Plant Foods for Human Nutrition 42: 257-273, 1992. 9 1992 Kluwer Academic Publishers. Printed in the Netherlands.

Certain functional properties of defatted pumpkin seed flour EVANGELOS S. LAZOS Department of Food Technology, School of Food Technology and Nutrition, TEl of Athens, Saint Spyridon Str., Egaleo, Athens 122 10, Greece Received 1 March 1991; accepted in revised form 20 July 1991

Key words: Cucurbita pepo, C. maxima, seed flour, electrophoresis, nitrogen solubility, viscosity, gelation, water and oil absorption, sorption isotherms, foaming properties. Abstract. Defatted pumpkin (C. pepo and C. maxima) seed flour has potential food uses because of its high protein content, 61.4 + 2.56%. The functional and electrophoretic properties of the defatted flour were investigated. Polyacrylamide gel electrophoresis and electrofocusing indicated 14 bands of water-soluble protein subunits with isoelectric points between 3.81-8.08 and apparent molecular weights between 19,200 and 97,000 daltons. Minimum nitrogen solubility was observed at pH values between 3.0-7.0 and exceeded 90% at pH above 9.0. Solubility was a function of ionic strength. It appeared that, even at the pH of minimum solubility, the pumpkin seed proteins could be dissolved up to high concentrations by increasing NaC1 molarity. The viscosity of flour-water dispersion was affected by flour and salt concentrations, and temperature. The least gelation concentration was 8 % (w/v) and the water and oil absorption 24.8 ___ 2.03 and 84.4 ___ 4.05 g/100 g respectively. Sorption isotherms, BET monolayer moisture and binding energy of sorption were also calculated. Both foam capacity and stability were pH dependent.

Introduction Many Cucurbitaceae produce seeds rich in oil and protein. Although none of these seeds has been utilized on an industrial scale, many are used as sources of cooking oil and protein in some countries in Africa and the Middle East (Girgis and Said, 1968; Ogunremi, 1978). In Greece no oil or protein from such seeds has been produced, but pumpkin seeds (Cucurbita pepo and Cucurbita maxima) are consumed in significant amounts as a snack in the form of salted roasted seeds, constituting a food rich in oil and protein. Compositionally, pumpkin seeds contain by weight 25-55% oil and 23-35% protein (Bemis et al., 1968; Lazos, 1986a, b; Lal et al., 1983). The oil is highly unsaturated, containing mainly linoleic and oleic acids, edible and might be an acceptable substitute for highly unsaturated oils such as corn oil in diets (Lazos, 1986a). So far there are only data available on amino acid composition (Pichl, 1976b) and

258 characterization of albumins and globulins isolated from pumpkin seeds (Hara et al., 1976a, b, c, 1978; Lott et al., 1971; Lott and Vollmer, 1973; O'Kennedy et al., 1979; Pichl, 1976a, 1978; Vickery et al., 1941). Cucurbit seed globulins, which account for about 70-90% of the total protein content, contain about 18% nitrogen, while the albumins contain about 12% nitrogen (Pichl, 1976b; Jacks, 1986). Globulins consist of 2-6 subunits and are rich in arginine, aspartic and glutamic acid, and deficient in lysine and sulfur-containing amino acids (Jacks, 1986; Pichl, 1976b). Albumins isolated from C.maxima are composed of 9-12 major components of lower molecular weight than globulins (Jacks, 1986; Pichl, 1978). Biochemically, pumpkin seed globulins are considered storage proteins while albumins are believed to be metabolic proteins, which also act as storage proteins. Nutritional values of the globulins are similar of other oilseed globulins (Jacks, 1986). Although data on structure, composition, and usefulness of pumpkin seeds are available in literature, little is known on the functional properties of pumpkin flour or proteins. Numerous researchers have reported the preparation and functional properties of flours, proteins, protein concentrates and isolates from plant sources, especially oilseeds (Gillberg and T6rnell, 1976; Hutton and Campbell, 1977; Lawhon and Cater, 1971; Lin and Humbert, 1974; McWatters and Cherry, 1975, 1977; Sathe et al., 1982; Sosulski and Fleming, 1977; Thompson et al., 1982). Such efforts were often aimed at effective utilization of inexpensive and under-utilized plant proteins for nutritional and functional purposes. The economic importance of the oil and protein in new and under-utilized oilseed sources is especially vital as many countries have to solve the problem of oil and protein shortage. Pumpkin seeds could be utilized successfully as a source of edible oil and protein for human consumption (Lazos, 1986a).The purpose of the present investigation was to study certain functional properties of dehulled, defatted pumpkin seed flour.

