Comparison of functional properties of edible insects and protein preparations thereof

LWT - Food Science and Technology 91 (2018) 168–174

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Comparison of functional properties of edible insects and protein preparations thereof

T

Ewelina Zielińska∗, Monika Karaś, Barbara Baraniak Department of Biochemistry and Food Chemistry, University of Life Sciences in Lublin, Skromna Str. 8, 20-704, Lublin, Poland

A R T I C L E I N F O

A B S T R A C T

Keywords: Edible insects Entomophagy Functional properties Protein preparations

This study investigated the functional properties of three species of edible insects: Gryllodes sigillatus, Schistocerca gregaria, and Tenebrio molitor. The water and oil holding capacity, solubility, and foaming and emulsion properties were evaluated. The protein solubility showed minimum values at pH 5. The highest water and oil holding capacity was noticeable for the T. molitor protein preparation (3.95 g/g) and for the G. sigilltus protein preparation (3.33 g/g), respectively. The G. sigillatus protein preparation also showed the highest foaming capacity, foam stability, and emulsion activity (99.0%, 92.0%, and 72.62%, respectively), while the protein preparation from S. gregaria exhibited the highest emulsion stability (51.31%). This study has shown that whole insects and protein preparations thereof can be suitable for development of new food formulations.

1. Introduction

2015) but there are only few data about the functional properties of insect protein. These properties could be helpful to clarify the use of insect powder or protein extracts in different food products, for example bread, pasta, and dairy products. Currently, many commercial food products are fortified in order to increase their nutritional value. For example, ham is enriched with protein derived from legumes and fruit juices are enriched with vitamins. Edible insects are a great material for food fortification for several reasons. First of all, they are rich in protein of high biological value with a good amino acid profile and a high level of digestibility. Moreover, insects are a good source of a variety of micronutrients such as minerals: copper, iron, magnesium, manganese, phosphorous, selenium, and zinc and vitamins: riboflavin, pantothenic acid, biotin, and folic acid (Ramos-Elorduy et al., 2012; Rumpold & Schlüter, 2013). Their lipid profile is desirable for humans. They are a source of unsaturated fatty acids, for example omega-3 (Zielińska et al., 2015). Given their nutritional value, insects can be a good product for food supplementation and entomophagy does not have to be associated with the consumption of whole insects any more. In this study, three species of insects (Tenebrio molitor, Schistocerca gregaria, Gryllodes sigillatus) were selected, which are well known and easy to breed in Europe; each of them belongs to a different order or family and is bred widely in Europe. These species have also been reported to have the biggest potential to be used as food and feed in the EU (EFSA, 2015). Moreover, the nutritional value of these insects was

In the last decade, the interest of entomophagy has been continuously growing. Currently, insects are consumed by two billion people worldwide and even insect foods have recently become available in the US and Europe. More than 2100 insect species have been documented in literature as edible (Jongema, 2017). Moreover, insects are still promoted as a good source of protein and the production of edible insects in developing countries is supported by various institutions such as the Food and Agriculture Organization of the United Nations. However, the use of insects in food production requires further investigations at different levels, for example to search for opportunities to use them in various forms. This may be necessary since Western consumers may be reluctant to accept insects as a protein source (Shelomi, 2015). In many countries, whole insects are often consumed but they can also be processed to pastes and powders; furthermore, insect proteins, fats, and chitin can be isolated before use in food products as well. This could be a useful way for increasing acceptability among wary consumers. Edible insects can also be processed into a more palatable form by grinding or milling. It is an easy way to obtain high-protein insect flour with other valuable components such as vitamins or minerals (Yi et al., 2013). Several studies have shown that edible insects are a good source of protein (Ramos-Elorduy, Moreno, & Camacho, 2012; Rumpold & Schlüter, 2013; Zielińska, Baraniak, Karaś, Rybczyńska, & Jakubczyk,

Abbreviations: G. sigillatus, Gryllodes sigillatus; S. gregaria, Schistocerca gregaria; T. molitor, Tenebrio molitor; TNBS, picrylsulfonic acid; OHC, oil holding capacity; WHC, water holding capacity; FC, foaming capacity; FS, foam stability; EA, emulsion activity; ES, emulsion stability ∗ Corresponding author. E-mail address: [email protected] (E. Zielińska). https://doi.org/10.1016/j.lwt.2018.01.058 Received 30 October 2017; Received in revised form 17 January 2018; Accepted 19 January 2018 0023-6438/ © 2018 Elsevier Ltd. All rights reserved.

