eChapters

Abstract

The objective of this chapter is to provide an overview of heat pump dryer (HPD) and recent developments in its applications for drying of agricultural and food products. The basics of heat pump dryer, classification, operating principle, configuration and control system have been presented for better understanding. Many researchers have concluded that HPDs use energy more efficiently than electrical dryers. The heat pump dryer is best suited for drying high value commodities such as fruits, vegetables, spices, condiments, herbs, medicinal and aromatic plants at near ambient temperature for producing better quality dehydrated product.

Abstract

Drying is a very important unit operation in food processing. Being an energy intensive unit operation, drying process demands improvement to make it energy efficient. Beside this operating conditions used in drying affect product quality substantially; however, traditional dryers do not allow enough flexibility to meet quality requirements for several products. This has resulted in development of number of new drying techniques, to cope with both energy efficiency and product quality.

Abstract

In recent years microwave processing have attained increasing recognition in food industries particularly in drying and dehydration. During microwave processing, electromagnetic energy is supplied directly to the food material for volumetric heating. This provides rapid temperature rise throughout the material with reduced thermal gradients. This unique heating mechanism reduces processing time and saves energy. In-spite of advantages of microwave heating it leads to overheating in food material and formation of cold and hot spots if applied improperly during drying. To overcome these challenges different microwave assisted hybrid drying technologies have been developed by many researchers. These techniques are microwave assisted hot air drying, microwave assisted osmotic dehydration, microwave assisted vacuum drying, microwave- infrared assisted hot air drying, microwave assisted rotary drying. This chapter comprises the fundamentals of microwave and provides comprehensive update of microwave assisted hybrid drying processes for food and agricultural materials.

Abstract

Hot air circulation is the most common industrial method of drying foods which has its own inherited disadvantages. Microwave drying can be an alternative method for removing moisture from foods and there has been a surge of interest in the application of microwave to process the foods, in past few years. The reason being that there is worldwide energy crisis and the growing acceptance and familiarity with domestic microwave ovens. It is well known that conventional means of heat processing irreversibly alter the flavor, colour, and texture of many foods. From the point of flavor alone, it is desirable to improve our present methods of processing foods. Some improvements have been made in this direction with a number of food products by use of high-temperature short- time processing.

Abstract

Spray drying is one of the most preferred methods of converting food and pharmaceutical solutions into powder form. Very high product throughput, hygienic and highly automated process and relatively benign thermal and dehydration stress on products associated with this process has made it ubiquitous in powder manufacture. Compared to freeze drying, spray drying is significantly less expensive both in terms of operation and capital costs. In this chapter, key features of spray drying such as underlying operational principle, types of spray nozzles used, the flow pattern of droplets/particles and drying medium within the drying chamber, the particle formation process of individual droplet are discussed in considerable detail. The modelling aspect of a single droplet subjected to spray drying environment has also been included. Finally, the most commonly considered characteristics of spray dried powders including morphology, crystalline/amorphous nature and solubility are highlighted and discussed.  The content presented in this chapter will be very useful for practising engineers, technologists, researchers as well as postgraduate and undergraduate students.

Abstract

Osmotic dehydration is gaining popularity due to several energy and product quality related advantages it offers. It has huge potential as a complementary process step prior to operations such as air-drying, microwave drying, freezing, frying etc, if not an alternative one, in the food process chain. It can be easily integrated with other processing steps in order to improve the overall efficiency of a given food process. Application of additional driving force either prior to or during osmotic dehydration can enhance the mass transfer rates in the osmotic dehydration. Role of mathematical modelling both in osmotic dehydration and rehydration have been discussed. Current limitations for the adaptation of osmotic dehydration in the food processing industry and possible solutions are also discussed in detail.

Abstract

Classification of the hundreds of possible dryers is essential to the logical selection of appropriate dryer for a given application. Diverse criteria for classification as well as selection of dryers are presented and discussed briefly. The advantages and limitations of different dryer types must be taken into consideration. Initial capital cost is often the key deciding criterion in industrial dryer selection. This is not a good strategy as the user must pay for the operating costs over a long period of life of the dryer. In general several different dryer types are suitable for a given product. Careful selection is essential for cost-effective operation of the dryer.

