CHAPTER II: SURVEY AND COMPREHENSIVE REVIEW OF LITERATURE

Transcription

1 CHAPTER II: SURVEY AND COMPREHENSIVE REVIEW OF LITERATURE 2.1 INTRODUCTION Agronomy is the art and underlying science of handling crops and soils to produce the highest possible quantity and the best quality of the desired crop from each unit of land, soil, water and light with a minimum use of resources. The science of agronomy strives to raise productivity, which is associated with profitability, lower cost and sustained competitiveness. Crop management and its scientific study encompasses four areas: the physical elements of climate, soil and land, the biological constituents of vegetation and soil, the economic opportunities and constraints of markets, sales and profit, and the social circumstances and preference of those who manage crop production. Such management plays a role in the handling of the soil, the manufacturing unit and the product output. Formatted: Font: Not Bold Formatted: Font: Elephant, Not Bold Formatted: Font: Not Bold Formatted: Font: 16 pt, Not Bold Formatted: Font: Elephant, Not Bold Formatted: Font: Not Bold Formatted: Justified, Space As far as the production of the finished product of Turmeric is concerned, a number of stages have to be considered. In order to get well-dried rhizome fingers of turmeric, the farmer has to pay attention to the preparation of suitable soil, the seed roots to be planted, the various stages of growth of the plant, and harvesting. Then, come the stages of post-harvest processing like drying the turmeric fingers, grinding the dried fingers into powder, packaging the product, and finally sending it to market. At every stage, the producer has to take the utmost care to avoid all unwanted effects and finally obtain a higher quantity, along with better quality, of the finished product. 2.2 SOIL FOR TURMERIC CROP Turmeric thrives well on loose and friable, well-drained loamy or alluvial soils. Coarse or heavy soils hinder rhizome development. The turmeric crop is sensitive to saline soils as well as to saline water irrigation. It grows in soil with a ph range of 4.3 to 7.5. It is intensively grown in Bangladesh in fertile land with sandy loamy soil. Researchers employed correlation analysis, path analysis, and cluster analysis to study the type of soil that favorably influences the yield and quality of turmeric. The rhizome yield and quality varied greatly with the type of soil texture. A clear correlation between the soil factors, rhizome yield and quality was found. [7] [20] [21] [29] [47] [56] [64] [78] [90] [96] [105]. 17

2 Measurement and control of soil microorganisms When using a pest-control method in organic farming, it is important that it only affects the target organisms and that there are no side effects causing damage to other living organisms. When sterilizing soil, the possible effects of the process on the soil s chemical and biological properties have to be considered, as they influence the growth of the crop. These properties are regulated by soil microorganisms, and changes in the microbial population can change the soil s biological and chemical characteristics. Soil sterilization may thus have both positive and negative effects on soil-borne plant pathogens. Soil microorganisms are the living components of the organic matter found in soil. Among a number of current methods to measure microbial biomass, including chloroform fumigation and substrate-induced inspiration, microwave irradiation has also been proposed as a rapid and non-toxic alternative [48] [55] [121]. 2.3 TURMERIC SEED RHIZOMES The importance of processing the turmeric seed rhizomes carefully for achieving higher yields of good quality is well-known since ancient times, as proved from our knowledge of early farming techniques. A survey of various techniques clearly indicates the improvements achieved in the turmeric seed selection method and in the storage environment. The effect of seed size on the growth and development of plants is very important. An optimum seed root size of a root crop would develop healthy seedlings and vegetative parts, which subsequently receive higher solar energy and result in a maximized yield. Preservation and plant growth The plant species Curcuma Longa (Linn.) (Turmeric) produces different sizes of daughter rhizomes and mother rhizomes, which are the only propagates for its cultivation. The effects of seed rhizome size on the growth and yield of turmeric fingers have already been evaluated. Daughter rhizomes of 5-50 g and mother rhizomes of g were tested previously by other researchers. It was found that the heavier the daughter rhizome (above 40 g), the better the plant growth. Also, seed rhizomes with a greater diameter developed vigorous seedlings. The shoot biomass and yield were highest in plants grown directly from the mother rhizome.[45] In this research work, an investigation has been made into the results of applying microwave radiation to the water given to turmeric seed rhizomes and to the soil, with varied, Bulleted + Level: 1 + Aligned at: 0.25" + Tab after: 0.3" + Indent at: 0.3", Tab stops: Not at 3.4" 18

