Influence of salting process on the structure and in vitro digestibility of actomyosin.

Salting process is widely used in the process of meat products, whereas few studies have revealed the digestibility of actomyosin after salting treatment, which is closely related with the nutrition of meat. This work reported effect of salting on the structural change and digestibility of actomyosin before and after heat treatment. Actomyosin in 0.4 M and 0.8 M of NaCl had higher content of disulfide bonds, and actomyosin in 0.4 M NaCl showed the largest particle sizes before and after heat treatment. In addition, actomyosin in 0.6 M and 0.8 M of NaCl was oxidized more severely after heat treatment. Based on peptidomics analysis by using liquid chromatography tandem mass spectrometry (LC-MS/MS), actomyosin in 0.6 M was digested more easily, which was followed by sample in 0.8 M and 0.4 M of NaCl in descending order. The lowest digestibility of actomyosin in 0.4 M NaCl was related with its higher content of disulfide bond and severer aggregation behavior. The lower digestibility of actomyosin in 0.8 M NaCl should be related with the higher content of disulfide bonds and surface oxidation. These results highlight the crucial role of salting process in affecting the digestibility of meat protein.

Interplay between Residual Protease Activity in Commercial Lactases and the Subsequent Digestibility of ß-Casein in a Model System.

One of the conventional ways to produce lactose-hydrolyzed (LH) milk is via the addition of commercial lactases into heat-treated milk in which lactose is hydrolyzed throughout storage. This post-hydrolysis method can induce proteolysis in milk proteins due to protease impurities remaining in commercial lactase preparations. In this work, the interplay between lactose hydrolysis, proteolysis, and glycation was studied in a model system of purified ß-casein (ß-CN), lactose, and lactases using peptidomic methods. With a lactase presence, the proteolysis of ß-CN was found to be increased during storage. The protease side-activities mainly acted on the hydrophobic C-terminus of ß-CN at Ala, Pro, Ile, Phe, Leu, Lys, Gln, and Tyr positions, resulting in the formation of peptides, some of which were N-terminal glycated or potentially bitter. The proteolysis in ß-CN incubated with a lactase was shown to act as a kind of "pre-digestion", thus increasing the subsequent in vitro digestibility of ß-CN and drastically changing the peptide profiles of the in vitro digests. This model study provides a better understanding of how the residual proteases in commercial lactase preparations affect the quality and nutritional aspects of ß-CN itself and could be related to its behavior in LH milk.

Physico-chemical and sensory characteristics of young dairy bull beef derived from two breed types across five production systems employing two first season feeding regimes.

BACKGROUND: The present study aimed to assess the physico-chemical and sensory characteristics of Longissimus thoracis muscle from young dairy bulls: Holstein-Friesian (HF) and Jersey × Holstein-Friesian (JEX). Bulls slaughtered at 15 months of age differed with respect to the finishing system, whereas 19-month-old bulls differed in energy consumption during a second grazing season and finishing period. All bulls were offered different diets during the first grazing season. RESULTS: Insoluble and total collagen contents increased with slaughter age, whereas collagen solubility and hue angle reduced with age. Bulls fed a higher concentrate finishing diet held a longer beef flavour. Intramuscular fat (IMF) content and beef flavour score were enhanced by higher concentrate intake during the second season and finishing period. Beef from a higher forage diet displayed a more intense red colour and higher thawing loss. There was limited effect of silage finishing or first and second grazing season on quality traits. Beef from JEX breed had a higher IMF content, higher flavour, juiciness and texture-related scores while lower moisture content compared to HF beef. CONCLUSION: The eating quality of beef from young dairy bulls was generally good. Slaughter age and the energy level of diet had obvious effects on quality characteristics. Cross-breeding Jersey with the HF breed can improve the beef quality of young dairy bulls. © 2017 Society of Chemical Industry.

Effect of castration and carcass suspension method on the quality and fatty acid profile of beef from male dairy cattle.

