pH AND COOKING TIME OF AFRICAN YAM BEAN SEEDS ... Key words: Water absorption, pH, cooking time, A YB soaking, salt solutions. .... Light Brown. 0.20.
GLOBAL JOURNAL OF PURE ANO APPLIED SCIENCES VOL 6 NO. 1 JANUARY 2(00: 67-73 COPYRIGHT (C) BACHUDO SCIENCE CO. ~TD. PRINTED IN NIGERIA ISSN 1118-0579
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EFFECT OF SOAKING IN SALT SOLUTIONS ON WATER ABSORPTION, pH AND COOKING TIME OF AFRICAN YAM BEAN SEEDS (SPHENOSTYLIS STENOCARPA HOCHST EX. A. RICH HARMS) EUGENE N. ONYEIKE and STELLA G. UZOGARA (Received 30 March 1999; Revision accepted 18 June 1999)
ABSTRACT The effect of soaking African yam bean (AYB) seeds in water and various concentrations of sodium sesquicarbonate (Na2C03.NaHC03.2H20) and sodium chloride (NaCl) on the water absorption, pH of soak solution and the cooking time of the pulse was. investigated. Hydration coefficient (HC) increased in all the solutions tested as soaking progressed from the 6th to the 18th hour (maximum hydration time) before a decrease occurred at the 24th hour of soaking. At the same concentration of both salts, HC was generally higher in samples soaked in Na£Q3.NaHCOJ.2H20 (akanwu) compared to those soaked in NaCl. pH was found to decrease in all the soak solutions tested and the drop in pH occurred over time of soaking. At the same concentration of both salts and for the same period of soaking ranging from, 6 - 36 hours, the pH drop was higher in the akanwu-soaked samples compared to those soaked in sodium chloride. Soaking, irrespective of ,the medium and salt concentration highly reduced the bean cooking time which decreases as salt concentration increases, and hence the soaking process is of economic and practical importance to food vendors in Nigeria. At the same salt concentration (1.0%
%)and at each of the soaking periods {6, 12, 18,
24,30 and 36 hours) investigated, the percentage reduction in cooking time was highest in akanwu-soaked samples compared to those soaked in sodium chloride. Key words:
Water absorption, pH, cooking time, A YB soaking, salt solutions.
INTRODUCTION Soaking has been shown to be a useful and essential step in the home cooking of legume seeds especially in areas .of high altitude (Silva, 1980), and has been reported to decrease the trypsin inhibitor and hemagglutinin activity in Phaseolus vulgaris (Kakade and In Egypt, lentil seeds are usually Robert, (1966). soaked before cooking (Abou-Samaha et al, 1985). The African yam bean (AYB) seed is an excellent source of proteins (21-29% on dry matter basis). Although the protein level of A YB is lower than that ·:of ..soybean which is 38%, amino acid analyses indicate that its lysine and methionine levels are equal to or better than those of soybean (Evans and Boulter, 1974). When properly cooked the A YB is very filling and laating, giving a lot of staying power and causing the consumer of its meal to drink much water probably as an aid to digestion (Ezueh, 1984). Constraints on the use of the A YB seeds as food especially for people of low socio-economic status (the hungry masses) have been the laborious traditional methods of preparation, long cooking times of 4-6 hours (Okigbo, 1973) and the presence of antinutritional
factors such as trypsin inhibitors which have been shown to be inactivated by heat treatment (Onyeike et al, 1991 ). In most Nigerian homes, the absence of electricity, the factor of low socio-economic status (most people now live below the poverty line), the negative effect of austerity measures and structural adjustment programme limit the use of otherwise simple gas cookers. The use of firewood in the cooking process is also becoming inadequate due to rapid deforestation without a corresponding , aforestation leading to more use of kerosene stoves for cooking. . The addition of salts such as NaC1, NaHC03 and Na2C03 to the soaking medium was found to lower the cooking times and gave the cookecl black beans better sensory properties (Varriano-Marston and De-Omana, 1979). Morris (1963) had earlier reported that the hard to cook phenomenon in legumes stored for long periods of time required long soaking and cooking to soften the seeds. The purpose of this investigation was therefore to assess the effect which soaking in water and various concentrations of sodiumsesquicarbonate and sodium chloride would exert on the seed weight/hydration, pH of soak solution and the extent of reduction in the bean cooking time as a function of fuel and energy economy.
