K. GANESH KUMAR, L. V. VENKATARAMAN, T. V. JAYA and K. S. KRISHNAMURTHY

Central Food Technological Research Institute

Mysore, 570013 India

COOKING CHARACTERISTICS OF SOME GERMINATED LEGUMES: CHANGES IN PHYTINS, CA++, Mg++ AND PECTINS

ABSTRACT Germinated greengram, cowpea and chickpea were studied for chemical characteristics after cooking, by estimating the changes in phytins, Ca++, Mg++ and pectin contents. Cooking time was drastically reduced on germination in chickpea, while an inverse effect was observed in greengram and cowpea. The phytin content decreased on germination. No appreciable change in phytin P/Total P value was seen on cooking. Ca++ content was reduced on germination and cooking in the three legumes, while Mg* content was relatively unaltered. A combined interaction of these chemical parameters, expressed as “PCMP number” was found to correlate with the cooking behavior of the legumes studied.

INTRODUCTION

IN INDIA, legumes are the primary source of dietary proteins (Patwardhan, 1961). The total production of legumes is about 99.50 million tons, cultivated in 22.02 million hectares (FAO Production Year Book 1972). Among the legumes, chickpea itself accounts for about 41% of the total area under legume cultivation. Greengram, cowpea and chickpea are commonly consumed in India. Conventionally they are also used in germinated form since the nutritional value is reported to be better (Chen et al., 1975; Ganesh Kumar and Venkataraman, 1976; Jaya et al., 1975).

One of the limitations in the use of legumes is their un- desirable cooking characteristics. In USA, where peas (Pisum sativum) and beans (Phaseolus vulgaris) are used, the per capita consumption is reported to be on the decline (Rockland and Metzler, 1967). This has been attributed to the prolonged cooking period. Chemical characteristics of peas as affected by cooking have been reported to involve phytates, divalent cations, pectates and lignins (Rosenbaum and Baker, 1969; Crean and Haisman, 1963, 1964;Muller, 1967). Detailed infor- mation on the chemical characteristics affecting the cooking quality are needed to develop legumes, with desirable attributes, either by genetic manipulation or by post-harvest processing.

Information regarding the cooking quality of greengram, cowpea and chickpea are limited. While the effect of varietal difference (Muller, 1967), maturity, (Burr et al., 1968) and processing (Rockland and Metzler, 1967; Desikachar and Subramanyan, 1965) on the cooking quality have been report- ed, extensive literature search has not revealed any informa- tion on the effect of germination on the cookability of leg- umes. The present study details some of the chemical changes that affect the cooking quality in germinated legumes.

MATERIALS & METHODS

Legumes and germination Greengram (Phaseolus aureus), cowpea (V&a sinensis) and chick-

pea (Cicer arietinum) were obtained locally. The seeds were soaked in water for 4 hr, followed by germination on moist cloth. Germinated seedlings were removed after 24 and 72 hr and used fresh for cooking. The ungerminated legumes were cooked without prior soaking. Freeze- dried materiaIs, powdered to 80 mesh, were used for chemical analysis.

Estimation of cooking time. Ungerminated and germinated leg- umes were cooked with six times their weight of distilled water. While being cooked, at definite intervals samples were drawn and evaluated by a panel for judging the uniform cooking and softness. Ten independent replicates were made to obtain the mean XT of legumes.

Percent dispersibility. The well stirred slurry of the cooked legumes was passed through a standard 1 mm sieve. The residue was washed with hot water and dried to constant weight at lOY’$. The percent ratio of the weight of fraction of the cooked sample passed through the sieve to the total weight of the sample passed was determined. The minimum time required to obtain the maximum dispersibility (98 + 2%) was taken as the optimal cooking time. Analytical methods.

The elemental phosphorus (P) was determined by AOAC (1965) method. Phosphates were extracted with distilled water and OSN hydrochloric acid. An aliquot of the extract was digested with per- chloric acid, sulphuric acid and hydrogen peroxide. The total P in the digest was estimated by Allens method (1940). The procedure of Crean and Haisman (1963) was used for the estimation of phytin P.

Ca++ and Mg++ contents were estimated in the perchloric acid digest by complexometric titration with EDTA (Vogel, 1961). The interfering ions were removed previous to titration by precipitating them with zirconium oxychloride (Derderian, 1961). The procedure of Dietz and Rouse (1953) was followed for quantitating the pectins. Anhy- drouronic acid content was determined by the carbazole method @Womb and M&ready, 1952).

