softening of pumpkin seeds (cucurbita moschata) by alkaline maceration

SOFTENING OF PUMPKIN SEEDS (CUCURBITA MOSCHATA) BYALKALINE MACERATION

S.M.B. CARAMEZ1, M. STEFANI2, J.D. MEDEIROS2, M.A. VIEIRA1,G.R. BRÜSKE3, A. DE FRANCISCO1 and E.R. AMANTE1,4

1Food Science and Technology Department – Rod. Admar Gonzaga,1346 – Itacorubi, CEP 88034001

2Botanic Department

3Cellular Biology, Embriology and Genetics Department/Santa Catarina FederalUniversity/Biological Sciences Center – Florianópolis, Santa Catarina, Brazil

Accepted for Publication June 21, 2007

ABSTRACT

The nutritional value of pumpkin seeds is widely recognized. This articleshows that alkaline maceration of pumpkin seed makes them soft and improvestheir market acceptability as an important source of fiber, unsaturated lipids,minerals and proteins. Microscopic characterization of pumpkin seeds wasrealized. The results indicate elimination of minerals from the seeds throughthe delignification process due to the nature of the phenolic compounds elimi-nated in the maceration liquid. The alkaline maceration process of pumpkinseeds may contribute to a larger consumption of fibers and other nutritiveelements from them.

PRACTICAL APPLICATIONS

This work shows that the pumpkin seeds softened by chemical macerationimprove sensory preferences, compared to nonmacerated products. Solid wastefrom pumpkin process can be converted to a new product as a snack rich in fiberand other important compounds, normally discarded as an industrial solidwaste.

INTRODUCTION

Several studies have been published about the correct use of raw materialssuch as seeds, husks, and animal and vegetable tissues, which are usually4 Corresponding author. TEL. +55-48-3721-53-71; FAX: +55-48-3721-99-43; EMAIL: eamante@

cca.ufsc.br

Journal of Food Process Engineering 31 (2008) 431–442. All Rights Reserved.© 2008, The Author(s)Journal compilation © 2008, Blackwell PublishingDOI: 10.1111/j.1745-4530.2007.00163.x

431

discarded in spite of their great nutritional and technological potential(Amante 1997; Pandey and Soccol 2000; Albuquerque et al. 2002).

Pumpkin, e.g., is consumed all over the world; however, its seeds areconsumed in only a few regions. Consequently, most seeds end up as wasteproducts from the production of jams and jellies in regions of malnutrition(Santos et al. 2004).

Pumpkin seeds are consumed in excessive quantities in Greece as toastedand salted snacks, and these seeds are very rich in oil and proteins (Lazos 1992).

According to Mansour et al. (1996), pumpkin seed protein isolate can beadded to bologna-type sausages, improving their nutritional quality and reduc-ing costs. Proteins from pumpkin seeds have good nutritional properties andmay be used in meat derivatives.

Ramirez and Modernell (1997) studied several formulations to controlinfant diarrhea. All formulations contained pumpkin (Cucurbita maxima) flourat 19%, which is the highest level allowed because of its high sugar andpotassium contents. The best formulation contained pumpkin flour (17.5%),pregelatinized rice flour (54.5%), dehydrated poultry meat (16%), vegetableoils (5%) and coconut oil (7%). This formulation’s acceptance was 78–86%;children who consumed this food three to four times per day recovered fromdiarrhea and the volume of feces diminished within 24 h.

In India, pumpkins are extensively consumed as a vegetable. Their pulp isconsumed as fruit, either ripe or green, and their seeds are an important sourceof nutrients and are consumed for their medicinal properties. In Nigeria,fermented pumpkin seeds are used in a local product named “ogiri,” which is aningredient in several kinds of Nigerian foods (Murty and Subrahmanyam 1989;Gupta et al. 1997).

Pumpkin (Cucurbita pepo L.) seed oil, commonly used as salad oil inSlovenia, Hungary and in southern parts of Austria, is dark green with highquantities of free fatty acids. Because of foam formation, pumpkin seed oilcannot be used for frying purposes (Murkovic et al. 1996).

The oil content in pumpkin (Cucurbita sp.) seeds is about 50%. The fourmain fatty acids are palmitic, stearic, oleic and linoleic acids. They constitute98.0 � 0.13% of the total fatty acids in the seeds. Other fatty acids make upabout 0.5%. The fatty acid composition depends on several factors: variety,location, weather, degree of maturation and others (Murkovic et al. 1996).

Pumpkin (C. pepo L.) seeds are rich in vitamin E, especially ing-tocopherol. In some varieties, a total of 620 mg/kg of g-tocopherol has beenfound (Murkovic et al. 1996).

