In vitro protein digestibility of pork products is affected by the method of processing

Effect of different thermal processing methods and thermal core temperatures on the protein structure and in vitro digestive characteristics of beef

This study aimed to investigate the effect of different thermal processing treatments on the protein digestion characteristics of beef. The beef samples were subjected to different cooking methods, namely steaming, boiling, and roasting, and different core temperatures (75 °C, 80 °C, 85 °C, and 90 °C), and were subjected to in vitro gastrointestinal digestion simulation. All the thermal processing treatments increased the protein digestibility; the samples that were steamed at 85 °C (S85), boiled at 80 °C (B80), and roasted at 80 °C (R80) showed the biggest gains. The S85 released more peptide species after gastrointestinal digestion, according to peptididomic studies. These differences were closely related to protein structure. Thermal processing treatments resulted in a higher degree of proteolysis and looser protein conformation, as evidenced by decreased intrinsic fluorescence and electrophoretic band intensity, increased surface hydrophobicity, and the change in protein secondary structure from α-helix to β-sheet and random coil. Based on the results, S85 was identified as the optimal thermal processing treatment for enhancing the digestibility of beef protein. The results provide valuable insights into the nutritional qualities and digestion of heat-processed beef protein.

Tracking bioactive peptides and their origin proteins during the in vitro digestion of meat and meat products

Existing reviews address bioactive peptides of meat proteins; however, comprehensive reviews summarizing the released sequences and their corresponding parent meat proteins in the digesta are limited. This review explores the bioactive peptides released during the in vitro gastrointestinal (GI) digestion of meat, connecting with parent proteins. The primary bioactivities of meat-derived peptides include angiotensin-converting enzyme (ACE) and dipeptidyl peptidase (DPP)-IV inhibition and antioxidant effects. Myofibrillar, sarcoplasmic, and stromal proteins play a significant role in peptide release during digestion. The release of bioactive peptides varies according to the parent protein and cryptides had short chains, non-toxicity, and great bioavailability and GI absorption scores. Moreover, the structural stability and bioactivities of peptides can be influenced by the digestive properties and amino acid composition of parent proteins. Investigating the properties and origins of bioactive peptides provides insights for enhancing the nutritional quality of meat and understanding its potential health benefits.

Improving the Nutritional Quality of Protein and Microbiota Effects in Additive- and Allergen-Free Cooked Meat Products

The primary objective of the meat industry is to enhance the quality and positive attributes of meat products, driven by an increasing consumer demand for healthier, less processed options. One common approach to achieving this goal is the replacement of additives and allergens with natural ingredients. Nevertheless, the nutritional impact of these changes has not been extensively studied. To address these gaps, two new meat products were developed: cooked turkey breast and cooked ham. The products in question exclude additives and allergens and instead incorporate a blend of natural extracts containing vitamin C, chlorogenic acids, hydroxytyrosol, catechins, epicatechins, vinegar, and inulin fibre. The objective of this study was to evaluate the impact of these reformulations on protein quality and gut microbiota. Protein quality was evaluated using the Digestible Indispensable Amino Acid Score (DIAAS) following in vitro digestion. The microbial composition and short-chain fatty acid (SCFA) production were analysed through in vitro colonic fermentations in both normal-weight and obese participants in order to gauge their effect on gut microbiota. The results demonstrated that the reformulation of cooked turkey breast increased its digestibility by 6.4%, while that of cooked ham exhibited a significant 17.9% improvement. Furthermore, protein quality was found to have improved significantly, by 19.5% for cooked turkey breast and 32.9% for cooked ham. Notwithstanding these alterations in protein digestibility, the microbial composition at the phylum and genus levels remained largely unaltered. Nevertheless, total SCFA production was observed to increase in both groups, with a more pronounced effect observed in the normal-weight group. In conclusion, the substitution of artificial additives with natural ingredients in reformulated cooked meat products has resulted in enhanced digestibility, improved protein quality, and increased production of short-chain fatty acids.

In vitro assay to determine inactivation of Toxoplasma gondii in meat samples

Consumption of raw and undercooked meat is considered as an important source of Toxoplasma gondii infections. However, most non-heated meat products contain salt and additives, which affect T. gondii viability. It was our aim to develop an in vitro method to substitute the mouse bioassay for determining the effect of salting on T. gondii viability. Two sheep were experimentally infected by oral inoculation with 6.5 × 104 oocysts. Grinded meat samples of 50 g were prepared from heart, diaphragm, and four meat cuts. Also, pooled meat samples were either kept untreated (positive control), frozen (negative control) or supplemented with 0.6 %, 0.9 %, 1.2 % or 2.7 % NaCl. All samples were digested in pepsin-HCl solution, and digests were inoculated in duplicate onto monolayers of RK13 (a rabbit kidney cell line). Cells were maintained for up to four weeks and parasite growth was monitored by assessing Cq-values using the T. gondii qPCR on cell culture supernatant in intervals of one week and ΔCq-values determined. Additionally, 500 μL of each digest from the individual meat cuts, heart and diaphragm were inoculated in duplicate in IFNγ KO mice. Both sheep developed an antibody response and tissue samples contained similar concentrations of T. gondii DNA. From all untreated meat samples positive ΔCq-values were obtained in the in vitro assay, indicating presence and multiplication of viable parasites. This was in line with the mouse bioassay, with the exception of a negative mouse bioassay on one heart sample. Samples supplemented with 0.6 %-1.2 % NaCl showed positive ΔCq-values over time. The frozen sample and the sample supplemented with 2.7 % NaCl remained qPCR positive but with high Cq-values, which indicated no growth. In conclusion, the in vitro method has successfully been used to detect viable T. gondii in tissues of experimentally infected sheep, and a clear difference in T. gondii viability was observed between the samples supplemented with 2.7 % NaCl and those with 1.2 % NaCl or less.

