The Pacific oyster (Crassostrea gigas) is an aquatic species that is a major seafood around the world. In most cases, oysters are consumed raw, however heat treatments are commonly applied for sterilisation prior to consumption. The heat treatment process can cause oxidation, side-chain modification, cross-linking, and aggregation of proteins., the thermal treatment step can significantly alter digestibility and peptide profiles. For example, tropomyosin (TM) is a known allergen that remains stable during gastrointestinal digestion, however, the effect of thermal treatment on the TM is unknown. To understand the effect of heating on proteins of Pacific oyster, steam cooking was chosen as a simple and popular heat treatment method. The main goals of this study were to examine the alteration in digestibility of proteins and perform peptide profiling of the oyster after heat treatment. Interestingly the steamed samples had a lower percentage of large molecular weight (>5 kDa) fractions compared with raw samples, revealing the improved digestibility of proteins as a result of steam cooking, without increasing further oxidation. In addition to size, the number of peptides identified from steamed oysters were greater than raw ones. Additionally, 17 peptides were identified in all samples that indicated the apparent stability of peptides after steam cooking. The researchers concluded that proteins from steamed oysters were more thoroughly degraded, while the analysis of raw samples showed more oligopeptides. However, some fragments with the potential of acting as an allergen were intact after steam cooking, which requires further studies to validate their allergenicities. These types of studies on food processing can improve the safety of food and reduce health-related costs.
How was PEAKS used?
PEAKS Studio X+ was used for analysing tandem mass spectra. PEAKS DB was used for searching the target database (choosing none as the digestion enzyme). Parent ion tolerance of 7 ppm and fragment ion tolerance of 0.02 Da were set as the search parameters. For both peptides −10lgP ≥ 20 was chosen and protein with ≥ 1 unique peptide and −10lgP ≥ 20 were filtered. Proteins found at least in 2 replicates were chosen for analysis and the Uniprot database (http://www.uniprot.org/, downloaded on November 16, 2020, 40,061 protein entries) was used.
Feng, Chunsong, et al. “The effect of steam cooking on the proteolysis of pacific oyster (Crassostrea gigas) proteins: Digestibility, allergenicity, and bioactivity.” Food Chemistry 379 (2022): 132160. doi:10.1016/j.foodchem.2022.132160
This study aimed to investigate the effect of steam cooking on the proteolysis of Pacific oysters (Crassostrea gigas) using the simulated oral-gastrointestinal digestion model and a NCM460 cell monolayer. Steam cooking changed the peptide profile 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 finally identified in the hydrolysates (WIS, WLS, LSL, SGPF, LGPI, and IGLP). Among them, LSL exhibited the highest ACEi activity (IC50 = 107.17 nM). Our findings provide supportive information on the effective utilization of oyster proteins.