RESULTS & DISCUSSION

Cookability of legumes The times involved for cooking ungerminated and germinat-

ed legumes are shown in Table 1. As seen in the table, chick- pea was most difficult to cook, while greengram required only a short cooking time. However, the cookability pattern of germinated legumes were markedly different. Germinated chickpea was more readily cooked compared to the ungermi- nated ones. In this legume, the time required for cooking progressively decreased with germination time. Germinated greengram was more difficult to cook and the percent increase in cooking time was about 336.0 (Table 1). Cowpea pattern was similar to that of greengram. The time needed for cooking the various germinated legumes was different.

Table l-Effect of germination on cooking time of legumesa

Period Cooking time fmin) Percentc

Legume

of ger- Subjective Percentb increaselde- mination cooking time dispersibility crease in cook-

(hr) Mean ? SD Mean + SD ing time

0 13.6 f 1 .3 14.1 * 0.4 -

Greengram 24 22.8 + 1.2, 23.2 f 0.2 + 67.7 72 59.4+ 1.5 58.8 + 0.6 +336.8

0 30.6 f 1.4 31.2 + 0.3 - Cowpea 24 46.4 _+ 1.2 44.0 f 0.7 + 51.6

72 60.4 i 1.6 61.1 * 0.5 + 97.4

0 79.0 + 3.9 78.6 f 0.5 -

Chickpea 24 41.6+ 1.0 40.9 f 0.4 - 47.4 72 20.0 f 0.9 20.6 f 0.7 - 74.7

a Values represent meen of ten independent observations. b Minimum time to get 98% dispersibility. c Percent increase/decrease with reference to ungerminated seeds

+ increase: - decrease.

Volume 43 (1978)-JOURNAL OF FOOD SCIENCE- 85

Changes in the chemical parameters affecting cookability of legumes

Phytin content. The total P content was about 0.19-0.33% of the total legumes on dry weight basis (Table 2). The inositol

Table l-phosphorus compounds of ungerminated legumes (dry wt basis)

Phytic Phytic Phytic

Total P acid acid P acid P Legume % % % Total P

Greengram ’ 0.270 0.65 0.185 0.685 Cowpea 0.325 0.43 0.123 0.378 Chickpea 0.193 0.28 0.078 0.399

Table d-comparison of water and acid extractable phytins in un- cooked and cooked legumes (dry wt basis)

Legume*

Aqueous Hydrochloric acid extraction extraction

Total P Phytin P Total P Phytin P (%I (%I (%I (%I

Greengram Uncooked Cooked

Cowpea Uncooked Cooked

Chickpea Uncooked Cooked

0.222 0.142 0.225 0.185 0.175 0.080 0.190 0.150

0.243 0.090 0.223 0.123 0.188 0.032 0.200 0.090

0.114 0.056 0.126 0.078 0.103 0.036 0.121 0.075

a The values presented are for ungerminated material

PERIOD OF GERMINATION (ha.)

Fig. ?-Changes in phytin P content as a function of period of Fig. 2-Changes in phytin P content as a function of period of germination in greengram:-Uncooked, - - - - Cooked. germination in cowpea:-Uncooked, - - - - Cooked.

66 -JOURNAL OF FOOD SCIENCE-Volume 43 (1978)

hexaphosphate content, determined as phytin P, varied be- tween 37-69% of the total P, of the legumes studied. Green- gram showed the highest phytin P content (Ql85 mg/lOOg). This corresponds to 70% of the total P. The lowest amount of phytin P was found in ungerminated chickpea. The phytin P content decreased with progressive stages of germination and this trend was seen in all the three legumes.

Table 3 shows the-extraction pattern of phytin P in aque- ous and OSN hydrochloric acid media. Hydrochloric acid (OSN) extracted the maximum amount of phytin P both in uncooked and cooked legumes compared to aqueous extrac- tion (Fig. l-3). The extractability of phytins in these legumes, in water, was lower compared to other types of legumes reported in literature. Lolas and Markakis (1975) have found the phytin P to be wholly water soluble in Phaseok vulgaris L. In peas, the phytin P could be equally extracted both in aqueous and HCl media (Crean and Haisman, 1963). The poor water extractability of phytin P in this study may be due to the nature of phytins which may be in the form of either Na, K or Ca, Mg salts.

Cooking resulted in the decrease of both water and acid extractable phytin P, though the extent of loss of acid extract- ables was much less compared to water extractable ones (Table 4, ‘Fig. l-3). There was little change in the ratio of phytin P/total P in the uncooked and cooked legumes (HCl extract, Table 4). In the germinated cooked samples, a reduction in the phytm P/total P ratio, both in water and acid extractables was observed.