EUGENE N. ONYEIKE. Department of Biochemistry, Nutrition and Toxicology Unit. Faculty of Science, University of Port Harcourt PM.B. 5323. Port Harcourt; Nigeri.a STELLA G. UZOGARA. Department of Biochemistry, Nutrition and Toxicology Unit Faculty of Science, University of Port Harcourt. P.M.B. 5323. Port Harcourt, Wigena
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EUGENE N. ONYEIKE and STELLA G. UZOGARA
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Hydration coefficient \HC)
MATERIALS AND METHODS MATERIALS:
weight of seeds after soaking weight ofseeds before x WO ·
;~~ki~g
uninfested
marble-
The coloured African yam bean (AYB) seeds were purchased from Afor Oru market in Ahiazu Mbalse, Imo State. They were sorted to remove broken one5 and extraneous materials, cleaned, wrapped with polyethylene bag, sealed in an air-tight container and stored tor 4 days in a refrigerator (4°C) until they were required for use. Tap water from the University of Port Harcourt water supply was ulfld in prefer~nce to distilled water since the latter is not uHd for drinking and cooking purposes by the consumers of AYB meal. Sodium. sesquicarbonate (1k1nwyf Imd spqi!:frn chloride were purchased from Choba markfiJt n@lf thli University of Port Harcourt. Akanwu is known as Nnu anwuru, kanwa, lkang, Karu, Kaun and other names in various Nigerian language3 gepending on the ethnic group or tribe. It is a naturally~ooourFiRQ alkffliml rock salt whose aqueous solution has a pH of 11.0 as measured. It i$ misnamed "potash" in Nigeria because of the erroneous belief thm it, is a complex potassium salt tuzogara et al, 1988). HoweYJr, @ktnwu is over 98% trona (Na2COs.NaHC0,.2H~o1 with trace amount of calcium, magnesium, iron, iine, sulphur, chlorine, silicon, phosphorous, potassium and aluminium (MakanjQdfa and Bettlestone, 1975). The akanwu was grm.md to a fine {1 oo.mft!ill acreen) powder, oven dried (t'05"C for 4 hr), cooled In a deaiQ@tor and stored ·1n an air-tight stoppered glass sample bottle until it was required for use. Sodium chloride (common salt) is known in various parts of Nigeria as Nnu (lbol, Iyo {Yoruba), Gishiri {Hausa), lnung (Efik and lbibio), Uwanka (Urhobo), Lo (Ogoni), Arah (lkwerre. in Rivers State), etc. The pure common salt sodium chloride was purchased and used as such in the soaking studies.
Determination of PH of Soak Solution: The PH of tap water and ot the salt solutions used in sample soaking was detrnrnilied to soaking by the use of a pH meter. rhe .A VB seeds were the~ weighed and soaked iri water and various salt solutions for periods ranging from 6'·36 hr at a bean to W~lOl' ratio of 1; 10
%. At the end of
the
sa{:llci" a higher level of wai.:r absorption b: ,!iu .,,,_,,,,vu soaked samples con. ·ared to thos(, ,,,>,,:,uc: .)ud1urn chloride. As the concentratinn of each , ,: ,uPased at any given soaking time the HC generally d(:Gr ,,ascd as lower salt ,:oncentrations generally caused increased water ab .orption.
Whole -dry bean seeds were weighed and soaked in plain tap water, . akanwu and sodium chloride solutions of concentrations 0.20, 0.40, 0.60, 0.80 and 1.00% respectively at a bean to water r,,tio of 1:10
%
for periods of 6, 12, 18, 24, 30 and ;J6
hr at room temperature (29 ±. 1°C). Tha soaked sampl.es were drained, blotted dry with filter paper to remove surface water, weigh~d and ·the amount of water absorbed determined as hydration coefficient (HC) according to the method of Hulse et al (1977) as :shown below:
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Table·t EFFECT OF SOAKING RAW AYB SEEDS INVARIOUS AKANWU AND SODIUM CHLORIDE soumONS ON THE HYDRATION COEFFICIENTS AND pH OF THE SOAK SOLUTION
Akanwu
Soaking
Cone(%)
time (hr.)
