Spectral Characteristics Of Pork Meat During The Freezing Process And Cold Storage And Rapid Detection Of Product Quality

Freezing is one of the most important means for preserving food. The low temperature environment it generates can inhibit the growth, reproduction, and biochemical activities of most microorganisms. Therefore, freezing technology plays a very important role for the long-term storage, convenient circulation, and secure consumption of food. Hyperspectral imaging (HSI), as an emerging rapid and non-destructive detection technology, has found more and more applications in the quality evaluation of agricultural products. However, most of the applications are focused on foods at ambient temperature, little studies has been conducted on the spectral characteristics of freezing foods.In this study, pork longissimus dorsi muscle was used as the raw material. And temperature and timing were taking as the main line, the spectra regularity of meat during freezing procedure and cold storage were studied. Meanwhile, spectroscopic techniques were used to achieve the rapid and non-destructive quality evaluation of freezing and cold preserved meat products. The main conclusions are as follows:New founds on the spectral characteristics of pork:the absorption of light in the spectral range of 900-2200 nm by the dry substance of pork, such as protein and fat, gradually increases, resulting in the gradually decreased profile of the pork reflectance spectra in the near-infrared region. The dry substance of pork has four prominent reflection peaks at 1100 nm,1300 nm,1680 nm, and 1890 nm. Water has strong absorptions in the whole range of 900-2200 nm, thus decreasing the overall reflectance value, especially completely covering the two peaks at 1680 nm and 1890 nm. While, since the processing procedures of freezing, drying, and cooking has the effect of squeezing out water, the two peaks at 1680 nm and 1890 nm can be observed at different degrees and features.The relationships between temperature and the spectra of pork were explored. When water exists, subtle variations in temperature can cause changes in the spectrum. Specifically, as the temperature decreases, the reflectance value increases, and the peaks at 1100 nm and 1300 nm shifts to longer wavelengths. The lower the temperature of pork, the more of the spectral characteristics of dry substances the fresh pork shows. When heating, the spectral changes of pork were correlated with the denaturation level of protein.The relationships between freezing condition and the spectra of freezing products were investigated. The results showed that the freezing conditions changed the intensity of the spectra, while the positions of the peaks were not changed. The lower the freezing temperature, the higher the spectral values of the freezing products. And the negative correlation between freezing temperature and the reflectance value at 1172 nm reached a very significant level (R=-0.841, P<0.01). When the freezing samples were dehydrated, the regular differences still existed. During freezing, different freezing conditions affected the ice crystal and protein, etc, finally reflected in the difference of the spectra. Meanwhile, the spectral changes of pork during 12 months storage were studied, and the results showed that the spectral ratio of 1300 nm/1890 nm is inversely proportional to frozen storage time.The relationship between temperature and spectrum were studied based on the visible and near-infrared hyperspectral imaging technique. By establishing the Partial least square regression model, the changes of the sample temperature can be accurately predicted (R2p= 0.933), thus realizing the real-time monitor of the cool-down process. With respect to timing, the relationships between the spectra of pork and physiochemical indicators were studied. And the attributes of the spectral and physiochemical indicators of pork at rigidity, tenderization, and spoilage period were investigated. Wavelet transform was used to separate the morphology and details of the spectrum, and the support vector machine was used to build the spectral model. The results demonstrated that hyperspectral imaging can precisely recognize the pork samples of different period, and the correct classification rate can reach 97.06%.The method system for detecting the quality of freezing meat at freezing state was build based on visible and near-infrared hyperspectral imaging technique. There were differences between the frosts on the freezing meat surface and freezing meat. By improving the method of ROI selection, the interference of frost can be eliminated, thus improving the prediction accuracy of the spectral model. The spectral information in the visible region is suitable for predicting color-concerned attributes, and the information in the near-infrared region has advantage in predicting water-concerned attributes. For predicting the L* value, cooking loss, freeze-thawed water loss, and a* value of freezing meat, the accuracy in prediction (R2p) were 0.907,0.845,0.814,0.762, and 0.716, respectively. While for predicting the pH and WBSF, the accuracy in prediction was low. By utilizing the regularity of the spectrum, the HSI spectral model can precisely predict the freezing temperature (R2p=0.844) and freezing rate (Rp2=0.829) of freezing products.This new method breaks the limitations of traditional methods for measuring freezing parameters. For predicting the storage time, TBARS, and TVB-N value of meat during cold storage, the Rp2 of HSI spectral model were 0.827,0.803, and 0.873, respectively.