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centrifuged at 8,000g for 15 min. The precipitate was weighed and the difference in the weight was calculated. The results were presented as gram of water absorbed per gram of the sample.

studied. The most important information for determination of the functional properties is the protein content, and the studied species contain 52.35, 76.0, and 70.0% of protein, respectively (Zielińska et al., 2015). The physicochemical properties of proteins, protein size, and flexibility play an important role in determining their functional properties, for example small molecular weight proteins give very good emulsion-forming abilities because of rapid diffusion to the interface. Proteins are commonly used to improve the functional properties of food compositions. In fact, the functional properties of proteins are dependent on pH. The aim of this study was to determine the functional properties of flours and protein preparations obtained from edible insects. In this study, the solubility, water and oil holding capacity, and foaming and emulsifying properties were determined.

2.5. Oil holding capacity Oil holding capacity (OHC) was determined according to the method of Haque and Mozaffar (1992) with a slight modification. The sample (0.5 g) was added to 10 ml of vegetable oil and mixed for 30 s in a vortex mixer. Afterwards, the dispersion was centrifuged at 8,000g for 15 min. The precipitate was weighed and the difference in the weight was calculated. The results were presented as gram of oil absorbed per gram of the sample.

2. Materials and methods

2.6. Foaming properties

2.1. Raw materials

Foaming capacity (FC) and foam stability (FS) were determined according to the method of Guo et al. (2015). Twenty milliliter of a 1% sample was homogenized in a high shear homogenizer mixer (pol-eko H500, Poland) at a speed of 16,000 rpm for 2 min. The whipped sample was immediately transferred into a cylinder. The total volume was read at time zero and 30 min after homogenization. The foaming capacity and foam stability were calculated from the formula:

The mealworms Tenebrio molitor (Linnaeus, Coleoptera: Tenebrionidae) (larvae), locusts Schistocerca gregaria (Forskal, Orthoptera: Acrididae) (adult), and crickets Gryllodes sigillatus (Fabricius, Orthoptera: Gryllidae) (adult) were obtained from a commercial supplier from Poland. All individuals of these species were fasted for approximately 48 h to clear their gastrointestinal tract of any residual food. For each species tested, approximately 0.5 kg of material was frozen and lyophilized. The insects were ground in a laboratory grinder.

Foaming capacity (FC) (%) = [(V0eV)/V] × 100 Foam stability (FS) (%) = (V30 /V0) × 100 Where: V – volume before whipping (ml), V0 – volume after whipping (ml), V30 – volume after standing (ml).

2.2. Method for obtaining the protein preparation

2.7. Emulsifying properties

Proteins were isolated according to the Girón-Calle, Alaiz, and Vioque (2010) method with slight modification. Briefly, insect flour was stirred for 1 h with 0.2% NaOH at a ratio of 1:10 (w/v), pH 11, at room temperature. After centrifugation at 8,000g, precipitation of proteins was carried out at the isoelectric point pH 4.5 and room temperature. Precipitated proteins were centrifuged at 4 °C for 20 min at 8000 g and washed with distilled water. Afterwards, the protein preparations were lyophilized and kept at −18 °C until further analysis.

Emulsifying properties were determined according to the method of Wu, Wang, Ma, and Ren (2009). The sample was dispersed in distilled water (1% w/v) and 15 ml of the dispersion were homogenized (pol-eko H500, Poland) with 15 ml of vegetable oil at a speed of 20,000 rpm for 1 min. Afterwards, the samples were centrifuged at 3000 g for 5 min and the volume of the individual layers were read. Emulsion stability was evaluated by heating the emulsion for 30 min at 80 °C. Then, the samples were centrifuged at 3000 g for 5 min. Emulsion activity and emulsion stability were calculated from the formula:

