Showing papers by "Central Tuber Crops Research Institute published in 2009"

Traditional and novel fermented foods and beverages from tropical root and tuber crops: review.

Abstract: Summary Tropical root and tuber crops [cassava, sweet potato, yams, colocasia (taro), etc] are important staples for food security for about a fifth of the world population. Bulk of cassava in Africa and Latin America are processed into fermented foods and food additives such as organic (acetic, citric and lactic) acids, mono-sodium glutamate, etc. The fermented foods from cassava are gari, fufu, lafun, chickwanghe, agbelima, attieke and kivunde in Africa, tape in Asia and ‘cheese’bread, and ‘coated peanut’ in Latin America. Lactic acid bacteria and yeasts are the major group of micro-organisms associated with cassava fermentation. Similarly, sweet potatoes can be fermented into soy sauce, vinegar, lacto-juices, lacto-pickles and sochu (an alcoholic drink produced in Japan), and yams into fermented flour. Most of these fermented food products are functional foods rich in phytochemicals, dietary fibres, anti-oxidant compounds (β-carotene, anthocyanin, etc) and probiotic components (lactic acid bacteria and yeasts).

Revision of ploidy status of Dioscorea alata L. (Dioscoreaceae) by cytogenetic and microsatellite segregation analysis.

Abstract: Dioscorea alata is a polyploid species with several ploidy levels and its basic chromosome number has been considered by most authors to be x = 10. Standard chromosome counting and flow cytometry analysis were used to determine the chromosome number of 110 D. alata accessions of the CIRAD germplasm collection. The results revealed that 76% of accessions have 2n = 40 chromosomes, 7% have 2n = 60 chromosomes and 17% have 2n = 80 chromosomes. Progenies were produced from 2n = 40 types of D. alata and the segregation patterns of six microsatellite markers in four different progenies were analysed. The Bayesian method was used to test for diploid versus tetraploid (allo- and autotetraploid) modes of inheritance. The results provided the genetic evidence to establish the diploidy of plants with 2n = 40 chromosomes and to support the hypothesis that plants with 2n = 40, 60 and 80 chromosomes are diploids, triploids and tetraploids, respectively, and that the basic chromosome number of D. alata is x = 20. The findings obtained in the present study are significant for effective breeding programs, genetic diversity analysis and elucidation of the phylogeny and the species origin of D. alata.

Morphological, biochemical and molecular characterization of Trichoderma harzianum isolates for their efficacy as biocontrol agents.

Abstract: The random amplified polymorphic DNA (RAPD) procedure was used to examine the genetic variability among 8 isolates of Trichoderma harzianum, and their ability to antagonize Sclerotium rolfsii using a dual culture assay was correlated with RAPD profiles. Eight oligodeoxynucleotide primers were selected for the RAPD assays, which resulted in 86 bands for 8 isolates of T. harzianum. The data were entered into a binary matrix and a similarity matrix was constructed using the DICE similarity (SD) index. An unweighted pair grouping mathematical averaging (UPGMA) cluster based on SD values was generated using the NTSYS computer program. A mean coefficient of similarity obtained for pairwise comparisons was c. 30% and it showed that the variability among the isolates of T. harzianum was very high. Using the dual culture method in antagonism experiments, the T. harzianum isolates were classified in to antagonism classes. Further, T. harzianum isolates were screened for chitinase and β-1,3-glucanase activity. RAPD was efficient in demonstrating the high intraspecific genetic variation among isolates. The dendrogram did not show the grouping of isolates by their level of antagonism. Relationship among polymorphism existent, the aggressiveness and the origin of isolates were not found.

Uses and Nutritional Data of Sweetpotato

Abstract: Sweetpotato (Ipomoea batatas Lam.) is cultivated throughout the tropics and warm temperate regions of the world for its starch roots, which can provide nutrition, besides energy. The edible tuberous root is either long and tapered, ovoid or round with a skin colour ranging from white, brown, purple or red and the flesh colour ranging from white, pale cream, orange or purple. Besides, the plant is also much valued for its green tops, which are a concentrated source of many essential vitamins and minerals. Although China is the largest producer of sweetpotatoes, accounting for more than 80% of the world supply, only 40% of the production is used for human consumption and industrial uses, while, the rest goes as animal feed. Per capita production is the greatest in Solomon Islands (160 Kg/person/year), followed by Burundi (130 Kg/person/year), where sweetpotatoes are a staple food. The roots are also used to a great extent in countries like Japan, New Zealand, Papua New Guinea and parts of America.

