Chemical Composition, Anti-Nutrients and Functional Properties of Composite Flours Formulated from Wheat and Three Cultivars of Cocoyam Corms (Xanthosoma sagittifolium) Commonly Found in Nigeria

Composite flours are mixtures of different vegetable flours-rich in starch, protein, and/or other nutrients, with or without wheat flour. Several institutions, including the Food and Agriculture Organization, have been involved in research designed to find ways of partially substituting wheat flour with those from other sources or replacing wheat all together [1].

Composite flours could also be regarded as blends of wheat and other flours, or wholly non-wheat blends of flours for the production of various food products including baked products, pastas, porridges, and snack foods [2]. According to the latter authors, the purpose of composite flour for making staple foods such as baking items is usually for economic and nutritional advantages. The use of composite flours of wheat and other vegetable flours for making baked food products such as biscuit and bread in tropical countries may be associated with scarcity of wheat, due to climatic reasons for its propagation. Composite flours are quite different from the ready-mixed flours familiar to millers and bakers, as the latter contain all the non-perishable constituents of the recipe for certain baked products.

Cocoyams (Xanthosoma sagittifolium) are used as subsistence staples in many parts of the tropics and sub-tropics, especially Nigeria. They are grown primarily for their edible starch contained in their corms, and secondarily the leaves are used as vegetable in most developing countries [3]. The proximate composition of cocoyam corm showed moisture (80.99%), ash (1.03%), crude protein (5.47%), crude fat (0.20%), crude fibre (1.28%) and total carbohydrate of 11.03% [4]. Nigeria is the largest producer of cocoyam in the world with an annual production of above 3.450 million metric tonnes; this represents 72.2%, 57.7% and 45.9% of total production in West Africa, Africa and the World respectively [5].

Cocoyam corms generally have been noted to contain anti nutrients and high moisture content; the latter has been associated with high rate of deterioration of the crop after harvest, resulting in its limited shelf life and unavailability. Processing of cocoyam into semi-finished forms such as flours could help prevent associated losses and promote its availability and utilization in various food applications.With the constant increase in the consumption of bread and other baked products in many developing countries, coupled with the high foreign exchange involved in wheat importation and ever-growing urban populations, the composite flour technology involving incorporation of cocoyam flour could be very useful. The present study therefore aimed at assessing certain quality indices of flours produced from three cultivars of cocoyam commonly found in Nigeria, along with their composites with wheat. Results may help proffer suggestions on their possible suitability in food applications such as baked products for likely commercialization.

Source of raw material

Figure 1: Flow chart of the production of cocoyam flour.

Formulations used for preparation of the wheat-cocoyam composite flours:

Evaluation of functional properties of the flours:

Data which depended on different percentages of substitutions of different flour samples were analyzed according to a completely randomized design with three replicates. Data were subjected to variance analyses and differences between means were evaluated by Duncan’s multiple range tests using SPSS statistic programmed, version 10.01. Significant differences were expressed at P < 0.05.

In this study, composite flours were formulated from wheat and five varieties of cocoyam (Table 1). The functional properties of the different flour formulations from the wheat-cocoyam flours are shown in table 2. The highest water absorption capacity (1.79 g/mL) was recorded for sample EOC113 while lowest values of 1.30 each were obtained for WHF101 and EUH122 samples. Significant difference (P < 0.05) was observed among some of the samples, which may have been impacted by the different cocoyam cultivars used in their formulations. The WHF101 sample recorded the highest oil absorption capacity (2.18 g/mL), and were closely followed by those obtained for EOF132, EOF133, EOC112 and EUH122 respectively, all of which did not differ significantly from each other (P > 0.05). The similarities in their oil absorption capacities may indicate their suitability for use in processing of same category of foods, especially baked products; although other useful functional properties should be taken into consideration. 

