Fleshed Sweet Potato Flour Amajor, J.U.*, Oti, E., Ekeledo, N., Omodamiro R., Amajor, E.E., Aniedu, C

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Nigerian Food Journal Official Journal of Nigerian Institute of Food Science and Technology www.nifst.org NIFOJ Vol. 32 No. 1, pages 45 – 53, 2014

Studies on the Characteristic Properties of Fermented, Sun-Dried Orange- Fleshed Sweet Potato Flour Amajor, J.U.*, Oti, E., Ekeledo, N., Omodamiro R., Amajor, E.E., Aniedu, C.

ABSTRACT Microbiological, functional, chemical and sensory properties of flours of two (2) cultivars of orange-fleshed sweet potato (centinnial and CIP 440293) being multiplied for distribution in South East and South-South Nigeria were investigated using standard techniques. The flours were observed to have good functional properties and high dry matter contents which were respectively 88.09 ± 0.00% and 86.0 ± 0.00%. The respective values for fat content (0.85 ± 0.00% and 1.75 ± 0.00 %), ash content (2.04 ± 0.00% and 2.40 ± 0.42%) and crude fibre content (2.90 ± 0.28% and 2.67 ± 0.00%) were low but the respective levels of carotenoids values (3.74 ± 0.00 and 5.28 ± 0.00 µg/g) were high indicating a promising source of pro-vitamin A. The sensory evaluation had no statistical difference among the parameters. The flours had high nutritive values with good functional and sensory properties. The microbial loads were within the acceptable limit of < 105 recommended by ICMSF, making the flour samples microbiologically safe and with appropriate packaging, the shelf life could be extended under good storage conditions.

Keywords: Orange-fleshed sweet potato, flour, sun-drying, physicochemical properties, functional properties.

Introduction population and pressure on land utilization (Woolfe, Sweet potato (Ipomoea batatas (L.) Lam) belongs to 1992). Increased production and consumption the convolvulaceae family and is a root crop cultivated of the oranged-fleshed sweet potato roots rich in in many countries. It is grown extensively in the β-carotene would improve the nutritional status of tropical and subtropical zones (Islam et al., 2002). the Nigeria population. With recent introduction Sweet potato has become an important global of orange-fleshed sweet potato OFSP varieties crop and is grown in diverse ecologies (Firon et al., having high beta-carotene from high land areas 2009) with a long history as a life saver. It has been of East Africa, there has been an upsurge of recognized as having an important role to play in interest to include the roots and leaves as part of improving household and national food security, the food based strategy to compensate vitamin A health and livelihoods of poor families in sub- deficiency in Nigeria. The clamour for the OFSP is saharan Africa (CIP, 2009). This is due to its wide due mainly to the health advantages over the white range of agronomic and nutritional advantages fleshed cultivars. The better health engendered by capable of combating the food shortages, mal- consumption of orange-fleshed sweet potato will nutrition that may arise as a result of increase in ultimately translate to reduced expenditure on hospital bills, provision of sound body to engage National Root Crops Research lnstitute, Umudike, Umuahia, in productive activities leading to more income Abia State corresponding author: [email protected] generation in rural communities (Echendu et al., 46 Nigerian Food Journal Vol. 32 No. 1, 2014 ... Full Length Article

