Central Tuber Crops Research Institute

The tropical tuber crops contain starch as the major component and thus act as important source of starch. Except cassava and to a smaller extent sweet potato, starch from other tuber crops has not been exploited for industrial applications partly because of difficulty in the extraction of the pure starches and partly because of non-availability of information about the properties of these lesser known starches. This review attempts at collating data available on the physicochemical and functional characteristics of the tropical tuber starches, highlighting their unique properties and potential field of applications. The physicochemical properties like granule shape and size, X-ray diffraction (XRD) patterns, amylose content, or content of non-starchy components, show considerable variation among the tuber starches. In addition, factors like genetic origin, environmental conditions and age of the plant also influence the properties. The starch granules of Colocasia esculenta and Dioscorea esculenta tubers are very small whereas those of Canna edulis are very large. XRD patterns of yam starches are generally ‘B’, while the aroid starches possess ‘A’ patterns. DSC gelatinisation temperatures are low for cassava starch and high for the aroid starches. The functional characteristics like viscosity, swelling power and solubility also depend on a number of factors such as varietal variation, method of extraction, processing conditions and instruments used for analysis. Viscosity is high for cassava and C. edulis starches, but low for most aroid starches. Clarity is good for cassava and yam starches compared to the others. Digestibility also varies among the starches. The diversity available in the tuber starches shows that some of the starches can be used in place of chemically modified starches available on the market. The realisation of their importance can help in value addition of these neglected crops and also provide starch with special properties for specific applications.

As world population increases, lactic acid fermentation is expected to become an important role in preserving fresh vegetables, fruits, and other food items for feeding humanity in developing countries. However, several fermented fruits and vegetables products (Sauerkraut, Kimchi, Gundruk, Khalpi, Sinki, etc.) have a long history in human nutrition from ancient ages and are associated with the several social aspects of different communities. Among the food items, fruits and vegetables are easily perishable commodities due to their high water activity and nutritive values. These conditions are more critical in tropical and subtropical countries which favour the growth of spoilage causing microorganisms. Lactic acid fermentation increases shelf life of fruits and vegetables and also enhances several beneficial properties, including nutritive value and flavours, and reduces toxicity. Fermented fruits and vegetables can be used as a potential source of probiotics as they harbour several lactic acid bacteria such as Lactobacillus plantarum, L. pentosus, L. brevis, L. acidophilus, L. fermentum, Leuconostoc fallax, and L. mesenteroides. As a whole, the traditionally fermented fruits and vegetables not only serve as food supplements but also attribute towards health benefits. This review aims to describe some important Asian fermented fruits and vegetables and their significance as a potential source of probiotics.

Nitrogen (N) is an essential element required for the growth and development of all plants. On a global scale, N is agriculture's most widely used fertilizer nutrient. Studies have shown that crops use only 50% of the applied N effectively, while the rest is lost through various pathways to the surrounding environment. Furthermore, lost N negatively impacts the farmer's return on investment and pollutes the water, soil, and air. Therefore, enhancing nitrogen use efficiency (NUE) is critical in crop improvement programs and agronomic management systems. The major processes responsible for low N use are the volatilization, surface runoff, leaching, and denitrification of N. Improving NUE through agronomic management practices and high-throughput technologies would reduce the need for intensive N application and minimize the negative impact of N on the environment. The harmonization of agronomic, genetic, and biotechnological tools will improve the efficiency of N assimilation in crops and align agricultural systems with global needs to protect environmental functions and resources. Therefore, this review summarizes the literature on nitrogen loss, factors affecting NUE, and agronomic and genetic approaches for improving NUE in various crops and proposes a pathway to bring together agronomic and environmental needs.

