Utilization of Edible-Insects as Protein Substitute in Food and Effects of Processing on Their Nutrient Contents and Protein Functionalities

Population growth, poverty and climate change dictate the need for additional protein sources. Edible insects are potential protein substitutes and can provide both humans and animals with the required amount of protein, essential amino acids, and other indispensable nutrients. Incorporating edible-insects into familiar products and subjecting them to adequate processing that masks their natural appearance will improve their consumption. This article provides insights on the potentials of edible-insects as novel ingredients in food processing and its various benefits. Effects of processing on their nutritional and functional properties were also discussed. Literature was gathered through an online search on the Science Direct database and Google Scholar. Edible-insect powders, protein isolates and concentrates and oils were reported to be incorporated into bugger, chips, chocolate, bread, cookies, and other baked snacks. The addition of insect products improves protein, fat, fiber, and minerals contents. Insects also contain healthier lipids when compared with conventional proteins. Edible-insects will provide essential nutrients to the rapidly growing world population when more attention is given to their production, processing, safety, and marketing. Efforts need to be strengthened to secure global acceptance of insect protein since the conventional sources are not reliable and cannot satisfy the world population in decades to come.


INTRODUCTION
Insects eating (entomophagy) was dated back to antiquity (Cartay et al., 2020;Liu and Zhao, 2019;Sun-Waterhouse et al., 2016) and the use of insects as food is as old as the history of mankind (Das et al., 2019). Insects can be processed into food that can provide essential nutrients (Cartay et al., 2020;Dube et al., 2013).
There is an increasing demand for protein-rich foods, more attention is given to the novel sources of protein, researchers and marketers are putting more efforts into promoting edible-insects among new consumers to meet the obligatory need to diversify protein sources (Pippinato et al., 2020). The desire to reconsider discarded eating habits and food sources into modern recipes has fascinated the interest of researchers, chefs, and businessmen on edible-insect potentials as an alternative protein source (Testa et al., 2016).
Reports from many researchers shown that insect proteins can be used as a substitute for conventional protein in many products without adverse effects on their sensory qualities. Their inclusion in food has proven to improve the nutritional values of many processed foods (Imathiu, 2020).
Research in entomophagy covered many areas of study including food science, human and animal nutrition, health, entomology, ecology, agriculture, biochemistry, anthropology, sociology, and history (Yen, 2015).
This article intended to provides insights on the potentials of edible-insects as novel ingredients in food processing and its various benefits. Effects of processing on their nutritional and functional properties were also discussed.

EDIBLE-INSECTS AS CONVENTIONAL PROTEINS SUBSTITUTE
Edible-insects and their products are used as ingredients in food processing, insect powders, protein isolates and concentrates, and oils were reported to be incorporated into burger, chips, chocolate, bread, cookies, and other baked snacks (Table 1).
The addition of insect products improved protein, fat, fibre, and minerals contents without affecting functional properties and sensory qualities. It also improved dough characteristics and baking properties (Table 1). Gravel and Doyen (2020) reported that insect proteins are potential functional ingredients in foods and can play important roles in large scale food production. Food scientists are working hard on the possibilities of incorporating insects into some staple foods. At present, more attention is given to bakery goods. Substitution of wheat flour with 5 % insect flour improves the protein and fibre content of bread without affecting the dough properties and acceptability of the bread (González et al., 2019).
Insect flour at a 7.5 % level of substitution improves the nutritional content of corn flour extrudates snack mixture without affecting extrusion parameters (Igual et al., 2020). Extrusion cooking of soy concentrate with honeybee drone brood produced protein-rich snacks with 66 % protein content (Ulmer et al., 2020). Inclusion of 25 % crude black soldier fly larvae fat as a butter substitute in the production of cakes and cookies and 50 % in the production of waffles have no effects on the texture, colour, and overall liking of these products (Delicato et al., 2020).
Substitution of wheat flour with grasshopper powder at 100 g/kg grasshopper powder has no effects on the sensory qualities of the grasshopper-based bread, the substitution increased the protein content by 60 % and softness of the bread (Haber et al., 2019). Cricket powder at 15 % inclusion Food Scientech Journal 4(2) 2022, pp 83-99 enhanced bread dough stability and reduced the degree of softening (Cappelli et al., 2020).
Leavened crunchy snacks produced with 30 % lesser mealworm powder exhibit low water activity (aw) and have pleasant sensory attributes and better mineral, protein, and amino acid contents than that produced from 100 % wheat flour (Roncolini et al., 2020). The low aw exhibited by lesser mealworm powder reveal the potential of using insect protein as a preservative in food.
Mulberry silkworm pupae and African palm weevil larvae can be used as a beef substitute in the production of filling for snacks and cuisines (Akande et al., 2020a). Skim milk can be replaced with locust and mulberry silkworm pupae powder in the production of high-energy biscuits, at 15 % inclusion, the nutritional value is above the minimum level prescribed by USAID (Akande et al., 2020b).
Another potential area of using insects is in improving the sensory properties of healthy foods with acceptance problems, silkworm powder was used by Biró et al. (2019) to mask the unpleasant sensory characteristic of buckwheat. Insects proteins are potential functional ingredients in food processing, the findings of Gravel and Doyen (Gravel and Doyen, 2020) revealed that insects protein concentrate and isolate are suitable ingredients with excellent functionality. The textural properties of insect proteins are amazing in 3D printing, their consumption can be improved through the production of foods with attractive, shapes, structure, and texture (Caporizzi et al., 2019).

