Prediction of beef meat emulsion quality with apparent light backscatter extinction

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Abstract

Normalized light backscatter intensity (IN) response as a function of fat/lean ratio (RFL; 0.075, 0.25, and 0.33), chopping time (CT; 2, 5 and 8 min) and fiber separation distances (d; 2, 2.5 and 3 mm), were measured using a fiber optic spectrometer. Models based on the apparent light extinction coefficient (model I), fat/nonfat solid concentrations (model II), and the intensity ratio between optical distances (model III), were tested for IN0 prediction (IN at d = 0). Model I was significantly (P < 0.0001) better than model II for prediction at 570 nm (λ), 8 min (CT), and 0.075 of RFL. Model III showed maximum geometry values and extinction coefficients for optical fiber separations of 2 and 2.5 mm, yielding the higher R2 as RFL and wavelength increased. The results demonstrated a high correlation between functional properties of meat emulsion (i.e., RFL) and optical wavebands that may have potential for predicting IN0 using an optic sensor technology.

Introduction

Improving meat emulsion control during manufacturing may require the development of an on-line optical backscatter sensor technology for monitoring and controlling emulsification of comminuted meat products during the chopping process. This would allow selection of the optimum level of emulsification to maximize cooking yield and quality or consistency of the final product. The motivation for this topic is the significant economical impact of emulsion breakdown in the meat industry and the non-existence of any effective on-line technology for controlling emulsion stability. The importance of meat quality sensors in the development of the meat-processing industry has been mainly reported in the last two decades (Krol, van Roon, & Houben, 1988). Several fiber optical technologies based on infrared spectrophotometry have been widely used for the analysis of food systems to evaluate different sources of paleness in meat (Swatland, 1982, Swatland, 1983), to monitor and control the functional properties of comminuted meat batters used in meat processing (Norris, 1984, Swatland and Barbut, 1990), as well as to determine chemical composition of raw beef/pork meat emulsions (Lanza, 1983).

An interesting application of light backscatter sensor technology has been proposed recently by Álvarez, Castillo, Payne, and Xiong (2009). The authors designed, built and tested this optical sensor prototype to measure light backscatter of comminuted meats at different optical probe distances, through which they identified and detected different physical–chemical changes occurring during chopping that were correlated to emulsion stability. Successful development of this unique on-line sensor technology to control meat emulsion stability would have a great impact on industry worldwide in terms of processing efficiency and product quality. However, the appropriate development of this optical sensor technology requires of a clear understanding of the chemical composition and optical heterogeneity of the meat emulsion matrix. This knowledge would aid in the development of a sensor technology capable of accurately measuring different concentrations and sizes of fat particles in meat matrixes so as to effectively detect quality changes during meat emulsification.

Comminuted meat products are a finely chopped, heterogeneous structures composed of water, fat, protein, salt and different amounts of non-meat ingredients. Although every constituent plays at least a minor role in the scattering of light, fat and proteins play major roles. The functional state of the myofibrillar proteins and the content of connective tissue proteins such as collagen and elastin are considered the most important proteins affecting the optical reflectance (Swatland & Barbut, 1990). Meat proteins serve as the natural emulsifying agent in meat emulsion. The most prevalent protein in meat and the most important for fat emulsification and water holding capacity of processed meats is myosin. In addition, fat concentration has a large effect on reflectance measurements at all visible wavelengths (Franke & Solberg, 1971), especially when fat is comminuted together with lean muscle. Light scattering by fat globules and myofibrillar proteins causes meat to appear dark or pale depending on the muscle pH (Swatland, 2002). These two components scatter light differently based on their differences in concentration, the number density, and the optical properties (e.g. index of refraction). However, because NIR spectrophotometry is sensitive to fat content, and fat content has many effects on product quality, it may be difficult to extract information that relates directly to protein functionality (Swatland, 2002).

The extinction of a beam of light passing through a scattering medium is governed by the radiative transfer equation (Modest, 2003). In an optically thin medium (less particles and less light scattering) this equation can be reduced to Beer’s law:If=Ioe(-βd)where Io is the intensity leaving the light source, If the intensity reaching the detector, d the distance between the source and detector, and β the light extinction coefficient. According to this equation the light extinction coefficient is used to describe how the original beam of light from the emitting fiber decreases as it travels trough the sample according to absorption and scattering principles. As reported by Crofcheck, Payne, Hicks, Mengüç, and Nokes (2000), the propagation of the light beam can be treated as a planar wave in these optically thin solutions. In this case first-order scattering prevails, meaning that scattering only occurs once before reaching the detector. However, in an optically mixed medium as meat emulsions where the number of particles increase during chopping process, scattering increases and higher order scattering becomes important and Eq. (1) no longer applies.

This study was undertaken to further study the scattering of light in beef meat emulsion and to test the feasibility of using a fiber optic technology to determine whether the apparent light extinction coefficient (β) or fat/nonfat solid (basically meat proteins) concentrations can be used for predicting the normalized intensity of the light signal. An ideal on-line optical system for measuring light scattering in meat emulsion making should basically respond to fat/nonfat solids concentration changes during emulsification, as well as structural or textural changes related to the redistribution of air bubbles in meat matrix.

Section snippets

Materials and methods

Data analyzed in this study correspond to the data set presented previously (Álvarez et al., 2009), where details of the materials and methods were presented. Hence, only a brief description of the main aspects of special relevance is provided here.

Effect of fat/lean ratio on normalized backscatter spectral scan

Fig. 2 shows the typical normalized backscatter spectral scan as a function of fat lean ratio. As can be observed, backscatter response intensity was inversely proportional to fat lean ratio, especially in the central spectral scan corresponding to the orange–red (610–640 nm) and red (670–700 nm) regions where IN showed a clear decrease as RFL increased from 0.075 to 0.33. Crofcheck et al. (2000) observed a similar behavior of the normalized intensity at 724 nm in milk samples with various fat

Conclusions

The behavior of normalized light backscatter response as a function of fat/lean ratio, chopping time and wavelength was studied using different models. Model I, where fat/lean concentration is constant and light scattering distribution is dominant, was significantly (P < 0.0001) better than model II (light extinction coefficient is considered in function of fat and nonfat solids (NFS) concentrations) for prediction of normalized light backscatter signal (IN0). This intensity prediction was

Acknowledgements

The authors wish to thank the Séneca Foundation (Consejería de Educación y Cultura. CC.AA. Murcia, Spain) and the Kentucky Science and Engineering Foundation (University of Kentucky, USA) for the financial support provided by the research projects “Applying optical sensor technologies for determining meat emulsion stability” and “Development of an optical backscatter sensor technology for monitoring and controlling meat emulsification during the chopping process”.

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