comparative study on the effectiveness of sodium metabisuphite, acetic acid and lemon juice in ...

135 Pages·2016·3.71 MB·English

COMPARATIVE STUDY ON THE EFFECTIVENESS OF SODIUM
METABISUPHITE, ACETIC ACID AND LEMON JUICE IN PRESERVATION
OF DRIED MANGOES AND TOMATOES

JOEL MHANGA

A DISSERTATION SUBMITTED IN PARTIAL FULFILMENT OF THE
REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE IN FOOD
QUALITY AND SAFETY ASSURANCE OF SOKOINE UNIVERSITY OF
AGRICULTURE. MOROGORO, TANZANIA.

2015
ii

ABSTRACT

Mango and tomato are widely grown in the World. The present study was carried out to
compare the effectiveness of three preservatives in retaining their quality attributes of
mango and tomato and substituting the use of sodium metabisulphite with either the lemon
juice or acetic acid. The three preservatives were sodium metabisulphite (0.1%), acetic
acid (0.5%) and lemon juice (0.5v/v) studied at the respective level in bracket. Mango and
tomato slices were dried in the walk - in solar dryer to attain the moisture range of 17 –
22% and packed in polythene package. The Completely Randomized Design (CRD) was
used to assess the effectiveness of three preservatives while Randomized Complete Block
Design (RCBD) was used in sensory evaluation test. Both descriptive and consumer test
by the use of trained and untrained panelist respectively were done to assess the sensory
profile and consumer acceptability. Microbial analysis for the total bacteria count and
shelf life prediction by using linear model equation at different storage temperatures (35
and 45oC) were carried out. The results showed that sodium metabisulphite and lemon
juice were the best in retaining the sensory attributes assessed. The reduction of microbial
load for all the three types of preservatives was promising as they all lied within the
acceptable values. The extensions of shelf life of the dried products were best achieved
using sodium metabisulphite and lemon juice as they had longer shelf life than acetic acid
treated samples, the results showed mango treated with sodium metabisulphite and lemon
juice is shelf stable for 501 days while the one treated with acetic acid was shelf stable for
457 days at 25oC. The results also showed that mango have longer shelf life (11/2 years)
than tomato (1/2 year) at 25oC and 28oC. The use of lemon juice was encouraged due to its
effectiveness, cheapness, availability and positive health effects to the human body.
iii

DECLARATION

I, Joel Mhanga do hereby declare to the Senate of Sokoine University of Agriculture that
this dissertation is my own original work done within the period of registration and that it
has neither been submitted nor being concurrently submitted in any other institution for a
degree award.

Joel Mhanga Date
(MSc. Food Quality and Safety
Assurance)

The above declaration is confirmed;

Professor B. Chove Date
(Supervisor)
iv

COPYRIGHT

No part of this dissertation may be reproduced, stored in any retrieval system, or
transmitted in any form or by any means without prior written permission of the author or
the Sokoine University of Agriculture on the behalf.
v

ACKNOWLEDGEMENTS

My sincere appreciation goes to my supervisor, Prof. B. Chove, who guided me right from
the time of proposal development to the end of this study. I am grateful to Mbeya
University of Science and Technology (MUST) for giving me this opportunity to study, I
am also thankful to Government of Tanzania for proving the scholarship through the
Higher Education Students Loan Board (HESLB). Special thanks also go to Professors B.
Chove, B. Ndabikunze and Dr. Anna Temu for giving me an opportunity to be attached to
their DANIDA PROJECT. I also thank Mr S. Mwanyika, Mama Mapunda and Mama
Mbije, for their tireless support, advice and encouragement during the research period. All
my colleagues, especially, Joseph Runyogote, Anna Mhalu and Honi Buzo. You were
always there for me whenever things would become tough, but also encouraging me
during all the time of my research work. In fair honesty, it is impossible to mention
everyone. I am immensely indebted for their help in and outside of the study, but to those
I didn’t mention, thank you and may all be blessed.
vi

DEDICATION

This work is dedicated to my lovely wife Diana Mwangoka who despite her loneliness has
always been my source of inspiration and happiness, to my mother Conjetha Lunyungu
my father Aaron Mhanga, my beloved children Emmanuela, Jonathan and Jackson and my
friend Zaharan Mgina whose support and motivation enabled me to conduct and complete
this study.
vii