BACKGROUND: The use of bulls rather than steers for beef production offers some considerable advantages; however, the eating quality of bull beef is an issue of marketing concern. This study assessed the physicochemical characteristics of young Holstein-Friesian (HF) bull and steer beef. Steer carcasses were suspended by the Achilles tendon (AS) and by pelvic suspension (PS). RESULTS: HF steer beef had higher redness, yellowness and chroma values, whereas bulls had higher ultimate pH and darker muscle. Warner-Bratzler shear force, cook loss at different ageing times, moisture, and insoluble and total collagen were higher for HF bull beef, whereas intramuscular fat, soluble collagen and collagen solubility were higher for steer beef. HF steer beef had a higher proportion of saturated fatty acids (SFA) and monounsaturated fatty acids (MUFA), whereas bull beef had higher proportions of polyunsaturated fatty acids (PUFA), PUFA/SFA and n-6/n-3 PUFA ratios. In comparison to AS, PS increased redness and chroma after 24 h blooming; PS improved tenderness up to 7 days of ageing and accelerated the ageing process. CONCLUSION: For young dairy cattle, steer beef would likely have superior eating quality but a relatively less favourable nutritional fatty acid profile to bull beef. Suspension method affected the tenderness and colour intensity of dairy steer beef at different ageing times. © 2018 Society of Chemical Industry.

Structure-property relationship of pea protein fibrils in stabilization of HIPEs and the encapsulation, protection, controlled release and oral delivery of carotenoids for alleviating intestinal inflammation.

Increasing attentions are paid to high internal phase emulsions (HIPEs) due to their unique properties. In this study, pea protein-based fibrils were used as emulsifier to stabilize HIPEs. We demonstrated that the molecular assembly pathway and interfacial behavior of pea protein-based fibrils are affected by ionic strength. And the increased abundance of highly flexible worm-like nanofibrils facilitated their adsorption and packing on oil droplets, resulting in improved emulsion properties to stabilize the HIPEs with the internal phase volume fraction as high as 90%. Based on this, high loading content of carotenoids up to 0.05 wt% in the prepared HIPEs, protection of their stability against heating, UV and iron ions, and significantly increased bio-accessibilities of the carotenoids were realized. Animal studies using a mouse model of DSS-induced colitis revealed that carotenoid loaded HIPEs can alleviate the colon injury, by downregulating the expression of inflammatory cytokines, and promoting intestinal barrier function. This work will deepen the understanding of the formation of pea protein fibrils and provide a reference for the rational use of carotenoid loaded HIPEs in IBD management.

Interfacial Protein Fibril Polymorphisms Regulate In Vivo Adipose Expansion for Control of Obesity.

Obesity is becoming a worldwide pandemic. Interfacial engineering of food lipid is expected to inhibit diet-induced obesity without damage to the eating enjoyment brought by high-fat diets. Unfortunately, this strategy has not been achieved yet. After screening different plant proteins, bromelain and papain were found to form wormlike and long-straight protein fibrils, respectively. The conversion of long-straight amyloid-like fibrils to wormlike fibrils was demonstrated in the fibrillation of bromelain. Using oil-in-water high internal phase emulsions (HIPEs) as a proof of concept, bromelain fibrils showed dramatically stronger interfacial stabilization capabilities than papain fibrils with high application potentials in the real-world formulation of high-fat food products such as mayonnaise. Compared with papain fibrils, oral administration of HIPEs stabilized by bromelain fibrils resulted in substantially higher fecal lipid contents and significantly decreased expression levels of the genes related to lipid absorption and transport in the intestine, including CD36, FATP-2, FATP-4, and APOA-4, without a difference in intervening gut microbiota. Consequently, dramatically less lipid absorption in the small intestine, markedly smaller chylomicron particles in the plasma, lower serum triglycerides, and controlled energy and lipid metabolism, as well as the inhibition of adipose expansion and overweight, were observed in the group with gavage of HIPEs stabilized by the bromelain fibrils rather than the papain fibrils. Furthermore, with the same calorie, substitution of all the fat in the standard high-fat feed of mice with the HIPEs emulsified by the bromelain fibrils showed a significantly stronger effect than the ones prepared by the papain fibrils on preventing high-fat-diet (HFD)-induced obesity including alleviation of adipose expansion and inflammation as well as fatty liver, also via inhibiting the absorption and transport of lipid in the intestine. The effect is ascribed to the suppressed lipolysis caused by a more compact and elastic interfacial layer formed by the wormlike fibrils than that of the long-straight fibrils, which are resistant to gastric environments and replacement by bile acids in digestion. Therefore, we provide an appealing and general strategy for controlling obesity by reducing the supply of free fatty acids (FAs) for absorption in the enteric lumen through protein fibril polymorphisms at the interface.

Protecting meat color: The interplay of betanin red and myoglobin through antioxidation and coloration.