2.3. Solubility

Emulsion activity (EA) (%) = (Ve/V) × 100 The protein solubility was determined according to the method of Castellani, Martinet, David-Briand, Guérin-Dubiard, and Anton (2003) with a slight modification. The sample was dispersed in distilled water and the pH of the mixture was adjusted to 2, 3, 4, 5, 6, 7, 8, 9, 10, and 11 using 1 or 6 mol/L HCl and 1 or 6 mol/L NaOH. The volume of the mixture was adjusted to obtain the final concentration of protein (10 mg/ml). Total protein content in the sample was determined after solubilization of the sample in 0.5 mol/L NaOH. The mixture was stirred for 90 min and centrifuged at 8,000g for 15 min. The protein content in the supernatant was determined using the Bradford method (1976). Protein solubility was calculated from the formula:

Emulsion stability (ES) (%) = (V30/Ve) × 100 Where: V – total volume of tube contents, Ve – volume of the emulsified layer, V30 – volume of the emulsified layer after heating. 2.8. The sensory evaluation

Solubility (%) = (Ps/Pt) × 100

The panel for sensory analysis was composed of 75 members aged from 21 to 30 years (58 women, 17 men). The characteristics of the flours and protein preparations, such as color, consistency, smell, and overall acceptability were evaluated on a scale of 1–5 (1–bad, 5–very good).

where: Ps – protein content in the supernatant, Pt – total protein content in the sample.

2.9. Statistical analysis All experiments were run in triplicate and the results were presented as means ± standard deviation. Statistical analysis was performed using the STATISTICA v. 10.0 for one-way analysis of variance (ANOVA) and the differences of the means between the samples were determined using the Tukey test. P-values below 0.05 were considered significant.

2.4. Water holding capacity Water holding capacity (WHC) was determined according to the method of Diniz and Martin (1997) with a slight modification. The sample (0.5 g) was dispersed in 20 ml of distilled water and stirred with a shaker at 540 rpm for 30 min. Afterwards, the dispersion was 169

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A

Functional properties of proteins are determined by the specific properties of their molecules such as size, structure, or configuration (Kilara & Harwalker, 1996). In an earlier study, Zielińska, Baraniak, and Karaś (2017) obtained the protein profile of insect flour. The proteins from three insect species exhibited a varied range of molecular mass. The Schistocerca gregaria showed two major proteins with molecular mass of ∼36 kDa and ∼97 kDa, Gryllodes sigillatus had ∼55.3 kDa and ∼116 kDa proteins, while the Tenebrio molitor protein profile did not show dominant proteins. Nevertheless, the bands observed in the T. molitor protein profile ranged from 6.5 to 95 kDa. The differences in the molecular mass clearly differentiated the functional properties of the studied insect species. Functional properties can be also associated with a varying amount of protein and other constituents in flours. The protein content in the studied species was as follows: T. molitor 52.35%, G. sigillatus 70.0%, and S. gregaria 76.0%. The fat content was 24.7%, 18.23%, and 12.97%, respectively, and the content of carbohydrates was 2.2%, 0.1%, and 1.7%, respectively (Zielińska et al., 2015). The amino acid and fatty acid spectra for the studied species were presented in a previous study (Zielińska et al., 2015).

5

water holding capacity (g/g)

3. Results and discussion

a 4

a

3

b

b

bc

2 c 1

0 Tenebrio molitor

Gryllodes sigillatus

Schistocerca gregaria

B 3.1. Solubility

4 a

oil holding capacity (g/g)

The results for the protein solubility are presented in Fig. 1. The protein solubility of all samples showed minimum values at around pH 5 with values of 3% for T. molitor, 4% for G. sigillatus, and 8% for S. gregaria. A significant increase in protein solubility was observed around pH 8 for T. molitor and G. sigillatus, and around pH 9 for S. gregaria. The highest solubility of all samples was noticeable at pH 11 (T. molitor – 97%, G. sigillatus – 96%, and S. gregaria – 90%), but a high solubility value was shown also at pH 2 and 3 for T. molitor (86 and 52%, respectively) and S. gregaria (87 and 69%, respectively), and at pH 2, 3, and 4 for G. sigillatus (72, 65, and 57%, respectively). These results correspond well with those obtained by Zhao, Vázquez-Gutiérrez, Johansson, Landberg, and Langton (2016) in similar assay conditions but for defatted T. molitor protein extraction. Generally, the insect protein solubility was similar to data reported for legumes, for example kidney bean flour (Wani, Sogi, Wani, & Gill, 2013), especially the kidney bean globulin fraction (Mundi & Aluko, 2012) and other plants like the Ginko biloba seed albumin fraction (Deng et al., 2011) or fenugreek (El Nasri & El Tinay, 2007). It should be noted that the solubility of the materials mentioned above was similar although the authors used different dilutions of the samples and the protein was determined with different methods. Solubility is one of the most important physicochemical and functional properties of protein and depends on hydration and the degree of hydrophobicity of protein molecules (Sathe & Salunkhe, 1981). Good solubility of proteins is important in many uses, mainly for formation of emulsions, foams, and

solubility (%)