3 radiation times. The present investigations include not only an improvement in processing conditions and procedures, but also the application of microwave treatment before the preservation and planting of turmeric seed rhizomes. Careful selection of microwave power and exposure time can finally result in not only better plant growth but also in improved quality and increased yield of turmeric. These results along with the earlier improvements will be definitely beneficial to needy farmers in the process of turmeric harvesting. About 15 to 20% of the harvested turmeric crop is retained by farmers as seed material. The preservation of seed rhizomes is one of the most important aspects in the cultivation of turmeric. At the time of harvesting, a requisite quantity of sound undamaged well-developed rhizomes of turmeric fingers must be carefully selected and cleaned for preserving as seeds. From the time of harvesting of the rhizomes, the seed rhizomes of turmeric fingers are to be stored for 90 to 105 days in healthy and viable conditions. Generally, a pit of 60 cm deep and large enough to hold the seed rhizomes is dug in a cool, shady, dry location. The seed rhizomes are placed in the pit and covered lightly with loose, dry soil and turmeric, banana or other leaves. Ilyas (1978) observed that the seed rhizomes are usually stored under shade and covered with turmeric leaves plastered together with mud and cow dung [45]. Thus, the seed rhizomes can be preserved in good condition until needed for planting. Gorbal et al. (2002) concluded on the basis of their experiments that turmeric seed rhizomes can be best stored with minimum storage losses due to physiological loss if they are stored in polyethylene bags with 5% ventilation in a dry and cool room; under field conditions, they could be stored in pits lined with wheat straw [42]. Effect of microwave radiation on seeds Previous research has not been consistent. Reddy et al. (1998) investigated relationships between microwave operating conditions and resulting seed quality in terms of germination and seedling vigor. They applied microwave radiation to wheat seeds for 20, 30, 40, and 50 seconds and allowed them grow for 7 days in glass jars. Then they measured the plumule and the height in cm [12]., Bulleted + Level: 1 + Aligned at: 0.25" + Tab after: 0.3" + Indent at: 0.3" Murakami et al (2001) studied Brassica campestris (known as Brassica Rapa var. silvestris in the US) [74]. They used an enclosure with the broadcast antenna supported on an outdoor pole with a frequency of MHz with intensities varying from 1.0 to 15.0mW/cm 2. They observed slight growth acceleration at the lowest intensity which they attributed to a slight increase on the soil temperature. 19

4 Urech et al. (1996) studied the lichens Parmelia tiliacea and Hypogymnia physodea in field experiments of duration ranging from 1 to 3 years [118]. They found a reduced growth rate due to thermal effects. Picazo et. al. (1999) investigated the effects of electromagnetic fields on thistles and lentils [88]. They found that the thistles decreased in both weight and length and the stem length of lentils increased over 3 weeks. Their experiments tested how microwave energy affects the growth of those plants. 2.4 STABILIZATION OF CONSTITUENTS OF STORED TURMERIC FINGERS Since the qualities of turmeric rhizomes for food and medicinal uses are based directly on the content of the curcuminoids and the volatile oil, carbohydrates, proteins, fats and moisture content, it is important that rhizomes are handled and stored correctly in order to maintain the levels of the active principles in the harvested raw material. Turmeric rhizomes are exposed to a variety of conditions during processing, packaging and storage, and some of these may have a detrimental effect on the stability of the active constituents of turmeric rhizome fingers, as has previously been investigated [5] [87]. The content of active constituents can also be affected by environmental factors such as temperature, ph, light, moisture and air [11] [17] [19] [24] [92] [107] [124] Effect of insect pests on stored turmeric fingers In India turmeric is widely used in food preparation. During storage, turmeric fingers and turmeric powder are attacked by insect pests leading to deterioration in quality as well as loss of quantity. Turmeric is normally affected by Stegobium Paniceum L. (Drugstore beetle), Lasioderma serricorne F. (Cigarette Beetle) and Araecerus fasciculatus (Coffee bean weevil) which are the most common insect pests of dried turmeric fingers. Such insect infestations have a destructive effect, and result in quality deterioration, loss of nutritional components and loss of quantity. In addition, due to these insect pest attacks, the uric acid level within the turmeric also rises beyond the maximum specified limit. The checking of various constituents like proteins, volatile oil, carbohydrates, ash, curcuminoids, etc. at regular intervals helps to determine the effect of insect infestations. Formatted: Justified, Space Insect pest control Various techniques have been used for the management of storage pests of turmeric fingers and other spices. These include: suitable containers, fumigation, heat treatment, application of insecticides and radiation. 20

