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PROJECT TOPIC – Effects of Domestic Processing on the Cooking Time, Nutrients, Anti-nutrients and in Vitro Protein Digestibility of the African Yambean (Sphenostylis Senocarpa)

Effects of Domestic Processing on the Cooking Time, Nutrients, Anti-nutrients and in Vitro Protein Digestibility of the African Yambean (Sphenostylis Senocarpa)



The effects of processing (soaking, dehulling, fermentation and heat treatment) on the cooking time, protein, mineral, tannin, phytate and in vitro protein digestibility (IVPD) of the african yambean (AYB) were examined. The cooking time ranged from 9&155 minutes. Soaking reduced cooking time by about 50 percent. Soaking for 12 hours was the most appropriate to reduce cooking time, tannin and phytate levels. It improved in vitro protein digestibility (IVPD).

Prolonged soaking (24 hours) decreased calcium (Ca) and iron (Fe) values by 19 percent and 35 percent, respectively. Dehulling showed that Ca, Fe, magnesium (Mg) and zinc (Zn) were concentrated in the seed coat of the AYB. The seeds soaked and dehulled retained Mg and Zn.
Dehulling reduced tannin but hod no significant efTect on phytate and the IVPD of the AYB except for seeds soaked for 12 hoors before dehulling. Soaking for 24 hoors before dehulling significantly increased crude protein content by 16 percent (p<0.05).

Blanching and roasting increased the IVPD by 8-1 1 percent. Fermentation had no effect on the crude protein, Ca, Fe, Mg and Zn but significantly reduced phytate content of the AYB. Fermentation had no advantage over heat treatment with respect to improving the in vitro protein digestibility of the AYB.


Most foods, whether of plant or animal origin, are rarely fit for direct consumption. Thus processing of food has been used as a necessary step before consumption for a variety of reasons. These include increasing stability, improving flavor, decreasing the possibility of toxicity and introducing functionality [I]. Appropriate processing method for legumes is probably more important than for any other food group.

This is because of high levels of toxin and the indigestible nutrients in raw legumes. The AYE is an under-utilized legume whose potential as food is currently being investigated in order to reintroduce it into the fare of the population. Its protein content is similar to that of some commonly consumed legumes while its amino acid profile is comparable if not better than those of cowpea and soybean [2].

Studies on raw AYB showed that it contains more trypsin inhibitor (TI) than cowpea and pigeon pea and lower phytic acid content. Its trypsin inhibitor content was negatively correlated with the in vitro protein digestibility of the legume [3]. It is a well cherished legume in areas where it is grown and consumed. It has various uses and is as cheap as cowpea in terms of protein and energy.

Consumption studies have shown that some of the constraints to its optimum utilization are non-availability due to low production,
long cooking time and lack of appropriate processing technology [3]. The present study was undertaken to determine the effect of simple domestic processes (soaking, dehulling, fermentation and heat treatment) on the cooking time, protein, mineral, anti-nutrient content and in vitro protein digestibility (IVPD) of the AYB.


Effects of Domestic Processing on the Cooking Time, Nutrients, Anti-nutrients and in Vitro Protein Digestibility of the African Yambean (Sphenostylis Senocarpa)


Materials and methods

Three cultivars of the AYB (cream,..brown, and speckled) were used in this study. They were obtained from Orba local market in Enugu State and Asaga in Abia State, Nigeria. They were picked and sorted to remove dirt and stored in a well covered plastic container until ready for processing. The following processing were used.

(1) Soaking: About 2 kg AYB samples were soaked in distilled water for 6, 12, 18 and 24 hours using a 1 : 3 (w/v) bean to soaking water ratio in all cases. At the end of the soaking period, the samples were drained and divided into two parts. One part was used for the cooking experiment while the other was dried immediately in an air oven at about 5&55 “C [4].

The samples were allowed to cool in the open and put in an air tight container. The cooking time of the AYB was determined by boiling 100 g sample of the soaked seeds in sufficient water on a gas range (Gas mark 6) until they were soft as felt between fingers and the cooking time recorded. Raw AYB, pigeon pea (PP) and cowpea (CP) samples were also boiled to serve as control.

(2) Dehulling: Two types of dehulling techniques were adopted. (a) Soaked dried seeds resulting from (i) above were manually dehulled by rubbing between fingers. The hulls were winnowed and the dried splits ground into fine flour using a Tecator mill to pass through 60 mesh sieve and (b) raw AYB seeds were blanched for 10 minutes at 100°C and then manually dehulled as is traditionally done for cowpea.

The dehulled seeds were again dried and ground as described above.

(3) Fermentation: The flours produced from the blanched dehulled seeds (b) above and the 12 hours soaked, dried and dehulled seeds (a) above, were fermented. To a known quantity of the flour distilled water was added in a ratio of 1 : 2.5 (w/v) to form a thick batter. These were allowed to ferment for 12 hours and 24 hours by natural microflora present in the batter.

After fermentation, the pastes were dried into flakes in an air oven at 5&55 “C and milled into fine flour to obtain homogeneous samples.
(4) Roasting: About 100 g of dry clean seeds were put in a hot sauce pan and roasted on a gas range (Gas mark 6) for 10 minutes. The curved surface of a stainless steel spoon was used to rub and turn the seeds as they roasted.

The friction developed helped to dehull the grains. A part of the seeds blanched for 10 minutes (as in (ii) (b) above) was also roasted as
above. The roasted seeds were then milled into fine flour as described earlier.

All processed samples were put in air-tight plastic sample containers and stored in the refrigerator until analysed for protein, mineral, calcium (Ca), iron (Fe), zinc (Zn), phosphorus (P), magnesium (Mg), phytic acid, tannin and IVPD. Residual moisture was determined [5,6] for each dried sample and all value obtained during the chemical analysis converted to dry weight basis in order to allow for comparisons.
Chemical Analysis: Protein content was determined by the automated micro Kjeldahl procedure 141. Mineral analysis was done by wet ashing of the sample followed by the determination of the Ca, Fe, Zn, and Mg content using a Perkin-Elmer 372 atomic absorption spectrophotometer (AAS). ~ h o s ~ h o r u s (P) was determined by the molybdovanzdate method [4].

Phytic acid was determined by the ion-exchange procedure 171. Tannin was determined by the Vanillin-method [8]. Corrections for background colour were made as described by Price et al. 191, using appropriate sample blanks. In vitro protein digestibility was by the multi-enzyme technique for estimating protein digestibility [lo].

Mean + standard deviation (SD) or standard error (SE) were calculated where appropriate. Analysis of variance and Duncan’s New Multiple Range Test (DNMRT) were used to separate means. Percentage increases or decreases in the parameters measured were calculated and used to show the effects of processing. Results and discussion Some of the factors limiting the optimal utilization of grain legumes as food
are their long cooking time, laborious preparatory procedures, anti-nutrients, indigestible protein and lack of appropriate processing technology among others.

It is therefore necessary to identify which processing methods would eliminate these problems. Soaking Soaking is an important part of bean processing method such as cooking, germination, fermentation and toasting [I 11. Results from this study showed that soaking the AYB for varying periods reduced cooking time by at least 50 percent (Table 1).

This had been established by Molina et al. 11121. Presoaking lengthens the hydrated bean cooking exposure and promotes more rapid
softening [13]. The cooking time of the AYB ranges between 90-155 minutes


Effects of Domestic Processing on the Cooking Time, Nutrients, Anti-nutrients and in Vitro Protein Digestibility of the African Yambean (Sphenostylis Senocarpa)

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