Differences between ordinary and dark muscle of skipjack tuna (Katsuwonus pelamis) including proximate composition, flavor, color, texture, and freshness were investigated. Ordinary muscle had a higher crude protein content, but a lower crude lipid content than dark muscle. Alcohols (30.41%) and aldehydes (25.56%) were the prominent flavor compounds present in ordinary muscle, whereas hydrocarbons (39.51%) and ketones (21.81%) were more abundant in dark muscle. Different L*, a*, and b* values were also observed. Texture profile analysis (TPA) showed that dark muscle had higher values for adhesiveness, and lower values for cohensiveness, chewiness, and resilience. After mechanical breaking, large myofibril fragments were observed in ordinary muscle under phase contrast microscopy, but not in dark muscle. Freshness indices, including K values, total volatile basic nitrogen (TVB-N), and thiobarbituric acid (TBA) values of dark muscle were higher than for ordinary muscle.

This paper reports a study of the influence of konjac glucomannan (KGM) on the gel properties of low-quality surimi. Compared with the surimi control, adding KGM significantly improved its gel properties. KGM content, heating temperature and heating time had significant effects on gel properties. Response surface methodology (RSM) was applied to optimize the processing parameters of adding KGM to low-quality surimi for improving the gel properties. The optimal conditions for gel properties were as follows: KGM content 1.50%, heating temperature 32.3 °C and heating time 184.6 min. The predicated gel strength for optimum conditions was 3578 g mm. The predicated results for optimum conditions coincided well with experiment values.Highlights► Effect of processing conditions on gel properties of low-quality surimi was studied. ► RSM was applied to optimize the processing conditions. ► Processing conditions had significant effects on the gel properties. ► Optimal conditions to improve gel properties of low-quality surimi were obtained.

Chemical, microbiological and sensory changes of dried Acetes chinensis during 28 days of accelerated storage at 37 °C were studied. Eighty volatile components including alcohols, aldehydes, acids, ketones, esters, alkanes, nitrogen-containing components, aromatic components and terpenes were identified by headspace sampling and gas chromatography–mass spectrometry (GC–MS) method during storage. Among these volatile components, the relative content of trimethylamine was the highest during storage, which increased from 11.36 ± 1.02% at day 0 to 14.60 ± 0.58% at day 28. Values of total volatile base nitrogen (TVB-N), trimethylamine (TMA), thiobarturic acid reactive substances (TBARS), total viable mesophilic count (TVC) and sensory characteristics of colour and odour for dried A. chinensis changed significantly during storage. Volatile components, TVB-N, TMA, pH, TBARS, TVC, colour and odour characteristics at different storage time were statistically interpreted by principle component analysis (PCA) method in order to found the main indices for the freshness of dried A. chinensis. The results suggested that colour, TMA, TVB-N, TBARS, odour, TVC and some volatile components could reflect the quality changes perfectly.Research highlights► Effect of accelerated storage on the quality changes of dried shrimp was studied. ► Eighty volatile components were found in the dried shrimp during accelerated storage. ► Volatile components were interpreted by principal component analysis. ► Some volatile components well reflected quality changes of dried shrimp.