1. Introduction
Industrial hemp (
Cannabis sativa L.) contains less than 0.2–0.3% of delta-9-tetrahydrocannabinol (THC) and has been traditionally cultivated to obtain fibers, paper, and grain as a coproduct for animal feed. The development of other natural fibers and synthetic polymers, as well as the abuse of chemotypes with high THC content and narcotic effects, which led to taxation by the administration, finally denigrated this crop in the last century [
1,
2]. However, many farmers are currently interested in the reintroduction of hemp cultivation in Southern Europe. According to the European Industrial Hemp Association (EIHA), this sector is experiencing an upward trend, and in 2018, the hemp cultivation area in Europe was 50,081 ha [
3]. Industrial hemp is a multipurpose crop, with opportunities in several industries from construction to textile to food and beverage applications, whose market share is rising [
2,
4].
Hemp seed composition makes it an interesting raw material for the food industry due to its nutritional, technological, and organoleptic properties [
2,
4,
5]. It is composed of 23–35% fat [
1,
6] and 20–25% protein, mainly edestin and albumin, with a desirable content of essential amino acids, comparable to other plant proteins of high nutritional value [
5,
7,
8,
9]. Hemp seeds also contain 20–38% carbohydrates, mostly accounting for insoluble fiber [
8], bioactive compounds such as terpene hydrocarbons, sterols, polyphenols, tocopherols [
10,
11], and carotenoids, as well as a low amount of antinutritional constituents (condensed tannins, cyanogenic glycosides, and saponins) [
1,
4,
9]. Besides whole seeds, other products containing hulls or dehulled seeds, seed cake, seed oil, and seed protein isolates can be found in the market [
4]. Hemp seed is an emerging ingredient in the food industry, and researchers are still conducting studies to evaluate its techno-functionality to develop new products like bakery [
12,
13,
14], beverages, plant-based meat, and confectionary and snacks [
2,
4,
15,
16]. However, most studies consider other raw materials or byproducts derived from hemp seed preprocessing, such as cold pressing, instead of whole seeds [
10,
17,
18,
19] and mainly focus on the characterization of the protein fraction and its use as a food ingredient [
5,
9,
14,
20], neglecting the lipidic fraction.
On the other hand, Rusu et al. (2021) [
12] performed a complete chemical analysis of the seed flour from two hemp varieties and compared them with wheat flour, concluding that the former presented high nutritional quality, especially regarding fatty acid and amino acid composition. Hemp seed flour might be used in many food processes. Therefore, they reinforced a wheat bread with hemp flour, improving its nutritional properties due to a higher content of essential fatty acids, amino acids, minerals, and fiber [
13]. However, producers should note that these components also affect the rheological and textural behavior of the final product [
14,
16]. Thus, traditional products should be fortified with a concentration of hemp seeds that also meet the technological requirements.
Although further research is needed to correlate health benefits with the consumption of hemp-based food, there seems to be an increasing acceptance of edible seeds by consumers, mostly because of the awareness of their health-promoting effects [
2,
11,
21]. Hemp seed composition is genetically and environmentally mediated, but it is characterized by a high polyunsaturated fatty acid (PUFA) content, regardless of variety or crop location, with linoleic (LA, C18:2n-6), α-linolenic acid (ALA, C18:3n-3), and oleic (OA, C18:1n-9) being the major unsaturated fatty acids [
1,
6,
7,
12]. These are also the predominant FAs in hemp seed oil and flour [
22]. Thus, food products containing hemp seeds may be a valuable source of C18:2n-6 and C18:3n-3, which are classified as essential fatty acids, which may contribute to the proper functioning of human metabolism. As lipid quality indicators, hemp seeds should be considered valuable edible oilseeds because of the proportion of PUFA/SFA and the n-6/n-3 fatty acids (3:1 to 5:1), which help lower the atherogenicity and thrombogenicity indexes [
7,
22]. Moreover, hemp seed oil and flour have been shown to lower blood cholesterol levels, decrease body weight gain, and reduce epididymal and perirenal adipose tissue, suggesting that both products may be used to prevent obesity [
2]. The content of microelements such as K or Mg present in hemp seeds is comparable to that found in flaxseeds, hazelnuts, or walnuts and might exert a cardioprotective effect [
12].
Regardless of the susceptibility to oxidation of the fatty acid profile, hemp seed and its oil are considered oxidatively stable due to the presence of tocopherols in the unsaponifiable fraction and phenolic compounds, which contribute to preventing lipid peroxidation [
1,
11]. Indeed, tocopherols are present in higher amounts in the oil (562.8–971.3 mg/kg) because of their non-polar nature and the extraction process, but several studies report that polyphenols predominate in the seed (770–51,600 mg/kg). These authors also observed a significant correlation between total phenolic content (TPC) and antioxidant activity in whole hemp seed extracts and a weak correlation between tocopherol and antioxidant capacity [
1].
