Fundamental and Derived Properties of Yam (Dioscorea Spp.) Starch Powders and Implications in Tablet and Capsule Formulation

A comparative investigation of the fundamental and derived properties of starches from some species of yam (Dioscorea spp.) was conducted with a view to establishing their suitability as excipients in tablet and capsule formulations. Variations were observed in the mean granular diameter of the starches obtained from the different Dioscorea species. Granular diameter ranged from 5.4 µm (Chinese yam) to 34.5 µm (Round leaf yellow yam). Chinese yam and Bitter yam had the highest specific surface area (625.91 m²/kg and 258.76 m²/kg, respectively) while Round leaf yellow yam and Negro yam had the lowest (117.4 m²/kg and 154.34 m²/kg, respectively). Chinese yam had the lowest granular volume (6.00 µm³), surface area (5.67 µm²) and granule surface‐mean diameter (6.74 µm), while Round leaf yellow yam had the largest mean granular diameter, highest granular volume (35.2 µm³), surface area (34.8 µm²) and granule surface mean diameter (35.88 µm). Particle size distribution plots of Chinese yam, Round leaf yellow yam and Negro yam displayed a Gaussian size distribution pattern while Bitter yam displayed a negatively skewed distribution. The variations observed in the granular size and shape may influence the observed derived properties of the starches.     

INTERFERENCE OF CARBOHYDRATES DURING PURIFICATION OF PEROXIDASE FROM PALM (EUTERPE EDULIS MART.)*

Palmito (Euterpe edulis Mart.) peroxidase was initially prepared as an acetone powder to eliminate phenols and lipids. A 30–80% (NH₄)₂SO₄ fraction was used to characterize some biochemical properties of this enzyme. The main interference during enzyme purification was found to be the interaction of acid carbohydrates with peroxidase. The optimum condition to eliminate this interference was found to be extraction at pH 4.0, which preferentially extracts most of the carbohydrates but not the enzyme. CaCl₂ was found to be a compound which selectively precipitates with acid carbohydrates and proteins and increased peroxidase activity. Gel isoelectrofocusing was used to study the interaction between the acid polymers and the proteins. The pH optimum of the enzyme was found to be around 4.0. The molecular weight of the enzyme was estimated to be 40,000. The Km of peroxidase with H₂O₂ was 2times10⁻³M and with guaiacol, 4.8 times 10⁻³M. NaCl, NaF and NaN₃ were found to inhibit peroxidase as a function of pH; as the pH decreased, the inhibition increased.     

Acceleration of mass transfer rates in osmotic dehydration of elephant foot yam (Amorphophallus paeoniifolius) applying pulsed-microwave-vacuum

The elephant foot yam slices were processed with combined pulsed-microwave-vacuum osmotic drying. Osmotic dehydration at ambient (28 °C and 45% RH) was carried out using different levels of sucrose concentration (30, 40, 50 and 60% w/w), salt concentration (5, 7.5, 10 and 12.5% w/w) and dehydration time (10, 20, 30, 50, 70, 90 and 120 min). During the osmotic dehydration, pulsed microwave vacuum (15 kPa pressure, 1 W/g power density and 1.853 pulsating ratio) was maintained for 2 min over the sample and solution to enhance the mass transfer. For this purpose, the osmotic dehydration experiments were conducted in the microwave-vacuum cavity. Azuara model predicted the moisture loss and solid gain by elephant foot yam slices during osmosis. It was observed that both the moisture loss and the solid gain increased with increasing concentration of the osmotic solution. The optimum conditions found in the process were 40% w/w sucrose concentration, 6% w/w salt concentration and 70 min osmotic dehydration time, resulting in to 42.80% moisture loss (initial weight) and 14.65% solid gain (initial weight). Further, samples were dried using microwave vacuum dryer up to moisture content of 5–6% d.b. by varying microwave power density (2, 4, 6 and 8 W/g) and pulsating ratio (1.312, 1.625, 1.983 and 2.250). Page model was fitted to the data to study the microwave vacuum drying kinetics. The microwave vacuum drying at 1.625 pulsating ratio with microwave power density 4 W/g yielded a product with the highest overall acceptability score. Guggenheim, Anderson and deBoer (GAB) model was used in the study of the sorption behavior of dehydrated elephant foot yam and shelf life prediction.Industrial relevanceThe production of elephant foot yam in India and South East Asia is comparatively higher than other vegetables. Although, it is nutritious product and good source of energy, food industries are not interested to process elephant foot yam using a time consuming traditional osmotic dehydration process followed by hot air drying. Therefore, present research work was undertaken from industry suggestion to develop accelerated osmotic dehydration process for elephant foot yam using novel pulsed-microwave-vacuum combination followed by finish drying by microwave-vacuum. This research has been carried out to decrease industrial processing time, energy consumption and improving quality of the product. Industry will start adopting this new hybrid process of drying elephant foot yam on large scale.     