Analytical Methods and Effects of Bioactive Peptides Derived from Animal Products: A Mini-Review

Peptides with bioactive effects are being researched for various purposes. However, there is a lack of overall research on pork-derived peptides. In this study, we reviewed the process of obtaining bioactive peptides, available analytical methods, and the study of bioactive peptides derived from pork. Pepsin and trypsin, two representative protein digestive enzymes in the body, are hydrolyzed by other cofactors to produce peptides. Bicinchoninic acid assay, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, chromatography, and in vitro digestion simulation systems are utilized to analyze bioactive peptides for protein digestibility and molecular weight distribution. Pork-derived peptides mainly exhibit antioxidant and antihypertensive activities. The antioxidant activity of bioactive peptides increases the accessibility of amino acid residues by disrupting the three-dimensional structure of proteins, affecting free radical scavenging, reactive oxygen species inactivation, and metal ion chelating. In addition, the antihypertensive activity decreases angiotensin II production by inhibiting angiotensin converting enzyme and suppresses blood pressure by blocking the AT1 receptor. Pork-derived bioactive peptides, primarily obtained using papain and pepsin, exhibit significant antioxidant and antihypertensive activities, with most having low molecular weights below 1 kDa. This study may aid in the future development of bioactive peptides and serve as a valuable reference for pork-derived peptides.

In vitro digestion mimicking conditions in adults and elderly reveals digestive characteristics of pork from different cooking ways

This study aimed to investigate the impact of three cooking ways (sous vide (SV), frying (FR) and roasting (RO)) on pork protein digestion characteristics under conditions simulating healthy adult (control, C) and elderly individuals with achlorhydria (EA). Changes in degree of hydrolysis (DH), SDS-PAGE profiles, zeta potential, particle size and secondary structure during digestion were evaluated. Our results revealed the EA condition markedly affected the protein digestion process of pork with different cooking ways. The DH values of SV (25.62%), FR (21.38%) and RO (19.40%) under the EA condition were significantly lower than those of under the control condition (38.32%, 33.00% and 30.86%, respectively). Moreover, differences were also observed among three cooking ways under the EA condition. For a given cooking way, the differences between control and EA conditions gradually diminished from the gastric to the intestinal phase. Under a certain digestion condition, SV maintained the highest degree of digestion throughout the process, particularly under the EA condition. Therefore, we conclude that pork cooked by sous vide is more recommendable for the elderly considering protein digestibility.

Cooking-Induced Oxidation and Structural Changes in Chicken Protein: Their Impact on In Vitro Gastrointestinal Digestion and Intestinal Flora Fermentation Characteristics

Meat digestion and intestinal flora fermentation characteristics are closely related to human dietary health. The present study investigated the effect of different cooking treatments, including boiling, roasting, microwaving, stir-frying, and deep-frying, on the oxidation of chicken protein as well as its structural and digestion characteristics. The results revealed that deep-fried and roasted chicken exhibited a relatively higher degree of protein oxidation, while that of boiled chicken was the lowest (p < 0.05). Both stir-frying and deep-frying led to a greater conversion of the α-helix structure of chicken protein into a β-sheet structure and resulted in lower protein gastrointestinal digestibility (p < 0.05), whereas roasted chicken exhibited moderate digestibility. Further, the impact of residual undigested chicken protein on the intestinal flora fermentation was assessed. During the fermentation process, roasted chicken generated the highest number of new intestinal flora species (49 species), exhibiting the highest Chao 1 index (356.20) and a relatively low Simpson index (0.88). Its relative abundance of Fusobacterium was the highest (33.33%), while the total production of six short-chain fatty acids was the lowest (50.76 mM). Although stir-fried and deep-fried chicken exhibited lower digestibility, their adverse impact on intestinal flora was not greater than that of roasted chicken. Therefore, roasting is the least recommended method for the daily cooking of chicken. The present work provides practical advice for choosing cooking methods for chicken in daily life, which is useful for human dietary health.

Impact of Sustained Fructose Consumption on Gastrointestinal Function and Health in Wistar Rats: Glycoxidative Stress, Impaired Protein Digestion, and Shifted Fecal Microbiota

The gastrointestinal tract (GIT) is the target of assorted pathological conditions, and dietary components are known to affect its functionality and health. In previous in vitro studies, we observed that reducing sugars induced protein glycoxidation and impaired protein digestibility. To gain further insights into the pathophysiological effects of dietary sugars, Wistar rats were provided with a 30% (w/v) fructose water solution for 10 weeks. Upon slaughter, in vivo protein digestibility was assessed, and the entire GIT (digests and tissues) was analyzed for markers of oxidative stress and untargeted metabolomics. Additionally, the impact of sustained fructose intake on colonic microbiota was also evaluated. High fructose intake for 10 weeks decreased protein digestibility and promoted changes in the physiological digestion of proteins, enhancing intestinal digestion rather than stomach digestion. Moreover, at colonic stages, the oxidative stress was harmfully increased, and both the microbiota and the intraluminal colonic metabolome were modified.

