Chapter One

Introduction

1.1          Introduction

Fruits and vegetables are important sources of essential dietary nutrients such as vitamins, minerals and fibre. Since the moisture content of fresh fruits and vegetables is more than 80%, they are classified as highly perishable commodities (Orsat et al. 2006). Keeping the product fresh is the best way to maintain its nutritional value, but most storage techniques require low temperatures, which are difficult to maintain throughout the distribution chain. On the other hand, drying is a suitable alternative for post harvest management especially in countries like India where exist poorly established low temperature distribution and handling facilities. It is noted that over 20% of the world perishable crops are dried to increase shelf-life and promote food security (Grabowski et al. 2003). Fruits, vegetables and their products are dried to enhance storage stability, minimise packaging requirements and reduce transport weight. Nonetheless, in India hardly any portion of perishables are dried which leads to enormous loss in terms of money and labour besides steep rise in prices of commodities during the off season.

The dry berries are worthy products since it contains all the vitamins spectrum, for that reason, drying process for the food is producing valuable output. Drying process for the food is not interest in vitamins amount only, it’s about the maintenance level for minor, and macro substances (Ceylan, 2007). Drying process has several advantages like producing low weight product, not expensive from packing side, long life storing, and no need for cooling application during storing or transportation (Chen X. D., 2007).

Vacuum drying technology is considered as the most applicable way. Negative pressure is applying while using vacuum drying. Vacuum drying is allowing to be operated with less expensive conditions, like reducing the input power. This drying process is applied in many kind of manufacturing process, like cream, yoghourt, fruit milk, and curd cakes production. This technology had overcome the usual way for drying by using hot-air (Sunjka, Microwave- convective and microwave-vacuum drying of cranberries: A comparative study, 2004). In another term, sometimes, vacuum dryer has been called as Microwave vacuum drying system.

1.2          VACUUM DRYER

This drying equipment is consisting from 70 L volume of a steel cylindrical chamber. The inside pressure is 2 mbar, which is provided by the vacuum pump. Inside the dryer, there is aluminium try, which is connected to a balance (Zdravko M and Tepi, 2015). Microwave drying is preferred in many fields since it has inherent advantages. Several industries had reported that using vacuum dryer in food manufacturing is applicable but its high cost (Giri, 2007; Clary, 2007). Sometimes, it’s better to use hot-air, in order to remove all the water, before the drying process implementation (Andres, 2004). Drying process is removing all the interior water of the fruit. Sunjka (2004) had found that using air system with the microwave is increasing the quality and the drying rates (Sunjka, Microwave-convective and microwave- vacuum drying of cranberries: A comparative study, 2004).

Vacuum drying has disadvantage, which is known as field inhomogeneity. This problem is occurring as some regions in the dryer are overheated, so that it is producing hotpot (Vadivambal, 2007). The hardest step in drying process is maintaining the dryer power, as well as temperature to gain product with the required properties (Lombra, 2010). There are four parameters, which are considered as major basics for proceed the drying process which are known as nutritional quality, microbial, chemical, and physical.

1.3          Statement of Problem

The preservation of fruits and vegetables through drying dates back many centuries and is based on sun and solar drying techniques. The poor quality and product contamination lead to the development of alternate drying technologies (Bezyma and Kutovoy 2005). The most applicable method of drying includes freeze, vacuum, osmotic, cabinet or tray, fluidized bed, spouted bed, Ohmic, micro wave and combination thereof (George et al. 2004). Except for freeze drying, applying heat during drying through conduction, convection and radiation are the basic techniques used to force water to vaporizes, while forced air is applied to encourage the removal of vapour.

 A large number of food and biomaterials are dehydrated in a variety of units with diverse processing conditions. The choice of drying method depends on various factors such as the type of product, availability of dryer, cost of dehydration and fi nal quality of desiccated product. Energy consumption and quality of dried products are other critical parameters in the selection of a drying process. To reduce the use of fossil fuel, electrical energy is an alternate source of energy for drying applications especially where electricity is generated by a renewable energy source such as hydro power or wind power (Raghavan and Orsat 1998, Raghavan et al. 2005). Keeping these in view, the present review is focussing on recent developments in drying and dehydration and future scope for better drying.

1.4          OBJECTIVE

There are different kind of berries, such as strawberry, black currant, raspberry, and cranberry. The objective of this project is to simulate the drying process for berry fruits by using vacuum dryer.

1.5          SCOPE

The scope of this project is employing vacuum dryer to dry berry fruits during sufficient time for complete drying process. This drying process had conducted by using simulation software which is knowing as COMSOL. In this software, several parameters were manipulated which are similar to the aimed raw material (Berry).

1.6          PROJECT ORGANIZATION

In chapter One, full introduction and explaining about vacuum dryer with the used raw material. Also, brief expression about the main objective and the scope.

In chapter Two, literature review about the previous researchers who had use vacuum dryer for drying fruits and precisely berries.

A whole explanation regarding COMSOL methodology for simulating vacuum drying process for the berries in chapter Three. In addition, all the used properties and parameters such as temperature are mentioned in details in chapter Three.

After finishing the simulation process by COMSOL software, a whole result where had gained such as drying time. The results were showed as tables and graphs for easy understanding. In addition, chapter Four is including full discussion regarding the drying process and the simulation process before and after the converge.

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