Myoglobin (Mb) responsible for meat color is easily oxidized resulting in meat discoloration. Here, betanin red (BR), as a natural pigment and antioxidant, was chosen for enhancing redness and inhibiting oxidation. Multiple spectroscopies, isothermal titration calorimetry and molecular docking demonstrated that BR changed the microenvironment of heme group and amino acid residues of Mb, inhibited the oxidation of oxymyoglobin. The main interaction force was hydrogen bond and one variable binding site provided a continuous protective barrier to realize antioxidation. The combination of antioxidation with the inherent red color of BR offered dual color protection effect on processed beef with the addition amount of 0.2 % BR. BR treatment enhanced the redness by 25.59 âˆ¼ 53.24 % and the sensory acceptance by 4.89 âˆ¼ 14.24 %, and decreased the lipid oxidation by 0.58 âˆ¼ 15.92 %. This study paves a theoretical basis for the application of BR and its structural analogues in meat color protection and other quality improvement.

Purification of Egg White Lysozyme Determines the Downstream Fibrillation of Protein and Co-assembly with Phytochemicals to Form Edible Hydrogels Regulating the Lipid Metabolism.

Although the synthetic chemistry or synthetic biological systems have already shown the power of biomaterials engineering, natural bioresource matter is still a valuable library of raw ingredients for the production of biomaterials, in particular, the edible ones. However, the influence of upstream isolation and purification of the raw materials on their performance in the downstream processing procedures is still unexplored, which is essential for the engineering of biomaterials. Based on the comparison of conventional techniques, heating-induced precipitation combined with resin-blending ion exchange was developed as a simple and cheap method for the utilization of egg whites to produce the lysozyme that is found to be exclusively feasible for fibrillation. Even with similar purities, only the lysozyme prepared by this method could be utilized to form ordered linear aggregate fibrils. Fibrillation was recently pursued as a new approach to utilize bioresource mass for high-tech end-products. Phytochemicals, totally replacing salts, induced the lysozyme fibrils to form hydrogels spontaneously, which was further demonstrated in an in vivo study to prevent obesity induced by a high-fat diet (HFD) by reducing lipid absorption and lipogenesis, promoting energy expenditure, and inhibiting inflammation. The agri-food bioresource was successfully employed as a proof of concept in edible biomedical materials for the regulation of lipid metabolism.

Acetylation inhibition alleviates energy metabolism in muscles of minipigs varying with the type of muscle fibers.

In this study, we investigated whether preslaughter chemical-induced acetylation affected postmortem energy metabolism and pork quality. Thirty pigs were randomly assigned to control, acetyltransferase inhibitor (ATi) or deacetyltransferase inhibitor treatments. Serum, trapezius, longissimus lumborum, psoas major, semimembranosus and semitendinosus muscles were taken for analyses. The results indicated that ATi treatment significantly reduced the activities of lactate dehydrogenase and creatine kinase and heat shock protein 70 in serum (P < 0.05). ATi treatment increased ATP and glycogen content, but decreased lactic acid content in trapezius, psoas major and semitendinosus muscles (P < 0.05). A total of 13 acetylated proteins bands were identified and the deacetylation of creatine kinase may play a key role in slowing down the postmortem energy metabolism in ATi-treated group. In addition, ATi treatment reduced the rate of postmortem glycolysis in muscles with higher oxidative but lower glycolytic fibers. These findings provide a new insight into the underlying mechanism on muscle-specific postmortem changes of pork quality.

Higher affinity of polyphenol to zein than to amyloid fibrils leading to nanoparticle-embed network wall scaffold to construct amyloid fibril-zein-EGCG hydrogels for coating of beef.

Globally, 800 million are undernourished and 2 billion are deficient in micronutrients. A regular dietary intake of meat is one of effective strategies to fight against undernourishment and deficiency of micronutrients. However, meat is a typical perishable food; proper handling to extend the shelf life of meat is required. In the present study, homogenous hydrogels composed with high contents of lysozyme amyloid fibrils, zein and green tea polyphenol epigallocatechin gallate (EGCG) were developed via the orchestration of protein-protein interaction and polyphenol-protein interaction for coating of beef. The protein-protein interaction between amyloid fibrils and zein showed higher affinity than that of the polyphenol-protein interactions. In addition, polyphenol EGCG was found to be more inclined to bind with zein than to the amyloid fibrils. Thus, the amyloid fibrils performed as the scaffold, in which EGCG on one hand induced the zein aggregate nanoparticles and on the other hand deposited on the surface of amyloid fibrils, leading to the dense multi-pore network with the nanoparticle-embed wall. It served as the microstructure mechanism for the enhanced gel strength. Coating of fresh chilling beef with the amyloid fibril-zein-EGCG hybrid hydrogels effectively protected the freshness and tenderness through inhibiting the over-growth of microorganisms and oxidation of lipid. This study paves the way to develop functional edible biomaterials via polyphenol induced coordination of the protein-protein interaction and polyphenol-protein interaction, where polyphenol acts as the molecular glue. This strategy shows high application potentials in health promotion related fields, including edible coating to extend the shelf-life of fresh meat.