Effect of pH treatment on egg white protein digestion and the peptidomics of their in vitro digests

The pH treatment significantly enhanced the functional properties of egg white protein (EWP), but little is known about the relationship between pH treatment and in vitro digestion of EWP. In this paper, we explored the effect of pH treatment (pH 2, pH 2-7, pH 12 and pH 12-7) on the digestibility of egg white protein and peptide profiling using the digestion kinetics and peptidomics methods, separately. The results implied that all pH treatment reduced the protein digestibility in gastric phase, while alkaline pH (pH 12 and pH 12-7) showed greater digestion level and more gastric peptides, and more importantly, produced a greater amount of potentially bioactive peptides than acid treated samples. Besides, the least number of potentially bioactive peptides was obtained at pH 2, but this could be improved by adjusting pH 2 back to 7. Notably, the unique bioactive peptides induced by pH were mainly relevant to DPP IV inhibitor. These differences of digestibility and peptide profiling might be attributed to the change of protein structure and the formation of molten sphere, altering cleavage sites of digestive enzymes. This work would give an enlightening insight into the digestive and nutritional characteristics of the pH-induced EWP to expand their application in the field of food and healthcare.

Physicochemical and structural changes of myofibrillar proteins in muscle foods during thawing: Occurrence, consequences, evidence, and implications

Myofibrillar protein (MP) endows muscle foods with texture and important functional properties, such as water-holding capacity (WHC) and emulsifying and gel-forming abilities. However, thawing deteriorates the physicochemical and structural properties of MPs, significantly affecting the WHC, texture, flavor, and nutritional value of muscle foods. Thawing-induced physicochemical and structural changes in MPs need further investigation and consideration in the scientific development of muscle foods. In this study, we reviewed the literature for the thawing effects on the physicochemical and structural characters of MPs to identify potential associations between MPs and the quality of muscle-based foods. Physicochemical and structural changes of MPs in muscle foods occur because of physical changes during thawing and microenvironmental changes, including heat transfer and phase transformation, moisture activation and migration, microbial activation, and alterations in pH and ionic strength. These changes are not only essential inducements for changes in spatial conformation, surface hydrophobicity, solubility, Ca2+ -ATPase activity, intermolecular interaction, gel properties, and emulsifying properties of MPs but also factors causing MP oxidation, characterized by thiols, carbonyl compounds, free amino groups, dityrosine content, cross-linking, and MP aggregates. Additionally, the WHC, texture, flavor, and nutritional value of muscle foods are closely related to MPs. This review encourages additional work to explore the potential of tempering techniques, as well as the synergistic effects of traditional and innovative thawing technologies, in reducing the oxidation and denaturation of MPs and maintaining the quality of muscle foods.

The dynamic change in the degradation and in vitro digestive properties of porcine myofibrillar protein during freezing storage

The myofibrillar protein (MP) degradation and in vitro digestive properties of porcine longissimus during freezing at -8, -18, -25 and - 40 °C for 1, 3, 6, 9 and 12 months were investigated. As the freezing temperature and duration of frozen storage increased, the amino nitrogen and TCA (trichloroacetic acid)-soluble peptides of the samples were significantly increased, while the total sulfhydryl content and band intensity of myosin heavy chain, actin, troponin T, tropomyosin were significantly decreased (P < 0.05). At higher freezing storage temperatures and durations, the particle size of MP samples and the green fluorescent spots detected using a laser particle size analyzer and confocal laser scanning microscopy became large. After 12 months of freezing, the digestibility and the degree of hydrolysis of the trypsin digestion solution of the samples frozen at -8 °C were significantly decreased by 15.02 % and 14.28 %, respectively, when compared to fresh samples, whereas, the mean surface diameter (d_3,2) and mean volume diameter (d_4,3) were significantly increased by 14.97 % and 21.53 %, respectively. Therefore, frozen storage induced protein degradation and impaired the ability of digestion in the pork proteins. This phenomenon was more evident as the samples were frozen at high temperatures over a long storage period.

Characteristics and antioxidant properties of Harpadon nehereus protein hydrolysate-xylose conjugates obtained from the Maillard reaction by ultrasound-assisted wet heating in a natural deep eutectic solvents system

BACKGROUND

Harpadon nehereus is a high-protein marine fish. A valuable way to add value to H. nehereus is to convert it into protein hydrolysate. The Maillard reaction is an effective way to improve the functional properties of peptides and proteins, which are affected by many factors such as reactant concentration, water activity, pH, temperature, and heating time. However, the traditional Maillard reaction method is inefficient. The purpose of this study was therefore to explore the effect of the ultrasound-assisted wet heating method on the Maillard reaction of H. nehereus protein hydrolysate (HNPH) in a new-type green solvent - a natural hypereutectic solvent (NADES).

RESULTS

Harpadon nehereus protein hydrolysate-xylose (Xy) conjugates were prepared via a Maillard reaction in a NADES system using an ultrasound-assisted wet heating method. The effects of different treatment conditions on the Maillard reaction were studied. The optimized glycation degree (DG) of HNPH-Xy conjugates was obtained with a water content of 10%, a reaction temperature of 80 °C, a reaction time of 35 min, and an ultrasonic power level of 300 W. Compared with HNPH, the structure of HNPH-Xy conjugates were significantly changed. Moreover, the functional properties and antioxidant activity of HNPH-Xy were all superior to the HNPH.