5 Suitable containers Polypropylene more than 20 m is resistant to biting by L. Serricorne and S. Paniceum. S. Paniceum did not bite low-density black polyethylene (250 m), aluminum foil laminated with low density polypropylene (50 m), or printed polypropylene (50 m) indicating the potential use of these materials for packaging spice products including turmeric fingers [87] [92]. Fumigation 1. 1:19 mixture of ethylene-di-bromide and carbon tetrachloride applied at 8lb per 1000 cu. ft. for 24 hours. This was found to be the most effective method for controlling storage infestation in turmeric fingers [109]. Formatted: Space Before: 12 pt,, Bulleted + Level: 1 + Aligned at: 0.25" + Tab after: 0.3" + Indent at: 0.3" Formatted: Indent: Left: 0", First line: 0.5", Space, Bulleted + Level: 1 + Aligned at: 0.25" + Tab after: 0.3" + Indent at: 0.3" Formatted: Space After: 4 pt Formatted: Bullets and Numbering 2. Fumigation of storage rooms (godowns) with phophine gas produced from celphos tablets applied at the rate of 140 tablets per 100 m 3 : This result in mortality of adult insects and larvae [57]. 3. Impregnation of jute bags (lined with alkathene of 50 gauges) with Malathion 0.2%.: This prevents infestation of turmeric fingers [1]. 4. Fumigation with methyl bromide for 6 hours. It can be used for prevention of infestation of turmeric fingers. 5. Fumigation with aluminum phosphide tablets in an airtight store-room for 2 to 3 days for controlling the pest infestation [50]. 6. Fumigation of dry turmeric fingers with fumes of burning sulphur in a chamber is widely practiced by many traders in India. Muthu and Majumdar (1974) have furnished the concentration, time of exposure, and residual effects of various fumigants recommended for controlling insect infestations in various spices including turmeric fingers [75]. Radiation: Gamma radiation treatments of eggs and larvae of L. Serricorne and S. Paniceum indicated that the dose of 25 Gy prevented eggs from developing into adult stages and a dose of 50 Gy was require to prevent older larvae from developing. Doses above 30 Gy produce sterilizing effect on both the species., Bulleted + Level: 1 + Aligned at: 0.25" + Tab after: 0.3" + Indent at: 0.3", Tab stops: 0.25", Left Formatted: Indent: Left: 0", Space After: 6 pt 21

6 Padwal-Desai et al. (1987) suggested that dry turmeric fingers could be treated with cobalt-60 gamma radiation at 1 kgy and stored at 28 o C to 30 o C [81]. Rezaur et al. (1982) also mentioned that L. Serricorne could be effectively controlled by gamma radiation [93]. Irradiation is an increasingly accepted technique to sterilize spices and other food products. The process does not affect the chemical or physical properties of the material [62]. The process is also known as cold pasteurization or irradiation pasteurization. In irradiation, sterilization is effected by the energy of the ionizing radiation. When ionizing radiation strikes bacteria and other microbes, its high energy breaks the chemical bonds in their molecules that are vital for cell growth and integrity. As a result microbes die or can no longer multiply and cause spoilage. The irradiation process requires specially built and secure facilities. The common dose of 5 to 10 kgy applied to dry turmeric fingers effectively kills bacteria, molds and yeasts. Insects and other pests in all life stages are also killed. It has been reported that irradiation of turmeric rhizomes with 10 kgy at a dose rate of 19 Gy/min showed no modification of the composition of volatile oil extracted after 1 week of storage at 5 o c. The antioxidant activity was also reported to be unaffected by irradiation [18]. Storage after irradiation further enhances the sanitization effect, because injured cells are unable to repair themselves, and they die off over time. Spore-forming bacteria require higher dosage levels to kill them because spores are less sensitive to radiation. The extent of reduction of microbial load in spices by irradiation is dependent on the radiation dose, the type and the initial population of the microorganisms present. The turmeric packaging materials are compatible with irradiation. Irradiation does not require the opening of the packages, so the aroma characteristics of turmeric are better maintained. Also, the color of turmeric is stable to irradiation treatment. Irradiation, when compared with thermal and fumigation treatments, results in cleaner spices with fewer changes in the sensory characteristics. The aroma of the food product does not change [19]. Moisture content and the essential oil are also not changed by the irradiation process [24]. In the case of turmeric fingers, no color change is observed at a dosage level of kgy. Effects of microwave radiation on the control of insect pests: Microwave treatment prior to and during storage of turmeric fingers is found very useful against possible infestation by S. Paniceum, and L. Serricorne. Turmeric constituents Formatted: Indent: Left: 0", First line: 0.5", Space Formatted: Font: Not Bold, Bulleted + Level: 1 + Aligned at: 0.25" + Tab after: 0.3" + Indent at: 0.3" 22

