Rapid detection of frozen pork quality without thawing by Vis–NIR hyperspectral imaging technique

• Spectral characteristics of frozen pork meat were studied.
• Relationship of spectral reflectance with freezing temperatures was revealed.
• Frozen pork quality without thawing was evaluated directly by HIS.
• The improved ROI method was able to withstand interference on spectral modeling.
• Model performances for different quality indicators were compared.

Quality determination of frozen food is a time-consuming and laborious work as it normally takes a long time to thaw the frozen samples before measurements can be carried out. In this research, a rapid and non-destructive determination technique for frozen pork quality was tested with a hyperspectral imaging (HSI) system. In this study, 120 pieces of pork meat were frozen by four kinds of methods with various freezing temperatures from −20 to −120 °C. The hyperspectral images of the samples were acquired at the frozen state. Quality indicators including drip loss, pH value, color, cooking loss and Warner–Bratzler shear force (WBSF) of the samples were measured after thawing. The spectral characteristics of the frozen meat samples were studied and it was revealed that the reflectance at 1100 nm had a close relationship with the freezing temperature (R=−0.832, p  <0.01). Partial least squares regression (PLSR) was applied to establish the spectral models, and the models were then optimized. Results showed that the improved region of interest (ROI) method could be used to extract effective spectral information to withstand the interference of freezing, and choosing appropriate spectral bands and spectral pretreatment techniques were crucial to develop robust mathematical model. The performances of the models established were diverse based on different quality indicators. The coefficients of determination for prediction (Rp2) for L*, cooking loss, b*, drip loss and a  * were 0.907, 0.845, 0.814, 0.762, and 0.716, respectively. However there were low correlations (Rp2) for pH and WBSF measurements. The current study indicated that HSI had the potential for non-destructive determination of frozen meat quality without thawing.

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