CONCLUSIONS

An ultrasound-assisted wet-heating Maillard reaction between HNPH and Xy in the NADES system could be a promising way to improve the functional properties of HNPH. © 2023 Society of Chemical Industry.

In vitro digestibility of proteins, peptidomic analysis and antioxidant ability of sodium-reduced pork sausage with partial substitution of NaCl by KCl

High salt (NaCl) consumption can impact on human health, and KCl is the most widely used replacement salt in meat products. This study investigated the effects of 0% NaCl (NS), 3% NaCl (HS), 1.95% NaCl (RS), 1.95% NaCl+1.05% KCl (RS + K) on protein digestibility of pork sausage in vitro. The results indicated that RS + K showed the highest gastrointestinal digestibility (GID) because of the structure of looser cross-linked strands and uniform cavities, while HS exhibited the lowest GID. RS + K released more peptides (2499) during gastrointestinal than NS (2301), RS (2130) and HS (2235), with a higher proportion of peptides with molecular weights <1000 Da, and more unique peptides. Meanwhile, the digestion product of RS + K exhibited excellent radical scavenging activity and improved the antioxidant abilities to reduce oxidative injury which was induced by H₂O₂ in HepG2 cells. These results demonstrated that partial substitution with KCl can be an effective strategy for improving the digestibility of sodium-reduced gel-type meat products.

Dynamic alterations in protein, sensory, chemical, and oxidative properties occurring in meat during thermal and non-thermal processing techniques: A comprehensive review

Meat processing represents an inevitable part of meat and meat products preparation for human consumption. Both thermal and non-thermal processing techniques, both commercial and domestic, are able to induce chemical and muscle's proteins modification which can have implication on oxidative and sensory meat characteristics. Consumers' necessity for minimally processed foods has paved a successful way to unprecedented exploration into various novel non-thermal food processing techniques. Processing of meat can have serious implications on its nutritional profile and digestibility of meat proteins in the digestive system. A plethora of food processing techniques can potentially induce alterations in the protein structure, palatability, bioavailability and digestibility via various phenomena predominantly denaturation and Maillard reaction. Apart from these, sensory attributes such as color, crispness, hardness, and total acceptance get adversely affected during various thermal treatments in meat. A major incentive in the adoption of non-thermal food processing is its energy efficiency. Considering this, several non-thermal processing techniques have been developed for evading the effects of conventional thermal treatments on food materials with respect to Maillard reactions, color changes, and off-flavor development. Few significant non-thermal processing techniques, such as microwave heating, comminution, and enzyme addition can positively affect protein digestibility as well as enhance the value of the final product. Furthermore, ultrasound, irradiation, high-pressure processing, and pulsed electric fields are other pivotal non-thermal food processing technologies in meat and meat-related products. The present review examines how different thermal and non-thermal processing techniques, such as sous-vide, microwave, stewing, roasting, boiling, frying, grilling, and steam cooking, affect meat proteins, chemical composition, oxidation, and sensory profile.

Study on the in vitro digestion process of green wheat protein: Structure characterization and product analysis

In this study, the in vitro digestion process of green wheat protein (GWP) was explored by simulating the gastrointestinal digestion. The digestibility of GWP was 65.23%, and was mainly digested by trypsin. During the digestion process of GWP, large-size particles are digested by pepsin, and medium-sized particles are digested by trypsin into smaller particles; irregular large block structure with smooth surface was gradually turned into smaller blocks with porous surface; and the spatial conformation was loosened mainly by the unfolding of β-sheet structure. Gel electrophoresis demonstrated that HMW glutenin and ω-gliadins in GWP were completely digested, while LMW glutenin and α/β/γ-gliadins were partially digested. Additionally, the peptide lengths were relatively dispersed after pepsin digestion. Most of the peptides (76.5%) fell into the range 3-15 amino acid after pepsin and trypsin digestion. The molecular weight (MW) of most pepsin digestion products was above 2000 Da, whereas the MW of trypsin digestion products was mainly concentrated in 500-2000 Da. Besides, the sensitizing peptide sequence of wheat protein was detected in the final digestion products of GWP. This research provided a theoretical guidance for the development and application of GWP.

Effect of gastrointestinal alterations mimicking elderly conditions on in vitro digestion of meat and soy proteins

Among the physiological functions declining with aging, decreased secretion of gastric fluid, achlorhydria, is commonly observed. We evaluated the digestion of meat (chicken, beef, and pork) and soy proteins using in vitro conditions mimicking gastrointestinal (GI) digestion in adults (control, C) and elderly individuals with achlorhydria (EA). Changes in degrees of hydrolysis (DH), SDS-PAGE profiles, peptide concentrations, and proteomic profiles during digestion were investigated. Digestion under the EA conditions markedly decreased DH, especially for soy proteins. SDS-PAGE profiling and proteomics showed that myofibrillar/sarcoplasmic proteins from meat and glycinin/beta-conglycinin from soy were most affected by digestion conditions. Our results indicated that differences in the digestibility of meat protein between EA and control conditions gradually narrowed from the gastric to the intestinal phase for meat protein, while a pronounced difference persisted in the intestinal phase for soy protein. Our work provides new insight of value for future dietary recommendations for elderly individuals.