2011). There is need to promote the consumption Research Institute, Umudike, Umuahia, Abia State, of OFSP involving households with young children Nigeria. Two orange-fleshed sweet potato cultivars: in rural areas in Nigeria in regular consumption Centinnial and CIP 440293 were harvested at of OFSP which is rich in β-carotene, significantly maturity from the field trial of the institute. alleviates the vitamin A deficiency in children (Low Processing and storage of orange-fleshed et al., 2007). It is also important to create awareness sweet potato flour on marketing and consumption of OFSP in Fresh undamaged oranged-fleshed sweet potato Nigeria where new ways of consuming OFSP such roots were washed with tap water peeled and as confectionery products; its use in bread making chipped into 2 mm-thickness slices with the use will produce nutritional benefits. Prolonged storage of a manual chipping machine. Fermentation for a is achieved by drying (usually sun-drying) slices. period of 24 h was carried out (Achi and Akubor, During the period of drying, microorganisms settle 2000). After steeping, the chips of each variety on the exposed surfaces of the slices and the high were laid out on clean polythene sheets for sun- moisture of the sweet potato permits the growth drying. Each variety was sun-dried for 6 days with of these microorganisms during sun-drying. Sweet- an average temperature of 32.9oC during the dry potato flours are refined products from sun-drying season. After sun-drying, the fermented chips were which are produced by a milling machine. Orange- pulverized using a milling machine into flour with fleshed sweet potato flour produced by grinding particle size of about 200 µm and the resulting flour dried sweet potato slices could either be used as was sieved with muslin cloth to obtain a fine flour. whole flour or as a composite. Orange-fleshed The flours were properly packaged in cellophane sweet potato flour being a food product with bags (1 kg) per bag, sealed and stored at ambient high nutritional content can harbour a variety of temperature (28 ± 2oC) for 12 weeks (3 months). bacteria including pathogenic and non-pathogenic From which samples were taken for microbial, forms (Berghofer et al., 2003). Micro-organisms chemical, functional and sensory evaluations at can cause diseases and food spoilage whenever monthly intervals. they exceed their threshold as a result of increase in certain parameters such as moisture (Delong, Microbiological analysis 2001). Fresh roots can not be stored beyond three Total viable counts of microorganisms in the months under ambient temperature (Tomlins et orange-fleshed sweet potato flours were done by al., 2007). The processing of the roots into chips pour plate techniques (Morton, 2001). Five grams and flours could extend the shelf life of the sweet of the flours were dissolved in 45 ml sterilized potato for more than three months. There is scanty water to obtain a dilution of 1:10, from which information on the microbial, functional, chemical subsequent dilutions were made and appropriate and sensory properties of fermented and sun- aliquot used to determine the total viable counts dried flours of orange-fleshed sweet potato which (TVC) on Trypton soya agar plates incubated at can be utilized as composite or whole flour. It is 37oC for 48 h while potato dextrose agar plates therefore the objective of this study to evaluate the used for the fungal counts were incubated at 25oC microbiological, chemical, functional and sensory for 72 h. At the end of incubation period, colony properties of the fermented, sun-dried orange forming units (cfu/g) were estimated using colony fleshed sweet potato flour. counter. Colonies were purified by sub-culturing on fresh Trypton soya Agar and gram stained for Materials and Methods morphological examination and biochemical tests Materials (Catalase, coagulase, oxidase, citrate, glucose, sucrose, The study was carried out in the post harvest mannitol, lactose, maltose, and inositol) were done for technology programme of National Root Crops characterization and identification of the isolates, Studies on the Characteristic Properties of Fermented, Sun-Dried Orange-Fleshed Sweet Potato Flour ... Amajor et al. 47 as described by Buchanan and Gibbons (1975). Analysis of the functional properties of the flour The colonies of the fungi emerging within 2-5 samples days of inoculation were identified under the light Gelatinization Temperature (GT) microscope (× 40) and recorded using the scheme The method of Onwuka (2005) was used for of Barnett and Hunter (1992). Each experiment gelatinization temperature determination. A 10% was performed in triplicates. flour suspension of each sweet potato cultivar Chemical analyses of orange-fleshed sweet was prepared in a test tube. The suspensions were potato flours heated in a boiling water bath with continuous The flour products were stored at ambient stirring. The temperature at