Schistocerca gregaria

Fig. 2 shows the result of the water holding capacity. Higher water holding capacity was noticeable for the protein preparations than the whole insects and the highest water holding capacity was noted in the Tenebrio molitor protein preparation (3.95 g/g), while the lowest value was noted for the whole ground T. molitor (1.29 g/g). This is important information for the use of these forms in food industry. The big difference in water holding capacity between protein preparations and insect flour might be a good indicator of the applications of these forms for different food products. An opposite situation was observed in the case of Schistocerca gregaria – similar WHC values were noted for the protein preparation and the insect flour (2.31 g/g and 2.18 g/g, respectively). This is also important information that could be helpful in the analysis of the cost-effectiveness and benefits brought by the use of one of the presented forms of insects. Protein isolates are obviously richer in protein than whole insects but do not contain vitamins,

50 40 30 20 10 0 10

Gryllodes sigillatus

3.2. Water holding capacity

60

8

1

gels in designed food products. As a result, molecules in colloidal systems are homogeneously dispersed, which improves the interfacial properties (Zayas, 1997).

70

6

d

Fig. 2. Water holding capacity (A) and oil holding capacity (B) of insect protein preparations (pale) and insect flours (dark). Different letters indicate significant difference (p < 0.05).

80

4

d 2

Tenebrio molitor

90

2

bc

c

0

100

0

3

ab

12

pH

Fig. 1. Protein solubility with changes at pH 2–11. Tenebrio molitor (square), Gryllodes sigillatus (triangle), Schistocerca gregaria (circle).

170

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Table 1 Functional properties of studied insect species and selected plant seeds rich in protein. Insects

Form

WHC (g/g)

OHC (g/g)

FC (%)

FS (%)

EA (%)

ES (%)

Tenebrio molitor

whole protein preparation whole protein preparation whole protein preparation

1.29 3.95 2.34 3.44 2.18 2.31

± ± ± ± ± ±

0.19 0.2 0.28 0.13 0.07 0.19

1.71 2.74 2.82 3.33 1.98 3.22

± ± ± ± ± ±

0.13 0.06 0.08 0.11 0.16 0.16

31.0 ± 1.41 32.67 ± 0.94 41.0 ± 1.41 99.0 ± 1.41 22.33 ± 1.41 32.0 ± 1.88

26.0 ± 0.94 30.33 ± 0.47 34.67 ± 2.82 92.0 ± 1.88 19.33 ± 0.94 6.17 ± 0.71

65.96 ± 1.5 66.6 ± 2.16 62.0 ± 1.25 72.62 ± 1.9 69.17 ± 0.59 67.78 ± 1.6

27.59 ± 1.18 51.31 ± 0.46 31.65 ± 0.92 38.3 ± 0.8 48.11 ± 0.57 50.41 ± 1.99

whole whole whole protein isolate protein isolate protein isolate whole whole whole defatted flour

1.19 1.33 1.30 4.47 1.68 1.68 2.60 2.25 2.65 1.30

± 0.01 ± 0.02

1.10 0.93 0.84 1.54 1.43 1.56 2.40 1.52 1.23 0.90

± 0.02 ± 0.00

52.00 80.00 70.00 235.00 89.29 70.00 109.5 ± 1.8 45.70 ± 1.40 38.20 ± 0.90 51.00

83.0 99.0 nd nd 43.91 55.0 70.0 41.20 ± 1.80 43.30 ± 1.60 96.00

61.14 65.75 18.00 25.00 59.94 61.00 nd 55.00 60.50 57.00

94.19 91.99 nd nd 95.78 61.00 nd 52.40 62.30 nd

Gryllodes sigillatus Schistocerca gregaria Plant seeds chickpea lentil soy lupin fenugreek indian kidney bean red kidney small red kidney peanut