Comparative production of glucose and high fructose syrup from cassava and sweet potato roots by direct conversion techniques

Abstract: High fructose syrup (HFS) is a highly valued liquid sweetener for beverage, confectionery and processed food industry, owing to its special attributes like high solubility and non-crystalline nature. Even though 85% HFS production is from corn, increased food demand has necessitated the search for alternative substrates and starchy root crops like cassava and sweet potato are potential raw materials. However, the economic production needs direct use of the roots and simplification of the cost-intensive steps. This study aims at the direct enzymatic conversion of roots for HFS production. Glucose yield was compared from six treatment systems viz., liquezyme–dextrozyme (T1), Stargen (T2), Stargen in two split doses (T3), Spezyme–Stargen (T4), Stargen (60 °C;T5) and Spezyme–Stargen (60 °C; T6). Glucose was higher (22–25%) from cassava than sweet potato (14.0–15.7%), owing to the high starch content in cassava. Conversion to glucose was higher in T1–T4 (95–98%) compared to 88–92% for T5 and T6. Although the fructose yield was more from cassava (8.36–9.78%) than sweet potato (5.2–6.0%), percentage conversion was similar (37–38%) for both the roots. The cost of production of HFS could be reduced by the direct hydrolysis of root slurry using Stargen. Industrial relevance The conventional process for HFS production involved three cost-intensive enzyme steps such as liquefaction, saccharification and isomerization and the major raw material is starch. Economic production using cheaper raw materials and simplification of the process are the decisive factors for the widespread use of HFS in the developing and less developed countries. The present study aimed at the direct conversion of cassava and sweet potato root slurry (without conversion to starch) through the use of improved enzymes like Spezyme and Stargen and mild operating conditions of pH and temperature. The cost of production of HFS could be reduced by using the wet root slurry and performing the Stargen aided saccharification at room temperature, followed by isomerization at 60 °C using Sweetzyme T.

Physical and Functional Properties of Arrowroot Starch Extrudates

Abstract: Arrowroot starch, a commercially underexploited tuber starch but having potential digestive and medicinal properties, has been subjected to extrusion cooking using a single screw food extruder. Different levels of feed moisture (12%, 14%, and 16%) and extrusion temperatures (140, 150, 160, 170, 180, and 190 degrees C) were used for extrusion. The physical properties--bulk density, true density, porosity, and expansion ratio; functional properties such as water absorption index, water solubility index, oil absorption index, pasting, rheological, and textural properties; and in vitro enzyme digestibility of the extrudates were determined. The expansion ratio of the extrudates ranged from 3.22 to 6.09. The water absorption index (6.52 to 8.85 g gel/g dry sample), water solubility index (15.92% to 41.31%), and oil absorption index (0.50 to 1.70 g/g) were higher for the extrudates in comparison to native starch (1.81 g gel/g dry sample, 1.16% and 0.60 g/g, respectively). The rheological properties, storage modulus, and loss modulus of the gelatinized powdered extrudates were significantly lower (P < 0.05) and these behaved like solutions rather than a paste or a gel. Hardness and toughness were more for the samples extruded at higher feed moisture and lower extrusion temperature, whereas snap force and energy were higher at lower feed moisture and temperature. There was a significant decrease in the percentage digestibility of arrowroot starch (30.07% after 30 min of incubation with the enzyme) after extrusion (25.27% to 30.56%). Extrusion cooking of arrowroot starch resulted in products with very good expansion, color, and lower digestibility, which can be exploited for its potential use as a snack food.

Lactic acid fermentation of anthocyanin‐rich sweet potato (Ipomoea batatas L.) into lacto‐juice

Abstract: Summary Sweet potato (SP) is an important root crop grown all over the world and consumed as a vegetable, boiled, baked or often fermented into food and beverages. The grated SP roots [non- boiled and fully boiled (boiled in water at 100 °C for 15 min) were treated with 0.05% of commercial pectinase enzyme (Pectinex, Novoenzyme) in order to extract the juice. The fresh juice was inoculated with Lactobacillus plantarum MTCC 1407 culture at 28 ± 2 °C for 48 h to produce lacto-juice (LJ). The anova analysis of analytical data revealed that there was significant effect of boiling conditions (fully boiled and non-boiled) on pH [F (1, 4) = 220.5, P < 0.001), TA [F (1, 4) = 78.89, P < 0.01], starch [F (1, 4) = 26.63, P < 0.01), total sugar [F (1, 4) = 61.36, P < 0.01) and anthocyanin [F (1, 4) = 32.86, P < 0.01) but not on reducing sugar [F (1, 4) = 2.48, P = 0.19). Sensory evaluation rated the SP LJ acceptable based on texture, taste, aroma, flavour and after taste. LJ prepared from fully boiled roots with 10% cane sugar was most preferred by a consumer’s panelist based on Linear Discriminant Analysis. Principal component analyses (PCA) reduced the seven original analytical variables to three independent components (factors), which accounted for 99.9% of the total variations. Similarly, six original sensory variables were reduced to two independent components, which accounted for 65.7% of the total variations.

