| Sweet potato(Ipomoea batatas [L.] Lam)is rich in protein,dietary fiber,minerals,vitamins,and antioxidants,such as ?-carotene,phenolic acids,anthocyanins,and tocopherols,etc.Orange-fleshed sweet potato(OFSP)is an excellent source of ?-carotene that can supply significant amounts of vitamin A and energy simultaneously,thus helping to address the problem of vitamin A deficiency and undernutrition.In this study,nutritional and functional properties of 25 cultivars of sweet potato and effects of cooking process on carotenoids and antioxidant activity of orange fleshed cultivar were studied.In addition,behaviour of ?-carotene nanoemulsion with emulsifiers of whey protein isolate(WPI)and soy protein isolate(SPI)was assessed,as well as the improvement of its stability with Epigallocatechin Gallate(EGCG).Nutritional and functional properties of 25 cultivars of sweet potatoes were studied.Starch,crude protein,crude fat,total dietary fiber,reducing sugar and ash contents ranged between 51.88–69.21,2.36–7.79,0.24–1.11,5.02–14.35,1.07–9.78,1.95–4.29 g/100 g dry weight(DW),respectively.Cultivars of Longshu 515,Pushu 32 and Qinshu No.7(Shanxi province)displayed the highest values in total polyphenol contents(9.38,9.11 and 8.76 mg GAE/g DW respectively),Huangmeigui showed higher flavonoids content(2.54 mg RE/g DW),Xiangshu 2 presented higher anthocyanin content(1.02 mg/g DW),whereas Pushu 32 had the highest ?-carotene content(208.11 ?g/g DW).Strong significant positive correlations were presented between antioxidant activities and total polyphenol and flavonoid contents,indicating that polyphenols and flavonoids are essential antioxidants in sweet potatoes.Among all cultivars,Pushu 32 presented the highest grey relational grade(GRG)value(0.7811),suggesting its importance as a healthy diet.Effects of different cooking processes(boiling,steaming,microwaving,roasting,and frying)on proximate composition,carotenoids and antioxidant activities of OFSP with cultivar of Pushu 32 were investigated.Retentions of 66.30-82.19% of ?-carotene content was observed after boiling(15-35 min),steaming(15,35 and 45 min)and microwaving(15 min).High retentions of(9Z)-?-carotene were noted after all cooking processes,being 515.40% after steaming at 45 min.?-carotene was highly retained after boiling at 15-35 min(103.77-106.74%).A high retention of 91.37% in total polyphenol content was noted after steaming(35 min),whereas 98.98-102.36% of vitamin C was retained after steaming(15-45 min)and microwaving(15 min).All cooking processes improved antioxidant activities of OFSP,and the correlation analysis between carotenoid contents and antioxidant activity suggested that antioxidant activity could be attributed to the higher contents of(9Z)-?-carotene.It was suggested that boiling and steaming are preferable to maintain carotenoids and antioxidant activities of OFSP.The incorporation of ?-carotene into food has a high impact due to its important biological properties.To potentially apply ?-carotene in food,the effect of different emulsifiers(WPI and SPI)on behaviour of ?-carotene nanoemulsion was evaluated.The droplet particle size of initial nanoemulsions stabilized by 1% WPI and 2% SPI were 206 and 210 nm respectively.Significant increases in droplet particle sizes and ?-potential of ?-carotene nanoemulsion were observed after storage under light and dark conditions.The viscosity of all nanoemulsions showed a pseudo plastic behaviour with increase in shear rate.Separation phase was not observed in ?-carotene nanoemulsion stabilized by 1% and 2% WPI under light,and 1% WPI and 2% SPI under dark as compared to others.The retention of ?-carotene decreased significantly after storage under both light and dark.Among which,?-carotene nanoemulsion by 1% WPI under dark displayed the highest retention value 55.93 ?g/ml of ?-carotene and presented better stability after 30 days of storage.Improvement of the stability of ?-carotene nanoemulsion by EGCG was investigated.The initial nanoemulsions with 1% WPI + EGCG,2% WPI + EGCG and 2% SPI + EGCG displayed smaller droplet particle sizes of 193.80,194.46,277.06 and 194.53 nm respectively.After 30 days of storage,significant increases in droplet particle size and ?-potential of ?-carotene nanoemulsion were observed.The viscosity of all nanoemulsions showed a pseudo plastic behaviour with an increase in shear rate.The ?-carotene nanoemulsion stabilized by 1% WPI + EGCG under light and 1-2% WPI + EGCG under dark did not show any separation phase as compared to others during storage.The high ?-carotene content was recorded in the initial nanoemulsion with 1-2% WPI + EGCG(174.08 and 173.24 ?g/mL respectively)and the lowest was found in 1% SPI + EGCG(135.83 ?g/mL)under light.After in vitro digestion,the content of ?-carotene in all digestion phases were significantly decreased,among which the bioaccessibility was higher in nanoemulsion with 1% SPI + EGCG(55.04%).DPPH and ABTS radical scavenging activity of all nanoemulsions after storage revealed significantly decreases as compared to the initial ones.These results suggested that WPI and EGCG showed better binding capacity for protecting ?-carotene nanoemulsion stability.Taken together,OFSP with cultivar of Pushu 32 could be considered as an excellent natural source of ?-carotene for the functional food market.Steaming and boiling are preferable to maintain carotenoids and antioxidant activities of Pushu 32.In addition,?-carotene nanoemulsion stabilized by WPI + EGCG was more stable,while that by SPI + EGCC displayed the highest bioaccessibility after in vitro digestion,which could be potentially utilized in functional food. |
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