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The global population increase has increased the demand for food products. However, post-harvest deterioration because of oxidation and discoloration results in a drastic loss of food quality and supply. Thus, research has focused on developing strategies to minimize such losses. One of those strategies includes the application of ergothioneine (ET), a potent hydrophilic antioxidant, to several food products to overcome their short shelf-life. ET can be synthetic or derived from several species of edible mushrooms and their extracts, which are known sources of natural ET. Given the reported potential of ET in food quality preservation, this review compiles the recent applications of ET as a preservative for maintaining the quality of food commodities.

To optimize the hydrolysis conditions in the production of antioxidant hydrolysates from tuna cooking juice concentrate (TC) to maximize the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity, TC containing 48.91% protein was hydrolyzed with Alcalase 2.4 L, and response surface methodology (RSM) was applied. The optimum hydrolysis conditions included a 2.2% (w/v) Alcalase concentration and 281 min hydrolysis time, resulting in the highest DPPH radical scavenging activity of 66.49% (0.98 µmol Trolox/mg protein). The analysis of variance for RSM showed that hydrolysis time was an important factor that significantly affected the process (p < 0.05). The effects of different drying methods (freeze drying, hot air drying, and vacuum drying) on the DPPH radical scavenging activity and amino acid (AA) profiles of TC hydrolysate (TCH) were evaluated. Vacuum-dried TCH (VD) exhibited an increase in DPPH radical scavenging activity of 81.28% (1.20 µmol Trolox/mg protein). The VD samples were further fractionated by ultrafiltration. The AA profiles and antioxidant activities in terms of the DPPH radical scavenging activity, 2,2'-azino-bis(3-ethylbenzthiazoline)-6-sulfonic acid (ABTS) radical scavenging activity, ferric reducing antioxidant power, and ferrous ion chelating activity were investigated. Glutamic acid, glycine, arginine, and cysteine were the major AAs found in the TCH fractions. The highest DPPH radical scavenging activity was found in the VD-1 fraction (< 5 kDa). The VD-3 fraction (> 10 kDa) exhibited the highest ABTS radical scavenging activity and ferric reducing antioxidant power. The ferrous ion chelating activity was the highest in VD-1 and VD-2 (5 to 10 kDa). In conclusion, this study provided the optimal conditions to obtain high antioxidant activities through TCH production, and these conditions could provide a basis for the future application of TCH as a functional food ingredient.

Skipjack tuna (Katsuwonus pelamis) liver (TL) contains high-quality proteins which can potentially serve as an excellent source of functional protein ingredients. Thus, this study was conceptualized to evaluate the physicochemical, functional, and biological properties of proteins from TL using the pH shift process. The pH shift process was conducted through solubilization of TL at pH from 1.5 to 12.5, and the solubilized proteins at pH 2.5, 3.5, 10.5 and 11.5 were precipitated at pH 5.5. Finally, the tuna liver protein powders after the processes at pH 2.5 and 11.5 (TLP 2.5 and TLP 11.5, respectively) were obtained by freeze-drying, i.e. those with the highest extraction and protein recovery yields under acidic and alkaline conditions. Protein and lipid contents of TLPs were higher and lower, respectively, compared to the TL powder (control). Glutamic acid, aspartic acid, and alanine were prominent amino acids found in both TLPs. Foaming properties and water/oil holding capacity were higher in TLP 11.5, while protein solubility and emulsion properties were greater in TLP 2.5 compared between groups. Additionally, the DPPH • and ABTS •+ scavenging activities, as well as the angiotensin I-converting enzyme inhibitory activity, were remarkably higher in TLP 11.5 than in TLP 2.5. On the other hand, significant ferrous-ion chelating activity was observed in TLP 2.5. In conclusion, TLP 11.5 could serve as an alternative functional protein ingredient that provides essential amino acids, functional properties, and bioactivities.