± 0.01 ± 0.13 ± 0.20

± 0.32 ± 0.11 ± 0.08

± 0.61 ± 0.11

± 0.13 ± 1.80 ± 1.90

± 1.64 ± 4.75

± 0.13 ± 1.80 ± 2.20

Source: Siddiq, Ravi, Harte, & Dolan, 2010; Du, Jiang, Yu, & Jane, 2014; Piornos et al., 2015; Ma et al., 2017; Kinsella, 1979; El Nasri & El Tinay, 2007. WHC: Water Holding Capacity, OHC: Oil Holding Capacity, FC: Foaming Capacity, FS: Foam Stability, EA: Emulsion Activity, ES: Emulsion Stability.

Nasri and El Tinay, 2007). OHC is required in many food applications, e.g. in bakery products, ground meal formulation, and meat substitutes; therefore, it is suggested that the studied species of insects could be used in food industry due to their high OHC. The oil holding capacity of whole insects and protein preparations is presented in Fig. 2. The lowest water holding capacity of the insect flour coincided with the lowest oil holding capacity (T. molitor 1.29 g/g and 1.71 g/g, respectively). This is probably related to the fact that T. molitor contains substantially less protein than the other insect species tested (52.35%) and considerably more fat (24.7%) (Zielińska et al., 2015). The differences in OHC were possibly due to the different conformational characteristics, surface hydrophobicity, or lipophilicity of these proteins (Deng et al., 2011). The low OHC value for T. molitor may be the result of the lowest non-polar amino acid content in protein among the tested species (257.6 mg/g) (Zielińska et al., 2015). Furthermore, the protein preparation from T. molitor was shown to exhibit the lowest oil holding capacity among all the preparations (2.74 g/g). This value corresponds well with the value for a T. molitor protein extract obtained by Zhao et al. (2016) using a similar method to that used in this study (2.33 g/g). T. molitor was also characterized by the lowest OHC among the whole ground insects (1.71 g/g), while OHC for the T. molitor flour prepared by Bußler et al. (2016) using a different method was lower (0.6 g/g dry mass). In turn, G. sigillatus was found to have the highest OHC among the whole insects and protein preparations (2.82 g/ g and 3.33 g/g, respectively). The S. gregaria protein preparation was found to have an equally high value (3.22 g/g). Generally, the oil holding capacity for the studied species range from 1.71 g/g to 3.33 g/g and can be compared to the similarly determined OHC for silkworm (Bombyx mori) larvae and pupae (252.18% and 284.87%, respectively) (Omotoso, 2015), or legumes such as kidney bean flour (2.2–2.3 kg/kg) (Wani et al., 2013). The studied species show higher OHC than almost all plant seeds rich in protein listed in Table 1, which suggests an opportunity to substitute these materials in food products that require high OHC values.

minerals, fatty acids, or chitin and their production is more expensive than milling insects. Moreover, flour from S. gregaria can be a valuable addition enriching bread with not only protein but also vitamins, minerals, or chitin. Due to the high WHC of this flour, it can be additionally contribute to improvement of the selected properties of bread products. Omotoso (2006) studied the functional properties of Cirina forda (Lepidoptera: Saturniidae) – one of the most widely eaten insects in Southern Nigeria. The water holding capacity of dried ground insect was 300% and this value is the most similar to the WHC of the Gryllodes sigillatus protein preparation (3.44 g/g). Besides, WHC for the whole T. molitor (1.29 g/g) is similar to that determined analogically by Omotoso (2015) for the silkworm larvae and pupae (Bombyx mori) (175% and 115%, respectively). In turn, Zhao et al. (2016) reported the WHC for a Tenebrio molitor protein extract to be 1.87 ml/g, while our studies showed two times higher results (3.95 g/g). Probably these differences result from the protein extraction method used by authors as well as the insects' origin. Moreover, Bußler, Rumpold, Jander, Rawel, and Schlüter (2016) reported the WHC of 0.8 g/g dry mass for T. molitor flour, while our studies showed a value of 1.29 g/g, which may be caused by the different method of flour production and different trial conditions. Among the insect flours, the highest WHC was noted in the G. sigillatus flour (2.34 g/g) and a similar WHC value was found for the S. gregaria flour (2.18 g/g). This is probably a result of the high content of hydrophilic amino acids in these insects (390.6 and 371.4 mg/g, respectively) (Zielińska et al., 2015). 3.3. Oil holding capacity The fat/oil holding capacity is physical entrapment of oil (Kinsella, 1979). The oil absorbing mechanism involves capillarity interaction, which allows the absorbed oil to be retained. Hydrophobic proteins play the main role in oil absorption. According to Sathe, Deshpande, and Salunkhe (1982), the OHC can be related to the protein contents, protein types, and the amino acid composition of proteins, in particular to hydrophobic residues that interact with hydrocarbon chains in fat molecules. Furthermore, Kinsella (1976) investigated that more hydrophobic proteins show superior binding of lipids, indicating that nonpolar amino acid side chains bind the paraffin chains of fats. Therefore, the OHC of different insect flours and protein preparations thereof are influenced by particle sizes, contents, composition and conformation of protein ingredient. OHC plays an important role in enhancing the mouth feel, the flavor retention, or improvement of palatability (El

