Rapid noninvasive monitoring of freshness variation in frozen shrimp using multidimensional fluorescence imaging coupled with chemometrics

Abstract

Shrimp is one of the most delicious and popular food commodities worldwide due to its exceptional taste and characteristics. Freshness is considered as a key factor for shrimp consumers because freshness has a significant relationship with taste and shelf-life of shrimp. However, post-mortem metabolism of shrimp differs from that of fish as they are highly susceptible to post-harvest quality loss, and it is hard to distinguish the freshness variation of shrimp at frozen state instantly. Thus, instant monitoring of frozen shrimp freshness is challenging for the seafood and aquaculture industries and a reliable, expeditious, and noninvasive technique to estimate shrimp quality is in high demand. Accordingly, this study aimed to visualize changes in post-mortem freshness of frozen shrimp using multidimensional fluorescence imaging. Live coonstripe shrimp (Pandalus hypsinotus) were harvested and instantly killed by beheading, cooled on ice for 0, 6, 24, 48, 72 and 96 h (n = 8), followed by processing into frozen peeled deveined shrimp product and stored at -60 °C. 50% of frozen shrimp were analyzed for excitation-emission matrix (EEM), ATP-related compounds, and pH using a fiber optic supported fluorescence spectrophotometer (F-7100), high performance liquid chromatography (HPLC) and pH meter, respectively at each time point (n = 4). Then, fluorescence images were obtained from the remaining 50% of frozen shrimp (n = 4) by computer vision method equipped with a charge-coupled device (CCD) camera, MAX-303 xenon light source for an excitation light (Ex. 330 nm), and an automatic filter changer for emission band-pass filters (Em. 380-610 nm at 10 nm intervals). Chemical analysis of frozen shrimp revealed that K-value and pH of shrimp increased from 1.61 to 66.56% and 6.49-7.31, respectively, during storage on ice. Repeated partial least squares regression (PLSR) models of EEM for K-value prediction suggested an efficient excitation wavelength (330 nm) and its corresponding emission wavelengths (380-610 nm) to produce fluorescence images. Spatial-temporal changes of K-value and pH were visualized successfully in frozen shrimp by fluorescence imaging. K-value visualization was then validated effectively using another group of frozen shrimp (0-72 h ice stored) with different killing method (super chilling) and the prediction accuracy was R² = 0.80. This novel approach using a CCD camera coupled with EEM provides a state-of-the-art authentication method for practical assessment of frozen seafood freshness.

Keywords: CCD camera; Frozen shrimp; K-value; Multidimensional fluorescence imaging; pH.