Formation of different flavor characteristics of raw- and boiled-dried oysters

Abstract

The release of flavor compounds in dried oysters, particularly umami amino acids, is highly dependent on the proteolytic degradation efficiency of specific targeted proteins, which is critically influenced by processing techniques. However, systematic studies on this mechanism remain scarce. This study elucidated how processing techniques govern flavor formation in dried oysters. Mild drying 50 °C in raw oysters triggered intense protein degradation, increasing glutamic acid and maximizing umami intensity, but accumulated bitter compounds. Conversely, 90 °C drying suppressed bitterness yet reduced umami and caused extreme yellowing. Mass spectrometry revealed that hydrophilic domains in ∼35 kDa oyster proteins (mainly glutamic acid-rich proteins, such as β-tubulin chain and actin-like proteins) were enzymatically targeted, releasing free glutamic acid as the core umami contributor. This work demonstrated the synergistic effects of pre-cooking and temperature on flavor, and findings provide a scientific basis for optimizing dried oyster processing.

Keywords: Dried oyster; Flavor formation; Glutamic acid release; Protein degradation.

Graphical abstract

Fig. 1

Morphological characteristics of oysters: (A) Appearance of oyster samples, including raw oyster (RO), boiled oyster (BO), and their dried products under mild drying at 50 °C (designated RDO-50 and BDO-50, respectively) or high-temperature drying at 90 °C (designated RDO-90 and BDO-90, respectively); (B) Total color difference (ΔE) between groups; (C) Micro-structrues (SEM) of oyster samples.

Fig. 2

Gustatory analysis of oysters: The radar map of flavor profiles (i.e., bitterness, astringency, sourness, saltiness, umami, aftertaste of sourness, aftertaste of astringency, and richness of umani) of oyster samples, including RO, BO, RDO-50, BDO-50, RDO-90, and BDO-90.

Fig. 3

Contents of amino acids in oyster samples (i.e., RO, BO, RDO-50, and BDO-50): (A) Contents of basic, acid and other amino acids (basic amino acids including Lys, Arg, His, Orn and 3MHis with positive charges at physiological pH, acidic amino acids including Asp, Glu and Aad with negative charges at physiological pH, and other amino acids including all other amino acids and analogues listed in the Table 1); (B) Contents of umami amino acids (i.e., Glu, Asp, Gln, and Asn).

Fig. 4

Endogenous enzyme activities and SDS-PAGE profile of oysters: (A) The enzyme activities of serine protease and cathepsin L in oyster samples (i.e., RO and BO); (B) SDS-PAGE profile of proteins in oyster samples (lanes 1–6 referring to RO, BO, RDO-50, BDO-50, RDO-90 and BDO-90 samples, respectively).

Fig. 5

Amino acid sequences of five proteins with high Glu contents in the 35 KDa protein band: (A) Alpha-crystallin B chain-like, (B) Tubulin beta chain, (C) Actin cytoplasmic-like, (D) Actin-like, and (E) Tubulin alpha chain. (Note: The red triangle marking the location of Glu.) (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)