Showing papers by "Central Tuber Crops Research Institute published in 2010"

Hydrothermal Modifications of Tropical Tuber Starches. 1. Effect of Heat-Moisture Treatment on the Physicochemical, Rheological and Gelatinization Characteristics

Abstract: Cassava, sweet potato and arrowroot starches have been subjected to heat-moisture treatment (HMT) under different conditions using a response surface design of the variables. A comparative study was performed on the pasting properties, swelling behaviour and the gelatinization properties of the modified starches and also on the rheological and textural properties of their pastes. X-ray diffraction studies have shown that cassava starch exhibited a slight decrease in crystallinity, whereas sweet potato and arrowroot starches showed an increase in crystallinity after HMT at 120oC for 14 h with 20% moisture. The swelling volume was reduced and the solubility was enhanced for all three starches after HMT, but both effects were more pronounced in the case of arrowroot starch. The decrease in paste clarity of the starch after HMT was higher in the case of cassava and sweet potato starches. Viscosity studies showed that the peak viscosity of all three starches decreased after HMT, but the paste stability increased as seen from the reduced breakdown ratio and setback viscosity. Studies on rheological properties have shown that storage and loss moduli were higher for the starches heat-moisture treated at higher moisture and lower temperature levels than the corresponding native starches. Storage of the gel at -20oC resulted in a significant increase in storage modulus for all the three starches. All the textural parameters of the gels were altered after the treatment which depended on the nature of the starch and also the treatment condition.

Starch Graft Copolymers: Novel Applications in Industry

Abstract: Starch, which is a natural carbohydrate biopolymer, has been the subject of academic and industrial studies for many decades, basically due to its low cost, biodegradability and versatility of use Chemical modification of starch by grafting various monomers onto it imparts increased hydrophilicity, hydrophobicity or polyelectrolyte nature to starch depending on the reagent and conditions used The starch graft copolymers are synthesized by the free radical initiated reaction of starch with acrylic monomers in presence of a free radical initiator such as ceric ammonium nitrate High viscosity, thermal stability, biodegradability, good film forming properties and water absorption capacity are some of the properties shown by the graft copolymers of starch Graft copolymers find various applications in industry as flocculants, waste water treatment and heavy metal ion removal, for sizing cotton, as mulch films, in oil drilling, as biodegradable polymers and in superabsorbents Starch graft copolymers are als

Effect of pre-soaking treatments on the nutritional profile and browning index of sweet potato and yam flours

Abstract: The use of sweet potato and yams for product development is hindered by the discoloration from enzymatic and non-enzymatic browning. The effect of pre-soaking treatments on the nutritional changes and browning index (BI) of sweet potato and yam (greater yam and white yam) flours was investigated. Ascorbic acid (AsA), citric acid (CA), acetic acid (AA) and sodium metabisulfite (SMS) were used for soaking at three concentrations (0.25%, 0.50% and 1.00%) and two durations (1 h and 2 h). AsA and SMS removed more starch during soaking of sweet potato, while CA and AA removed more starch from greater yam and CA removed more starch from white yam. Highest removal of reducing sugars was observed in sweet potato in AA, while CA removed maximum reducing sugars from both the yams. Phenol and total free amino acid (TFA) levels were more in SMS treatment than the control sweet potato flour, and least in AA (2 h). Whilst AsA raised the phenols and TFA in greater yam, it removed phenols to the maximum in white yam. Maximum BI was in AsA treatment for the three crops, and least for flour from CA (0.25%) treated yams and AA (1.00%) treated sweet potato. Industrial Relevance Browning resulting from enzymatic and non-enzymatic reactions is a major drawback in the processing of sweet potato and yams for product development. The study showed that this could be successfully tackled through soaking the slices in low cost chemicals like acetic acid or citric acid and sodium metabisulfite at low concentrations. The treated slices yielded flour with very low browning indices compared to the respective native flours, which could enhance the potential of such flours in the development of food products.

Optimization of thermostable α- amylase production by Streptomyces erumpens MTCC 7317 in solid-state fermentation using cassava fibrous residue

Abstract: Production of α- amylase under solid state fermentation by Streptomyces erumpens MTCC 7317 was investigated using cassava fibrous residue, one of the major solid waste released during extraction of starch from cassava (Manihot esculenta Crantz). Response surface methodology (RSM) was used to evaluate the effect of the main variables, i.e., incubation period (60 h), moisture holding capacity (60%) and temperature (500C) on enzyme production by applying a full factorial Central Composite Design. Varying the inoculum concentration (5-25%) of S. erumpens showed that 15% inoculum (v/w, 2.5 x 106 CFU/ml) was the optimum for α- amylase production. Among the different nitrogen sources supplemented, beef extract was most suitable for enzyme production. The application of S. erumpens enzyme in liquefaction of soluble starch and cassava starch was studied. The maximum hydrolysis of soluble starch (85%) and cassava starch (70%) was obtained with the application of 5 ml crude enzyme (17185 units) after 5 h of incubation.