Polyphenol oxidase properties,anti-urease,and anti-acetylcholinesterase activity of Diospyros lotus L. (Plum Persimmon)

Diospyros lotus fruit polyphenol oxidase was purified using affinity chromatography, resulting in a 15-fold enrichment in specific activity. The purified enzyme, having 16.5 kDa molecular weight on sodium dodecyl sulfate-polyacrylamide gel electrophoresis, exhibited the highest activity toward 4-methylcatechol. Maximum diphenolase activity was reached at pH 7.0 and 60°C in the presence of 4-methylcatechol. K_m and V_max values were calculated as 3.8 mM and 1250 U/mg protein, respectively. Ascorbic acid was a promising inhibitor with an IC₅₀ value of 0.121 µM. The activity of the purified enzyme was stimulated by Fe²⁺, Sr²⁺, Zn²⁺, and K⁺ and deeply inhibited by Hg²⁺, at 1 mM final concentration. Aqueous extract of Diospyros lotus L. fruit showed strong substantial urease and acetylcholinesterase inhibition, with IC₅₀ values of 1.55 ± 0.05 and 16.75 ± 0.11 mg/mL, respectively.     

A new amperometric biosensor for hydrogen peroxide determination based on HRP-nanogold-PTH-nanogold-modified carbon paste electrodes

A new strategy for immobilization of horseradish peroxidase (HRP) has been developed by self-assembling gold nanoparticles to multiporous polythionine (PTH) film modified carbon paste interface. A thionine film was initially electropolymerized onto carbon paste interface in a mildly acidic thionine solution at a bias voltage of −1.0 to 1.5 V. This process is accompanied by the hydrogen evolution reaction, and the released hydrogen gas made the PTH film with multiporous structure. The multiporous PTH film provided a biocompatible microenvironment for gold nanoparticles and enzyme molecules, and greatly amplified the coverage of HRP molecules on the electrode surface. Voltammetric and time-based amperometric techniques were employed to characterize the properties of the derived biosensor. The performance and factors influencing the performance of the biosensor were also proposed. The immobilized HRP displayed a catalytic property to the reduction of H₂O₂. The H₂O₂ biosensor achieved 95% of the steady-state current within 2 s, and exhibited a linear range of 9.6×10⁻⁶ to 1.2×10⁻³ M H₂O₂ with a detection limit of 7.5×10⁻⁷ M (S/N = 3). Furthermore, the biosensor remained at about 90% of its original sensitivity after 2 weeks’ storage.     

