eChapters

6.1 INTRODUCTION

Water in soils is essential to plant growth, being the medium through which inorganic nutrients are translocated to the root surface and carried through the plant. Most of the water in soils at or near field saturation can be considered as equivalent to bulk water, and only bulk properties need be considered in discussing its movement through soil interstices and its retention in soil capillaries; this is the field with which soil physics deals. But, in the first molecular layer in contact with soil particles, and perhaps for several molecular layers beyond, the behaviour of water molecules is very different from that in the bulk. Strong adsorptive forces can reduce the volatility of these molecules and restrict their mobility. Such an adsorbed layer of water competes with other polar molecules for adsorption sites, and so has an important role in determining the release and retention of fertilizers and pesticides. Such strongly adsorbed layers confer wettability on soils, but hydrophobic surfaces can also be present and these lead to non-wettable soils with serious consequences in run off and inefficient use of precipitation. This region of distinctive molecular interactions between water and soil particles falls within the field of soil chemistry.

5.1 INTRODUCTION: THE PHYSICAL CHEMISTRY OF COLLOIDAL SUSPENSIONS

This chapter is concerned with understanding the factors which influence the partition of ions between solid surfaces and aqueous solutions. There are many aspects of soil science such as some of those concerned with soil formation, transfer of nutrient ions from soil particles to plant roots, soil pollutant interaction and soil management which are critically dependent on what happens in the space of the order of 1 nm wide between solid and equilibrium solution. A broad survey of the development of ideas on soil-electrolyte interaction shows that there have been two main avenues of approach. One views the soil as an electrically charged surface with its adsorbed hydrated ions as one phase in equilibrium with solution, which is seen as the second phase. The other approach focuses on the electrical double layer extending from the charged solid surface out into the solution. In the latter approach the solid surface, the outer equilibrium solution and the make up of the transition zone between these two phases must all be involved in any detailed consideration of the micro structure of the system. For a full and proper understanding of soil-electrolyte interaction anything less than a detailed analysis of the micro-structure is likely to be inadequate and in this it must be remembered that the interaction between electrical double layers which overlap with one another is likely to be important.

4.1 INTRODUCTION

It has been suggested that the relationship of surface chemistry to soil science is similar to that of biochemistry to biology. Certainly the fact that surfaces of soil particles are extensive and reactive leads to a dominance of surface chemistry in soil behaviour, but it is not an exclusive relationship, because many precipitation reactions, oxidation and reduction processes, and biological reactions take place more or less independently of the surface processes. Nevertheless it is difficult to understand soil properties fully without an appreciation of the nature and extent of the surfaces of the soil constituents, and this chapter is devoted to a discussion of this topic.

3.1 INTRODUCTION

The complete soil organic fraction is made up of live organisms, and their undecomposed, partly decomposed and completely transformed remains. Soil organic matter is the term used to refer more specifically to the non-living components which are a heterogeneous mixture composed largely of products resulting from microbial and chemical transformations of organic debris. These transformations, known collectively as the humification process, give rise to humus, a mixture of substances which have a degree of resistance to further microbial attack.

2.1 INTRODUCTION

Textural assessment has long been used to indicate quality in agricultural soil and although it contains an element of subjective judgement, a skilled surveyor can differentiate many grades of texture. Soil texture correlates with the distribution of particle size in the soil, though this is not the only component in texture. Although particle size distribution is an objective attribute of soils and can, in principle, be measured with accuracy, the determination is in practice quite difficult and certainly laborious, so that it is customary in soil mechanical analysis to divide the soil into several broad fractions: sand, silt and clay are the principal categories. The clay fraction, which comprises the smallest particles in the soil, is generally defined as the fraction smaller than a nominal diameter of 2 jam. The practical division is, however, based on the velocity of fall of soil particles through a fluid, calculating the diameter of the particles from the equation of Stokes

1.1 THE IMPORTANCE OF SOILS

Soils are the medium in which crops grow, and so they are essential to the provision of the food and fibre to sustain mankind. But besides the immense importance of this role they are an essential component to life as we know it because of their action as a buffer to control the flow of water between sky, land and sea. They are also a sink, and usually a safe sink, for many of the chemicals that might otherwise make life difficult or unpleasant.

As with other natural resources, it is important that soils are used conservatively, so that the advantages we enjoy from them now can continue to be enjoyed in the future. To do this we need to understand them, to understand the flow of nutrients from soil to plants, and back to the soil or the sea in food chains and water flow. We need to understand the processes by which rocks alter to form soils, and how fast or how slowly the process occurs in different conditions. We need to understand the decay of plant materials in the soil, and how the products of decay help to make the soil a better place for plants to grow.