Hydrogels as promising carriers for the delivery of food bioactive ingredients.

The burden of public health challenges associated with the western dietary and living style is growing. Nutraceuticals have been paid increasing attentions due to their effects in promotion of health. However, in the gastrointestinal (GI) tract, the nutraceuticals suffer from not only the harsh acidic environment of the stomach and a variety of digestive enzymes, but also the antibacterial activity of intestinal bile salts and the action of protease from the gut microbiota. The amount of the nutraceuticals arriving at the sites in GI tract for absorption or exerting the bioactivities is always unfortunately limited, which puts forward high requirements for protection of nutraceuticals in a certain high contents during oral consumption. Hydrogels are three-dimensional polymeric porous networks formed by the cross-linking of polymer chains, which can hold huge amounts of water. Compared with other carries with the size in microscopic scale such as nanoparticle and microcapsules, hydrogels could be considered to be more suitable delivery systems in food due to their macroscopic bulk properties, adjustable viscoelasticity and large spatial structure for embedding nutraceuticals. Regarding to the applications in food, natural polymer-based hydrogels are commonly safe and popular due to their source with the appealing characteristics of affordability, biodegradability and biocompatibility. Although chemical crosslinking has been widely utilized in preparation of hydrogels, it prefers the physical crosslinking in the researches in food. The reasonable design for the structure of natural polymeric hydrogels is essential for seeking the favorable functionalities to apply in the delivery system, and it could be possible to obtain the enhanced adhesive property, acid stability, resistant to bile salt, and the controlled release behavior. The hydrogels prepared with proteins, polysaccharides or the mix of them to deliver the functional ingredients, mainly the phenolic components, vitamins, probiotics are discussed to obtain inspiration for the wide applications in delivery systems. Further efforts might be made in the in situ formation of hydrogels in GI tract through the interaction among food polymers and small-molecular ingredients, elevation of the loading contents of nutraceuticals in hydrogels, development of stomach adhesive hydrogels as well as targeting modification of gut microbiota by the hydrogels.

High Internal Phase Emulsions Stabilized with Polyphenol-Amyloid Fibril Supramolecules for Encapsulation and Protection of Lutein.

High internal phase emulsions (HIPEs), also called highly concentrated emulsions with a minimal internal phase volume fraction of 74%, have been paid increasing attention in the development of functional foods due to their high potential in loading with large amounts of hydrophobic nutriceuticals. In the present study, HIPEs stabilized by polyphenol-amyloid supramolecular filaments were prepared for encapsulation of olive oil and loading with lutein. Binding and stacking of the green tea polyphenol epigallocatechin gallate (EGCG) on the surface of amyloid fibrils fabricated from hen egg lysozyme resulted in the hybrid supramolecules, which assembled to form hydrogels. The amyloid fibril clusters shrouded by EGCG were observed in the microstructure of the hydrogels characterized by atomic force microscopy (AFM). HIPEs stabilized by the EGCG-amyloid fibril supramolecules showed the typical microstructure of highly packed polyhedral geometric oil droplets. The gel strength of the HIPEs stabilized by the hybrid supramolecules was greater than that of HIPEs stabilized by pure amyloid fibrils. The droplet size of the HIPEs first decreased and then increased with the increase of EGCG contents in the hybrid supramolecules, which was consistent with the corresponding emulsion morphologies obtained from the images of confocal laser scanning microscopy (CLSM). Aggregation of the protein-based nanofibrils appeared in the continuous phase at higher EGCG contents. The droplet size of the HIPEs decreased with the increase of the amyloid fibril concentration, accompanied by more packed and homogenously dispersed lipid droplets, as shown in the CLSM images. A high loading content of lutein of up to 10 mg/mL in the prepared HIPEs was realized, and the stability of lutein against ultraviolet irradiation, heat, iron, and hydrogen peroxide was promoted significantly. In addition, encapsulation with the HIPEs prevented the oxidization of olive oil, and this effect was enhanced with the increase of the EGCG content in the hybrid supramolecules ranging from 0 to 0.25 wt %. The protection function of the HIPEs might be ascribed to the membrane of interfacial amyloid fibrils and the crowded oil droplet environment, both of which could shield the pro-oxidation factors.

