Polyphenol oxidase, a bi-functional enzyme, has been implicated in enzymatic browning of yam and other tubers in a negative way. The objective of this present study was to examine the activity of polyphenol oxidase in...Polyphenol oxidase, a bi-functional enzyme, has been implicated in enzymatic browning of yam and other tubers in a negative way. The objective of this present study was to examine the activity of polyphenol oxidase in Dioscorea rotundata. Var. laasirin and the efficiency of heat and chemical treatments in inhibiting this enzyme. Crude Polyphenol Oxidase （PPO） of Dioscorea rotundata.Var. Laasirin was isolated and the kinetics studied using the lineweaver-burk plot. The activity of the enzyme was evaluated using spectrophotomeric method. Yam PPO catalyzes oxidation of various substrates with catechol being the most readily oxidized substrate. The Michaelis-Menten constant （Km） and maximum reaction velocity （Vmax） for yam PPO were 0.00037 and 0.3125 respectively. Inhibition data showed that the enzyme had least activity （71.70） when blanched at 95℃ for 7 mins with chemical treatment involving a combination of 0.5% Sodium metabisulphite （Food grade） and 0.5% Ascorbic acid （Food grade）. The activity was highest （83.02） when it was blanched at 95 ℃ for 7 rains. This study has shown that it is possible to inhibit polyphenol oxidase activity in white yam using the chemical pretreatments and processing conditions described in this study for possible adoption in the production of packaged frozen yam chips by food industries.展开更多
In a completely randomized blocks （RCB） plot, we planted seed from the three segments of Kponan tubers： head, median and tail portions with control Krengle. Germination began 10 d and lasted 67 d. The mean sproutin...In a completely randomized blocks （RCB） plot, we planted seed from the three segments of Kponan tubers： head, median and tail portions with control Krengle. Germination began 10 d and lasted 67 d. The mean sprouting rate of the Kponan full season harvest tuber was 78.1% compared to 94% in Krengle. However, the tuber germination was progressive from head to tail with a linear evolution of the top fragments with sprouting rate up to 90% similar to Krengle. The median and distal portions sprout two and three weeks later with final raising rates reaching 68% and 71%, respectively. The full season tuber of Kponan sprouts with a good rate gave good yields for any portion of the tuber. It had a sprouting gradient oriented from the proximal portion to the distal one, while yield was better for medium seeds. The sprouting delays two weeks between proximal and medium portions and three weeks between proximal and distal portions were acceptable with regards to the total cycle of eight to nine months period. Thus, its small tubers could be planted as well as the top portion of big tuber. In terms of yield, Kponan medium seed gave the best yield 34.25 t/ha and the whole Kponan tuber yield was more than Krengle. That led to a better multiplication factor for Kponan full season tuber. The type of tuber, if available, could be used as seed for yam production. That could improve its distribution and contribute to food security.展开更多
To study the characteristics of tuber starchgranules,firstly,three kinds of common tuber starches were separated and characterized by gravitational field-flow fractionation(GrFFF)instrument,and the ratios of large and...To study the characteristics of tuber starchgranules,firstly,three kinds of common tuber starches were separated and characterized by gravitational field-flow fractionation(GrFFF)instrument,and the ratios of large and small starch granules A/B were calculated.Then,the liquid of peak A and peak B was collected and observed by scanning electron microscope(SEM)to verify the separation result of GrFFF.Secondly,the particle size distribution and crystal characteristics were characterized by particle size analyser,X-ray diffraction(X-ray)and fourier transform infrared spectroscopy(FT-IR).Three kinds of tuber starches all had the bimodal distribution in GrFFF.Peak A contained large particles,and peak B contained small particles.For yam starch,the ratio of starch granules A/B was much higher than 1;for sweet potato starch the ratio was approximately equal to 1;for tapioca starch,the ratio was much lower than 1.Moreover,the starch granules of sweet potato and tapioca were both A-type crystallinity,while yam starch granules were C-type crystallinity.GrFFF could be used to characterize and separate large and small granules of tuber starches and estimate the ratio of starch granules A/B.Yam starch was suitable for the development of slowly digestible starch(one kind of functional food),which could delay the occurrence of metabolic syndrome,diabetes and cardiovascular diseases.Tapioca starch was suitable for plant capsules,which were safer than gelatin capsule and could prevent the"poison capsule"incident from happening.展开更多