Nutritional and textural studies on dietary fiber‐enriched muffins and biscuits from cassava‐based composite flours

Abstract: The demand for designer food products having specific nutritional/functional attributes is on the increase worldwide. Composite flours prepared from malted and pregelatinized cassava through appropriate blending with cereal and/or legume and bran sources were used for making muffins and biscuits with high fiber content. Muffins made from Termamyl-malted and pregelatinized cassava flour had lower starch content (38.84–41.82%) than those from germinated gram amylase malted flour. The products had protein contents of 4.50–5.60% (<1.0% in cassava flour). High dietary fiber content of 2.77–3.44% and 3.20–3.40%, respectively, was obtained in muffins and biscuits made from cassava–bran blends. The spread ratio of the test biscuits was fewer by five to eight units than the control biscuits made from refined wheat flour. The low in vitro starch digestibility of muffins/biscuits from cassava–bran blends (24–29 units and 31–34 units, respectively) was a specific advantage, suggesting their therapeutic use for obese and diabetic people. Muffins made from Termamyl-malted mixes had lower hardness and toughness than those from gram amylase malted flour. The high dietary fiber content of the two baked goods indicates their use for cardiovascular patients and also for conditions such as constipation and its related problems. PRACTICAL APPLICATIONS The study focuses on the use of cassava flour for making two baked goods viz., muffins and biscuits. The nutritional and functional properties of cassava flour were modified through malting and pregelatinization and further by blending with cereal and/or legume flours and bran sources. The composite flours that have high protein content and dietary fiber (DF) content were further enriched through the addition of wheat bran at levels of 10.0 g per formula. The products developed had high DF content of 2.77–3.44% and protein content of 4.50–5.60% (dwb). The low in vitro starch digestibility of muffins and biscuits from cassava–bran blends was an additional advantage, suggesting their use in medical nutrition therapy for treating obese and diabetic people as well as for management of cardiovascular and intestinal problems.

Response Surface Methodology for the Optimization and Characterization of Cassava Starch‐graft‐Poly(acrylamide)

Abstract: Response surface methodology (RSM) was employed for the synthesis of cassava starch-graft-poly(acrylamide) using ceric ammonium nitrate as free radical initiator. Concentration of acrylamide, concentration of ceric ammonium nitrate, reaction temperature and duration of reaction were optimized using a 4-factor 3-level Box-Behnken design. The dependent variables were percentage grafting (%G) and grafting efficiency (GE). Second order polynomial relationships were obtained for %G and GE, which explained the main, quadratic and interaction effects of factors. The highest%G and GE obtained were 174.8% and 90.7%, respectively. The optimum values of parameters predicted through RSM were 20 g acrylamide/10 g dry starch, 3.3 g/L ceric ammonium nitrate, 180 min reaction duration and 45°C temperature with a %G of 190.0. For GE, the predicted levels of factors for the optimum value of 90.8% were 17.5 g acrylamide/10 g dry starch, 4.1 g/L ceric ammonium nitrate, 180 min reaction duration and 55°C temperature. The graft reaction was confirmed by FTIR analysis, where the absorption bands corresponding to the C=O stretching and N-H bending of the -CONH 2 group were observed. Scanning electron microscopic studies on grafted starches revealed that the granular structure of the starch was affected by the reaction. X-ray diffraction analysis showed that the crystallinity of starch was decreased as a result of grafting and the reduction was higher for the grafted starches with higher percentage grafting.

Short‐duration cassava genotypes for crop diversification in the humid tropics: growth dynamics, biomass, yield and quality