Abstract
 
Food products can have moisture content as high as 90% which needs to be lowered to acceptable limits to prevent microbial growth and deteriorative reactions. Drying is one of the most common and cost effective techniques for removal of excess moisture from the food by application of heat. In addition to its role of extending the product shelf life and providing stability, drying also helps to produce variety of products from agricultural, horticultural and industrial products. But to obtain the desired quality product, adequate drying is essential which depends on type of dryer and drying technique employed which further requires proper understanding of drying process. Despite being important unit operation in food processing industry, appropriate scientific knowledge of the drying process is still limited. So, the fundamental principles and associated terminologies with drying has been discussed in detail in this chapter to have thorough understanding of the drying process. In addition, different models and calculation procedures for drying of different types of commodities has also been reviewed.

In the Asian and Pacific ‘region, it is China alone which produces the largest quantities of agricultural waste and also crop residues. This is followed by India. From the production of rice, corn and wheat alone 587 million tons of residues are generated per year in China. Maheshwari (2014) has surveyed the proportions of waste that Malaysia generates from the production of rice, palm oil, rubber, coconut and forest products. In Myanmar the crop waste and residues constitute about 4 million tons per year out of which more than half constitutes rice husk.

The possibility of making genetic changes in the laboratory in plants, animals and microbes used in food started almost 10,000 years ago. Along with natural changes taken place during the evolution totally different species have come into existence. This has helped in increased food production with better taste and nutrition. The losses caused by biotic and abiotic stresses from fungi and bacterial pathogens have reduced.

All these methods of utilization and the conversion to useful energies depend on the climate, population density of the area and the basic infrastructure. It is important to work out the market for the products which are produced.
 
Bio-waste management: It needs to take from small actions to the ambitious ones. European Commission proposes to use wastes which could make up to 25% of total energy consumption by 2020. They propose to have directives for the promotion of renewable electricity (Directive 2001/77/EC) and biofuels (Directive 2003/30/EC). The waste production in Europe has gone upto 2 kg per capita per day. Recycling rates are also rising (European Commission, 2017). The Member states must develop a national action plan and outline the national policies to develop existing biomass resources and mobilise new biomass resources for different uses. A European project has studied the amount of renewable energy to be used in 2020. According to them it will be around 195 million tons of oil equivalents (Mton) of biomass which is biodegradable part of MSW. This will be 20% of renewable energy target. It has also been estimated that the amount of bio-energy from the MSW will be 20 Mton, which would account for around 7% of all renewable energy in 2020. This may be available after composting and anaerobic digestion (Atanasiu, 2010).

3a. Sources and problems of agricultural wastes
3b. Waste Reduction
3c. Waste Treatment
3d. Waste Disposal
3e. Clean Technology

Different Kinds of Agricultural Wastes
Table 1: Common Hazardous Wastes: Community Source

After the agricultural activities a number of by-products are obtained and these are known as agricultural waste. These include residues of different crops like stalks, straws, leaves, roots, husks and shells. The animal waste is in the form of manure. All these agricultural wastes are free of cost however; they can be utilized as an important resource (Lionel and Arnold, 1931). Agrawal (1998) has mentioned India as the final dumpyard. The wastes obtained from various resources can be converted into heat, steam, charcoal, methanol, ethanol, biofuel, compost, energy, biogas, construction and high valued chemical compounds. Many times these agri-industrial wastes are not completely utilized and either they rot in open areas or are burned in the fields.

In today’s times, a lot of innovation has come into agriculture. This very hard occupation requires an amalgation of farmers with the scientists. From the rural areas after education the technocrats are moving to the cities and this is creating a great loss to the agriculturists. As the population is growing so is the demand for food. Due to shortage in the storage systems the amount of wastage has increased a lot. It is an important aspect to be looked into. A lot of waste material is seen in the vegetable markets, city markets and near the slums. This causes a lot of pollution and spoils the environment. It is important to know why is it increasing and why the facilities for wastes do not exist.