3.4. Foaming properties Foam formation is governed by transportation, penetration, and reorganization of molecules at the air–water interface. To exhibit good foaming, a protein must be capable of migrating rapidly to the air–water interface, unfolding, and rearranging at the interface (Halling, 1981). Foaming properties are dependent on the proteins and some other components, such as carbohydrates, present in the flours (Sreerama, Sashikala, Pratape, & Singh, 2012). The factors influencing 171

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A

A

120

74

emulsion acƟvity (%)

foaming capacity (%)

70

80 60 b 40

a

72

a

100

c

c

c

d

ab

ab

a

ab

68 66

b

64 62 60 58

20

56 0

54 Tenebrio molitor

Gryllodes sigillatus

Schistocerca gregaria

Tenebrio molitor

100

60

a

a

90

emulsion stability (%)

foam stability (%)

a

50

80 70 60 50

30

Schistocerca gregaria

B

B

40

Gryllodes sigillatus

bc

b c d

20

a

b

40

c c

30 20 10

e

10

0

0 Tenebrio molitor

Gryllodes sigillatus

Tenebrio molitor

Schistocerca gregaria

Gryllodes sigillatus

Schistocerca gregaria

Fig. 3. Foaming capacity (A) and foam stability (B) of insect protein preparations (pale) and insect flours (dark). Different letters indicate significant difference (p < 0.05).

Fig. 4. Emulsion capacity (A) and emulsion stability (B) of insect protein preparations (pale) and insect flours (dark). Different letters indicate significant difference (p < 0.05).

foam formation include surface hydrophobicity, location of hydrophobic amino acid residues on the protein surface, presence of thiol groups, cations and anions, carbohydrates and lipids. Moreover, the amphiphilicity of protein structures is a prerequisite for proteins with good surface properties, including emulsifying and foaming. In food technology, foams are used to improve the texture, consistency, and appearance of foods. The results of the foaming capacity and foam stability of the whole insects and protein preparations are presented in Fig. 3. The highest value of foaming capacity among both protein preparations and whole insects was found for G. sigillatus (99% and 41%, respectively). Generally, higher foaming capacity was noted in the protein preparations. The foam stability ranged from 19.33% to 34.67% for the whole insects and from 6.17% to 99.0% for the protein preparations. Generally, the highest value among both the protein preparations and whole insects was found in G. sigillatus (92.0% and 34.67%, respectively) and the lowest value was noted in S. gregaria (6.17% and 19.33%, respectively). These results are not consistent with the highest hydrophobic amino acid content in the protein of the studied species, but it may be dependent on the location of hydrophobic amino acid residues on the protein surface in the case of G. sigillatus. The differences in FC of proteins may be due to their different conformational characteristic. Globular proteins were found to have reduced ability to unfold at the air-water interface, which limits the capacity to encapsulate air bubbles

Table 2 Sensory analysis of edible insect flours and protein preparations thereof. Insects

Form

Color

Consistency

Smell

Overall acceptability

Schistocerca gregaria

protein preparation whole protein preparation whole protein preparation whole

3.99a

4.10a

3.12a

3.79a

3.15b 3.29b

3.23bc 3.42bc

3.33a 2.45b

3.38b 3.16bc

3.30b 3.19b

3.15bc 3.55b

2.45b 2.58b

3.03c 3.19bc

3.11b

3.05c

1.75c

2.64d

Gryllodes sigillatus Tenebrio molitor

Different letters in the same column indicate significant difference (p < 0.05).

