Progress 11/15/03 to 11/14/06
Outputs
Anthocyanins in purple-flesh sweet potato (PFSP) cultivar Terlaje grown in the Western Pacific island of Guam were investigated from September 15, 2003 to September 14, 2007. The flesh of the PFSP cultivar Terlaje possessed about equivalent pn 3-caf.sop-5-glc 80 mg/100 g fresh weight. The spectrum of the anthocynin extract from PFSP demonstrated anthocyanins were dominantly acylated with caffeic acid. Steaming PFSP tubers for 30 minutes stabilized anthocyanins content and freeze and air dehydration of steamed PFSP at 60C for 24 hours retained the anthocyanin content in PFSP powder. The PFSP powder exhibited antioxidant capacity at 7600-9300 ORAC unit and total phenols at 400-500 mg gallic acid/100 g dry weight. The PFSP powder exhibited purplish color with a hue angle at -18-24 degree and Chroma at 16-27. The noodles made with PFSP powder at 40% exhibited pleasant purple color and equivalent sensory quality to commercial noodles and were accepted by consumers.
Heat treatment of PFSP anthocyanins extract at pH 1 and 3 for 3 hours resulted in a substantial loss of anthocyanin content. During 30 day storage of anthocyanin extract from PFSP powder, the anthocyanin content retained 100% at pH 1, 80% at pH 3, 65% at pH 5, 35% at pH 7, 7% at pH 9. In fluorescent light treatment for 64 days, anthocyanin extract from PFSP powder lost about 60% of anthocyanin content at pH 1, while anthocyanin extract covered with aluminum foil did not exhibit a change of anthocyanin content. Compared the stability of anthocyanin extract from PFSP with anthocyanin extracts from red cabbage and grape skin, PFSP anthocyanins were more stable than that of grape skin but less stable than that of red cabbage. The research results of this purple-flesh sweet potato project were presented in the IFT annual meeting in 2005 and 2006, in the 2006 Western Pacific Tropical Research Center conference, and in the regional conference at the University of Guam. One research
manuscript was completed and in the process of review. Two more research manuscripts will be written and submitted to refereed journals.
Impacts
Anthocyanins in purple sweet potato are stable in neutral pH during steaming and dehydration. Steaming and dehydration can be used to process purple sweet potato powder as food ingredient with good pleasant purple color. Although purple sweet potato possessed high content acylated anthocyanins, the anthocaynin of purple sweet potato was not stable to light. Application of anthocyanin extracts of purple sweet potato in acidic foods requires no exposure to light during storage. This research information will be useful for food industries to consider applying purple sweet potato powder or anthocyanin extract from purple sweet potato in food products.
Publications
- Yang, J and Gadi RL. 2007. Anthocyanin content, color charateristics, and antioxidant capacity of Western Pacific Purple Sweet Potatoes (Ipomoea batatas) as affected by steaming and dehydration. Journal of Food Sciences. In the process of review.