Introduction

Maize (Zea mays, or corn as it is known in some countries) is the principal cereal crop in tropical and subtropical regions throughout the world. The increasing use of maize as a staple food reflected the much higher yields per hectare, compared with wheat, rye and barley. Because maize was cheap, it became the dominant food and main source of dietary energy and protein for poor people, particularly those in rural and underprivileged segments of society. Maize is considered to be a native of the Americans. There are different views about the introduction of maize in India. One view is that maize was introduced into India by the Portuguese during the seventh century. Other view is that maize was introduced in Pre-Colombian era through the Atlantic Arabian trade route. This is supported by the more recent variability that has been observed in the maize collections made from the north eastern Himalayan region. However, the historic records regarding the cultivation of maize in India date back only to the Maratha Empire.

Introduction

Rice is grown in more than 100 countries in the world and is an important crop for nutritional security of large part of the population. World rice production in 2007 was approximately 645 million tones. Around 50 countries have an annual production of more than 1 million tones. Ninety percent of the total rice is produced in Asian countries, with two countries, China and India, growing more than half the total crop. Top ten rice producing countries are China, India, Indonesia, Bangladesh, Vietnam, Thailand, Myanmar, Japan, Philippines, and Brazil. In Bangladesh, Cambodia, Indonesia, Lao PDR, Myanmar, Thailand, and Vietnam, rice provides 50-80% of the total calories consumed. Major part of the rice is consumed locally where produced and only 6-7% of world rice production is traded internationally.

Introduction

Barley is an important cereal crop grown all over the world and is used mainly for feed and malt purposes and little for human food. Barley is the world’s oldest grain, as evidenced by discoveries in ancient cities in the Middle East and North Africa. It has been cultivated for about 8,000 years, and today is the world’s fourth largest cereal crop. Considerable evidence is available that points to the role of barley as sustaining food source in the evolution of humans. Additionally, alcoholic beverages of various types and fermented foods prepared from barley are commonly referred to in the ancient literature. As other food crops (wheat, rice, corn and rye) became more abundant, barley was relegated to the status of “poor man’s bread”. In the United states, barley used as food is 1.5%, as animal feed 65% and in malt and alcohol production 30% (Newman and Newman, 2006). In 1991, barley used as food in European countries was even lower (0.3%) than the United States. In contrast, during the same time period food was the largest for barley in Morocco (61%), China (62%), India (73%), and Ethiopia (79%). However, current consumer interest in nutrition and human health may help restore barley’s status in the human diet. Nutritional qualities of barley have been known since ancient times. For example, Ajgaonkar 1972 described how ancient Indian physicians effectively stabilized type II diabetics some 2400 years ago. Treatment was remarkable simple and not really different from recommendations that are given to diabetic patients today, i.e., lose weight, change diet, and increase exercise.

Introduction

Improvement of wheat grain quality depends on the knowledge of quality requirements of different end-use products and the genetic components controlling different quality traits. In previous chapters we have dealt in-depth with quality requirements of different end-use products and their genetic components. Depending upon the goal of quality improvement, different strategies are adopted to improve wheat quality. It depends upon the number of genes controlling the traits as well as the availability of the simple methods for phenotyping the traits especially during early segregating generations. In addition stability analysis of the traits across the environments is essential before we go for breeding. Constraints in time, cost, and sample availability usually necessitate the use of predictive tests during early generations, followed by milling and baking tests on advanced lines that have met a number of agronomic, disease and predictive quality criteria. Knowledge of germplasm lines having specific quality traits is needed to initiate breeding for the improvement of wheat grain quality for different end-use products. The quality requirements of different major end-use products are provided in the following table (Table 1).

Introduction

Nutritional value of food stuff is defined by its ability to provide nutrients required by the body. Proteins, carbohydrates, fats, minerals and vitamins are main ingredients in food stuffs. Wheat is an important source of these nutrients. The distribution of nutrients within wheat kernel is typical of many cereals. Nutrients are generally found in the highest concentrations in the germ or embryo and in the aleurone cells surrounding the starchy endosperm followed by bran, whole wheat flour and white flour in decreasing order. Of special importance is that it contains the entire B complex, except for vitamin B12. B vitamins function as cofactors in many metabolic reactions involved in the release of energy. The germ, which includes the scutellum, is especially rich in vitamins B and E, high quality protein, unsaturated fats, minerals, and carbohydrates. The bran consists mostly of the insoluble carbohydrate cellulose, and contains incomplete protein, traces of B vitamins, and minerals including zinc and iron. The endosperm is the largest part of the grain, and consists mostly of the carbohydrate starch, incomplete protein, and trace amounts of vitamins and minerals. Significant variations in the content of grains occur because of variety, crop year, area, fertilizer, and soil type.