PROCESSING OF EDIBLE INSECTS
Insects are consumed either raw, fried, or roasted (Das et al., 2019). The most common processing methods for insects are trimming, boiling, sun-drying, roasting, and pan-frying (Akullo et al., 2017;Ebenebe et al., 2017). In India, insect meals are prepared by boiling and roasting, sometimes with spices (Chakravorty, 2014), other processing methods are sand-roasting and osmotic drying using rock salt (Bose, 2020). Surplus catches during the season are preserved by sun-drying and stored for future use (Akullo et al., 2017), this ensures the continuous supply of insect protein year-round (Dube et al., 2013). The crude techniques used in the processing and preparation of insects improve their safety, shelf-life, nutritional value, and palatability (Akullo et al., 2017;Dube et al., 2013;Mézes and Erdélyi, 2020). Köhler et al. (2019) reported that insects purchased from the supermarket have better nutrient content than those gathered from the street, therefore, adopting modern techniques in insect processing will further improve their safety, commercial value, and versatility (Akullo et al., 2017). Edible insects were reported to contain many important nutrients but there is little information regarding the effects of different processing on their nutritional qualities, nutrients bioavailability, and toxicity (Ayensu et al., 2019).

Effects of Processing on the Qualities and Functionalities of Insect Products
The findings in Table 2 revealed that cooking affects nutrient contents and their bioavailability, digestibility, pH, and functional properties. Thermal processing of insects generally lower microbial counts and affects their distribution and activities during storage. The higher temperatures involved in cooking increase acidity due to the breaking down of glycogen into lactic acid. Higher temperature and low pH affect gelling and foaming properties, trigger coagulation, and increase surface hydrophobicity. Hydrolyses of both protein and lipid were observed during prolonged heating. Cooking has no effects on fatty acids composition and protein secondary structure, but heating with NaCl decreases α-helix structure and surface hydrophobicity.
Drying affects macronutrient contents, protein solubility, and oxidation (Table 2). Thermal processing of insects improved their safety, acceptability, digestibility, palatability (Garofalo et al., 2019;Megido et al., 2018;Murefu et al., 2019) nutritional quality, and bioavailability of sulfur-containing amino acids (Poelaert et al., 2018). Higher temperatures during cooking can have damaging effects on lipid and protein (Megido et al., 2018). Cooking methods can affect nutrients content and their bioavailability in insect, boiling, and vacuum cooking maintains good levels of polyunsaturated fatty acids and proteins in mealworms (Megido et al., 2018).
Reports in Table 2 show that extraction conditions can affect the properties of edible-insect protein extract. The solubility of the protein extract depends on the extraction pH. Increased protein content was recorded at pH of 10 in combination with Ultrasound treatment. Pressurised-liquid assisted extraction lower cholesterol level and increases PUFAs contents. Alkaline hydrolysis lower foam stability and emulsification properties of the protein extract. Exposure to ultrasound improved antioxidant activity, solubility, and foam expansion of the protein extract over a wide range of pH (2-12) ( Table 2). Liceaga (2019) reported that the functional properties of insect flour can be improved by controlled enzymatic hydrolysis. Physical properties such as turbidity, dispersibility, and particle size of insect proteins can be modified by ultra-sonication. An increase in the sulfur hydride value, dispersibility, and zeta potential, and a decrease in turbidity and particle size in protein preparations and hydrolysates were observed in soldier fly larvae subjected to ultrasonic treatment (Mintah et al., 2020). Increased foaming and emulsifying abilities, and protein value were observed in grasshopper and honey bee brood protein extracts obtained using alkaline and sonication-assisted extraction (Mishyna et al., 2019a). Mishyna et al. (2019b) demonstrated the mechanism of gel aggregate formation by both covalent and non-covalent intermolecular interaction occurs during heat denaturation of freezedried honey bee brood protein, this unveils the potential of using insect proteins as a gelling agent. Fermentation is a promising technique for producing a wide range of edible insect products including extracts, sauces and paste (Castro-López et al., 2020).
The addition of insect proteins into wheat flour affects the dough and baking properties of baked foods. At 15 % incorporation, cricket flour increase dough tenacity and reduces extensibility, this led to poor volume in the baked product. The addition of insect flour also lowers expansion and crunchiness in extruded products. Defatting improved overall liking, digestibility, and lower hydrophobicity (Table 2) The killing method of insects can affect the appearance and qualities of insect products. Killing generally increases the browning index and lowers radical scavenging. Killing in the absence of oxygen minimizes lipid oxidation and improves its nutritional qualities (Table 2). Killing methods affects the acceptability of insect by influencing saltiness and umami taste ( Table  2). Leni et al. (2019) compare freezing (the most common killing method) with balancing and found out that the slow killing process involves in freezing gave room for many enzymic reactions including melanization reaction, killing by balancing inhibit browning, increase extractability and digestibility of protein and maintain essential amino acids. The killing method also affects the lipid composition of the insect products during storage, Caligiani et al. (2019) reported that killing by balancing provides more stable lipid while killing by freezing causes the formation of free fatty acids during storage probably due to the activation of lipases.

