General background Crop

The pumpkin is grown in warm climates from 20 to 27 °C, as it is a sensitive product to cold and frost³. In Chile, the cultivation area is located in the central region and the northern center of the country, especially the Metropolitan, Libertador Bernardo O'Higgins, Maule and Coquimbo regions. The Cucurbita maxima fruit is harvested during the months of March and April, when the ripe fruit can be properly stored for several months under conditioned cellars and reception centers, which allow the product to be stocked throughout the whole year¹⁶.

Taxonomy

The family of Cucurbitaceae has around 118 genus and more than 825 species¹⁷. The taxonomy classification of Cucurbita maxima is shown in the table 1.

Botany

It is important to know the botany of the maximum Cucurbita species in order to understand the differences and procedures for obtaining its by-products. Botany gives very important information from at the macroscopic level, structure and function of a vegetable. Thus, the plant will be described to understand its main by-product, the seeds.

Plant

Cucurbita maxima is a yearly, herbaceous diclinomonoecious plant. The plant has a radial system that reach a profundity of 1.8 m, but most of it is in the first 60 cm. The stems are rough, often angular, with tendency to produce roots in the knots. There are creeping stems with guides between 10 and 30 m long, have semierect stems (trunk varieties) with short internodes. The leaves of the Cucurbita maxima are large, suborbicular, frequently lobed rounded and single-layered¹⁸.

The flowers are yellow, commonly solitary, and occasionally the masculine ones are in fascicles. The male flowers have long peduncles, three stamens, free filaments, linear anthers, connivent, one of them being monothecae. The female flowers are short pedunculate, with an inferior, oblong or unipolar ovary, with 3-6 pluriovulated placentas, shirt styled and 3-5 lobed stigma. During pollination (of entomophily form) the stigma remain open and with receptive stigma for 12 hours¹⁸.

The fruit is a berry (unilocular with many seeds), indehiscent, of various size and coloration. It has an inner cavity where fibers and seeds are located¹⁸.

Seeds

The seeds are large, flat, oval-shaped and end in a tip. They have an approximate weight between 50 and 250 mg as well as small and big fruits. The large size provides an excellent reserve that favors the germination and establishment of the seeds¹⁸.

Mature seeds do not contain functional endosperms. The embryo completely fills the seed coat and the reserves (in the form of lipids, in small spherical bodies called spherosomes, and proteins in protein organelles) are stored in the cotyledons¹⁸. The optimum temperature for germination ranges from 25 to 30 °C and it is inhaled below 15 °C¹⁸.

Chemical composition of pumpkin seeds

In relation to pumpkin seeds (Cucurbita maxima), the moisture content can vary by variety and regions. The seeds var. Béjaoui showed a moisture content of 8.46%¹⁹, while a slightly low values between 3.08 and 5.40%, were showed for seeds collected from Akure, Ondo State in Nigeria and the province of Didymotikhon Evros, Greece, respectively^20,21. Cucurbita maxima seeds present nutritional composition mainly characterized by a high concentration of fatty acids and proteins¹¹. Cucurbita maxima seeds present nutritional composition mainly characterized by a high concentration of fatty acids and proteins¹¹. Table 2 shows the nutritional composition reported in different articles on Cucurbita maxima seed^20,21,22. Based on this evidence, seeds have a high nutritional value, provide good quality oil and tocopherols and have a good vegetable cover²⁷.

Figure 1 Flower and fruit. 

Figure 2 Cucurbita maxima seed. 

Figure 3 The diagram represents the industrial treatment process of pumpkin and the precise stage in which the seeds are separated for obtaining by-products. 

Regarding proteins contained in Cucurbita maxima seeds, the presence of amino acids is noteworthy, with glutamic acid and arginine being the most abundant^22,23,24 (Table 3). Moreover, species belonging to the Cucurbitaceae family have an unusual amino acid known as cucurbitin, chemically defined as (-)-3-amino-3-carboxipirrolidine; and is attributed to anti-inflammatory and antiparasitic functional properties²⁵.

Ash content is also high and is mainly characterized by the presence of key minerals that are generally deficient in food intake such as zinc, iron and manganese^19,20,22. Table 4 shows the mineral content of Cucurbita maxima seeds. The differences observed could be explained by soil conditions, seed status, and mineral determination methodology, among others.

Fatty acids content in Cucurbita maxima seeds is up to 50% of total weight of the seed²⁰, with predominance of unsaturated-short chain fatty acids. As a result, seeds have a high stability to oxidative rancidity process, which is also coincident with a low peroxide value, as can be appreciated in table 5 ²⁰. Peroxide value is used as an indicator of oil deterioration and acid value is used as an indicator of oil edibility²⁰. These values change according to the place of origin and the references analyzed.