Mattson (1946) had attributed poor cookability of peas to reduction in phytin P content. The phytin P content of un- germinated legumes showed a comparable pattern, chickpea req,uiring a long cooking time, had the lowest amount of phytin P (%80 mg/lOOg) while greengram with lowest cooking time showed the highest amount of phytin P (sl85 mg/lOOg). However, the extent of phytin P may not be the sole contribu- tory factor affecting the cooking time as reported by Mattson (1946), since the pattern of germinated legumes ,were totally

PERIOD OF GERMINATION Ihrs.1

LEGUME COOKING CHARACTERISTICS. . .

different (Fig. 1-3). Greengram which had a dramatic increase in cooking time (Table 1) did not show a corresponding change in the phytin P. This trend was comparable in cowpea and chickpea also.

Crean and Haisman (1963) had attributed the decrease in the water extractables, to the complexing of inositol hexa- phosphate and calcium and magnesium to form insoluble phytates which could be extracted only with dilute acids. This may possibly explain the decrease in water extractables ob- served in this study. The progressive decrease in the phytin P with germination may also be due to increase in phytase activity during germination (Belavady and Banerjee, 1953; Fordham et al., 1975; Walker, 1974). Changes in the divalent cations on cooking and germination

The Ca* content of the three legumes differs (Table 5). Chickpea showed the highest value (5.54 meq/lOOg), followed by cowpea and greengram. A reduction in Caf+ content was observed in all the three legumes, as a result of cooking. The loss of Ca++ was low in greengram (11.6%) while in chickpea it was considerably higher (42.2%). A similar trend of mineral loss during cooking was reported in different legumes by Meiners et al. (1976). In the later stages of germination (72 hr) significant loss in Ca* was found in all the legumks. On cooking the germinated legumes, the percent loss of Ca+ was more pronounced in chickpea compared to cowpea or green- gram.

0 72

PERIOD OF GERMINATION fhrs.1

Fig. J-Changes in phytin P content as a function of period of germination in chickpea:-Uncooked, - - - - Cooked.

In the ungerminated legumes the Mg* content was comparable (Table 5) and the loss of Mg++ on cooking was more noticeable in greengram. During germination the reduc- tion in Mg* content was more evident in greengram com- pared to chickpea or cowpea. The loss of Cat+ and Mg++ may be due to leaching during the bulk germination of seeds. Leaching of inorganic and organic compounds have been reported for legumes during germination in literature (Koller, 1972; Linhart and Pickett, 1973).

Table 4-Changes in phytin P/total P ratio during cooking and ger- mination

Legume

Parind nf Phytin P/total P (extracted) . _..-- -.

germina- tion

H, 0 extract HCI extract

(hr) Uncooked Cooked Uncooked Cooked

It is possible that during cooking which involves a complex reaction system, where the Ca* which is concentrated in the parenchyma cells (Crean and Haisman, 1964), migrates into the cell content complexing with phytate ions. Further the permeability of cell wall is altered by the presence of Ca* and Mg++ ions. More soluble Ca++ salts might be formed during these changes which get leached out. Changes in pectins during cooking and germination

No noticeable change in free pectin (FP) content was ob- served in ungerminated chickpea on cooking while cowpea and greengram showed considerable reduction (Table 6). The FP content in germinated legumes was strikingly different. There was a marked increase in the FP of greengram and cowpea at 72 hr of germination, while in chickpea the FP content was reduced.

Greengram

Cbwpea

Chickpea

0 0.64 0.46 0.82 0.79 24 0.60 0.30 0.73 0.68 72 0.53 0.16 0.89 0.42

0 0.37 0.17 0.55 0.45 24 0.16 0.12 0.48 0.45 72 0.08 0.06 0.45 0.42

0 0.44 0.35 0.62 0.62 24 0.42 0.34 0.56 0.50 72 0.34 0.16 0.52 0.36

Decrease in FP may be due to the synthesis of newer polysaccharides which are incorporated in the acidic pectic substances resulting in a more branched structure. A decrease in demethylating activity could be envisaged at this stage re- sulting in the consequent reduction in FP (Barnes and Patchett, 1976; Matheson and Saini, 1977). A reverse trend is possible, as in greengram with depletion of polysaccharides from the acidic pectic substances, (Matheson and Saini, 1977) and increase in demethylating activity, particularly when the seeds are metabolically active due to enhanced germination.

