PROTEOLYTIC CHANGES DURING PROCESSING IN TURKISH DRY‐CURED MEAT PRODUCT (PASTIRMA) WITH DIFFERENT SALT LEVELS

ABSTRACT

The effects of different salt (NaCl) contents on proteolytic changes during processing in the dry‐cured meat product past?rma were investigated. Past?rma samples were produced with three different NaCl levels (3, 6 and 9%) and proteolytic changes were monitored. A progressive increase in nonprotein nitrogen (NPN) and free amino acids (FAAs) was detected during processing. High‐salt past?rma samples had the highest FAAs. Drying and pressing stages before pasting with çemen resulted in a decrease in water‐soluble nitrogen (WSN) and a slight increase in NPN and FAA. High salt level and processing time resulted in the accumulation of FAAs. The increase in WSN, NPN and FAA contents after çemen treatment indicated that the çemen used in the pasting process had an impact on accumulation of these components in past?rma. However, no significant effect of salt level was observed on WSN and NPN. Sarcoplasmic proteins decreased considerably after salting due to drainage. Myofibrillar proteins degraded during processing, particularly in samples with 6 and 9% NaCl.

PRACTICAL APPLICATIONS

Proteolysis is one of the most important biochemical changes occurring during the processing of dry‐cured meat products such as ham or past?rma. The effect of additional salt concentrations and processing stages on proteolysis in Turkish dry‐cured meat product, past?rma, was studied during processing. Processing stages (salting, drying, pressing and pasting with çemen mixture) resulted in increases in NPN and FAA contents. High salt level (9% NaCl) and processing stages, particularly pasting with çemen mixture, facilitated the accumulation of FAA. Salting resulted in denaturation or insolubilization of proteins. Insolubilization of sarcoplasmic proteins was clearly seen in samples with 6 and 9% NaCl, depending on increased salt concentration during processing. In contrast, myofibrillar proteins in samples with 6 and 9% NaCl degraded during processing. From these results, processing conditions (salt concentration of past?rma and pasting with çemen) can determine the compounds released from protein breakdown during processing.

     

Curing and diffusion coefficient study in pastırma,a Turkish traditional meat product

Changes in water activity (a_w), moisture and salt contents and salt effective diffusion coefficients (D_eff) of past?rma samples during the curing process were determined. At the end of the curing stage, a_w values decreased to 0.942. The average initial moisture content of the samples decreased from 74.56% to 66.64%, depending on the curing time and the average salt content increased to 15.65 g NaCl/100 g dry matter at the end of the 48-hour curing process. Past?rma samples were assumed the geometry of endless slices, and the analytical solution of Fick's second equation was used for determination of salt D_eff values. Salt D_eff values were found to vary between 1.49 × 10^− 9–4.08 × 10^− 9 m²/s.     

Changes in the composition of volatile compounds and in microbiological and physicochemical parameters during pastırma processing

Changes in the composition of volatile compounds and in microbiological and physicochemical parameters of past?rma (Turkish dry-cured meat product) were studied during traditional processing. The pH value increased during the last stages of processing. While a_w values decreased throughout processing, TBARS and NPN levels increased regularly depending on the processing time. The microbiological analyses showed that Gram positive-catalase positive cocci were predominant microorganisms in past?rma. A total of forty eight volatile compounds were tentatively identified during past?rma processing, including esters, aliphatic hydrocarbons, sulphur-containing compounds, alcohols, aldehydes, ketones, aromatic hydrocarbons, terpenes and furans. Aldehydes reached their maximum level at the end of second drying. Among aldehydes, hexanal was the major component. In the final product, aromatic hydrocarbons had become the dominant chemical compounds.     

Effect of storage temperatures and time on shelf‐life of sliced and modified atmosphere packaged Pastırma,a dried meat product,produced from beef