The market share of hemp seed and hemp-based food will continue to grow steadily [
2,
21], and new products might be required. However, Burton et al. (2022) [
4] highlighted that there are still some issues that need further attention to build a consistent supply chain and strengthen this market opportunity. Some of them are related to breeding, postharvest handling, and seed processing, particularly regarding the presence of non-allowed constituents in food products. On this subject, it is worth noting that regulation [
23] established a maximum permissible THC content of 3 mg/kg in whole hemp seed, milled hemp seed, or in its flour. However, cannabinoids accumulate essentially in the inflorescences and leaves and are absent in roots and seeds; they are not naturally present in the latter because of cross-contamination during harvesting or seed cleaning [
1]. There are also dietary exposure assessments stating that hemp-derived foods cause no psychoactivity, allergenicity, or other toxic effects due to their THC content [
2]. Moreover, other issues are related to testing applications of hemp seed in traditional food, as well as in emerging market niches [
4].
Appetizers are consumed worldwide, and within this category of food products, research in recent years has focused on the nutritional improvement of corn-based extruded snacks by adding novel raw materials from plants or food industry byproducts [
24,
25]. Extruded corn snacks are trending due to their excellent expansion and texture properties, as well as the capacity of the process to include health benefits [
26]. Using extrusion to process bioactive mixtures can achieve not only nutritional improvement but also calorie decrease and inhibition of starch digestion [
27].
Considering all this information, hemp seeds might be exploited as an ingredient to obtain potentially functional foods, but more studies must be conducted to reach a balance between technological requirements and quality standards. Previous studies have characterized the proximal composition and focused on the fat profile of different varieties of hemp seed [
6] in order to select an appropriate variety to formulate an innovative food product. Thus, considering the high nutritional value of hemp seeds and the need for continuous innovation to obtain easily consumed and ready-to-eat products, the aim of this work is to formulate and elucidate the technological viability of a conventional snack fortified with hemp seeds of the Futura 75 variety and to evaluate the properties and functionality of the final product.
3. Materials and Methods
3.1. Raw Materials, Formulations, and Extrusion Process
Maicerías Españolas S.L. (Valencia, Spain) supplied corn grits. Hemp seeds (HSs) of Futura 75 variety were supplied by Trichome Pharma (Madrid, Spain) for research purposes only. The HSs were ground (Minimoka, Taurus, Lleida, Spain) to obtain powder.
The corn grits were mixed manually using a whisk, with increasing HS powder percentages of 2.5, 5, 7.5, 10, and 12.5%, to produce the extrusion mixtures.
Extrusion was performed using a single-screw laboratory extruder with a barrel diameter of 19 mm and a length–diameter ratio of 25:1 (Kompaktextruder KE 19/25; Brabender, Duisburg, Germany).
Figure 3 shows the conditions during extrusion. Screw speed, motor torque, melt pressure (P), and barrel temperatures (T
1 and T
2) were monitored using Extruder Winext software (version 4.4.3) (Brabender). The extrudates were cooled at 23 °C and sealed in plastic bags for further analysis.
3.2. Total Phenol (TP) and Antioxidant Capacity (AC) Determination
TP was determined based on the Folin–Ciocalteu method. Phenolic compound extraction consisted of mixing 0.5 g of the sample and 4 mL methanol for 1 min; the resulting mixture was transferred to an ultrasonic bath (Ultrasons H-D, J.P. Selecta, Barcelona, Spain) for 5 min. Then, the samples were centrifuged (10,000 rpm, 10 min, 4 °C) to obtain the supernatant using Eppendorf Centrifuge 5804 R (Hamburg, Germany). For determination, 15 mL of distilled water and 1.25 mL of Folin–Ciocalteu reagent (Sigma-Aldrich, Steinheim, Germany) were added to 250 μL of the supernatant. The samples were mixed and allowed to stand for 8 min in darkness before adding 3.75 mL of 7.5% sodium carbonate aqueous solution. Water was added to adjust the final volume to 25 mL. The samples were allowed to stand for 2 h at room temperature before measurement. Absorbance was measured at 765 nm using a UV-3100PC spectrophotometer (VWR, Leuven, Belgium). The total phenolic content was expressed as mg of gallic acid equivalents (GAE) (Sigma-Aldrich, Steinheim, Germany) per 100 g. The analysis was carried out in triplicate.
AC was assessed using the free radical scavenging activity of the samples evaluated with the stable radical 2,2-diphenyl-1-picryl-hydrazyl-hydrate (DPPH) following Igual et al.’s [
33] methodology in triplicate. The samples were mixed with methanol. The homogenate was centrifuged (10,000 rpm, 10 min, 4 °C) to obtain the supernatant. Then, 0.1 mL of supernatant was added to 3.9 mL of DPPH• (0.030 g/L, Sigma-Aldrich, Steinheim, Germany) in methanol. A UV-3100PC spectrophotometer (VWR, Leuven, Belgium) was used at an absorbance of 515 nm. The results were expressed as milligrams of Trolox equivalents (TE) per 100 g.