Cooking affects pork proteins in vitro rate of digestion due to different structural and chemical modifications

The effect of thermal processing on the in vitro digestibility of pork proteins was studied. Raw samples were considered the control group, while the thermal treatments included 58, 80, 98 and 160 °C for 72 min, 118 °C for 8 min and 58 °C for 17 h, resembling a range of different cooking procedures. Samples were subsequently subjected to pepsin digestion at pH 3.00 in the gastric phase followed by trypsin and α-chymotrypsin at pH 8.00 in the intestinal phase. Pork cooked at 58 °C for 72 min had a significantly higher pepsin digestibility rate than meat cooked at 80 °C or 160 °C. The trend was similar in the intestinal phase, with samples cooked at 58 °C for 72 min having enhanced digestion rate over other treatments after 120 min of digestion. A PLS model pointed out to an inverse relationship between in vitro proteolysis rate and variables like Maillard reaction compounds or protein structural changes.

Digestibility of Meat Mineral and Proteins from Broilers Fed with Graded Levels of Chlorella vulgaris

The incorporation of sustainable protein sources in animal feeding is a growing trend. So far, no study has investigated in vitro digestion of meat, from broilers fed microalgae, in a human model. This research aimed to evaluate the effect of incorporating Chlorella vulgaris in the broilers diet on human protein digestibility, and mineral bioaccessibility. The study used 240 male Ross 308 broilers randomly allocated to groups fed a control diet or a diet where soybean meal was replaced with 10% (CV10%), 15% (CV15%), or 20% (CV15%) of C. vulgaris for 40 days. The microalga supplementation increased the protein and lowered the fat content in the muscle. Results on the percentages of amino acids highlighted that arginine and threonine proportions increased and lysine and cysteine proportions decreased with microalga inclusion. CV15% and CV20% meat had higher amount of K, Ca, Mg, P, and Fe in raw breasts, improving the nutrient composition of the meat. Cooking caused a decrease in Na and K and an increase in other minerals. CV20% had higher bioaccessibility of K, Ca, Mg, P, and Mg, compared to the control. Replacing soybean meal in broiler feed with higher concentrations of C. vugaris could improve the digestibility of meat protein and minerals.

Reconsidering Meat Intake and Human Health: A Review of Current Research

Meat consumption is gradually increasing and its impact on health has attracted widespread attention, resulting in epidemiological studies proposing a reduction in meat and processed meat intake. This review briefly summarizes recent advances in understanding the effects of meat or processed meat on human health, as well as the underlying mechanisms. Meat consumption varies widely among individuals, populations, and regions, with higher consumption in developed countries than in developing countries. However, increasing meat consumption may not be the main cause of increasing incidence of chronic disease, since the development of chronic disease is a complex physiological process that involves many factors, including excessive total energy intake and changes in food digestion processes, gut microbiota composition, and liver metabolism. In comparison, unhealthy dietary habits and a sedentary lifestyle with decreasing energy expenditure are factors more worthy of reflection. Meat and meat products provide high-value protein and many key essential micronutrients. In short, as long as excessive intake and overprocessing of meats are avoided, meat remains an indispensable source of nutrition for human health.

Combined Effects of Pressure cooking and Enzyme Treatment to Enhance The Digestibility and Physicochemical Properties of Spreadable Liver Sausage

This study aimed to determine the effect of enzyme, guar gum, and pressure processing on the digestibility and physicochemical properties of age-friendly liver sausages. Liver sausages were manufactured by adding proteolytic enzyme (Bromelain) and guar gum, and pressure-cooking (0.06 MPa), with the following treatments: control, without proteolytic enzyme; T1, proteolytic enzyme; T2, proteolytic enzyme and guar gum; T3, pressure-cooking; T4, proteolytic enzyme and pressure-cooking; T5, proteolytic enzyme, guar gum, and pressure-cooking. The pH was high in the enzyme- and pressure-processed groups. The pressure-processed groups had lower apparent viscosity than other cooking groups, and it decreased during enzyme treatment. Hardness was lower in the enzyme- and pressure-processed groups than in the control, and the T4 was the lowest. Digestibility was the highest in T4 at 82.58%, and there was no significant difference with that in T5. The general cooking group with enzyme and guar gum also showed higher digestibility than the control (77.50%). As a result of the sodium dodecyl sulfate-polyacrylamide gel electrophoresis, the enzyme- and pressure-treated groups (T4, T5) were degraded more into low-molecular-weight peptides (≤37 kDa) than the control and other treatments. Viscoelasticity showed similar trends for viscous and elastic moduli. Similarly, combined pressure processing and enzymatic treatment decreased viscoelasticity, while guar gum increased elasticity but decreased viscosity. Therefore, the tenderized physical properties and improved digestibility by enzyme and pressurization treatment could be used to produce age-friendly spreadable liver sausages.

