eChapters

Abstract

Design, operation and optimization of dryers demands the calculation of energy consumption, in most cases in the form of thermal energy, equipment sizing, temperature and moisture distribution of solids as well as temperature and humidity distribution of drying air. Energy calculations are very important as drying is a widespread process in a variety of industries and is highly energy demanding. In the energy analysis of the process the first step is the estimation of the minimum energy requirement followed by the estimation of energy rejection through solids stream and especially through drying air. Increase of thermal efficiency is always willing and the two most common ways for its achievement is the application of heat exchange between cold feeding air and relatively hot rejecting drying air and hot air recirculation. The later is also employed for the adjustment of air temperature and humidity gradient through the dryer. The combination of a heat pump with the dryer decreases considerably the thermal energy consumption but demands electricity and the method can be beneficial in cases of excess electricity production in the process plant, e.g. by cogeneration. Utilization of exhaust hot air from the main drying unit for the predrying of wet solids can also decrease the total energy requirement. The application of humidity adsorption from the feed air increases its drying potential, but regeneration of adsorbent is required. Grand composite curve of the process plant can reveal potential heat sources from different unit operations.

Abstract

The increasing interest in polyphenolic compounds in industries has led to the exploration and exploitation of rich bio-compounds from natural sources, essentially plants and their by-products. Solid-liquid extraction is mostly applied for the recovery of these valuable compounds from plants. Since the extraction process is often difficult in a fresh matrix, a drying operation is needed to reduce the moisture content, and preserve the targeted valuable compounds. An uncontrolled drying operation will lead to product damage and hence, loss in quality, reason why, several studies have been carried out to understand and control the drying process. The present chapter aims to present some data on drying for bioactive compound recovery from plants and their by-products, mainly polyphenolic compounds. Our main interest is the mathematical tools used to model the drying process.

1.1. Introduction

The significance of milk as the most wholesome single food available in nature has never been debated. It is as ancient as mankind itself, as it is the substance created to feed the mammalian infant. All species of mammals, from the lowly rat to the mighty whale, produce milk for this purpose. Several centuries ago, perhaps as early as 6000-8000 BC, ancient man learned to domesticate species of animals for obtaining their milk for consumption. These included cows, buffalos, sheep, goats and camels, all of which are still used in various parts of the world for the production of milk for human use (Fig. 1.1 & 1.2).

Milk is the secretion of the mammary glands of animals. For human consumption, milk is that liquid obtained from the cow or the buffalo during the period following at least 72 hours after calving or until the milk is colostrums-free. It is a complex biological fluid consisting of seven main components: water, fat, protein, sugar (lactose), minerals, vitamins and enzymes. Milk is a white opaque fluid in which fat is present as an emulsion, protein and some mineral matters in colloidal suspension and lactose together with some minerals and soluble proteins in true solution. The opacity of milk is due to its content of suspended particles of fat, proteins and certain minerals. The colour varies from white to yellow depending on the carotene content of the fat. Skimmed milk is more transparent with a slightly bluish tinge. Milk of a good flavour has a pleasant, slightly sweet taste, and no odour. It is an excellent source of calcium, phosphorous and riboflavin. Vitamin A and D are currently added to whole milk, partly skimmed and skimmed milk.

Milk production in India is a subsidiary activity of agriculture in contrast to the organized dairy sector in the western countries. Farmers and landless labour maintain one to five milch animals. As a result, small quantities of milk are produced in a scattered manner. Due to this reason, milk procurement models from western countries, such as bulk cooling and bulk transportation are not applicable under Indian conditions. Collection of small amounts of milk is scattered over long distances and, therefore, poses a formidable challenge in maintaining the quality attributes and keeping costs down.

3.1. Rural Milk Collection

A systematic approach to rural milk collection suitable for the tropical climate and techno-economic conditions prevailing in India has been developed, based on the indigenous experience gained over the past few decades. In the first phase, extensive surveys are undertaken in the milkshed areas, where the milk plant is to be established. The second phase involves ‘route planning’ taking into account, availability of quantities of milk, access to roads for plying vehicles and distance from the site of dairy plant. Then zones are identified, representing equal costs of collection and transportation. In the third phase, planning is done for locating the primary collection centres as well as chilling centres, where, milk can be cooled to 4ºC before transporting to the milk plant. Milk may be collected from individual producers either by the contractor or by forming village level cooperative societies.

Milk, on reception at the dairy factory is subjected to various unit operations on its way to product manufacture. Processing is applied as a means to convert liquid milk into products or to render the milk (and products) safe from harmful organisms. The basic processing operations to which milk is subjected at processing units have been described in this chapter. The common processing operations employed are depicted in Fig. 4.1. Several of these operations are routine compulsory processes common to all dairies, while certain others are undertaken for specialized purposes in some dairies.

