As an indicator of the antioxidant capability of plants, catalase can detoxify reactive oxygen species (ROS) generated by environmental stresses. Sweet potato is one of the top six most important crops in the world. However, its catalases remain largely unknown. In this study, a catalase encoding gene, IbCAT2 (accession number: KY615708), was identified and cloned from sweet potato cv. Xushu 18. It contained a 1479 nucleotides' open reading frame (ORF). S-R-L, Q-K-L, and a putative calmodulin binding domain were located at the C-terminus of IbCAT2, which suggests that IbCAT2 could be a peroxisomal catalase. Next-generation sequencing (NGS) based quantitative analyses showed that IbCAT2 was mainly expressed in young leaves and expanding tuberous roots under normal conditions. When exposed to 10% PEG6000 or 200 mmol/L NaCl solutions, IbCAT2 was upregulated rapidly in the first 11 days and then downregulated, although different tissues showed different degree of change. Overexpression of IbCAT2 conferred salt and drought tolerance in Escherichia coli and Saccharomyces cerevisiae. The positive response of IbCAT2 to abiotic stresses suggested that IbCAT2 might play an important role in stress responses.

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The objective of this study was to evaluate the relative effects and interactions of combined soaking treatment using citric acid (CTA) and apple polyphenol (APP) at mild heating temperatures for the inactivation of the external and internal microflora (mesophilic aerobic bacteria, mesophilic anaerobic bacteria, and fungi) in Chinese Tuber indicum, as well as to analyze the microbiological and sensory changes under modified atmosphere packaging (MAP)- and vacuum atmosphere packaging (VAC)-packed Chinese T. indicum stored at 4 °C for up to 55 d. Chinese T. indicum was soaked with CTA and APP alone or in combination for 10, 20, and 30 min at 35, 45, and 55 °C. A disinfection method using CTA and APP (3% CTA + 3% APP for 20 min at 45 °C) was obtained. Under this set of combination, the experimental values of microbial counts of mesophilic aerobic bacteria, mesophilic anaerobic bacteria, and fungi were 2.31 ± 0.4 log CFU/g, <1.0 log CFU/g, and <1.0 log CFU/g, respectively. Through the analysis of sensory qualities and microbial populations for MAP- or VAC-packed Chinese T. indicum, the shelf life of soaked truffles was prolonged to 45 or 40 d, respectively. The synergistic effect of CTA and APP may provide valuable insight into the reduction of microorganisms on fresh truffles.

Summary In this study, by dipping grass carp fillets with 10 mM di‐ and tri‐carboxylic acid solutions individually before storage at 4 °C for 10 days, the application potential of these acids in mitigating softening of fish was investigated through analysing shear force, pH, endogenous cathepsin activities, myofibrillar proteolysis and histomorphological characteristics. The results suggested that maleic acid, fumaric acid and tartaric acid were significantly effective against softening of grass carp muscle, as shown by shear force 26%–31% higher than that of control after storage. Acid treatments led to a decline in the pH of muscle. Besides, the inhibitory effect of these acids on cathepsins was demonstrated by activity reduction by 20%–90%. Further, sodium dodecyl sulphate–polyacrylamide gel electrophoresis and heat shock protein (HSP) analysis supported the protection of these acids against degradation and dissociation of myosin and actin through suppressing HSP loss. Moreover, histomorphological images with higher intensity of acridine orange fluorescence in muscle revealed the improvement of tissue integrity by acid treatments. The inhibitory potential of these acids in suppressing softening of fish muscle is particularly relevant to their capacity of mitigating cathepsin‐induced proteolysis and improving lysosome stability. Therefore, di‐ and tri‐carboxylic acids could play pleiotropic functions in the quality control of fish fillets.