Changes in the Profiles of Metabolites Originating from Protein Degradation During Ripening of Dry Cured Ham

Generation of kokumi γ-glutamyl short peptides in Spanish dry-cured ham during its processing

The typical dry-cured ham flavor is rich in umami and brothy perceptions, for which short peptides may contribute. Particularly, γ-glutamyl peptides could be the responsible of these previously reported attributes, as they exert a synergistic interaction with other basic tastes and modify the intensity of salty, sweet, and umami tastes. The content of peptides has been reported to evolve along the processing, but no kokumi γ-glutamyl peptides have been identified in Spanish dry-cured hams yet. In this research, nine γ-glutamyl dipeptides (γ-EA, γ-EC, γ-EE, γ-EF, γ-EL, γ-EM, γ-EV, γ-EW, and γ-EY) and two γ-glutamyl tripeptides (GSH and γ-EVG) have been quantitated at 6, 12, 18 and 24 months of traditional processing of Spanish dry-cured ham by performing a Q Exactive Orbitrap-based tandem mass spectrometry. The results show an increase of γ-EA, γ-EE, γ-EF, γ-EL, γ-EM and γ-EVG, obtaining maximums at 24 months of curing ranging from 0.14 (γ-EVG) to 18.86 (γ-EL) μg/g dry-cured ham. Otherwise, γ-EV, γ-EW and γ-EY accumulated until the 18th month of storage to 15.10, 0.54 and 3.17 μg/g dry-cured ham, respectively; whereas γ-EC and GSH amounts decreased starting from 0.0676 and 4.41 μg/g dry-cured ham, respectively at earlier stages. The concentration dynamics of these compounds may be linked with proteolytic and oxidative reactions during processing. In addition, due to their synergistic effect on kokumi activity, this could constitute insights of the brothy perceptions of dry-cured ham, and these peptides probably contribute to the sensory differences existing in long processed Spanish dry-cured hams.

Comparative Quantitation of Kokumi γ-Glutamyl Peptides in Spanish Dry-Cured Ham under Salt-Reduced Production

Salting is a crucial step during the production of dry-cured ham and it is not well known whether it has an impact on the generation of taste-active peptides. The present study focused on the quantitation of kokumi γ-glutamyl peptides in low-salted Spanish dry-cured hams with 12 months of processing. By using mass spectrometry, peptides were quantitated from samples obtained after ethanolic deproteinization-based and non-ethanolic deproteinization-based extraction methods. Peptides γ-EA, γ-EE, and γ-EL registered mean values of 0.31, 2.75, and 11.35 µg/g of dry-cured ham, respectively, with no differences observed between both extraction protocols. However, γ-EF, γ-EM, γ-EV, γ-EW, γ-EY, and γ-EVG presented significantly (p < 0.05) higher concentrations in the ethanolic deproteinized samples showing values of 5.58, 4.13, 13.90, 0.77, 3.71, and 0.11 µg/g of dry-cured ham, respectively. These outcomes reflect the importance of protocols for the extraction of peptides to achieve the most feasible results. In addition, potential precursors for the formation of γ-glutamyl peptides are generated during dry-curing under salt restriction. The kokumi activity of these γ-glutamyl peptides could enhance the sensory attributes countering the taste deficiencies caused by the salt restriction.

Penicillium chrysogenum as a fungal factory for feruloyl esterases

Plant biomass is a promising substrate for biorefinery, as well as a source of bioactive compounds, platform chemicals, and precursors with multiple industrial applications. These applications depend on the hydrolysis of its recalcitrant structure. However, the effective biological degradation of plant cell walls requires several enzymatic groups acting synergistically, and novel enzymes are needed in order to achieve profitable industrial hydrolysis processes. In the present work, a feruloyl esterase (FAE) activity screening of Penicillium spp. strains revealed a promising candidate (Penicillium rubens Wisconsin 54-1255; previously Penicillium chrysogenum), where two FAE-ORFs were identified and subsequently overexpressed. Enzyme extracts were analyzed, confirming the presence of FAE activity in the respective gene products (PrFaeA and PrFaeB). PrFaeB-enriched enzyme extracts were used to determine the FAE activity optima (pH 5.0 and 50-55 °C) and perform proteome analysis by means of MALDI-TOF/TOF mass spectrometry. The studies were completed with the determination of other lignocellulolytic activities, an untargeted metabolite analysis, and upscaled FAE production in stirred tank reactors. The findings described in this work present P. rubens as a promising lignocellulolytic enzyme producer. KEY POINTS: • Two Penicillium rubens ORFs were first confirmed to have feruloyl esterase activity. • Overexpression of the ORFs produced a novel P. rubens strain with improved activity. • The first in-depth proteomic study of a P. rubens lignocellulolytic extract is shown.