Abstract: BACKGROUND: Short-duration (6–7 months) cassava provides opportunities to smallholder farmers for effective utilisation of resources such as land, moisture and nutrients as well as diversification of enterprise and income. The variation in biomass production and partitioning, seasonal course of growth indices, yield, quality and nutrient uptake of ten short-duration/early-bulking genotypes of cassava and their impact on nutrient contents in soil in a lowland situation akin to rice fallow were examined in this study. RESULTS: Triploid 2–18 gave the highest yield (38.34 t ha−1), followed by triploid 4-2, Sree Vijaya, Sree Jaya and Vellayani Hraswa, which were on a par (30–32 t ha−1). Vellayani Hraswa, Sree Vijaya and triploid 4-2 had significantly higher tuberous root dry matter content (370–380 mg g−1) and fairly higher starch content (270–280 mg g−1). All genotypes except triploid 4-2, triploid 2–18 and H-165 had low cyanogen content (29.2–43.8 µg g−1), well within the tolerable limit. Tuberous root dry matter and total dry matter production, crop growth rate, tuberous root bulking rate and harvest index at the last phase, number of tuberous roots, mean weight of tuberous roots and nutrient uptake showed significant positive correlations with tuberous root yield. Principal component analysis also showed a similar trend. CONCLUSION: The diploids Sree Vijaya, Sree Jaya, Vellayani Hraswa and Kalpaka are ideal for cultivation in rice fallow for food use owing to their high yield, good cooking quality and low cyanogen content. The triploids are better suited for industrial use owing to their high tuberous root dry biomass production. Copyright © 2009 Society of Chemical Industry

Production, Characterization and Application of a Thermostable Exo-polygalacturonase by Bacillus subtilis CM5

Abstract: Exo-polygalacturonase (exo-PG) (PG, EC 3.2.1.67) has various applications in food processing industries, such as in juice extraction and clarification, bakery, and distillery processing. This study reports the exo-PG production by Bacillus subtilis CM5 isolated from cow ruminant microflora, which was comparable to marketed pectinase (Pectinex®, Novozyme, Denmark). The optimum temperature, pH, and incubation period for optimum exo-PG production (82.0–83.2 units) were 50˚C, 7.0, and 36 h, respectively. B. subtilis produced more exo-PG in culture medium with peptone (1%) than other nitrogen sources such as beef extract, casein, yeast extract, ammonium sulphate, and ammonium acetate. However, ammonium chloride and urea (1%) inhibited enzyme production. In laboratory fermentor studies, exo-PG production by B. subtilis was 25.6% higher than shake flask cultures. Application of crude exo-PG from B. subtilis resulted in 13.3% increase in yield of carrot juice as compared to juice extracted with Pectinex.

Insect pests and their management in yam production and storage: a world review

Abstract: Yam (Dioscorea spp.) is a tropical tuber crop produced for food and medicinal purposes. Yams are infested by a broad taxonomic diversity of insect pests. We reviewed a total of 73 insect species associated with Dioscorea species in different parts of the world. Yam is infested by 48 species when the crop is in the field, and after harvest (i.e. in storage) the tubers are attacked by 27 species. The majority of these insects belong to the order Coleoptera (35 species) followed by the orders Hemiptera (15), Lepidoptera (13), Isoptera (5), Hymenoptera (2), Diptera (1), and Thysanoptera (1). Yam scales, mealybugs, and a few beetles cause significant losses to tubers both in the field and in storage. We review various methods of management for these insect pests. An integrated approach towards managing these pests, both in the field and in storage, is essential. Post-harvest losses in storage of yam can be reduced, partly, by using biocontrol agents for mealybugs and scales. Alternative strategies for the mana...

Isozyme and PCR-based genotyping of epidemic Phytophthora colocasiae associated with taro leaf blight.

Abstract: The Oomycetous fungus Phytophthora colocasiae causing leaf blight of taro is widely distributed in India. Wide geographic range or sexual recombination provides genetic differentiation within this species. To determine how genetic variation is partitioned in P. colocasiae, 14 isolates were isolated from different regions of India, where the incidence of leaf blight is great. Molecular and biochemical techniques were employed for assessing and exploiting the genetic variability among isolates of P. colocasiae. Seven polymorphic enzyme systems revealed 23 isozyme patterns, each uniquely characterised by the presence or absence of electromorphs. Further, 10 oligodeoxynucleotide primers were selected for random amplified polymorphic DNA (RAPD) assays, which resulted in 123 polymorphic bands for 10 isolates of P. colocasiae. The data were entered into a binary matrix and a similarity matrix was constructed using a DICE similarity (SD) index. A UPGMA cluster based on SD values was generated using a NTSYS comput...

A species-specific polymerase chain reaction assay for rapid and sensitive detection of Sclerotium rolfsii

Abstract: The failure to adequately identify plant pathogens from culture-based morphological techniques has led to the development of culture-independent molecular approaches. The timely and accurate detection of pathogens is critical in the study of epidemiology and management of plant diseases. A polymerase chain reaction (PCR)-based method was developed for the identification and detection of Sclerotium rolfsii in Amorphophallus paeoniifolius plants. A PCR primer pair specific for S. rolfsii was designed based on the sequence of the internal transcribed spacer region. The designed primer pair SCR-F/SCR-R amplified a 540-bp product from S. rolfsii DNA and did not amplify DNA from A. paeoniifolius or several other fungi pathogenic to A. paeoniifolius. In conventional PCR, the limit of detection of pure fungal gDNA was 6 pg ml−1, which was reduced 2-fold within a plant DNA background. S. rolfsii DNA was detected in inoculated A. paeoniifolius and 12 h after inoculation in symptomless tuber samples. The protocol was assessed for the detection of S. rolfsii in infected soils.