3.3. Lipid Content and Fatty Acid Profile Determination
The total fat content was determined gravimetrically using acid hydrolysis and Soxhlet extraction following a procedure similar to AOAC 922.06 [
53]. The fatty acid (FA) composition was determined using the gas chromatography technique (Bruker Scion 436, Bruker, Billerica, MA, USA) after lipid extraction, and FA methyl ester synthesis performed according to Rufino-Moya et al. (2022) [
54]. FA composition was measured in the control extrudates without hemp seed (0HSE), extrudates with 7.5% hemp seed enrichment (7.5HSE), and extrudates with 12.5% hemp seed enrichment (12.5HSE). Separation was performed in an SP-2560 capillary column (100 m × 0.25 mm × 0.2 μm) (Supelco, Saint Louis, MO, USA) after 1 μL injection with a split ratio of 1:125 using helium as carrier gas at a flow of 1.5 mL/min. The injector was set at 280 °C and the oven temperature was set at 125 °C for 15 min and increased at a rate of 5 °C/min to 190 °C. The operating conditions of the flame ionization detector were 280 °C and 30 and 300 mL/min of hydrogen and combustion gas, respectively. C19:0 was used as an internal standard in the extraction of FA methyl esters (FAMEs), and identifications were based on FAME retention times, which were compared with those of the standard mixtures GLC-(401, 463, 532, 538, 642, 643), C18:1n-7, and tC18:1n-7 (Nu-Chek Prep, Elysian, MN, USA) or with relative retention times found in the literature [
55,
56] in the case of C18:4n3. Quantification was performed as described in ISO 12966-4:2015 [
57].
3.4. Determination of Physicochemical Properties
Water content (x
w) (g/100 g) was determined using vacuum oven drying at 105 °C until a constant weight was achieved [
58] for the mixtures and extruded samples. The samples were analyzed in triplicate.
One of the most interesting properties of extruded products is expansion. This can be measured by different parameters, among which the surface expansion index (SEI) of the die and bulk density stand out (ρ
b). While ρ
b considers expansion in all directions, SEI considers expansion only in the direction perpendicular to the extrudate flow [
47]. SEI was calculated as the quotient between the square of the measured extrudate diameters and the square of the die diameter [
49]. In total, 20 diameters of extruded pieces were measured for each sample with an electronic Vernier caliper (Comecta S.A., Barcelona, Spain). For ρ
b determination, measurements were taken 10 times, where the diameter and height of cylinders were measured with an electronic Vernier caliper (Comecta S.A., Barcelona, Spain), and the samples were weighed with a precision scale (±0.001 g) (Mettler Toledo, Greifensee, Switzerland).
The porosity (ε), percentage of air volume related to the total volume, was calculated from the true (ρ) and bulk (ρ
b) densities according to Igual et al. [
24]. The ρ of the extruded products was determined in triplicate using a helium pycnometer (AccPyc 1330, Micromeritics, Norcross, GA, USA).
To evaluate the hydration properties, the water absorption index (WAI) and water solubility index (WSI) were used. The WSI and WAI were determined using the method of Singh et al. [
59] and calculated according to Uribe-Wandurraga et al. [
21]. The swelling index (SWE) also was measured using the bed volume technique. The bed volume was recorded and expressed as mm of swollen sample per g of dry initial sample [
24].
Texture properties were measured using puncture tests with a TA-XT2 Texture Analyzer (Stable Micro Systems Ltd., Godalming, UK) and Texture Exponent software (version 6.1.12.0). A 2 mm diameter cylinder was used, and the crosshead speed was kept at 0.6 mm/s [
25]. From the force–time curve, the area under the curve plot, which represented work done for a time of displacement of the puncturing device, was obtained from the extrudates (8 times). The force drop of each peak was also obtained, and it represented the local resistance of cell walls. The number of peaks (No) were also recorded [
60]. These parameters were used to calculate the average puncturing force (Fp), average specific force of structural ruptures (Fs), spatial frequency of structural ruptures (Nsr), and crispness work (Wc) according to Igual et al. [
30].
Color was determined in the powdered samples. Flours and extrudates were ground and placed in a cup specially designed for this purpose. Color was measured using a Minolta spectrophotometer CM-3600d (Tokyo, Japan). CIE*L*a*b* color coordinates were determined considering standard light source D65 and a standard observer at 10° for the mixtures and extrudates (8 times). Hue (h*) and chroma (C*) color attributes were calculated from the CIE*L*a*b* color coordinates. The total color differences of the extrudates with HSs (ΔE) were calculated relative to the 0HSE sample [
25].
3.5. Statistical Analysis
Analysis of variance (ANOVA), with a confidence level of 95% (p < 0.05), was applied using Statgraphics Centurion XVII, version 17.2.04, to evaluate the differences among the samples. Fisher’s least significant difference procedure was used to discriminate between means. Correlation analyses were performed with a significance level of 95% (Statgraphics Centurion XVII, Statgraphics Technologies, Inc., The Plains, VA, USA).