Macromolecular characteristics of ten yam (Dioscorea spp) starches

Starches from ten yam (Dioscorea) species were compared with those of maize, wheat, potato and cassava, and characterized by high‐performance size‐exclusion chromatography coupled with multiangle laser light scattering. Treatment with 95% (v/v) dimethylsulphoxide and microwave heating in a high‐pressure vessel led to complete dissolution of the starch samples. For yam starches, M?_w were between 1.88 × 10⁸ and 3.27 × 10⁸ g mol^?1 and R?_G were between 258 and 396 nm. The hydrodynamic coefficients of amylopectins were between 0.36 and 0.44, indicating that those of maizes and esculenta 5 and dumetorum yam species had particularly highly branched structures. Multidimensional analysis of the macromolecular characteristics of yam starches indicated three classes: dumetorum cultivar (Dioscorea dumetorum), esculenta 5 cultivar (Dioscorea esculenta) and the other eight yam starches, including cultivars of Dioscorea alata and Dioscorea cayenensis‐rotundata species. Some yam starches were also leached at 90 °C. The macromolecular characteristics of the leached fractions confirmed the previous typology. Copyright © 2003 Society of Chemical Industry     

Improvement of productivity of active horseradish peroxidase in Escherichia coli by coexpression of Dsb proteins

Coexpression of two classes of folding accessory proteins, molecular chaperones and foldases, can be expected to improve the productivity of soluble and active recombinant proteins. In this study, horseradish peroxidase (HRP), which has four disulfide bonds, was selected as a model enzyme and overexpressed in Escherichia coli. The effects of coexpression of a series of folding accessory proteins (DnaK, DnaJ, GrpE, GroEL/ES, trigger factor (TF), DsbA, DsbB, DsbC, DsbD, and thioredoxin (Trx)) on the productivity of active HRP in E. coli were examined. Active HRP was produced by very mild induction with 1 μM isopropyl-β- -thiogalactopyranoside (IPTG) at 37°C, whereas the amount of active HRP produced by the induction with 1 mM IPTG was negligibly small. Active HRP production was increased significantly by coexpression of DsbA-DsbB (DsbAB) or DsbC-DsbD (DsbCD), while coexpression of molecular chaperones did not improve active HRP production. The growth of E. coli cells was inhibited significantly by the induction with 1 mM IPTG in a HRP single expression system. In contrast, when HRP was coexpressed with DsbCD, the growth inhibition of E. coli was not observed. Therefore, coexpression of Dsb proteins improves both the cell growth and the productivity of HRP.     

A novel polysaccharide prepared from Chrysanthemum morifolium cv. Fubaiju tea and its emulsifying properties

In this study, a novel chrysanthemum polysaccharide (CP) was obtained and investigated from Chrysanthemum morifolium tea in Hubei province, China. Molecular characterisation and emulsifying properties of the CP were elucidated. The effects of different factors, including storage time, metal ions, pH value and heat treatment, were studied on the stability of emulsion. Results showed that the mean particle diameter (MPD) (d₃₂) varied from 5.54 to 0.49 μm with the polysaccharide concentration ranging from 0.5wt% to 3.0wt%. The MPD (d₃₂) of emulsions stabilised by chrysanthemum tea polysaccharide (ECP) was smaller than that of GA at 2wt%, and the MPD (d₃₂) of ECP remained stable with no stratification occurred at 25 °C for 10 days. ECP also showed good stability under acidic conditions (3.0–7.0). With increase of Na⁺ and Ca²⁺ concentration, MPD(d₃₂) and zeta potential values raised significantly, from 2.24 to 7.24 μm and from −40.52 to −35.35 mV respectively. After high-temperature heat treatment, MPD (d₃₂) and zeta potential showed no significant change, indicating ECP presented good storage stability. In conclusion, CP helped stabilised emulsions that could be used as a natural emulsifier for future application.     