Bioactive and Sensory Di- and Tripeptides Generated during Dry-Curing of Pork Meat

Dry-cured pork products, such as dry-cured ham, undergo an extensive proteolysis during manufacturing process which determines the organoleptic properties of the final product. As a result of endogenous pork muscle endo- and exopeptidases, many medium- and short-chain peptides are released from muscle proteins. Many of them have been isolated, identified, and characterized, and some peptides have been reported to exert relevant bioactivity with potential benefit for human health. However, little attention has been given to di- and tripeptides, which are far less known, although they have received increasing attention in recent years due to their high potential relevance in terms of bioactivity and role in taste development. This review gathers the current knowledge about di- and tripeptides, regarding their bioactivity and sensory properties and focusing on their generation during long-term processing such as dry-cured pork meats.

Quantification and in silico analysis of taste dipeptides generated during dry-cured ham processing

Small peptides such as dipeptides contribute to a great extent to the characteristic taste of dry-cured hams. In this study, hydrophilic interaction liquid chromatography (HILIC) combined to tandem mass spectrometry was used to separate, identify, and quantify seven dipeptides in dry-cured hams sampled at different processing times (6, 12, 18, and 24 months). Results showed an increased concentration of dipeptides DA, DG, EE, ES, and EV with the length of processing, obtaining values up to 23 μg/g of dry-cured ham, which suggests an intense action of muscle enzymes dipeptidyl peptidases during the process. The dipeptide VG significantly decreased from 7 to 4 μg/g of dry-cured ham as the processing increased from 6 to 24 months, whereas the dipeptide PA showed low values between 380 and 550 ng/g of dry-cured ham at all the sampling times. Additionally, in silico analyses reported the sensory characteristics of the studied dipeptides, mostly giving bitter and umami taste, and predicted their allergenicity, toxicity, and physicochemical properties. These results could be useful for further studies related to the pleasant taste of dry-cured hams.

Identification of dipeptides by MALDI-ToF mass spectrometry in long-processing Spanish dry-cured ham

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A simpler strategy was carried out to identify dipeptides in dry-cured ham.

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Ultrafiltration following MALDI-ToF MS allows a rapid peptide identification.

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AH, AL, DD, EV and VF were identified in samples with different processing times.

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Bioactive or tasting food-derived dipeptides can be identified by this methodology.

The processing of dry-cured ham results in the generation of small peptides by the action of endogenous enzymes on muscle proteins. Common proteomic workflows involve previous separation techniques based on liquid chromatography which are expensive and time-consuming. In this study, a convenient proteomic approach based on MALDI-ToF is proposed for the first time for the detection of dipeptides in Spanish dry-cured ham. Dipeptides AH, AL, DD, EV, and VF were identified in hams of 18 and 24 months of dry-curing. This work provides insights on the efficiency of a new peptidomic workflow for the short peptide identification from a complex food matrix and permits to evaluate the sample in terms of the presence of taste-related and bioactive dipeptides.

The Effect of Catabolic Transformations of Proteins and Fats on the Quality and Nutritional Value of Raw Ripened Products from Zlotnicka Spotted and Zlotnicka White Meat

The aim of the study was to compare the advancement of the ripening as well as catabolic changes in proteins and fats of Zlotnicka Spotted (ZS) and Zlotnicka White (ZW) meat and their impact on the quality and nutritional value of ready-to-eat products. The meat of the breeds ZS and ZW differed not only in the basic chemical composition but also in the susceptibility to catabolic transformations of proteins and lipids, which translated into a separate technological and nutritional quality as well as the profile of volatile odor compounds. Loins due to their compact histological structure, low pH (5.4) and decreased water activity (0.92–0.93) were characterized by a lower number of coagulase-negative cocci (3.3 log cfu/g) compared to hams. The products of both breeds differed in the content of selected neutral glucogenic amino acids with a pI in the range of 5.6–6.1 mainly. The content of biogenic amines was therefore completely dependent on the metabolic potential of acidifying bacteria. Larger number of lactic acid bacilli (7.5–7.7 log cfu/g) and lactic acid cocci (7.9–8.3 log cfu/g), as well as a higher content of saturated (55.2–53.7%) and polyunsaturated fatty acids (6.4–7.0%) shaped the final pH of hams (5.3). Presence of aldehydes, ketones and alcohols indicated existing fat oxidation despite the small values of the TBA index of hams (1.1 mg/kg) and loins (0.4–0.6 mg/kg). The volatile compounds that differentiated products of ZS and ZW formed by the oxidation and microbial activity, were, primarily: octanal, 1-hydroxypropan- 2-one, 3-methylpentan-2-one, propane-1,2-diol, 2,5-dimethylfuran and 3-hydroxybutan- 2-one, butane-2,3-dione, butane-1,2-diol, respectively.