Material and methods

Preparation of defatted pumpkin seed flour (DPSF) Ripe fruits of Cucurbita pepo and Cucurbita maxima were collected from the same field from the province of Didymotikhon Evros, Greece. The ripe fruits were crushed and the seeds were separated, washed and sun-dried. The sun-dried seeds were dehuUed and then ground to a powder by a Brabender mill to pass through a 1.00 mm sieve. The ground seeds were extracted for

259 18 h with petroleum ether (b.p. 40-60~ in large Soxhlet extractors, and then the defatted meal was heated to 50 + 5 ~ in an air-circulated oven for solvent removal. The defatted meal was re-ground in a Brabender mill to pass through a 0.5mm sieve. The fine ground defatted flour was put in polyethylene bags and used for further analysis and functional properties determination

Chemical analyses of defatted flour Proximate defatted flour analyses including moisture, crude protein (N x 6.25), crude fat, crude fiber and ash were performed according to AOAC (1975) procedures. Reducing sugars were extracted with 80% ethanol according to the method of Hymowitz et al. (1972) and quantitatively determined by the colorimetric method of Dubois et al. (1956). Minerals (A1, Ca, Cd, Co, Cr, Cu, Fe, K, Li, Mg, Mn, Mo, Na, Ni, Zn) were determined by atomic absorption spectroscopy, using a Perkin-Elmer 2380 instrument and phosphorus by the spectrophotometric molybdovanadate method (AOAC, 1975) after dry ashing.

Polyacrylamide gel electrophoresis and electrofocusing (PAGE) DPSF samples were dispersed in distilled water adjusted to pH 7.0. The dispersion was centrifuged at 10,000g for 10rain and filtered. PAGE was performed similarly to the method of Weber and Osborn (1969) on an LKB 2117 MULTIFPHOR II instrument. Samples were electrophoresed without prior reduction with fl-mercaptoethanol. After electrophoresis, gels were first fixed in 5% trichloroacetic acid solution, and then stained with Coomassie blue G250 (SERVA), and destained with acetic acid : methanol : water (3 : 2 : 35). Reference pI-marker proteins used were amyloglucosidase (3.5), ferritin (4.4), albumin bovine (4.7), fl-lactoglobulin (5.34), conalbumin (5.9), myoglobin horse (7.3), myoglobin whale (8.3), ribonuclease (9.45), and cytochrome c (10.65). For apparent molecular weight determination, reference proteins used where cytochrome c (t2,500), trypsin inhibitor (21,000), carbonic anhydrase (29,000), albumin egg (45,000), albumin bovine (67,000) and phosphorylase B (92,500). pI and molecular weight marker proteins were obtained from SERVA Feinbiochemica GmbH, FRG.

Functional property measurements Nitrogen solubility Nitrogen solubility was determined according to the method described by

260 Lawhon and Cater (1971) using a 2% flour suspension. Following centrifugation, aliquots of the supernatant were analyzed for nitrogen by both the standard Kjeldahl and Lowry et al. (1951) methods. Nitrogen solubility was determined for the water-flour suspensions after pH was adjusted to the values of 2, 3, 4, 5, 6, 7, 8, 9, 10 and 11. To study the effects of salt (NaC1) concentration on nitrogen solubility, 2% suspensions were used. Salt concentrations of 0.0, 0.2, 0.4, 0.6 and 0.8 M at the above pH range were investigated.

