Melatonin is an endogenous micromolecular compound of indoleamine with multiple physiological functions in various organisms. In plants, melatonin is involved in growth and development, as well as in responses to biotic and abiotic stresses. Furthermore, melatonin functions in phytohormone-mediated signal transduction pathways. There are multiple melatonin biosynthesis pathways, and the melatonin content in plants is greatly affected by intrinsic genetic characteristics and external environmental factors. Although melatonin biosynthesis has been extensively studied in model plants, it remains uncharacterized in most plants. This article focuses on current knowledge on the biosynthesis, regulation and application of melatonin, particularly for fruit quality and preservation. In addition, it highlights the links between melatonin and other hormones, as well as future research directions.

Polycarboxylic acids (PACs) are important metabolic products in almost all living bodies, yet current analytical methods for detection of PACs in tea beverages are still unsatisfactory due to the complex matrix and physicochemical properties of PACs. In this work, a rapid method was developed for the simultaneous determination of 7 PACs, including tartaric acid, α-ketoglutaric acid, malic acid, malonic acid, cis-aconitic acid, succinic acid, and fumaric acid, in beverages, based on selective removal of the matrix in combination with liquid chromatography–mass spectrometry (LC-MS) analysis. By stirring with activated carbon and the Na2CO3 solution, the matrix in beverages was selectively removed, and PACs were almost retained in the supernatant of diluted Na2CO3 solution. Under optimized parameters, the limit of quantitation for the PACs was in the range of 1–50 ng/mL, and the content of the PACs in 8 beverages was determined with the recovery range of 72.2%–122.5%. The contents of malic acid, malonic acid, and succinic acid in tea beverages were found to be greater than those in non-tea beverages. Moreover, the concentration of these PACs in beverages was found to be multiplied many times in their deterioration period, especially for fumaric acid and α-ketoglutaric acid. These results indicated that PACs can be selected as a criterion to differentiate qualified tea beverages from spoiled beverages.

Low-salt meat (salt content <2%) is gaining popularity for its lower health risks, while the food industry faces technical challenges in improving its quality. Twenty-one studies involving meat quality improvement measures in low-salt meat products were included in this meta-analysis. The outcomes of these studies were assessed to derive conclusions about their effects on meat hardness and cooking losses. The results demonstrated that higher power ultrasound treatments (300–1500 W) significantly increased the hardness of low-salt meat, while a similar outcome was also achieved by low-strength (50–200 MPa) high-pressure processing (HPP) treatment, which was beneficial for alleviating the undesirable too-soft texture of the low-salt meat products. Furthermore, when salt reduction was greater than 50%, the application of ultrasonic treatment and HPP of 50–200 MPa significantly reduced the cooking losses, and the addition of hydrocolloids also increased the cooking yield of the salt-reduced meat products. Among all the interventions, HPP exhibited the most significant effects in low-salt meat quality improvement, which warrants future studies on the combination of this method with salt reduction strategies in the reduction of salt content in processed meat products.

Proteins are important ingredients in the food industry for their excellent nutritional, functional and biological properties, while the application is limited by their sensitivity to environmental stresses such as high temperature, pH changes and ionic strength. The Maillard reaction and transglutaminase-catalyzed glycosylation are the two main effective glycosylation ways to improve the stability and biological properties of proteins by mainly attaching monosaccharides or disaccharides to proteins, while protein–polysaccharide conjugates with superior functional properties are rarely discussed. Therefore, the present study reviews current state of the synthesis, biological activities and applications in the food system of protein–polysaccharide conjugates formed via the Maillard reaction and transglutaminase-catalyzed glycosylation. The biological activities including antioxidant, antimicrobial and immunomodulatory activities of proteins are improved after glycosylation, and the formed protein–polysaccharide conjugates can be applied to stabilize emulsions or deliver bioactive compounds in foods. The bioactivities produced under precisely controlled glycosylation conditions would make protein–polysaccharide conjugates a promising application in foods with healthy properties.

Background Acacia seyal gum (ASG) is an abundant source of natural polyphenolic compounds (NPPCs) and antioxidant activity with numerous benefits and is often used in cancer treatment. The type of extraction technique can significantly impact the yield and isolation of NPPCs from ASG. The traditional use of maceration extraction reportedly yields fewer NPPCs. Objectives This study investigated five extraction techniques for NPPCs and ASG antioxidant activity, namely: homogenisation, shaking, ultrasonication, magnetic stirring, and maceration. Materials and methods The evaluation of the antioxidant activity (AoA) of the extracted NPPCs from ASG used five assays, namely: total flavonoids content, Folin–Ciocalteu index, 2,2-diphenyl-1-picrylhydrazyl radical scavenging activity, ferric reducing antioxidant power, and cupric reducing antioxidant capacity. Results To minimise the data set dimensionality requires principal component analysis. The ultrasonic and maceration techniques were the best techniques to extract NPPCs and examine the AoA of ASG, with a high correlation between the NPPCs and AoA. However, the maceration process was slow (12 h) compared to ultrasonication (1 h). Slow extraction can result in a decline of the NPPCs due to polyphenol oxidase–enzyme and impact productivity. Conclusions These findings provide an essential guide for the choice of extraction techniques for the effective extraction of NPPCs from ASG and other plant materials.