The effects of modified atmosphere on some physical, chemical and microbiological properties of sliced past?rma made from beef Longissimus dorsi muscle were investigated. Sliced‐past?rma samples (moisture 43.65 ± 0.15%, pH 5.71 ± 0.02) were stored in modified atmosphere packages (50% N₂ + 50% CO₂) at 4 and 10 °C for 150 days. The storage period had a significant effect (p < 0.01) on moisture, pH, thiobarbituric acid reactive substances, free fatty acid, non‐protein nitrogen, water‐soluble nitrogen, colour values and total aerobic bacteria, lactic acid bacteria and Micrococcus/Staphylococcus counts. The storage temperatures (4 and 10 °C) also had a significant effect (p < 0.01) on moisture, pH, thiobarbituric acid reactive subctances, free fatty acid, water soluble nitrogen, a* values, total aerobic bacteria lactic acid bacteria, and Micrococcus/Staphylococcus counts. It was determined that the storage period × the storage temperature interactions had a significant (p < 0.01) effect on the values of pH, a* and the counts of total aerobic bacteria, lactic acid bacteria, Micrococcus/Staphylococcus. It was also observed that the yeast and mold count was the highest in the first storage period and decreased throughout storage. Enterobacteriaceae count was also below the detectable level (<2.00 cfu g^?1) throughout the storage period. Copyright © 2005 Society of Chemical Industry     

Chemical composition and physical properties of extruded snacks containing crab‐processing by‐product

The crab‐processing industries generate millions of pounds of by‐product annually, which results in a loss of edible product and presents a considerable waste disposal problem. The purpose of this research was to investigate the use of crab‐processing by‐product (CB) in the development of a calcium‐rich expanded snack. The specific objectives were to examine the effects of type of CB (wet or dry), feed composition and screw speed (150 or 250 rpm) on selected properties of extruded snacks. Product formulations consisting of 0–400 g kg^?1 CB combined with corn meal and potato flakes were processed in a twin‐screw extruder. The resulting extrudates were analysed for proximate and mineral (calcium, sodium) composition, pH, water activity (a_w), total plate count, bulk density, expansion ratio and colour. Both CB type and level of incorporation had significant effects (P < 0.05) on the calcium content, expansion ratio, bulk density and pH of the extrudates. Increasing the CB level resulted in increased calcium content (from 5.1 to 52.4 mg g^?1) and pH (from 6.1 to 8.8). Screw speed had no significant effects (P > 0.05) on expansion ratio and bulk density. A high processing temperature (157 °C) and low a_w resulted in undetectable microbial growth on the extrudates. This research demonstrates that ground crab‐processing by‐product can be successfully incorporated into an expanded snack product. Further research will evaluate consumer response to this novel value‐added product. Copyright © 2003 Society of Chemical Industry     

Study of the Maillard reaction in model systems under conditions related to the industrial process of pasta thermal VHT treatment

Non‐enzymatic browning (NEB) due to the Maillard reaction (MR) was studied in a closed starch/glucose/lysine model system (20 g kg⁻¹ glucose, 10 g kg⁻¹ lysine) in order to analyse conditions favouring reactivity during an industrial process of pasta VHT (very high temperature) thermal treatment. The closed model pastes gave data on the NEB progress during the pasta drying cycle as a function of temperature, time and water activity (a_w). Indicators such as headspace CO ₂ , optical density and colour showed an increase of MR as the initial a_w increased from 0.50 to 0.91. During the initial stages of drying, a combination of high temperatures and high a_w led to the most likely conditions for NEB. © 1999 Society of Chemical Industry     

Water activity,water glass dynamics,and the control of microbiological growth in foods

Water is probably the single most important factor governing microbial spoilage in foods, and the concept of water activity (a_w) has been very valuable because measured values generally correlate well with the potential for growth and metabolic activity. Despite some drawbacks (e.g., solute effect), the concept of a_w has assisted food scientists in their effort to predict the onset of food spoilage as well as to control food‐borne disease hazards in food products. In the last decade the concept of a_w has been challenged. It has been suggested that reduced‐moisture food products (e.g., low and intermediate) may be nonequilibrium systems and that most of them are in the amorphous metastable state, which is very sensitive to changes in moisture content and temperature. It has been proposed that the glass transition temperature T_g (temperature at which the glass‐rubber transition occurs), is a parameter that can determine many product properties, the safety of foods among them. The concept of water dynamics, originating in a food polymer science approach, has been suggested instead of a_w to better predict the microbial stability of intermediate‐moisture foods. The usage of a_w to predict microbial safety of foods has been discouraged on the basis that (1) in intermediate‐moisture foods the measured water vapor pressure is not an equilibrium one, and because a_w is a thermodynamic concept, it refers only to equilibrium; and (2) the microbial response may differ at a particular a_w when the latter is obtained with different solutes.

This review analyzes these suggestions on the basis of abundant experimental evidence found in the literature. It is concluded that nonequilibrium effects (e.g., inability of water to diffuse in a semimoist food) appear to be in many cases slow within the time frame (food's shelf life) of the experiments and/or so small that they do not affect seriously the application of the a_w concept as a predictor of microbial stability in foods.

