The effects of low-frequency, high-power ultrasound (40 kHz, 1,500 W) on meat quality and connective tissue collagen of beef semitendinosus muscle were assessed. Beef steaks were sonicated for 10, 20, 30, 40, 50 or 60 min. The effects of ultrasound on exudate yield, water-loss rate, cooking loss, meat tenderness, and connective tissue and collagen properties were assessed. The results revealed that ultrasound increased meat exudate and water-loss rates and reduced Warner-Bratzler shear force values. However, ultrasound had no effect on cooking loss or insoluble collagen content and little effects on collagen content and solubility. The mechanical strength of connective tissue decreased in ultrasound-treated beef samples. Following ultrasound treatment of ≥10 min, muscle fibers shrank, the endomysium was disrupted and the perimysium thickness decreased. Protein aggregates formed in the extracellular space. Lowfrequency, high-power ultrasound had significant effects on meat texture and connective tissue properties. PRACTICAL APPLICATIONSIntramuscular connective tissue (IMCT) and collagen are related to meat quality, especially meat tenderness and texture. Ultrasound treatment enhances tenderness and sensory attributes of meat by changing cellular structures. However, there are limited data on the effectiveness of ultrasound on meat quality from the viewpoint of IMCT. In this study, we reported the meat quality attributes affected by changes in connective tissue and collagen as a result of ultrasound treatment. The results obtained in this study would be useful for the scientific community and the meat industry.

Low-frequency and high-power ultrasound (40 kHz, 1,500 W) was tested for its effects on the characteristics of intramuscular heat-insoluble collagen and meat quality and textural properties of beef semitendinosus muscle. Meat steaks (2.5×5.0×5.0 cm, 100± 5 g) were sonicated for 10, 20, 30, 40, 50, and 60 min, respectively. Characteristics changes of collagen and meat quality and texture were estimated. The results indicated that ultrasound treatment had no significant (P>0.05) effects on L* (lightness) and a* (redness) values but decreased b* (yellowness) value significantly when sonicated for 30 min (minimum 6.98). Ultrasound treatment significantly (P<0.01) reduced the muscle fiber diameter and filtering residues but had no significant effects on the content of heat-insoluble collagen. Significant differences (P <0.05) in β-galactosidase and β-glucuronidase activity were found between ultrasound treated for 10 min (reached the minimum were 5.2×10 −3 and 1.6×10 −3 umol ml −1 min −1 , respectively) and control samples. Thermal characteristics analysis of collagen suggested that ultrasound treatment weaken the average stability of collagen. After ultrasound treatment, collagenous fibers were disordered and staggered significantly; fiber arrangement became loose; and the denaturing, granulation, and aggregation of collagen fiber appeared in the extracellular space. Those changes on collagen characteristics had significant effects on meat textural properties. The results suggested that low-frequency and high-power sonication had a significant effect on collagen characters and meat textural properties.

Beef semitendinosus (ST) muscle was marinated for 24 h in 2% NaCl solution, and 1.5% lactic, acetic and citric acid solutions individually and in mixed marinades for the combination of NaCl and three kinds of weak organic acids, respectively. The effectiveness of marinades on beef ST muscle was investigated. Changes in denaturation characteristics of connective tissue collagen were examined using differential scanning calorimetry; microstructural changes of collagenous fibers were observed with scanning electron microscopy; and textural properties of meat were studied by texture profile analysis. The results showed that: marinating with organic acids and NaCl increased filtering residue contents of connective tissue significantly, especially for the presence of NaCl in organic acids compared with marinating in acids alone. Meat marinated in 2% NaCl and the presence of NaCl in citric acid significantly increased the mechanical strength (MS) of connective tissue, and other marinating treatments had a significant reduction on MS. CorrespondingMarinating resulted in denaturation of the intramuscular heat-insoluble collagen as exhibited by the lower onset (To) and peak (Tp) temperature compared with the control samples. After marinating, fiber diameter and perimysial thickness were decreased and arrangements of collagenous fibers were disordered. These changes of collagen characteristics contributed to the significant effects on meat quality and textural properties. PRACTICAL APPLICATIONSCharacteristics of connective tissue and collagen are related to meat quality, especially for meat tenderness and texture. While marinating is recognized as a means of improving palatability by enhancing or complementing the flavor of meat, despite numerous recipes for meat marination, there are limited data concerning the effectiveness of weak organic acids and NaCl solutions on the texture of beef meat. Marinations in acidic solutions, e.g., lactic, acetic, citric acid, have been traditionally used as a means of softening and flavoring meats. These treatments decrease the mechanical resistance of meats, including those of high connective tissue content. Based on those responses, we reported the textural properties affected by characteristics changes of connective tissue and collagen by marinating with weak organic acids and NaCl. Results reported in this article would be useful either for the scientific community or for the beef processing industry.

The effects of heat-induced changes of intramuscular connective tissue (IMCT) and collagen on meat texture properties of beef Semitendinosus (ST) muscle were investigated in this study. ST muscle was heated to core temperature from 40 to 90 • C with an increment of 5 • C in a water bath and microwave oven, respectively. Characteristics changes of IMCT collagen and meat texture were estimated. The results indicated that: cooking loss, total collagen and soluble collagen content increased with the increase in heating temperature and time. Collagen solubility of thermally treated meat was relatively high at 65 • C irrespective of heat treatment mode. The granulation changes of connective tissue collagen occurred at 60 • C and increased during heating to higher core temperatures. The instrumental texture profile analysis (TPA) data of heated meat showed also significant differences between two heating modes and studied temperatures. Results indicated that heating internal core temperature of 60 • C and 65 • C were critical for affecting meat texture properties owing to the thermal effects of collagen in water bath and microwave heating, respectively.