which gelatinization temperature for 12 weeks before samples were taken was observed was recorded as the gelatinization from the stored products for chemical, functional temperature (GT) after 30 sec. properties and sensory evaluation. Oil Absorption Capacity (OAC) The ash, moisture/dry matter, fat and crude fibre The oil absorption capacity of the flour samples contents were determined by the AOAC (2000) were determined using the method of Beuchat methods. (1977) as modified by Adepeju et al. (2011). One gram of each flour sample was mixed with 10 ml Total carotenoids content analysis of oil (pure canola) for 60 sec. The mixture was The Harvest Plus procedure for β-carotene analysis allowed to stand for 10 min at ambient temperature, was used to analyze the total carotenoids content centrifuged at 4000 x g for 30 min and the oil that of the fresh orange-fleshed sweet potato roots and separated was carefully decanted. The tubes were the orange-fleshed sweet potato flour. Five grams allowed to drain at an angle of 45oC for 10 min of each fresh root sample was ground with the and then weighed. Oil absorption capacity was aid of hyflosupercel in 50 ml of cold acetone and expressed as percentage increase of the sample filtered with suction through a Buchner funnel with weight. filter paper; the filtrate was extracted with 40ml of petroleum ether (P.E) using separating funnel. Water Absorption Capacity (WAC) Saturated sodium chloride solution was used to One gram of each flour sample was dispersed in 10 prevent emulsion formation. ml of distilled water in a graduated centrifuge tube. The samples were thoroughly mixed for 30 sec and The lower phase being water was discarded while the allowed to stand at ambient temperature for 30 upper phase was collected into a 50 ml volumetric min. The volume of the supernatant was measured flask, making the solution pass through a small directly from the graduated centrifuge tube. The funnel containing anhydrous sodium sulfate to amount of the water absorbed was multiplied by remove residual water. Then, the separating funnel the density of water (1 g/ml) and results were was washed with P.E and the standard flask made expressed as g/100 g (Onwuka, 2005). up to 50 ml mark. The absorbance of the solution at 450 mµ was taken using spectrophotometer and Bulk Density (BD) the total carotenoids content was calculated as The method of Okezie and Bello (1988) was used follows: to determine the bulk density. A graduated cylinder of (10 ml) previously tarred was gently filled with 4 1% Total carotenoid (µg/g) = ( A × V × 10 )/( A1cm the sample. The bottom of the cylinder was gently × W (g)) tapped on a laboratory bench several times until Where A = absorbance, V = total volume of there was no further diminution of the sample 1% levels after filling to the 10 ml mark. The bulk extract (50 ml), W = Sample weight (g) A1cm = absorption coefficient ofβ -carotene in P.E. (2590) 48 Nigerian Food Journal Vol. 32 No. 1, 2014 ... Full Length Article density of the samples was calculated as weight of acceptability using a 9-point hedonic scale, 9 for the sample per unit volume of sample (g/ml). like extremely, 5 for neither like nor dislike and 1 for dislike extremely. The flour samples were Swelling Index (SI) reconstituted using 250 ml of boiled clean water Ten grams of each flour sample were weighed into (100oC) to 100 g of flour samples; which was stirred a calibrated measuring cylinder. Then, 80 ml of continuously until the consistency was thick and water was added and the cylinder was gently tapped brought to doneness; the dough (fufu) was rolled, to remove air void after which the initial volume wrapped, labelled and put in a food warmer for the was recorded. The cylinder containing the sample panelists. in water was allowed to stand for 1 h undisturbed at room temperature (25oC). At the end of 1 h, the Statistical analysis swelling capacity of the sample was expressed as an Data was subjected to analysis of variable using index, that is, the ratio of the final volume (Narayana the “Statistical Package for Social Sciences” (SPSS) and Narasinga, 1982). Measurement were made in version 15.0. Statistically significant differences duplicates and average values recorded. (p < 0.05) among meals were separated using the Sensory evaluation Duncan multiple range text. The sensory evaluation of the oranged-fleshed Results and Discussion sweet potato flour samples were determined using The results of Tables 1 and 2 show the total viable the method of Larmond (1977). A 20-member counts for bacteria and fungi observed in the panel comprising semi-trained panelists were used fermented and sun-dried flours of orange-fleshed for sensory evaluation. The scores were based on sweet potato cultivars, after processing (0-week) the degree of preference of organoleptic qualities and during storage at ambient temperature (28 ± of colour, odour, texture, moudibility and overall 2oC ) for 12 weeks.