ABILITY OF VARIOUS CHEMICALS TO REDUCE COPPER AND TO INACTIVATE MUSHROOM TYROSINASE1

Treatment of mushroom tyrosinase with reducing agents such as hydrogen peroxide, ascorbic acid, phenylhydrazine, gallic acid, ferrocyanide and NH₂OH resulted in inactivation of the enzyme. Under the conditions tested, 50% inactivation of the enzyme was obtained with 4 μM H₂O₂, 20 μM ascorbic acid, 40μM phenylhydrazine, 6 mM gallic acid, 12 mM ferrocyanide and 22 mM NH₂OH. The ability of the reducing agents to reduce Cu²⁺ in a chemical model system was determined and it was found that gallic acid, phenylhydrazine, ascorbic acid and NH₂OH are relatively good reductants of Cu²⁺ while H₂O₂ and ferrocyanide are relatively poor ones. The copper content of mushroom tyrosinase before and after inactivation by each of the reducing agents was determined. The copper content of the enzyme inactivated by H₂O₂, NH₂OH, phenylhydrazine, ferrocyanide, gallic acid and ascorbic acid was 100%, 90%, 90%, 85%, 85% and 76% compared to that of the control (enzyme not treated). It was concluded that the degree of inactivation of mushroom tyrosinase by the reducing agents was not correlated with the decrease in the copper content of the enzyme nor with their ability to reduce Cu²⁺ in a chemical model system.     

Laundry detergent-stable lipase from Pacific white shrimp (Litopenaeus vannamei) hepatopancreas: Effect of extraction media and biochemical characterization

Extraction and biochemical properties of a new lipase from the hepatopancreas of Pacific white shrimp were studied. Recovery of the hepatopancreas powder with 50 mM Tris-HCl, pH 7.0 containing 0.2% (v/v) Brij35 gave a higher recovery of lipase activity than other extractants tested (p < 0.05). The optimal pH and temperature for lipase activity were 8.5 and 60°C, respectively, when p-nitrophenyl palmitate was used as a substrate. The enzyme was stable to heat treatment up to 40°C and over a pH range of 7.0–10.0 for 30–120 min. Lipase activities continuously decreased as the sodium deoxycholate (NaDC) concentration increased, but activities increased as NaCl concentration increased up to 3.0 M. Hydrolytic activity was enhanced by NaN₃, but strongly inhibited by Hg²⁺, Cu²⁺, Al³⁺, and phenylmethanesulfonyl fluoride. The lipase was evaluated as highly stable against surfactants (Tween 20, Tween 80, Triton X-100, and gum arabic). However, the enzyme was unstable against sodium dodecyl sulphate. Stability of the lipase with commercial liquid and solid detergents (Attack^®, Bres^®, Omo^®, and Pao^®) was also investigated. The lipase exhibited substantial stability and compatibility with tested commercial liquid and solid laundry detergents for 30–60 min. The overall properties of the lipase from Pacific white shrimp hepatopancreas, thus leading us to propose that it is an excellent candidate for use as biocatalysts for better detergent formulation.     

Isolation of obligate anaerobic rumen bacteria capable of degrading the neurotoxin β‐ODAP (β‐N‐oxalyl‐L‐α,β‐diaminopropionic acid) as evaluated by a liquid chromatography/biosensor analysis system

Six pure strains of obligate anaerobes capable of degrading the toxin β‐N‐oxalyl‐L ‐α, β‐diaminopropionic acid (β‐ODAP) contained in grass pea (Lathyrus sativus) have been isolated from cow rumen. The new isolates were identified as Megasphaera elsdenii (five different genotypes) and Clostridium bifermentans using 16S rDNA analysis. The β‐ODAP degrading efficiency of the isolates was evaluated by measuring the amount of β‐ODAP in the growth medium, which contained β‐ODAP as the only carbon source, before and after incubation with the microbes. The method of analysis was liquid chromatography employing bioelectrochemical detection. The biosensor is based on co‐immobilising two enzymes, glutamate oxidase (GlOx) and horseradish peroxidase (HRP), on the end of a spectrographic graphite electrode. β‐ODAP is oxidised by GlOx to form H₂O₂, which in turn is bioelectrocatalytically reduced by HRP through a mediated reaction using a polymeric mediator incorporating Os^{2 + /3+} functionalities rapidly shuttling electrons with the electrode_giving rise to the analytical signal. On the basis of this analysis system, the new isolates are capable of utilising β‐ODAP as sole carbon source to a maximum of 90–95% within 5 days with concomitant increase in cell protein. Copyright © 2005 Society of Chemical Industry     

Zearalenone reduction by commercial peroxidase enzyme and peroxidases from soybean bran and rice bran