7 deteriorate during storage due to insect infestation. During storage, insects consume the product, contaminate it and create favorable conditions for their own further growth, thus leading to deterioration of product quality, reduction in nutritive values and loss in quantity. 2.5 STABILIZATION OF CONSTITUENTS OF TURMERIC POWDER Turmeric powder is the most common form of turmeric, sold through the retail market and used in home kitchens as well as by bulk food manufacturers and processors. To make turmeric powder, the dried rhizomes are ground to the required particle size. The powder is said to be fine if 98% of it passes through a 300 m sieve [49] Grinding of turmeric fingers Grinding the turmeric fingers is the simple process of disintegrating the rhizomes into small particles, and then they are sifted them through a series of screens. Depending upon the type of mill and the speed of crushing, the turmeric rhizome fingers may heat up and the volatile oil may be lost. In the case of turmeric, the generation of heat and oxygen during the process may contribute to curcumin degradation. Cryogenic milling with the aid of liquid nitrogen prevents oxidation and the loss of the volatile oil, but this type of milling is expensive and not widespread in the industry. Turmeric rhizome fingers are put through grinders, and the output is then size-sorted through screens; larger particles can be further ground. Turmeric powder sold in the Indian domestic market should conform to the quality standards specified by the Spice Board, Government of India. The requirements for ground turmeric in international trade should be as per standard specifications [49]. Dried rhizomes are roughly cleaned prior to grinding. The list of cleanliness specifications are prescribed for ground turmeric in the UK [108]. In addition to being sensitive to alkaline ph, turmeric pigments are also sensitive to light and oxygen [106] [112]. Hence, turmeric powder must be protected from all these factors. No change in the Hunter CIE color characteristics, expressed as L*, a*, b* was observed in cured ground turmeric fingers stored for 60 days at 25 o C in polyethylene bags in the absence of excess air [6]. Moisture levels above 12% can affect the free-flow characteristics of turmeric powder. Aluminum foil laminate packing offers the maximum protection against loss of the 23

8 volatile oil and the absorption of excess moisture into the packaged product. Polyethylene pouches alone are inadequate to give the desired protection against loss of volatile oils. Dried turmeric fingers are hard to grind and this results in excessive wear of the contact parts inside the grinding machinery, as compared to the process for other spices. This results in higher iron contamination in turmeric powder when compared to other spice powders [83]. This has to be subsequently treated with other methods by the manufacturer Controlling microorganisms to deliver a hygienic product Spices are prone to microbial contamination after harvest and at various stages of subsequent processing. Contaminated ingredients can be hazardous when used in processed foods. Therefore, it is important that ingredients enter the food processing area with negligible bacterial load. The maintenance of high levels of hygiene and sanitary conditions is important to reduce the risk of contamination by mold, spores, yeasts, aerobic / anaerobic bacteria and fungi during the processing and storage of turmeric fingers and turmeric powder. The microbial load in turmeric fingers and turmeric powder can be controlled by using techniques such as steam sterilization, fumigation and irradiation [92] Microwave irradiation to remove moisture Combined microwave-convective drying is one of the current methods of food preservation, and has been hitherto extensively studied and used in the fruit-processing industry. However, it is a difficult food-processing operation mainly because of undesirable changes in the quality of products dried in this way. The high temperatures and the long drying times required to remove water from the fruit materials containing sugar in conventional hot-air drying may cause serious damage to flavor, color and nutrients, as well as a reduction in the bulk density and rehydration capacity of the dried product. [65]. The major disadvantages of hot-air drying of foods are the low energy efficiency and long drying times during the falling rate period of the drying process. Because of the low thermal conductivity of food materials, heat transfer to the inner sections of foods during conventional heating is limited [2] [34]. The desire to eliminate this problem, prevent significant quality loss and achieve fast, effective and efficient thermal processing has resulted in the increasing use of a combined microwave-convective drying method in the fruit-processing industry. Formatted: Space Before: 30 pt, 24