Secondary metabolites in plants have been recognized as a novel basis of potential bio-pesticides, paving the way for their use in sustainable agriculture. Plant secondary metabolites have pivotal roles in plant-pathogen interactions. Some important secondary metabolites of plants are terpenoids, flavanols, flavones, etc., are stress-inducible phytochemicals playing an important role in plant immune response development. Pathogen enters into host cell, multiply and utilise the biological mechanism of plants, causing a hazard to world food assembly. Under stressed circumstances, plants evolve a powerful and intricate system of growth and defensive action. On the other hand, transcription factors (TFs) assist host plants to counter adverse environments by acting as mediators of stress signal and regulating the stress-responsive gene expression. The transcriptional and post-transcriptional manipulation of transcriptional factors is capable of aid in molecular breeding and genetic modification meant for improved secondary metabolite synthesis. Although the presence of numerous secondary metabolites has been established in plant life, very slight is known about their interaction with pathogens and the specific mechanisms involved in leading to plant immunity. Chemical pesticides are wreaking havoc on our environment. As a consequence, environmental-friendly alternatives to disease management, like plant-based metabolites, should be explored. In this appraisal, we have reviewed plant secondary metabolites in relation to pathogens, their contribution to innate immunity, mechanism of action, and regulation of TFs in response to combating plant infections in an eco-friendly approach.

Abstract Cassava starch was cross‐linked with epichlorohydrin (EPI) at 45°C for 2 h in three different media which include water, water in the presence of a phase transfer catalyst (PTC) and N , N ‐dimethylformamide (DMF). The products were characterized by determining their physicochemical, thermal and retrogradation properties. In aqueous medium, the use of a PTC, tetrabutylammonium bromide (TBAB) produced derivatives with higher degree of cross‐linking than those prepared without the use of the catalyst. The degree of cross‐linking was found to be higher using the same concentration of EPI when the reaction was carried out in DMF. At low levels of cross‐linking, the peak viscosity of the cross‐linked starches increased in comparison to that of the native starch. With increasing degree of cross‐linking, the peak viscosity showed a significant reduction. The swelling volume, solubility and light transmittance of the starch pastes were lower for the modified starches. The cross‐linked starches showed slightly reduced values for the gelatinization temperatures, T onset , T peak and T end . The enthalpy of gelatinization of the modified starches increased with increase in the degree of cross‐linking. The modified starches exhibited higher water‐binding capacities (WBC) than the native starch; but with increase in the degree of cross‐linking, there was a gradual decrease in WBC. The in vitro alpha amylase digestibility of the modified starches decreased gradually with increase in the level of cross‐linking.

Cassava (Manihot esculenta Crantz) is an important tropical root crop providing energy to about 500 million people. The presence of the two cyanogenic glycosides, linamarin and lotaustralin, in cassava is a major factor limiting its use as food or feed. Traditional processing techniques practiced in cassava production are known to reduce cyanide in tubers and leaves. Drying is the most ubiquitous processing operation in many tropical countries. Sun drying eliminates more cyanide than oven drying because of the prolonged contact time between linamarase and the glucosides in sun drying. Soaking followed by boiling is better than soaking or boiling alone in removing cyanide. Traditional African food products such as gari and fufu are made by a series of operations such as grating, dewatering, fermenting, and roasting. During the various stages of gari manufacture, 80 to 95% cyanide loss occurs. The best processing method for the use of cassava leaves as human food is pounding the leaves and cooking the mash in water. Fermentation, boiling, and ensiling are efficient techniques for removing cyanide from cassava peels.