4.1. Filtration and Clarification

At the time of milking various foreign materials such as dirt, feed, manure, dandruff, hair, flies, dust particles, worn out cells, cell debris and many other undesirable substances may find their way into milk. The process of removal of this extraneous matter (solid particles of higher density than that of milk) is called filtration or clarification. This can be achieved either by simple filtration through specially woven filter cloth or continuous process of centrifugal clarification that helps

Milk, as secreted in the udder of a healthy animal is practically sterile, but during its transit to the processing plant, becomes heavily contaminated with a variety of micro-organisms. These may be responsible for spoilage of milk or for causing diseases in animals and human beings. It thus becomes imperative that adequate heat treatment is given to milk to destroy these micro-organisms, thus increasing the shelf-life of milk as well as making it safe. Varied heat treatments offer the potential of producing different kinds of processed milk to satisfy the needs of the consumer. To cater to the ever-increasing demand of consumers, several varieties of processed milk are available in the market, some of which are discussed below.

5.1. Pasteurised Milk

Pasteurisation was named after the renowned French scientist Louis Pasteur, who discovered that spoilage organisms could be inactivated in wine by applying heat at temperatures below its boiling point. The process was later applied to milk and remains the most important operation in the processing of milk.

It is the process by which every particle of milk is heated to such temperature-time combinations (usually to 63°C for not less than 30 minutes or to 72°C for not less than 15 seconds) and promptly cooled to 4°C or below so as to destroy any harmful bacteria that may be present without affecting flavour and food value. Pasteurisation does not involve the use of any additives. Apart from making milk safe to drink, pasteurisation increases the length of time it can be kept before it spoils. The nutrient losses due to pasteurisation are so small, that they are considered insignificant.

Packaging is a tool that is used to contain the product, protect the product from environmental hazards and help in marketing the product. Examples of ideal natural packaging systems are that of a banana, orange, coconut and egg, where the packaging is provided by nature. The major step forward in the food processing arena has been the ability to protect and preserve products with packaging and hence ensuring the availability of fresh and processed products out of season and over long distances in various forms. Milk is a highly perishable product and is not uniformly available round the year to the whole country due to geographical and genetic variations. If dairy products are to be available all the year round the country, irrespective of the season and area, it must be presented in packages that are convenient to purchase and use.

Packaging has additional responsibilities of providing convenience, safety and facilitating, besides handling, storage and distribution of products. It should prevent spoilage of food by microbial or insect attack. It also preserves the quality and nutritive value of many foods by the exclusion of oxygen and the control of moisture loss or gain. It increases the shelf-life and ensures longer availability and contributes to the product image through structural and graphic design. Product information is also given out through the medium of labeling, which acts as a tool for marketing and advertising.

Cleaning and sanitisation are the two processes employed in dairy industry to ensure hygiene and product safety. The safety of milk and milk products is a very important aspect and every attempt should be made, during processing, to minimize contamination through handling and processing equipments. The accumulated dried milk solids (milk stones) consist largely of calcium phosphate, milk proteins (precipitated, coagulated and baked on by heat) and insoluble calcium salts from water and washing detergents. The surface can also contain biofilms, which are formed by the incorporation of bacteria into the accumulated inorganic and organic materials that attach to most surfaces. With time and in the presence of nutrients, a biofilm and the bacteria within the biofilm will grow and become strongly attached to the surface. The removal of dairy soil, milk stones as well biofilms is the prime objective of the cleaning process. International Dairy Federation (IDF) defines a clean surface as one which is free from residual film or soil that will not contaminate the food products coming in contact with it.

While cleaning refers to the removal of soil from the surface of the equipment, sanitisation implies destruction of all pathogenic and almost all non-pathogenic organisms. Cleaning and sanitisation are complimentary processes. Either of the processes alone will not achieve the desired result, which is to leave the surface as free as possible from soil and viable organisms. In actual practice cleaning and sanitisation overlap to some extent, as during cleaning a high proportion of bacteria are destroyed and others get removed in the detergent solution. Inadequate or faulty cleaning and sanitisation can have serious consequences, as milk is a prefect nutrient in which bacteria can multiply. A thorough understanding of the cleaning methods is, therefore, necessary for economic production of high quality food products.

India has achieved a commendable position of being the highest milk producing country in the world. Nearly 110 million tons of milk per annum is contributed by small and marginal farmers having 2-3 milch animals which are scattered in lakhs of villages across the length and breath of India. The poor socio-economic conditions are serious constraints in producing raw milk of good quality. The quality of milk is further deteriorated during subsequent handling and transportation. Milk being a product of biological origin, is extremely vulnerable to attack by microbes. It is also a good vehicle for additives and adulterants without any apparent changes in its appearance. Thus, milk is susceptible to several post-secretion changes, some natural and some man-made.