9 2.6 PROPOSED WORK Turmeric in the post-harvest and storage stages and in its processed form (powder) is sought to be treated for two purposes: firstly, for the removal of the moisture content, and secondly, for reducing the microbial load during both the post-harvest and storage periods. For the removal of moisture, conventional thermal drying methods have some limitations / disadvantages Limitations of conventional thermal drying methods 1. Solar drying is time-consuming and labor-intensive. The aroma may also get lost. 2. Hot-air convective drying, though it reduces the drying time, adversely affects the taste, color and over-all quality of the dried product. Additionally, it is not energyefficient., Numbered + Level: 1 + Numbering Style: 1, 2, 3, + Start at: 1 + Alignment: Left + Aligned at: 0.5" + Tab after: 0.75" + Indent at: 0.75", Tab stops: Not at 0.63" 3. Freeze drying is expensive and requires technical sophistication. 4. Vacuum drying is expensive. Costly equipment is required Limitations of conventional insect pest control methods 1. Steam sterilization: It causes condensation of steam in the charge, which then requires a vacuum process, and it is expensive. The excess residual moisture in the product can lead to spoilage during storage. During steam sterilization, due to the insulating effect of solid materials, the exposure time and temperature required for the effective killing of microbes throughout the load can lead to a loss of quality and quantity., Numbered + Level: 1 + Numbering Style: 1, 2, 3, + Start at: 1 + Alignment: Left + Aligned at: 0.5" + Tab after: 0.75" + Indent at: 0.75" 2. Fumigation: The gases and chemicals used in fumigation are suspected to be carcinogens and mutagens, and hence need to be handled with care. Unwanted chemical residues may permeate the product, and may make it unhealthy for human consumption. 3. Irradiation: The equipment used is costly, and cesium-137 has got a lowpenetrating gamma beam. Considering the limitations of previously-used thermal drying and insect pest control methods, it is now proposed to use the combined microwave convective drying process for turmeric rhizome fingers as it is rapid, more uniform and more energy-efficient when compared to merely hot-air drying. In the case of microwave drying the removal of moisture 25

10 is accelerated and, furthermore, the heat transfer to the solid parts of the equipment is slowed down significantly due to the absence of convection. Due to the concentration of microwave energy, less floor space is required as compared to conventional drying equipment [2] [39] [43]. It has been suggested earlier by that microwave energy should be applied in the latter part of the thermal drying process, during the falling rate period or at a low moisture content for finish drying [89] [39]. In the present research, it is proposed that a microwave drying applicator be used with a hi-tech microwave power controller, supported by hot-air convective drying for processing turmeric fingers during the post-harvest and storage periods. 2.7 ADVANTAGES OF THE PROPOSED METHODS, AND THE PRECAUTIONS REQUIRED The advantages of microwave drying process have been listed below. Along with certain definite advantages, microwave drying may also have some limitations if proper precautions are not taken during the drying process Advantages of microwave heating / drying Heating is instantaneous: Since the transfer of energy is from inside to outside, heating is instantaneous. Furthermore, heat is generated within the material, and thus, the internal temperature gradient tends to be smaller. Formatted: Space After: 4 pt, Bulleted + Level: 1 + Aligned at: 0.05" + Tab after: 0.2" + Indent at: 0.2" Significant energy savings: Microwave energy couples directly to the material being heated. The transfer of energy to the air, the walls of the oven, the conveyor or to other parts is minimal, since their dielectric constants are very small. This can lead to significant energy saving. Efficient and accurate control of heating rates: Efficient and accurate control of heating rates can be achieved by controlling the output power of the microwave generator. Eliminate case hardening: Since the moisture flow is partly pressure-driven from the interior, there is no receding moisture front as in the convection ovens, which eliminate case hardening. Increases the drying rate: In conventional drying, moisture is initially flashed off from the surface, and the remaining water diffuses to the surface slowly. In the microwave process, internal heat generation leads to an increase in internal vapor generation, which 26

