Effect of storage period on the quality characteristics of two varieties of African Mango Seed Flour at ambient temperature

The effects of storage of Ogbona seed fl our (Irivingia gabonensis and Irivingia excelsa), at ambient condition (30±20C, 65-74% RH) for 0-4 months on some physical characteristics were investigated. The samples were subjected to storage in air tight polyethylene bags for up to four months. Samples were removed at intervals of 0, 1, 2, 3 and 4 months for analysis. The chemical: proximate constituents, free-fatty acids and peroxide values; selected functional properties: water/oil absorption capacity, foam capacity and viscosity and sensory attributes of the samples were investigated. The result shows that there was no observable change in the chemical composition, selected functional and sensory properties of the two varieties of Ogbona seed fl ours when stored up to two months but decreased from third to fourth month during storage at ambient temperature. Therefore, storage at ambient temperature (30±20C, 65-74% RH) could extend the shelf life of the samples for up to two months in air-tight polyethylene bags of 0.7mm thickness without losing its quality characteristics. Research Article Effect of storage period on the quality characteristics of two varieties of African Mango Seed Flour at ambient temperature


INTRODUCTION
Irvingia gabonensis and Irvingia excelsa are highly, economically important trees native to most southern rain forest of Nigeria [1]. Both varieties top the list of nontimber forest products being clamored for domestication [2,3], and it is fast becoming the tree of choice in agroforestry practices [4][5][6][7][8].
Irvingia gabonensis and Irvingia excelsa are sometimes called bush mango or African mango because the trees bear mango-like fruits [9]. The fruits are broadly ellipsoid, about 4-7cm long, green when unripe and yellow when ripe with a leshy mesocarp. The fruit pulp is juicy although the taste varies between sweet and bitter [10], and has been shown to have great commercial potentials ranging from the preparation of juices, jams and jellies to wine and soap making [2,4].
Ogbona is widely produced and consumed in Nigeria because of its mucilaginous (draw) property which aids consumption of staple food gels such as tuwo, pounded yam and fufu [11]. 'Ogbono' (Irvingia gabonensis) popularly known as bush mango or African mango or wild mango is an indigenous forest tree belonging to the group of plant classi ied as non-timber forest products [12]. Ogbono (bush mango) belong to the lrvingiaceae family of plant in the species 'gabonensis' of lrvingia. The two species: lrvingia gabonensis var. gabonesis and Irvingia gabonensis var. excelsa have some differences. The pulp of the Irvingia gabonesis var. excelsa is said to be eaten, although bitter and acrid with the lavour of turpentine and slightly slimy. Its kernel (seed) contains 54-67% of fatty matter [13], hence it can be classi ied as an oil seed.
The kernel serves as condiment used in thickening and lavouring soups. The more the ground kernel 'draws' in soup, the more acceptable it is. Thus, Irvingia gabonensis var. excelsa which draws more than the Irvingia gabonensis var. gabonensis and is more acceptable in soup making in Nigeria [12,13]. On the other hand the pulp of the Irvingia gabonensis var. gabonensis is sweet, smooth in the mouth and has brittle pulp but its kernel draws less than that of Irvingia gabonensis var. excelsa [14]. This study therefore investigated changes in some chemical composition, functional and sensory properties of the two varieties of "Ogbona" powder stored at ambient condition.

MATERIALS
Fresh Irvingia gabonensis and Irvingia excelsa and other ingredients were purchased from a local market: Igbona market, Osun state, Nigeria. They were stored in high density polyethylene bags of 0.7mm at ambient condition (30±2'C, 65-74% RH) for a period of 4 months.

Preparation of Ogbono Seeds Flours
Five hundred (500) g of each ogbono seeds were cleaned, sorted, oven dried (50 o C, 24 h) in a local hot air oven to a constant weight. The dried seeds will be milled into ine powder using Merlex Excella dry mill (Marlex Appliances PVT, Daman) and screened through a 0.50 mm British Standard Sieve. Ten bags each of the samples were separately vacuum sealed in air tight, high density polyethylene bags of 0.7mm thickness.