Protein Oxidation in Muscle Foods: A Comprehensive Review

Muscle foods and their products are a fundamental part of the human diet. The high protein content found in muscle foods, as well as the high content of essential amino acids, provides an appropriate composition to complete the nutritional requirements of humans. However, due to their special composition, they are susceptible to oxidative degradation. In this sense, proteins are highly susceptible to oxidative reactions. However, in contrast to lipid oxidation, which has been studied in depth for decades, protein oxidation of muscle foods has been investigated much less. Moreover, these reactions have an important influence on the quality of muscle foods, from physico-chemical, techno-functional, and nutritional perspectives. In this regard, the loss of essential nutrients, the impairment of texture, water-holding capacity, color and flavor, and the formation of toxic substances are some of the direct consequences of protein oxidation. The loss of quality for muscle foods results in consumer rejection and substantial levels of economic losses, and thus the control of oxidative processes is of vital importance for the food industry. Nonetheless, the complexity of the reactions involved in protein oxidation and the many different factors that influence these reactions make the mechanisms of protein oxidation difficult to fully understand. Therefore, the present manuscript reviews the fundamental mechanisms of protein oxidation, the most important oxidative reactions, the main factors that influence protein oxidation, and the currently available analytical methods to quantify compounds derived from protein oxidation reactions. Finally, the main effects of protein oxidation on the quality of muscle foods, both from physico-chemical and nutritional points of view, are also discussed.

Freezing of meat and aquatic food: Underlying mechanisms and implications on protein oxidation

Over the recent decades,protein oxidation in muscle foods has gained increasing research interests as it is known that protein oxidation can affect eating quality and nutritional value of meat and aquatic products. Protein oxidation occurs during freezing/thawing and frozen storage of muscle foods, leading to irreversible physicochemical changes and impaired quality traits. Controlling oxidative damage to muscle foods during such technological processes requires a deeper understanding of the mechanisms of freezing-induced protein oxidation. This review focus on key physicochemical factors in freezing/thawing and frozen storage of muscle foods, such as formation of ice crystals, freeze concentrating and macromolecular crowding effect, instability of proteins at the ice-water interface, freezer burn, lipid oxidation, and so on. Possible relationships between these physicochemical factors and protein oxidation are thoroughly discussed. In addition, the occurrence of protein oxidation, the impact on eating quality and nutrition, and controlling methods are also briefly reviewed. This review will shed light on the complicated mechanism of protein oxidation in frozen muscle foods.

Thermal processing implications on the digestibility of meat, fish and seafood proteins

Thermal processing is an inevitable part of the processing and preparation of meat and meat products for human consumption. However, thermal processing techniques, both commercial and domestic, induce modifications in muscle proteins which can have implications for their digestibility. The nutritive value of muscle proteins is closely related to their digestibility in the gastrointestinal tract and is determined by the end products that it presents in the assimilable form (amino acids and small peptides) for the absorption. The present review examines how different thermal processing techniques, such as sous-vide, microwave, stewing, roasting, boiling, frying, grilling, and steam cooking, affect the digestibility of muscle proteins in the gastrointestinal tract. By altering the functional and structural properties of muscle proteins, thermal processing has the potential to influence the digestibility negatively or positively, depending on the processing conditions. Thermal processes such as sous-vide can induce favourable changes, such as partial unfolding or exposure of cleavage sites, in muscle proteins and improve their digestibility whereas processes such as stewing and roasting can induce unfavourable changes, such as protein aggregation, severe oxidation, cross linking or increased disulfide (S-S) content and decrease the susceptibility of proteins during gastrointestinal digestion. The review examines how the underlying mechanisms of different processing conditions can be translated into higher or lower protein digestibility in detail. This review expands the current understanding of muscle protein digestion and generates knowledge that will be indispensable for optimizing the digestibility of thermally processed muscle foods for maximum nutritional benefits and optimal meal planning.

Sous Vide Cook Temperature Alters the Physical Structure and Lipid Bioaccessibility of Beef Longissimus Muscle in TIM-1

Changes in the physical states, induced with different sous vide cooking temperatures, significantly (P < 0.05) altered lipid bioaccessibility measured in the TNO-simulated gastrointestinal tract model-1 of AAA boneless beef striploin, containing the longissimus lumborum muscle. The denaturation of actin significantly correlates with the total cumulative free fatty acid (FFA) bioaccessibility, whereby the striploin cooked to 60 °C presents the maximum lipid bioaccessibility (15.8 ± 1.0%), rate constant (k_a) for FFA hydrolysis (0.087 ± 0.003 min^-1), and greatest actin denaturation enthalpy (-0.57 ± 0.06 ΔH). Thus, thermal treatments above 60 °C significantly decrease the kinetics of lipolysis (70 °C = 0.042 ± 0.002 min^-1 and 80 °C = 0.047 ± 0.002 min^-1) and the resultant total lipid bioaccessibility (70 °C = 8.6 ± 0.7 and 80 °C = 8.3 ± 0.5%). This research highlights the potential to manipulate the physical food structure to alter digestion kinetics, supporting the need to understand supramolecular structures in food and their nutritional outcomes.

Changes in the digestion properties and protein conformation of sturgeon myofibrillar protein treated by low temperature vacuum heating during in vitro digestion

The digestion properties of sturgeon myofibrillar protein (MF) treated by low temperature vacuum heating (LTVH) at different processing temperatures (50, 60 and 70 °C) and times (15 and 30 min) were studied and compared with those of sturgeon MF treated by traditional cooking (TC). The results showed that as the temperature and time increased, the protein digestibility decreased, whereas the particle size and protein aggregation increased. It was observed that the band intensity of myosin heavy chain and myosin heavy chain 7 weakened; however, the band intensity of actin showed little change. MALDI-TOF-MS analysis revealed that the digested products of the samples treated by LTVH had a larger proportion of 750-1000 Da peptides than those treated by TC, which was consistent with the trend of the number of unique peptides identified in each group. Fourier transmission infrared (FT-IR) spectroscopy showed that the contents of α-helices and β-sheets exhibited negative and positive correlations with the temperature, respectively. Overall, compared to TC, LTVH can relieve the heat stress of protein conformation, reduce protein aggregation to improve the accessibility of the protein to digestive protease, and increase digestibility.