Ethanol fermentation of mahula (Madhuca latifolia) flowers using free and immobilized bacteria Zymomonas mobilis MTCC 92

Abstract: Mahula (Madhuca latifolia L.) is a deciduous tree commonly found in the tropical rain forests of Asian and Australian continent. Corolla, the edible part of its flowers, is rich in fermentable sugar (37 ± 0.23%; on dry weight basis). Batch fermentation of mahula flowers was carried out using Zymomonas mobilis MTCC 92 free cells and cells immobilized in calcium alginate matrix. The ethanol productions were 122.9 ± 0.972 and 134.6 ± 0.104 g/kg flowers on dry weight basis using free and immobilized cells, respectively, after 96 h of fermentation, which showed that cells entrapped in calcium alginate matrix yielded 8.7% more ethanol than free cells. Further, the immobilized cells were physiologically active up to three more cycles of fermentation producing 132.7 ± 0.095, 130.5 ± 0.09 and 128.7 ± 0.056 g ethanol per kg flower in first, second and third cycle, respectively.

Nutritional, Functional and Physical Properties of Extrudates from Blends of Cassava Flour with Cereal and Legume Flours

Abstract: Low protein and poor functionality limit the use of cassava flour in snack foods, which were modified using blends with cereal and/or legume flours. Native, malted (using alpha-amylase) as well as malted and pre-gelatinized was blended with cereal (finger millet and whole wheat flours) and/or legume (chick pea flour). Extrudates were prepared at a screw speed of 100 rpm and die temperature of 180 °C. Malted flour based extrudates had lower starch content than native flour. Gram malted cassava based blends gave products with the highest protein. In vitro starch digestibility was the highest for pre-gelatinized flour based mixes. Extrudates with low fat and energy have scope as low calorie snacks for obese and diabetic people.

Kinetics of thermal softening of cassava tubers and rheological modeling of the starch

Abstract: Cassava or tapioca (Manihot esculenta Crantz) tubers having high amount of carbohydrate are utilized after boiling or processing into starch and flour. Textural properties of raw and cooked tubers depend on variety, maturity, growing environment, physico-chemical and starch properties. Starch is used in food preparations as gelling and thickening agent, stabilizer and texture modifier. This study aims at analyzing and modeling the textural, dynamic rheological and gelatinization properties of selected cassava varieties. The thermal softening behavior was analyzed by linear regression and fractional conversion techniques, rheological properties of the gelated starch by Maxwell and power law models. The varieties were classified based on their physico-chemical, texture profile, rheological and gelatinization properties by multivariate analysis. The textural, rheological and gelatinization properties were significantly affected by the varieties (p < 0.05). Thermal softening of tubers was modeled by dual mechanism first order kinetic model with rate constant values ranging from 0.081 to 0.105 min−1. Linear regression models with extremely good fit were obtained to explain the relationship between the degree of cooking and relative firmness. The dynamic spectra of the gelated starch showed the characteristics of concentrated biopolymer dispersion and described using Maxwell and power law model. The results showed that textural, rheological and gelatinization properties varied considerably among the varieties and besides the physico-chemical properties, interaction between them and structural make up of the tuber parenchyma had a great influence on cooking quality and rheological properties.

Consumer acceptance of lactic acid-fermented sweet potato pickle

Abstract: The success of any novel food product is largely determined by the consumer acceptance of its sensory quality. The objective of the present study was to evaluate the sensory attributes of lactic acid-fermented sweet potato (SP) pickles with the prospective consumers to develop a statistical model for predicting consumer acceptance decisions. The pickles prepared from β carotene- and anthocyanin-rich SP varieties in 8 and 10% salt (NaCl) solutions were evaluated for their sensory attributes, i.e., appearance, color, texture, aroma and sourness, by 100 rural consumers from the Orissa State of India during 2008. The consumers liked SP pickle made in 8% NaCl solution. The logistic regression modeling of the sensory and consumer attributes revealed that the sourness (Wald statistic = 11.328, P = 0.001) and aroma (Wald statistic = 8.374, P = 0.004) of the SP pickle determined the consumer acceptability. Analysis also showed that the highly educated consumers were most likely to accept this SP pickle (Wald statistic = 5.038, P = 0.025). PRACTICAL APPLICATIONS The rural people living in the geographically and socially isolated places of developing countries are often plagued by acute malnutrition. Fortifying the staple foods with essential nutrients is an effective strategy to eradicate malnutrition through natural means. Sweet potato (SP) is cultivated extensively in the rain-fed and hilly tracts of India and is a popular secondary staple food for tribes during off season. Vegetable pickles are popular adjuncts in India, which are consumed regularly along with staple foods. Thus, the pickles prepared from antioxidant-rich SP can provide essential nutrients like β-carotene and anthocyanin which can help the rural people to eradicate malnutrition at a cheaper cost. Besides, statistical modeling of the SP pickle acceptance decisions can help the policymakers to identify potential consumer segments for promoting this pickle.

