Physicochemical characterization of quinoa, amaranth, foxnut and pumpkin seeds

Introduction

The increasing demand for nutrient-rich, plant-based foods has intensified research on pseudocereals and edible seeds because of their high nutritional value and functional properties. These ingredients are rich sources of proteins, dietary fibre, essential minerals, and bioactive compounds that contribute to human health and may help reduce the risk of chronic diseases (Kosicka-Gębska et al., 2022; Sharma et al., 2021) [11,22] . Consequently, their utilization in food and nutrition research has gained considerable attention (Baraniak & In addition to their nutritional composition, the physicochemical and engineering properties of these plant materials, including moisture content, bulk density, true density, porosity, angle of repose, and thousand-kernel weight, are important parameters influencing storage, handling, processing, and product quality (Mohsenin, 1986; Dutta et al., 1988) [15,5] . Comprehensive evaluation of these characteristics provides valuable information regarding their nutritional quality and technological suitability for food applications (AOAC, 2019) [3] . Therefore, the present study aimed to evaluate the physicochemical, nutritional, mineral, and physical properties of quinoa, amaranth, foxnut, and pumpkin seeds using standard analytical methods. The findings provide comparative information on their nutritional composition and functional characteristics, supporting their potential application as nutrient-rich plant-based food ingredients.

Materials and methods

Collection and preparation of raw material

Quinoa, Amaranth grains, foxnuts Pumpkin seed were purchased from a local market in (Chhatrapati Sambhajinagar, Maharashtra) India. Grains were cleaned and stored in an airtight container till further used.

Proximate Analysis

The proximate composition of the samples was analysed for moisture using a hot air oven from Kamak India, crude fat with a hot air oven from Biotechics India and a Soxhlet apparatus model Soxtron SOX-2, crude protein with a Kjeltron KGIDB4M from India, and total ash using a muffle furnace from Biotechnics India. All analyses were performed in triplicates (n = 3). The total carbohydrate was determined using a different method (AOAC, 2019) [3] .

Physical properties

Various physical properties of includes thousand kernel weight, true density, bulk density, porosity and angle of repose were determined to evaluate the quality of raw materials as per the methods given by Dutta et al., (1988) [5] .

Thousand kernel weight

Count the 1000 kernels randomly and weigh a thousand grains in three replications using digital weighing balance and the mean value was noted.

Bulk-Density

Approximately 25 grams of sound grains were measured using the digital weighing balance and subsequently added to the measuring cylinder, which had previously been filled with a reference solution of hexane. The elevation of the liquid level was recorded following the addition of the grains. It is the bulk density expressed in kg/m 3 .

Bulk density (ρ) = 𝑊𝑒𝑖𝑔ℎ𝑡 𝑜𝑓 𝑔𝑟𝑎𝑖𝑛𝑠 (𝑔) 𝑉𝑜𝑙𝑢𝑚𝑒 (𝑚𝐿)

True density

True density is defined as the ratio of the mass of the seed sample to the solid volume it occupies. This was determined using an electronic balance with a precision of 0.0001 g and a pycnometer with a capacity of 50±0.1 ml, employing the liquid displacement method. Toluene was utilized in place of water due to its reduced absorption by grains. Given the limited timeframe of the experiment, the absorption of Toluene was deemed negligible, leading to the decision not to coat the seeds to prevent its absorption.

Porosity

Porosity is defined as the fraction of space within the bulk seed that remains unoccupied by the grain itself. The porosity was determined using a specific formula.

Angle of repose

The steepest angle is established between the base and the slope of the cone created during the free vertical descent of a grain mass onto a horizontal surface, occurring when the material is either free falling or sliding. The determination was made by constructing a circular pile of the grains as they fell freely. The height of the pile was recorded (h), and its radius (r) was assessed. The angle of repose was established utilizing a technique outlined by Mohsenin N.N. in 1986 [15] .

𝐴𝑛𝑔𝑙𝑒 𝑜𝑓 𝑅𝑒𝑝𝑜𝑠𝑒 (𝜃) = 𝑡𝑎𝑛⁻¹ ( ℎ 𝑟 )

Where, h = Height of grain hip (cm) r = Radius of circle

Mineral analysis

Concentrations of calcium, iron, magnesium, zinc, and phosphorus were assessed in raw material samples employing the standard methods outlined by AOAC, 2019 [3] . The samples underwent dry ashing in a muffle furnace at 550°C, followed by dissolution in dilute hydrochloric acid and subsequent filtration. The minerals calcium, iron, magnesium, and zinc were analysed using Atomic Absorption Spectrophotometry (AAS), while phosphorus was quantified through calorimetric estimation. The findings were presented in milligrams per 100 grams of sample. [17] reported comparable findings, noting that quinoa is abundant in protein, essential amino acids, and dietary fiber when contrasted with conventional cereals. Amaranth showed elevated levels of protein (14.8 ± 0.5 g) and fat content (7.0 ± 1.0 g), alongside notable carbohydrate amounts (65.0 ± 2.5 g). Alvarez-Jubete et al. (2010) [2] indicated that amaranth has exceptional protein quality and mineral content, rendering it appropriate for functional and gluten-free food products. Foxnut exhibited a significant carbohydrate content (77.0 ± 1.5 g), accompanied by minimal fat (0.5 ± 0.2 g) and protein (9.8 ± 0.4 g), suggesting its viability as a low-fat energy source. Comparable findings were reported by Jha et al.