OTHER INDUSTRIAL APPLICATIONS
Scientists strongly believe that insects will play a vital role when the insect industry becomes well established and it will have positive impacts in many areas including industries, government, business, and research (Dossey et al., 2016) and its financial repercussions will impact the economy in general (Costa-Neto and Dunkel, 2016). In addition to the provision of food and feed insects can convert organic waste into important industrial raw materials. Insects have been foreseen as potential raw materials for many industrial processes (Tang et al., 2019) including food fortification during processing. Insects have higher anti-microbial peptides than any other animal, therefore, can be used as a novel source of antibiotic (van Huis, 2020a). Black soldier fly is a potential candidate for the production of antibiotics, textured protein, and bioplastic (van Huis, 2020b). Insect when used as feed have positive benefits on livestock health and welfare and their use as feed can reduce the use of antibiotics in livestock production (Dicke, 2018;Veldkamp and Eilenberg, 2018). Insect postproduction waste is used as plant manure, and in an advanced way, can be used in the production of bio-methane gas using an anaerobic digestion process (Bulak et al., 2020).

RECOMMENDATIONS AND CONCLUSION
Authors recommends several points such as: at present, only few species are produced commercially, for effective promotion of entomophagy, the idea of insects gathering must be discarded, edible insects should be produced in large quantities at an industrial scale; People involve in traditional insect gathering should be transformed into insect farmers by providing them with the required skills and capital; Understanding the interaction between insect products and other food ingredients is critical in using insects as a novel ingredient in foods; Observing good personal hygiene throughout the production chain and the use of an appropriate HACCP system can improve the safety of edible insects; Processing into delicious, attractive, and irresistible meals with no visible insects, or their parts, and the use of an appropriate and eye-catching packaging system will promote edibleinsects' acceptance.
Authors concluded that processing improves safety, stability, nutritional value, palatability, digestibility, nutrients bioavailability, acceptability, commercial value, functional properties, and versatility of edible-insects. The addition of processed insects into familiar foods improves their nutritional qualities and ingredients' functionality. Killing and processing methods affect protein functional properties, nutrient contents, and their bioavailability. Edible-insects and their products are used as ingredients in food processing. Insect powders, protein isolates, and concentrates, and oils were reported to be incorporated into burger, chips, chocolate, bread, cookies, and other baked snacks.   Effect of degree of processing and incorporation on the acceptability Degree of processing affects acceptability, insect-based products should contain processed insects, not whole insects (Gmuer et al., 2016) Protaetia brevitarsis larvae

Wild
Defatting using hexane 1. decrease in hydrophobicity and tryptophan fluorescence intensity was observed 2. digestibility is higher than that of beef Alkaline hydrolysis improved protein solubility, but lower forming stability and emulsifying properties. Ultrasound treatment improves antioxidant strength, solubility, and foam expansion properties over a wide pH range (2-12) (Mintah et al., 2019) Honey bee brood (Apis mellifera) Effects of pH and temperature on aggregation and gelation Highest coagulation achieved at 85 °C and pH 5-7 The least gelation concentrations vary between 5 to 11 % at pH of 7 and 3 respectively (Mishyna et al., 2019c) House cricket (Acheta domesticus)

Farmed
Effects of different killing method: blanching, steaming, freezing, carbon dioxide, vacuum, plastic bag, and carbon dioxide + blanching 1. all the killing methods were found to increase the browning index and reduce radical scavenging activity. 2. better proximate values were obtained by carbon dioxide, vacuum, and plastic bag killing 3. killing by freezing, carbon dioxide, vacuum, and plastic bag provide healthier lipids and minimize lipid oxidation (Singh et al., 2020) Mealworms (Tenebrio molitor)

Laboratory reared
Comparing the effects of different drying methods (fluidized bed drying, microwave drying, freeze-drying, vacuum drying, and rack drying) 1. all the drying methods affect the macronutrient contents 2. protein solubility is higher in freeze-drying and lower in microwave drying, fluidized bed drying, and vacuum drying 3. oxidative status is higher in freeze-dried samples (Kröncke et al., 2018) Yellow mealworm (Tenebrio molitor) and lesser mealworm (Alphitobius diaperinus) larvae

Farmed
Production of a minced meat-like product by addition of salt, binding agent, and spices to steamed/fried and pulverized larvae before frying Processing methods lower microbial counts and affect their distribution in the finished products and during storage under different conditions