Volatile compounds in high-pressure-treated dry-cured ham: A review

The use of high pressure processing (HPP) for the treatment of dry-cured ham and other meat products has considerably increased worldwide. Its well-documented lethal effect on pathogenic and spoilage bacteria ensures the microbial safety of dry-cured ham and extends its shelf life. However, the effects of HPP on the volatile compounds, odor and aroma of dry-cured ham are less known. In the present review, the effects of HPP on the enzymes and microorganisms responsible for the generation of volatile compounds in dry-cured ham and the changes in the levels of the main groups of volatile compounds resulting from different HPP treatments are discussed. Particular attention is devoted to the fate of odor-active compounds after HPP treatments and throughout further commercial storage. The use of efficient sensory techniques yielding odor and aroma outputs closer to those perceived by consumers is encouraged. Needs for future research on the volatile compounds, odor and aroma of HPP-treated dry-cured ham are highlighted.

Biochemical Properties Affecting the Nutritional Quality, Safety, and Aroma of Dry-Cured Products Manufactured from Meat of Rare Native Pig Breeds

The aim of study was to compare the biochemical properties affecting the nutritional quality, safety, and aroma of dry-cured products manufactured from valuable meat of rare native pig breeds: Pulawska (Pul) and Zlotnicka Spotted (ZS). The count of lactic acid bacteria (4.4 log cfu/g) and the release of palmitic (23.1% and 25.9%), oleic (44.1% and 42.2%), and linoleic acids (8.3% and 7.8%), as well as arginine (30.0 and 44.3 mg/kg), histidine (25.8 and 20.6 mg/kg), and lysine (26.8–22.9 mg/kg), shaped the final pH (5.3 and 5.4) in Pul and ZS products during the 4 week maturing, respectively. Lastly, Pul and ZS meat differed in the proportion of decanoic, lauric, stearic, arachidic, and conjugated linoleic acids. The high content of putrescine (23.7 mg/kg), cadaverine (54.3 mg/kg), and tyramine (57.2 mg/kg), as well as a twofold greater share of histamine (163.2 mg/kg) and tryptamine (9.1 mg/kg), indicated a more advanced decarboxylation of ZS meat. Volatile compounds differentiating Pul and ZS meat were primarily hexanal, 3-hydroxybutan-2-one, phenylacetalaldehyde, 2,3-dimethyl-2-cyclopenten-1-one, 2-cyclopenten-1-one, and 3-methyl- and 2-cyclopenten-1-one. Most marked volatile compounds were obtained as a result of microbial activity (acetic acid, 3-methylbutan-1-ol, ethanol, acetone, and 3-hydroxybutan-2-one), advanced lipid oxidation, and decomposition of secondary oxidation products (hexanal, phenylacetaldehyde, and 2-cyclopenten-1-one).

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.

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.

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.

Variation of Microbiological and Biochemical Profiles of Laowo Dry-Cured Ham, an Indigenous Fermented Food, during Ripening by GC-TOF-MS and UPLC-QTOF-MS

Fermented foods have unique microbiota and metabolomic profiles that can support dietary diversity, digestion, and gut health of consumers. Laowo ham (LWH) is an example of an indigenous fermented food from Southwestern China that has cultural, ecological, economic, and health significance to local communities. We carried out ethnobiological surveys coupled with metagenomic and metabolomic analyses using GC-TOF-MS and UPLC-QTOF-MS to elucidate the microbiota and metabolic profiles of LWH samples at different ripening stages. The results from high-throughput sequencing showed a total of 502 bacterial genera in LWH samples with 12 genera of bacteria and 6 genera of fungi identified as dominant groups. This is the first study to our knowledge to report the bacteria of Lentibacillus and Mesorhizobium along with fungi Eremascus and Xerochrysium on a fermented meat product. Findings further revealed that the metabolite profiles among LWH samples were significantly different. In total, 27 and 30 metabolites from GC-TOF-MS and UPLC-QTOF-MS analysis, respectively, were annotated as highly discriminative metabolites. Among the differential compounds, the relative contents of most amino acids showed the highest in the LWH sample ripened for two years, while some metabolites with potential therapeutic effects such as levetiracetam were the most abundant in the LWH sample ripened for three years. The correlation analysis indicated that the dominant microbes were closely related to differential metabolites, highlighting the importance of their functional characterization. Findings indicate that the consumption of LWH contributes to microbiological and chemical diversity of human diets as well as suggests efficacy of combining GC-MS and LC-MS to study the metabolites in dry-cured meat products.

Sensory properties and metabolomic profiles of dry-cured ham during the ripening process

Dry-cured ham with a long ripening period is a valuable product worldwide. Ripening time is a key determinant of the endogenous metabolites that characterize the flavor and taste of ham products. While various studies have analyzed the relationship between ripening duration and sensory characteristics, no studies have evaluated ham products produced in Japan. Here, we conducted time-course metabolomic profiling, taste sensor-based analyses, and sensory evaluations by non-trained consumers during ripening. Capillary electrophoresis-mass spectrometry was used to quantify non-volatile metabolites, such as amino acids, organic acids, and nucleotides. In an analysis of eight time-points during 680 days of ripening, the highest score for the after-taste of umami was observed on day 540, despite subtle changes in the scores for other properties. The concentrations of aspartic acid and glutamic acid relative to those of total amino acids were the highest at this point. This approach can contribute to the understanding of the relationship between the metabolite profile and ripening duration.