Evolution of the bulk optical properties of bovine muscles during wet aging

Applications of optical property measurement for quality evaluation of agri-food products: a review

Spectroscopic techniques coupled with chemometric approaches have been widely used for quality evaluation of agricultural and food (agri-food) products due to the nondestructive, simple, fast, and easy characters. However, these techniques face the issues or challenges of relatively weak robustness, generalizability, and applicability in modeling and prediction because they measure the aggregate amount of light interaction with tissues, resulting in the combined effect of absorption and scattering of photons. Optical property measurement could separate absorption from scattering, providing new insights into more reliable prediction performance in quality evaluation, which is attracting increasing attention. In this review, a brief overview of the currently popular measurement techniques, in terms of light transfer principles and data analysis algorithms, is first presented. Then, the emphases are put on the recent advances of these techniques for measuring optical properties of agri-food products since 2000. Corresponding applications on qualitative and quantitative analyses of quality evaluation, as well as light transfer simulations within tissues, were reviewed. Furthermore, the leading groups working on optical property measurement worldwide are highlighted, which is the first summary to the best of our knowledge. Finally, challenges for optical property measurement are discussed, and some viewpoints on future research directions are also given.

Post-mortem ultrasound and freezing of rabbit meat: Effects on the physicochemical quality and weight loss

High intensity ultrasound (HIU) is a technique with the potential to improve meat quality, however, more research is needed on its application within the chain of cold storage and freezing. This study evaluates the effect of HIU (40 kHz, 9.6 W/cm2, 20 and 40 min) and post-mortem development on the yield and physicochemical quality of rabbit meat in samples treated with HIU pre- and post-storage in a freezer (120 h at -20 °C). Twenty rabbit carcasses were vacuum packed 12 h post-mortem, placed in a fridge at 4 °C for 24 h, and divided in two groups (HIU application before or after freezing), before assigning the treatments. The results show that HIU before freezing produced intense and bright orange-yellow colours, whereas its application after freezing resulted in pale red tones. HIU application accelerates rigor mortis resolution when it is applied before freezing and causes a significant decrease in pH immediately following the HIU treatment. Post-freezing application of HIU is not recommended because it considerably increased weight loss and toughening of the meat when long exposure times were used (40 min). In contrast, a short treatment duration with HIU mitigated the effects of freezing and produced significant increases in water-holding capacity (WHC) after cold storage. The yield (weight loss) of the rabbit meat was not affected when HIU was applied pre-freezing. The application of HIU pre-freezing constitutes a promising technology because it increased the tenderness and the WHC of rabbit meat. However, more research is needed to improve the appearance before scaling up to industrial levels.

Anisotropic effect on the predictability of intramuscular fat content in pork by hyperspectral imaging and chemometrics

The fibrous structure of meat muscle makes it an anisotropic optical material. As such, spectral information varies with the orientation of the muscle. In this study, spectral data from pork cuts were obtained by a transverse scan (TRANSCAN), radial scan (RADISCAN), and longitudinal scan (LONGSCAN) by using hyperspectral imaging. The information was used to develop and compare the prediction models for intramuscular (IMF) content prediction by partial least square regression (PLSR), support vector machines regression (SVMR), and backpropagation artificial neural network (BPANN). The three modeling algorithms showed equal capability for modeling IMF in pork. The accuracy of the prediction models from the three scans was in the order of TRANSCAN ≥ RADISCAN ≥ LONGSCAN. Successive projection algorithm reduced the wavelengths to 93%. The reduced wavelengths were used to build new models that showed similar accuracy to the models of the original wavelengths. This study shows that muscle orientation influences the accuracy of the prediction models.

Polarimetric comparison of fresh and frozen skeletal muscle tissues of goat

Optical properties can provide rich information about morphology and structure of tissues. Fresh and frozen muscle tissue samples of goat are investigated using imaging polarimetry to understand its structural nature. The outcomes demonstrate that the muscle tissues lose, to some extent, their integrity and organization on freezing. The fresh tissues offer very small circular retardance as compared to frozen samples. However, linear retardance is the main contributor in fresh muscle samples. Ultimately, linear and circular retardance can be used to differentiate fresh and frozen tissues. These investigations illustrate the capabilities of optical polarimetry for the characterization of muscle tissue structures. Specifically, the structure of biological tissue samples can be differentiated using real-time, cost effective and non-invasive optical polarimetry in the field of meat industry and biomedical diagnosis.

Investigation of optical properties of dissected and homogenized biological tissue

Knowledge of tissue optical properties, in particular the absorption μa and the reduced scattering coefficient μs', is required for diagnostic and therapeutic applications in which the light distribution during treatment has to be known. As it is generally very difficult to obtain this information with sufficient accuracy in vivo, optical properties are often approximately determined on ex vivo tissue samples. In this case, the obtained optical properties may strongly depend on the sample preparation. The extent of the expectable preparation-dependent differences was systematically investigated in comparative measurements on dissected and homogenized porcine tissue samples (liver, lung, brain, and muscle). These measurements were performed at wavelengths 520, 635, 660, and 785 nm, using a dual-step reflectance device and at a spectral range of 515 to 800 nm with an integrating sphere setup. In a third experiment, the density of tissue samples (dissected and homogenized) was investigated, as the characteristic of the packaging of internal tissue structures strongly influences the absorption and scattering. The standard errors of the obtained absorption and reduced scattering coefficients were found to be reduced in case of homogenized tissue. Homogenizing the tissues also allows a much easier and faster sample preparation, as macroscopic internal tissue structures are destroyed in the homogenized tissue so that a planar tissue sample with well-defined thickness can easily and accurately be prepared by filling the tissue paste into a cuvette. Consequently, a better reproducibility result was obtained when using homogenized samples. According to the density measurements accomplished for dissected and homogenized tissue samples, all types of tissues, except lung, showed a decrease in the density due to the homogenization process. The presented results are in good agreement for μs' regardless of the preparation procedure, whereas μa differs, probably influenced by blood content and dehydration. Because of faster and easier preparation and easier sample positioning, homogenization prior to measurement seems to be suitable for investigating the optical properties ex vivo. Additionally, by means of using the homogenization process, the sample size and thickness do not need to be particularly large, as is the case for most biopsies from the OR.

Chemometrics and hyperspectral imaging applied to assessment of chemical, textural and structural characteristics of meat

Spectroscopy in the visible near-infrared spectral (Vis-NIRS) range combined with imaging techniques (hyperspectral imaging, HSI) allows assessment of chemical composition, texture, and meat structure. The use of HSI in the meat and food industry has observed a significant growth in the last decade, yet its use for assessment of meat it is not optimal yet. The application of HSI for assessment of meat is reviewed with focus on its ability to capture meat unique chemical and structural characteristics. While HSI is widely used for assessment of chemical composition, a limited number of evidences on its ability to handle the effect of different sources of variation on the assessment is found. The use of spatially resolved spectroscopy has been able to detect structural information related to animal background, muscle type, rigor process and ageing. Similarly the use of texture features seem to capture unique characteristics of meat.