Results and Discussion

(2019) [9] , indicating that foxnut is abundant in carbohydrates while exhibiting low lipid content. Pumpkin seed demonstrated the highest levels of fat (45.6 ± 2.0 g) and protein content (30.2 ± 1.5 g) compared to all other samples, in addition to elevated crude fiber and ash values. Yadav et al. (2022) [26] noted that pumpkin seeds serve as outstanding sources of protein, beneficial lipids, essential minerals, and dietary fiber. Overall, the proximate composition results indicated that the samples exhibit complementary nutritional characteristics, potentially enhancing the nutritional and functional quality of the developed food products. The analysis of minerals in quinoa, amaranth, foxnut and pumpkin seed showed significant variations in their micronutrient profiles, underscoring their nutritional value in the development of functional foods. Quinoa is rich in magnesium (197 ± 5 mg), phosphorus (457 ± 10 mg), and potassium (563 ± 15 mg), highlighting its impressive mineral composition. Repo-Carrasco-Valencia et al. (2010) [20] reported comparable findings, noting that quinoa is abundant in essential minerals, especially magnesium and potassium. Amaranth showed elevated levels of calcium (159 ± 6 mg), iron (7.6 ± 0.5 mg), magnesium (248 ± 8 mg), and phosphorus (557 ± 12 mg) when compared to quinoa and foxnut. Mlakar et al. (2009) [14] indicated that amaranth grains contain significant amounts of iron, calcium, and magnesium, which enhance their nutritional value. Foxnut exhibited a moderate presence of calcium and magnesium, while displaying reduced levels of iron and zinc. The reduced mineral concentration could be linked to its composition, which is rich in starch. Comparable findings were reported by Mishra et al. (2021) [13] , who noted that foxnut possesses moderate amounts of essential minerals in addition to a high carbohydrate content. Pumpkin seed demonstrated the highest concentration of minerals compared to all other samples, especially in magnesium (550 ± 10 mg), phosphorus (1174 ± 20 mg), potassium (809 ± 25 mg), iron (8.8 ± 0.4 mg), and zinc (7.6 ± 0.5 mg). Nawirska-Olszanska et al. (2013) [16] reported elevated levels of phosphorus, magnesium, zinc, and iron in pumpkin seeds, highlighting their significant nutritional potential.

Overall, the chosen raw materials exhibited a favourable mineral composition, particularly quinoa, amaranth, and pumpkin seed, which could play a crucial role in enhancing the nutritional quality of functional food products. The physical properties of quinoa, amaranth, foxnut, and pumpkin seed exhibited notable differences attributed to variations in seed size, shape, and structure. The quinoa grains exhibited a cream white hue and a circular shape, whereas the amaranth seeds presented a pale-yellow color and a spherical form. Foxnut displayed a white oval form, while pumpkin seeds were characterized by a dark green, flat oval shape. Vilche et al. (2003) [25] reported similar observations concerning the physical characteristics of pseudocereals and seeds, noting that quinoa features small cream-coloured grains with favorable processing attributes. The thousand kernel weight of quinoa was measured at 2.32 ± 0.16 g, suggesting a smaller grain size in comparison to pumpkin seed and foxnut. Abalone et al. (2004) [1] noted that the kernel weight of amaranth seeds is reduced due to their small seed structure. Bulk density values varied from 98.4 ± 0.36 kg/m³ in foxnut to 790.5 ± 0.42 kg/m³ in amaranth. The reduced bulk density of foxnut could be attributed to its porous, puffed structure. Jha and Kumar (2018) [8] reported comparable findings, noting low density and high expansion characteristics in foxnut.

Porosity values suggested sufficient inter-particle air spaces, potentially enhancing aeration and storage stability. The angle of repose values indicated a satisfactory flowability of all samples, implying their appropriateness for mixing and processing operations. Madan and Prasad (2014) [12] reported that pumpkin seeds exhibit favourable handling and flow characteristics that are suitable for food processing applications.

Conclusion

The present study demonstrated that quinoa, amaranth, foxnut, and pumpkin seeds possess complementary nutritional, mineral, physicochemical, and functional properties, making them promising ingredients for valueadded functional foods. Pumpkin seeds exhibited superior protein, lipid, and mineral contents, while foxnut was characterized by high carbohydrate and low-fat levels. Quinoa and amaranth provided balanced amounts of protein, dietary fibre, and essential minerals. Significant differences in bulk density, true density, porosity, thousand-kernel weight, and angle of repose further indicated their distinct processing and handling characteristics. Collectively, the complementary nutritional and technological attributes of these ingredients provide a strong scientific basis for developing protein-and mineral-rich functional food products.

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