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Food, larvae-ly food...

Dr Jo Gould of the University of Nottingham discusses the potential for incorporating insect proteins into foods as both nutritional and functional ingredients.

Introduction

Inadequate protein intake and protein energy malnutrition affects 1 billion people worldwide. The global population is projected to reach 9.6 billion by 2050 leading to a global food demand increase of up to 70% compared with our current food requirements. Conventional sources of protein will not be sufficient for the global human population and alternative sources, such as vegetables, algae, microorganisms, insects and cell cultured meat will be required. Insects, classified in the arthropod phylum alongside crustaceans, are invertebrates with a chitinous exoskeleton and a jointed body. Proteins have been recorded to be the dominant nutrient in edible insects.

Recently, Mr Yde Jongema, a taxonomist at Wageningen University, compiled a list of edible insects found globally which totalled 2,111 insect species consisting of beetles, caterpillars, ants, bees, wasps, grasshoppers, locusts, dragonflies, termites, flies, cockroaches and spiders, all of which could offer a resolution to the global protein shortfall.

How does insect protein stack up?

Protein quality is not defined by one measure, instead overall protein content, indispensable amino acid content and digestibility are all required to evaluate a protein source. Protein contents of insects have been reported to be between 35 and 61%[1] making many species of insects greater in protein content than beans, lentils and soybeans. In a recent study, comparisons on a dry matter basis showed that the average protein content of edible insects is generally comparable in density to that of conventional high quality animal protein[2].

Mean protein content was however found to vary between insect order from 40% for termites (order Isoptera) to 64% for cockroaches (order Blattodea) as well as within species belonging to the same order. The variation in protein content, which will also be reflected in amino acid content and digestibility, is a result of differences in order, species, diet, sex, life stage and habitat of the insect. In addition, factors such as analysis method, insect processing to remove inedible parts and the presence of a chitin rich exoskeleton will all impact on the protein quality assessment of insects.

Amino acids, the building blocks of protein, are characterised as dispensable and indispensable. Indispensable amino acids cannot be synthesised by the body and therefore must be provided in the diet. Fulfilling the requirement for each of the nine indispensable amino acids - leucine, isoleucine, valine, lysine, threonine, tryptophan, methionine, phenylalanine and histidine – defined by the WHO/FAO/UNU 2002 report is used to define protein quality. Indispensable amino acid content of edible insects has been found to vary, due to factors outlined above. Some studies have found insects to be deficient in tryptophan, methionine and/or lysine, however in one study, insects from orders Coleoptera (Beetles), Hymenoptera (flies), Lepidoptera (butterflies) and Orthoptera (grasshoppers, locusts, crickets) on average meet or exceed current indispensable amino acids contents for adults with these contents being comparable to beef, eggs, milk and soy[2].

Finally, protein digestibility must be considered as it dictates the availability of amino acids to the body after consumption. Based on an enzymatic in-vitro assay, the protein digestibility of a selection of edible Mexican insects has been reported to range between 77 and 98%[3]. This is higher than for some vegetable based proteins and, for some species, only slightly lower than values reported for animal protein sources (egg 95%, beef 98%, casein 99%)[4].

Overall results from studies are promising in terms of protein composition, although there is a need for further studies to gain a more comprehensive nutritional assessment of insects. The evidence does suggest that some species of edible insects are relatively high in protein, have contents comparable to animal derived and soy protein on a dry matter basis, provide an adequate indispensable amino acids content and can be classified as highly digestible. So why are we not eating more insects?

As of May 2017, Switzerland became the first European country to authorise the sale of food items containing three types of insects: crickets, grasshoppers and mealworms.

Supermarket shelf of the future….Insect protein isolate, insect flour and whole insects

Insect consumption

Disgust? Distaste? A history of trying to keep insects out of food products? Yes! Several studies conducted in developed, non-insect consuming countries found a reluctance to consume due to their association with nature, animalness, appearance and a certain degree of food neophobia as insects have never played a substantial role in the diet. However, honey and Carmine E120 (a red food dye extracted from the female cochineal insect) have been widely accepted and we are starting to see an increase in interest in consumption of insect containing food products from the novelty ‘bush-tucker trial’ lollipop stick to insect flours, energy bars, pasta and sauces.

In Switzerland, this offering has been extended to insect burger and balls all made with mealworms, because as of May 2017, Switzerland became the first European country to authorise the sale of food items containing three types of insects: crickets, grasshoppers and mealworms. Insects for human consumption must be bred under strict supervision for four generations before they are considered appropriate for human consumption, according to Swiss law.