TABLE OF CONTENTS

ABSTRACT ........................................................................................................................ ii
DECLARATION ............................................................................................................... iii
COPYRIGHT .................................................................................................................... iv
ACKNOWLEDGEMENTS ................................................................................................ v
DEDICATION ................................................................................................................... vi
TABLE OF CONTENTS ................................................................................................. vii
LIST OF TABLES ........................................................................................................... xii
LIST OF FIGURES ........................................................................................................ xiii
LIST OF APPENDICES ................................................................................................... xv
LIST OF ABBREVIATIONS AND SYMBOLS .......................................................... xvi
CHAPTER ONE .................................................................................................................. 1
1.0 INTRODUCTION .................................................................................................... 1
1.1 Background Information ............................................................................................ 1
1.2 Problem Statement and Justification .......................................................................... 4
1.3 Objectives of the Study .............................................................................................. 4
1.3.1 General objective ........................................................................................... 4
1.3.2 Specific objectives ......................................................................................... 5
CHAPTER TWO ................................................................................................................. 6
2.0 LITERATURE REVIEW ........................................................................................ 6
2.1 Introduction to Fruits and Vegetables ........................................................................ 6
2.1.1 Mango (Mangifera indica) ............................................................................ 7
2.1.2 Tomatoes (Lycopersicon esculentum) ......................................................... 14
2.1.2.1 The composition of tomato ........................................................ 16
2.1.2.2 Potential health benefits of tomatoes ......................................... 16
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2.1.2.3 Tomato toxicity ........................................................................... 17
2.2 Overview of the Preservation Technology ............................................................... 17
2.2.1 Food preservation methods ......................................................................... 20
2.2.2 Use of chemicals ......................................................................................... 22
2.3 Overview of Food Preservatives .............................................................................. 25
2.3.1 Sodium metabisulphite ................................................................................ 25
2.3.2 Acetic acid ................................................................................................... 28
2.3.3 Lemon juice ................................................................................................. 30
2.4 Overview of Shelf Life ............................................................................................. 32
2.4.1 Factors affecting shelf life of fruits and vegetable ...................................... 33
2.4.2 Packaging materials ..................................................................................... 33
2.4.3 Shelf life prediction and kinetics of deteriorative reactions in dried
foods ............................................................................................................ 34
2.5 Factors Affecting the Kinetics of Reactions in Dried Foods ................................... 35
2.5.1 Temperature ................................................................................................ 35
2.5.2 Water activity .............................................................................................. 36
2.5.3 Oxygen ........................................................................................................ 37
2.6 Mode of Deterioration .............................................................................................. 37
2.6.1 Mango .......................................................................................................... 38
2.6.2 Tomato ........................................................................................................ 39
CHAPTER THREE .......................................................................................................... 41
3.0 MATERIALS AND METHODS ........................................................................... 41
3.1 Study Area ................................................................................................................ 41
3.2 Materials ................................................................................................................... 41
3.2.1 Raw materials .............................................................................................. 41
3.2.2 Chemicals .................................................................................................... 41
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3.3 Methods .................................................................................................................... 41
3.3.1 Research design ........................................................................................... 41
3.3.2 Application of preservatives and drying procedure .................................... 42
3.3.3 Determination of moisture content of fruits and vegetable ......................... 44
3.3.4 Sensory evaluation ...................................................................................... 45
3.3.4.1 Quantitative Descriptive Analysis (QDA) ..................................... 45
3.3.4.2 Consumer test ................................................................................. 46
3.3.4.3 Relationship between sensory and consumer data
(preference mapping) ..................................................................... 46
3.3.5 Microbiological analysis (total bacteria count) ........................................... 47
3.3.6 Prediction of shelf life ................................................................................. 47
3.3.6.1 Browning measurement ................................................................. 48
3.3.6.2 Procedure ....................................................................................... 48
3.3.7 Statistical data analysis ................................................................................ 49
CHAPTER FOUR ............................................................................................................. 50
4.0 RESULTS AND DISCUSSION ............................................................................. 50
4.1 Moisture Content ...................................................................................................... 50
4.1.1 Mango moisture content .............................................................................. 50
4.1.2 Tomato moisture content ............................................................................. 50
4.2 Water Activity .......................................................................................................... 51
4.2.1 Water activity of mango .............................................................................. 51
4.2.2 Water activity of tomato .............................................................................. 52
4.3 Sensory Quality ........................................................................................................ 53
4.3.1 Mango quantitative descriptive analysis ..................................................... 53
4.3.1.1 Panel performance ......................................................................... 53
4.3.1.2 Sample difference .......................................................................... 54
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4.3.1.3 Principal component of descriptive sensory data .......................... 56
4.3.1.4 PCA scores ..................................................................................... 57
4.3.2 Consumer tests ............................................................................................ 58
4.3.2.1 Consumer characteristics ............................................................. 58
4.3.2.2 Hedonic test ................................................................................. 59
4.3.2.3 Hedonic liking or overall acceptability ........................................ 60
4.3.3 Relationship between descriptive and hedonic data (preference
mapping) ...................................................................................................... 60
4.3.4 Tomato quantitative descriptive analysis .................................................... 62
4.3.4.1 Panel performance ....................................................................... 62
4.3.4.2 Sample difference ......................................................................... 62
4.3.4.3 Principal component of descriptive sensory data ........................ 64
4.3.4.4 PCA scores ................................................................................... 65
4.3.5 Consumer studies ........................................................................................ 66
4.3.5.1 Consumer characteristics .............................................................. 66
4.3.5.2 Hedonic test .................................................................................. 67
4.3.5.3 Hedonic liking .............................................................................. 68
4.3.6. Relationship between descriptive and hedonic data (preference
mapping) ...................................................................................................... 68
4.4 Microbial Analysis Results of Treated and Control Fruits and Vegetables
Products .................................................................................................................... 71
4.4.1 Microbial results for mango ........................................................................ 71
4.4.2 Microbial results for tomato ........................................................................ 72
4.5 Shelf life Prediction of Mango Fruits ....................................................................... 74
4.5.1 Initial absorbance of mango ........................................................................ 74
4.5.2 Absorbance of mango at 35oC and 45oC ..................................................... 74