Impact of Water Activity and Moisture Sorption Characteristics on Mould Relations in Garri

Impact of Water Activity and Moisture Sorption Characteristics on Mould Relations in Garri.

ABSTRACT

The moisture content of garri samples were determined  by standard  method  at 105⁰C. The mean moisture content of yellow and white garri was 11.10% and  10.81%, respectively within 24 hrs of sampling from the market and  17.27%  and  16.14% following 3 months of storage at room temperature in hessian bags.

The water activity of the garri samples varied from 0.587  to  0.934.  Moisture  sorption isotherms,  determined by static gravimetric techniques based on isopiestric transfer of water vapour at 20⁰C and 30⁰C using inorganic saturated salt solution in the range of 0.225 – 0.973 showed  sigmoidal behaviour (Brunauer- Emmet- Teller, BET II type) which is typical of dry carbohydrate rich foods.

There was a general increase  in  the  equilibrium  moisture content (%) with increasing water activity. Water  sorption was temperature dependent  as is typical of food system.

The equilibrium moisture content decreased with increase in temperature at constant water activity. A total of 44 fungal (mould) species were isolated from the garri samples.

Based on the examination of their macroscopic (colonial) and microscopic characteristics, the isolates were identified to belong to the following fungal genera; Mucor, Penicillium, Cephalosporium, Aspergillus, Scopulariopsis, Rhizopus and Paecilomyces, with the range of isolations  increasing with  increase  in moisture  content of the samples.

Moisture migration into this food is critical to its shelf life. Therefore, to enhance shelf life they should be stored in moisture proof bags.

TABLE OF CONTENTS

Title page – – – – – – – – – i
Certification – – – – – – – – – ii
Dedication – – – – – – – – – iii
Acknowledgement – – – – – – – – iv
Table of content – – – – – – – – v
List of tables – – – – – – – – – – viii
List of figures – – – – – – – – – ix
Abbreviations – – – – – – – – – x
Abstract – – – – – – – – – xi

CHAPTER ONE INTRODUCTION AND LITERATURE REVIEW

1.1 Introduction – – – – – – – – 1
1.2 Statement of problem – – – – – – – 3
1.3 Aims – – – – – – – – – 3
1.3.3 Objectives – – – – – – – – 3
1.4 Literature Review – – – – – – – – 4
1.4.1 Water availability – the concept – – – – 4
1.4.2 Water activity – – – – – – – – 5
1.4.3 Water potential – – – – – – – – 6
1.4.4 Thermodynamics of water activity – – – – – 7
1.4.5 Osmotic Pressure – – – – – – – 10
1.5 Factors affecting water activity – – – – – – 11
1.5.1 Freezing – – – – – – – – – 11
1.5.2 Drying – – – – – – – – 11
1.5.3 Specific solutes – – – – – – – – 12
1.6 Water activity and Food stability – – – – – – 13
1.6.1 Chemical stability – – – – – – – 14
1.6.1.1 Maillard reaction – – – – – – – 15
1.6.1.2 Lipid oxidation – – – – – – – 16
1.6.1.3 Enzymatic reaction – – – – – – – 16
1.6.2 Physical stability – – – – – – – 17
1.6.2.1 Water and crispness – – – – – – – 18
1.6.2.2 Water activity and stickiness, caking and collapse – – – 18
1.6.3 Microbial stability – – – – – – – 19
1.6.3.1 Metabolic activities of microorganisms – – – – 20
1.7 Measurement of water activity – – – – – – 22
1.8 Models for predicting water activity – – – – – 23
1.8.1 Non-electrolytic solutions – – – – – – 24
1.8.1.1 Money and Born equations – – – – – – 24
1.8.1.2 Grover equation – – – – – – – 25
1.8.2 Electrolytic solution – – – – – – – 25
1.8.2.1 Pitzer equation – – – – – – – 26
1.8.2.2 Ross equation – – – – – – – – 27
1.9 Sorption phenomena and sorption isotherms – – – – 27
1.9.1 Isotherms prediction model – – – – – – 28
1.9.1.1 Langmuir isotherm – – – – – – – 28
1.9.1.2 Bruanuer – Emmet – Teller (BET) isotherm – – – – 28
1.9.1.3 Guggenheim – Anderson – de Boer isotherm – – – 29
1.9.2 Moisture sorption isotherm determination – – – – 30
1.10 Moisture content and Food quality – – – – 30
1.10.1 Moisture content determination – – – – 31
1.10.2 Moisture migration – – – – – – 32
1.11 Garri – – – – – – – – – 33
1.11.1 Principle of preservation and processing of cassava – – – 34
1.11.2 Raw material – – – – – – – – 34
1.11.3 Hygiene – – – – – – – – 35
1.11.4 Process control – – – – – – – 36
1.11.5 Packaging and storage – – – – – – 36
1.12 Mould – – – – – – – – – 36
1.12.1 Factors governing growth of moulds in garri – – – – 37
1.12.2 Damages caused by mould – – – – – – 38

