PHYICO CHEMICAL CHARACTERIZATION, FATTY ACID COMPOSITION

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PHYICO CHEMICAL CHARACTERIZATION, FATTY ACID COMPOSITION AND RHEOLOGICAL BEHAVIOUR OF THREE AVOCADO CULTIVARS PULP OIL BY ATUAKE, IYORNIM RACHEL EBSU/PG/M.SC./2016/08829 DEPARTMENT OF FOOD SCIENCE AND TECHNOLOGY FACULTY OF AGRICULTURE AND NATURAL RESOURCE MANAGEMENT EBONYI STATE UNIVERSITY, ABAKALIKI SUPERVISED BY: DR. O. J. IKEGWU

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ABSTRACT

Avocado ( Persea Americana Fruit) is one of the most abundant fruits in the tropics Three cultivars of avocado; Fuertes, Bacon and Reed were sourced from Obudu Local Government Area of Cross River State were used in this study The study was aimed at characterizing physicochemical and fatty acids content of avocado pulp oil and also to determine rheological behaviour of same oils at different temperatures The oil was extracted from the avocado fruit pulp using local cold press method It was observed that avocado contains a substantial amount of oil in its pulp

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ABSTRACT

Physicochemical properties that were analyzed are; free fatty acid, iodine value, saponification value, density pH, refractive index and carotenoid The oil were analyzed for fatty acids using chromatography method in which oleic acid was the predominant fatty acid It was also observed that viscosity decreases with increase in shear rate and temperature respectively The activation energy of the three oil samples were found to be 8.274KJmol-1, 6.129KJmol-1 and 5.189KJmol-1 for Reed, Bacon and Guertes respectively. This indicates that Reed was more sensitive to temperature changes

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INTRODUCTION

The Avocado tree ( Persea Americana) is a fruit plant which has its origin in America Quite a large number of varieties are found in different parts of the world Generally, fruits are very crucial in our life as they provide essential vitamins, dietary antioxidants, fibres and other benficial effects on human health Avocado fruit has outstanding high nutritional value and it is beneficial to growth and development (USDA, 2011) It is useful in human nutrition as a source of various nutrients especially energy and monounsaturated fatty acids The pulp of Avocado fruits shows excellent significance as a result of the 5% to 30% oil composition

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The oil from avocado pulp is rich in Omega 3 fatty acids which may have beneficial effects to health in relation to the prevention of cardiovascular diseases (Ahmed and Barmore , 1990) Oil extraction is an important process in the food industry which adds value to the fruit and also yield profits to the companies (Tango and Carvalho , 2004) Rheological properties of avocado oil are important because they predict the resistance of fluid and their behaviour during flow It is an important characteristics to consider in process design, quality control and cooking

INTRODUCTION

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abstract

STATEMENT OF RESEARCH PROBLEM

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There is an increasing demand for vegetable oils

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This is because today's dietary trend has changed from animals fat to vegetables including countries where people conventionally consume fat

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This is due to the high cholesterol level of animal fats leading to a high incident rate of cardiovascular disease

There is an abundance of underutilized plant species which can be a source of healthy and heart friendly oils for human consumption

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Avocado fruit is one of the most abundant fruits in Nigeria that is commonly eaten in its crude form, but can be a rich source of alternative oil

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JUSTIFICATION OF STUDY

This research will help to create awareness for utilized locally available avocado fruits as a raw material for the production of alternative vegetable oil

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This will curtail the consumption of animal fats which is high in cholesterol

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It will also help to develop a system for post harvest management in sustainable way since avocado fruits when fully mature can easily go bad after harvest

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OBJECTIVES

OF STUDY

BROAD OBJECTIVES

THE MAIN OBJECTIVE OF THE STUFY WAS CHARACTERIZATION OF PHYSICOCHEMICAL PROPERTIES DETERMINATION OF FATTY ACID COMPOSITION AND TO STUDY THE RHEOLOGICAL BEHAVIOUR OF OIL FROM THREE CULTIVARS OF AVOCADO PULP

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SPECIFIC OBJECTIVES

Determination of physicochemical properties of Avocado Pulp Oil >>><<<< Determination of fatty acids in avocado pulp oil >>><<<< Determination of rheological behaviour of Avocado pulp oil whe n subjected to different temperatures and calculation of activation energy of the oil