Sweetpotato storage roots are subjected to several forms of post harvest spoilage in the tropical climate during transportation from farmers' field to market and in storage. These are due to mechanical injury, weight loss, sprouting, and pests and diseases. Sweetpotato weevil is the single most important storage pest in tropical regions for which no control measures or resistant variety are yet available. Several microorganisms (mostly fungi) have been found to induce spoilage in stored sweetpotatoes. The most important among them are Botryodiplodia theobromae, Ceratocystis fimbriata, Fusarium spp., and Rhizopus oryzae. The other less frequently occurring spoilage microorganisms include Cochliobolus lunatus (Curvularia lunata), Macrophomina phaseolina, Sclerotium rolfsii, Rhizoctonia solani, Plenodomus destruens. Microbial spoilage of sweetpotato is found associated with decrease in starch, total sugar, organic acid (ascorbic acid and oxalic acid) contents with concomitant increase in polyphenols, ethylene, and in some instances phytoalexins. Several methods are used to control microbial spoilage. Curing to promote wound healing is found as the most suitable method to control microbial spoilage. Curing naturally occurs in tropical climates where mean day temperature during sweetpotato harvesting season (February-April) invariably remains at 32-35 degrees C and relative humidity at 80-95%. Sweetpotato varieties varied in their root dry matter content, and low root dry matter content attributed for their high curing efficiency. Curing efficiency of varieties also differed in response to curing periods. Fungicide treatment, bio-control, gamma irradiation, hydro warming, and storage in sand and saw dust were found to have intermediate impacts in controlling spoilage and enhancing shelf life of sweetpotato roots. Breeding program has to be chalked out to develop new varieties suitable to curing under tropical conditions in addition to developing varieties having multi-spectrum resistance to major post harvest rot pathogens and sweetpotato weevils.

Sweet potato (Ipomoea batatas L.) is among the major food crops in the world and is cultivated in all tropical and subtropical regions particularly in Asia, Africa, and the Pacific. Asia and Africa regions account for 95% of the world's production. Among the root and tuber crops grown in the world, sweet potato ranks second after cassava. In previous decades, sweet potato represented food and feed security, now it offers income generation possibilities, through bioprocessing products. Bioprocessing of sweet potato offers novel opportunities to commercialize this crop by developing a number of functional foods and beverages such as sour starch, lacto-pickle, lacto-juice, soy sauce, acidophilus milk, sweet potato curd and yogurt, and alcoholic drinks through either solid state or submerged fermentation. Sweet potato tops, especially leaves are preserved as hay or silage. Sweet potato flour and bagassae are used as substrates for production of microbial protein, enzymes, organic acids, monosodium glutamate, chitosan, etc. Additionally, sweet potato is a promising candidate for production of bioethanol. This review deals with the development of various products from sweet potato by application of bioprocessing technology. To the best of our knowledge, there is no review paper on the potential impacts of the sweet potato bioprocessing.

Cassava contributes significantly to the nutrition and livelihood of up to 500 million people and thousands of processors and traders around the world. Besides serving as the primary staple food of millions of people in the tropics and subtropics, it can also be used as a carbohydrate source in animal feed. Cassava is used as a raw material in the manufacture of processed food, animal feed and industrial products. Wider utilization of cassava products can be a catalyst for rural industrial development and raise the incomes for producers, processors and traders. It can also contribute to the food security status of its producing and consuming households (Plucknett et al., 1998).

The drug-excipient compatibility studies were carried out with the possible excipients viz. Tween 80, Carbopol 940, chitosan, sodium alginate, and polycaprolactone (PCL) for their possible use in the formulation of eugenol loaded nanoemulsion gels and nanoparticles. The eugenol-excipient compatibility studies were carried out by visual observations, differential scanning calorimetry (DSC), infrared spectroscopy (FTIR), and high-performance thin-layer chromatography (HPTLC). No notable change was observed in the samples on visual observation. From the results of the DSC studies, to a much extent, it was assumed that eugenol was not subjected to any interaction with the selected excipients for the proposed nanoemulsion gel and nanoparticles. But in some cases viz. polycaprolactone and Carbopol, though not to a significant level, slight deviation of the nature and position of the endothermic peaks of eugenol were observed. The results of the IR spectroscopy confirmed the compatibility of eugenol with Tween 80, Carbopol 940, chitosan, sodium alginate, and polycaprolactone. The retention factor of the HPTLC densitogram peaks for all the physical mixtures was well within the retention factor (Rf) value range observed for pure eugenol. The study results confirmed that eugenol is compatible with the selected excipients for the development of nanoemulsion gels and nanoparticles.

