Effect of Drying and Roasting on the Quality Attributes of Fufu Powder

Abstract

The effect of drying and roasting on the physicochemical and sensory qualities of fufu powder were investigated. The four samples of fufu: cooked dried fufu, cooked roasted fufu, dried fufu slurry and roasted fufu slurry, respectively, were subjected to physicochemical and sensory analysis. The water binding index, water solubility index, and water absorption index, varies between 3.44 and 0.17 (g/g sample), 0.07 and 0.01 (g/g), and 4.73 and 0.83 (g/g) respectively, while the starch damage and amylose content varies between 50.8% and 0.4%, 10% and 13% respectively, with roasted fufu slurries recording the highest values. The proximate composition of dried and roasted fufu samples showed the values of fat (0.6%–0.4%), protein content (0.2%–0.1%), ash content (37.8%–1.0%), moisture content (8.2%–10.2%), crude fibre (1.25%–8.5%) and carbohydrate content (43.0%–84.65%) respectively. Generally, there were no appreciable differences in the proximate composition of dried fufu samples. The pasting temperature of fufu samples varies from 78 to 95°C with roasted fufu slurries recording the highest values. The peak viscosity of dried fufu samples ranges between (80 and 900BU) and viscosity at 50°C ranges between (260 and 460BU). There are no significant differences (P > 0.01) for the sensory qualities in term of color, taste, and overall acceptability except for odor and texture at (P < 0.01).

Keywords:

• Drying
• Roasting
• Quality
• Fufu powder

Introduction

Cassava plays a very important role in food security of Africa that is the largest cassava‐producing continent in the world.[1] In Africa, cassava is traditionally processed before consumption into various products such as lafun, fufu, gari, pukuru, tapioca, and farinha de mandioca.[2] Fufu, lafun, and gari are the most common and important cassava foods used in Africa especially in West Africa.

Fufu is a fermented wet‐paste from cassava.[3] Fufu is traditionally sold in wet form, which renders it highly perishable. The poor shelf life of fufu is a serious limitation for large‐scale processors. A practical approach to improving the shelf life and marketability of fufu is drying the fufu to a dried product.[4] Okpokiri et al.[5] reported that good quality dried fufu was produced when wet fufu was dried in the oven at 55°C for the first 8 hours and thereafter increasing the drying temperature to 80°C.

Drying of fufu in an oven at 60°C for 48 hours reduced the strong odor of fufu but the product was sticky, bland, and unacceptable compared to wet fufu.[6] Fufu has also been dried using three different drying methods namely sun, cabinet, and rotary drying methods.[7] The effect of these drying methods on the physicochemical and sensory qualities of fufu was studied. However, dried fufu was also reported to be sticky in texture.[7] For this work, the qualities of roasting and cabinet drying of wet fufu slurry and fufu paste leading to fufu powder were investigated.

Materials and Methods

Production of Wet Fufu

Freshly harvested cassava root (11–12 months old; variety TMS 30570, IITA) obtained from the University of Agriculture, Abeokuta farm was processed into wet fufu using the method described by Sanni and Akingbala.[7]

Preparation of Fufu Paste

Wet slurry was cooked directly in an open pan, with constant stirring using a wooden ladle till a strong paste or dough is formed.

Drying of Wet Fufu Slurry and Fufu Paste

Wet fufu slurry and paste were dried in a cabinet dryer (Model LEEC F2). The cabinet dryer consists of an insulated chamber fitted with perforated trays. A system of duct and baffles was used to direct hot air over and through each tray to promote uniform distribution. The drying process was achieved at 65°C for 7 h.

Roasting of Wet Fufu Slurry and Fufu Paste

The traditional roasting method for gari production was adopted. The roasting was done by pressing the wet fufu slurry and fufu paste against the hot surface of the pan, which resulted into pre‐gelatinization of the products. According to Nweke et al.,[1] the roasting method is the simultaneous cooking and dehydration of fermented product like gari where fresh roots are peeled, grated into mash, and then put in sacks. The sacks are pressed, using heavy objects, to express excess liquid from the pulp during fermentation. After 3–4 days, the dewatered and fermented mash is sieved and garified in a pan. Palm oil is often added during garifying to prevent burning. Addition of oil also changes the color of the product from white to yellow. The roasting process was achieved at 120°C for 20 min. The dried products were further cooled, milled, sieved, and packed in polythene bag.

Methods

Proximate Composition

The proximate composition was determined according to AOAC (8).

Water Absorption Index and Water Solubility Index

Water absorption index and water solubility index were assessed using the method of Ruales et al.[9] 2.5 g of dried fufu was suspended in 30 mL distilled water at 30°C in a 50 mL centrifuge tubes, stirred for 30 min intermittently and than centrifuge at 3000 rpm for 10 min. The supernatant was decanted and the mass of the gel was taken. The supernatants were dried in the evaporating dish at 105°C for 4 hours. The water absorption index was calculated as grain bound water/2.5 g of dried sample and the water solubility index was calculated as the mass of dry solid after drying/2.5 g of dried sample. Determinations were in triplicate.