Introduction

Carbohydrates constitute nearly 80% of the total dry matter of wheat kernel. Starch is the predominant form, with cellulose, hemicellulose and pentosans present in lesser amount. Starch is present in discrete granules within the cells of the endosperm. Starch content is available in the range of 65% to 75% and generally related negatively to the protein content. Starch structure is a crucial determinant of many end-product uses of wheat. While the amylose /amylopectin ratio is a useful descriptor of starch structure, a more complete analysis of the population of the molecules which constitute a particular starch is considerably more revealing. The molecules range from the high degree of polymerization (10⁷ – 109 glucose units) and heavily branched amylopectin population, to the lower degree of polymerization (103 -106 glucose units), and infrequently branched amylopectin population. Starches with widely differing structures are suited to particular end uses. For example, starches with no amylose, the so called waxy starches are particularly suited to use as thickeners or gel forming agents because they form a clear stable gel with little retrogradation. In contrast, starch with high amylose content form hydrogen bonded insoluble aggregations which are suited to use in adhesives, plastics and as a source of dietary-fibre starch. The size and branching pattern of starch are also important determinants of the suitability of starches for particular end-uses due to the effects these parameters have on gelatinization temperature, starch swelling and viscosity.

Introduction

Bread wheat (Triticum aestivum L.) is one of the most widely cultivated and consumed crops in the world. Wheat is perhaps best known for its different end-use baking properties as determined by grain texture, protein content and quality. Wheat is generally traded by and classified into “hard” and “soft” market classes on the basis of grain hardness or texture of the wheat kernel (caryopsis). Soft wheats have softer endosperm texture that fractures easily, therefore requiring less energy to mill, yields smaller particles, and has less starch damage after milling when compared to hard wheats. Hard and soft are used with slightly different connotations in different parts of the world. In Western Europe, hard is applied primarily to durum wheats and the soft applied to bread wheat. Elsewhere the term is applied to different cultivars within the species Triticum aestivum. In general, hard wheats are used for bread baking, while soft wheats are used for cookies and cake making. Hard wheat requires more force to crack the kernel, maintains a larger particle size, passes through sieves more easily and has more damaged starch MacRitchie (1980). Higher starch damage is required for good bread making quality Tipples et al. (1994) but is detrimental to the biscuit making quality.

Introduction

Wheat is the most important cereal crop to the human kind. It is the main source of energy and nutrition in human diet. Wheat is consumed in the form of large number of end products as chapati, bread, biscuit, cakes, pretzels, noodles and pasta products. Millions of people are involved in milling, baking and pasta products industry with huge turnover per annum. However, each end-use product of wheat has it’s own specific requirement for example basically hard wheats along with strong gluten and high protein content are used for bead making. Soft wheat with weak gluten and low protein content are required for biscuit making Souza et al. (1994). Durum (tetraploid) wheat is used for pasta products as macaroni, vermicelli and spheghatti and Dicoccum for therapeautic purposes. Often chemical improvers are used to improve the dough properties for these products. Most of these chemicals have been banned because of their toxic effects. Therefore, only alternative is to develop varieties suited to meet the requirements of these end-use products. This needs better understanding of molecular basis of grain quality to accelerate breeding for producing wheat varieties for each end-use product separately. Storage proteins are the major component of grain which determines end-product quality. In this chapter detailed structure, genetics and functionality of gluten proteins are described.

