Abstract
To study the texture, microstructural changes, and classification of cold-fresh (C-F), freeze-thawed once (F-T0), and freeze-thawed twice Tan mutton (F-Tt), the aforementioned three types of Tan mutton were subjected to near-infrared hyperspectrum scanning, scanning electron microscopy, and TPA testing. The original spectrum of Tan mutton was obtained at a wavelength range of 900∼1,700 nm after hyperspectrum scanning; a spectrum fragment ranging from 918 nm to 1,008 nm was intercepted, and the remaining original spectrum was used as a studied spectrum (“full spectrum” hereafter). The full spectrum was pretreated by SNV (standard normal variate), MSC (multiple scattering correction), and SNV + MSC and then extracted feature wavelengths by SPA (successive projections algorithm) and CARS (competitive adaptive reweighted sampling) algorithm, and 25 feature wavelengths were obtained. By combining these feature wavelengths with classified variables, the SNV + MSC−CARS−PLS-DA (partial least squares-discriminate analysis, PLS-DA) and SNV + MSC−SPA−PLS-DA models for classification of C-F and F-T Tan mutton were established. In contrast, SNV + MSC−CARS−PLS-DA yielded the highest classification rate of 98% and 100% for calibration set and validation set, respectively. The results indicated that the texture and surface microstructure of F-T Tan mutton deteriorated, and more worsely with F-T time. SNV+MSC-CARS-PLS-DA could be well used to classify C-F, F-T0, and F-Tt Tan mutton.
Highlights
Tan sheep (Yanchi, Ningxia, China) is a representative meat sheep breed with Chinese regional characteristics, even fat distribution, minimal mutton taste, tender meat, and reasonable nutritional composition [1]
After F-T treatment (Figure 1(b)), the structure of the muscle fibers showed slight “deterioration”, which includes slight contraction, deformity, slight protrusion on the surface, a decrease in smoothness of the muscle fiber, an increase in the gap among bundles, and variable degrees shape of muscle bundle distortion. ese features may be attributable to the elasticity of the connective tissue membrane in muscles, which plays a role in maintaining muscle integrity and preventing muscle fiber damage [28]
The formation and growth of ice crystals in the muscle cells caused crush damage to the connective tissue membrane. e internal structure integrity of the muscle cells was destroyed [29]. e smaller gaps in the muscle bundles were due to thawing and stiffening, and the sarcomere contracts 36 h after slaughter, thereby resulting in a decrease of muscle fiber gap and an increase of muscle bundle space. These changes may be due to cold contraction of the carcass as these were immediately placed in a frozen environment [30]
Summary
Tan sheep (Yanchi, Ningxia, China) is a representative meat sheep breed with Chinese regional characteristics, even fat distribution, minimal mutton taste, tender meat, and reasonable nutritional composition [1]. Due to deep processing and low level of conversion technology, more than 90% of Tan mutton is sold as cold-fresh (C-F) and frozen Tan mutton [2]. Freezing is the most e ective means of preservation in the circulation and sale of Tan mutton products [3]. In addition to e ectively inhibiting microbial growth and prolonging shelf life, it can lead to some unexpected changes in Tan mutton products such as the destruction of microstructure, loss of cell sap, and deterioration of texture. The taste, avor, and nutrient levels decrease after freeze-thaw (FT) treatment [4]. Criminals use F-T Tan mutton instead of C-F Tan mutton in selling for illegal pro t [5]
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