Statistical optimization of alpha-amylase production with immobilized cells of Streptomyces erumpens MTCC 7317 in Luffa cylindrica L. sponge discs.

Abstract: The purpose of this investigation was to study the effect of Streptomyces erumpens cells immobilized in various matrices, i.e., agar–agar, polyacrylamide, and luffa (Luffa cylindrica L.) sponge for production of α-amylase. Luffa sponge was found to be 21% and 51% more effective in enzyme yield than agar–agar and polyacrylamide, respectively. Response surface methodology was used to evaluate the effect of three main variables, i.e., incubation period, pH, and temperature on enzyme production with immobilized luffa cells. The experimental results showed that the optimum incubation period, pH, and temperature were 36h, 6.0, and 50 °C, respectively. The repeated batch fermentation of immobilized cells in shake flasks showed that S. erumpens cells were more or less equally physiologically active on the support even after three cycles of fermentation (3,830–3,575 units). The application of S. erumpens crude enzyme in liquefying cassava starch was studied. The maximum hydrolysis of cassava starch (85%) was obtained with the application of 4ml (15,200 units) of crude enzyme after 5 h of incubation.

Anthocyanin‐rich sweet potato lacto‐pickle: production, nutritional and proximate composition

Abstract: Summary Anthocyanin pigment-rich sweet potato (SP) cubes were pickled by lactic fermentation by brining the cut and blanched cubes in common salt (NaCl, 2–10%) solution. They were then inoculated with a strain of Lactobacillus plantarum (MTCC 1407) and incubated for 28 days. Treatment with 8–10% brine solution was found to be organoleptically most acceptable. The final product with 8% and 10% brine solutions had a pH (2.5–2.8), titratable acidity (TA) (1.5–1.7 g kg−1), lactic acid (LA) (1.0–1.3 g kg−1), starch (56–58 g kg−1) and anthocyanin content (390 mg kg−1) on fresh weight basis. Sensory evaluation rated the anthocyanin-rich SP lacto-pickle acceptable based on texture, taste, aroma, flavour and after taste. Principal component analyses reduced the eleven original analytical and proximate variables (pH, TA, LA, starch, total sugar, anthocyanin, organic mater, ash, fat, protein and calories) to three independent components (factors), which accounted for 91% of the total variations.

Identification and characterization of differentially expressed genes in the resistance reaction in taro infected with Phytophthora colocasiae

Abstract: Leaf blight disease caused by Phytophthora colocasiae represents a major constraint to the growth and yield of taro (Colocasia esculenta L.). Ongoing research on model plant systems has revealed that defense responses are activated via signaling pathways mediated by endogenous signaling molecule such as salicylic acid, jasmonic acid, and ethylene. Activation of plant defenses is associated with changes in the expression of large number of genes. To gain a better understanding of defense responses, virulent race of P. colocasiae was used to inoculate the taro cultivar UL-56 (compatible) and its nearly isogenic line Muktakeshi (incompatible). We have employed suppressive subtractive hybridization (SSH), cDNA libraries, Northern blot analysis, high throughput DNA sequencing, and bioinformatics to identify the defense-related genes in taro induced by P. colocasiae infection. Two putative resistance genes and a transcription factor were identified among the upregulated sequences. The expression of several candidate genes including lipid transfer proteins (LTPs), and other pathogenesis-related genes were evaluated following 8–48 h of appearance of symptom in compatible and incompatible interactions. Results confirmed the higher overall expression of these genes in Muktakeshi (resistant) compared to UL-56 (susceptible). This study constitutes the first attempt to characterize the taro differential transcriptome associated with host–pathogen interactions from different genotypes. All the generated ESTs have been submitted to GenBank for further functional studies.

Dietary mucilage promotes regression of atheromatous lesions in hypercholesterolemic rabbits.