Changes in the structure and digestibility of myoglobin treated with sodium chloride

Myoglobin is a protein not easily broken down by digestive enzymes due to its rigid structure. This study evaluated the structural characteristics of myoglobin under various sodium chloride treatments (0.4-0.8 mol/L for 5-10 h) and the impacts on its digestibility using spectroscopic and molecular dynamics simulation techniques. Myoglobin digestibility was 40% following pepsin digestion and 60% after being sequentially digested by pepsin and trypsin. The α-helix content of myoglobin did not change significantly following sodium chloride treatment but hydrophobic amino acids were exposed and the binding of phenylalanine targeted by some digestive enzymes became more stable, leading to the reduced digestibility.

Taste compounds generation and variation of broth in pork meat braised processing by chemical analysis and an electronic tongue system

The aim was to unveil the generation and variation rule of the main taste components in braised broth for 10 quantitative repeated braising cycles. The major taste compounds of three groups (MS, broth cooked with meat and spices; M, broth cooked with meat; and S, broth cooked with spices) were systematically analyzed by the state-of-art chromatography and electronic sensory technology. As braising cycles progressed, contents of free 5'-nucleotides and amino acids were increased in MS and M, while those nucleotides were not detected in S. A significant discrimination of taste in MS and M was revealed by electronic tongue evaluation during the process. As the formation rates (FR) of taste compounds and the transformation rates (TR) of taste compounds to volatile compounds were mainly accounting for the generation and variation of flavor in broth, a hypothesis was proposed to illustrate the whole variation of taste compounds in the process integrally that the ratio of FR/TR dividing the process into three stages, Degradation, Balance, and Accumulation. PRACTICAL APPLICATIONS: The traditional braising process and formula are empirical and extensive, which impede the increase in meat products output. Nowadays, the industry of braising products is facing a problem of standardization and quality control, and needs to carry out scientific and quantitative process improvement efficiently. Therefore, the developed comprehensive approach demonstrates great potential for braised meat broth flavor monitoring and quality control in an objective and holistic manner. It provides data support and new ideas of technology development for quality control in the process of meat braising.

Non-thermal processing has an impact on the digestibility of the muscle proteins

Muscle proteins undergo several processes before being ready in a final consumable form. All these processes affect the digestibility of muscle proteins and subsequent release of amino acids and peptides during digestion in the human gut. The present review examines the effects of different processing techniques, such as curing, drying, ripening, comminution, aging, and marination on the digestibility of muscle proteins. The review also examines how the source of muscle proteins alters the gastrointestinal protein digestion. Processing techniques affect the structural and functional properties of muscle proteins and can affect their digestibility negatively or positively depending on the processing conditions. Some of these techniques, such as aging and mincing, can induce favorable changes in muscle proteins, such as partial unfolding or exposure of cleavage sites, and increase susceptibility to hydrolysis by digestive enzymes whereas others, such as drying and marination, can induce unfavorable changes, such as severe cross-linking, protein aggregation, oxidation induced changes or increased disulfide (S-S) bond content, thereby decreasing proteolysis. The underlying mechanisms have been discussed in detail and the conclusions drawn in the light of existing knowledge provide information with potential industrial importance.

In vitro and in vivo digestion of red cured cooked meat: oxidation, intestinal microbiota and fecal metabolites

Mechanisms explaining epidemiological associations between red (processed) meat consumption and chronic disease risk are not yet elucidated, but may involve oxidative reactions, microbial composition alterations, inflammation and/or the formation of toxic bacterial metabolites. First, in vitro gastrointestinal digestion of 23 cooked beef-lard minces, to which varying doses of nitrite salt (range 0-40 g/kg) and sodium ascorbate (range 0-2 g/kg) were added, showed that nitrite salt decreased protein carbonylation up to 3-fold, and inhibited lipid oxidation, demonstrated by up to 4-fold lower levels of 'thiobarbituric acid reactive substances', 32-fold lower 4-hydroxynonenal, and 21-fold lower hexanal values. The use of ascorbate increased the antioxidant effect of low nitrite salt levels, whereas it slightly increased protein carbonylation at higher doses of nitrite salt. The addition of a low dose of ascorbate without nitrite salt slightly promoted oxidation during digestion, whereas higher doses had varying antioxidant effects. Second, 40 rats were fed a diet of cooked chicken- or beef-lard minces, either or not cured, for three weeks. Beef, compared to chicken, consumption increased lipid oxidation (2- to 4-fold) during digestion, and gut protein fermentation (cecal iso-butyrate, (iso-)valerate, and fecal indole, cresol), but oxidative stress and inflammation were generally not affected. Cured, compared to fresh, meat consumption significantly increased stomach protein carbonylation (+16%), colonic Ruminococcaceae (2.1-fold) and cecal propionate (+18%), whereas it decreased cecal butyrate (-25%), fecal phenol (-69%) and dimethyl disulfide (-61%) levels. Fecal acetaldehyde and diacetyl levels were increased in beef-fed rats by 2.8-fold and 5.9-fold respectively, and fecal carbon disulfide was 4-fold higher in rats consuming cured beef vs. fresh chicken. Given their known toxicity, the role of acetaldehyde and carbon disulfide in the relation between meat consumption and health should be investigated in future studies.