The swelling capacity ranged from 7.40 to 8.50 g/g with varying degrees of significant difference being noted among samples; WHF101 similarly had the highest value (0.71 g/mL) of bulk density, and this was observed to differ significantly from those recorded for some of the other samples. In contrast, WHF101 had the lowest gelling capacity (6.0%) compared with those observed for others. The highest gelling capacity (8.0) was recorded for each of EOC111, EOF131 and EUH121. The results of the functional properties of the flour samples in this study were similar to those contained in research investigations of other researchers; Pasha et al. [16], reported the rheological and functional properties of pumpkin-wheat composite flour in Pakistan. Chandra et al. [2], also carried out evaluation of functional properties of rice/sweet potato and wheat composite flours; the investigators used the composite flours to produce biscuits and concluded favorable comparison with those produced from whole wheat flour. More recently, Okoye and Obi [17] determined the chemical composition and sensory properties of wheat-African yam bean composite flour cookies. It thus becomes apparent that the composite flours of the wheat-cocoyam in the present study may be of significance in the production of baked food items; this may possible be scaled up to commercial level in reducing cost of importation of wheat which does not normally thrive in Nigeria for climatic reasons [18]. However, their successful trials in pilot experiments will be necessary before probable commercialisation.

All the functional properties recorded in this study, with the exception of bulk density, were slightly lower than those reported in a previous investigation by Olaoye et al. [19]. The difference may be attributed to varietal difference in the cocoyam cultivars used in the respective studies. Functional properties are intrinsic physico-chemical characteristics which affect the behaviour of properties in food systems during processing, manufacturing, storage and preparation [20]. Oil absorption capacity is one of the functional properties of flours which is influenced by the lipophilic characteristics; the low level of this functional property in the flour samples being reported is therefore justified by the low fat nature of cocoyam, being a carbohydrate crop. Furthermore, Tharise et al. [10], noted that protein may also have effect on the oil absorption capacity, which further justifies the low level of this property recorded in the cocoyam flour samples because cocoyam is low in protein. Judging from the results of their functional properties, the wheat-cocoyam flour samples in this study may be suitable in food applications involving baking, especially in the making of bread and biscuits/cookies [10,17].

The antinutrient compositions (%) of the flours are presented in table 3. Results indicate that EOC111 had the highest phytate content of 0.190 compared with the lowest (0.021) recorded for EOC113; hence the Ede Ocha cocoyam cultivar was lower in phytate content than other cultivars. The highest value of 1.60 was obtained for antinutrient content of oxalate, and this was noted for the EUH121 flour, while the lowest value (0.66) was recorded for WHF101 (whole wheat flour). Among the flours prepared from the various cocoyam cultivars, EOF132 had the lowest oxalate, 0.68. The oxalate content of the whole wheat flour was significantly different (P < 0.05) from most of the other composite flours of wheat and cocoyam. Tannin contents ranged from 0.773 to 0.929, with the lower and upper values being obtained for WHF101 and EOF131 samples respectively; this indicates that the latter had the highest tannin among other cocoyam flours. However, no significant difference (P > 0.05) was observed among most of the composite flours and their whole cocoyam counterparts, with the exception of EOC111, EOF131 and EUH121. Alkaloid assumed similar trend to that of tannin, with the WHF101 flour sample having the lowest content (0.19) while EUH121 had the highest, 0.49. Significant difference (P < 0.05) was recorded in the alkaloid contents of the whole wheat flour and other whole flours of the different cocoyam cultivars. The whole wheat flour also had the lowest saponin among the flour samples; the whole cocoyam flours were higher than their wheat-cocoyam composites. Therefore composites of cocoyam and wheat flours may help lower the risk of antinutrients in food processing and applications.

