The effects of four thawing methods (low-temperature air thawing, room temperature thawing, flowing water thawing and ultrasonic thawing) on the water-holding capacity and texture of the dorsal muscle of frozen farmed Takifugu obscurus were investigated, and the underlying mechanism was analyzed by evaluating the changes in the physicochemical properties of myofibrillar and sarcoplasmic proteins. The results showed that the low-temperature air thawing (210 min) group had better water-holding capacity and texture, higher sensory scores, and the most complete muscle structure. The thawing loss rate of the ultrasonic thawing group (10 min) was the highest (12.34%). The texture of the flowing water (22 min) and room temperature thawing (120 min) groups were poor with a greater degree of muscle tissue destruction. Moreover, the degree of protein denaturation was lower in the low-temperature air thawing group than in the other three groups. Partial least squares regression (PLS-R) analysis result indicated that protein denaturation would destroy the texture and sensory properties, but have little effect on the thawing loss. Generally speaking, although low-temperature air thawing was the most time consuming, it is an ideal way to maintain the water-holding capacity and texture of cultured Takifugu obscurus meat to the greatest extent, with the least damage to muscle fibers and proteins.

As one of the five basic tastes, umami makes an important contribution to food taste and quality, and has received widespread attention in recent years. This article introduces readers to the umami substances in foods, including free amino acids, nucleotides, and umami peptides, summaries several evaluation methods of umami taste, including chemical analysis, artificial sensory evaluation and intelligent sensory evaluation, and outlines the physical and biological methods of obtaining umami. Furthermore, this review points out that food raw materials and processing methods can have a significant effect on umami, and proposes future directions for umami research. We expect this review to provide a reference for the research on umami substances in foods.

In order to explore the quality changes of frozen aquatic products during distribution in the cold chain, tilapia (Oreochromis niloticus) fillets were repeatedly frozen and thawed for up to seven cycles. The differences in the basic nutrients in eight samples (i.e., one frozen-thaw sample and seven repeatedly frozen-thawed samples) were evaluated. Then, the differences in overall taste profile were determined by electronic tongue, and the contents of free amino acids, flavor nucleotides and taste inorganic ions were also measured. In addition, the changes of flavor substances were analyzed by sensory evaluation. The results showed that the overall flavor profile of tilapia fillets could be effectively distinguished during freeze-thaw cycles. With the increase in the number of freeze-thaw cycles, the contents of umami and sweet amino acids and nucleotides decreased, while the contents of bitter amino acids and nucleotides increased, which was consistent with the trend of sensory scores. The total content of free amino acids showed a decreasing trend, and decreased significantly after the fourth freeze-thaw cycle (P < 0.05). The content of Na⁺, which had an adjunctive effect on umami taste, was also significantly decreased. The above results showed that the overall taste profile was gradually deteriorated as the number of freeze-thaw cycles increased. The results of this study may provide a theoretical basis for further research on quality control of frozen aquatic products.

In order to explore the effect of antifreeze protein (AFP) on the water-holding capacity and texture of frozen scallop (Patinopecten yessoensis) adductor muscle, muscle samples were vacuum-impregnated in aqueous solutions containing each of the three antifreeze agents, 0.2 g/100 mL AFP, 3.0 g/100 mL sodium pyrophosphate and 3.0 g/100 mL trehalose. The yield, centrifugal loss, texture, color, moisture distribution and mobility, ice crystal morphology and microstructural structure of these samples were detected. The results showed that the hardness, cohesiveness and brightness of proton density images of the AFP group were in agreement with those of the fresh sample, and were significantly higher than those of the sodium pyrophosphate and trehalose groups. Compared with the other groups, the yield, springiness and shear force of the AFP group were significantly increased, and T₂₁ relaxation time was significantly shortened (P < 0.05). As observed by optical microscopy and scanning electron microscopy (SEM), the ice crystals in the AFP group were small and spherical, and the muscle fiber structure was clear and complete. The average cross-sectional area of ice crystals was 65.06% lower than that in the blank group, treated with NaCl. This study confirmed that AFP can adsorb onto the surface of ice crystals to inhibit their growth and modify their shape. It is more effective than sodium pyrophosphate and trehalose in regulating the water-holding capacity and texture of frozen scallop muscle and thus can be considered as an effective means to control the quality of frozen products.

China is a big producer and consumer of grains and oils. The development of high-yield grains is closely related to chemicals such as pesticides. With the improvement of people’s living standards, residents’ requirements for foods have changed from ‘security of output’ to ‘equal emphasis on quality and output’. In order to strengthen the management of grain quality and safety, it is urgent to comprehensively understand the status of pesticide pollution in grains and develop more efficient, convenient and rapid detection technologies. This paper briefly summarizes the characteristics of pesticides and pesticide residues, analyzes the current status of the use and residues of pesticides in raw materials for grains and oils in China, reviews the existing rapid detection methods and technologies for pesticide residues in grains, and compares the advantages and disadvantages of various rapid detection methods and products. This review is expected to provide a reference for quality inspection during grain purchase.