The claims that a food science polymer approach to understanding the behavior of aqueous sugar glasses and concentrated solutions may be used to predict the microbial stability of food systems is not substantiated by experimental evidence. This approach does not offer, at the present time, a better alternative to the concept of a_w as a predictor of microbial growth in foods.

It is also recognized that a_w has several limitations and should be always used carefully, and this must include precautions regarding the possible influences of nonequilibrium situations. This aspect may be summarized by simply saying that anyone who is going to employ the term water activity must be aware of the implications of its definition.     

EFFECT OF PROCESS VARIABLES ON THE QUALITY OF SWORDFISH FILLETS FLAVORED WITH SMOKE CONDENSATE

An alternative technique to traditional smoking of swordfish was evaluated. Fillets were dry salted and/or brine salted in 30% NaCl, and smoked by dipping in smoke condensate solution at different concentrations. Chemical (water‐phase salt, pH, total volatile basic nitrogen, lipid oxidation), microbiological (total mesophilic count and fecal coliforms count) and sensory analyses were carried out in order to establish which technique gave the best results in terms of sensory quality. The different salting techniques gave different water‐phase salt contents, which influenced the microbial growth and the production of volatile bases. The smoke condensate concentration was ineffective toward microbial growth, but it was a differentiating factor for sensory panel. The dry‐salted product smoked with 5% smoke condensate was preferred because it maintained the natural taste of fish, coupled with a pleasant flavor of smoke.     

Rinse Treatment and Oxygen Barrier Properties of Films for Improving Quality Retention in Vacuum-Skin Packaged Fresh Chicken

Fresh chicken drumsticks rinsed with water or salt solution (28% NaCl) were vacuum‐skin packaged in films differing in oxygen transmission rate (OTR) (< 10, 3000, ≥ 7000 cm³/m²/24 h). Salt rinsing decreased surface lightness (CIE L*). Higher OTR films maintained surface redness (CIE a*) better than oxygen barrier film. Neither rinse nor film OTR had any effect on yellowness (CIE b*). Salt rinsing drumsticks also reduced drip loss. Counts of aerobic and coliform bacteria increased during storage for product in all films. Within each film, salt‐rinsed drumsticks had lower counts at 3 and 6 d of storage (through 12 d) for total aerobic and coliform bacteria, respectively. Product in low OTR (barrier) film generally had lower bacteria counts than product in higher OTR films.     

Microbial Growth Estimation in Liquid Media Exposed to Temperature Fluctuations

Comparisons of linear, square root and Arrhenius specific growth rate-temperature models showed no clear overall preference. At low a_w and refrigeration temperature, the linear model was satisfactory for Brochothrix thermosphacta and Pseudomonas fluorescens. A linear relationship between (specific growth rate)^?1 and lag phase was observed for these two psychrotrophs. The R² for B. thermosphacta in 3% (a_w= 0.968), 6% (a_w= 0.950), and 9% NaCl (a_w= 0.943) media was 0.865, 0.946 and 0.994, respectively. In 8% (a_w= 0.973) and 20% (a_w= 0.948) glycerol media, the R² was 0.998 and 0.999, respectively. R² for P. fluorescens growth in NaCl (3 or 4%) or glycerol (10 or 20%) media was >0.99. A cumulative growth adaptation function successfully estimated microbial growth at fluctuating temperatures.     

Non-destructive analysis of aw, salt and water in dry-cured hams during drying process by means of computed tomography

Computed tomography (CT) has been previously used as a non-destructive technology to accurately determine salt and water content in dry-cured ham at the initial stages of the elaboration process. However, since the accuracy of predictive models has been affected by the dry level of the sample, in this study, prediction models for salt and water contents and also for a_w to be applied during drying process were developed. Results showed that the number of independent variables needed to obtain regression models with a similar accuracy to the models previously developed is higher in drier samples. Furthermore, an important effect of fat content is also observed since prediction of a_w, salt content and water content were significantly improved when the fattiest samples were removed from the calibration or when fat content was included in the predictive models. Because of the different physicochemical characteristics of muscles, models developed specifically for Semimembranosus (SM), Biceps femoris (BF) or Semitendinosus (ST) muscles were more accurate. It can be concluded that models for prediction during the drying process were accurate enough to consider CT as a useful tool applicable for controlling and optimizing the dry-cured ham elaboration processes.     