(Mundi & Aluko, 2012). In turn, the lower FS of T. molitor and S. gregaria is probably due to the high level of sugars (2.2 and 1.7%, respectively) (Zielińska et al., 2015), which reduces protein-protein interactions and leads to formation of weak interfacial membranes that are unable to stabilize the foams (Mundi & Aluko, 2012). Furthermore, the analyzed species exhibit substantially higher values of foaming properties than Cirina forda. The foaming capacity and foam stability of Cirina forda were 7.1% and 3%, respectively (Omotoso, 2006). Moreover, whole giant cricket (Gryllidae sp.) powder was 172

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were better rated and they exhibited better functional properties, which makes them more useful in food industry.

reported to have a FC of only 6% and a FS of 3.05% after 2 h which were determined using a similar method to that employed in this study (Adebowale, Adebowale, & Oguntokun, 2005). Acid-extracted protein fractions from five different insects species, including the cricket (Acheta domesticus) protein or the mealworm (Tenebrio molitor) protein were shown to have poor or no foam capacity, over a range of pH, but the foaming capacity was differently determined than in our study - the solutions were aerated with nitrogen gas (Yi et al., 2013). In turn, crickets (Gryllodes sigillatus) heated at 50 °C for 30 min were found to have a FC of 100% with a FS of 90% after 1 h (Hall, Jones, O'Haire, & Liceaga, 2017), which corresponds with our results for the G. sigillatus protein (99% and 92%, respectively) obtained using a similar assay method. Currently, research is directed towards exploration of alternatives for eggs, a common foaming agent, in food products (Hall et al., 2017). The data from this study suggests that G. sigillatus protein preparation exhibited excellent foaming properties; hence, it can be a desirable foaming agent and has potential for such food applications.

4. Conclusion Good protein solubility is often associated with its good functional properties (Kinsella, 1976). The results of our study are in agreement with this statement. Protein from G. sigillatus exhibited good solubility in the widest range of pH and the flour and protein preparation thereof were generally found to have the best functional properties among the studied species. In this study, we demonstrated that edible insects could be considered an alternative source of protein. The good solubility of the insect protein in a wide pH range facilitates the varied use in food ingredient formulations - as a food additive in acid and alkaline food. Our result show that insects have high water and oil holding capacity, high emulsion activity, and moderate foaming capacity and foam stability; therefore, they certainly can be used in food formulations requiring these properties. It can also be concluded that edible insects can be a good source of protein ingredient in food systems.

3.5. Emulsifying properties

Funding

The results of the emulsion activity and emulsion stability of the whole insects and protein preparations are presented in Fig. 4. The differences between the emulsion activities and emulsion stabilities are related to the amphiphilicity of the protein surface, protein contents (soluble and insoluble), and other components. For emulsion activity, the highest value was noted in the G. sigillatus protein preparation (72.62%) with emulsion stability of 38.3%. Similarly, Omotoso (2015) reported EA of 75% for silkworm B. mori but with lower ES (23%). The emulsion activities for the whole insects were similar and ranged from 62% (G. sigillatus) to 69.17% (S. gregaria). S. gregaria was also characterized by the highest emulsion stability (48.11%) among the whole insects which may be associated with the highest protein content and the highest amount of hydrophobic amino acids (398.3 mg/g) (Zielińska et al., 2015). Furthermore, the relatively high content of sugars is important (1.7%) (Zielińska et al., 2015) because some types of polysaccharides can help stabilize the emulsion by increasing the viscosity of the system (Wani et al., 2013). Generally, higher emulsion stability was noted in the protein preparations and the highest value was found in the T. molitor protein preparation (51.31%). This value corresponds well with that obtained by Kim, Setyabrata, Lee, Jones, and Kim (2016) with the use of an analogical method for T. molitor flour (50.28%). Currently, casein and whey protein are the most widely used protein emulsifiers in the food industry but still alternative protein sources are being sought (Phillips & Williams, 2011). The studied species show similar or higher emulsion activity than plant seeds rich in protein listed in Table 1 and they can be an alternative protein emulsifier in existing foods as well as in new food formulations.

