PHYSICOCHEMICAL AND COLOUR PROPERTIES CHANGES IN FRUITS AND VEGETABLES DURING DRYING PROCESS: A REVIEW

The shelf life of eatable needs to be high so it can be consumable after a long period of time. Various methods for increasing the shelf life of food include drying method which primary reduce the moisture contain in food and restrict the growth of fungi and decrease it decomposition rate. Drying leads to change in physicochemical properties of food and its colour. This review paper aims to study the various physicochemical parameters changes which take place during drying period and colour variation base on hunter colorimetric system. INTRODUCTION The demand of preserve eatables increase during World War II. The troops deploy in field needs fresh and healthy food to eat which has good nutrition value. Many company out form during that period providing the requirement of army. Casserole and Eggs are some of the starting tin can product which has high shelf life and also able to maintain the nutrition value. [1] Nutrition bar [2]provided by United State Army under Meal, Ready to eat [3] was one of the best eatables containing all the required nutrition for a solider. During processing of food, it’s physicochemical and nutrition level gets change which affects the appearance and the quality of food product. Many research have been conducted worldwide aiming to understand the variation of such properties and to maintain the nutrition level of food. Food drying is one of the food processing process which removes the moisture from food and increase its shelf life. It use a heat source and fan or blower for force convection to circulate air over food and reducing its moisture contain. This process restrict the growth of bacteria and increase the life of food. The moisture reduction make food light in weight and easy to transport. [4] Most commonly hot air drying is used for drying eatables as it reduce the packaging cost and storage as the final product has low volume to weight ratio. [5] Moreover, the shelf life of eatables having low moisture contain is more as compare to those eatables which has high moisture contain. [6] Some food are highly sensible to temperature and there nutrition value get reduce during drying process. Functional properties like oxidation value, shrinkage, loss of colour and texture are important to consider during drying of fruits and vegetables. [7] Hot air drying (AD) leads to degradation of flavor, colour and nutrition value because of its high temperature operational process whereas Microwave drying (MD) and infrared radiation (ID) result in more promising result in terms of colour and flavor preservation during drying process. Freeze drying (FR) yields high quality dried product but it consume high energy. [8]Many researcher had used L*a*b colour space [9] to measure the colour value of fresh fruits and vegetables and processed ones. L*a*b colour space as compare to RGB colour space and CYMK colour space has uniform colour distribution and perception of colour which is easy to human eye to read and understand. [10] This review paper focus on different drying technique used to remove moisture, change in colour and physicochemical properties of fruits and vegetables. IMPORTANT CONCEPT A. PHYSICOCHEMICAL PROPERTIES Physicochemical properties of food are important to design the food processing, storage and handling system. [11] This properties include moisture, protein, fat, fiber and ash contain in food. NOVATEUR PUBLICATIONS INTERNATIONAL JOURNAL OF INNOVATIONS IN ENGINEERING RESEARCH AND TECHNOLOGY [IJIERT] ISSN: 2394-3696 VOLUME 4, ISSUE 1, Jan.-2017 42 | P a g e 1) Moisture It is most common measure quantity in processed food as there are legal standard of moisture contain in food. [12] Moisture in food is the amount of water present in food. The quantity of moisture effect the chemical and physical aspect of food. [13] 2) Protein Protein are basically long chain of amino acid found in fruits and vegetables. [14] They are structurally classified in four groups as primary, secondary, tertiary and quaternary. During drying process the fruits and vegetables are expose to high temperature result in denaturation of proteins structure. The α-helix and β-sheet structure of protein get disturbed and attained random structure. [15] 3) Fat Fat are fatty acid belonging to carboxylic acid group which are solids at room temperature. [16] This acids are very unstable in nature and react actively to oxygen and form reactive aldehydes. [17] To reduce the oxidation of fatty acid, antioxidant are added. Vitamin C are naturally occurring antioxidant in fruits and vegetables. Processed food generally added with synthesis antioxidant like TBHQ (tertiary butylhdroquinone), BHA (butylatedhydroxyanisole) and BHT (butylatedhydroxytoluene). [18] 4) Fiber The fiber are classified in two types, soluble and insoluble. [19] The soluble fiber are pectin and gum found inside the plant cell of fruits and vegetables whereas the insoluble fiber are found in the cell wall of cellulose and lignin. [20] Both this soluble and insoluble fiber form crude fiber which are generally knows as dietary fibers. [21] Crude fiber is the total amount of fiber in food which is plant residue remains after hydrolysis by digestive enzymes. [22] 5) Ash They are the inorganic component found in food around 7%. [23]The ash are basically material that are remain even after the food is burnt to very high temperature. It contain sodium, potassium, calcium and magnesium in major quantity and iodine, fluorine, arsenic, zinc, aluminum, iron, copper in minor quantity. [24] B. COLOUR VARIATION Fruits and vegetables after getting picked from farm undergoes many chemical changes due to detachment from plant and expose to different surrounding condition. This changes include colour change, flavor change and also texture change. [25] The variation of colour of fruits and vegetables are measure by instruments like spectrophotometer. The colour space used is basically L*a*b colour space defined by Hunter Labs (1996). [26] Consumer prefer food items which are fresh in colour as it signify that the food itself is fresh. [27] The process which improve the shelf life of food many times lower the saturation of real colour of food items. Therefore nowadays many artificial colour agents are used to enhance the appearance of fruits and vegetables. [28] STUDIES OF PHYSICOCHEMICAL PROPERTIES Margarita et al. [29] dried aloe vera using convective tray dryer at 50 °C, 60 °C, 70 °C, 80 °C and 90 °C with air velocity of 2 m/s. They found the moisture content in fresh aloe vera was 56.08 ± 1.11 g/100g d.m. which was higher than the dried aloe vera moisture contain ranging from 16.19 ± 0.54 g/100g d.m. to 18.81 ± 0.37 g/100g d.m. The moisture contain decrease significantly with increase in drying time. This is due to cell wall damage by lengthy drying time. [30][31] The moisture contain remain higher at 70 °C as compare to other drying temperature. Same was notice by Elsa et al. [32] where they dried olive-waste cake using convective dryer at 40 °C, 50 °C, 60 °C, 70 °C, 80 °C and 90 °C. Form Fig. 1, the moisture contain of fresh olive-waste cake decreases from 208.53 ± 4.17 g/100g d.m. to 1.39 ± 0.08 g/100g d.m. as drying temperature increases. Luciano et al. [33] used forced convective dryer to dry onion at 30 °C, 40 °C, 50 °C, 60 °C and 70 °C and the moisture contain decrease from 91.24 ± 0.54 g/100g d.m. to 13.32 ± 0.88 g/100g d.m. at drying temperature 40 °C. Eun et al. [34] dried the sweet potato flour at 55 °C, 60 °C and 65 °C using convection drying oven. The moisture contain of sweet potato flour decreases from 8.67 g/100g d.m. NOVATEUR PUBLICATIONS INTERNATIONAL JOURNAL OF INNOVATIONS IN ENGINEERING RESEARCH AND TECHNOLOGY [IJIERT] ISSN: 2394-3696 VOLUME 4, ISSUE 1, Jan.-2017 43 | P a g e to 6.18 g/100g d.m. with increase in drying temperature as similar reported by Van Hal. [35] This shows that higher the drying temperature, higher will be moisture removed with respect to drying period. 30 40 50 60 70 80 90 2 4 6 8 10 12 14 16 18 20 22 Aloe Vera