Production of High Fructose Syrup from Cassava and Sweet Potato Flours and their Blends with Cereal Flours

Abstract: Despite being a rich source of starch, root crops such as cassava and sweet potato have not been widely exploited for the production of high fructose syrup (HFS), which is a highly valued sweetener for the food and beverage industries. The major factors contributing to the cost of production of HFS are the cost and labor-intensive steps in the production of starch, different processing temperatures and pH for the enzyme reactions, poor extractability of starch, etc. With the objective of overcoming the cost associated with the preparation of starch, the feasibility of using native cassava/sweet potato flours and their blends with rice flour and wheat flour, as the raw material for HFS production was investigated. The saccharified slurry from cassava--rice flour blends contained 70-72 g reducing sugars/100 g, which was higher than that released from native cassava flour (~69%). Blends of sweet potato with rice or wheat yielded saccharified mash with lower content of reducing sugars (60-66%). Although the percentage conversion to fructose after isomerization was similar for cassava/sweet potato or their blends with cereal flours (42-43%), fructose yield was higher in native cassava flour and cassava-rice blends (28-29 g/100 g) than the other flour blends.

Biochemical Changes in Leaf Tissues of Taro [Colocasia esculenta L. (Schott)] Infected with Phytophthora colocasiae

Abstract: The changes in some biochemical parameters due to Phytophthora leaf blight infection were assessed in leaf tissues of one resistant (DP-25), two moderately resistant (Duradim and Jhankri) and one susceptible (N-118) genotypes of taro [Colocasia esculenta (L.) Schott]. Phytophthora spore suspension (15 000 spore ⁄ ml water) was sprayed onto the in vitro raised taro plantlets at 30 days after establishment in pots to induce disease. In comparison with the uninoculated leaves, blight infected leaves showed reduction in protein content and activity of nitrate reductase and increase in total soluble sugar, reducing sugar content and activities of acid phosphatase and alkaline phosphatase among the studied genotypes. Changes in biochemical parameters under induced blight stress as compared with uninoculated control were less in resistant genotypes than that in susceptible genotype. The deviations in biochemical contents were highest in susceptible genotype N-118. Based on the variations of above parameters under stress and non-stress control among the four tested genotypes, the overall pattern of changes was N-118 > Duradim > Jhankri > DP-25, which is in accordance with the pattern of increasing resistance. The resistant genotypes could be used for commercial cultivation and genetic improvement programme to develop resistant varieties to Phytophthora leaf blight disease.

Rapid and sensitive detection of Phytophthora colocasiae associated with leaf blight of taro by species-specific polymerase chain reaction assay

Abstract: The failure to adequately identify plant pathogens from culture-based morphological techniques has led to the development of culture-independent molecular approaches. The timely and accurate detection of pathogens is a critical aid in the study of epidemiology and biology of plant diseases. In the case of regulated organisms, the availability of sensitive and reliable assay is essential when trying to achieve early detection of pathogens. We developed and tested the PCR assay for detection of Phytophthora colocasiae, an oomycetes pathogen of leaf blight of taro and of rotting of taro tubers. The method described here is specific for P. colocasiae when tested across fungal, bacterial, and other Phytophthora species. In conventional (single-round) PCR, the limit of detection was 20 pg DNA for both primer sets, whereas in nested PCR the detection limit for both was 0.2 pg. In sampling studies, P. colocasiae-specific primers were used to detect leaf blight in infected leaves and tubers of taro cultivar. The causal pathogen P. colocasiae was detected by PCR from artificially infected tubers after 16 h of post inoculation, before any visible symptoms were present. The method was also tested to detect fungal DNA in infected leaves and infested soils. The PCR assay and direct tissue extraction methods provide tools which may be used to detect P. colocasiae pathogens in taro planting material and thus limit the transmission and spread of new, aggressive strains of P. colocasiae in taro-growing regions.