The saponification index of the oil could be used as a parameter for checking adulteration of the oil sample²⁰. The saponification index, varying from 126 to 201, shows that among fatty acids present in the examined oils, these have a higher number of carbon atoms. The oils have high iodine values, thus reflecting a high degree of unsaturation. In addition, high values indicate that the oil has a high content of unsaturated fatty acids relative to palm oil^{22,23,24,25,26,27}. As mentioned, oil extracted from Cucurbita maxima consists mainly of stearic, oleic and linoleic acids, among other, as it can be observed in table 6.

A study carried out by Stevenson¹¹ evaluated seed oil content and fatty acid composition of twelve pumpkin cultivars (Cucurbita maxima D.) grown in Iowa. Oil and total unsaturated fatty acid content ranged between 10.9-30.9% and 73.1-80.5%, respectively. The predominant fatty acids were linoleic, oleic, palmitic, and stearic acid. The range of fatty acid composition was shown in table 6 ^11,19,21.

Phytosterols are usually classified as d-7 and d-5 sterols, with d-7 sterols predominant in pumpkin oil seeds²⁸. Tocopherols content in Cucurbita maxima oil extract varied from, as follows: between 27,1-75,1 μg/g oil for α-tocopherol; 74,9-492,8 μg/g γ-tocopherol oil; and 35,3-1109,7 μg/g δ-tocopherol oil.

This fact about tocopherols composition in Cucurbita maxima seeds is the reason for high oxidative stability and makes Cucurbita maxima oil a good choice to use in industrial applications and to incorporate into human diet¹¹.

Nutritional benefits of pumpkin seeds

There are several uses and applications of pumpkin by-products. For Curcubita maxima, the seeds can be used for oil and flour. Its application focuses on providing added value from the nutritional point of view for human and animal feeding. What follows is a summary of the research regarding the nutritional capacity of seeds and pumpkin shells.

Direct consumption of pumpkin seed has had a high demand. One study found that the consumption of dietary milled sesame/pumpkin/flax seed among hemodialysis patients lowers markers of inflammation, such as triglycerides²⁹.

Pumpkin (Cucurbita maxima) seeds and plant seeds belonging to the Cucurbitaceae family are edible, abundant and big. However, they are mostly discarded as agro-industrial waste, except for certain of these seeds that have been used in folkloric and traditional medicine as a remedy for kidney, bladder and prostate disorders³⁰.

Pumpkin seed oil has diverse phenolic compounds such as tyros (phenylethanoid), vanillic acid, vanillin, luteolin and sinapic acid. When administered to mice, the oil stressed with aflatoxin, lowered the toxic effect of the mycotoxin. The supplementation of pumpkin seed oil also attenuated the cytotoxicity and genotoxicity of the immunosuppressive agent azathioprine and restored the glutathione content and DNA integrity following supplementation³⁰.

Consumption of pumpkin seed reduces markers of inflammation, increases lymphocyte count, enhances phagocytic activity, and inhibits the progression of fatty liver to steatohepatitis (determined from low MDA and TNF-α content)³⁰. Supplementation of pumpkin seed oil has cardioprotective, hypolipidemic, antihypertensive, hypoglycemic, anthelmintic and wound healing effects. Oral intake of Cucurbita maxima seed oil extract in doses of 10 g/day for 6-12 weeks reduces the bladder over-activity of patients preventing urinary disorders and producing an effect on urinary health³⁰, also it causes inhibition of formation of crystals and aggregation on urinary tract, thus decreasing the risk of bladder and kidney calculus³¹.

Lipid extract from Cucurbita maxima seeds slows the progress of hypertension and decreases hypercholesterolemia because of the unsaturated fatty acids and phytosterols content. Moreover, there is evidence that seeds can decrease the risk of diabetes, promotes hypoglycemic activity³², and decrease levels of breast, gastric, colon-rectal and pulmonary cancers³³. Furthermore, Cucurbita maxima seeds have been used in traditional medicine as a vermifuge and their consumption in the raw and roasted form helps relieve abdominal pain produced by intestinal parasites³¹.

Use and application of pumpkin seeds by-products: oil

Pumpkin seed oil is rich in various bioactive compounds including unsaturated fatty acids, sterols, tocopherols, squalene and carotenoid pigments¹¹ and it has been recognized for several health benefits such as the prevention of growth and reduction of prostate size, the slowing of hypertension progression, mitigation of hypercholesterolemia and arthritis, reduction of bladder and urethral pressure and improving bladder compliance, alleviation of diabetes by promoting hypoglycemic activity, and lowering levels of gastric, breast, lung, and colorectal cancer^11,20. In addition, Morrison³⁴ showed that the substitution of saturated dietary oil with pumpkin seed oil was related to the amelioration of metabolic and cardiovascular disease.

Nishimura³⁵ studied the effect of seed oil on urinary dysfunction in human overactive bladder associated with age. Results indicated that the Cucurbita pepo variety proved to be useful for the nocturnal treatment of patients with urinary disorders in several western countries. The diurnal frequency, night frequency, urgency and urgency incontinence of the subjects under investigation were evaluated. Pumpkin seed oil of Cucurbita maxima significantly reduced the degree of overactive bladder symptoms in subjects³⁵.