The peroxidase (POD) enzyme, obtained from different sources, has been described in the literature regarding its good results of reduction in concentration or degradation levels of mycotoxins, such as aflatoxin B1, deoxynivalenol and zearalenone (ZEA). This study aimed at evaluating the action of commercial POD and POD from soybean bran (SB) and rice bran (RB) in ZEA reduction in a model solution and the characterisation of the mechanism of enzyme action. POD was extracted from SB and RB in phosphate buffer by orbital agitation. Evaluation of the action of commercial POD and POD from SB and RB in ZEA reduction was carried out in phosphate buffer and aqueous solution, respectively. Parameters of (Michaelis–Menten constant) (K_M) and maximal rate (V_max) were determined in the concentration range from 0.16 to 6 µg mL^?1. ZEA reduction was determined and the mechanism of enzyme action was characterised by FTIR and high-pressure liquid chromatography-electrospray tandem mass spectrometry. Commercial POD and POD from RB and SB reduced ZEA concentration by 69.9%, 47.4% and 30.6% in 24 h, respectively. K_M values were 39.61 and 8.90 µM, whereas V_max values were 0.170 and 0.011 µM min^?1 for commercial POD and POD from RB, respectively. The characterisation of the mechanism of enzyme action showed the oxidoreductive action of commercial POD in the mycotoxin. The use of commercial POD and POD from agro-industrial by-products, such as SB and RB, could be a promising alternative for ZEA biodegradation.     

Acid phosphatase in the tubers of Dioscorea species and its purification from the white yam (D. rotundata poir)

Acid phosphatase activity was determined in 15 cultivars from four species of yam. A 12-fold purification of the enzyme from Dioscorea rotundata (cv. chikakwondo) gave a homogeneous preparation as demonstrated by polyacrylamide gel electrophoresis. This enzyme preparation has an apparent molecular weight of 115 000 ±2000 and an optimum activity at a pH of 5·20 and a temperature of 50°C. The K_m of the enzyme is 3·81 mM with disodium p-nitrophenylphosphate (p-NNP) as a substrate. The energy of activation, heat of activation, energy of inactivation and heat of inactivation are 7·0, 6·4, 4·41 and 4·34 kcal M^?1, respectively. Although it has very little activity with most organic phosphoric acid esters, it is significantly inhibited by Ca²⁺, Hg²⁺ and EDTA and activated by Mg²⁺. The enzyme has a half-life of 50,17 or 13 days, respectively, when stored at 6-8°C, 0°C or room temperature (29±2°C).     

O-dihydroxyphenoloxidase action on natural polyhydric phenolics and enzymic browning of edible yams

Ten cultivars of five edible yam species were examined for o-dihydroxyphenoloxidase (o-DPOase) activity against yam extracts containing phenolic compounds, and for their propensity to brown when cut slices are exposed to air. (+)-Catechin levels in Dioscorea cayenensis (260 mg kg^?1) and D. bulbifera (240 mg kg^?1) were similar to those in D. dumetorum (270 mg kg^?1), but the latter contained less o-DPOase and showed less tendency to browning. D. alata contained more (+)-catechin than other yams, and one cultivar with a higher (+)-catechin content (660 mg kg^?1) showed more browning than another cultivar containing 430 mg kg^?1 (+)-catechin. Five cultivars of D. rotundata showed less tendency to brown, and had lower (+)-catechin content (90–190 mg kg^?1) than the other yams examined, but showed marked variation in o-DPOase activity. o-DPOase activity, assayed by recording the rate of oxygen consumption, varied between 75 units (1 unit=μmol O₂ consumed min^?1 100 g^?1 fresh yam tissue) in D. dumetorum and 2380 units in one D. rotundata cultivar when a crude extract of phenolic compounds diluted to contain 10 mM (+)-catechin was used as substrate and from 60 to 3480 units for these same two enzyme extracts when assayed using crude extracts of phenolic compounds (also adjusted to contain 10 mM (+)-catechin) prepared from the same yam as the enzyme extract. However, in general, the o-DPOase activities recorded using the D. alata extract showed little correlation with the activity when the phenolic extract was prepared from the same yam as the enzyme extract. Incubation of crude extracts containing phenolics with crude extracts of o-DPOase at 20°C for 24 h resulted in a decrease in the quantity of (+)-catechin estimated by h.p.l.c. Cyanidin released by hydrolysis with HCl under mild conditions was also measured. The level in D. alata was sufficiently high to account for ‘pinking’ when this species is boiled. It is concluded that the o-DPOase-catalysed oxidation of (+)-catechin is largely responsible for the browning of yams. The possible influence of other factors, including the reducing agent ascorbic acid in moderating the rate and extent of browning observed, is discussed.     