Viscosity For viscosity measurements, the appropriate sample was dispersed in distilled water and magnitically stirred for 2 h at room temperature (25 ~ prior to measurements as described by Sathe and Salunkhe (1981). Each sample was prepared at concentrations !, 2, 5 and 10% (w/v) and viscosity measured at 25 ~ using a Brookfiled LVT viscometer with a No 1 spindle rotating at 30 rpm. To study the effects of temperature and salt concentration, sample dispersions of 5 and 10% in distilled water and in 5% salt solution, were blended at high speed for 1 min, centrifuged at a low speed to remove entrapped air (Thompson et al., 1982) and measured for viscosity at 10, 25, 35, 45, 60, 70 and 80 ~ using the same instrument and operational conditions. Gelation Gelation concentration was determined by the method of Coffmann and Garcia (1977). Appropriate sample suspensions of 2, 4, 6, 8, 10, 12, 14 and 16% (w/v) were prepared in 5ml distilled water. The test tubes containing these suspensions were heated for 1 h in boiling water bath followed by rapid cooling under running cold tap water. The test tubes were then further cooled for 2 h at 4 ~ The least gelation concentration was determined as the concentration when the sample from the invert test tube did not fall down or slip. Water and oil absorption For water and oil absorption determination, the method of Lin and Humbert (1974) was followed. One gram of the sample was mixed with 10 ml distilled water or corn oil to a 15-ml conical graduated centrifuge tube for 1 min. After a holding period of 30 min, the tube centrifuged at 3000 rpm for 15 rain and the volume of free water or oil was read. Percent water or oil absorption was the amount of distilled water or corn oil per 100 g sample. Water sorption Equilibrium moisture contents of DPSF at various equilibrium relative

261 humidities (ERH) were determined at 15, 25, 40 and 60 ~ using a method similar to that reported by Saravacos et al. (1986). ERH of 6.4, 8, 23, 33, 58, 65, 75, 85 and 97% (25 ~ were maintained in closed jars containing LiBr, KOH, CH3COOK, MgC12, NaBr, NaC1, NaNO3, KC1 and K 2sO 4 respectively. Also, water activity (aw) sift due to temperature change was taken into account. A few crystals of phenol were added in jars with high ERH to avoid sample molding. Dublicate 2-g samples were removed from the jars after 21 days of equilibration, weighed and moisture content was determined by heating at 70 ~ under vacuum (AOAC, 1975).

Foaming properties Foaming properties were determined on 100 ml of a 2% (w/v) water suspension adjusted to the desired pH (2-10) and whipped for 5 rain in a kitchen mixer (Chef, Kenwood) at maximal speed. The contents were transferred to a graduated cylinder and liquid and foam volumes were measured. Percent volume increase was calculated. The foam stability was evaluated by measurements of liquid and foam volumes at time intervals of 0.0, 0.25, 0.5, 1, 2, 3, 4, 8, and 12 h.

Results and Discussion

Proximate Composition Crude oil content of dehulled pumpkin seed was 49 + 2.8% and fell in the range previously reported (Bemis et al., 1968; Lal et al., 1983; Lazos, 1986a, b). The composition of DPSF is shown in Table 1. As can be seen the flour was rich in protein and minerals, and poor in fat and crude fiber, while moisture content was relatively high. These results confirm previously reported values (Lazos, 1986a) and also indicate the presence of a significant amount of water soluble constituents which possibly could be removed by a diffusion-extraction process with water. In addition, utilization in various food products could contribute significant amounts of nutritionally important minerals such as K, P, Mg, Ca, Fe and Mn.

PAGE of Proteins Electrophoretic patterns of water-soluble proteins of DPSF showed 14 bands (Fig. 1). The isoelectric points of water-soluble pumpkin seed proteins were 3.81, 3.94, 4.29, 4.80, 5.13, 5.39, 6.34, 6.56, 7.05, 7.23, 7.33, 7.60, 7.80 and 8.08. Hence, the isoelectric points fell in two main regions of 3.81-5.39

262 Table 1. P r o x i m a t e c o m p o s i t i o n a n d m i n e r a l c o n t e n t o f defatted p u m p k i n seed flour Assay M o i s t u r e (%) C r u d e protein (N • 6.25) (%) C r u d e fat (%) C r u d e fiber (%) A s h (%) R e d u c i n g s u g a r s (%) C a r b o h y d r a t e s (by difference) (%) Minerals, mg/100 g (dry basis) A1 Ca Cd Co Cr Cu Fe K Li Mg Mn Mo Na Ni P Zn