In Asia, cassava (Manihot esculenta) is cultivated by more than 8 million farmers, driving the rural economy of many countries. The International Center for Tropical Agriculture (CIAT), in partnership with national agricultural research institutes (NARIs), instigated breeding and agronomic research in Asia, 1983. The breeding program has successfully released high-yielding cultivars resulting in an average yield increase from 13.0 t ha–1 in 1996 to 21.3 t ha–1 in 2016, with significant economic benefits. Following the success in increasing yields, cassava breeding has turned its focus to higher-value traits, such as waxy cassava, to reach new market niches. More recently, building resistance to invasive pests and diseases has become a top priority due to the emergent threat of cassava mosaic disease (CMD). The agronomic research involves driving profitability with advanced technologies focusing on better agronomic management practices thereby maintaining sustainable production systems. Remote sensing technologies are being tested for trait discovery and large-scale field evaluation of cassava. In summary, cassava breeding in Asia is driven by a combination of food and market demand with technological innovations to increase the productivity. Further, exploration in the potential of data-driven agriculture is needed to empower researchers and producers for sustainable advancement.

Amorphophallus konjac (konjac) is one among the major vegetable (tuber) crops grown in Asian countries. In China and Japan, it has been used as food and a food additive for more than 1000 years. Over the last few decades, the purified konjac flour, commonly known as konjac glucomannan (KGM), a dietary fiber hydrocolloidal polysaccharide, has been introduced as a food additive as well as a dietary supplement in many Asian and European countries. The present article reviews the literature (up to January 2015) covering the development of various functional foods, food additives from KGM and their derivatives, Also, this review deals with global nutritional aspects and value added products of konjac corm. The bioprocessing techniques such as preparation, purification, and extraction of KGM from konjac flour and methods to improve quality of KGM are discussed.Abbreviations: 13C NMR: carbon-13, nuclear magnetic resonance spectroscopy; CHD: coronary heart disease; CKF: crude konjac flour; CVD: cardiovascular disease; DA: degree of acetylation; DMSO: dimethyl sulfoxide; DOB: degree of branching; EC: European Commission; EFSA: European Food Safety Authority; EFY: elephant foot yam; FCC: Food Chemical Codex; FDA: Food and Drug Administration; GM: glucomannan; KG: konjac gel; KGM: konjac glucomannan; KGMOS: KGM octenyl succinate; KM: konjac mannan; OSA: octenyl succinic anhydride; PKF: purified konjac flour; SEM: scanning electron microscopy; USDA: United States Department of Agriculture; WHO: World Health Organization; WVP: water vapor permeability

Taro (Colocasia esculenta (L.) Schott) is widely distributed in tropical and sub-tropical areas. However, its origin, diversification and dispersal remain unclear. While taro genetic diversity has been documented at the country and regional levels in Asia and the Pacific, few reports are available from Americas and Africa where it has been introduced through human migrations. We used eleven microsatellite markers to investigate the diversity and diversification of taro accessions from nineteen countries in Asia, the Pacific, Africa and America. The highest genetic diversity and number of private alleles were observed in Asian accessions, mainly from India. While taro has been diversified in Asia and the Pacific mostly via sexual reproduction, clonal reproduction with mutation appeared predominant in African and American countries investigated. Bayesian clustering revealed a first genetic group of diploids from the Asia-Pacific region and to a second diploid-triploid group mainly from India. Admixed cultivars between the two genetic pools were also found. In West Africa, most cultivars were found to have originated from India. Only one multi-locus lineage was assigned to the Asian pool, while cultivars in Madagascar originated from India and Indonesia. The South African cultivars shared lineages with Japan. The Caribbean Islands cultivars were found to have originated from the Pacific, while in Costa Rica they were from India or admixed between Indian and Asian groups. Taro dispersal in the different areas of Africa and America is thus discussed in the light of available records of voyages and settlements.

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).

Gene regulatory networks play an important role the molecular mechanism underlying biological processes. Modeling of these networks is an important challenge to be addressed in the post genomic era. Several methods have been proposed for estimating gene networks from gene expression data. Computational methods for development of network models and analysis of their functionality have proved to be valuable tools in bioinformatics applications. In this paper we tried to review the different methods for reconstructing gene regulatory networks.