Abstract: The antihypercholesterolemic and antiatherogenic effect of the mucilage galactomannan isolated from fenugreek seeds was studied in experimental rabbits maintained on a high cholesterol diet for 3 months. Changes in the levels of cholesterol and triglycerides in serum and tissues and aortic fatty lesions were analysed in animals receiving mucilage (40 mg/kg body weight) daily and compared with the control. A significant decrease in serum total cholesterol, LDL cholesterol and triglycerides and cholesterol and triglycerides in liver and aorta and a decrease in Sudan IV staining of aorta indicated antihypercholesterolemic and antiatherogenic effects of the mucilage. Regression studies showed that administration of mucilage for 3 months caused a significant decrease in serum total and LDL cholesterol and aortic cholesterol. Mucilage accelerated the regression of atheromatous lesions in the aorta as evidenced by significantly low sudanophilic staining. Recovery from inflammation in hypercholesterolemic animals receiving mucilage was evidenced by a faster decrease in C-reactive protein (CRP) in serum to basal levels. The lipid lowering and antiatherogenic effects of mucilage from fenugreek which is used as a food flavoring spice highlights the importance of dietary intervention in the regression of atherosclerosis.

Economics of Sweetpotato Production and Marketing

Abstract: The major Roots and Tubers, Cassava, Potato, Sweetpotato and Yam occupied about 53.93 million ha world wide, producing 736.747 million tonnes annually (FAO, 2008). Individually Cassava, Potato, Sweetpotato and Yam rank among the most important food crops worldwide and in terms of annual volume of production. Cassava, Potato and Sweetpotato rank among the top ten food crops produced in developing countries. Many of the developing world’s poorest producers and the most undernourished house holds depend on roots and tubers as an important source of food and nutrition (Scott et al., 2000). Roots and tubers produce large quantities of energy per day, in comparison of cereals. Sweetpotato is an important tropical root and tuber crop as it ranks second after cassava among the tropical tuber crops. The crop can be considered promoting nutritional security particularly in agriculturally backward areas. Besides carbohydrates, it is a rich source of protein, lipid, calcium and carotene. It becomes an ideal crop for popularisation in areas with poor soils and poor agricultural infrastructure facilities. In annual production, sweetpotato ranks as the fifth most important food crop on a fresh-weight basis in developing countries after rice, wheat, maize, and cassava. Sweetpotato is cultivated in 114 countries and ranks among the five most important food crops in over 50 countries. Asia has the world’s major production area for sweetpotato. In Asia, the greatest share of production is in China that accounts for about 85% of global production. Feed, processed food and other non-food uses for sweetpotato expanded considerably in Asia over the last three decades (Pham et al., 1996; Scott, 1992; Titapiwatanakun, 1998). Rapid growth in demand for meat has created growth opportunities in more remote areas to use Sweetpotato as animal feed like in Sichuan province, China (Huang, 1999). Small farmers in China who have long cultivated

Lactic acid production from cassava fibrous residue using Lactobacillus plantarum MTCC 1407.

Abstract: During extraction of starch from cassava, fibrous residue is a major waste released into the environment. Owing to the high starch content (60-65% on dry weight basis) and organic matter of cassava fibrous residue (CFR), an attempt has been made to utilize it for the production of lactic acid (LA) in semi solid state fermentation using Mann Rogassa Sharpe medium containing [5 % (wv(-1))] CFR in lieu of glucose [2% (wv(-1))] as the carbon source. Response Surface Methodology (RSM) was used to evaluate the effect of main variables, i.e. incubation period, temperature and pH on LA production. The experimental results showed that the optimum incubation period, temperature and pH were 120 hr 35 degrees C and 6.5, respectively. Maximum starch conversion by Lactobacillus plantarum MTCC 1407 to LA was 63.3%. The organism produced 29.86 g of (L+) LA from 60 g of starch present in 100 g of CFR. The LA production yield (i.e. mass LA produced mass starch present in CFR(-1) x 100) was 49.76%.