CHAPTER TWO MATERIALS AND METHODS

2.1 Survey and collection of samples – – – – – – 39
2.2 Determination of moisture content – – – – – 39
2.3 Determination of water activity – – – – – – 40
2.4 Determination of moisture sorption isotherm – – – – 41
2.5 Media preparation- – – – – – – – 41
2.6 Isolation of moulds – – – – – – – 41
2.7 Identification of Moulds – – – – – – – 42
2.7.1 Slide culture techniques – – – – – 42

CHAPTER THREE RESULTS

3.1 Moisture content of garri – – – – – – – 44
3.2 Water activity changes in garri sample – – – – – 47
3.3 Moisture sorption characteristics of garri samples – – – 67
3.4 Fungal isolates – – – – – – – – 76

CHAPTER FOUR DISCUSSION AND CONCLUSION

4.1 Moisture sorption isotherm – – – – – – 87
4.1.1 Effect of temperature – – – – – – – 88
4.1.2 Effect of water activity – – – – – – – 88
4.2 Moulds – – – – – – – – – 89
4.3 Conclusion – – – – – – – – 93
REFERENCES – – – – – – – – 94
APPENDICES – – – – – – – – 107

INTRODUCTION

Garri is a creamy white or yellow (if palm oil is added), starchy, grit produced by fermentation of peeled, washed and mashed cassava roots (Manihot esculenta Crantz) which are dehydrated, sieved and roasted (Ogiehor et al., 2007).

Garri is the most commonly used form of cassava products in Nigeria and it accounts for over 70% of the entire cassava production in Nigeria (IITA, 2003; Sanni and Olubamiwa,  2004).

Its  ability to store well and its acceptance as a convenience food are responsible for its popularity in West and Central Africa where it is a staple food.

Garri  is  consumed  without further cooking (soaked in water) with sugar, smoked fish, roasted groundnuts, cooked cowpea and coconut, and sometimes with milk and beverages as complements.

It can also be prepared into a stiff paste called ‘Eba’ by adding the granules into hot water and stirring to make a paste of varied consistency which can be consumed  with local  soups or stews of various types by chewing or swallowing in morsels (Grace, 1997; Asegboyin and Onyimonyi, 2007).

The acceptability of garri is based on: organoleptic properties (colour,  taste,  aroma, absence of extraneous matter and texture); physical properties (swelling capacity, particle size distribution); and chemical properties (pH, water activity and residual hydrogen cyanide properties).

REFERENCES

Abdel – Gawal, K. M., and Zohri, A. A. (1993).  Fungal  flora and  mycotoxins of six kinds of nuts-seeds for human consumption in  Saudi-Arabia.  Mycopathologia, 124: 55 – 64.

Acker, L. (1963). Enzyme activity at low water content. In: Recent Advances in Food Science – 3 (eds) J. M. Leitch and D.N. Rhodes, Buterworths, London, pp. 239 – 247.

Adejumo, B.A., and Raji, A.O. (2010). An appraisal of garri packaging in Ogbomoso, Southwestern Nigeria. Journal of Agricultural and Veterinary Sciences. Vol. 2.

Adeniji, M.O. (1976). Fungi associated with the deterioration of garri. Nigeria Journal of Plant Protection, 2: 74-77.

Adisa, V.A. (2004). Fungi associated with the spoilage of stored yam chips and flour in Nigeria. Journal of Agricultural Food Chemistry, 19(2): 222 – 223.