Effects of apple polyphenols and chitosan-based coatings on quality and shelf life of large yellow croaker (Pseudosciaena crocea) as determined by low field nuclear magnetic resonance and fluorescence spectroscopy

In this study, the effects of apple polyphenols (AP) with chitosan (CS) coating on quality enhancement of large yellow croaker (Pseudosciaena crocea) during ice storage was assessed. Microbiological (total viable counts [TVC], psychrophilic bacteria counts [PBC], H2S-producing bacteria counts, Pseudomonas bacteria counts) and physicochemical (K-value, total volatile basic nitrogen [TVB-N], thiobarbituric acid [TBA], water-holding capacity [WHC] and color difference) indicators were measured periodically. Meanwhile, low field nuclear magnetic resonance (LF-NMR), magnetic resonance imaging (MRI), and fluorescence spectroscopy were used to study the changes in moisture and lipid. The results showed that AP combined with CS could inhibit the increase of TVC, K-value, TBA, and TVB-N. Meanwhile, the results of LF-NMR showed that group treated with 1.0%AP + 2.0%CS was superior in water retention, but overall water loss in different groups was less, which was similar to the change of WHC. For fluorescence intensity analysis, 1.0%AP + 2.0%CS group showed a slower increase than other groups during whole storage period, which was consistent with TBA value. In conclusion, the shelf life of large yellow croaker in control group was 8 days, while 1.0% AP combined with 2.0% CS could retard the quality deterioration and prolong the shelf life for another 8 days.