Presence of antinutrients, especially at high levels in vegetable flours may have adverse effect during food processing. This is due to their ability to react with certain components of food thereby forming complexes, which make such food components unavailable for use by the body [21]. Reed et al. [22], have reported the ability of tannin to react with protein, thereby making it nutritionally unavailable. Furthermore, phytates and oxalates have been noted to form insoluble salts with mineral elements such as zinc, calcium and iron and thereby such minerals for utilization in the body [23]. The antinutrients of the cocoyam flours in the current study were observed to be lower than those reported in previous studies [18,24], probably due to differences in the processing techniques adopted during production. This observation could be of benefit during eventual food applications of the cocoyam flours in reducing possibilities of unavailability of nutrients normally caused by presence of antinutrients. 

The results of proximate compositions of the different flours show that moisture ranged from 9.24 to 13.30 among samples, some of which show varying degrees of significance difference (Table 4). The WHF101 sample had lower ash content (2.50%) than others, indicating that ash contents were higher in all whole cocoyam flours and wheat-cocoyam composites, and these were noted to be significantly different (P < 0.05). The observation was consistent with various reports in the literature that vegetable flours normally contain relatively high mineral contents, and this constitutes one of reasons why composite flour technology has been advocated and encouraged in the production of composite breads and other baked products [1,2]. Fiber, fat and protein contents ranged from 2.07-3.15, 1.10-2.40, and 8.71-15.84 respectively among the flour samples; WHF101 recorded highest values in the three proximate parameters. However, no significant difference was recorded between the WHF101 sample and some of the composite flours in the attributes of fibre and fat, while protein differs significantly between WHF101 and other samples. In a research study by Olaoye et al. [19], which investigated the effects of sprouting on quality attributes of cocoyam flour and its performance as composite of wheat in bread production, protein content was reported to be higher in wheat than cocoyam. Malomo et al. [25], also demonstrated higher protein content in wheat flour than vegetable flours obtained from breadfruit and breadnut. It thus appears that except in cowpea vegetable flours and other few cases, protein contents of wheat flour are higher than their vegetable crop counterparts [26]. 

The mineral compositions (mg/100g) of the wheat-cocoyam flours are shown in table 5. Results indicate that the highest calcium content was recorded for sample EOC112 while EUH121 had the lowest. A value of 40.10 was recorded for whole wheat flour. Magnesium ranged from 22.30 to 26.01, obtained for samples EUH121 and EUH122 respectively. Sodium content was observed to be highest (124.44) for WHF101 and lowest (32.45) for EUH121 samples. A range of 104.53 to 146.43 was recorded for potassium, with WHF101 having the highest value. Phosphorus was also highest (38.18) for WHF101 while the lowest (36.30) was obtained EOC111; no significance difference (P < 0.05) was observed among most of the flour samples in terms of phosphorus contents. It is interesting to note that calcium, magnesium and phosphorous contents of whole cocoyam and wheat-cocoyam composite flour samples compare favourably with those of the Whole Wheat Flour (WHF101), indicating that useful mineral elements are contained in cocoyam which may be beneficial to consumers. The results of the calcium in the cocoyam flour samples in the present study are very similar to those reported in a research investigation by Alcantara et al. [24], in two cocoyam varieties (NSIC G-9 and VG-2) in the Philippines. The magnesium and calcium contents recorded in a cocoyam variety by Agoreyo et al. [27], also compared favourable with those obtained in the present study. 

There was no significant difference (P > 0.05) between the amylose and amylopectin contents of the various flour samples (Table 6). This indicates that the flour samples may assume similar viscosity patterns in recipe formulations and food products, where they form part of ingredients for production [28]. 

This study concluded that cocoyam flours possessed functional properties which may make them useful in composite flour technology for use in production of baked food products, especially in Nigeria where the cocoyam cultivars are common and have been underutilised. The minerals and minimal contents of antinutrients recorded in the cocoyam flours could also promote their potential for use in other food applications, and may help enhance nutritional intake among consumers. Further studies are however required to practically explore food application potentials of the cocoyam flours, the results of which may be scaled up to commercial level if successful in preliminary pilot trials.

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