Abstract
ABSTRACTWater holding capacity, texture characteristics, and qualitative structural properties had been mainly focused on heat-induced gelation of myofibrillar proteins; however, the quantitative analysis to ultrastructure of the proteins and heat-induced gel was rarely reported in the previous study. The objective of this study was to investigate quantitatively the effects of different pH values and ion concentrations on the ultrastructure of myofibrillar proteins and thermal-induced gel from swine longissimus dorsi using atomic force microscopy. Protein and gel groups in different conditions were set up, respectively, for the comparative study. The proteins of the gel group were treated first by water and 0.1 M, 0.3 M, 0.6 M NaCl solutions separately at pH 5.5, 6.5, 7.5, and then heated in the water bath. However, protein group were treated without the water bath but directly dried in the air at room temperature. Image roughness Rq were used as an index for quantitative analysis. Atomic force microscopy and related offline analysis software were used to collect the height images and determine the roughness of the myofibrillar proteins and heat-induced gel, respectively. It had been indicated that pH values and ionic concentrations had shown a significant effect on the roughness of heat-induced gel and myofibrillar proteins according to the atomic force microscopy (AFM) height images. The roughness of the gel is minimal while the myofibrillar proteins were treated by 0.6 M NaCl at pH 7.5. It is suggested that roughness of AFM height images could be used as an index to determine the gelling conditions.
Highlights
Meat is animal flesh which is eaten as one kind of food
The aim of this study was to investigate the effect of different sodium ionic strength, pH value on the ultrastructure of myofibrillar proteins, and their heat-induced gels from swine longissimus dorsi muscle
Myofibrillar proteins were prepared from swine longissimus dorsi, which bought from the TrustMart in Yangling at Shaanxi according to the method of Wu[16] with minor changes, and stored at −20°C until extraction
Summary
Meat is animal flesh which is eaten as one kind of food. Animals hunting, domestication, breeding, improvement had been used gradually for meat and meat production since prehistoric times. Due to the functional properties, which contribute to meat, the meat proteins are divided into three general classifications, i.e. myofibrillar, stromal, and sarcoplasmic proteins. Myofibrillar proteins are salt-soluble proteins, which are soluble in high ionic strength solution, i.e. 0.3 M or higher. Stromal proteins such as collagen, elastin, and reticulin are the main components in the connective tissues and extracellular matrix. Stromal proteins as insoluble proteins cannot be dissolved in high ionic strength of the salt solution. The sarcoplasmic proteins such as hemoglobin, myoglobin pigments, and a wide variety of enzymes help to contribute to the red color of muscle, and continue to function in meat aging. The forming force is mainly the interaction between proteins and water molecules, and the forces of attraction and repulsion among neighboring peptides to reach phase equilibrium between the adjacent peptides.[2,3] The gelation characteristics of myofibrillar proteins can reflect the quality of meat products and its performance during gelation, which has far-reaching significance to maintain quality and develop processed meat products.[4]
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