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Progress 01/01/05 to 12/31/05
Outputs
Anthocyanins are natural pigments alternative to synthetic colorants. Purple sweet potato (PSP) possesses high content of acylated anthocyanins, which are more stable than non-aclylated anthocyanins to pH, heat and light. The stability of anthocyanin of PSP was determined during steaming and dehydration. The PSP cultivar Terlaje were steamed for 0, 0.5, 1, 2 and 4 hours. The PSP steamed for 0.5 hour were dehydrated at 55 C for 0, 4, 8, 20, 24 hours. Anthocaynins were extracted with 1% HCl acidic water from steamed or dehydrated PSP. The total anthocyanin content was measured with the UV spectrophotometer based on monomeric anthocyanin pn 3-caf.sop-5-glc (mg/100 g fresh weight). Polymeric anthocyanins were assayed with bisulfite-treated extract. The hue angle and chroma (C) of PSP were calculated from color values L, a and b measured by a Chroma meter. Steaming PSP for 0.5 hour resulted in an increase of anthocyanin content from 42 to 60 mg/100 g and a decrease of h
from -8.5 to -26.5 and C from 28.7 to 21.6, indicating an enhancement of purple color of PSP. Steaming PSP for 1 to 4 hours caused a decrease of anthocyanin content from 47 to 42 mg/100 g and of h from -25.04to -1.94and of C from 21.6 to 19.7. Although dehydration for 24 hours resulted in an increase of about 50% of polymeric color, the dehydration did not decrease anthocayanin content of steamed PSP. After 24 hour dehydration, the PSP powder exhibited a color value at h -18.1 and C 27.9. The effect of light on PSP anthocyanin extracts was also investigated during storage. Semi-purified anthocyanin extracts were prepared with C-18 Sep-Pak catridges. The anthocyanin extracts at pH 1 were treated with fluorescence light for 2 months. The stability of anthocyanin were determined with total anthocyanin content or the UV/Vis spectrum and color value (L, a, b). The stability of anthocyanin of PSP was also compared with that of red cabbage, grape skin, and synthetic colorant Red #40. the The
Tinctorial strength of the colorants in pH 1 buffer was also measured. Light-treated PSP anthocyanin extracts exhibited a 5% increase in absorbance at 520 nm on the first day and then a decrease of 55% in absorbance after 2 months storage. The lightness (L) value is increased from 85 to 88. The red (a*) and blue (b) color values decreased from 9 to 3 and 4 to 2, respectively. Non-light-treated PSP extracts exhibited a 10% increase in absorbance and no significant changes in L*, a* and b* values during 2 month storage. The light stability of anthocyanin extracts and synthetic colorant was: Red #40 > red cabbage > purple sweet potato > grape skin.
Impacts
Anthocyanins in purple sweet potato are stable in neutral pH during steaming and dehydration. Steaming and dehydration can be used to process purple sweet potato powder as food ingredient with good pleasant purple color. Although purple sweet potato possessed high content acylated anthocyanins, the anthocaynin of purple sweet potato was not stable to light. Application of anthocyanin extracts of purple sweet potato in acidic foods requires no exposure to light during storage. This research information will be useful for food industries to consider applying purple sweet potato powder or anthocyanin extract from purple sweet potato in food products.
Publications
- Yang J. and Gadi R.L. 2006. The stability of anthocyanin in purple flesh sweet potato (Ipomoea batatas L.) during steaming and dehydration. The 2006th IFT Annual Meeting, Orlando, FL. Abstract of Presentation (Submitted).
- Gadi R and Yang J. 2006. The stability of anthocyanin extracts from purple flesh sweet potato (Ipomoea batatas L.) as affected by light. Annual Conference of College of Liberal ARTS and Social Sciences (CLASS), University of Guam, Abstract of Presentation (Submitted).
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Progress 01/01/04 to 12/31/04
Outputs
Fresh or steamed purple sweet potatoes were dehydrated with freeze dry, hot air, and vacuum oven. Powders were extracted with 1% HCL acidic water. The total anthocyanin content was measured with the UV spectrophotometer based on monomeric anthocynin pn 3-caf.sop-5-glc. Polymeric anthocaynins were assayed with bisulfite treated extracts. The noodle color preferences were evaluated with consumer acceptance test. The anthocyanin contents of powders from fresh and steamed sweet potatoes are 2.16 and 2.17 mg/gram by freeze dry, 1.03 and 1.48 mg/gram by hot air dry, and 1.19 and 1.18 mg/gram by vacuum oven dry, respectively. The polymeric anthocyanin contents of powders from fresh and steamed sweet potatoes are 9.4 and 36.8% by freeze dry, 19.5 and 21.1% by hot air dry, and 30.8 and 40.5% by vacuum oven dry, respectively.
Impacts
The purple sweet potato powders from the Western Pacific can be potentially applied in foods. An abstract Anthocaynin content and color characteristics of the Western Pacific sweet potato (Ipomoea batatas) powders was submitted to the 2005 IFT Annual Meeting for presentation in New Orleans, LA.
Publications
- No publications reported this period
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