Sweet Potato Anthocyanins Research Articles

Copigmentation effects and thermal degradation kinetics of purple sweet potato anthocyanins with metal ions and sugars

The copigmentation effects of purple sweet potato anthocyanins (PSPAs) with metal ions and sugars were investigated in model solutions at pH 4. The thermal stability of PSPAs was also explored in the presence of sugars and 5-hydroxymethylfurfural (5-HMF). Copigmentation are characterized by hyperchromic effect and bathochromic shift. The hyperchromic effect of Fe3+ reached 25.15 % even at a very low concentration 0.005 mol L−1, while the values of the other metal ions at 0.05 mol L−1 were ranked in the following ascending order: K+ < Ca2+ < Mg2+ < Zn2+ < Cu2+ < Fe2+ < Al3+. The bathochromic shift was not observed in all sugar reaction solutions; glucose showed the highest values of hyperchromic effect at the concentration range 150–300 g L−1, followed by fructose and sucrose; konjac glucomannan showed the highest effect even at a much lower concentration among the macromolecular sugars. Especially, the konjac glucomannan exhibited a much better color enhancement than glucose. Small molecular sugars accelerated the thermal degradation of PSPAs, whereas macromolecular sugars showed a protective effect particularly at high temperatures. Moreover, 5-HMF resulted in the deterioration of the thermal stability of PSPAs and was suggested to be an important labile factor for copigmented PSPA solutions.

Effects of deodorization on the physicochemical index and volatile compounds of purple sweet potato anthocyanins (PSPAs)

Abstract To produce high quality purple sweet potato anthocaynins (PSPAs) extract, a deodorization process was developed and its effects on the physicochemical index including total anthocyanins, total sugar and protein, soluble solids, color values, degradation index (DI), brown index (BI) and clarity were investigated. The product sensory quality was also evaluated. The volatile compounds were analysed by headspace solid-phase microextraction coupled with gas chromatography–mass spectrometry (HS-SPME-GC/MS). The results indicated that using AB-8 macroporous resin purification coupled with chitosan adsorption could be an effective method in deodorization of the anthocyanin crude extract from purple sweet potato. Some byproducts in the anthocyanin crude extracts, such as sugars and proteins, had been removed by about 85% and 76% respectively. Compared with the raw anthocyanin extract, the volatile substances in the final product of PSPAs were changed and the unpleasant characteristic odors, such as some alcohols, aldehydes, organic acids and alkanes, were decreased. However, the product yield was also decreased by about 26% after the deodorization process.

EFEKTIFITAS LARUTAN UBI JALAR UNGU (IPOMEA BATATAS) DENGAN BUAH NAGA BERDAGING MERAH (HYLOCEREUS POLYRHIZUS) SEBAGAI BAHAN IDENTIFIKASI PLAK (DISCLOSING SOLUTION)

TITLEEffectiveness of purple sweet potatoes (Ipomea batatas) and red dragon fruit (Hylocereus polyrhizus) as plaque identification agent (disclosing solution)ABSTRACTThe content of the dye in purple sweet potato anthocyanins and carotenoids content of dyes in the red dragon fruit, has the potential a source of natural dyes. Plaque is usually formed on a third surface of the gingival and the tooth surface is rough, form biofilm, known as plaque. Plaque can absorb dyes that can indicate the presence of biofilm. The research objective was to determine differences in the ability of the solution to the purple sweet potato red fleshed dragon fruit as materials identification plaque (disclosing solution).The method used is Experimental Research. Design used is Posttest Only Design. Samples were taken 30 people and divided into 2 groups. Group 1st amounted to 15 people given treatment solution dripping purple sweet potato, and the second group totaled 15 people given treatment solution dripping red dragon fruit. Analysis of the data used in this study is Test Independent Test.The results showed the averages value of the plaque index in a solution of purple sweet potato 2.221 and the average value of the plaque index in the red dragon fruit 2.875. Result of Independent T-test has Sig 0.13 means that there are differences in the ability to use the solution with a purple sweet potato red fleshed dragon fruit as materials identification plaque (p 0.05). As a material it is necessary to identify plaque dyes that can be embedded in dental plaque, antosianin amount of content that has the in herentability of the dye solution and based on research results more red dragon fruit can identify plaque compared with a solution of purple sweet potato. Keywords: Sweet potato purple, red dragon fruit, Plaque Index