Use and application of pumpkin seeds by-products: Flour

One of the most common ways to reuse pumpkin waste is flour, which can be obtained from both the seeds and peel. Pumpkin shells present a high protein and fiber content, in addition to ascorbic acid and calcium, which presented relevant concentrations compared to the pulp, a commonly consumed part³⁶. Therefore, the use of the pumpkin peel in flour production can lead to better nutrient exploitation. Burger³⁷ obtained pumpkin hull flour and as a technological application, made bread from this flour in order to partially replace wheat flour. The bread was made with 2.5% and 5% concentration of pumpkin hull flour. The use of pumpkin flour increased the total protein content in the bread, an attractive characteristic from the nutritional point of view; however, there was a small decrease in bread attributes such as cohesiveness, volume and elasticity, which was expected due to the low formation of gluten.

Likewise, the partial replacement of wheat flour for pumpkin seed flour in muffins for children was studied with positive results. As the substitution of wheat flour for pumpkin seed increased, the nutritional value of muffins improved. Increasing pumpkin seed meal content caused a decrease in saturated short chain fatty acids in the muffins. In addition, the partial replacement of wheat flour with pumpkin seed flour induced a decrease in long chain main saturated fatty acid content from extracted muffin fat (C14:0-myristic, C16:0-palmitic and C18:0-Stearic FA). Moreover, when sensorially properties were evaluated, over 71% of the children reported that muffins with a 33% of pumpkin seed flour were “tasty” and “very tasty”, for muffins stored for two weeks without special condition packaging³⁸.

Pumpkin seed flour is not only used as food alternatives for humans, but also as animal feed, which can have a positive impact on the animal. Cerqueira³⁹ evaluated the effect of pumpkin seed flour on glucose and lipid metabolism in rats, resulting in a significant decrease in glucose and triglyceride levels in the groups that consumed food that including whole and sifted pumpkin seed meal, without influencing growth. On the other hand, Martinez⁴⁰ analyzed the inclusion effect of squash seed meal on cholesterol and fatty acids of laying hens and their eggs. The fatty acids concentration increased in eggs due to added flour: octadecanoic (152 to 450 mg/100 g), oleic (1282 to 1918 mg/100 g), linoleic (22 to 667 mg/100 g), α-linolenic (457 at 649 mg/100 g); while reducing the amount of arachidonic acid (62 to 50 mg/100 g). Total cholesterol was also decreased by 28 to 30 mg/egg with respect to the control, thus enriching the egg.

In another study, combining both types of by-products, squash waste (husk, fruit fractions and seeds) was incorporated into an extruded snack product under different concentrations along with corn grains. Color, expansion ratio, bulk density, texture and rheological attributes were analyzed for an extruded product, obtaining optimal results with 10% flour⁴¹.

Extraction methods to obtain by-products

Conventional methods for extraction of oil from oilseeds are mainly based on the use of expeller pressing and organic solvent extraction (mainly hexane), which may result in high investment costs, human health hazards and unacceptable environment contamination⁴². In this sense, several green and economical methods have been designed to supersede the conventional ones, as table 7 shows. Supercritical CO₂ extraction (SFE-CO₂) avoids the use of organic solvents and large waste streams, but the system is complicated and expensive⁴³. Aqueous enzymatic process for oil extraction is undoubtedly an emerging technology in the fats and oil industry since it offers many advantages such as cost savings, environmental friendliness, and healthy nutrition⁴⁴. To enhance seed oil extraction efficiency, diverse accelerated enzyme-catalyzed reaction technologies are available. Apart from the methods such as microwave⁴⁵, ultrasound⁴⁶, high pressure⁴⁷, extrusion⁴⁸ and electrical discharge⁴⁹, there is some work on negative pressure cavitation systems for accelerated enzyme-catalyzed reaction.

Technical feasibility and processing

Development of a by-product from pumpkin seeds could give a high added value to different food products along with reducing waste and losses for manufacturers. This can be approached by processing the food commodity to support small producers and add activities for small and medium enterprises. Furthermore, a supply chain of three or more entities can also be directly involved in the upstream and downstream flows of products, services, finances and/ or information from a source to a customer.

Bahinipati⁵⁰ reviewed supply chain planning and focused on short-life products in a competitive marketplace. They found that this supply chain integrates a complex network of farmers and food processors to supply customers and enhance operational effectiveness. According to Fleming and Speare⁵¹, production of dehydrated vegetable powders could permit expanded production of vegetables by providing additional market opportunities for farmers. They note that pumpkin, as a perishable product, could be sold immediately to the fresh produce market, partially processed as puree and/or dehydrated products that can have a high shelf-life and stability during an extended time in markets. The result of a trial conducted by Chan⁵² on proportion of pumpkin fractions showed that the flesh made up of 79% of pumpkin total weight, while pulp and peel consisted of 15% and 6% seeds.