0.20 0.20 0.20
6
0.20 0.20 0.20 0.40 0.40 0.40 0.40 0.40 0.40 0.60 0.60 0.60 0.60 0.60 0.60 0.80 0.80 0.80 0.80 0.80 0.80 1.00
24 30 36 6 12 18 24 30 36 6 12 18 24 30 36
12 18
Hydration Co eff.(%)
l!H of Soak Solution Initial Final Decrease inpH
168.2 179.l 181.3
10.2 ,0.2 10.3
9.90 9.50 8.80
0.30 0.70 l.50
Colour of Soak Solution (Visual observation) Light Brown Brown Dark Brown
167.8 176.7 178.8 162.5 180.0 180.8 177.2 175.4 176.0 164.4 168.5 181.2 174.2 174.2 174.7 159.3 172.4 175.4 175.2 173.l 174.5 165.7 171.8 176.2 169.8 170.2 171.9
10.0 10.0 9.90 10.3 10.3 10.3
7.25 7.20 7.10 10.2 10.0 9.70 9.50 7.80 7.35 10.2 9.90 9.70 9.50 7.85 7.40 10.1 10.0 9.90 9.85 8.40 7.70
2.75 2.80 2.80 0.10 0.30 0.60 0.80 2.10 2.65 0.10 0.30 0.60 0.70 2.05 2.50 0.20 0.30 0.30 0.35 l.40 2.00 0.20 0.30 0.40 0.40 1.35 1.90
Dark Brown Dark Brown Dark Brown Brown Brown Dark Brown Dark Brown Dark Brown Dark Brown Brown Brown Dark Brown Dark Brown Dark Brown Dark Brown Brown Brown Dark Brown Dark Brown Dark Brown Dark Brown Brown Brown Dark Brown Dark Brown :nark Brown dark Brown
Sodium Chloride Cone.{%)
(hr.)
0.20 0.20 0.20
6 12 18
166.5 178.0 180.1
5.40 5.40 5.40
5.30 5.30 5.20
0.10 0.10 0.20
0.20 0.20 0.20 0.40 0.40 0.40 0.40 0.40 0.40 0.60 0.60 0.60 0.60 0.60 0.60 0.80 0.80 0.80 0.80 0.80 0.80 l.00 1.00 1.00 1.00 1.00 1.00
24 30 36 6 12 18 24 30 36 6 12 18 24 30 36 6 12 18 24 30 36 6 12 18 24 30 36
170.0 175.1 177.3 161.8 177.0 179.0 175.0 176.0 176.0 161.0 176.9 180.0 174.0 172.6 174.4 160.1 176.2 178.3 172.0 172.0 172.7 159.5 170.3 174.0 165.8 167.0 170.5
5.40 5.40 5.40 5.50 5.60 5.50 5.50 5.50 5.50 5.50 5.50 5.50 5.50 5.50 5.50 5.55 5.55 5.55 5.55 5.60 5.58 5.60 5.60 5.60 5.70 5.60 5.60
5.20 5.15 5.15 5.40 5.50 5.35 5.30 5.30 5.30 5.30 5.30 5.30 5.25 5.25 5.20 5.35 5.35 ·5.30 5.30 5.30 5.25 5.40 5.40 5.30 5.35 5.20 5.10
0.20 0.25 0.25 0.10 0.10 0.15 0.20 0.20 0.20 0.20 0.20 0.20 0.25 0.25 0.30 0.20 0.20 0.25 0.25 0.30 0.35 0.20 0.20 0.30 0.35 0.40 0.50
Soaking
Time
Hydration Co eff.(%)
12H of Soak Solution Initial Final Decrease inpH
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