Pre-heating and polyphenol oxidase inhibition impact on extraction of purple sweet potato anthocyanins

Purple sweet potatoes (PSP) have been used as a natural food colorant with high acylated anthocyanins concentrations. Commercially extracting pigments from PSP can be challenging due to firm texture and high polyphenol oxidase (PPO) content. These studies evaluated hot water immersions (30, 50, 70, and 90°C for 10min) as pre-heating treatments and addition of PPO inhibitors (citric acid, oxalic acid, and sodium borate) to aqueous extraction solutions to aid pigment recovery. Predominant PSP anthocyanins included acylated cyanidin or peonidin derivatives. Non-pigmented cinnamates acted as oxidase substrates and induced co-oxidation reactions with anthocyanins. Pre-heating PSP significantly increased polyphenolic yields in a temperature-dependent manner, consistent with tissue softening and PPO inactivation. The use of solvent modifiers in the extraction solution associated with heat helped minimize enzyme action and increased polyphenolic recovery. Minimizing the impact of PPO with heat was critical to the extraction and recovery of PSP anthocyanins, suitable for food use.

The physicochemical properties of microwave-assisted encapsulated anthocyanins from Ipomoea batatas as affected by different wall materials.

This study focuses on the impact of different wall materials on the physicochemical properties of microwave-assisted encapsulated anthocyanins from Ipomoea batatas. Using the powder characterization technique, purple sweet potato anthocyanin (PSPAs) powders were analysed for moisture content, water activity, dissolution time, hygroscopicity, color and morphology. PSPAs were produced using different wall materials: maltodextrin (MD), gum arabic (GA) and a combination of gum arabic and maltodextrin (GA + MD) at a 1:1 ratio. Each of the wall materials was homogenized to the core material at a core/wall material ratio of 5 and were microencapsulated by microwave-assisted drying at 1100 W. Results indicated that encapsulated powder with the GA and MD combination presented better quality of powder with the lowest value of moisture content and water activity. With respect to morphology, the microcapsule encapsulated with GA + MD showed several dents in coating surrounding its core material, whereas other encapsulated powders showed small or slight dents entrapped onto the bioactive compound. Colorimetric analysis showed changes in values of L, a*, b*, hue and chroma in the reconstituted powder compared to the initial powder.

The influences of purple sweet potato anthocyanin on the growth characteristics of human retinal pigment epithelial cells

BackgroundAnthocyanins have been proven to be beneficial to the eyes. However, information is scarce about the effects of purple sweet potato (Ipomoea batatas, L.) anthocyanin (PSPA), a class of anthocyanins derived from purple sweet potato roots, on visual health.ObjectiveThe aim of this study was to investigate whether PSPA could have influences on the growth characteristics (cellular morphology, survival, and proliferation) of human retinal pigment epithelial (RPE) cells, which perform essential functions for the visual process.MethodsThe RPE cell line D407 was used in the present study. The cytotoxicity of PSPA was assessed by MTT assay. Then, cellular morphology, viability, cell cycle, Ki67expression, and PI3K/MAPK activation of RPE cells treated with PSPA were determined.ResultsPSPA exhibited dose-dependent promotion of RPE cell proliferation at concentrations ranging from 10 to 1,000 µg/ml. RPE cells treated with PSPA demonstrated a predominantly polygonal morphology in a mosaic arrangement, and colony-like cells displayed numerous short apical microvilli and typical ultrastructure. PSPA treatment also resulted in a better platform growing status, statistically higher viability, an increase in the S-phase, and more Ki67+ cells. However, neither pAkt nor pERK were detected in either group.ConclusionsWe found that PSPA maintained high cell viability, boosted DNA synthesis, and preserved a high percentage of continuously cycling cells to promote cell survival and division without changing cell morphology. This paper lays the foundation for further research about the damage-protective activities of PSPA on RPE cells or human vision.