Table 1: Total viable count (cfu/g) of flours produced Table 2: Total fungal count (cfu/g) of flours from orange-fleshed sweet potato cultivars produced from Orange fleshed sweet potato cultivars Total viable counts (cfu/g) Total fungal counts (cfu/g) Months of Week 0 Week 4 Week 8 Week 12 storage Months of Week 0 Week 4 Week 8 Week 12 storage Samples samples Centinnial 4.3 × 105 6.6 × 105 7.3 × 105 9.3 × 105 Centinnial 4.0 × 103 4.3 × 103 5.6 × 103 7.3 × 103 CIP 440293 3.3 × 105 4.0 × 105 6.3 × 105 7.6 × 105 CIP 440293 2.3 × 103 3.0 × 103 6.3 × 103 8.0 × 103 Values are means of triplicate determinations Values are means of triplicate determinations

The total viable counts of the centennial and 103 and 2.3 × 103 (Table 2) which also increased CIP 440293 flour samples after processing were gradually to 7.3 × 103 for centinnial and increased respectively 4.3 × 105 and 3.3 × 105 (Table 1) to 8.0 × 103 for CIP 440293. The centinnial cultivar and increased during storage ranging from 4.3 × was more susceptible to bacterial growth while 105 to 9.3 × 105 for centinnial cultivar and 3.3 × CIP 440293 was susceptible to fungal growth at 105 to 7.6 × 105 for CIP 440293. The total fungal week 12. The study revealed a gradual microbial counts after processing were respectively 4.0 × increase during storage, which could be attributed Studies on the Characteristic Properties of Fermented, Sun-Dried Orange-Fleshed Sweet Potato Flour ... Amajor et al. 49 to contamination due to packaging and storage plate count and 103 for fungal count). ICMSF environment. However, the moisture content for recommended limit of microbial contaminants centennial and CIP 440293 flours were respectively for food of less than 105 cfu/g. Table 3 shows 11.1% and 12.0% and was not high enough to the dominant microorganisms isolated from the produce any harmful effect. The values of the samples. The organisms were Staphylococcus aureus, TVC and total fungal count (TFC) obtained were Lactobacillus bervis, Bacillus cereus, Aspergillus niger, and within the recommended range of 30 – 250 cfu/g Rhizopus stolonifer. The presence of Staphylococcus (ICMSF, 1978). This makes the flour product safe aureus in the samples could be due to contamination and acceptable for formulation of foods. The flour from handlers during processing. And its presence products obtained from the sweet potato cultivars has been associated with fermented foods of plants had total plate count and total fungal count within origin (Adams and Moss, 1995). the limit recommended by ICSMF (< 105 for total Table 3: Morphological and biochemical characteristics of bacterial and fungal isolates Cultural and morphological Gram Mortility Catalase Coagulase Oxidase Citrate Glucose Sucrose mannitol Lactose Maltose lnositol characteristic reaction Wet, shiny +ve _ + + _ _ A + A _ A + Staphylococcus aureus surface, regular smooth raised clonies 1-2um Gray +ve rods _ + _ + + A A A A A _ Bacillus cereus round, wavey edge flat and irregular rods 2-5um on TSA White to +ve _ _ _ _ _ + + + + _ _ Lactobacillus bervis cream round rough-edged colonies, slightly rocished with dull appearance

FOR FUNGI Cultural ldentification Staining Identified Isolates Black, + ve with hyphae Aspergillus niger irregular roughened and powdery Gray-white, + ve with hyphae Rhizopus stolonifer brown-Black patches. Hyphae rapidly cover the madia KEY: += positive, - = negative, A = acid production. 50 Nigerian Food Journal Vol. 32 No. 1, 2014 ... Full Length Article

Bacillus cereus is a frequent inhabitant of the soil processors/handlers; it determines the shelf life and leaf surfaces. Its presence in the flours might of foods and brings about organoleptic changes in be due to sun-drying on the ground. The isolation stored foods (Berghofere et al., 2003). of fungi like Aspergillus niger and Rhizopus stolonifer The result of the chemical composition of the stored as well as Bacillus cereus and Staphylococcus aureus is orange-fleshed sweet potato flours is presented in also in agreement with the finding of Akinreleet al. Table 4. Moisture is an important parameter when (1970) who worked on a traditional African starch considering flour quality because it significantly cake, Eko. affect the shelf life and growth of the microbes The low microbial counts recorded from the samples (ICMSF, 1998). The moisture level (11.1 – 12.0%) is likely to preclude them from causing health hazard attained in this study is in agreement with Codex and the high temperature commonly involved in Alimentarius Standards (1995). This indicates that preparation of confectionaries (cooking, frying) is moisture is important when considering flour sufficient to eliminate them. The total viable count quality. The low moisture content of the flour is a is used as an indicator of bacterial population on good attribute for storage quality. This agrees with a sample; the level of hygiene practised by food the report of Destrosier (2004), that low moisture content prolonged storage.

Table 4: Chemical composition of stored orange-fleshed flours Sample Moisture % Fat % Ash % Crude fibre % Carotenoids ( µg/g) Centinnial 11.1 ± 0.00a 0.85 ± 0.00a 2.04 ± 0.00a 2.90 ± 0.28a 3.74 ± 0.00a CIP 440293 12.0 ± 0.00b 1.75 ± 0.07b 2.40 ± 0.42a 2.67 ± 0.00a 5.28 ± 0.00b Values with different superscripts down each column are significantly different (p < 0.05) Values are means of duplicate determinations.

