Isolation and Identification of Antioxidant Peptide Derived from Cricket (Gryllus bimaculatus) Protein

Abstract

The foresight that the world population will exceed 9 billion by 2050 has led to research on how to increase the availability of food to cater to global citizens. Various research has shown that insects are a promising solution to global food security due to their nutritional composition and less environmentally destructive impacts. In fresh weight, insects contain an almost equal amount of protein as found in meat. Research has proven that insect protein has high protein quality as it is constituted by essential amino acids. The efficiency ratio of protein in many insects is about 75% DW protein. This and their high digestibility rate allow them to be compared with protein from stable foods like meat, fish, etc. Cricket is an insect that belongs to this category. The species Acheta domesticus and Gryllus bimaculatus are the most commonly found species of crickets for food in Thailand. The solubility and rate of precipitation of cricket protein are major factors during its extraction. Different extraction mechanisms are pivotal in the extraction yield of cricket proteins including the different pH in which there are allowed to be separated especially during a process known as Osborne fractionation during which proteins are fractionated into Albumin, Globulin, Glutelin, and Prolamin of differing yields. The present research is on Cricket as a source of protein, its high protein content, and Osborne fractionation as a mechanism of extraction of protein from edible cricket based on protein solubility. In this context, Cricket Protein fractions (albumin, globulin, glutelin, and prolamin) were hydrolyzed by cleaving the peptide bonds between amino acids by protease enzymes (alcalase, flavorzyme, and protamex). The hydrolysate was collected, purified, and the antioxidant activities were determined by 2,2-Azino-bis-3-ethyl- benzothiazoline-6- sulfonic Acid (ABTS) and metal chelating activities. The result shows that the Glutelin fraction has the highest extraction yield after Osborne fractionation. Globulin hydrolysates had a high degree of hydrolysis, but low antioxidant activity, whereas glutelin had a moderate degree of hydrolysis and increased antioxidant activity. The result of the antioxidant activity following enzymatic hydrolysis suggests that glutelin hydrolysates from the three enzymes should be further purified using three consecutive purification steps. Glutelin was further purified by membrane ultrafiltration to obtain <3 kDa, 3-10 kDa, and >10 kDa. <3 kDa was selected for further purification using gel filtration chromatography because of its high ABTS radical scavenging activity. The sequences found in GA-1(<3kDa) were TEAPLNPK, EVGA, KLL, TGNLPGAAHPLLL, and AHLLT while those found in GA-2 (<3kDa) were LSPLYE, AGVL, VAAV, VAGL, QLL. The molecular weight of the peptides is within the range of 359.23-721.37 Da. All the peptides identified contained hydrophobic and essential amino acids including alanine, leucine, and valine. Hydrophobic amino acids can enhance peptide solubility and scavenge free radicals. The presence of these amino acids in the peptide chains explains its high antioxidant activity. The significance of the study shows that cricket proteins contain high protein content and they are an alternate source of edible protein apart from the mainstream. The antioxidant peptides extracted from cricket protein have a very high antioxidant activity upon purification.