KARAKTERISTIK WARNA DAN AKTIVITAS ANTIOKSIDAN ANTOSIANIN UBI JALAR UNGU [Color Characteristics and Antioxidant Activity of Anthocyanin Extract from Purple Sweet Potato

Anthocyanin is a natural pigment with color varying from red, purple, blue to yellow. The stability of its anthocyanin color is affected by pH, temperature and light. Purple sweet potato is rich in anthocyanin, particularly a stable acylated anthocyanin. This research was conducted to study the effect of pH on color and antioxidative activity of anthocyanin extracted from purple sweet potatoes harvested from Cilembu-Sumedang, Banjaran-Bandung, and Pakembangan-Kuningan. The experiments applied a completely randomized design with two replicates analyzed triplo.The results showed that the total number of monomeric anthocyanin in purple sweet potato harvested from Cilembu (3.78±0.08 mg cyanidin-3-glucoside/g dry weight, dw) was higher than that of Banjaran (3.18±0.01 mg/g) and Pakembangan (2.25±0.01 mg/g). The color of purple sweet potato anthocyanin extract was pH dependent. The color changed from red, faded red, purple, blue, green and yellow along with the increase of pH from 1 to 14. The content of anthocyanins from three locations of purple sweet potatoes differed from each other (p<0.05). Radical scavenging activity and reducing power of purple sweet potato anthocyanins extract at pH 1 was higher than that at pH 4.5 and pH 7.

Buffering colour fluctuation of purple sweet potato anthocyanins to acidity variation by surfactants

Anthocyanins are intriguing natural pigments with beneficial bioactivities and their colour is extremely susceptible to acidity variation. Minimisation of colour fluctuation is essential to maintain quality consistency in food industry. A new strategy employing surfactants to mimic encapsulation was attempted with typical anionic, cationic and nonionic surfactants and proved effective although the traditional copigmentation method was inactive. The exceptional colour fluctuation buffering effect of anionic surfactants especially sodium dodecyl sulphate (SDS) was revealed and then carefully analysed by colorimetric and spectroscopic methods. The outstanding activity of SDS presumably resulted from effective shielding of anthocyanins from external acidity through strong interaction with the positively charged flavylium cations owing to its anionic nature. These results suggest SDS is a valuable additive for buffering colour fluctuation of anthocyanins. The strategy of surfactant will be useful for buffering colour fluctuation of natural colourants.

Oral Hepatoprotective Ability Evaluation of Purple Sweet Potato Anthocyanins on Acute and Chronic Chemical Liver Injuries

In recent years, chemical liver injury cases increased significantly in Asian countries, and the imbalance in redox system was believed to be the main cause. Purple sweet potato anthocyanins (PSPA) have been shown to exert antioxidant activity and oxidative-stress-associated functional protein modulation through various signaling pathways, so it is considered to have the potential of liver injury preventive activity. In order to evaluate the hepatoprotective potency of PSPA according to its free radical scavenging and antioxidant effects, three acute chemical liver injury models were set up with ethanol, acetaminophen and carbon tetrachloride. PSPA at moderate and high doses obviously attenuated the tested serum biomarker levels and liver index in our experiments. Besides, one chronic liver injury model set up with carbon tetrachloride was also applied, in which PSPA was orally administrated after the liver damage had been formed. Both the serum biomarker levels and histopathological analysis showed that PSPA was able to attenuated chronic liver injury. Our experimental results demonstrated the potential of PSPA as an oral hepatoprotective agent against chemical liver injury from food plant.