11 promotes liquid flow towards the surface, and also leads to higher internal temperatures, both of which increase the drying rate. Great potential for energy saving: In microwave drying, there is great potential for energy saving, due to the speed of drying and lower specific energy needs in the case of high dielectric loss materials like fruit gel and even turmeric. Drying times can be shortened by 50%: Drying times can be shortened by 50% or more depending on the moisture level of the product and on the drying conditions, such as power levels and temperatures. Requires less space and handling time: Microwave drying equipment occupies less space and reduces the handling time. Improvement in product quality: Due to microwave drying, the product quality of the output improves significantly. Reduction in case hardening, internal stresses and cracks: Microwave drying eliminates case hardening, internal stresses and cracks on the surface of the product. Easy interface: The microwave source can be conveniently combined with other methods of drying, such as hot-air drying, freeze-drying and vacuum drying. Reduction in production cost: Major financial and environmental savings may be realized through reduced use of energy, labor reduction, reduced heat in the heating cavity, increased efficiency of the system and reduced maintenance costs of the microwave drying applicator, when compared to conventional hot-air dryers Precautions to be taken during microwave heating / drying Many chemical and physical reactions are promoted by heat generation due to the microwave source, leading to puffing, drying, melting, protein denaturizing, and starch gelatinization. Therefore the microwave power and the radiation time have to be carefully adjusted for each type of turmeric product, i.e. fingers, slices and powder. 2.8 METHODOLOGY In the present research work, the methodology has been implemented which includes two main sections, 1. Design of equipment required for experimentation and 2. Experimentation and result analysis. 27

12 2.8.1 Design of equipment 1. A microwave drying applicator was designed, supported by hot-air convective drying, facilitating the measurement of the temperature, moisture, weight of the sample and radiation time, along with a data acquisition system interfaced to a PC, using a multimode microwave power controller. Formatted: Space After: 4 pt, Numbered + Level: 1 + Numbering Style: 1, 2, 3, + Start at: 1 + Alignment: Left + Aligned at: 0.5" + Tab after: 0.75" + Indent at: 0.75" 2. The following were also designed and produced, and their performance characteristics were analyzed - i. The integral cycle controller, ii. The phase controller iii. The PWM controller, iv. The linear controller Experimentation and result analysis Experimentation and result analysis was performed at various stages of turmeric processing such as- 1. Disinfestations of the soil used for growing turmeric rhizome seeds and measurement of soil microorganisms 2. Effects on turmeric rhizome seeds during storage and subsequent plant growth of treated seeds. Formatted: Indent: First line: 0.13", Space After: 4 pt, Numbered + Level: 1 + Numbering Style: i, ii, iii, + Start at: 1 + Alignment: Right + Aligned at: 1" + Tab after: 1.25" + Indent at: 1.25" Formatted: Space After: 4 pt, Numbered + Level: 1 + Numbering Style: 1, 2, 3, + Start at: 1 + Alignment: Left + Aligned at: 0.5" + Tab after: 0.75" + Indent at: 0.75", Tab stops: 1.13", Left + Not at 0.88" 3. Stability of constituents of stored turmeric fingers 4. Insect infestations in stored turmeric fingers 5. Microbial load and compositions of constituents of stored turmeric powder. 2.9 CONCLUDING REMARKS The advantages of the microwave drying / heating system can be clearly perceived. The use of combined microwave-convective drying process is found to be a suitable approach for coping with certain drawbacks of the conventional methods formerly used for thermal treatment of foods, especially in the fruit and vegetable processing industries [50] [65]. In the present submission, the use of microwave energy supported by a convective drying system has been found to be a very efficient and economical approach for coping with certain drawbacks of the traditional treatment methods used for post-harvest processing and the control of insect pests in stored turmeric fingers and stored turmeric powder. This will be of immense benefit to farmers and traders in the future. Formatted: Justified, Space Formatted: Space After: 24 pt 28