Abstract Cassava starch extracted from six varieties at different period of growth was examined for various physiochemical properties. The granule size increased in all the six varieties upto 6th month from time of tuber initiation and thereafter remained almost constant. The amylose content and reducing values did not vary much at different stages of growth. The swelling volume and swelling power of starch showed large variations particularly after 10th month. Such changes of four varieties were not noticed in other varieties. Associative binding forces of starch molecules largely determine the stability characteristics of starch under varied environmental conditions.

The most viable and practical option for the management of plant diseases is disease resistance. However, in most of the crop plants, natural resistance against pathogens is rare. Breeding resistant varieties is a long-term process and the possibility of resistance being broken always exists. Induced resistance exploiting natural defense machinery of plants is indeed an alternative, nonconventional and ecologically friendly approach for plant protection. Its introduction into agricultural practice could minimize the scope of chemical control, thus contributing to the development of sustainable agriculture. Induced resistance can be defined as an increased expression of natural defense mechanisms of plants against various types of pathogens, provoked by a range of factors: pathogens causing hypersensitive necrotic reaction, avirulent or attenuated pathogenic strains, and elicitors of pathogenic origin (glucans, proteins, lipids, etc.). Induced resistance, being based on the expression of latent genetic information present in plants, is not underlaid by genome alterations (mutations, introgression of foreign genetic material), thus enhancing its biological safety. In this communication, classes of elicitor, their signal perception, transduction and induced defense gene activation has been described.

Bacillus subtilis strains (CM1-CM5) isolated from culturable cowdung microflora were investigated for indole-3-acetic acid (IAA) production in nutrient broth (NB). All the strains tested produced IAA in NB; albeit in very low concentrations (0.09-0.37 mg/l). The addition of L-tryptophan (0.1 - 1.0 g/l) into NB substantially enhanced IAA production (6.1 - 31.5 folds) indicating that L-tryptophan was the precursor for IAA biosynthesis by these bacterial strains. Maximum IAA production was observed after 8 days of incubation (in late stationary phase of bacterial growth). The variation in IAA production was attributed to the genetic make up of these strains as evaluated by RAPD analysis of these isolates and B. subtilis type strain MTCC 441. Application of B. subtilis suspension (8 x 10(9) CFU/ml) on the surface of yam (Dioscorea rotundata L.) minisetts increased the number of sprouts, roots and shoots length, root and shoot fresh weights and root: shoot ratio over those minisetts not treated with bacterial suspension. Fresh cowdung slurry treatment on yam minisetts also produced similar results as obtained with B. subtilis application.

The review focuses on some of the high value-end biocommodities, such as fermented beverages, single-cell proteins, single-cell oils, biocolors, flavors, fragrances, polysaccharides, biopesticides, plant growth regulators, bioethanol, biogas and biohydrogen, developed from the microbial processing of fruit and vegetable wastes. Microbial detoxification of fruit and vegetable processing effluents is briefly described. The advances in genetic engineering of microorganisms for enhanced yield of the above-mentioned biocommodities are elucidated with selected examples. The bottleneck in commercialization, integrated approach for improved production, techno-economical feasibility and real-life uses of some of these biocommodities, as well as research gaps and future directions are discussed.

Abstract The efficiency of different processes in reducing the cyanoglucoside (CNG) content of cassava was studied. Maximum retention of CNG (>80%) was observed in baked, fried and steamed tubers. CNG retention in sun‐dried chips varied from 30–60%, the retention being governed by the chip thickness. In case of cassava boiled in water, smaller chip size and sufficient water was found to be the ideal condition for maximum CNG removal. There was 25–75% CNG retention in this process, depending on the chip size used. The most effective method for CNG removal was by crushing fresh tuber and subsequent sun‐drying, whereby >95% CNG was eliminated. The studies indicated that the mode of processing greatly influenced the CNG content of cassava foods. It was concluded that since CNG can be greatly reduced by suitable processing, it may not be a limiting factor in the utilisation of cassava for food and feed purposes.