Table B-Changes in Ca+* and Mg’+ content on cooking and ger- mination of some legumesa (dry wt basis)

Ca+ content Period of ger-

Ma++ content

(meq/lOO g) -

mina- % loss % loss tion Un- on Un- on

Legume (hr) cooked Cookedcooking cooked Cooked cooking

PCMP number as an index of cooking pattern Since any of the parameters, viz., phytates, Ca*, Mg* and

FP content cannot individually account for the cooking pat- tern in legumes, Muller (1967) has suggested the cumulative effect of these as PCMP number in the following mathematical formula:

0 2.24 1.98 11.6 8.07 6.35 21.4 Greengram 24 1.60 1.44 10.0 8.00 5.28 34.0

72 1.37 1.29 6.0 4.52 4.48 0.92

0 2.40 1.76 26.7 7.06 6.41 9.3 Cowpea 24 2.08 1.60 23.0 6.26 6.00 4.1

72 1.27 1.06 16.5 5.91 5.80 1.9

0 5.54 3.20 42.2 7.38 6.41 13.2 Chickpea 24 5.16 2.27 47.3 7.27 6.08 16.3

72 4.32 2.40 44.5 6.45 5.58 13.6

PCMP number = Free pectin + (Ca++ + % Mg++) - Phytin * Mean values based on four independent observations

Volume 43 (1978kJOURNAL OF FOOD SCIENCE- 87

Table 6-Changes in pectin content on cooking and germination in Table 7-“PCMP number“ as an index of cooking quality of the some legumesa (dry wt basis) legumesa

.

Legume

Period of germina-

tion (hr)

Anhydro galacto uranic acid content heq/lOOg)

Uncooked Cooked

Greengram 0 6.19 2.58

72 11.86 6.96

Cowpea 0 6.70 2.58

72 8.76 6.44

Chickpea 0 3.35 3.40

72 1.85 1.55

* Mean values based on four independent observations

The concept of PCMP number as applied to both ungermi- nated and germinated legumes used in this study were shown in Table 7. Muller (1967) has shown in peas that the hardness of the seed can directly be correlated to higher PCMP number. A similar trend has been found in this study also. Greengram which was easily cookable had the lowest PCMP number while chickpea requiring prolonged cooking, had higher PCMP value. The shortening of cooking time in germinated chickpea and the lengthening of cooking period in greengram and cowpea could be directly correlated with corresponding changes in PCMP number (Table 7).

Work on the chemical characteristics affecting cooking had been primarily on peas and beans (Rosenbaum and Baker, 1969; Crean and Haisman, 1964). While it is relatively easier to explain the chemical characteristics contributing to hardness or softness of dormant or stored seeds (Burr et al., 1968) germinated ones present a more complex system with the interplay of enzymes particularly phytase and pectinase (Belavady and Banerjee, 1953) which affect the solubility of pectins and phytins with a corresponding change in divalent cations like Mg* and Ca*. Though correlation could be derived by the application of PCMP number to explain the sum total of major chemical characteristics, the validity of this concept would need more critical study.

The relative affinity of divalent Ca* and Mg* to phytic and pectic acids perhaps play a primary role in affecting the cookability of legumes. The change in pH, degree of hydra- tion, stability of the complex salts and the cell wall uranic acids may also play a role in the cooking process. Since green- gram and chickpea in germinated and ungerminated forms present a totally contrasting cookability pattern, they may be considered as a model system for more detailed study on the interaction of various chemical principles involved in the cooking process.

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Legumes

Period Ca++ + of ger- Pectins % Mg++ Phytins

mination heql (meq/ (me4 PCMP (hr) 100 9) loo 9) 100 gl no.b

Greengram 0 6.19 6.28 5.87 6.60

72 11.86 3.63 5.16 10.33

Cowpea 0 6.70 5.93 3.87 8.76

72 8.76 4.23 3.37 9.62

Chickpea 0 3.35 9.23 2.52 11.06

72 1.80 7.55 2.10 7.25

a The values presented are for the uncooked material b PCMP number = Free pectin + (Ca++ + ‘/. Mg++) - phytins

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MS received 2126177; revised 5126177; accepted 613177.

Presented in part at the 44th Annual General Meeting of the Society of Biological Chemists (India) held at Calcutta. India, during November 1975.

This work was carried out as a part of a Research Project at the Central Food Technological Research Institute (CFTRI). Mysore. India.

The authors gratefully acknowledge the facilities extended by Dr. M.S. Narasinga Rae. Project Coordinator, Protein Technology Disci- pline. and Director, CFTRI, Mysore. The authors (K. Ganesh Kumar and T.V. Jaya) thank the Council of Scientific and Industrial Research. India for providing the Research Fellowships during the tenure of this work.

88 -JOURNAL OF FOOD SCIENCE-Volume 43 (19781

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