Value ___ SD a 11.5 61.4 0.2 1.0 7.5 4.6 13.8

___ 0.14 _ 2.56 + 0.08 + 0.05 + 0.23 ___ 0.68 ___ 0.93

5.5 ___ 0.83 55.8 + 9.62 ND b 0.3 0.8 3.0 25.4 2100.0 4.6 470.0 21.7 ND 15.6 1.3 1250.0 7.2

___ 0.13 _ 0.22 _ 0.39 _ 2.41 + 60 _ 1.37 __+ 46 + 1.16 _ 1.76 ___ 0.13 ___ 32 ___ 1.12

a S D = S t a n d a r d deviation. b N D = Below detection limits o f the assay.

and 6.34-8.05. Pichl (1978) has made the assumption that the main isoelectric region of the C. maxima seed albumins was between 5.10-5.75. Cucurbit seed globulins account for about 70 to 90% (Jacks, 1986) and serve as the source of nitrogen necessary for the synthetic processes required for the growth (Ashton, 1976; O'Kennedy et al., 1979). Hara et al. (1976b) have reported that cucurbitin from pumpkin has a molecular weight of 112,000 daltons as determined by ultracentrifugation, which can be separated to subunits of 63,000 and 56,000 daltons. In contrast, Pichl (1976a) reported that globulins from different cucurbits have molecular weights of 218,000 to 256,000 daltons as determined by Sephadex G-200 column chromatography. In both cases polymeric structures were assumed. In the presence of sodium dodecyl sulfate, the globulins separated into subunits of molecular weight 63,000 and 56,000 daltons and upon reduction with fl-mercaptoethanol subunits separated into two peptides with molecular weights of 36,000 and 22,000 daltons (Hara et al., 1976a, b, 1978).

263

MW

19,200

......

"//////]

J

22,000 23,000 25,500 26,600

28,400

34,200 37,200

53,100 58,700 66,600 80,700

i

92,000 97,000

Fig. 1. Schematic diagram for molecular weight (MW) distribution profiles of defatted pumpkin seed four water-soluble proteins.

O'Kennedy et al. (1979) have reported that globulins of C. maxima and C. pepo contained proteins with molecular weights of 63,000, 58,000 and 56,000 daltons. After reduction with /~-mercaptoethanol globulins from dormant seeds of C. pepo and C. maxima had molecular weights of 40,000, 36,000, 22,000 and 20,000 daltons. Albumins isolated from C. maxima have been reported that composed of 9-12 components (Jacks, 1986; Pichl, 1978) with molecular weights in the range of 4,200-70,000 daltons. The results obtained by PAGE showed that water-soluble proteins of pumpkin seeds have molecular weights in the range of 19,200-97,000 daltons (Fig. 1). These values were in good agreement with those previously reported for pumpkin seed globulins and albumins. The protein fraction with molecular weights of 80,700 to 97,000 may be attributed to dimer structures.

264

Nitrogen Solubility At constant extraction time, nitrogen solubility of DPSF was dependent upon pH (Fig. 2). The solubility curve indicated a board range of minimum nitrogen solubility from pH 3.0 to 7.0. Less than 10% of the total pumpkin seed nitrogen was soluble in this pH range. The nitrogen solubility was increased with alkalinity and reached 92% at pH 11. On the acid side, pH2.0, 13% of the nitrogen was in solution. Similar results have been reported for egusi (Colocynthis citrullus L.) seed protein product by Akobundu et al. (1982). Also, nitrogen solubility profile of DPSF was similar to that of melon seed flour (Onuora and King, 1983; King and Onuora, 1984). Solubility of nitrogen at pH 5-7 was increased by addition of salt (Fig. 2), since globulins constitute the major part of pumpkin seed proteins. As can be seen from Fig. 2, increasing NaC1 molarity resulted in an increase in nitrogen solubility. It appeared that, even at the isoelectric point, the pumpkin seed proteins could be dissolved by increasing the ionic strength of the solution (salting-in). Similar findings have also been reported for other seed proteins (Anderson et al., 1973; Ruiz and Hove, 1976; Shen, 1976; Sosulski and Fleming, 1977; van Megen, 1974). The amount of nitrogen extracted increased from 4.5-8.7% in the absence of salt to 12-55% with 0.6-0.8 M NaC1. It should also be pointed out that at alkaline pH, 8.0-11.0, a decrease in solubility occured with salt addition (Fig. 2). This could be attributed to salting-out of proteins which follows salting-in when the ionic strength is increased sufficiently (Shen, 1976; van Megen, 1974).

