Food Chemistry 379 (2022) 132160 Available online 15 January 2022 0308-8146/© 2022 Elsevier Ltd. All rights reserved. The effect of steam cooking on the proteolysis of pacifc oyster (Crassostrea gigas) proteins: Digestibility, allergenicity, and bioactivity Chunsong Feng a , Li Tian a , Yadan Jiao a , Yuqing Tan a , Chune Liu b , Yongkang Luo a , Hui Hong a, * a Beijing Laboratory for Food Quality and Safety, College of Food Science and Nutritional Engineering, China Agricultural University, Beijing 100083, China b Institute of Yantai, China Agricultural University, Yantai 264670, China A R T I C L E INFO Keywords: Oyster proteins Steam cooking Peptide profle ACEi peptides ABSTRACT This study aimed to investigate the effect of steam cooking on the proteolysis of Pacifc oysters (Crassostrea gigas) using the simulated oral-gastrointestinal digestion model and a NCM460 cell monolayer. Steam cooking changed the peptide profle of the digests of oysters considerably and induced more thorough hydrolysis. However, the heat-stable allergen, Cra g 1, still had remnant fragments in the intestinal phase, which could be allergenic epitopes. Two regions of Cra g 1 (residues 224–228 and 245–248) were digestion-tolerant. Furthermore, more oligopeptides were derived from raw proteins than from steamed proteins. After molecular docking and in vitro determination, six novel angiotensin I-converting enzyme inhibitory (ACEi) peptides were fnally identifed in the hydrolysates (WIS, WLS, LSL, SGPF, LGPI, and IGLP). Among them, LSL exhibited the highest ACEi activity (IC 50 = 107.17 nM). Our fndings provide supportive information on the effective utilization of oyster proteins. 1. Introduction The Pacifc oyster (Crassostrea gigas) is a species in the phylum Mollusca, and it is also a major seafood around the world. It is cultured widely and had a global aquaculture production of 643,549 tons in 2018 (FAO FAO Yearbook, 2018). In addition to its delicate favor, the Pacifc oyster is of high nutritional value because it contains glycogens, pro- teins, polyunsaturated fatty acids, and minerals (Zhu, Li, Yu, & Kong, 2018). Unlike terrestrial meat, living oysters of high quality are often consumed raw. To meet safety and sensory requirements, oysters of mediocre quality are usually sterilized by certain heat treatments before eating. However, improper oxidation, side-chain modifcation, cross- linking, and aggregation occur together with protein denaturation during cooking (Yin et al., 2020). The conformational alteration is often irreversible, due to the breakage of hydrogen bonds and the exposure of hydrophobic residues. Generally, a more compact structure emerges, and the binding of proteins to proteases changes after cooking (Zhang et al., 2020). The digestibility and peptide profles during digestion can be affected signifcantly by thermal treatment, although the current understanding of the transport mechanism and bioavailability of pep- tides is still not comprehensive. Few studies have focused on the peptide profle in the oral-gastrointestinal digestion of oyster proteins. Many bioactive peptides have been extracted from oysters, such as antithrombotic (Chen et al., 2019), anticoagulant (Cheng et al., 2018), immunostimulating, anti-fungal, and anti-cancer peptides (Wang et al., 2010). The oral bioavailability of food-derived bioactive peptides was notably low, due to a complex food matrix and physiological enzymatic deactivation (Sun et al., 2020). Therefore, a different peptide profle would probably induce disparate bioactivity in the human body. Addi- tionally, tropomyosin (TM) in Pacifc oysters is a well-recognized allergen, which could be a major risk. Allergenic TM is expected to be suffciently stable against gastrointestinal digestion because immune sensitization occurs in the intestines (James et al., 2018). Therefore, it is necessary to explore the effect of thermal treatment on the bioavail- ability and allergenicity of oyster proteins. Furthermore, according to the herbal literature of traditional Chinese medicine, oyster meat has a calming effect as a sleep aid (Wei et al., 2020). Some studies have revealed poorer sleep quality for patients with Abbreviations: TM, tropomyosin; ACE, angiotensin I-converting enzyme; ACEi, angiotensin I-converting enzyme inhibitory; Rw, raw; St, steamed; OGD, samples from oral-gastric digestion; OGID, samples from oral-gastrointestinal digestion; NCM460, the normal human colon-derived mucosal epithelial cell; BL, basolateral side; DMEM, Dulbecco’s modifed Eagle’s medium; HBSS, Hank’s Balanced Salt Solution; HPLC-MS/MS, high-performance liquid chromatographymass spec- trometry/mass spectrometry; ACN, acetonitrile; GRAVY, Grand Average of Hydropathy; WIS, Trp-Ile-Ser; WLS, Trp-Leu-Ser; LSL, Leu-Ser-Leu; SGPF, Ser-Gly-Pro-Phe; LGPI, Leu-Gly-Pro-Ile; IGLP, Ile-Gly-Leu-Pro; MW, molecular weight; FC, fold change. * Corresponding author. E-mail address: hhong@cau.edu.cn (H. Hong). Contents lists available at ScienceDirect Food Chemistry journal homepage: www.elsevier.com/locate/foodchem https://doi.org/10.1016/j.foodchem.2022.132160 Received 10 August 2021; Received in revised form 11 January 2022; Accepted 12 January 2022