1. Introduction
Edible insects have attracted both researcher and commercial attention as viable protein substitutes for animal products. Interest is particularly high because of the small environmental footprint related to insect farming, together with its high economic value and potential [
1,
2]. It has been estimated that, across the globe, at least 2 billion people depend on eating insects for their diet, with consumer interest in insect-based foods steadily increasing. In this regard, many different types of edible insects were successfully used for the production of fortified flour-based foods, including breads [
3,
4], cookies [
5], pasta [
6], and chips [
7]. Insect industrialization is on the rise, showing great potential for application across a variety of sectors such as agriculture, forestry, and many others [
8]. Among the variety of insects that are edible yellow mealworm (
Tenebrio molitor L.) has grown in popularity, specifically in relation to industrial farming and food processing. In 2021, the European Food Safety Authority issued a positive scientific opinion on the safety of dried yellow mealworm (
T. molitor) as a novel food, according to Regulation (EU) 2015/2283 [
9]. Powder from the mealworm larva can provide up to 50% protein and up to 28% fats that include essential amino and fatty acids [
4,
10]. The use of mealworm larva powder in bakery products not only enriches baked goods with healthy proteins, but also improves the quality of the proteins as well as sensory properties of the goods. Severini et al. [
11] added ground mealworm larva in amounts of up to 20/100 g to wheat dough for 3D-printed snacks. The resulting printed snacks were enriched with 10 and 20% amounts of ground insects and significantly increased the total essential amino acids in the snacks, from 32.5 g (0% insects) to 38.2 g (10% insects) and 41.3 g (20% insects)/100 g protein. Roncolini et al. [
3] substituted mealworm (
T. molitor) powder into bread doughs at 5 and 10% amounts in replace of wheat flour and found that the addition of mealworm powder did not negatively affect the technological features of either doughs or breads. Kowalski et al. [
4] studied the effect of four kinds of insect flour on bread supplementation and found that 10% insect powder increases the amino acid score for lysine from 40% to almost 70%, compared to traditional wheat bread. These studies have revealed that edible insects, ground into powder such as mealworm powder, are both viable and beneficial options for use in bakery products.
Adding additional protein sources to bakery products not only affects the nutritional properties of the products but also greatly affects its processing properties. Additives in dough interfere with gluten, disturbing the formation of a gluten network and resulting in changes in rheology, subsequently affecting the quality of the product [
12]. In the food industry, an improved understanding of farinograph properties of flour dough during processing is needed, especially in response to the relationship between properties and final product quality. Some studies have revealed that the rheology of wheat dough was affected by insect ingredients. Roncolini et al. [
3] revealed that the development time of bread flour and dough stability were not affected by the addition of 5 and 10% mealworm powder. Roncolini et al. [
13] found that a 10 and 30% substitution of lesser mealworm (
Alphitobius diaperinus) powder decreased water absorption, dough development time and dough stability. Osimani et al. [
14] assessed the blends of bread flour and cricket powder and found that a 10% substitution did not alter the mixing properties of the flour, whereas a 30% addition of cricket powder led to a higher dough development time and lower dough stability. Previous research has revealed that powders from different insect species can exert different effects on the rheology properties of wheat flour.
Owing to the low moisture content and long shelf life of biscuits, they differ from other bakery products [
15,
16]. Even though there is growing interest in biscuit consumption as a ready-to-serve caloric snack by the majority of the population, it lacks in nutrients [
17]. Therefore, the demand for nutritionally improved biscuits has increased with the growing number of consumers who are inclined to follow healthy dietary patterns [
18]. Among novel protein sources, mealworm powder has been a popular ingredient. Recently, Sriprablom et al. [
5] added
Tenebrio molitor and
Zophobas atratus powders in wheat flour up to 30% supplementation for cookie making and found the nutritional values and the hardness of cookies significantly increased. However, little is still known about the effect of mealworm powder on the low-gluten wheat dough rheology (pasting, farinograph, and extensograph), which would affect the processing process and product properties of biscuit.
Hence, the study hypothesized that the substitution of mealworm powder for flour would not only affect the physical, nutritional and sensory properties of biscuits, but also affect the rheology of the wheat flour. The aim of this work was to investigate the effect partial substitution of low-gluten wheat flour with mealworm powder on the rheology properties of the dough and properties of soda biscuit. The pasting characteristics, farinographic, and extensograph properties were evaluated in order to analyze the rheology of the wheat dough formulated with mealworm powder. The physical properties, including color, microstructure, texture, baking expansion ratio of the soda biscuit were characterized. The proximate composition and amino acid composition were assessed to evaluate the nutritional improvement effect of mealworm substitution. The sensory evaluation was conducted by consumer acceptance test.