Degradation kinetics of anthocyanins from purple sweet potato (Ipomoea batatas L.) as affected by ascorbic acid

Storage (4°C and 25°C, 28 days) and thermal (70°C–90°C, 6 h) stabilities of purple sweet potato anthocyanins (PSPAs) with varying concentrations of ascorbic acid (AA) were investigated in a model soft drink medium. For storage stability, the model drink was sterilized at 85°C for 15 min prior to storage. Zero-order kinetics and first-order kinetics were fitted for storage degradation at 4°C and 25°C, respectively. However, all data for thermal degradation fitted first-order kinetics. The temperature dependence on degradation was modeled after the Arrhenius equation. Storage degradation of PSPAs was increased by the presence of AA (40–360 mg/L). Retarded thermal degradation was be achieved by adding 120 mg/L of AA, while accelerated thermal degradation resulted from 360 mg/L of AA. Heat treatment did not markedly change the DPPH radical-scavenging activity of PSPAs.

Identification of Anthocyanins in Purple‐fleshed Sweetpotato and Stability during Various Cooking Conditions

We previously selected a purple‐fleshed sweetpotato P40 that prevented colorectal cancer in a murine model. This study is to identify anthocyanins and tested stability. P40 contains anthocyanins up to 13 mg/g dry matter. Total 12 acylated anthocyanins have been identified by HPLC‐MS/MS. The top three anthocyanins are cyanidin 3‐caffeoyl‐p‐hydroxybenzoyl sophoroside‐5‐glucoside, peonidin 3‐caffeoyl sophoroside‐5‐ glucoside, and cyanidin 3‐(6″ ‐caffeoyl‐6″‐feruloylsophoroside)‐5‐ glucoside. Seven acylated cyanidin species and five peonidin species contribute for 69% and 31% of total anthocyanins, respectively. Over 80% belong to cyanidin as measured by acid hydrolysis. Therefore, as a cyanidin‐predominated variety, P40 is unique when compared with other purple‐fleshed sweetpotatoes that usually contain more peonidin than cyanidin. While baking does not impact overall anthocyanins, steaming, high pressure cooking, microwaving, and frying significantly reduce 20% of total anthocyanins. Mono‐acylated anthocyanins show a higher resistance against heat than di‐ and non‐acylated. Among of which, cyaniding 3‐p‐hydroxybenzoylsophoroside‐5‐glucoside exhibits the best thermal stability. Better understanding of sweetpotato anthocyanins and stability may lead the development of a functional product for health benefits (supported by USDA Cooperative KS410–0214022).

Identification and thermal stability of purple-fleshed sweet potato anthocyanins in aqueous solutions with various pH values and fruit juices

Thirteen anthocyanins were identified in the purple-fleshed sweet potato cultivar Jihei No. 1. The main anthocyanins were 3-sophoroside-5-glucoside derivatives from cyanidin and peonidin, acylated with p-hydroxybenzoic acid, ferulic acid, or caffeic acid. A unique anthocyanin, delphinidin-3,5-diglucoside was also found. The thermal stability of purple-fleshed sweet potato anthocyanins (PSPAs) followed a first-order kinetics model. Aqueous solutions with various pH (2, 3, 4, 5, and 6) and fruit juices (apple, pear, grapefruit, orange, tangerine, kiwifruit, and lemon) were coloured with PSPAs. The enrichment and degradation kinetics of anthocyanins in these matrices were investigated at 80, 90, and 100°C. A higher stability of anthocyanins was obtained in aqueous solutions with pH 3 and 4 and in apple and pear juices. Moreover, the activation energies for PSPA degradation in aqueous solutions with various pH and fruit juices ranged from 66.56kJ/mol to 111.57kJ/mol and 46.76kJ/mol to 75.68kJ/mol, respectively.