2,4,5-TRIHYDROXYBUTYROPHENONE (2,4,5-THBP) AS A SUBSTRATE FOR HORSERADISH PEROXIDASE1

2,4,5-trihydroxybutyrophenone (2,4,5-THBP), in the presence of hydrogen peroxide (H₂O₂), is a substrate for horseradish peroxidase (HRP) with a Km value of 2.5 mM. An intermediate red product(s), probably 2,4,5-THBP quinone, characterized by a peak at 490–500 nm, was detected and the time course of its conversion to the final red product(s) was studied. The relationships between the rate of 2,4,5-THBP oxidation to pigmented product(s) as a function of various concentrations of H₂O₂, 2,4,5-THBP and HPR are described.     

Purification and characterization of highly active and stable polyphosphatase from Saccharomyces cerevisiae cell envelope

Saccharomyces cerevisiae cell envelope polyphosphatase was isolated in highly active and stable form by extraction from cells with zwittergent TM-314 followed by chromatography of the extract on phosphocellulose and QAE-Sephadex in the presence of 5 mM -MgCl₂, 0·5 mM -EDTA and 0·1% Triton X-100. The enzyme possessed a specific activity of 220 U/mg and after 30 days retained 87% of its activity at ?20°C. Polyphosphatase molecular mass was determined to be about 40 kDa by gel filtration and polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. The enzyme hydrolysed polyphosphates with various chain lengths (n = 3–208), had low activity for GTP and did not split pyrophosphate, ATP and p-nitrophenylphosphate. On polyphosphates with chain lengths n = 3, 9 and 208, K_m values were 1·7 × 10^?4, 1·5 × 10^?5 and 8·8 × 10^?7 M respectively. Polyphosphatase was most active and stable at pH 6·0–8·0. The enzyme showed maximal activity at 50°C. The time of half inactivation of polyphosphatase at 40, 45 and 50°C was 45, 10 and 3 min, respectively. In the absence of divalent cations and also with Ca²⁺ or Cu²⁺, the enzyme showed practically no activity. The ability of divalent cations to activate polyphosphatase was reduced in the following order: Co²⁺ > Mg²⁺ > Mn²⁺ > Fe²⁺ > Zn²⁺. Polyphosphatase was completely inhibited by 1 mM -ammonium molybdate and 50 μM -Zn²⁺ or Cu²⁺ (in the presence of Mg²⁺).     

Inhibitory effects of selected pesticides on peroxidases purified by affinity chromatography

The objective of this study was to determine the in vitro inhibition effects of seven commonly used pesticides including 2,4-d-acid dimethylamine, fenoxaprop-p-ethyl, glyphosate isopropylamine, haloxyfop-p-methyl, cypermethrin, λ-cyhalothrin, and dichlorvos on the peroxidase purified from turnip (Brassica rapa L.) and black radish (Raphanus sativus L.) using 4-amino benzohydrazide affinity column chromatography. The purification factors for the turnip and black radish peroxidases were found to be 263.29-fold (with a yield of 12.89%) and 36.20-fold (with a yield of 6.90%), respectively. Among these compounds, λ-cyhalothrin showed the strongest inhibitory effect against turnip peroxidase (K_i: 1.23 × 10^?2 ± 0.21 × 10^?2 mM) as noncompetitive inhibition. On the other hand, cypermethrin demonstrated the highest inhibition effect against black radish peroxidase (K_i: 2.14 × 10^?2 ± 0.08 × 10^?2 mM) as competitive inhibition.     

