Changes in nutritional composition, functional, and sensory properties of yam flour as a result of presoaking

Adewale Olusegun Obadina; Bukunola Olaide Babatunde; Ifeoluwa Olotu

doi:10.1002/fsn3.150

. 2014 Jul 30;2(6):676–681. doi: 10.1002/fsn3.150

Changes in nutritional composition, functional, and sensory properties of yam flour as a result of presoaking

Adewale Olusegun Obadina ^1,^✉, Bukunola Olaide Babatunde ¹, Ifeoluwa Olotu ¹

PMCID: PMC4256572 PMID: 25493185

Abstract

This study investigated the effect of soaking pretreatments on some of the properties of flour obtained from two varieties of yam namely;Dioscorea alata andDioscorea rotundata with a view of providing information that will enhance their end use. The yam varieties were washed, chipped, parboiled at 50°C, soaked for different periods (0, 6, 12, and 18 h), dried at 60°C, and milled into flour. The flour samples were analyzed for their nutritional composition, pH, color, and functional properties. The flour samples were also made into pastes and were sensorially analyzed and 0 h soaked samples were used as control. The protein content of 18 h-soakedD. rotundata andD. alata flour samples was significantly different from the control and soaking had no effect (P > 0.05) on the fat and ash content but the carbohydrate content of the flour samples ranged from 83.08% to 86.13%. The 18 h-soakedD. rotundata flour sample had the lowest peak viscosity, breakdown value, and final viscosity among theD. rotundata variety samples. Pasting temperature ranged from 79.80 to 83.60°C and 6-h soakedD. alata flour sample had the lowest water absorption capacity and the highest bulk density. On the basis of sensory analysis, the panelist preferred the taste, texture, color, and appearance of paste made from the 18-h soakedD. rotundata flour to the paste of other flour samples. The results of this study show that D.rotundata should be soaked for 18 h prior to drying and milling in order to obtain a good-quality flour and paste.

Keywords: D. alata, D. rotundata, nutritional composition, paste, soaking, yam flour

Introduction

The genusDioscorea (familyDioscoreaceae) consists of some species that are commonly known as yam which are consumed perennial in Africa, Asia, Latin America, and Oceania (http://en.wikipedia.org/wiki/Yam_%28vegetable%29). Throughout the world, over 150 species are grown (Purseglove 1991) and about six species are known as important staples in the tropics.D. rotundata (white yam),D. esculenta (Chinese yam),D. alata (water yam),D. bulbifera (aerial yam), andD. dumenterum (trifoliate yam) are among the economically important species (Ike and Inoni 2006). Yam serves as an important source of carbohydrate and serves as a major source of income in countries where they are cultivated. In 2007, 96% of the worldwide production of yam (52 million tons) was from Africa while 94% of the yam was from West Africa with Nigeria alone producing 71% (http://www.iita.org/yam). Yams are usually processed into dry-yam tubers/slices and flour in West African countries such as Ghana, Benin, and Nigeria (Bricas et al. 1997). Yam tubers are usually processed into flour called “gbodo” in Yoruba land of Nigeria by peeling, slicing, parboiling in hot water (40–60°C for 1–3 h), soaking, and sun drying (Onayemi and Potter 1974).

Majority of foods sold in the market presently are exposed to a certain degree of processing (Akingbala et al. 1995) and processing is also prerequisite for yam consumption. Gbodo—traditionally processed dry yam—gives an intermediate flour product upon milling which is called “elubo.” Elubo is usually stirred in boiling water to obtain a paste which is usually eaten with soups called “amala” (Akissoe et al. 2000). The quality attributes that consumers look out for in these products are their color, texture, and taste (Akissoe et al. 2000). Yam is still being processed to gbodo and elubo through traditional methods and their quality attributes differ from one processor/location to another (Hounhouigan et al. 2003). However, to the best knowledge, little information is available on how soaking as a processing variable affects the quality attributes of yam flour and this type of knowledge becomes important when the development of flour is considered. This study investigated the effect of different soaking time on the chemical composition, functional, and sensory properties of flour fromD. rotundata andD. alata.

Materials and Methods

Yam was obtained from Kuto market in Abeokuta, Ogun State, Nigeria. The two varieties of yam (D. alata andD. rotundata) were converted to chips using the method described by Ige and Akintunde (1981). The white and water yam tubers were washed with portable water. The yam was cut into chips (150 g) and parboiled at a temperature of 50°C. The parboiled samples were soaked in portable water at different times (0, 6, 12, and 18 h) 0 h-soaked samples of the two yam varieties were used as control. The soaked yam slices were dried to a constant weight using a cabinet drier (Jinan Food Machinery Co., Ltd., Jinan, China) at 60°C for 2 h. The dried yam chips were milled into flour, sieved using 0.25 μm sieve, and were subjected to analyses.

Nutritional composition analysis

The nutritional composition of yam flour, including protein and fat, fiber, ash, and carbohydrate was determined according to the methods of AOAC (2000).

Functional properties analysis

Bulk density

The bulk density of the yam flour was determined with the method of Wang and Kinsella (1976).

Water absorption capacity

The water absorption capacities of the flour samples were carried out by the modified method of Prinyawiwatkul et al. (1997).

Dispersibility

A method described by Kulkarni and Ingle (1991) was used to measure dispersibility.

Pasting property

The pasting properties of the samples were measured using a Rapid Visco Analyzer, RVA (Model RVA-SUPER3; Newport Scientific ¹⁹⁹⁸, Australia) of the yam flour.

pH

The pH of the sample was measured with a pH meter.

Color intensity

One gram of each sample was weighed into a 100 ml beaker. 25 ml Hcl was measured and added to the beaker to extract the color by shaking and homogenizing with glass rod for 30 min. The mixture was allowed to stand for 10 min after which it was filtered through hardened Whatman No 42 filter paper into another 100 ml conical flask. The organic filtrate obtained was used to determine color by taking the absorbance at wavelength of 520 nm on a spectrophotometer (Cecil 2483, Cambridge, UK).

Sensory analysis

The yam flour samples were prepared by stirring them in hot water to make amala paste and served to 20 taste panelists who are regular consumers of amala. The pastes were rated for aroma, texture, color, and taste using a 9-point hedonic scale according to Iwe (2002).

Statistical analysis

All analyses were carried out in triplicates and the data were subjected to analysis of variance (ANOVA). SAS version 9.0 (SAS Institute Inc., Cary, NC) for windows was the statistical software that was used.

Results

Table1 shows the nutritional composition of the flour samples as affected by soaking. The protein content of the 6 h-soakedD. rotundata andD. alata flour samples was lower than that of the control and this reduction was significant while the reduction inD. alata was insignificant. The protein content of 18 h-soakedD. alata flour sample was insignificantly different from the control. There was no significant difference in the moisture content of the 6- and 12 h-soakedD. rotundata flour samples but the moisture content of the 18 h-soakedD. rotundata flour sample was significant compared to the control. The highest moisture content (10.12%) was observed in 6 h-soakedD. alata flour sample while the 12 h-soakedD. alata had the lowest moisture content (8.16%). Table1 also reveals that there were no significant differences in the ash and fat contents of all the samples but their carbohydrate content ranged from 83.08% to 86.13%.