Thesis Abstract

The effect of different consecrations of citric acid on the physicochemical properties of orange juice was studied. Four samples of the orange juice were prepared, three of which were added (O.ICA), O.2 (B) and 0.3% (C) Citic acid respectively to the forth sample (D) No preservative was added. They were stored on the shelf for a period of one week and they were analyzed for pH, Pitaminac, dilatable acidity total solids, brix content, specific gravity, total plate count coliform count, fest & mold count and finally sensory evaluation. The results showed that over the days, the vitamin C content reduced from 62 mg to 30mg with the most retention in sample C. The pH of the samples reduced from 3.5. to 2.8 over the storage period with the most decrease in sample D (NP).

The total solids varied from 5.7% to 8.8% with the lesst solids in sample B (0.2%). The Torix content decreased over the storage period from 12.59 to 12 08 with the lesst decrease in sample D (N.P.). the titratable acidity ranged from 0.37% to 0.03 % within the storage period. The microbial analysis showed that there were growths in the nutriment agar, two yeast growths in the potatoedextrose agar which occurred in sample D and no growth in the McConkay agar. Sensory evaluation revealed that all the samples have similar colour and taste while samples A and D had the best flavour. This analysis shows that the use of citric acid in undiluted juice is not recommended except it is made into a drink.

Thesis Overview

INTRODUCTION

Oranges, demons, grape fruit and limes are the fruits of trees belonging to the citrus geaus. The sweet orange (citrus sinensis) is the most widely grown of the citrus trees and the fruits are either eaten fresh or made into orange juice. The edible portion is refereed to as the endocarp and consists of a series of segments carpels or loculs which contain the thin walled juice vesides surrounding the endocarp is the peel which comprises of 20-50% of the weight of the weight of the fruit and consists of the flavedo and the albeds (ihekoronye and Ngoddy,1985). The flavedo or outer peel is a layer of tissue underlying the epidermis and contains the chloroplast and oilsacs. The albedo or inner peel is a layer of spongy white tissue which is connected to the core and supplies the water and nutrient from the tree which are necessary for the fruit growth and development.

The proximate composition of the edible portion of the orange fruit is

Water – 86%

Protein – 0.6%

Fat – 0.1%

Micronutrients per 100g

Calcium – 24mg

Iron – 0.3.mg

Vit. A – 120mg

Thiamin – 0.06mg

Riboflavin – 0.02mg

Niscia – 0.1.mg

Ascorbic Acid – 36mg (source: Ihekoronge & Ngoddy 1985).

The colour of fruits when unripe is greatly influenced by the presence of chlorophyll, caroteaoids and anthocycanins. (Enwere 1998). Due to its high moisture content, fruits are susceptible to spoilage and are also highly perishable. Orange fruits are seasonal and hence in order to preserve them, they are processed into various food products such as juices, squashes, satadinaine etc.

Fruit juice is the liquid pressed by pressure or other mechanical means from the edible portion of the fruit (Simmond 1984). According to Faye (1973) orange juice was defined as the unfermented juice of mature oranges of the citrus sineasis specie. Fruit juices serve as part of meals and they aid in the digestion of human diet. They supply minerals and vitamins in addition to energy when consumed but they deteriorate over a long storage period unless they are preserved by the addition of chemicals and by the application of heat.

Preservatives are food additives added to foods with the intention of arresting or retarding the deterioration of the food. Preservation involved the protection of food from the deterioration of microorganisms, enzymes and oxidation. This can be achieved by the application of heat and addition of chemical preservatives (Arnold 1982).

Preservatives include anti-ripening agents, anti-oxidants, antimicrobial agents and sprouting inhibitors. They may be added intentionally to food or may appear in foods as a result of pre – processing treatments, processing and storage (Ihekornye and Ngoddy, 1985).

The addition of chemical preservatives is governed by government departments which must give approval before it is permitted for use. In General it should not adversely affect the nutritive value of food.

Preservatives used in food include benzoic acid, ascorbic acid, vinegar, propanoic acid, citric acid etc. Although their limits in terms of individual specified preservatives, they may also be incorporated into the foods as permitted salts like sodium benzoate (Harold etal, 1992). Also the use of citric acid has been recognized by all major national and international food regulatory agencies as a good preservative for food and beverages.

The use of citric acid in fruit juices like pineapple juice has been found to give a positive result but in this work, it is aimed at investigating the effect of the different concentrations of citric acid on come physicochemical properties of orange juice.