곤충 키토산과 단백질의 물리화학적 특성 연구

Abstract

ABSTRACT

Studies on Physicochemical Properties of Insect Chitosan and Protein -Mealworm Beetle & Rhinoceros Beetle

Shin, Chae -Shim Dept. of Food and Nutrition The Graduate School Hanyang University

Recently, edible insects have come into the spotlight at a global level as a new alternative and potential functional food resource of the future. Using insects for food could delay global warming caused by the large-scale breeding of livestock as a new eco-friendly and sustainable food resource. Currently, four insects species; Tenebrio molitor, Protaetia brevitarsis seulensis, Allomyrina dichotoma, and Gryllus bimaculatus; have been approved as food to eat safely for a limited time by the Ministry of Food and Drug Safety. Many studies on the various physical and chemical properties of polymers from soybean and whey protein have been performed, but the structural or functional properties of polymers from insects have not been thoroughly analyzed. The objects of this study were to investigate chitosan extraction methods, analyze the composition of two edible insects, and measure antimicrobial activities of chitosan. Also, this study focused on finding the best method to isolate protein from Mealworm Beetle (T. molitor) and investigating the physicochemical properties of Mealworm Beetle (T. molitor) protein extracts. In chapter 1, the nutritional composition of Mealworm Beetle (T. molitor) and Rhinoceros Beetle (A. dichotoma) was analyzed and the antibacterial activity of chitosan was measured. The protein contents of T. molitor and A. dichotoma were around 47.4% and 40.15%, respectively. Their total fat contents were 33.3% and 30.5%, with unsaturated fatty acids (UFAs) accounting for 24.1% and 21.9%, and SFA accounting for 7.9% and 7.8%, respectively. In this fatty acids contents, UFAs is higher than SFA. Their calcium contents were 30.38 mg/100 g and 28.5 mg/100 g, zinc was 10.62 mg/100 g and 11.5 mg/100 g, and iron was 5.62 mg/100 g and 6.1 mg/100 g, respectively. As such, these insects could provide not only high quality protein, fat, and dietary fiber, but also abundant minerals like calcium, zinc, and iron. Furthermore, both T. molitor and A. dichotoma contain a high amount of essential amino acids that are likely to be deficient in grain food sources. Chitin was isolated from the larvae, adult, and superworm of Mealworm Beetle and the larvae, pupa, and adult of Rhinoceros Beetle by deproteinization and demineralization. Chitin yields were 4.6%, 8.4%, and 3.9% in the larvae, adult, and superworm of Mealworm Beetle and 10.5%, 12.7%, and 14.2% in the larvae, pupa, and adult of Rhinoceros Beetle, respectively. Chitosan was obtained by deacetylation of chitin extractions from all stages of both beetle species. Chitosan yields from chitin were 80.0%, 78.3%, and 83.3% in the larvae, adult, and superworm of Mealworm Beetle, and 83.3%, 83.3%, and 75% in larvae, pupa, and adult of Rhinoceros Beetle, respectively. The yield of chitosan was highest in the adult stage, but the yield of chitosan induced from the chitin was the lowest in adult stage. However, the difference between them was not significant. The Fourier transform infrared spectroscopy (FTIR) and X-ray powder diffraction (XRD) analysis of the chitosan from the two insect species showed the similar structural characteristics as those of commercial shrimp chitosan. In antimicrobial tests, chitosan from the Mealworm Beetle showed about 1-2 mm inhibition zones, indicating antimicrobial activity against four strains of bacteria: Staphylococcus aureus, Bacillus cereus, Listeria monocytogenes, and Escherichia coli. Between the two species, chitosan from Mealworm Beetle showed the highest antimicrobial activity against Staphylococcus aureus with a 2 mm inhibition zone. Commercial shrimp chitosan showed no antimicrobial activity against any of the four bacterial strains tested. In chapter 2, Mealworm Beetle larvae protein physicochemical properties were analyzed. The color of the extracted protein was dark brown by visual observation, but after freeze-drying and washing in distilled water, the color of T. molitor protein turned to light ivory. The protein extraction yield was highest when treated in ammonium sulfate [(NH4)2SO4]. A few bands were observed with SDS-PAGE, but the major proteins of T. molitor were apparent at 75 kDa and 60 kDa. The zeta potential of a 0.5% T. molitor protein solubility was positive at pH 2, pH 3, pH 4, and pH 5 levels, but it was negative at pH 6, pH 7, pH 8, and pH 9. Zeta potential was the closest to zero at pH 5. Gel formation was affected by the protein concentration, temperature, pH value, and time. As the solubility of the protein increased, gel formation improved. At pH 3 and pH 5, big air bubbles were formed slowly, the foaming stability maintained constant, and bubbles were drained slowly. Whereas, at pH 7 and pH 9, small bubbles and lots of foam formed quickly and easily, and then ruptured. The separation of oil from water was better at pH 3 and pH 5 than at pH 7 and pH 9, which means that the emulsifying stability (ES) and the emulsifying activity (EA) decreased at low pH values whereas they increased at high pH values. The zeta-potential value of the dispersed oil droplets in 0.5% protein solution after 0, 7, and 24 hours at pH 3 and pH 5 was positive, but at pH 7 and pH 9, they were negative. Over time, the particle diameters of dispersed oil droplets in emulsions became bigger at pH 3 and pH 5, but they became bigger only slightly at pH 7 and pH 9. The water holding capacity (WHC) and the oil holding capacity (OHC) of T. molitor protein was 292 (g/100 g) and 611.5 (g/100 g), respectively. The OHC of T. molitor protein was higher than BSA and α-lactoalbumin. Currently, insects are getting attention as a future food resource and the insect industry is growing quickly in line with changing attitudes toward insects as not only a good food ingredient for high-quality protein and low-calorie foods, but also as a sustainable and alternative food protein resource of the future. Under these circumstances, it is expected that this study will be helpful to understand physicochemical properties of edible insects and to serve as a basis for further studies on edible insects and foster the insect industry in Korea.