Application of artificial neural networks to predict multiple quality of dry-cured ham based on protein degradation

This study investigated protein degradation and quality changes during the processing of dry-cured ham, and then established the multiple quality prediction model based on protein degradation. From the raw material to the curing period, proteolysis index of external samples were higher than that of internal samples, however, the difference gradually decreased from the drying period to the maturing period. Protein degradation can be used as indicators for controlling quality of the hams. With protein degradation index as input variables, the back propagation-artificial neural networks (BP-ANN) models were optimized, with training function of trainlm, transfer function of logsig in input-hidden layer and tansig in hidden-output layer, and 20 hidden layer neurons. Furthermore, the relative errors of predictive data and experimental data of 12 samples were approximately 0 with the BP-ANN model. Results indicated that the BP-ANN has great potential in predicting multiple quality of dry-cured ham based on protein degradation.

Structural Changes and Evolution of Peptides During Chill Storage of Pork

In this work, we investigated changes in protein structures in vacuum-packed pork during chill storage and its impact on the in vitro protein digestion. Longissimus dorsi muscles were vacuum packed and stored at 4°C for 3 days. Samples were subjected to Raman spectroscopy, in vitro digestion and nano LC-MS/MS. The 3 d samples had lower α-helix content, but higher β-sheet, β-turn, and random coil contents than the 0 d samples (P < 0.05). SDS-PAGE revealed significant protein degradation in the 3 d samples and the differences in digested products across the storage time. Proteome analysis indicated that the 3 d samples had the higher susceptibility to digestion. Increasing protein digestibility was mainly attributed to the degradation of myofibrillar proteins. Thus, exposure of more enzymatic sites in loose protein structure during chill storage could increase protein degradation in meat.

Influence of Sonication and Taraxacum Officinale Addition on the Antioxidant and Anti-ACE Activity of Protein Extracts from Sous Vide Beef Marinated with Sour Milk and after In Vitro Digestion

The present study assessed the effect of pretreating beef as a raw material for sous vide steak preparation. The pretreatment involved maceration of a batch of meat in sour milk with the simultaneous use of ultrasound (250 or 500 W) as well as the addition of Taraxacum officinale. The biological activity profile of the peptides was assessed in terms of their antioxidant activity and inhibiting activity against angiotensin-converting enzyme (ACE). Changes in the biological activity of peptides under the influence of hydrolysis by gastrointestinal enzymes, i.e., pepsin and pancreatin, were also considered. There was no significant effect of T. officinale addition and sonication of beef batches on the protein content (except for lot S6, after sonication at 500 W as acoustic power and with the addition of dandelion). It was observed that the interaction of maceration in sour milk with simultaneous ultrasound treatment as the initial production step of sous vide beef steak generates the formation of peptides with antioxidant properties. Moreover, peptide formation can be further enhanced by adding dandelion (based on the results of antiradical and chelating activity tests). In addition, the progression of hydrolysis under the influence of gastrointestinal enzymes promotes the release of peptides with antioxidant and anti-ACE activity.

"Rigid" structure is a key determinant for the low digestibility of myoglobin

Myoglobin, a critical protein responsible for meat color, has been shown insusceptible to digestion. The underlying mechanism is not clear. The present study aimed to evaluate whether the structural properties of myoglobin are associated with its insusceptibility to digestion using spectroscopic and computational techniques. Myoglobin was degraded by only 7.03% by pepsin and 33.00% by pancreatin. The structure of myoglobin still maintained α-helix after the two-step digestion, with the exposure of some aromatic residues. In addition, molecular dynamics modeling suggested that hydrophobic amino acid residues (Phe 111, Leu 10, Ala 115, Pro 116) in pepsin and polar amino acid residues (Tyr 146, Thr 95) in myoglobin were found in the proximity of binding sites, which could result in the low digestibility of myoglobin. Our findings provide a new insight into the underlying mechanisms on the difficulty in digestion of myoglobin.

Changes in the extent and products of In vitro protein digestion during the ripening periods of Chinese dry-cured hams

A long ripening period is essential for developing dry-cured ham flavor, but the effect of ripening process on its in vitro digestion product has not been extensively studied. Here, we investigated the in vitro digestion profiles from Chinese dry-cured ham (Jinhua, Rugao and Xuanwei) with different ripening periods by particle size measurement, gel eletrophoresis analysis and nano liquid chromatography-tandem mass spectrometry. The results showed that the in vitro digestibility of ham was in a good agreement with the particle size of digestion products. Among the three types dry-cured ham, Xuanwei showed the highest digestibility (93.46%), followed by Jinhua (74.46%). In term of ripening period, the 2-year Xuanwei and Jinhua showed the diversity of peptides (especially for peptide with molecular weight < 2500 Da), besides their good digestibility. Moreover, the highest amount of peptides (404) was observed in 2-year Jinhua compared to other hams. Our finding gave a new insight into the digestion profiles and nutritional properties of Chinese dry-cured hams.