively.Physicochemical and functional properties study showed that HBSS had the highest thermal stability and emulsifying activity,CHSS had the best moisture retention;DASS has the best hygroscopicity and CASS displayed the greatest solubility,fat-binding capacity,foam capacity,foam stability and emulsifying stability.Rheological properties study of these ACLPs(0.5–2.5%)revealed that CHSS was of the largest apparent viscosity,and the viscosity was decreased under conditons as acid(p H=4.0),alkaline(p H=10.0)and higher temperature(90°C)whereas the viscosity was increased at low temperature(-20°C);in addition,the apparent viscosity of ACLPs solutions was also affected by the type and concentration for metal ions.The value of G'(storage modulus)and G”(loss modulus)was increased with increasing oscillation frequency,the crossover value decreased with increasing concentration.Antioxidant activities study of the four ACLPs showed that HBSS had the greatest reducing power,hydroxyl,DPPH radical scavenging ability,whereas CHSS possessed the strongest Fe2+chelating ability,superoxide anion and ABTS radical scavenging ability.DASS performed the largest ?-carotene bleaching inhibition ability and CASS exhibited the strongest lipid peroxidation inhibition ability.Regarding the antibacterial activity of ACLPs,DASS performed better toward four differentbacterials than other ACLPs.The results descibeled above indicated that onion polysaccharide can be used as functional ingredients in the food industry.