Wenli et al. (2004) compared the oil from black and white pumpkin seedsby supercritical extraction. Major compounds in both types of pumpkin seedoils were 9, 12-octadecadienoic acid, 9-octadecenoic acid, stearic acid andpalmitic acid. Heptadecanoic acid (0.27%), tetracosanoic acid (0.1%),

432 S.M.B. CARAMEZ ET AL.

9-dodecaenoic acid (90.45%) and pentadecenoic acid (0.05%) were found inwhite seed oil but not in black seed oil. The black seed oil contained moreunsaturated fatty acids than the white seed oil.

The richest known dietary source of lignans is flaxseed. Flaxseed hasbeen reported to contain glycosides of secoisolariciresinol as the major lignan,combined with small amounts of matairesinol, isolariciresinol and pinoresinol.Secoisolariciresinol has so far been identified in pumpkin seeds and is believedto protect against hormone-dependent cancer (Sicilia et al. 2003).

The stability of stored pumpkin seeds can be related to the presence oflypoxigenase. Al-Khalifa (1996) studied lypoxigenase activity in pumpkinseeds before and after toasting and concluded that toasting diminishes lypoxi-genase activity as a result of temperature increase.

Hunkeler (2002) has patented a product, “snack food made from pumpkinseeds,” comprising whole husked pumpkin seeds with a chocolate coating.

The low application of the properties of pumpkin seeds as a raw materialis due to the lack of knowledge about more adequate means of processing andconsumption.

The main objective of this work was to apply chemical maceration tosoften the husk of pumpkin seed, rich in fiber and other functional compounds,normally discarded, so that they could be consumed as snacks. Texture evalu-ation was determined by sensory analysis of preference tests, to obtain anincrease in the use of pumpkin seeds in the human diet by a simple process forseed softening.

MATERIALS AND METHODS

Cristalina Agroindustrial, in Arroio Trinta, Santa Catarina, Brazil,donated Cucurbita moschata seeds from matured pumpkins collected fromseveral batches of pumpkin pulp production. The seeds were washed in coldwater and dried in an air circulation dryer at 65C for 24 h. The seeds were thenrefrigerated (4C).

Alkaline Maceration

Pumpkin seeds were macerated by immersion in a sodium carbonatesolution (10%) for 24 h, washed and dried with an air dryer at 65C forapproximately 24 h, according to Caramez (2000).

Sensory Evaluation

Sensory analysis was used to determine consumer preference in relationto maceration treatment. The preference test was carried out according to themethods described by Murray et al. (2001).

ALKALINE MACERATION OF PUMPKIN SEEDS 433

Six seeds macerated and nonmacerated were dried, toasted on a skilletand identified by three random numbers. These samples were offered to a totalof 285 consumers at three different supermarkets in the city of Florianopolis,Santa Catarina state, Brazil. The consumers’ choice was between two samples:macerated or nonmacerated seeds.

Optical Microscopy

The seeds were fixed in formaldehyde (50 mL) – acetic acid (50 mL) –ethanol (70oGL) (900 mL) – for 24 h (Johansen 1940).

Permanent slides were prepared from the fixed material, dehydrated inn-butyl alcohol followed by xylene and embedded in paraffin. Twelve-micrometer sections were cut with a disposable microtome blade and fixed onglass slides with Haupt’s adhesive. After storage at 50C for 24 h, the paraffinwas removed, and the slides were stained with safranin/fast green (Sass 1951).

Semipermanent slides were hand cut, both longitudinally and cross-sectioned. Clarification was carried out with sodium hypochlorite (Quintas1963; Berlyn and Miksche 1976). The semipermanent slides were stained withtoluidine blue for 5 min and rinsed with distilled water (O’Brien et al. 1965).Glycerin 40% was used over the sections and the cover slips were sealed withnail polish.

Scanning Electron Microscopy

Whole pumpkin seeds were sliced longitudinally or cross-sectionally,fixed on aluminium stubs with wax. The stubs were gold coated in a PolaronE5000 sputter coater (Quorum Technologies, Wattford, U.K.) (Grimstone1980) and observed with an electronic microscope (Phillips XL 30 SEM).

RESULTS AND DISCUSSION

Anatomic Description of the Pumpkin Seed

Optical and scanning electron microscopy of pumpkin seeds revealed anintegument formed by several layers: cuticle, epidermis, pointed parenchyma,chlorophyll containing sclerenchyma and internal epidermis, all structurallydifferent from each other (Figs. 1 and 2).

The epidermis is unistratified, with radial elongated cells and surroundedby sclerified walls. In the anticlinal wall, there are differentiated furrows,which are also sclerified, with basal and apical ramifications (Figs. 3–5).

Adjacent to the epidermis, there is a parenchymal layer, with about fourstrata. The cells of this parenchyma show lignified walls provided with con-spicuous points (Figs. 6 and 7).