Myricetin,an antioxidant flavonol,is a substrate of polyphenol oxidase

The present study demonstrates the antiradical efficiency of myricetin, a flavonol widely distributed in fruits and vegetables, by testing its ability to react with two different free radicals, ABTS^+· and DPPH^·. The polyphenolic nature of myricetin led us to consider the possibility of its oxidation by polyphenol oxidase (PPO). The results reported show that myricetin can be oxidised by PPO extracted and partially purified from broad bean seeds. The reaction was followed by recording spectral changes with time, maximal spectral changes being observed at 372 nm. The presence of two isosbestic points (at 274 and 314 nm) suggested that only one absorbing product was formed. The spectral changes were not observed in the absence of PPO. The oxidation rate varied with the pH, reaching its highest value at pH 5.5. The myricetin oxidation rate increased in the presence of SDS, an activing agent of polyphenol oxidase. Maximal activity was obtained at 1.3 mM SDS. The kinetic parameters were also determined: V _m = 1.35 µM min⁻¹, K _m = 0.3,mM , V _m/ K _m = 4.5 × 10⁻³ min⁻¹. Flavonol oxidation was inhibited by a selective PPO inhibitor such as cinnamic acid (K_I = 1 mM ). The results reported show that myricetin oxidation was strictly dependent on the presence of polyphenol oxidase. © 1999 Society of Chemical Industry     

Effect of Amylopectin Structure on the Gelatinization and Pasting Properties of Selected Yam (Dioscorea spp.) Starches

This study was aimed at elucidating the decisive structural parameters of amylopectin which govern the gelatinization or pasting behavior of yam starch dispersions, exemplified with four selected yam starches from Dioscorea alata and D. batatas with very similar amylose contents (32.2–34.6%). The results indicated that the yam amylopectins examined showed an average degree of polymerization (DP) of 3469–4474 anhydroglucose units (AGU), average chain length (CL) of 18.8–28.5 AGU, average exterior CL (ECL) of 11.8–16.4 AGU, average interior CL (ICL) of 6.0–11.1 AGU, and a noticeable proportion of extralong (> 100 AGU) and long (40–100 AGU) chains that gave the chain ratio r_(el+l)/s (the weight ratio of extralong and long chains to short chains) of 0.88–1.40. Generally, the yam amylopectin with a lower DP and NC possessed a greater CL, ECL, ICL, and r_(el+l)/s, associating with a higher blue value (BV) and maximal wavelength (λ_max) for their complexes with iodine. D. alata amylopectins exhibited a lower DP, longer chain lengths and greater r_(el+l)/s than the D. batata amylopectins. Statistically, r_(el+l)/s was decisive for the BV and λ_max; while CL and phosphate content were crucial for the gelatinization peak temperature and pasting viscosities of the yam starches examined. The role of swelling power or the volume fraction of dispersed remnants instead in governing the pasting viscosity was also mathematically explored.     

ALUMINUM STABILIZES TURMERIC IN PICKLE BRINE AGAINST DECOMPOSITION BY LIGHT,HEAT AND PEROXIDASE1

Turmeric in solutions typically used for cucumber pickle manufacturing was protected by Al³⁺ from decomposition caused by fluorescent light, heat and peroxidase. Levels of 1.3–1.5 mM Al³⁺ significantly reduced light-and peroxidase-catalyzed decomposition of turmeric, and the amount of retardation increased with increasing Al³⁺ concentration. Alone, neither peroxidase nor hydrogen peroxide affected turmeric; however when combined, turmeric was rapidly destroyed. Peroxidase destruction of turmeric was uncompetitively inhibited by Al³⁺. Turmeric decomposition increased with increasing temperature from 20 to 90°C. No thermal destruction of turmeric was observed in the presence of 2 or 4 mM Al³⁺.