Quality Characteristics
Ten sealed bags each of the ogbono seed lours were properly labeled and stored at ambient condition (30±2 0 C, 65-74% RH) on cleaned trays in an open space covered with net to keep away house hold insects and pests for up to 4 months. Samples were removed at intervals of 0, 1, 2, 3 and 4 months during storage period and were analysed for quality characteristics: proximate composition (peroxide values and free fatty acid), vitamins: A and C; minerals: K, Mg, Na, Fe; functional properties (viscosity, foaming capacity, water and oil absorption capacity) and sensory properties.

Analysis
Determination of Chemical composition: Peroxide value (PV) and free fatty acid (FFA) content were determined using the methods described by Egan et al. [15], proximate constituents; Vit A, C and minerals were determined according to AOAC [16].
Det ermination of Functional Properties: Ground Ogbono seeds lours for selected functional properties were defatted using solvent extraction in a soxhlet apparatus for 10h using n-hexane. Viscosity was determined as described by Fleming et al, [17]. Foam capacity was determined as described by Coffman and Garcia [18] water and oil absorption capacities were determined according to the method of Beuchart [19].

Preparation of Ogbono Soups:
The method of Akusu et al. [13], was used in the preparation of the soups. One hundred (100g) each of ground ogbono seed lour that has been air-tight sealed and frozen for 0, 1, 2, 3 and 4 months were removed at intervals and used in the preparation of ogbono soup, respectively based on the recipe in table 1 and according to the procedure outlined in igure 1. After all the ingredients had been added, the pot was allowed to boil for 30 min to make the soups. The soup is allowed to cool, after 30 min, sensory evaluation was conducted on both soups.

Sensory Evaluation
A panel of twenty consumers comprising of staff and students of the Department of Food Science and Technology who were used to evaluate the sensory properties of the two varieties of Ogbono (Bush mango) soup prepared from their respective seed lours that were stored at ambient temperature (30±2 0 C, 65-74% RH) for 0, 1, 2, 3 and 4 months. The panelists were selected based on their familiarity with sensory qualities of Ogbono soups and were served in Sensory laboratory at room temperature (30±2°C). A nine-point hedonic scale was used to evaluate appearance, taste, aroma, thickness and overall acceptability of the soups, where 1 and 9 represents dislike extremely and like extremely, respectively according to [20] Iwe method. Water was provided to rinse the mouth between evaluations.

STATISTICAL ANALYSIS
All analysis was done in triplicate determinations±SD and means were separated using Duncan Multiple Range Test.

Effe c t of ambient storage on the chemical composition of Irivingia excelsa and Irivingia gabonensis seeds fl our
The chemical composition of Ogbona seed powder of both varieties decreased with storage period tables 2 and 3. There were observable decreases for carbohydrate contents from (33.60±1.04 to 26  3.74±0.02) % for both Irivingia excelsa and Irivingia gabonensis respectively. This may be due to the possible utilization by the associated micro-organisms, slight nutrient depletion, pooled effect of by-products of metabolism and bioconversion into organic acids and other organic compound [21].
For the minerals, there were observable decreases from third to fourth month of storage especially for iron (44.59±1.20 to 44.43±1.15) mg/100g and (34.08±2.12 to 34.03±2.01) and magnesium (0.15±0.00 to 0.10±0.00)mg/10g and (0.05±0.00 to 0.03±0.00)mg/100g in tables 2 and 3. Remarkable decreases in vitamin A and C contents were observed during storage period especially after the 2nd month of storage for both Irivingia excelsa and Irivingia gabonensis respectively. Values for Vitamin A and C were (0.07±0.01 to 0.01±0.00) mg/100g and (0.05±0.00 to 0.00±0.00) mg/100 g; (2.00±0.01 to 1.47±0.00)mg/100g and (1.00±0.02 to 0.01±0.00)mg/100g respectively at zero to fourth month storage for both Irivingia excelsa and Irivingia gabonensis respectively. The general decrease in some of the chemical composition of Ogbona seeds lour with increase in storage period may not be unconnected with depletion of nutrient reserve caused by dehydration, respiration and probably gradual disintegration of Ogbona seed lour with storage period [22][23][24][25].
The effect of storage at ambient temperature on moisture, free fatty acid content and peroxide values of both Irivingia excelsa and Irivingia gabonensis stored for four months is presented in tables 2 and 3. There was no observable decrease in both Irivingia excelsa and Irivingia gabonensis seed lour stored at ambient temperature for up to two months but there were remarkable decreases after third and fourth months of storage at ambient temperature for free fatty acid content (1.05±0.50 to 1.02±0.35) % and (1.30±0.00 to 1.00±0.00) % and peroxide value (55.41±1.80 to 50.77±1.70)  MEq/kg and (45.41±2.32 to 40.77±2.11) MEq/kg. This might be due to the effects of lipid oxidation which causes off-odours and off-lavours, hence the storage life of fatty foods is more limited than non-fatty foods [26]. The observable decrease in Irivingia excelsa and Irivingia gabonensis respectively seed lours after third and fourth months of storage at ambient temperature could also be attributed to the slow diffusion of oxygen through the gas-impermeable polyethylene bag of 0.7mm thickness used in packaging the Ogbono seed lours. Egan et al., 1981 reported that acidity and a [15] rancid taste often begins to be noticeable in foods when free fatty acid content is about 0.5 to 1.5% oleic acid and peroxides values are between 20 to 40 MEq/kg. The result obtained in this study reveals that after four months of storage at ambient temperature (30±2 0 C, 65-74% RH), the free fatty acid contents of both varieties of Ogbono seed lours were slightly above the safe limit while the peroxide values were still within the safe limit.

