| The effect of temperature and extractant?sodium hexametaphosphate?SHMP??concentration on sweet potato pectin recovery from sweet potato starch process waste was investigated and its physico-chemical characteristic and functional properties was studied.Moreover,the effect of ultrasonic treatment on sweet potato pectin physico-chemical properties,and its antioxidant and iron chelation capacity was assessed.Finally,the effect of ultrasonic treated pectin on breast and colon cancer cells was investigated in-vitro.It was noted that temperature and extractant concentration had significant?P<0.01? influence on pectin yield,molecular weight?MW?,and its side chain composition,particularly rhamnose,arabinose and galactose.In addition,it is worth pointing out that the neutral polysaccharide side chains of the extracted sweet potato pectin consisted mainly of galactose,similar to citrus and apple pectin.The maximum pectin yield of 14%w/w dry matter basis was achieved by 90oC and 0.05%SHMP,the pectin degree of methoxylation?DM?and MW values were approximately 12%and 645 kDa,respectively.The FTIR structure analysis confirmed the pectic material as a low methoxyl pectin,with similar band profile as apple pectin.The pectin possessed good antioxidant and high ferrous ion chelation activity.The effect of ultrasound factors?time,power,and duty cycle?on sweet potato pectin molecular weight,neutral sugar composition,pectin structure,and antioxidant activity was studied.Sweet potato pectin dispersions?2.5,5 and 10 mg/mL?in deionized water were sonolyzed for 5,10 and 20 min to assess the effect of pectin concentration on sonolysis.For further experiments 2.5mg/pectin concentration was used to assess the effect varying ultrasonic power and duty cycle levels on pectin sonolysis.Subsequently the molecular weight,galacturonic acid content,DM and antioxidant activity of sonicated pectin products were investigated.Results showed that,sonication of pectin at 200W and400W power led to a reduction in pectin molecular weight from 645 kDa in native pectin to 199.75±30.62 kDa and 103.40±4.10 kDa for 200W and 400W treatment,respectively.The degree of methoxylation decreased to 6.28±0.9 and 5.25±1.3%for 200W and 400W sonication,respectively.On the contrary,the polydispersity did not show a clear trend,which characterized random pectin scission.On the other hand,increasing duty cycle from20%to 80%resulted in 2.8 times reduction in molecular weight,and 100,200 and 400W sonication power led to significant increase in galacturonic acid content from 72.0±1.2%in native pectin to 85.0±3.2%,89.29±3.2%and 92.0±2.7%,respectively.The degree of methoxylation significantly reduced from 12.0%in native pectin to between5.46%,6.28%and 5.25%,at 100,200 and 400W sonication,respectively.Sonication led to increase in galactose and decrease in rhamnose consistent with debranching of pectin.Sonication led to increased antioxidant capacity,with both 200W and 400W sonicated pectin higher oxygen radical absorbance capacity?ORAC?and ferric reducing ability of plasma?FRAP?with highest pectin concentration 4 mg/mL in ORAC and 0.8 mg/mL in FRAP giving substantially high antioxidant activity than native and 100W treated pectin.The ORAC value of 400W sonicated pectin increased five-fold above the native pectin,and it's FRAP value was almost three fold higher than native pectin for the concentrations used.Ultrasound did not alter pectin primary structure as showed by FTIR and high performance exchange chromatography?HPAEC?results and scission was probably random as showed by polydispersity.The effect of 200W and 400W sonication power treatment on sweet potato pectin anticancer activity on human colorectal cancer?HT-29?cell and human breast cancer?MCF-7?cell lines was assessed.Cell proliferation was evaluated by MTT assay,cell cytotoxicity was evaluated by the lactate dehydrogenase?LDH?assay,and apoptosis was assessed by Annexin V/PI flow cytometer,caspase-3 activity,acridine orange-ethidium bromide staining,DAPI staining and DNA laddering assay.Autophagy was assessed by neutral red staining.Finally,the clonogenic capacity of the cells was assessed.The sonicated pectin inhibited cell proliferation with the IC50 values 0.5 mg/mL and 0.75mg/mL for 400W and 200W sonicated pectin,respectively.In addition,it induced cell cytotoxicity?LDH activity?up to 14.41±1.64%for 400W pectin and 6.83±0.80%by 200W sonicated pectin for the concentrations used,significant apoptosis was induced by both pectins and with 400W sonicated pectin showing higher activity.The 400W sonicated pectin induced 19.42%and 42.21%apoptosis at 0.1 mg/mL and 0.5 mg/mL pectin concentrations,respectively.On the other hand,200W pectin induced 13.79%and 39.50%apoptosis at 0.1 mg/mL and 0.5 mg/mL,respectively.The autophagic assay indicated increased autophagic cells with increasing concentration.The 0.5 mg/mL concentration of both 200W and 400W sonicated pectin,induced substantial red stained lysosomes in both MCF-7 and HT-29 cells indicating increased autophagy compared to control and 0.1mg/mL pectin concentration.Sonicated pectins inhibited cancer cells ability to form colonies after treatment by over 30%The results were consistent with increased activity with increased pectin concentration and sonication intensity.Taken together,sweet potato residues is rich in pectin with good anticancer,iron chelation and antioxidant activities.These pectin activities were enhanced by ultrasonic modification,except its ferrous ion chelation capacity. |
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