Production, quality and possible uses of cashew gum

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The cashew tree gum is seen as a promising plant exudate for the food industry in Ghana, however, there is a lack of understanding of its basic physico-chemical, rheological and toxicological properties thus limiting its utilization in foods. The long term strategy for promoting the use of cashew gum in the food industry is therefore to understand and exploit the agricultural production, harvesting, physico-chemical and rheological properties of the gum. An initial study of cashew gum yield trends per tree and picking in relation to age of tree and the location of tree was conducted at four cashew growing districts (Sampa, Wenchi, Bole, Damango and Jirapa) in Ghana for a period of 24 months. This was to develop cashew gum production for the food industry and to generate extra income for cashew farmers. Trees used in the study were of two age groups, 10 years and below and above 10 years. Yield trends in relation to raiijfall were also compared. The results showed that age and location of cashew trees have no significant effect on the production of gum. The physico-chemical and rheological properties of cashew gum collected from the four cashew growing districts were studied to help promote the utilization of cashew gum in the food industry. The gums collected from trees of the two different age groups were compared to gum Arabic in terms of pH, total ash, protein content, total sugars, total phenols, moisture content and insoluble matter. Gum from mature trees was generally found to have higher levels of protein, moisture, sugars and phenols than that from young trees, with the exception of pH which was lower in gums from mature trees. The predominant minerals in cashew tree gum were Ca, K, Na and Fe. Gelation properties of cashew gum showed that the gum gelled at a higher concentration of 80%. A study of the viscosities of aqueous gum solutions showed that the concentration increased with viscosity while an increase in temperature reduced the viscosity. Gum produced during the rainy season was less viscous than that produced in the dry season. Viscosities of gum reduced slightly after 6 and 12 months storage. The results showed that location, maturity and storage had no significant effects on the viscosity of cashew gum. Toxicological evaluation (acute toxicity) of cashew gum showed that the median lethal dose (LD50) for cashew gum was more than 30 g/kg b.w. Due to the limited supply and high cost of gum Arabic, cashew gum was assessed as a quick coating agent in the production of chocolate pebbles, using gum from both young and mature cashew trees. Pebbles produced with cashew gum samples were compared with those produced with gum Arabic. Although chemical parameters determined showed significant differences among the three products (p < 0.05), sensory analysis did not. The overall acceptability of the products were similar and the mean scores were 7.4, 6.8 and 7.1 for pebbles produced with gum Arabic, that produced with cashew gum from young and mature trees respectively. The optimum formulations for the production of pineapple jam and cashew juice drink with cashew gum as gelling agent and stabilizer were determined using response surface methodology (RSM). Cashew gum was found to be suitable as a clarifying agent rather than a stabilizer in cashew juice and a fat replacer in baked dough nuts.  
A thesis submitted to the Department of Food Science and Technology, Kwame Nkrumah University of Science and Technology in partial fulfillment of the requirements for the degree of Doctor of Philosophy, 2008