Interplay between transglutaminase treatment and changes in digestibility of dietary proteins.

The changes in digestibility of TG-treated myofibrillar protein (MP), soybean protein isolate (SPI) and mixed proteins were evaluated by measuring liberation of primary amino groups, monitoring structural changes and investigating peptide fingerprints. TG treatment generally increased gastric digestion of treated proteins, possibly due to the structural changes occurred during TG treatment. In contrast, the initial intestinal digestion was suppressed by TG treatment. Compared with MP, the digestibility and peptide composition of SPI were affected by TG treatment to a larger degree, possibly due to the higher level of glutamine in SPI. Peptidomics analysis indicated that the changes in peptide composition of digests of TG-treated samples were related with the loss of Lys residues during TG treatment. Larger quantities of bioactive peptides KIEFEQFLPM, EVHEPEEKPRPK and TVKEDQVFPMNPPK were released after digestion of TG-treated MP. These results highlighted the complex and substantial influence of TG treatment on the digestibility of dietary proteins.

Effect of Sous-vide cooking on the quality and digestion characteristics of braised pork.

This study aimed to evaluate the effect of Sous-vide (SV) cooking on the quality, flavor and digestion characteristics of braised pork. Traditional (TD) sample had the highest fat content and malondialdehyde (MDA) value, but the lowest protein content and total sulfhydryl (SH) content (P < 0.05). The SH content in SV samples decreased with the heating time, but MDA content increased (P < 0.05). In addition, α-helix content of TD samples was higher but ß-sheet content was lower than SV samples. LC-MS/MS indicated that SV samples at 65 °C for 8 h had potential bioactive and antioxidant peptides. GC-MS mainly identified 395 volatile components and SV samples at 70 °C for 8 h and 75 °C for 8 h had similar flavor compounds to TD samples. Thus, Sous-vide cooking produced better quality and digestion characteristics of braised pork. These findings give a new insight into the associations of processing methods with meat quality.

The effects of high pressure treatment on the structural and digestive properties of myoglobin.

The effects of high pressure treatment (100-400 MPa for 20 min) on the structural and digestive properties of myoglobin were investigated by UV-vis absorption spectroscopy, intrinsic and synchronous fluorescence spectroscopy and molecular dynamics simulation. High pressure treatment induced the exposure of aromatic residues and changed the interaction between heme and globin, which in turn increased the gastrointestinal digestibility of myoglobin. Molecular dynamics simulation indicated that the hydrophobic interaction and hydrogen bonds of the myoglobin-pepsin complex were weakened after high pressure treatment, but the dipolar interaction was strengthened. The findings revealed the mechanisms on high pressure-induced increase in digestibility of myoglobin.

Ultrasound treatment can increase digestibility of myofibrillar protein of pork with modified atmosphere packaging.

We explored whether ultrasound treatment affected digestibility of myofibrillar protein (MP) isolated from modified atmosphere packed (MAP, 70% N2 and 30% CO2) pork. MP digestibility under pepsin and pancreatin treatments decreased significantly with storage time. Ultrasound treatment increased the digestibility and produced a greater number of smaller peptides. However, the total peptide count and unique peptide counts were significantly reduced. Moreover, active sulfhydryl, total sulfhydryl, particle size, turbidity and surface hydrophobicity of MP increased with time, while protein solubility and ATPase activity decreased. Compared with the untreated samples, ultrasound treatment increased protein solubility, surface hydrophobicity, and active sulfhydryl content, but decreased total sulfhydryl content (except 10 d), particle sizes, turbidity and ATPase activity. Ultrasound treatment resulted in a decline in ß-turn and α-helix contents. Therefore, ultrasound is conducive to the digestion. Additionally, structural and functional properties of protein in MAP were less stable than those in vacuum-packed pork reported before.

Casein-fed mice showed faster recovery from DSS-induced colitis than chicken-protein-fed mice.