Effect of Graft-Copolymerization with Poly(acrylamide) on Rheological and Thermal Properties of Cassava Starch

Abstract: Graft copolymers of different grafting levels were synthesised by the free radical initiated reaction of cassava starch with acrylamide in presence of ceric ammonium nitrate. The viscosity properties of the native granular starch and the grafted starches were determined using a Rapid visco analyzer (RVA) and rheological properties by frequency sweep test under different conditions using a rheometer. Some of the grafted starches exhibited significantly higher and some others exhibited drastically reduced peak viscosity values irrespective of the percentage grafting. All the grafted starches exhibited very good viscosity stability as evidenced from the highly reduced breakdown and higher final viscosity values in comparison to native cassava starch. Thermal analysis of the pure granular cassava starch and grafted starches was carried out using a differential scanning calorimetry (DSC) and thermogravimetry. DSC studies showed that in comparison to native starch, the grafted starches showed lower temperatures of transition. The thermal stability of cassava starch was enhanced by grafting as observed from the thermogravimetric data. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Changes in Phenolics, Polyphenol Oxidase and its Isoenzyme Patterns in Relation to Resistance in Taro against Phytophthora colocasiae

Abstract: The effect of Phytophthora leaf blight disease, caused by Phytophthora colocasiae Raciborski, on the accumulation of phenolics and polyphenol oxidase (PPO) activity in ex vitro plants was studied in three resistant (DP-25, Duradim and Jhankri) and one susceptible (N-118) genotypes of taro [Colocasia esculenta (L). Schott]. The inoculation of taro leaves with P. colocasiae spores resulted in a quantitative change in both biochemical parameters and induction of PPO isoforms in resistant genotypes. The amount of phenolics was increased owing to blight by 68.02%, 58.87%, 52.67% and 11.50% in DP-25, Duradim, Jhankri and N-118, respectively. The per cent increase in PPO under stress over non-stress condition was also highest in DP-25 (49.14%) followed by Duradim (41.56%), Jhankri (40.55%) and N-118 (17.08%). The resistant genotypes showed higher activity of PPO as compared with susceptible ones, which was reflected through its banding pattern in isoenzyme analysis, detecting four different isoforms. The intensity of the bands was higher in the resistant genotypes than in susceptible N-118. The appearance of high intensity bands and/or reduction in the intensity of particular isoform(s) in the zymograms of all the three resistant taro genotypes studied, led to the apparent conclusion of linking PPO isoenzyme expression with blight resistance in taro. The blight incidence (per cent leaf infection and leaf area infection) was lower in the resistant genotypes than in susceptible, N-118. The yield reduction owing to blight was below 20% in DP-25, Jhankri and Duradim, while the same was more than 40% in N-118. The phenolics and PPO activity was negatively correlated with disease incidence and yield reduction owing to blight. Based on the results of disease incidence, biochemical contents and yield, the pattern of stress tolerance was DP-25 > Duradim > Jhankri > N-118. The studied parameters, i.e. phenolics and PPO could be used as biochemical markers for leaf blight stress tolerance studies in taro.

Statistical optimization of α -amylase production by Bacillus brevis MTCC 7521 in solid-state fermentation using cassava bagasse

Abstract: Production of α-amylase under solid-state fermentation by Bacillus brevis MTCC 7521 has been investigated using cassava bagasse as the substrate, one of the major solid wastes released during extraction of starch from cassava (Manihot esculenta). Response surface methodology was used to evaluate the effect of the main variables, i.e. incubation period (36 h), moisture holding capacity (60%), pH (7.0) and temperature (60°C) on enzyme production by applying a full factorial central composite design. The maximum hydrolysis of soluble starch (85%) and cassava starch (75%) was obtained with the application of 4 mL (≈ 14,752 units) of B. brevis crude enzyme after 5 h of incubation.

Differential response of short- and long-duration cassava cultivars to applied mineral nitrogen

Abstract: The differential response of two contrasting cassava cultivars to different rates of soil-applied nitrogen (N) on the number of tuberous roots, harvest index, yield, nitrogen uptake, and fertilizer-nitrogen-use efficiency was studied over a period of 2 years on a typic Plinthustults in Kerala state in Southern India. The experiment was laid out in a split-plot design with two popular cultivars of cassava, namely Sree Vijaya (6 months) and M-4 (10 months) in the main plots, and eight urea-N rates (0, 12.5, 25, 50, 75, 100, 150, and 200 kg ha–1) in subplots. Half of the N was applied at the time of planting and the other half 60 d later. The study revealed significant differences between the two cultivars regarding their response to fertilizer-N application. The tuberous-root yield of the short-duration cultivar Sree Vijaya increased significantly up to 100 kg N ha–1 whereas the yield of the long-duration cultivar M-4 increased significantly only up to 50 kg N ha–1 rate. Also the N-use-efficiency parameters (i.e., agronomic, recovery, and physiological efficiencies) were higher in Sree Vijaya than in M-4 but declined at N rates beyond 100 kg ha–1. The more efficient N use in the short-duration cultivar was associated with a higher N uptake and a more efficient internal use.

