Mónica Flores

The Role of Muscle Proteases and Lipases in Flavor Development During the Processing of Dry-Cured Ham

The processing of dry-cured ham is very complex and involves numerous biochemical reactions that are reviewed in this article. Muscle proteins undergo an intense proteolysis, resulting in a great number of small peptides and high amounts of free amino acids. The enzymes responsible of these changes are proteinases (cathepsins B, D, H, and L and, to a less extent, calpains) and exopeptidases (peptidases and aminopeptidases). Muscle and adipose tissue lipids are also subject to intense lipolysis, generating free fatty acids by the action of lipases that, in a second stage, are transformed to volatiles as a result of oxidation. Sensory profiles of dry-cured ham are strongly affected by these enzymatic reactions. In addition, the activity levels of the muscle enzymes significantly depend on the properties of raw ham, such as age and crossbreeding as well as the process conditions such as temperature, time, water activity, redox potential, and salt content. Thus, the control of the muscle enzyme systems, mainly proteases and lipases, is essential for the standardization of the processing and/or enhancement of flavor quality of dry-cured ham.

Dry-cured ham flavour: enzymatic generation and process influence

Abstract The processing of dry-cured ham is very complex and involves numerous biochemical reactions that are reviewed in this paper. Muscle proteins undergo an intense proteolysis resulting in a great number of small peptides and high amounts of free amino acids. The enzymes responsible of these changes are proteinases (cathepsins B, D, H and L and, to a less extent, calpains) and exopeptidases (peptidases and aminopeptidases). Muscle and adipose tissue lipids are also subject to intense lipolysis generating free fatty acids by the action of lipases that, in a second stage, are transformed to volatiles as a result of oxidation. Sensory profiles of dry-cured ham are strongly affected by these enzymatic reactions. In addition, the activity levels of the muscle enzymes significantly depend on the properties of raw ham, such as age and crossbreeding as well as the process conditions such as temperature, time, water activity, redox potential and salt content. Thus, the control of the muscle enzyme systems, mainly proteases and lipases, is essential for the optimal standardisation of the processing and/or enhancement of flavour quality of dry-cured ham.

Contribution of muscle aminopeptidases to flavor development in dry-cured ham

Abstract The activity of muscle aminopeptidases (alanyl, arginyl, leucyl and pyroglutamyl aminopeptidases) have been assayed along the processing of dry-cured ham. The generation of free amino acids resulting from aminopeptidase action on N-terminal of proteins and peptides has been also analyzed. The assayed aminopeptidases, except pyroglutamyl aminopeptidase, showed good stability. Alanyl and arginyl aminopeptidases have optimal neutral pH near the pH in ham and, in addition, their spectrum of activity against terminal amino acids is in coincidence with the observed release of free amino acids in ham. So, both aminopeptidases appear to be the main contributors to the generation of free amino acids during the processing of dry-cured ham.

Effect of Debaryomyces spp. on aroma formation and sensory quality of dry-fermented sausages

The effect of Debaryomyces spp. used in combination with starter cultures (lactic acid bacteria and staphylococci) was studied in the development of dry-fermented sausage aroma and final sensory quality. Volatile compounds were extracted by solid-phase micro extraction and analysed by gas chromatography-mass spectrometry. A paired comparison test was done to determine which sausage was preferred. Debaryomyces spp. showed an important effect on volatile generation during ripening by inhibiting the generation of lipid oxidation products and promoting the generation of ethyl esters that contribute to proper sausage aroma. However, the amount of Debaryomyces spp. used is important because larger amounts produced high generation of acids that mask the positive effect.

The influence of nitrite and nitrate on microbial, chemical and sensory parameters of slow dry fermented sausage

Nitrate and/or nitrite are used in the manufacture of dry-fermented sausages. However, research has mainly been focusing on nitrite and its effect on flavour development whereas little attention has been paid to nitrate. The aim of the present work was to study the effect of nitrate and nitrite as curing salts on the quality of a slow fermentation process. Two different batches containing nitrate or nitrite were manufactured. Microbial and chemical parameters were monitored during ripening and after vacuum packed storage, as well as their fatty acid composition and their profile of volatile compounds. The oxidation, measured as TBARS (Thiobarbituric acid reactive substances), was greater in the samples with added nitrite than in the samples with added nitrate. FFA (free fatty acids) release was higher in the samples containing nitrite throughout the process. Volatile compounds arising from amino acid degradation and carbohydrate fermentation were generated at higher levels in the samples with added nitrate, probably due to the higher population of microorganisms in these samples and the effect of nitrate on their metabolism.