The seeds from C. moschata show a characteristic unistratified epider-mis, with highly visible elongated cells in its anticlinal axis, with sclerifiedfurrows. The furrows are shown on the anticlinal walls, with intense ramifi-cation at both ends. Adjacent to the epidermis, there is a differentiated layer

FIG. 1. LONGITUDINAL DIAGRAM OF THE INTEGUMENT AND CUTICLE (CU),EXTERNAL EPIDERMIS (EPE), POINTED PARENCHYMA (PQP), SCLERENCHYMA (EC),

SPONGY PARENCHYMA (PQE), CHLOROPHYLL-CONTAINING PARENCHYMA (PQC)AND INTERNAL EPIDERMIS (EPI)

Bar 10 mm.


with about four lignified and pointed parenchymal cell strata. This paren-chyma layer is limited by a unistratified furrow of highly stretched stonecells. Additional spongy parenchyma layers, containing cells with lignifiedand punctuated walls, are observed (Fig. 8). The central layer is representedby the internal epidermis, unistratified and composed of small cells, in somecases, with chloroplasts (Fig. 8; see 8a). At the extremities, the tegumentkeeps the previously described organization. However, the cell layers arewider and close to the spongy parenchyma; the bicollateral vascular beamsare differentiated.

FIG. 2. A CROSS-SECTION OF A NONMACERATED PUMPKIN SEEDEpidermis (EP), pointed parenchyma (PQP), spongy parenchyma (PQE), endosperm (EN) and

cotyledons (CO), internal epidermis (EPI). Stained with safranin/fast green.Bar 10 mm.


The high water solubility of some hemicelluloses shows that they are verycovalently bonded to lignin (Dimitriu 1998). These bonds between lignin andpolysaccharides in vegetable fibers can be the susceptible point for the reactionof alkaline maceration. Hence, alkaline maceration can soften pumpkin seedsto increase their use.

FIG. 3. SCANNING ELECTRON MICROGRAPH OF THE NONMACERATED INTEGUMENTEPIDERMIS OF PUMPKIN SEEDS

FIG. 4. CROSS SECTION OF THE APICAL REGION INTEGUMENT OF NONMACERATEDPUMPKIN SEEDS IN TRANSVERSAL CUT (BAR 10 mm)

4a and arrows show detail of furrows. Bar 10 mm.


Microscopy and Sensory Properties of Macerated Pumpkin Seeds

Seed maceration promotes a light epidermal cell disorganization, reduc-ing the thickness of the anticlinal walls (Fig. 9), when compared to nonmac-erated seed (Fig. 3) This reduction in wall thickness is interpreted as a positiveeffect of maceration. Macerated and nonmacerated seeds showed differences

FIG. 5. TRANSVERSAL CUT FROM BASAL REGION OF NONMACERATEDPUMPKIN SEEDS

Arrows show details of furrows. Bar 10 mm.

FIG. 6. POINTED PARENCHYMA OF A NONMACERATED PUMPKIN SEED INTEGUMENTIN A TRANSVERSAL CUT STAINED WITH SAFRANIN/FAST GREEN

Notice arrows. Bar 10 mm. 6a shows the parenchymal cell detail; bar 1.25 mm.


related to tegument softness and to expansion during toasting, resulting in ahigher internal diameter of the macerated seeds as a result of the combinationof both treatments, chemical and thermal, which in turn increased palatability.

The positive effect of the treatment on the seeds’ texture was confirmedby sensory analysis carried out in three major supermarkets in Florianópolis –

FIG. 7. SCANNING ELECTRON MICROGRAPH OF PARENCHYMA CELLS OF THETEGUMENT OF A NONMACERATED PUMPKIN SEED

FIG. 8. EPIDERMIS FROM NONMACERATED PUMPKIN SEEDS IN A CROSS-SECTIONEDCUT (BAR 5 mm)

8a shows detail of epidermal cell walls (arrows) stained with safranin/fast green. Bar 1.25 mm.


Santa Catarina. The consumer distribution according to their preferences isshown in Table 1.

The results indicate that chemical maceration changed the texture ofpumpkin seeds and, therefore, increased the consumer’s preference for theseseeds.

CONCLUSIONS

The influence of the softening process was shown by scanning electronmicroscopy. A diagram of the seed’s tegument was drawn because there is norecord of this in the literature.

FIG. 9. SCANNING ELECTRON MICROGRAPH OF THE MACERATED INTEGUMENT OFPUMPKIN SEEDS

TABLE 1.CONSUMER DISTRIBUTION ACCORDING TO PREFERENCE OF TREATED AND

UNTREATED PUMPKIN SEEDS

Samples Number ofconsumers

Percentage Confidenceinterval 95%

Macerated 187 65.61 59.78–71.12Nonmacerated 98 34.39 28.88–40.22Total 285 100.0


Alkaline maceration of pumpkin seeds, which can be easily developed,caused softening in the toasted product and promoted consumption ofthis source of dietetic fibers with elevated concentration of importantnutrients.

The alkaline maceration process may be suggested as a path to increaseconsumption of pumpkin seeds for human nutrition.

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softening of pumpkin seeds (cucurbita moschata) by alkaline maceration

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