Effect of water activity on the inactivation kinetics of Escherichia coli O157:H7 by electron beam in ground beef, chicken breast meat, and trout fillets

Water activity (a_w) of ground beef, chicken breast meat, and trout fillets was modified to intermediate (a_w 0.98–0.99) and lowest (a_w 0.94–0.96) levels. The meat samples with modified and unaltered (native, a_w 1.00) a_w were inoculated with Escherichia coli O157:H7 and subjected to electron beam (e‐beam). Survivor curves were plotted and the D₁₀‐values were calculated. The D₁₀‐values ranged from 0.22 kGy for trout at native a_w to 0.33 kGy for beef at intermediate, and chicken and trout at lowest a_w. Regardless of the species, a_w reduction increased E. coli resistance to e‐beam, suggesting that even small depletion of unbound water from food increases survival. The difference of the D₁₀‐values between the samples at intermediate and lowest a_w was insignificant. E‐beam could be used before a_w‐reducing techniques are applied to food products. However, this would require stringent microbial control following e‐beam processing. The ‘tailing’ of survivors was observed for some samples with reduced a_w.     

Effects of Water-Glycerol and Water-Sorbitol Interactions on the Physical Properties of Konjac Glucomannan Films

Konjac glucomannan (KGM)‐edible films were prepared with different amounts of glycerol or sorbitol as a plasticizer. Films were characterized by moisture sorption isotherm, and following conditioning at different relative humidities, by differential scanning calorimetry and tensile tests. Moisture and polyols (sorbitol and glycerol) were found to plasticize KGM‐based films with respect to their tensile properties. However, thermal properties and water sorption capacity (WSC) of polyolplasticized KGM films were found to vary with water activity (a_w), namely at low a_w (< 0.6), WSC and melting enthalpy were decreased with increasing in polyol content and the opposite was true at higher a_w (>0.6). This was attributed to extensive interactions between plasticizer and KGM that reduced the available active site (‐OH groups) for water adsorption. The presence of polyols at low a_w appeared to suppress crystalline structures due probably to restricted molecular mobility. These effects were diminished when the moisture content was >20%.     

Comparative Study on Organoleptic,Microbiological and Chemical Qualities of Dried Fish,Goldstripe Sardinella(Sardinella Gibbosa) with Low Salt Levels and Spices

Dried fish is very important component in Sri Lankan fishery productswhile current domestic production is estimated at around 40,000 tons per year. Generally, dried fish production in Sri Lanka is based on traditional methodology where 30% of salt is used averagely. Use of excess amount of salt can have negative health effects. Therefore production of dried fish with low salt is very important.Accordingly, partial substitution of salt with alternative substances can be done. Current study aimed at evaluating the effect of low levels of salt and combined effect of low salt and spices on quality of dried fish. The study was carried out using eviscerated and cleaned up GoldstripeSardinella with 0% (T1), 5% (T2), 10% (T3) salt levels and two different combinations of salt and spices (1%salt with 0.2%turmeric, 0.5%chlli, 0.5%pepper (T4) and 2%salt with 0.2%turmeric, 0.2%chlli, 0.2%pepper (T5)). Hot air dehydrator (65-70 °C) was used for fish drying. Chemical (moisture, water activity (a_w), Total volatile nitrogen (TVN), and sodium chloride), physical (texture and rehydration), microbiological (APC, mould and yeast count and coliform count) properties and sensory attributes of experimentally prepared dried fish were investigated. The chemical parameters for all treatments were significantly different (p<0.05) while physical parameters were not (p>0.05). T2 indicated the best chemical quality. The values for moisture, a_w, sodium chloride, TVN, texture and rehydration for T2, were 11.6584±0.03, 0.591±0.002, 12.43±0.15, 59.43 mg/100g±12.86, 1.54kg±0.14 and 12.70±3.54 respectively. T2 and T3 had least microbial counts while T1 and T5 had highest microbial count. But T5 had highest scores for all sensory attributes indicating consumer preference for low salt and spicy taste regardless of high TVN content and poor microbial quality.Therefore it is essential to improve the methodology to enhance the quality of low salt and spices added dried fish.     