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors. Conflicts of interest None. References Adebowale, Y. A., Adebowale, K. O., & Oguntokun, M. O. (2005). Evaluation of nutritive properties of the large African cricket (Gryllidae sp.). Pakistan Journal of Scientific and Industrial Research, 48(4), 274. Bradford, M. M. (1976). A rapid and sensitive method for the quantitation of microgram quantities of protein utilizing the principle of protein-dye binding. Analytical Biochemistry, 72(1), 248–254. Bußler, S., Rumpold, B. A., Jander, E., Rawel, H. M., & Schlüter, O. K. (2016). Recovery and techno-functionality of flours and proteins from two edible insect species: Meal worm (Tenebrio molitor) and black soldier fly (Hermetia illucens) larvae. Heliyon, 2(12), e00218. Castellani, O., Martinet, V., David-Briand, E., Guérin-Dubiard, C., & Anton, M. (2003). Egg yolk phosvitin: Preparation of metal-free purified protein by fast protein liquid chromatography using aqueous solvents. Journal of Chromatography B, 791(1–2), 273–284. Deng, Q., Wang, L., Wei, F., Xie, B., Huang, F., Huang, W., et al. (2011). Functional properties of protein isolates, globulin and albumin extracted from Ginkgo biloba seeds. Food Chemistry, 124(4), 1458–1465. Diniz, F. M., & Martin, A. M. (1997). Effects of the extent of enzymatic hydrolysis on the functional properties of shark protein hydrolysate, 30, Lebensmittel-Wissenschaft undTechnologie266–272. Du, S. K., Jiang, H., Yu, X., & Jane, J. L. (2014). Physicochemical and functional properties of whole legume flour. LWT-Food Science and Technology, 55(1), 308–313. EFSA Scientific Committee (2015). Risk profile related to production and consumption of insects as food and feed. EFSA Journal, 13(10). El Nasri, N. A., & El Tinay, A. H. (2007). Functional properties of fenugreek (Trigonella foenum graecum) protein concentrate. Food Chemistry, 103(2), 582–589. Girón-Calle, J., Alaiz, M., & Vioque, J. (2010). Effect of chickpea protein hydrolysates on cell proliferation and in vitro bioavailability. Food Research International, 43(5), 1365–1370. Guo, F., Xiong, Y. L., Qin, F., Jian, H., Huang, X., & Chen, J. (2015). Surface properties of heat-induced soluble soy protein aggregates of different molecular masses. Journal of Food Science, 80(2), C279–C287. Halling, P. J. (1981). Protein stabilized foams and emulsions. CRC Critical Reviews in Food Science, 12, 155–203. Hall, F. G., Jones, O. G., O'Haire, M. E., & Liceaga, A. M. (2017). Functional properties of tropical banded cricket (Gryllodes sigillatus) protein hydrolysates. Food Chemistry, 224, 414–422. Haque, Z. U., & Mozaffar, Z. (1992). Casein hydrolysate II. Functional properties of peptides. Food Hydrocolloids, 5, 559–571. Jongema, Y. (2017). List of edible insects of the world. Wageningen, The Netherlands: Wageningen University. http://www.wur.nl/en/Expertise-Services/Chair-groups/ Plant-Sciences/Laboratory-of-Entomology/Edible-insects/Worldwide-species-list. htm, Accessed date: 10 October 2017. Kilara, A., & Harwalker, V. R. (1996). Denaturation. In S. Nakai, & H. W. Modler (Eds.).

3.6. Sensory evaluation The results of the sensory evaluation of the whole insects and protein preparations are presented in Table 2. In order to introduce insects to food, in addition to the assessment of functional properties, sensory evaluation should be considered. Color, consistency, smell, and overall acceptability were evaluated. The S. gregaria protein preparation was rated the best (3.99 for color, 4.10 for consistency, and 3.79 for overall acceptability) except for the smell where the highest score was found for whole S. gregaria (3.33). The worst scores in all categories for which assigned to whole T. molitor (3.11 for color, 3.05 for consistency, 1.75 for smell, and 2.64 for overall acceptability). This low result of sensory evaluation coincided with the poor functional properties. The T. molitor protein preparation was evaluated better and similar to G. sigillatus protein preparation. In turn, whole G. sigillatus and protein preparation thereof received similar ratings. Generally, the protein preparations 173

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