2. Materials and Methods
2.1. Materials
Low-gluten wheat flour with protein contents of 8.5% were purchased from Xinxiang Xinliang Cereals Processing Co., Ltd. (Xinxiang, Henan, China). Mealworm powder was purchased from Qingdao Sino Crown Biological Engineering Co., Ltd. (Qingdao, China). The salt, baking soda, butter, and yeast were purchased from a local supermarket.
2.2. Preparation of Wheat Flour Formulated with Mealworm Powder
The low-gluten wheat flour was substituted by mealworm powder at weight ratios of 0% (M0), 5% (M5), 10% (M10), 15% (M15), and 20% (M20), respectively.
2.3. Pasting Characteristics
The pasting properties of the wheat flour formulated with or without mealworm powder were tested by a rapid viscosity analyzer (RVA-Eritm, PerkinElmer, Waltham, MA, USA) according to American Association of Cereal Chemists (AACC) method 76–21 (AACC, 2000) [
19].
2.4. Farinographic and Extensograph Property
As per the AACC Method 54–21 (AACC, 2000), a dough rheology test was performed using a farinograph (JFZD, Beijing Dongfu Jiuheng Instrument Technology Co., Ltd., Beijing, China) [
20]. The elastic properties of dough formulated with mealworm powder were measured using a JMLD150 Extensograph (Dongfu, Beijing, China).
2.5. Biscuit Preparation
A schematic illustration of the biscuit preparation process is shown in
Figure 1. Briefly, 2 g of salt and 1 g of baking soda were added into 150 g of the mixed wheat flour, followed by the addition of 3 g of yeast that was pre-dissolved in 60 g of milk. Then 30 g of melted butter was added into the dough, followed by kneading and fermentation at 30 °C for 30 min. Then the dough was shaped into thin sheets and cut into squares. The squares were pricked by a fork to create perforation and then baked for 14 min with up and down temperature of 165 and 145 °C.
2.6. Physiochemical Analysis
2.6.1. Color
The color of the biscuit dough and biscuit formulated with mealworm powder was measured by a colormetric (CS-820N, Hangzhou CHNSpec Technology Co., Ltd., Hangzhou, China) on the basis of the L*, a*, b* color system: L* is the lightness, a* goes from green to red and b* goes from blue to yellow.
2.6.2. Texture
The texture of the biscuit dough and biscuit were measured by a Texture Analyzer (TA-XT plus, Stable Micro Systems Ltd., Surrey, UK) equipped with P36R probe to 25% of the original sample height with a test speed of 2 mm/s under a Texture Profile Analysis (TPA) model. The assessed parameters were hardness, springiness, cohesiveness, gumminess and resilience for the dough and hardness, cohesiveness, chewiness and resilience for the biscuit, respectively [
21].
2.6.3. Baking Expansion Ratio
The baking expansion ratio of the biscuit was characterized by the change in the thickness of the biscuit before and after baking. The thickness of the biscuit was measured by a digital Vernier caliper.
2.6.4. Scanning Electron Microscopy (SEM)
Wheat dough formulated with mealworm powder was freeze-dried and then sprayed with gold by ion sputtering under vacuum conditions. The dough and biscuit were observed with a scanning electron microscopy (TESCAN MIRA LMS, Brno–Kohoutovice, Brno, Czech Republic) with a secondary electron detector (SE) at an acceleration voltage of 15 kV.
2.6.5. Proximate Compositions and Amino Acid Compositions
The proximate composition of mealworm powder was tested at the Pony Testing International Group (Beijing, China). The moisture, ash, protein, crude fat, and dietary fiber content are determined with reference to GB 5009.3-2016, GB 5009.4-2016, GB 5009.5-2016, GB 5009.6-2016, and GB 5009.88-2014 [
22]. The carbohydrate content was calculated based on the sum of other contents. The amino acid compositions were analyzed according to the procedure of Son et al. [
10] with modification. The tryptophan was not detected due to the acid hydrolysis.
2.7. Sensory Analysis
Soda biscuits were subjected to a sensory evaluation by 40 untrained panelists recruited from the university community [
23]. Minimal information about the study was given to the panelists to reduce bias. Panelists consisted of 20 women and 20 men between the ages of 18 and 24 years. A consumer acceptance test was made on the biscuits using a nine-point hedonic scale form, where 1 indicated maximum dislike, 5 corresponded to neither like nor dislike, and 9 indicated maximum appreciation [
24]. Sensory properties (appearance, odor, texture, taste, saltiness, and overall acceptability) were evaluated.
2.8. Statistical Analysis
The data were expressed as mean ± standard deviation and all the experiments were performed at least three times. The statistical analysis was performed using one-way analysis of variance (ANOVA) by Origin 8.0 software (OriginLab, Northampton, MA, USA). The significance level was set at p value < 0.05.