Effect Of Cutting Styles And Cooking Methods On The Quality And Antioxidant Activity Of Fresh-Cut Sweet Potato(Ipomoea Batatas L.) Cultivars

This research was designed to investigate and compare the effects of three different cutting styles(slice,pie,and shred)and four different cooking methods(frying,boiling,steaming,and microwaving)on the quality characteristics and then analyze antioxidant activity of two different flesh(Purple and Yellow)sweet potato cultivars during six days of storage at 4;And also analyse the effect of cutting styles on the sugar content,membrane integrity and antioxidative enzyme activity of the same fresh-cut sweet potato cultivars.The results were as follows:(1)The effect of cutting styles(slice,pie and,shred)on the quality characteristics and antioxidant activity of purple and yellow flesh sweet potato(PFPT and YFPT)cultivars for six days storage at 4 was investigated.We found that the cutting styles had no significant(p>0.05)effect on the firmness,weight loss and vitamin C content of the sliced and pie-cut samples in both cultivars while that of the shredded sample was negatively affected during the storage.The pie sample had the highest total phenolics,flavonoid and carotenoid accumulation hence had the highest DPPH radical scavenging activity among the cuts in both cultivars.Moreover,the shredded sample had significantly(p<0.05)higher polyphenol oxidase(PPO)activity and,lower antioxidant activity hence had the lowest quality characteristics among the samples.Thus,the finding of this study showed that fresh-cut processing increased the quality and antioxidant activity in the pie-cut while the shredded sweet potato cultivars had reduced quality characteristics.(2)The effect of cutting styles on sugar content,membrane integrity and antioxidative enzyme activity of purple and yellow flesh sweet potato cultivars for six days storage at 4?was investigated.The study found that,initially the sucrose,glucose and fructose levels were not significantly(p>0.05)affected by the fresh-cut processing but decreased significantly among the fresh cuts compared to the whole sweet potato after day four of the storage but slightly decrease in day six of the storage while the sucrose content decreased progressively till the end of the storage period.The yellow sweet potato cultivar had higher sugar content compared to the purple sweet potato and the shredded purple and yellow sweet potato had the lowest.The high MDA content and electrolyte leakage in the shredded sweet potato cultivars indicates a loss of cell membrane integrity and high membrane permeability because of excessive wounding stress.The result further disclosed the excessive wounding stress increased the rate of production of reactive oxygen species(ROS)and which activated the antioxidative enzymes(SOD,APX and CAD)to modulate excessive ROS level.Thus,the finding of this study further revealed that fresh-cut processing using the shredding cutting styles decreased the sugar content,the membrane integrity and consequently increased the levels of ROS while the pie-cut sweet potato cultivars maintained the sugar content and the membrane integrity of the fresh-cut sweet potato cultivars.(3)Based on the previous experimental results,the pie-cut style was selected to further study the effects of different cooking methods on the chemical,antioxidant and sensory quality of fresh-cut purple and yellow-sweet sweet potatoes.The results showed that boiling produced the highest increase in the total phenolics,flavonoids,and carotenoids content among the four cooking methods in the pie fresh-cut sweet potato cultivars while frying resulted in the significant(p<0.05)reduction in the total phenolics,flavonoids,and carotenoids content.The total phenolics.flavonoids and carotenoids content of steamed and microwaved cultivars were not significantly(p>0.05)affected by the cooking methods compared to the raw sample.The DPPH radical scavenging activity and the ferric reducing antioxidant power in both purple and yellow flesh sweet potato cultivars increased in the boiled,steamed and microwaved samples while the fried sample had lower antioxidant activity compared to the raw sample.Furthermore,the sensory evaluation of pie-cut sweet potatoes with different cooking methods showed that the fried sample received the highest rating for flavor and color while the boiled,steamed and microwaved sweet potato cultivar had the best taste and sweetness with the same general acceptability rating.This signifies that pie fresh-cut processing is an important procedure for increasing the chemical,antioxidant and sensory attributes of purple and yellow flesh sweet potato cultivars.The result of this study provides useful information that will help improve the health-promoting properties of processed sweet potatoes and develop a functional product.