Sensory acceptability of slow fermented sausages based on fat content and ripening time

Low fat dry fermented sausages were manufactured using controlled ripening conditions and a slow fermented process. The effect of fat content and ripening time on the chemical, colour, texture parameters and sensory acceptability was studied. The fat reduction in slow fermented sausages produced an increase in the pH decline during the first stage of the process that was favoured by the higher water content of the low fat sausages. Fat reduction did not affect the external appearance and there was an absence of defects but lower fat content resulted in lower sausage lightness. The sausage texture in low fat sausages caused an increase in chewiness and at longer ripening times, an increase in hardness. The sensory acceptability of the fermented sausages analyzed by internal preference mapping depended on the different preference patterns of consumers. A group of consumers preferred sausages with high and medium fat content and high ripening time. The second group of consumers preferred sausages with low ripening time regardless of fat content except for the appearance, for which these consumers preferred sausages of high ripening time. Finally, the limit to produce high acceptability low fat fermented sausages was 16% fat content in the raw mixture that is half the usual content of dry fermented sausages.

Effect of fat content on aroma generation during processing of dry fermented sausages.

Dry fermented sausages with different fat contents were produced (10%, 20% and 30%). The effect of fat content and ripening time on sensory characteristics, lipolysis, lipid oxidation and volatile compounds generation was studied. Also, the key aroma components were identified using gas chromatography (GC) and olfactometry. High fat sausages showed the highest lipolysis and lipid oxidation, determined by free fatty acid content and thiobarbituric acid reactive substances (TBARS), respectively. A total of 95 volatile compounds were identified using SPME, GC and mass spectrometry (MS). Fat reduction decreased the generation of lipid derived volatile compounds during processing while those generated from bacterial metabolism increased, although only at the first stages of processing. The consumers preference in aroma and overall quality of high and medium fat sausages was related to the aroma compounds hexanal, 2-nonenal, 2,4-nonadienal, ethyl butanoate and 1-octen-3-ol which contributed green, medicinal, tallowy, fruity and mushroom notes.

The effect of post-mortem aging on meat flavor quality in Brangus beef. Correlation of treatments, sensory, instrumental and chemical descriptors

The flavor of muscle foods is dependent upon factors such as the animals age, breed, sex, nutritional status and manner of cooking. Most important to the final flavor of the meat is relative age in the post-mortem aging process as it is during this time that many chemical flavor components are formed (Spanier et al., 1990). These components serve either directly as flavor components or as a pool of reactive flavors and intermediates that form many of the characteristic meat flavors after cooking. The post-mortem aging process is identified with enhancement of beef sensory quality due to enhanced tenderization. While this is true for beef texture, it is not true for the overall flavor of meat. Data is shown indicating that, during post-mortem aging, desirable flavors such as beefy, brothy, browned-caramel, and sweet decline while off-flavors such as bitter and sour increase.

The use of muscle enzymes as predictors of pork meat quality

Muscle endo-protease (calpains and cathepsins) and exo-protease (dipeptidyl-peptidases and aminopeptidases) activities were assayed at 2 h post-mortem in different meat qualities (PSE, RSE, RFN and DFD). The sensory characteristics of the different pork meat qualities were also evaluated in order to correlate them to the proteolytic activity. The assay of aminopeptidase and dipeptidylpeptidase activities (AAP, RAP, LAP, DPPI and DPPIV) at 2 h post-mortem discriminate between exudative and non-exudative classes explaining 74.6% of the variability. Also, at 24 h post-mortem 71.2% of the variability was detected by the measurement of PGAP, AAP, RAP, DPPII and DPPIV. Therefore, the exoprotease activities can constitute a novel and adequate technique to predict early post-mortem pork meat quality allowing its assay till 24 h post-mortem because of the good stability of the enzymes during this post-mortem time.

Effect of high pressure treatment on colour, microbial and chemical characteristics of dry cured loin.

The effect of high pressure on sliced and vacuum packaged commercial dry-cured pork loin was determined by analysing the induced colour changes, the residual enzymatic activities of cathepsins, aminopeptidases and dipeptidilpeptidases and the changes in the content of free amino acids and also its effect on lipid oxidation, as TBARS (Thiobarbituric reactives substances) and volatile flavour compounds. High pressure treatments above 300MPa affected the colour of dry cured pork loins producing an increase in lightness and decreased redness and these differences were detected during all vacuum storage. High pressure produced a reduction in the activity of aminopeptidases and dipeptidylpeptidases. The untreated samples showed an increase in free amino acid content during vacuum storage while the pressurised samples showed no significant increases probably due to the reduction in aminopeptidase activity. The oxidative stability of the pressurised dry-cured loins was not affected as observed by the absence of differences in TBARS values and in the abundance of volatile compounds from the lipid oxidation. However, the pressurised treatment produced a reduction of several flavour compounds, particularly those derived from Maillard reactions, although they are regenerated during vacuum storage. In summary, high pressure treatment after the ripening of dry-cured loin affects its quality but the differences can be minimised by vacuum storage.