The legal situation for production and marketing of all types and/or forms of insects and insect containing products within the EU will however change under the new Novel Food Regulation (Regulation No 2015/2283, in force from 1st January 2018) making these products subject to pre-market authorisation based on safety evaluation. This will be followed by EU Regulation 2017/893, which allows the use of seven insect species in aquaculture feed as of July 2017. These regulatory changes are starting to pave the way for wider consumption of insects.

With all of this in mind, insects are beginning to tick boxes – nutritionally and legally – showing potential as a solution to the growing food demand. What remains however is the ‘yuck factor’. One particular study asked 1083 consumers in the Netherlands to score the attractiveness of 13 vegetarian meals and found that all photos containing insects were rated negatively. However, the image of a pizza containing processed insect protein was rated more positively than chocolate coated locusts, fried mealworm salad and locust salad, indicating that meals with invisible insects trigger less aversion than visible insects[5]. The inclusion of ingredients produced from insects in food products has been suggested as a vehicle to enhance consumer acceptance of insects and eventually prepare the way for consumption of whole insects in the future.

Functional ingredients

Ingredients derived from insects do not need to just be fillers in products to maintain the nutritional label – protein is not eaten solely for nutrition.

Proteinaceous ingredients are responsible for creating a range of textures, be that the aeration of an egg foam in a chocolate mousse or the wobbly egg custard of a Quiche Lorraine, which consumers not only expect but drives their enjoyment of eating and repeated purchase of the product.

For many products where incorporation of air, emulsification or binding of water and oil as well as fibre and gel structures are important, texture and shelf life stability cannot be guaranteed without the presence of protein. It is in these products that insect ingredients have the potential to offer functionality as well as nutrition, whilst reducing the pressure on traditional unsustainable sources of protein.

Our current understanding of the properties of insect flours and protein extracts is in its infancy compared to traditional sources of protein but it is growing. As evidenced by the increasing numbers of published documents over the last 30 years (Figure 1), it is clear that insect protein and its application in food is prompting research interest.

Initial studies, dating back to 1998, investigated insect flours produced by the grinding of various insect species including crickets, caterpillars, silkworm pupae, westwood larvae, mealworm larvae and grasshoppers. These flours contain a mixture of protein, fat, carbohydrate and fibre. Typical tests that have been carried out include emulsifying capacity and stability, foaming capacity and stability, gelation, water absorption and oil adsorption. Water and oil absorption of these flours was found be high – between 250 and 350% – whereas the foaming ability of the flours was very low, more than likely due to the mixed composition of the flour, particularly the presence of fat, which acts as an anti-foaming agent. More recently, summarised below, studies have focused on understanding the properties of isolated proteins from insects rather than flours. It is often hypothesised, as it was for dairy and more recently vegetable protein, that the inclusion of insect proteins in different foods will be driven by the added functionality they can bring to a product formulation and for this it is necessary to understand the physio-chemical properties of the protein.

Figure 1 Published documents over last 30 years, top ten sources, featuring either “Insect AND protein AND food” or “Dairy AND protein AND food”
Scopus Search

Insect ingredients have the potential to offer functionality as well as nutrition, whilst reducing the pressure on traditional unsustainable sources of protein.

Functional properties of insect protein

The ability to generate gel, emulsion and foam microstructures creates added value for a food ingredient and hence has been a topic of study for insect protein. Preliminary investigations have shown varying results as a consequence of the use of different species and insect processing methods, but some promising findings have been reported.

A gel, classically defined as the product of the conversion of a fluid to a solid by the formation of a continuous network, possesses a degree of elasticity most often quantified rheologically. Formation of a suitable protein gel structure, which is affected by the protein type, concentration and gelation conditions, plays an important role in food texture perception of food products, such as yoghurt, dessert, tofu, processed meats and cheddar cheese.

In order to create this continuous network, protein dispersions are processed (often heated) to allow for an increased amount of intermolecular interactions. Heated aqueous insect extracts from five insect species (yellow mealworm, superworm, lesser mealworm, house cricket and dubia cockroach) were found to form gels, with properties comparable to those formed from conventional food proteins. Further rheological investigations showed that gel strengths were affected by the species and growth stage of the insect[6], indicating not only a need to further understand these differences in terms of protein structure but also point to the potential to use different insect ingredients to create customised product textures.

Emulsions (mixtures of two immiscible liquids e.g. water and oil) require a third ingredient to allow for the formation of stable droplets of one liquid dispersed in the other; as with foams this third ingredient can be protein.