Indian dairy industry faces a mammoth task to meet the world quality standards, particularly in the present context of globalization and increasing quality conscious consumers. In view of the highly perishable nature of milk soon after it is secreted, it is important to monitor its quality by having a firmly installed quality assurance programme along the entire production-to-supply chain. This can be possible with application of sensitive, accurate and rapid methodologies as a tool in quality assurance programmes.

Quality comprises of several attributes ranging from physical, chemical, technological and bacteriological through nutritional to aesthetic. All dairy plants have a quality assurance laboratory (Fig. 8.1) and usually follow chemical quality control with the intention of payments to contractors/producers, processing of milk and meeting mandatory requirements for end products. Quality is judged both by objective and subjective tests.

The dairy processing industry in India deals mainly with the fluid milk and/or short shelf life products, despite India being the largest producer of milk in the world, with an output bordering the 110 million ton mark. This feature offers immense potential in the area of R&D in dairy processing in terms of value addition. The potential gains are many, including higher returns for producers and advantages in terms of health, therapeutic, nutritional and/or gastronomy for the consumers. However, the Indian Dairy Industry can amass possible benefits by being a global contender in trade only when its products are at par with those available in the rest of the world in terms of price and quality. It is evident from the post-WTO scenario that for sustainability, Indian dairy industry will need to maintain wholehearted commitment to quality management right from the farm to the consumer, shedding its inhibitions and resistance to changes.

9.1. WTO Agreements and Food Industry

The General Agreement on Tariffs and Trade (GATT) was formed in 1947 and lasted until 1994, when it was replaced by the World Trade Organization (WTO) in 1995. The WTO is the only global international organization dealing with the rules of trade between nations. It provides a forum for negotiating agreements aimed at reducing obstacles to international trade and ensuring fair deal for all, thus contributing to economic growth and development. Currently, there are 16 agreements to which all WTO members are parties and two agreements to which only some WTO members are parties. WTO currently has 153 members, of which 117 are developing countries or separate customs territories. The Head Quarters of WTO is at Geneva (Switzerland) and the official languages are English, French and Spanish.

India is a second largest producer of fruits and vegetables after China. These share are 10% and 16% respectively in total world production. Horticulture crops occupy 23.548 million ha and production is estimated around 260.063 million tones. Total area of fruits, vegetable, plantation crops, spices, loose flower and aromatic plant are 7012, 9083, 3606, 3092, 218 and 537 thousand ha, respectively and production are 79400, 156445, 16388, 5786, 1421 and 622 thousand tones, respectively with productivity are11.32, 17.22, 4.54, 1.87, 6.59, 1.19 thousand tones per ha, respectively (2012-2013). The total productions of cut flowers are 74305 Lakh stem (2012-2013). The annual horticulture export volume is 2733145 metric tonnes (2010-2011) with total exported value of Rs 696461 lakh. In terms of volume, fresh fruits & vegetables comprised about 76 % of exported horticulture produce followed by processed fruits & vegetables (23 %) and floriculture & seeds (1%). After that losses found 20-30 % in fruit and 30-40 % in vegetable while harvesting to consumption in India. It’s due to the perishable nature of horticulture commodity, non availability of appropriate post harvest infrastructure transportation, inadequacy of the market or lack of processing.

India is a major horticulture producer, even though processing is less than 2 %. This is very low as compare to 80 % of Malaysia, 78 % of Philippine, 70 % of Brazil and 30 % of Thailand. The most of developed country 40-60 % fruits and vegetables utilize in processing.

Proper handling, packaging, transportation and storage reduce the post harvest losses of fruits and vegetables. For every one percent reduction in loss will save 5 million tons of fruit and vegetable per year. Processing and preservation technology helps to save excess fruit and vegetable during the glut season. The technology has become a necessity to improve the food safety and strengthen nations food security. The technology helps to boost export of agricultural commodities in the form of preserved and value added products.

Fruits and vegetables are important part of our dietary, which are rich source of nutrient (carbohydrates, protein, fat, vitamins, minerals, and dietary fiber). Carbohydrates, protein and fat are macronutrients, considered as energy sources. Vitamins and minerals are micro nutrient, play important role in body building. Fibers have several direct and indirect advantages. ICMR, New Delhi recommends 125g of leafy vegetables, 100g of root and tuber vegetables and 75g of other vegetables (total 300g/day) and 85g of fruits per capita every day for balance diet.

Maturity

It is derived from Latin word ‘Maturus’ which means ripen. It is that stage of fruit development, which ensures attainment of maximum edible quality at the completion of ripening process.

