EFFECT OF AIR OVEN DRYING PROXIMATE TEMPERATURE COMPOSITION THERMAL PASTING AND FUNCTION PROPERTIES OF TRIFOLIATE OF YAM FLAVOR
CHAPTER ONE
INTRODUCTION
1.1 BACKGROUND OF THE STUDY
Yam is an important food in many tropical countries particularly in West Africa, South Asia and Caribbean, where it also has a social and cultural importance for about 300 million people throughout the world (Manuel et al. 2005 ;Ettien et al .2009 ). Total world production of yam had been estimated to be 40 million tonnes per year while Nigeria (the leading producer) produced 34 million tonnes which accounts for 69.8 % of the yam (FAO 2006 ; IITA 2007).
Yam flour production is a way of preserving yam tubers in a storable form so as to make it available during the off season (Oni 2006 ), thereby reducing storage losses as well as marketing and transportation costs (Iwuoha 2004 ). The process involved in yam flour production includes harvesting, sorting, peeling, slicing, blanching, drying and.milling. This is the age-old traditional method of processing yam into dry yam (gbodo), and subsequently yam flour (elubo ). The quality of gbodo and elubo varies with the processor location, yam species, processing methods and conditions (Akissoe et al. 2003 , 2004 ;.Hounhonigan et al. 2003 ).
The dried chip and its flour (elubo ) are one of the traditional transformation methods for processing and storage of yam (Abiala et al. 2011 ). Yam flour is the major ingredient in making ‘ amala ’ largely eaten by ethnic Yorubas of South Western part of Nigeria when reconstituted. Amala is a popular starchy food that is prepared by reconstituting (cooking and stirring with boiling water).fermented or unfermented yam flour (elubo ), produced traditionally from the processed tuber flesh of white yam (D. rotundata or D. alata ) (Awoyale et al. 2010 ). It is a traditional thick paste prepared from blanched dried yam flour with a particular texture (Akissoe et al. 2006 ). Color and taste are permanent features of amala obtained from yam chips flour (Akissoe et al. 2004 ).
Literature is available on the production of yam chips and amala from other white yam, water yam and other yam species (Akissoe et al. 2003, Abiala et al. 2011 ). The use of trifoliate yam tubers in making amala had not been explore due to the alkaloid contents which cause bitterness in the tuber. Trifoliate yam being among the neglected tuber crop was reported to be highly nutritious with yield higher than other yam species (Treche and Agbor-Egbe 1996 ; Afoakwa and Sefa-Dedeh 2001 , 2002). Various researchers have studied the chemical, biochemical and textural changes of trifoliate yam tubers, flours and starch after harvesting (Afoakwa and Sefa-Dedeh 2001 , 2002; Medoua et al. 2005 , 2007 ; Akinoso and Abiodun 2013 ).
However, in the drying method of the yam using air-ovens which are electrical devices which use dry heat to sterilize . They were originally developed by Pasteur. Generally, they can be operated from 50 to 300 °C, using a thermostat to control the proximate temperature of the Oven composition. Their double walled insulation keeps the heat in and conserves energy , the inner layer being a poor conductor and outer layer being metallic. There is also an air filled space in between to aid insulation. An air circulating fan helps in uniform distribution of the heat. These are fitted with the adjustable wire mesh plated trays or aluminium trays and may have an on/off rocker switch, as well as indicators and controls for temperature and holding time. The capacities of these ovens vary. Power supply needs vary from country to country, depending on the voltage and frequency ( hertz ) used. Temperature sensitive tapes or biological indicators using bacterial spores can be used as controls, to test for the efficacy of the device during the use drying yam flour.
However, the process of yam pounding is very stressful and time-consuming as it largely taken by Southeast Igbo; therefore, it has become less popular among the elites. The need to reduce the labour associated with the preparation of pounded yam brought about instant yam flour which can be reconstituted into dough similar to the pounded yam. The instant yam flour is mixed with a stipulated proportion of hot water until a thick paste is formed. The alternative, instant yam flour, which mimics closely the properties of traditionally pounded yam, is sought after by a large number. Aworh elucidated different methods of the production of instant yam flour. Consumer perspectives on the quality properties of instant yam flour when reconstituted have been linked to how different the product is when compared to traditionally pounded yam. However, these differences may be somewhat due to technological variables i.e. air-oven drying machine and production parameters (drying methods, time) and/or agronomical conditions (yam cultivar, genetic, harvest time). Therefore, study on the influence of two or more of these variables, for example, drying techniques and harvest season on the functional characteristics of the instant yam flour become necessary. Drying is a critical factor in the process technology for instant yam flour as physical or chemical changes may occur thus resulting in extreme changes in product quality.
Researches have been carried out in diverse ways on Instant yam flour but there remains little or no information regarding the effect of harvest season, drying technique and the interaction of these variables on the functional properties of instant yam flour. The aim of this research is to evaluate the impact of harvest season and various drying methods on the functional properties of instant yam flour.
 Effects of air oven methods on the proximate compositions and temperature contents of yam flour trout the influences on the air drying and microwave drying on nutritional and function properties of thelma yam flour while it effects on the proximate and fatty acid compositions of yam flour. Hence, these are widely used to sterilize articles that can withstand high temperatures and not get burnt, like glassware and flour.
EFFECT OF AIR OVEN DRYING PROXIMATE TEMPERATURE COMPOSITION THERMAL PASTING AND FUNCTION PROPERTIES OF TRIFOLIATE OF YAM FLAVOR