Purple sweet potato anthocyanins attenuate hepatic lipid accumulation through activating adenosine monophosphate–activated protein kinase in human HepG2 cells and obese mice

Purple sweet potato is a functional food rich in anthocyanins that possess disease-preventive properties. Anthocyanins are known to possess potent antidiabetic properties. However, the effect of the anthocyanin fraction (AF) from purple sweet potato on hepatic lipid metabolism remains unclear. Our hypothesis is that AF inhibits hepatic lipid accumulation through the activation of adenosine monophosphate-activated protein kinase (AMPK) signaling pathways in vitro and in vivo. In this study, we evaluated body weight, liver histology, and hepatic lipid content in high-fat diet (HFD)-fed ICR mice treated with AF. In addition, we characterized the underlying mechanism of AF's effects in HepG2 hepatocytes through Western blot analysis. Anthocyanin fraction (200 mg/kg per day) reduced weight gain and hepatic triglyceride accumulation and improved serum lipid parameters in mice fed an HFD for 4 weeks. Anthocyanin fraction significantly increased the phosphorylation of AMPK and acetyl-coenzyme A carboxylase (ACC) in the liver and HepG2 hepatocytes. In addition, AF down-regulated the levels of sterol regulatory element-binding protein 1 and its target genes including ACC and fatty acid synthase (FAS). The specific AMPK inhibitor compound C attenuated the effects of AF on the expression of lipid metabolism-related proteins such as SREBP-1 and FAS in HepG2 hepatocytes. The beneficial effects of AF on HFD-induced hepatic lipid accumulation are thus mediated through AMPK signaling pathways, suggesting a potential target for the prevention of obesity.

Protective effect of supplemental anthocyanins on Arabidopsis leaves under high light

Ten anthocyanin components have been detected in roots of purple sweet potato (Ipomoea batatas Lam.) by high-performance liquid chromatography coupled to diode array detection and electrospray ionization tandem mass spectrometry. All the anthocyanins were exclusively cyanidins or peonidin 3-sophoroside-5-glucosides and their acylated derivatives. The total anthocyanin content in purple sweet potato powder obtained by solid-phase extraction was 66 mg g(-1). A strong capacity of purple sweet potato anthocyanins (PSPA) to scavenge reactive oxygen species (superoxide, hydroxyl radical) and the stable 1,1-diphenyl-2-picrylhydrazyl organic free radical was found in vitro using the electron spin resonance technique. To determine the functional roles of anthocyanins in leaves in vivo, for the first time, supplemental anthocyanins were infiltrated into leaves of Arabidopsis thaliana double mutant of the ecotype Landsberg erecta (tt3tt4) deficient in anthocyanin biosynthesis. Chlorophyll fluorescence imaging showed that anthocyanins significantly ameliorated the inactivation of photosystems II during prolonged high-light (1300 micromol m(-2) s(-1)) exposure. Comet assay of DNA revealed an obvious role of supplemental PSPA in alleviating DNA damage by high light in leaves. Our results suggest that anthocyanins could function in vitro and in vivo to alleviate the direct or indirect oxidative damage of the photosynthetic apparatus and DNA in plants caused by high-light stress.

Functional New Acylated Sophoroses and Deglucosylated Anthocyanins in a Fermented Red Vinegar