The chemistry of the constituents of soils, and of the processes by which changes occur, is not simple. Nevertheless we have learnt much about it, and can apply that knowledge to ensure that soils continue their important functions, and are not exploited so that they become infertile, nor used in such a way that the fertile topsoil is lost by erosion by wind or water.

Several fruits and vegetables are unexploited for proper utilization and product development. Due to lack of utilization, there is a lot of wastage and ultimately the great loss to the people as well as nation. Some unexploited fruits and vegetables have potential for introducing new products. Therefore unexploited fruits and vegetables have to be exploited for new product development especially from underutilized sub-tropical and tropical fruits and vegetables. Research and development should be undertaken to utilize these fruits and vegetables.

Unexploited Fruits

Unripe Green Mango: Although pickles are prepared but droped green mango fruits are not preferred for pickle preparation. They can be dried and utilized for preparation of dried slices or amchur. Amchur is used to develop flavor and taste in Ice cream. These products are used to develop flavor and taste in meal or food. It is also used to prepare chatney. But utilization of Amchur is not known to common people.

Avocado: It is found in tropical and sub-tropical climatic regions having more humidity and rainfall. In Ethiopia it is found throughout the country but not utilized properly by people. They prefer to eat ripe fruits with salt and lime juice. It is very healthy fruit for chronic disease like cardiac and diabeted diseases. This is seasonal use but no product is available for off season. Therefore researches should be carried out for different products development of Avocado products.

Packaging

Packaging is a mean or system by which a fresh or processed product will reach from the production center to consumer in safe and sound condition at an affordable price.

Objectives of packaging and packaging materials

The primary objective or packaging is to protect the contents during storage, transportation and distribution against deterioration. It may be physical, chemical or biological. However, followings are objectives of packaging and packaging materials.

Several products of fruits and vegetables are prepared on commercial and home scale. Products development from fruits and vegetables is the best way to utilize excess produces and save them from post harvest losses..

Value Addition

This is the process of improving the value of a commodity through processing by changing its form, increasing its shelf life or better presentation like packaging. Value addition can be done through the ways.

Process of preservation of food stuffs such as fruits and vegetables whole or in pieces in sugar syrup or brine by heating them in hermetically sealed containers for long storage is known as canning. In other words canning is the process of sealing food stuffs hermetically in containers and sterilizing them by heat for long storage.

Preservation of food (fruits and vegetables) in common salt sand vinegar is called pickling. It is one of the most ancient method of preservation of fruits and vegetables. Pickling is the result of fermentation by Lactic acid forming bacteria which are found in large number on the surface of fruits and vegetables. They can grow in acidic medium and in the presence of 8-10 percent salt solution. The growth of majority of undesirable bacteria is inhibited. Lactic acid most active at 30 °C temperature. This temperature should be maintained during the process of pickling.

Preparation of pickles

Pickles are prepared with salt, vinegar and oil or combination of these ingredients. Spices are also used for pickle preparation.

Fermentation

The decomposition of carbohydrates by microorganisms and enzymes is known as fermentation. During fermentation process of food organic acids and alcohol etc are produced which act as preservatives and also provide fine flavor and aroma that increase the value of raw materials. Most fermented foods contain a complex mixture of carbohydrates, proteins and fats etc. Fermentation occurs when microorganisms consume susceptible organic substances as a part of their own metabolic processes. Natural fermentation is probably oldest form of food preservation.

Sugar also acts as preservative at high concentration 70% or more in food products (fruit and vegetable products). High concentration of sugar in food materials create unfavourable conditions for microbial survival and prevent spoilage. Based on this principle of preservation, sugar based products are prepared from fruits and vegetables so that they can be preserved for long time. This method of preservation with high sugar concentration is principally based on the reduction in moisture content to arrest or stop microbial spoilage. Preparation of sugar based products is one of the most important aspects of home scale as well as industrial level processing of fruits and vegetables. Sugar based value added products include.

In the previous chapter the physical methods of fruit and vegetables processing and preservation have been discussed. The present chapter deals with chemical method of fruit and vegetable preservation. In this method of preservation of fruits and vegetables, chemicals as preservatives are used to prevent the spoilage of fruit and vegetable products. These preservatives react with food (produce) constituents or microorganisms and create unfavourable conditions which hinder growth, activities and multiplication of microbes responsible for spoilage of food products. These chemical agents have maximum permissible limit of their use as law. They can be classified into two classes class I and class II.