The formation and stability of an emulsion is required in food products, such as salad dressings, sauces, processed meat products, coffee whiteners and frozen desserts. An aqueous extraction precipitate from edible house crickets with a protein content of 67% was found to have good emulsifying capacity and stability higher than the non-water soluble fraction and hexane soluble fraction from the same flours[7]. A recent study at the University of Nottingham provided further validation of the emulsifying properties of insect protein by demonstrating that protein isolated from mealworm larvae stabilised oil-in-water emulsions for a storage period of two months with no change in stability following the addition of salt or temperature variation (-20 °C to 80 °C), indicating a wide range of potential food product applications.

Comparisons with whey protein also found that a smaller quantity of mealworm larvae protein was required to generate the same emulsion microstructure[8].

Finally, foams (gas bubbles in a continuous liquid or solid phase) are components of many foods, such as cakes, meringues, ice cream and bread. A functional property of proteins is the ability to form an interfacial film, similar to that occurring in emulsion formation, which, alongside an increased viscosity of the continuous phase, will result in a reduced rate of foam destabilisation.

The water soluble protein fraction from superworms produced a stable foam, while in the same study, extracts from yellow mealworm, lesser mealworm, house cricket and dubia cockroach were unable to form foams. However, the results will have been affected by the relatively low protein concentration and the presence of oil in the extracta. In comparison, unpublished data from the University of Nottingham indicates that isolated proteins from mealworm larvae can produce stable foams, the microstructure of one such foam is shown in Figure 3, with foam capacity and stability being comparable to that of egg white protein. These findings are supported by published surface tension data showing the ability of proteins extracted from mealworm larvae to adsorb at a gas bubble interface thus reducing the surface tension and creating an interfacial film. Values of surface tension of mealworm larvae proteins were comparable to those of other commonly used proteins, and, interestingly, proteins extracted from mealworm larvae that underwent a thermo-mechanical pre-treatment allowed for a greater reduction in surface tension, which may provide higher foaming functionality[9].

Figure 2, top, Oil-in-water emulsion stabilised by mealworm larvae protein

Figure 3, above, Air-in-water foam stabilised by mealworm larvae protein

Salad creams and egg foams – typical food products that could be stabilised by insect protein in the future

Conclusions

It is clear that there is still a need for more information and understanding of the physiochemical properties and indeed the nutritional composition of insects and insect extracts to allow for integration of these ingredients into food products.

Interestingly, in both aspects, results vary between insects and understanding why these differences exist and how they could be exploited in food products is a challenging and

exciting area opening up to food scientists globally. Although the journey to the supermarket shelf is only just starting, edible insect protein has the potential to be a future food ingredient providing nutrition and functionality in a more sustainable manner than conventional sources of protein.

Dr Jo Gould

Assistant Professor in Food Science

Division of Food Science, University of Nottingham, Nottingham NG7 2RD.

Email joanne.gould@nottingham.ac.uk

References

1. Rumpold, B.A. and O.K. Schluter, Nutritional composition and safety aspects of edible insects. Molecular Nutrition & Food Research, 2013. 57(5): p. 802-823.

2. Churchward-Venne, T.A., et al., Consideration of insects as a source of dietary protein for human consumption. Nutrition reviews, 2017. 75(12): p. 1035-1045.

3. Ramos-Elorduy, J., et al., Nutritional Value of Edible Insects from the State of Oaxaca, Mexico. Journal of Food Composition and Analysis, 1997. 10(2): p. 142-157.

4. Mlcek, J., et al., A Comprehensive Look at the Possibilities of Edible Insects as Food in Europe - a Review. Polish Journal of Food and Nutrition Sciences, 2014. 64(3): p. 147-157.

5. Schösler, H., J. De Boer, and J.J. Boersema, Can we cut out the meat of the dish? Constructing consumer-oriented pathways towards meat substitution. Appetite, 2012. 58(1): p. 39-47.

6. Yi, L., et al., Extraction and characterisation of protein fractions from five insect species. Food Chemistry, 2013. 141(4): p. 3341-3348.

7. Ndiritu, A.K., et al., Extraction technique influences the physico-chemical characteristics and functional properties of edible crickets (Acheta domesticus) protein concentrate. Journal of Food Measurement and Characterization, 2017. 11(4): p. 2013-2021.

8. Gould, J. and B. Wolf, Interfacial and emulsifying properties of mealworm protein at the oil/water interface. Food Hydrocolloids, 2017.

9. Azagoh, C., et al., Extraction and physicochemical characterization of Tenebrio molitor proteins. Food Research International, 2016. 88: p. 24-31.



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