Viscosity The results of viscosity measurements are presented in Table 2. As can been seen, viscosity appeared to be a function of solid and salt concentrations, and temperature. Although low, viscosities tended to increase with flour concentration in dispersion, as a result of increased protein concentration in solution. It should be pointed out that viscosity is a function of the type of protein, e.g. globulins, albumins or mixture of them (Sathe and Salunkhe, 1981). Because of the fact that up to 90% of pumpkin seed proteins are globulins, which are salt-soluble, addition of NaC1 at concentration of 5% increased the apparent viscosity of pumpkin flour dispersions. The temperature increase of 5 and 10% dispersions in distilled water and in 5% NaC1 solution resulted to a viscosity decrease. This decrease generally occured in the range of 10-60~ but when measurement temperature exceeded 60 ~ a viscosity increase was observed which could be attributed

265

100

90-

o0.0M

NaCI

o0.2M

NaCI

,0.4M

NaCI

§

80-

M NaCI

~0.8 M NaCI

70.

80 . m

.m

_

50 84

== 40 o

30

20

10

0

I

I

I

I

I

I

I

I

I

1

2

3

4

5

6

7

10

11

pH Fig. 2. Nitrogen solubility of defatted pumpkin seed flour.

-266

q--I -H q-I q-I q-I q-I -H

O

t",l

+1 +1 +1 +1 +1 +1 +l

O

O

--H -H --H -H --H -H --H O ',~ ',,~1- ee~ t"-,I t'q ' , ~ ee'~

+1+1+1+1+1+1+1 O

O O

+1

+1 O

o~,

+1

I~11111

G,

y,?

,
8.0) resulted to over 90% nitrogen solubility. The bulk of pumpkin seed proteins consists of globulins that can be solubilized even at their isoelectric points by adding salt. The protein solubilities depend in part upon molecular size and the salting-in phenomenon. As has been stated by Anderson et al. (1973) the smallest molecules dissolve at the lowest salt concentration, while the largest molecules are solubilized at the highest salt concentration. PAGE electrophoresis of water soluble proteins showed 14 protein subunits with apparent molecular weights between 19,200 ___ 200 and 97,000 + 1,900 daltons. These values where in accordance with those previously reported for pumpkin as well as for other Cucurbitaceae (Hara et al., 1976a, b, 1978; Pichl, 1976a; O'Kennedy et al., 1979). DPSF was low in water absorption, while fat absorption was comparable to other oilseed flours. Because of the poor water solubility pumpkin flour may appear to have limited application in low pH liquid food products, while it may be applied in salt containing products such as meat, some bakery and imitation milk products. Of course, pumpkin protein con-

271

centrates and isolates as well as various treatments may alter these characteristics resulting in a wider range of applications. Foaming properties were depended on protein solubility which is affected by pH and ionic strength. Apparent viscosity of flour dispersions in water was concentration, salt and temperature dependent. Water sorption capacity was increased at high equilibrium relative humidities (65-97%) and decreased with temperature increase. BET monolayer moisture content was also temperature dependent and maximum binding energy of sorption was 33.0 kJ/mole at 0.06 g H20/g dry solids. Many interactions were observed throughout the study. In addition, protein preparation, treatments such as heating, dialysis, acylation etc., and the presence of substances such as salts, sugars etc. may alter functional behaviour of pumpkin seed proteins. So complex systems will show different responses to variations in different factors. Functional performance of pumpkin seed flour in a food system does not necessarily parallel that in simple systems and caution is needed in extrapolation of results from simple systems to food systems. Application to various food formulations could be of interest in future studies.