The fat contents were 0.85 and 1.75% for centinnial 0.05) difference between the cultivars. The crude and CIP 440293, respectively. There was significant fibre is important in the diet, since it increases difference (p < 0.05) in the fat content between the faecal output, lowers faecal pH and the daily the cultivars’. Some microorganisms may have excretion (Cummings et al., 1996) and prevents utilized some level of fat to thrive during steeping gastrointestinal diseases in man. (fermenting) (Talaro and Talaro, 2002). Ash content The total carotenoids content of the orange- refers to the mineral content of the flours. There fleshed sweet potato flours as shown in Table 4 was no significant difference in the ash content indicates some good level of carotenoid content between the two cultivars. retention during storage. The carotenoid content The ash contents were low and this may be of the fresh orange-fleshed sweet potato were attributed to leaching during steeping. Sun-drying 13.68 µg/g for centinnial and 12.45 µg/g for CIP at high temperature for 6 days may also have 440293, respectively. The carotenoid values after effect on the ash content since heat strongly affect storage were 3.74 and 5.28 µg/g for centinnial and some minerals such as phosphorus, and calcium CIP 440293, respectively. The percentage retention (Ihekeronye et al., 1985). of carotenoid during storage. This is about 27.3% Crude fibre content of the flours were low with for centinnial and 42.4% for CIP 440293. There values 2.90% and 2.67% for centinnial and CIP was significant (p < 0.05) difference between the 440293, respectively. There was no significant (p > cultivars, CIP 440293 having a higher retention of Studies on the Characteristic Properties of Fermented, Sun-Dried Orange-Fleshed Sweet Potato Flour ... Amajor et al. 51 carotenoid content during storage. The carotenoid starch-based food products such as stability, values obtained in this work were better when texture and digestibility (Tsakama et al., 2010). compared with yellow roots cassava fufu flours that Gelatinization is the temperature at which starch gave 1.20 – 2.00 µg/g (Omodamiro et al., 2012). molecules in a food substance lose their structure The level of sun-drying may have contributed to the and leach out from the granules as swollen amylase. reduction of carotenoid content in agreement with Gelatinization affects the time required for the the report of Bechoff et al., (2009) that carotenoid cooking of food. The gelation temperature of losses from sweet potato chips during sun-drying the flour samples were 089.0 C and 87.50C. With are usually low and that losses of carotenoid are this gelation temperature the flour samples can be more critical during storage. However, losses incorporated in food formulation that requires such could have been sustained during processing as gelation temperatures such as in bread making. the carotenoids are sensitive to heat treatments The oil absorption capacity of the flours contained (Rodriguez-Amaya and Kimura, 2004). considerable levels of oil absorption capacity. Table 5 shows the functional properties of the The values were 1.45% and 1.90% for centinnial flours. Functional properties help to determine the and CIP 440293 cultivars, respectively. The water behaviour of nutrients in food during processing, absorption capacity values were 2.20% and 2.50%, storage and preparation, since they affect the overall respectively. The water absorption capacity helps quality of foods, as well as their acceptability. to determine the ability of the flours to absorb water and swell for improved consistence in food. Gelation is one of the important factors that Flours are used as food ingredient because of their determine starch behaviour in various food and interaction with water (Nide et al., 2001). Bulk industrial applications. It affects the quality of

Table 5: Functional properties of stored orange-fleshed sweet potato flours Sample Gelatinization Bulk Density (g/ml) Swelling Water Oil Absorption Temperature (0C) Index (%) Absorption Capacity (%) Capacity (%) Centinnial 89.0 0.59 175 2.20 1.45 CIP 440293 87.5 0.52 136 2.50 1.90 Values are means of duplicate data. diversity of the flours are 0.59 g/ml and 0.52 g/ Table 6 shows the sensory evaluation of the ml for the cultivars, respectively. This indicates the orange-fleshed sweet potato flours. There were no flours heaviness and its suitability to be used for significant (p > 0.05) differences in the colours, production of confectioneries. Increase in bulk odour, mouldibility, texture and overall acceptability density offers a greater advantage for packaging. of the flours of the two cultivars. The result Hence greater quantity may be packed within a revealed that the flours had no much difference in constant volume (Fagbemi, 1999). The swelling all the parameters and were acceptable. The quality indices were 1.75% and 1.36%, respectively. This is of flours and storage condition after milling is vital related to associative binding within starch granules, in shelf life and sensory properties of the flours strength and character of the micelle network (Akpe et al., 2010). as related to the amylose content. High amylose content produces low swelling index (Adebowale, et al., 2005). 52 Nigerian Food Journal Vol. 32 No. 1, 2014 ... Full Length Article

Table 6 : Sensory evaluation of stored orange-fleshed sweet potato flours Sample Colour Odour Moldibility Texture Overall acceptability Centennial 3.5 ± 0.70a 4.5 ± 0.70a 4.5 ± 0.20a 5.0 ± 1.40a 4.5 ± 0.70a CIP 440293 4.0 ± 1.40a 5.5 ± 1.40a 5.0 ± 0.00a 5.5 ± 0.70a 5.5 ± 0.70a

Means with different superscripts along each column are significantly different (p < 0.05). Values are means of the duplicate experiments.

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