Starch Damage

The starch damage was determined using standard method in AOAC.[8] Dissolving 0.5 g flour samples along with 20 mL of extractant made sample solution. Extraction of the flour sample was carried out for 15 min by shaking each flask for 10 seconds every 3 min at 30°C and filtered. Two milliliter of filtrate was pipette into 25 mL volumetric flask containing 15 mL‐distilled water at 21°C and 1 mL iodine solution. The mixture was allowed to stand for 10 min and absorbance measured at 600 nm against blank using a spectrophotometer (NOVA SPEC II, England). Starch damage was determined using the regression equation of Farrand (1964):

The analyses were in triplicate.

Water Binding Capacity

Water binding capacity was determined using the method of Medcalf and Gillies.[10] Fufu samples (2.5 g) were weighed into a 50 mL centrifuge tube. Distilled water (37.5 mL) was added. The tubes were capped and agitated manually for 1 h then centrifuged for 10 min at 7500 rpm. The supernatant was decanted and the tubes were allowed to drain for 10 min. The mass of centrifuge tube with content were determined and the amount held by starch, determined by difference. The water binding capacity was calculated as gram bound water divided by 2.5 g. Determinations were in triplicate.

Amylose

A method described by Williams et al.[11] was employed. A rapid colorimetric method for estimating amylose content of starches and flours was employed. An aliquot of the starch solution was put into a 50 mL volumetric flask with addition of 5 mL of 0.l N HCl and 0.5 mL of iodine reagent. The volume was diluted to 50 mL and the absorbance measured at 620 nm after 5 min and amylose content calculated as:

The analyses were in triplicate.

Pasting Characteristics

The procedures of Mazurs et al.[12] were followed for studying the Pasting properties. The Pasting properties were determined with a Brabender Viscoamylograph (Model 486044, Brabender OHG Duisburg, Germany) equipped with a 700–CMG sensitivity cartridge. Bowl speed was 75 rpm. The sample was suspended in 360 mL‐distilled water in a 450 mL Brabender bowl. The temperature was raised at l.5°C/min from 30°C to 95°C allowed to remain for 30 min at 95°C and cooled to 50°C at the same rate. Pasting temperatures were read from the viscograph. The analyses were in triplicate.

Sensory Evaluation

Ten trained panelists, who were familiar with the product as acceptable in the locality, carried out the sensory evaluation of the samples produced under the various drying and roasting conditions. Fufu was prepared by first reconstituting the powder in water at a ratio of 2:3 and cooked on fire, with constant stirring using a wooden ladle till a consistent paste was formed. Cooked fufu samples were coded with 3‐figure random numbers and presented in random order to each taster at ambient room conditions (25–30°C). Evaluations were made on a five‐point hedonic scale for intensity of color, odor, and texture with score “5” having excellent attributes similar to normal and “1” indicating high characteristic difference from normal.[13] Panelists independently examined the samples and record their impressions. The final scores represented the average of all panelists' impression, as agreed in open discussion.

Statistical Analysis

Data were analysed using Analysis of Variance (ANOVA) and means separated using Duncan's Multiple Range Test. These analyses were carried out using a statistical package (MINITAB 1989, Version 7.0).

Results and Discussion

Effect of Drying and Roasting Methods on the Proximate Composition of Dried Fufu

The result of the effect of drying and roasting of fufu slurries on the proximate composition of dried fufu is presented in Table 1. There were no significant differences (P > 0.05) in the fat (0.4–0.6%) and protein (0.1–0.2%) contents of the fufu samples, which may be due to the fact that fufu is mainly a carbohydrate source.[3] However, there were significant differences in the ash, moisture, crude fibre, and carbohydrate contents of wet and fufu flour samples. Meanwhile, the values for the moisture content of dried and roasted fufu samples were very close (8.2–10.2%, db). Generally, the control fufu samples (wet fufu) have very close values of fat, protein when compared with dried and roasted fufu samples.

Table 1. Effect of drying and roasting on the proximate composition of dried fufu

Samples	Ash (%)	Moisture (%)	Crude Fibre (%)	Carbohydrate (%)
Wet fufu slurry	2.2d	50.0b	6.5c	45.7b
Cabinet dried fufu slurry	1.0d	8.2a	1.9a	81.3a
Paste dried fufu slurry	4.0c	9.4a	1.4b	84.7a
Unsieved roasted fufu slurry	37.8a	10.2a	8.5c	43.0b
Sieved roasted fufu slurry	17.3b	9.6a	1.3b	70.3a

Note: Means with same letters in the same column are not significantly different (P > 0.05), n = 3.