References Akobundu ENT, Cherry JP, Simmons JG (1982) Chemical, functional, and nutritional properties of egusi (Colocynthis citrullus E.) seed protein products. J Food Sci 47:829-835 Anderson RL, Wolf WJ, Glover D (1973) Extraction of soybean meal proteins with salt solutions at pH4.5. J Agr Food Chem 21:251-254 AOAC (1975) Official Methods of Analysis, 12th ed. Association of Official Analytical Chemists, Washington DC Ashton FM (1976) Mobilization of storage proteins of seeds. Annu Rev Plant Physiol 27: 95-117 Bemis WP, Berry JW, Kennedy MJ, Woods D, Moran M, Deutschman JrAJ (1968) Oil composition of Cucurbita. JAOCS 44:429-430 Beuchat LR (1977) Functional and electephoretic characteristics of succinylated peanut flour protein. J Agr Food Chem 25:258-261 Cherry JP, McWatters KH, Beuchat LR (1979) Oilseed protein properties related to functionality in emulsions and foams. ACS Syrup Ser 92:1-26 Childs EA, Park KK (1976) Functional properties of acylated glandless cottonseed flour. J Food Sci 41:713-714 Chou DH, Morr CV (1979) Protein-water interactions and functional properties. JAOCS 56: 53A-62A Coffmann CW, Carcia W (1977) Functional properties and amino acid content of a protein isolate from mung bean flour. J Food Technol 12:473-478 Dubois M, Gilles KA, Hamilton JK, Reberts PA, Smith F (1956) Colorimetric method for determination of sugars and related substances. Anal Chem 28:350-356 Fleming SE, Sosulski FW, Kilara A, Humbert ES (1974) Viscosity and water absorption characteristics of slurries of sunflower and soybean flours, concentrates and isolates. J Food

272 Sci 39:188-191 Gillberg L, Trmell B (1976) Preparation of rapeseed protein isolates. Precipitation of rapeseed proteins in the presence of polyacids. J Food Sci 41:1070-1075 Girgis P, Said F (1968) Lesser known Nigerian edible oils and fats. I. Characteristics of melon seed oils. J Sci Food Agric 19:615-616 Hara I, Ohmiya M, Matsubara H (1978) Pumpkin (Cucurbita sp.) seed globulin. III. Comparison of subunit structures among seed globulins of various Cucurbita species and characterization of peptide components. Plant Cell Physiol 19:237-243 Hara I, Wada K, Matsubara H (1976a) Pumpkin (Cucurbita sp.) seed globulin. II. Alterations during germination. Plant Cell Physiol 17:815-823 Hara I, Wada K, Wakabayashi S, Matsubara H (1976b) Pumpkin (Cucurbita sp.) seed globulin. I. Purication, characterization, and subunit structure. Plant Cell Physiol 17: 799-814 Hutton CW, Campbell AM (1977) Functional properties of a soy concentrate and a soy isolate in simple systems and in a food system. Emulsion properties, thickening function and fat absorption. J Food Sci 42:457--460 Hymowitz T, Collins FI, Panczner J, Walker WM (1972) Relationship between the content of oil, protein, and sugar in soybean seed. Agron J 64:613-616 Jacks TJ (1986) Cucurbit seed protein and oil. ACS Symp Set 312:249-260 King RD, Onuora JO (1984) Effect of processing factors on some properties of melon seed flour. J Food Sci 49:415--418 Kinsella JE (1982) Relationships between structure and functional properties of food proteins. In: Fox PF, Condon JJ (eds), Food Proteins. Applied Science Publishers, pp. 51-103 Labuza TP, Kaanane A, Chen JY (1985) Effect of temperature on the moisture sorption isotherms and water activity sift of two dehydrated foods. J Food Sci 50:385-391 Lal BM, Datta N, Madaan TR (1983) A study of kernel oils of some cultivated cucurbits. Qual Plant Foods Hum Nutr 32:83-85 Lawhon JT, Cater CM (1971) Effect of processing method and pH of precipitation on the yields and functional properties of protein isolates from glandless cottonseed. J Food Sci 36:372-377 Lazos ES (1986a) Nutritional, fatty acid and oil characteristics of pumpkin and melon seeds: J Food Sci 51:1382-1383 Lazos ES (1986b) Some chemical and physical characteristics of pumpkin seed oil. Chim Chron New Series 15:91-96 Lin MJY, Humbert ES (1974) Certain functional properties of sunflower meal products. J Food Sci 39:368-370 Lott JNA, Larsen PL, Darley JJ (1971) Protein bodies from cotyledons of Cucurbita maxima. Can J Bot 49:1777-1782 Lott JNA, Vollmer CM (1973) The structure of protein bodies in Curcubita maxima cotyledons. Can J Bot 53:687-688 Lowry OH, Rosebrough N J, Farr AL, Randall RJ (1951) Protein measurement with the Folin phenol reagent. J Biol Chem 193:265-275 McWatters KH, Cherry JP (1975) Functional properties of peanut paste as affected by moist heat treatment of full-fat peanuts. J Food Sci 40:1205-1209 McWatters KH, Cherry JP (1977) Emulsification, foaming and protein solubility properties of defatted soybean, peanut, field pea and pecan flours. J Food Sci 42: 1444-1447, 1450 Ogunremi EA (1978) Effects of nitrogen on melon (Citrullus lanatus) at Ibadan Nigeria. Exp Agric 14(4): 357-365 O'Kennedy BT, Reilly CC, Titus JS, Splittstoesser WE (1979) A comparison of the storage protein (globulin) of eight species of Cucurbitaceae. Can J Bot 57:2044-2049