Leaf Color Chart and Chlorophyll‐Meter‐Based Leaf Nitrogen Estimation and Their Threshold Values for Real‐Time Nitrogen Management in Cassava

Abstract: The critical leaf and the threshold values of leaf color chart (LCC) and chlorophyll meter (SPAD‐502) for cassava have been evaluated. The nitrogen (N) rates and cultivars had a significant effect on LCC score, SPAD values, and leaf N concentration of leaf 1 in most cases. Among the three leaf positions studied, the youngest fully expanded leaf (YFEL) blade (leaf 1) had significant, positive correlation of tuber yield with LCC score, SPAD value, and leaf N concentration. The regression between LCC score and leaf N concentration of leaf 1 was LCC = 0.358 (Leaf N) + 0.78 (r2 = 0.81) and that between LCC score and SPAD value was SPAD = 10.981 (LCC) – 3.51 (r2 = 0.82). A threshold LCC score of 2.65 and threshold SPAD value of 25 were suitable to determine the optimal timing of N top‐dressing for cassava.

Oxalic acid production by Fusarium oxysporum Schlecht and Botryodiplodia theobromae pat., post-harvest fungal pathogens of yams (Dioscorea rotundata L.) and detoxification by Bacillus subtilis CM1 isolated from culturable cowdung microflora.

Abstract: Fusarium oxysporum Schlecht and Botryodiplodia theobromae Pat., two important post-harvest pathogens of yam (Dioscorea rotundata L.) tubers in storage were found to produce oxalic acid (OA) in vitro and in vivo. The rate of OA accumulation was proportional to fungal growth (cell mass) in Potato Dextrose liquid medium during 10 days incubation period. Further, simultaneous co-culturing of either of the fungi with Bacillus subtilis CM1 isolated from cowdung culturable microflora resulted in 92% reduction in OA accumulation compared with that in the culture of the individual fungus. The effect was more prominent in pH 5 – 6 than in pH 7 – 8. B. subtilis CM1 was capable of detoxifying OA and several proteins were detected in the culture filtrates when it was grown in peptone-mineral salt medium containing OA. SDS-PAGE analysis of 70% ammonium sulphate fraction of the culture filtrate exhibited the presence of a predominant 97 kDa protein.

Polymer induced structures in cetylpyridinium chloride–octanol micellar system

Abstract: The effect of octanol on the interaction of polyethylene glycol (PEG) and cetylpyridinium chloride (CPC) were investigated by viscosity, conductivity, differential scanning calorimetry (DCS), polarizing microscopy, Fourier transform infrared spectroscopy (FTIR) and rheology analysis. The aggregation of polymer-surfactant micelles takes place at a surfactant concentration higher than the critical micelle concentration. The long chain aliphatic alcohol (n-octanol) induced rapid structural transformation in the mixed micellar system by unusual cooperative micellization. The rheological behavior of the viscoelastic system reveals the presence of giant aggregates in this system. The lyotropic nature of the giant aggregates was monitored by DSC and polarizing microscopic studies, and which was confirmed by cryo-TEM.

A Rheological Approach to Viscoelastic Worm-Like Micelles of Tunable Properties

Abstract: The rheological behavior of micellar solutions of cationic surfactant, cetyl trimethyl ammonium bromide in the presence of a salt (KBr) and a co-surfactant (n-octanol) were analyzed. Shear viscosity and shear moduli were measured as a function of concentrations of the co-surfactant and additive. When these concentrations attained a certain critical threshold value, the micellar solution was found to exhibit a nonlinear viscoelastic behavior. It is due to the formation of supramolecular structures, which has been described by the Maxwell model of a viscoelastic fluid typical of worm-like micelles. The rheological behavior was also analyzed using Carreau and Carreau–Gahleitner models which were found to be in good agreement with the experimental results.

Production system-specific differences in farmers' demand for greater yam (Dioscorea alata) varietal attributes in Orissa State, India.

Abstract: Greater yam (Dioscorea alata), a popular crop in India, is cultivated widely in Orissa state, India. In spite of the availability of several improved varieties, farmers preferred the local landraces. An investigation was carried out to identify whether the varietal preferences of yam farmers in two production systems, subsistence and commercial, were different. While the subsistence farmers demanded the yam varieties adaptable to a wide range of soils, the commercial farmers preferred the anthracnose-resistant cultivars. This study demonstrated that the farmers' varietal preferences were highly influenced by the production systems. Identifying the convergence/divergence of varietal preferences across production systems can help breeders to develop the high impact varieties.