Moisture sorption isotherms and isosteric heat of sorption of coffee in different processing levels

The desorption isotherms and thermodynamic properties of coffee from different processing stages were obtained during the drying process of this product. The isotherms were determined by a static gravimetric method for various temperature and humidity conditions. Equilibrium moisture content (M_e) data were correlated by several mathematical models and an artificial neural network (ANN) model. The M_e for coffee fruits, pulped coffee and green coffee increased with an increase in the water activity (a_w) at any particular temperature. At a constant a_w, coffee fruits samples had higher M_e than the remaining coffee samples. Based on statistical parameters, the ANN model, modified Henderson and GAB models were adequate to describe the sorption characteristics of the samples. Isosteric heat of sorption was evaluated by means of the Clausius–Clapeyron equation. It decreased with increasing moisture content. The coffee fruits had higher isosteric heat of sorption than that pulped coffee and green coffee.     

A World Survey of Water Activity of Selected Saturated Salt Solutions used as Standards at 25°C

This paper presents and discusses the results of a world survey of water activity (a_w) of selected saturated salt solutions used as standards by different researchers engaged in a_w determinations for food-related applications. Salt slurries cover the range of a_w about 0.57-0.97 at 25°C and are NaBr, NaCl (NH₄)₂SO, KCl, BaC1₂. 2H₂O, KNO₃ and K₂SO₄. The results indicate that there is a good agreement on the exact value to be assigned to NaBr, NaCl, KC1 and BaC1₂.2H₂O, and to a lesser extent, to K₂SO₄. However, a significant discrepancy exists between researchers on the a_w value assigned to (NH₄)₂SO₄ and KNO₃.     

Influence of storage temperature on the quality of salted mackerel (Rastrelliger kangurta) and pink perch (Nemipterus japonicus)

Dry-salted mackerel and pink perch were stored at two temperatures: ambient (26·8 ± 3·3°C) and 2·5 ± 1°C. Changes in moisture content, salt content, water activity (a_w), peroxide value (PV), free fatty acid content (FFA), total volatile base nitrogen (TVBN) content, halophilic bacterial count and sensory scores for overall acceptability were studied. Loss of moisture and absorption of salt were considerably higher in the products stored at ambient temperature. The decrease in a_w was more pronounced at ambient temperature than at the lower temperature. Although the chemical indices of freshness (PV, FFA and TVBN) and the halophilic counts showed increasing trends, they were considerably lower in the products stored at the lower temperature. Sensory evaluation for overall acceptability indicated that storage at the lower temperature could considerably extend the shelf-life of salted fish.     

Salting, drying and sensory quality of dry-cured hams subjected to different pre-salting treatments: skin trimming and pressing

The effects of skinning in a V-shape and pressing of hams on salting, drying and sensory characteristics of dry-cured hams were assessed. Salt and water contents and a_w were determined in the central part of the ham during processing by computed tomography. Overall salt and water contents were also chemically analysed. Sensory analyses were performed on the final product. Partial skinning or pressing increased both salt uptake and final weight loss, but did not reduce the intra-batch variability in salt uptake. Moreover, trimmed hams exhibited a higher salt content in the inner areas of the hams after resting. Trimmed dry-cured hams showed less metallic flavour, higher saltiness and more mature flavour in the biceps femoris muscle, and lower pastiness and adhesiveness as well as higher crumbliness and aged flavour in both the biceps femoris and the semimembranosus muscles. Pressing treatment caused less metallic flavour only in biceps femoris muscle and higher saltiness.     

Short communication: Little change takes place in Camembert-type cheese water activities throughout ripening in terms of relative humidity and salt

Water activity (a_w) affects the growth and activity of ripening microorganisms. Moreover, it is generally accepted that a_w depends on relative humidity (RH) and salt content; these 3 variables were usually measured on a given day in a cheese without the microorganism layer and without accounting for a distinction between the rind, the underrind, and the core. However, a_w dynamics have never been thoroughly studied throughout cheese ripening. Experimental Camembert cheeses were ripened under controlled and aseptic conditions (temperature, gaseous atmosphere, and RH) for 14 d. In this study, only RH was varied. Samples were taken from the cheese (microorganism layer)–air interface, the rind, and the core. The a_w of the cheese–air interface did not change over ripening when RH varied between 91 and 92% or between 97 and 98%. However, on d 5, we observed a small but significant increase in a_w, which coincided with the beginning of growth of Penicillium camemberti mycelia. After d 3, no significant differences were found between the a_w of the cheese–air interface, the rind, and the core. From d 0 to 3, cheese rind a_w increased from 0.94 to 0.97, which was probably due to the diffusion of salt from the rind to the core: NaCl content in the rind decreased from 3.7 to 1.6% and NaCl content in the core increased from 0.0 to 1.6%. Nevertheless, a_w did not significantly vary in the core, raising questions about the real effect of salt on a_w.