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MATERIALS AND METHOD

The materials used fo r this study where three cultivars of Avocado

They were obtained from Obudu Local Government are of Cross River State

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SAMPLE PREPARATION

The avocado fruits were cut into halves around the pit A spoon was used to scoop around the pit to separate the pulp from the skin The pulp was weighed and tranfered into a food processor and pureed into a smooth paste The paste was spread onto a baking tray and placed in the oven at a temperature of 45 o C to remove moisture It was removed from the scraped and placed in a cotton cloth The cotton cloth containing the dry avocado paste was lifted from the corners and pinched together to make sack A force was applied using hands to squeeze the dry avocado to bring out the oil Percentage oil yield was the calculated determination of Physicochemical properties Density was dtermined according to Onwuka (2005)

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SAMPLE PREPARATION

The method of AOAC (1990) was employed to determine the refractive index of the oil It was determined according to the method described by Onwuka (2005) Free fatty acid was determined using the method described by Akubugwo et al.,(2008) Acid value was determined using the method of AOAC(1990) Saponification value was determined using the method of AOAC(1990) Iodine value was determined using the method of AOAC(1990) Determination of fatty acid was done according to the method of Rohman and Cheman (2011) Rheological behaviour of the oil was determined according to a method described by Vidal et al., (2004) Power law mode, Bingham plastic model and Newtonian model were employed to determine the flow of behavior of the oil Activation energy was calculated by plotting the consistency coefficient data as ink versus 1/T, the slope of each value multiplied by R was dtermined to equal the activation energy

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STATISTICAL ANALYSIS

Results obtained for physicochemical and fatty acid composition were subjected to analysis of variance using SPSS (version 20) Means were separated using Duncan test for 85% average confidence level Rheological properties were analyzed using statistical software Assistant (Version 7.6 beta) at 5% confidence level

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RESULTS

Percentage oil yield of the pulp of three avocado fruit

Physicochemical characterization of oil of the pulp of avocado oil

Fatty acid composition of oil of avocado pulp

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RHEOLOGICAL BEHAVIOUR

Apparent viscosity of the three oil samples decreased with Increasing shear rate

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RHEOLOGICAL BEHAVIOUR

Effects of variety on the viscosity of oil at different temperatures.

Bacon variety had the least effective of shear rate on the viscosity, while reed has the highest effect of shear rate on the viscosity

Effect of variety on the viscosity of oil samples at 30 o C

Effect of variety on the viscosity of oil samples at 65 o C

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RHEOLOGICAL BEHAVIOUR

Bacon had the least effect of shear rate on the viscosity, while reed had the highest effect of shear rate on the viscosity

Effect of variety on the viscosity of oil 110 o C

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RHEOLOGICAL BEHAVIOUR

Bacon had the least effect of shear rate on the viscosity, while Reed had the highest effect of shear rate on the viscosity

Effect of temperature on the Shear rate VS Shear stress of three varieties of avocado oil

At all temperatures, experimental results of the variation of Shear stress with Shear rate were found to indicate a Shear thinning non-Newtonian behaviour

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Correlation to rheological models

The correlation results are tabulated in Table 4-6

Newtonian, Binghamplastic and Power law model succesfully described experimental data Power law model is marginally more accurate than the Bingham plastic model and Newtonian model

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ACTIVATION ENERGY

The flow behaviour index, n and consistency coefficient, k were significally influenced by the change in temperature (Table 4) The activation energy value was found to be 8.247Jmol-1 for reed oil, 6.129KJmol -1 for Bacon and 5.189JKmol -1 for fuertes (Fig 10). This indicates that reed was more sensitive to temperature changes

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CONCLUSION

From the results obtained in this study it can be concluded that avocado oil is hear friendly oil owing to its high content of monounsaturated and polyunsaturated fatty acids which lowers bad cholesterol in the blood The physicochemical characteristics suggest that the oils have industrial potentials The flow characteristics of the oils at 30-110 o C was analyzed in the shear range of 0.1-1.05 -1 . At these temperature the oil exhibited non- newtonian , shearthining behaviour The appropriate viscosity of the oil samples increased with decreasing temperature The model parameters; The flow behavous index, n and the consistency coefficient are both affected by temperature The change of flow bheavious index with temperature dues not follow a descriptive trend, while consistency coefficient temperature relationship can successfully be described by Arhenius type equation

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RECOMMENDATION

With the observation made in this study avocado oil can be substituted with other vegetable oil for cooking and also used industrially in food processing

There should be public awareness to educate the public on the potentials and usefulness of this oil

Extraction of avocado oil should be done when fruit is in season using simples and cost effective methods in order to avoid waster, thereby increasing farmers’ income

Further research should be conducted to determine the shelf life, stability and sensory attributed of the oil in order to satisfy the end users

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