Effect of Drying and Roasting on the Physicochemical Properties of Dried Fufu

The effect of drying and roasting on the physicochemical properties of dried fufu are presented in Table 2. There were significant differences (P < 0.05) in the physicochemical properties studied except for amylose. The water absorption index ranges from 4.73 g/g for sieved roasted fufu slurry; 4.57 g/g for paste dried fufu slurry; 4.53 g/g for unsieved roasted fufu slurry and 1.46 g/g for cabinet dried slurry. However, wet fufu slurry recorded the lowest value of 0.83 g/g. Generally, the highest water absorption index occurs in the sieved roasted fufu slurry. High water absorption index is attributed to loose structure of the starch polymer,[14] that might have been caused due to stress created to the native starch structure of fufu during drying or roasting. The water solubility values are 0.01 g/g for wet fufu slurry and cabinet dried fufu slurry while paste dried fufu slurry recorded higher value of 0.07 g/g. The values for roasted fufu samples were extremely low. The water binding index is highest in sieved roasted fufu slurry (3.44 g/g), followed by unsieved roasted fufu slurry (3.22 g/g), paste dried fufu slurry (2.81 g/g), cabinet dried fufu slurry (0.39 g/g) and wet fufu slurry (0.17 g/g). The values of starch damage showed an increased in the fufu flour samples compared to the wet slurry. The values are 0.41%, 0.56%, 34.67%, 34.23%, and 50.79% for wet fufu slurry, cabinet dried fufu slurry, sieved roasted fufu slurry, unsieved roasted fufu slurry, and paste dried fufu slurry, respectively. The values of amylose content are 13.0, 12.8, 12.4, 11.8, and 10.7% for wet fufu slurry, sieved roasted fufu slurry, unsieved roasted fufu slurry, paste dried fufu slurry, and cabinet dried fufu slurry, respectively. There seems to be higher values for some physicochemical properties determined for roasted and dried fufu slurries compared to the wet fufu slurry. Also, sieving shows appreciable effects on the properties determined for roasted fufu slurries. The reduction in the physicochemical properties of wet fufu may be due to strong interactions in its native starch granules thereby reducing its surface energy[15] contrary to the processed fufu samples whose native starch granules might have been altered thereby affecting its association.

Table 2. Effect of drying and roasting on the physicochemical properties of dried fufu

Samples	Water absorption index (g/g solids)	Starch damage (%)	Water binding index (g/g solids)
Wet slurry	0.83c	0.4c	0.17b
Cabinet dried slurry	1.46b	0.6c	0.39b
Paste dried slurry	4.57a	51a	2.81a
Unsieved roasted slurry	4.53a	34b	3.22a
Sieved roasted slurry	4.73a	35b	3.44a

Note: Means with same letters in the same column are not significantly different (P > 0.05), n = 3.

Since leaching of amylose is responsible for most of the solubility of starch based product,[16] higher solubility implies higher leaching while lower solubility implies less leaching, which in fermented product means either that some of the amylose was hydrolysed and lost during processing such as fermentation, drying or cooking process or that its leaching is enhanced or hindered by new internal bonding.[17] The increase in solubility observed for fufu flour samples might be due to loss in the amylose fraction during processing.

Effect of Drying and Roasting on the Pasting Properties of Dried Fufu

Effect of drying and roasting on the pasting properties of dried fufu are shown in Table 3. The fufu samples started to form paste between 52.7 and 58°C with the cabinet dried fufu slurry recording the highest pasting temperature. The paste dried fufu slurry, sieved roasted fufu slurry and cabinet dried fufu slurry reached the pasting time within the shortest period of 11.0, 15, and 16.5 min, respectively faster than unsieved roasted fufu slurry and wet slurry.