Class I: Sugar, Salt and Oils

Class II: Sodium benzoate, Potassium metabisulphite (K M S) and Sorbic acid

In the physical methods of preservation, fruits and vegetables are preserved by (i) adding heat, (ii) removing moisture content of produce to prevent spoilage and (iii) irradiated by Gama rays which kill the microorganisms responsible for spoilage of foods. These methods are described below.

Processing and Preservation by Adding Heat or Heating

In this method, heat treatment is given to destroy the microorganisms which are responsible for spoilage of the produce. Heat treatment is given by many methods.

The basic processing and preservation techniques such as canning, freezing, dehydration, salting, pickling and freeze drying are designed to change perishable foods into more usable form and prevent undesirable changes caused by microorganisms, or by chemical, physical and biochemical reactions in the food itself. Hence an ideal processing technology would involve prevention of growth of microorganisms and at the same time retention of f lavor, texture, nutritive value and palatability of the products.

Processing and Preservation

Processing and preservation is the best way of utilizing surplus production of fruits during seasonal gluts.

The fruits and vegetables are highly perishable in nature. The losses in harvested fruits and vegetables start immediately after harvesting and the resulting spoilage caused by biochemical changes (enzymatic) and activity of microorganisms such as bacteria, moulds and yeast. The losses caused by the microorganism in fruits and vegetables products can be prevented by controlling or destroying these organisms in order to preserve fruits and vegetables by processing and preservation means. The processing and preservation is one of the most important activities among various types of activities of Horticultural Science.

Processing: The processing can be defined as an activity, which is performed to maintain or improve the quality or to change the form or characteristics of the product. Processing operations are undertaken to add value to horticultural produce after their production. The main purpose of processing is to minimize the qualitative and quantitative deterioration of produce after harvest.

Preservation: Preservation can be defined as the science which deals with the methods of prevention of decay or spoilage of produce and allow it to be stored in a fit condition for future use.

Fruits and vegetables can be preserved for short and long term. For short term preservation can be achieved by proper handling of produce and low temperature storage. Long term preservation can be achieved by canning, drying and dehydration, fermentation and by using chemical preservatives.

After harvesting the quality of fruits and vegetables begins to diminish and products is edible for only a limited time then products begin to spoil or rot. Losses occur during harvesting and handling of fruits and vegetables can be minimized by proper techniques but processed food spoilage is bit difficult to control and stop after infection and contamination of microorganism.

Spoilage

Spoilage is deteriorative process which results reduction in quality of food (fruits and vegetables) which become inedible. The changes in food that cause it to lose its desired quality and eventually become inedible is called food spoilage or rotting. After harvesting, the quality of fruits and vegetables begins to diminish and product is edible for only a limited time. The deterioration and spoilage of fruits and vegetables may occur at different ways.

The losses in harvested products begin immediately after detachment of products from their parental plants. After some time, theses products begin to spoil or rot. Spoilage can be defined as the deteriorative process which renders the food inedible or results in reduction in quality. Spoilage of fresh fruits and vegetables usually occurs during storage, transportation and during processing. They also get contaminated with spoilage organisms either from each other or from the containers. Mechanical injuries during harvesting and transportation further aggravates the deterioration process.

Processed fruit and vegetable are considered as staple food products throughout the world, and are becoming more popular with the increase of the global urban population. As a result, demand for processed fruit and vegetable products tends to increase with population growth in the world. There is strong demand for processed fruits and vegetables in the developing world over the past few years. In poor countries, people consume less fruits and vegetables due to the relatively high prices. All forms of preserved fruits and vegetables are available only to the urban elite people. But rural mosses producing more than 90 % of these fruits and vegetables are usually deprived of their uses.

Demand of Processed Fruits and Vegetables

Demand of processed fruits and vegetables is increasing in the developing as well as under developing countries of world. The following reasons are responsible for day by day increasing demand of processed fruits and vegetables.

Fruits and Vegetables are highly perishable in nature due to which huge spoilage (damage) takes place during the period between harvesting and consumption. Fruits and Vegetables after harvesting are often poorly handled and in many cases neither cleaned nor washed. Improper handling may cause physical damage due to tissue breakdown which results mechanical damages and physiological changes in harvested fruits and vegetables. Mechanical losses include bruising, cracking, cuts, microbial spoilage by fungi and bacteria and physiological losses include changes in respiration, transpiration, pigments, organic acids and flavour.