Maturation

It is the developmental process by which the fruit attains maturity. It is the transient phase of development from near completion of physical growth to attainment of physiological maturity. There are different stages of maturation e.g. immature, mature, optimally mature, over mature.

Maturity Indices

The factors for determining the harvesting of horticulture commodities according to consumer purpose and type of commodity.

Maturity Indices is two type

Fruits and vegetables are living tissues subject to continuous change after harvest. Some changes are desirable from consumer point of view but most are not. Post-harvest changes in fresh fruit cannot be stopped, but these can be slowed down within certain limits to enhance the shelf life of fruits. The post-harvest handling plays an important role in extending the storage and marketable life of horticultural perishables.

Post Harvest Treat ment of Fruits and Vegetables Washing

It is useful in removing surface adhering material water. Mechanically, it is also accomplished by passing the fruits/vegetables through machine arranged with water tank equipped with rotating brush. In some produce washing improves appeal by facilitating removal of sap as case in mango, papaya, jackfruit, kronda, dirt in case of carrot, reddish, turnip, sugar beet, sweet potato, etc. and for removal of debris in case of banana. The water use for the purpose should be cleaned otherwise fungal and bacterial levels may build up. Disinfected treatment using ultraviolet light, ozone, chlorine (100 ppm), calcium hydroxide, etc. help to clean water for washing purpose.

Flowers are highly perishable unlike other horticultural or agricultural crops. Owing to poor keeping quality the post harvest losses in floriculture are significantly higher than any other sector. Although there has been significant increase in the area, production and productivity of flower crops in the last two decades, there is an urgent need to minimize the huge post harvest losses in terms of the value of the produce which are estimated to be 30-40 per cent of farm value. The post harvest behavior of flowers is an outcome of the physiological processes, occurring in leave, stem, flower bud, leafless peduncle or scape connecting bud to the stem. Some of these processes may act independently to affect the senescence and vase life of cut flowers but most of them are inter-related. The nature and extent of post harvest damage is typical for each crop or cultivar. The post harvest losses become important especially when dealing with the export of fresh flowers to distant and foreign market. Therefore, patient, soft and expert handling of flowers is of utmost importance after harvest.

Ripe

This word is derived from Saxon word ‘Ripi’, which means gather or reap. This is the condition of maximum edible quality attained by the fruit following harvest. Only fruit which becomes mature before harvest can become ripe.

Ripening

Ripening involves a series of changes occurring during early stages of senescence of fruits in which structure and composition of unripe fruit is so altered that it becomes acceptable to eat. Ripening is a complex physiological process resulting in softening, colouring, sweetening and increases in aroma compounds so that ripening fruits are ready to eat or process. The associated physiological or biochemical changes are increased rate of respiration and ethylene production, loss of chlorophyll and continued expansion of cells and conversion of complex metabolities into simple molecules.

Ethylene (C₂H₄ also known as ethene) is a gaseous organic compound that is the simplest of the alkenes chemical structures (alkenes contain a carbon-carbon double bond). The hormone effects of ethylene on general plant growth were first noted in 1864 when leakage from gas street lighting systems caused stunting and deformation of nearby plants. In 1901 Neljubow identified the active component of the gas to be ethylene but it was not until 1934 that Gane identified that plants could synthesize ethylene and in 1935 Crocker proposed ethylene to be the hormone responsible for fruit ripening and senescence of vegetative tissues.

Ethylene play important role in many plant during development processes, including seed germination, vegetative growth, leaf abscission, flowering, senescence and fruit ripening. Ethylene also plays a role in response to water stress, chilling and mechanical injury.

Proper marketing of perishable commodities such as fruit and vegetables often requires some storage to balance day-to-day fluctuation between harvest and sale or for long term storage. Storage of horticulture produce is attempeted with a view to extend period of availability. Storage controls shelf life of produce by controlling rate of respiration, transpiration, ripening and biochemical changes all of which are responsible for shelf decomposition/deterioration of produce. Further, different types of storage have different attributes in minimizing microbial infection and thus add to better storability of produce.

Packaging is an important consideration in vegetable and fruit market. The use of properly designed containers for transporting and marketing of vegetables is significantly reduce losses and maintain their freshness succulence and quality for longer period. Packaging also provides protection from mechanical damage and undesirable physiological changes and pathological deterioration during storage, transportation and marketing.

Many vegetables are transported in gunny bags and bamboo baskets. Packaging material such as polythene films, paper boars, and boxes lived with polythene and other materials can effectively prolong the shelf life of vegetables. By using plastic films vegetables can be protected from dry air. Polythene packaging provides modified atmosphere and consequently reduces decay, softening, and loss of solids. The thickness and permeability to CO₂, O₂ and water vapour of films needs to be standardized for each vegetable.