Effect of ambient (30±2 0 C, 65-74% RH) storage on the functional properties of Irivingia excelsa and Irivingia gabonensis seeds fl our
Effect of storage on some functional properties of water/oil absorption, foam capacity and viscosity of vacuum sealed packaged ground Ogbono seed lours stored for four months at ambient temperature (30±2 0 C, 65-74% RH) is as shown in tables 4 and 5. There was no observable change in the selected functional properties of both Irivingia excelsa and Irivingia gabonensis seed lours stored for up to two months, however all the selected functional properties of both lour samples decreased during the third and four months of storage at ambient temperature. This observation is in agreement with the work of Fellow [27], that there is a slow loss of quality owing to both chemical changes in some foods and enzymic activities during food storage. The viscosity on the other hand decreased from (9.28±0.09 to 7.01±0.07 ) pa/s and (8.98±0.06 to 6.03±0.07 ) pa/s; foam capacity from (2.15±0.32 to 1.20±0.28) ml and (2.00±0.32 to 0.78±0.20 ) ml from 0 and 4months for both Irivingia excelsa and Keywords: Analysis was done in triplicate determinations ± SD. Irivingia gabonensis seed lour respectively.This became pronounced after two months of storage probably be due to increase in crude ibre and ash with possible decrease in pectic and mucilaginous (glycoprotein) substances which may have been caused by respiration with subsequent decrease in carbohydrate and energy [23,28]. Hence, Ogbona seed lour should be consumed after 2 months of storage in order to preserve its nutrients and retain its functional properties.
Eff e ct of ambient (30±2 0 C, 65-74% RH) Storage on the Sensory Properties of

Irivingia excelsa and Irivingia gabonensis Seed Flours
The effects of storage at ambient temperature on the sensory properties of soups prepared from Ogbono seed lours are shown in tables 6 and 7. There was no observable change in the sensory properties of soups prepared from both Irivingia excelsa and Irivingia gabonensis seed lour stored at ambient temperature up to two months. However, after third and fourth months, there was a remarkable change in sensory attributes of taste, aroma, thickness, drawability and overall acceptability of "Ogbono" seed lour. Cardello reported that to the consumer, the most important quality attributes of food are its sensory characteristics [29]. He further concluded that sensory attributes substantially in luence the acceptability of foods. He also stated that the aim of a food processor is to ind improvement in processing technology which retains or create desirable sensory qualities.

CO NCLUSION AND RECOMMENDATION
The results obtained from this study revealed that all the chemical composition, selected functional and sensory properties of both varieties of Irivingia excelsa and Irivingia gabonensis seed lours decreased after two months of storage at ambient temperature. This therefore suggests a need for additional method of preservation in order to extend the shelf life of the seed lour like inclusion of spices, frozen storage and the use of preservatives or irradiation. It is recommended that Ogbona seed lour stored at ambient temperature should be consumed within 2 months of storage in order to preserve the nutrients and retain its functional properties. However, Irivingia excelsa is much more preffered to Irivingia gabonensis because of its higher chemical composition and functional properties. This also agrees with the result of the sensory evaluation on Ogbona seed lour.