Introduction

Dough is a complex mixture of flour constituents, water, salt and other ingredients depending upon the requirements of end-products. It is the principal intermediate stage in the transformation of wheat into different end-use products. Rheological properties of dough determine the behaviour of dough during mixing, rounding and molding used in making different products and also effect on the quality of finished product. Therefore, understanding the various features of dough rheology and their relations with product quality is important. The importance is enhanced further because of mechanization and automation of baking industry. Dough is composed of continuous phase in which gas cells are dispersed. The continuous phase is called “dough phase”. It consists of starch granules embedded in protein matrix along with some lipids, cell remnants and yeast cells in fermented dough. Gas production and retention is the most comprehensive quality requirements of the dough for bread making. The ability of the wheat dough to retain gas during fermentation and oven rise is unique. This depends on the ability of the dough to be stretched into thin membranes because of protein phase.

Introduction

Durum or macaroni wheat (T. turgidum var. durum) is an important crop used chiefly for the production of pasta in Western Europe and North America, and two layered bread, single layered bread, burghul, couscous, pasta, frek and feed in other parts of the world (Table 1). In North Africa and the Middle East, durum is also used for producing flat breads. On a global basis only a small amount of durum wheat is used for baking of pan-style and hearth-style bread. Also, durum wheat for baking is often used in blends with common wheat. In India, durum occupies approximately 2.0 mha area and production is estimated to be around 2.5-3.0 million tones annually amounting to 3-4% of the total wheat production. The consumption of pasta is increasing at the rate of around 5% annually and currently it is estimated to be around 10 Lakh tones. The demand for pasta products may increase further due to increasing population and improving standard of living.

Introduction

For many years it has been an elusive task to provide a precise definition as to what constitutes quality in wheat. Each country has its own traditions in bread and other bakery products. Quality will mean different things to a miller, a baker, a grain handler or a plant breeder. As the baking industry becomes increasingly specialized, specific qualities are sought. Even among those wheat varieties generally recognized as having desirable quality traits, the influence of environment can be substantial, and this necessitates a high level of skill on the part of grain buyers to survey the current year’s crop and blend the wheat for a specific end-use. This genotype X environment effect on quality also limits the capacity of end-users to source identity-preserved wheat from a narrow geographic area. Those of us engaged in the field of plant breeding are concerned primarily with those traits that can be manipulated genetically, and we study their stability under a range of climatic conditions. Constraints in time, cost, and sample availability usually necessitate the use of predictive tests during early generations, followed by milling and baking tests on advanced lines that have met a number of agronomic, disease and predictive quality criteria.

Introduction

There are large numbers of wheat based products such as fermented pan bread, flat breads including chapati, biscuits, noodles and pasta products. Each product has its own specific requirements. For example fermented pan bread needs wheat with higher protein content, stronger and extensible gluten. Chapati requires hard wheat with high protein content and medium gluten strength. Waxy wheats have been found associated with improved shelf life of breads. White salted Japanese noodles need partial waxy wheats with soft grain characteristics and medium protein content and gluten strength. Partial waxy wheats with comparatively lower amylose content and higher starch paste viscosity improve texture of white salted noodles. Yellow alkaline noodles need comparatively harder wheat with medium strong gluten and without waxy trait. Pasta made from durum wheats requires stronger gluten, high protein content and higher content of yellow pigments. In this chapter detailed account of both fermented and flat breads will be given.

Introduction

Wheat is an important cereal crop and is widely cultivated across the world. Wheat is consumed in different forms and major products are chapati, bread, biscuit, noodles and pasta products. Wheat has three groups of cultivated species namely bread, durum and dicoccum wheats. The common or bread wheats account for approximately 95% of world production. Nearly all of the remaining 5% cultivated varieties are durum wheats used for pasta products and couscous and dicoccums represent very little of the total wheat production. The bread wheat is divided into two broad classes based on grain texture; hard and soft. Hard wheats with high protein content and strong gluten are used for making bread and some noodles while soft wheats with lower protein content and weak gluten for biscuit, cakes and pretzels. Semi-hard wheats having some combinations of the above characteristics are utilized for making unleavened breads such as chapati, Asian steamed bread and some noodles. There can be large disparity within wheats of various classes; therefore to provide consistent quality, it is divided into grades. The grading is determined by the test weight, protein content, moisture and foreign material. The major wheat exporting countries have distinct grading patterns designed to provide wheat for specific purposes and consistent quality.