文摘Polyphenol oxidase, a bi-functional enzyme, has been implicated in enzymatic browning of yam and other tubers in a negative way. The objective of this present study was to examine the activity of polyphenol oxidase in Dioscorea rotundata. Var. laasirin and the efficiency of heat and chemical treatments in inhibiting this enzyme. Crude Polyphenol Oxidase （PPO） of Dioscorea rotundata.Var. Laasirin was isolated and the kinetics studied using the lineweaver-burk plot. The activity of the enzyme was evaluated using spectrophotomeric method. Yam PPO catalyzes oxidation of various substrates with catechol being the most readily oxidized substrate. The Michaelis-Menten constant （Km） and maximum reaction velocity （Vmax） for yam PPO were 0.00037 and 0.3125 respectively. Inhibition data showed that the enzyme had least activity （71.70） when blanched at 95℃ for 7 mins with chemical treatment involving a combination of 0.5% Sodium metabisulphite （Food grade） and 0.5% Ascorbic acid （Food grade）. The activity was highest （83.02） when it was blanched at 95 ℃ for 7 rains. This study has shown that it is possible to inhibit polyphenol oxidase activity in white yam using the chemical pretreatments and processing conditions described in this study for possible adoption in the production of packaged frozen yam chips by food industries.
文摘In a completely randomized blocks （RCB） plot, we planted seed from the three segments of Kponan tubers： head, median and tail portions with control Krengle. Germination began 10 d and lasted 67 d. The mean sprouting rate of the Kponan full season harvest tuber was 78.1% compared to 94% in Krengle. However, the tuber germination was progressive from head to tail with a linear evolution of the top fragments with sprouting rate up to 90% similar to Krengle. The median and distal portions sprout two and three weeks later with final raising rates reaching 68% and 71%, respectively. The full season tuber of Kponan sprouts with a good rate gave good yields for any portion of the tuber. It had a sprouting gradient oriented from the proximal portion to the distal one, while yield was better for medium seeds. The sprouting delays two weeks between proximal and medium portions and three weeks between proximal and distal portions were acceptable with regards to the total cycle of eight to nine months period. Thus, its small tubers could be planted as well as the top portion of big tuber. In terms of yield, Kponan medium seed gave the best yield 34.25 t/ha and the whole Kponan tuber yield was more than Krengle. That led to a better multiplication factor for Kponan full season tuber. The type of tuber, if available, could be used as seed for yam production. That could improve its distribution and contribute to food security.
文摘To study the characteristics of tuber starchgranules,firstly,three kinds of common tuber starches were separated and characterized by gravitational field-flow fractionation(GrFFF)instrument,and the ratios of large and small starch granules A/B were calculated.Then,the liquid of peak A and peak B was collected and observed by scanning electron microscope(SEM)to verify the separation result of GrFFF.Secondly,the particle size distribution and crystal characteristics were characterized by particle size analyser,X-ray diffraction(X-ray)and fourier transform infrared spectroscopy(FT-IR).Three kinds of tuber starches all had the bimodal distribution in GrFFF.Peak A contained large particles,and peak B contained small particles.For yam starch,the ratio of starch granules A/B was much higher than 1;for sweet potato starch the ratio was approximately equal to 1;for tapioca starch,the ratio was much lower than 1.Moreover,the starch granules of sweet potato and tapioca were both A-type crystallinity,while yam starch granules were C-type crystallinity.GrFFF could be used to characterize and separate large and small granules of tuber starches and estimate the ratio of starch granules A/B.Yam starch was suitable for the development of slowly digestible starch(one kind of functional food),which could delay the occurrence of metabolic syndrome,diabetes and cardiovascular diseases.Tapioca starch was suitable for plant capsules,which were safer than gelatin capsule and could prevent the"poison capsule"incident from happening.