Table 3. Effect of drying and roasting on the pasting properties of dried fufu

Pasting properties	Wet fufu slurry	Paste dried fufu slurry	Cabinet dried fufu slurry	Sieved roasted fufu slurry	Unsieved roasted fufu slurry
Pasting temperature (°C)	75 ± 0.4	53 ± 0.4	78 ± 0.3	77 ± 0.4	76 ± 0.4
Pasting time (Mg) min	20 ± 0.2	11 ± 0.3	17 ± 0.4	15 ± 0.2	23 ± 0.2
Temperature at peak viscosity (Tvp) °C	86 ± 0.2	95 ± 0.2	80 ± 0.2	79 ± 0.2	91 ± 0.2
Peak viscosity during heating (Vp) BU	900 ± 70.7	80 ± 70.4	780 ± 70.5	460 ± 70.7	320 ± 70.7
Time to reach peak viscosity (Mn) min	26 ± 0.2	38 ± 0.3	22 ± 0.4	22 ± 0.2	26 ± 0.2
Viscosity at 95°C BU	900 ± 70.7	140 ± 70.7	760 ± 70.7	440 ± 70.7	340 ± 70.7
Viscosity after 15 min holding at 95°C (Vr) BU	625 ± 14.1	160 ± 14.0	420 ± 14.1	320 ± 14.1	340 ± 14.1
Viscosity on cooling to 50°C (Ve) BU	400 ± 14.1	260 ± 14.2	460 ± 14.1	435 ± 14.1	440 ± 14.1
Ease of cooking (Mn–Mg) min	6	7	6	7	3
Stability of the starch (Vp–Vr) BU	275 ± 56.6	−80 ± 56.4	320 ± 56.4	140 ± 56.6	20 ± 56.6
Set back value (Ve–Vp) BU	−500 ± −56.6	−180 ± −56.2	−320 ± −56.4	−25 ± −56.6	−120 ± −56.6
Pasting index (Ve–Vr) BU	775	100	40	115	100

Note: Standard deviation, n = 3.

The highest values were obtained in the peak viscosity of the wet slurry (900BU) followed by cabinet dried fufu slurry (780BU), sieved roasted fufu slurry (460BU), unsieved roasted fufu slurry (320BU), while the lowest value was obtained in the paste dried fufu slurry, showing that the starch granules of the paste dried fufu slurry were seriously damaged. The wet fufu slurry, cabinet dried fufu slurry and sieved roasted fufu slurry showed the highest values of viscosity at 95°C, followed by unsieved roasted fufu slurry and paste dried fufu slurry. This is indicative of resistance to shear stress by paste obtained during heating,[18] which is related to the method of producing fufu flour.

The ease of cooking is lowest in unsieved roasted fufu slurry, followed by wet fufu slurry and paste dried slurry of 5.5 min; while the sieved roasted slurry is 6.5 min and paste dried slurry is 27 min, respectively. The processed fufu samples has the highest tendency for retrogradation as manifested in the amount recorded for set back value, where sieved roasted fufu slurry, unsieved roasted fufu slurry, paste dried fufu slurry, and cabinet dried fufu slurry have the highest values compared to wet fufu slurry. The higher the set back value the higher the retrogradation tendency and the higher the tendency of the product to become hard during cooling or storage.[19]

Effect of Drying and Roasting on the Sensory Qualities of Dried Fufu

There were no significant differences in color (5.4–6.6), taste (5.8–6.7) and overall acceptability (6.0–6.2) of fufu samples, except for texture and odor (Table 4). The wet fufu slurry was rated highest in texture followed by unsieved roasted fufu slurry and cabinet dried fufu slurry, respectively. As there was a significant difference in the sensory texture of dried fufu, there are also comparable variations in the stability and set back values of fufu flour samples (Table 3). The odor of wet fufu recorded the lowest value compared to other values for dried and roasted fufu samples. During discussions with panelists, they indicated that fufu flour samples were rated higher due to the reduction in the level of their offensive odor as compared to wet fufu. Sanni et al.[18] had reported that butanoic acid was responsible for the offensive odor in wet fufu and that drying at 65°C, 4 m/s and 60% RH were adequate to reduce the concentrations of butanoic acid after drying. Drying (65°C) and roasting (120°C) employed in this study were adequate enough to reduce the offensive odor in fufu, thereby enhancing their acceptability by the consumers.

Table 4. Effect of drying and roasting on the sensory texture and odor of dried fufu

Samples	Texture	Odor
Wet fufu slurry	6.6 ± 0.5a	5.8 ± 0.5b
Cabinet dried fufu slurry	6.2 ± 0.1a	6.4 ± 0.1a
Paste dried fufu slurry	5.8 ± 0.2b	6.2 ± 0.2a
Unsieved roasted fufu slurry	6.4 ± 0.1a	6.2 ± 0.1a
Sieved roasted fufu slurry	5.8 ± 0.2b	6.1 ± 0.2a

Note: Means with same letters in the same column are not significantly different (P > 0.05), n = 10, ±standard deviation.

Conclusion

The research work has revealed that the proximate, functional, and pasting properties of roasted and dried fufu samples compared to wet slurry are processing‐dependent. The sensory qualities show that there is no significant difference for the color, taste, and overall acceptability (P > 0.01) except for odor and texture. This research has shown that cassava processors are at advantage of utilizing various drying regimes for the production of fufu. The other advantages of the improved drying method are hygienic production, high quality, long‐term storability, and a good taste. From the economic aspect, roasting and drying process would facilitate the use of cassava roots on a large scale for the production of fufu and an improvement in the income of cassava producers. It could assure an increase in consumption of fufu and, in consequence, that of cassava roots.

Acknowledgment

LOS acknowledges the financial support by the International Foundation for Science, Sweden.