273 Onuora JO, King RD (1983) Melon seed flour: Composition and factors affecting the extractability of nitrogenous constituents. Lebens Wiss u Technol 16:162-166 Pichl I (1976a) Seed globulins of various species of Cucurbitaceae. Phytochemistry 15:717-722 Pichl I (1976b) Amino acid composition and nitrogen content of seed albumins and globulins of various species of the Cucurbitaceae family. Biochem Physiol Pflanzen 170:509-515 Pichl I (1978) Characterization of albumins isolated from seeds of Cucurbita maxima L. Biochem Physiol Pflanzen 172:61-66 Ruiz JrLP, Hove EL (1976) Conditions affecting pro'daction of a protein isolate from lupin seed kernels. J Sci Food Agric 27:667-674 Saravacos GD, Tsiourvas DA, Tsami E (1986) Effect of temperature on the water adsorption isotherms of sultana raisins. J Food Sci 51: 381-383, 387 Sathe SK, Salunkhe DK (1981) Functional properties of the great northern bean (Phaseolus vulgaris L.) proteins: Emulsion, foaming, viscosity and gelation Properties. J Food Sci 46: 71-74, 81 Sathe SK, Deshpande SS, Salunkhe DK (1982) Functional properties of wing bean (Psophocarpus tetragonolobus L. DC) proteins. J Food Sci 47:503-509 Schmidt RH (1981) Gelation and coagulation. ACS Syrup Ser 147:131-147 Shen JL (1976) Solubility profile, intrinsic viscosity, and optical rotation studies of acid precipitated soy protein and of commercial soy isolate. J Agr Food Chem 24:784-788 Sosulski F, Fleming SE (1977) Chemical, functional, and nutritional properties of sunflower protein products. JAOCS 54: 100A-104A Thompson LU, Liu RFK, Jones JD (1982) Functional properties and food applications of rapeseed protein concentate. J Food Sci 47:1175-1180 van Megen WH (1974) Solubility behavior of soybean globulins as a function of pH and ionic strength. J Agr Food Chem 22:126-129 Vickery HB, Smith EL, Hubbel RB, Nolan LS (1941) Cucurbit seed globulins. I. Amino acid composition and preliminary tests of nutritive value. J Biol Chem 140:613-624 Weber K, Osborn M (1969) The reliability of molecular weight determinations by dodecylsulfate-polyacrylamide gel electrophoresis. J Biol Chem 244:4406--4412