The new acylated polyphenols were isolated from a red-colored vinegar produced via fermentation with purple-fleshed sweet potato storage roots, and identified mainly by MS and NMR. The three acylated sophoroses were determined as 6-O-(E)-caffeoyl-(2-O-(6-O-acyl)-beta-d-glucopyranosyl)-d-glucopyranoses, where acyl was (E)-caffeoyl, p-hydroxybenzoyl, and (E)-feruloyl, respectively. The four acylated anthocyanins were also determined as cyanidin 3-O-(6-O-(E)-caffeoyl-(2-O-(6-O-(E)-feruloyl)-beta-d-glucopyranosyl)-beta-d-glucopyranoside), in addition to peonidin 3-O-(6-O-(E)-caffeoyl-(2-O-(6-O-acyl)-beta-d-glucopyranosyl)-beta-d-glucopyranosides), where acyl was (E)-caffeoyl, p-hydroxybenzoyl, and (E)-feruloyl, respectively. The diacylated sophoroses showed higher antioxidant capacity than that of monoacylated analogue 6-caffeoylsophorose, so the multiacylation established to enhance their antioxidant capacity. Similarly, 5-deglucosylated anthocyanins also gave somewhat stronger antioxidation than corresponding sweet potato anthocyanins. In rat intestinal alpha-glucosidase inhibition study, the diacylated sophoroses preferably inhibited maltase rather than sucrase with an IC(50) value of <300 microM, indicating a potential role as antidiabetic phytochemicals. These acylated polyphenols in a red vinegar were expected to play important functional roles for health.

Effect of Purple Sweet Potato Anthocyanins on β-Amyloid-Mediated PC-12 Cells Death by Inhibition of Oxidative Stress

Amyloid-beta peptide (Abeta) is known to induce the redox imbalance, mitochondrial dysfunction and caspase activation, resulting in neuronal cell death. Treatment with antioxidants provided a new therapeutic strategy for Alzheimer's disease (AD) patients. Here we investigate the effects of purple sweet potato anthocyanins (PSPA), the known strong free radical scavengers, on Abeta toxicity in PC12 cells. The results showed that pretreatment of PC12 cells with PSPA reduced Abeta-induced toxicity, intracellular reactive oxygen species (ROS) generation and lipid peroxidation dose-dependently. In parallel, cell apoptosis triggered by Abeta characterized with the DNA fragmentation and caspase-3 activity were also inhibited by PSPA. The concentration of intracellular Ca(2+) and membrane potential loss associated with cell apoptosis were attenuated by PSPA. These results suggested that PSPA could protect the PC-12 cell from Abeta-induced injury through the inhibition of oxidative damage, intracellular calcium influx, mitochondria dysfunction and ultimately inhibition of cell apoptosis. The present study indicates that PSPA may be a promising approach for the treatment of AD and other oxidative-stress-related neurodegenerative diseases.

Cancer Prevention of Anthocyanins in the Purple Sweetpotato bred in Kansas

Anthocyanins are versatile and plentiful flavonoid pigments that account for the purple color in may plant foods such as red grapes, berries, red cabbages, and purple sweetpotato. Although anthocyanins have been epidemiologically associated with reduced cancer risk, the anticancer ability of the purple sweetpotato has not been well investigated. Considering the high contents of anthocyanin in the purple sweetpotato, we have bred purple‐fleshed sweetpotato cultivars using seeds from controlled crosses provided by the International Potato Center in Lima, Peru. Over 2000 seedlings from four full‐sib progenies cultured at the John C. Pair Horticulture Research Center, Kansas, have been segregated by multiple traits based upon flesh pigmentation and fiber contents. We and determined the prominent anthocyanin contents by HPLC‐MS, including cyanidin 3‐sophoroside‐5‐glucoside (m/z 774), p‐hydroxybenzoylated cyanidin 3‐sophoroside‐5‐glucoside (m/z 894), caffeoylated cyanidin 3‐sophoroside‐5‐glucoside (m/z 908), and peonidin 3‐(6,6′‐caffeoyl‐p‐hydroxybenzoylsophoroside)‐5‐glucoside (m/z 1055). Furthermore, the selected purple sweetpotato extracts with high levels of anthocyanins have been assessed in the human colon cancer SW480 cells for potential anticancer mechanisms. Better understanding of the underlying mechanisms may provide scientific evidence and health benefits of purple sweetpotato grown in Kansas.