This study aimed to examine whether casein- and chicken protein-fed mice had different capacities of recovering from dextran sulfate sodium (DSS)-induced colitis. Mice were fed a chicken protein or casein diet for 14 days, which was followed by 7-day DSS treatment and then a 6-day recovery period by gavage of Akkermansia muciniphila (A. muciniphila). Compared with the chicken protein diet, the casein diet increased the relative abundance of beneficial gut bacteria, whereas DSS treatment did not induce significant differences in physiological and pathological indicators between the diet groups. During the recovery period, gavage of A. muciniphila alleviated colitis symptoms by decreasing the score of the disease activity index (DAI), spleen weight, and TNF-α mRNA level but increasing the mucus thickness and MUC2 mRNA level. Several genera, including the Ruminococcaceae NK4A214 group, Bifidobacterium, Roseburia, Ruminiclostridium and Lachnospiraceae NK4A136 group, may play a critical role. In addition, the casein diet helped DSS-treated mice recover faster from colitis, in terms of their body weight, colon length and histological score, probably due to its higher digestibility.

Changes of the Microbiota Composition on the Surface of Pig Carcasses during Chilling and Its Associations with Alterations in Chiller's Temperature and Air Humidity.

In this study, we investigated changes of microbiota composition on the surface of pig carcasses during chilling and their associations with temporal and spatial changes of wind speed, air temperature, and air humidity. The composition of microbiota on a carcass surface varied greatly with sampling sites; in particular, the surfaces of forelegs and neck had higher load of microorganisms and different microbiota composition compared to in the air and other carcass parts. However, such a difference in the microbiota composition decreased as chilling time extended. The positive detection ratios of microbial genes resistant to sulfonamides, quinolones, tetracyclines, and ß-lactams were found different greatly with chilling time and sampling sites. The ß-lactam and tetracycline resistant genes were observed in higher ratios in airborne microorganisms in the chiller, while the sulfa and tetracycline resistant genes had higher ratios in the microbiota on pig carcasses. Actual measurements and dynamic simulation showed that air temperature and humidity varied greatly among different places in a chiller within the first 8 h of chilling, with higher values close to the door, but the differences became smaller afterwards. The micro-environmental differences and changes in the chiller may cause the different composition of microbiota on pig carcasses.

Influence of induction cooking on the flavor of fat cover of braised pork belly.

Fat has a great impact on texture and flavor of meat products, which is influenced by cooking methods. In this study, the profiles of fatty acids, volatile compounds, and texture of fat cover of braised pork belly were investigated after plane and concave induction cooking. The results showed that cooking time showed a great impact on fat content, textural properties, fatty acids composition, lipid oxidation, and volatile compounds of fat cover (p < 0.05). When cooking time was fixed, concave induction cooking caused lower hardness, chewiness, and saturated fatty acids but higher polyunsaturated fatty acids at 60 min than plane induction cooking. Electronic nose and GC-MS analyses showed that concave induction cooking had a greater impact on flavor of pork belly fat and produced a comparable flavor to plane induction cooked samples in a shorter time. Sensory evaluation showed that concave induction cooking had higher scores at 60 min. Thus, concave induction cooking could be a more efficient method for meat processing. PRACTICAL APPLICATION: Electromagnetic induction heating is an effective cooking technique. It is characterized by uniformity, efficiency, and safety of heating. The application of electromagnetic induction heating technology to the cooking of braised pork was studied, which provides information for further optimizing the cooking technology of braised pork and improving the quality of braised pork.

Ultrasonic treatment increased functional properties and in vitro digestion of actomyosin complex during meat storage.

We investigated the effects of ultrasonic treatment (400 W, 20 kHz, 45.52 W/L) and storage time (0 d, 3 d, 7 d and 10 d) on functional properties, structural changes and in vitro digestion of actomyosin complex isolated from vacuum-packed pork. As storage time increased, turbidity, surface hydrophobicity, active sulfhydryl and total sulfhydryl of actomyosin complex increased, while protein solubility decreased. Ultrasonic treatment increased surface hydrophobicity, protein solubility and active sulfhydryl content but decreased turbidity and total sulfhydryl content compared with the control. Ultrasonic treatment caused a reduction in α-helix content on 0 day and the fluorescence intensity of tryptophan and tyrosine residues. It increased pancreatin digestibility of actomyosin complex and the number of peptides of smaller than 1 kDa. However, it decreased the number of peptides. The findings provide a new insight into the application of appropriate ultrasonic treatment to promote meat digestibility.