Composition and colour stability of anthocyanins extracted from fermented purple sweet potato culture

The components and colour stability of anthocyanins in purple sweet potato were investigated. Anthocyanins were extracted from fermented purple sweet potato culture fermented by Suzhou wine starter (Rhizopus 3.851, 3.866 and Saccharomyces cerevisiae). In these purple sweet potato anthocyanins (PSPAs), five major anthocyanins were detected by high performance liquid chromatography (HPLC). Cyanidin and peonidin were found to be the major anthocyanidins in PSPAs by acid hydrolysis of anthocyanins. PSPAs were more stable under the acid conditions (pH 2.0–4.0) than the subacid conditions (pH 5.0–6.0) as per UV–Vis absorption spectra and CIELAB colour coordinates.

Effects of Purple Sweet Potato Anthocyanins on Development and Intracellular Redox Status of Bovine Preimplantation Embryos Exposed to Heat Shock

The development of cleavage stage preimplantation embryos is disrupted by exposure to heat shock, such as high temperatures in the summer season. In this study, we investigated whether addition of anthocyanins, which are strong scavengers of reactive oxygen species (ROS), improves development and intracellular redox status of heat-exposed bovine preimplantation embryos by reduction of heat shock-derived oxidative stress. After in vitro fertilization (IVF), embryos were cultured at 38.5 C through Day 8 (Day 0=day of IVF) with 0, 0.1, 1 and 10 microg/ml anthocyanins (non-heat-shocked group). On Day 2, embryos were cultured at 41.5 C for 6 h with 0, 0.1, 1 and 10 microg/ml anthocyanins followed by culture at 38.5 C until Day 8 (HS group). After exposure to heat shock, the intracellular ROS and glutathione (GSH) contents of individual embryos were measured in the non-heat-shocked and HS groups using fluorescent probes. On Day 8, the blastocysts formation rates of the embryos and total cell numbers of blastocysts were evaluated. Embryos exposed to heat shock without anthocyanins showed a significant decrease in blastocyst formation rate and GSH content (P<0.05) and an increase in intracellular ROS (P<0.05) compared with non-heat-shocked embryos. In contrast, addition of 0.1 microg/ml anthocyanins significantly (P<0.05) improved the blastocyst formation rate of the heat-shocked embryos. Addition of any dose of anthocyanins produced a significant decrease in the ROS levels (P<0.05) and tended to increase the GSH levels under heat-shock conditions. However, addition of higher concentrations (1 and 10 microg/ml) of anthocyanins to the culture media under heat shock did not improve the development of embryos. These results indicate that anthocyanins maintain the intracellular redox balance of heat-shocked bovine embryos by reducing intracellular oxidative stress and increasing the GSH levels. Thus, alterations of the redox state using natural antioxidative polyphenols is a useful approach for reducing heat shock-derived oxidative stress.

Anthocyanins in Sweet Potato Leaves-Varietal Screening, Growth Phase Studies and Stability in a Model System

The sweet potato genotypes in the CTCRI germplasm collection were screened for anthocyanin content in the young top leaves and the values varied from 20-200 mg/100g fresh weight of the leaf samples, the highest being recorded for the genotype S-406. Total anthocyanin content (TAcy) showed significant difference among genotypes, growth phases, and growing seasons. The TAcy in the leaves reached a peak at 20 days after planting, declined after 35 days, returned to 20 day levels or higher by 50-65 days and remained stable or exhibited a slight decrease by 105 days after planting, for most of the genotypes selected for growth phase studies. Approximately 50-60 % decrease was observed in the TAcy of the frozen/thawed leaf samples. The stability of anthocyanin pigments in a model sugar-citrate solution at ambient (30 ± 2 °C) and refrigerated (8 ± 2 °C) conditions was studied. The solutions stored at low temperature and in dark showed higher retention of pigments. Compared to anthocyanins extracted from grape pomace, the sweet potato anthocyanins were more stable as indicated by the higher values of half-life and pigment retention. The anthocyanins were more stable at the pH range of 3.2-3.4 and the colour shifted from red to pale yellow at higher levels.