Ripening effect on chemical composition, microstructure, collagen solubility, shear force, texture parameters, and sensory evaluation: a case study of kumpia wieprzowa

Abstract

The aim of this study was to determine the changes in the microstructure as well as some texture and sensory parameters of kumpia wieprzowa – a unique traditional Polish meat product, subjected to a 3-month ripening period. The product was dried consequently, and therefore a decrease in the water content was simultaneous with an increase of protein, fat, and salt content, approximately 45, 70, and 26 g/kg, respectively. The well-preserved structure of perimysium corresponded with the Warner-Bratzler (WB) shear force, texture profile analysis (TPA) hardness, and TPA chewiness values. The final results of TPA hardness (134.6 N) correlated with water activity of 0.88 (p = –0.88) and 15 g/kg content of soluble collagen (p = 0.91). Despite the significant decline of the water content (145 g/kg), the perception of juiciness did not change in the sensory evaluation (4.4 points). Apart from the tenderness, the flavor desirability, saltiness as well as the flavor and odor intensity affected the overall evaluation.

El objetivo del presente estudio consistió en determinar los cambios que se produjeron en la microestructura, así como en algunos parámetros sensoriales y de textura de kumpia wieprzowa – un producto cárnico polaco, único y tradicional – que fue sometido a un período de maduración de tres meses. El producto fue deshidratado, debido a lo cual presentó disminución del contenido acuoso y, simultáneamente, aumento de los contenidos de proteína, grasa y sal, que registraron valores de aproximadamente 45, 70 y 26 g/kg, respectivamente. La bien preservada estructura de perimisio mostró correspondencia con los valores de la fuerza de corte wb, del apt (análisis de perfil de textura) de dureza y del apt de masticabilidad. Para el apt de dureza, los valores finales (134,6 N) se correlacionaron con la actividad acuosa de 0,88 (p = –0,88) y con el contenido de 15 g/kg de colágeno soluble (p = 0,91). La significativa pérdida de contenido acuoso (145 g/kg), no modificó la percepción de su jugosidad en la evaluación sensorial (4,4 puntos). Mientras que la ternura, el sabor deseado, lo salado, así como la intensidad de sabor y de aroma afectaron la evaluación general.

Keywords:

• kumpia wieprzowa
• pork
• ripening
• microstructure
• collagen
• texture
• sensory evaluation

Palabras claves:

• kumpia wieprzowa
• carne de puerco
• maduración
• microestructura
• colágeno
• textura
• evaluación sensorial

Introduction

Podlasie represents one of the few regions in Poland where the tradition of producing uncured cold meats and sausages is still observed. Today’s cold meats’ production practices follow the Lithuanian school with pork as the core ingredient. Cold meats and especially smoked bacon produced according to the traditional recipes are characterized by a sustained shelf-life and they are non-drying even if stored for several years. An important aspect of the traditional cold meats production process is selecting suitable products. Perfect meat can be obtained from 12- to 15-month old calves, fed with grain, especially barley and rye with a small amount of potatoes. Meat obtained from older pigs that are fed mainly with potatoes, pigswill, corn, or remainders from distillery is always of a lower quality. This kind of meat can be utilized in a better way, for instance for the sausages or salami, particularly if mixed together with the meat from little bulls (Fiedoruk, 2006). Utilizing meat obtained from too young or too greasy broods can result in precocious drying in the process of curing. Raw cold meats and sausages, which undergo the curing process in the Podlasie region, are produced not only from gammon, but also from pork shoulders, pork neck, and loin. The way of salting (dry salting or pickle curing), the time of dry smoking (from 10 days up to 3 weeks), spices selection (black pepper, allspice, coriander, bay leaves, garlic, and cloves), additives selection (saltpeter, sugar, and honey), and insect-preventing method used during the month-long curing process (wrapping meat in tissue-thin linen), all depend on the individual formula and technology transferred from generation to generation in given families. The kumpia wieprzowa was entered into the Polish list of traditional products on 6 December 2005 and is presently being prepared for registration into the European system as a regional product. Its characteristics, and in particular the physico-chemical and biochemical changes during the 3-month ripening were described by Węsierska, Szołtysik, Palka, Lipczyńska, and Lipczyńska-Szlaur (2012) as well as the microflora succession and biogenic amines increase by Węsierska, Korzekwa, Foks, and Mickowska (2013). The changes in the meat’s microstructure and its impact on the product brittleness have not yet been extensively studied or published in the scientific literature, despite its very rare raw material composition (shoulder spontaneously fermented as an entire large primal cut). The aim of this study was to determine changes in the muscle tissue’s microstructure, the solubility of intramuscular collagen, Warner-Bratzler (WB) shear force, and some texture and sensory parameters of kumpia wieprzowa, subjected to the 3-month ripening.

Materials and methods

Processed meat product

Kumpia wieprzowa was manufactured in a small-scale plant using a traditional meat fermentation method. The meat from Polish landrace pig breed (pbz) and spices were obtained from local producers (the Podlasie region in Poland). The standard feeding of pigs was carried out with farm fodder, in accordance with the tradition of feeding farm animals in the Podlasie region (barley, rye, and moderate addition of potatoes). Smoking procedures and the composition of spices were confidential. The product, processed as one unit from pork shoulder with external fat, was comprised of m. supraspinatus, m. infraspinatus, m. subscapularis and m. triceps brachii with the humerus. The weight of the meat cut fluctuated between 4 and 7 kg, bound to the age of the animal. The shoulder was dry salted with non-iodinated salt and seasoned for 3-week cold storage at 4–7–C. The excess salt was removed by drenching for 24 h (intended NaCl content: approximately 70 g/kg in the ready-to-eat product). After draining, it was smoked with cold smoke (15–25°C) and ripened in 12–15°C with a relative humidity of 85–90% for 2–3 months in a ripening room, depending on the weight. Three batches were produced. Three products, as the replications in each batch, were wrapped in greaseproof paper, packed into thermo-isolated bags, stored at 4–6°C and immediately distributed by courier to the partner laboratories for analysis for up to 24 h.

Sampling

Samples of the raw meat were collected just before the smoking procedures, after dry salting (ripening period: 0). The cuts were also sampled at different times throughout the ripening process (after the first, second, and third month of the ripening). After separating the material for sensory and microstructure analysis, the chemical composition (moisture, protein, fat, and salt), the total and soluble collagen content as well as the WB shear force and texture profile analysis (TPA) parameters were estimated.

Analysis

The moisture was determined by drying samples to their stable weight (Kolar, 1992). The protein content was determined with the use of the Kjeldahl method with the set-type 322 (Büchi, Switzerland) (NMKL, 1976). Fat was evaluated with the use of the Soxlet method with ethyl ether extraction (Foster & Sharon, 1992) and the salt content with the use of Mohr’s method (Kirk & Sawyer, 1991). The quantity of total and soluble collagen was measured according to Palka (1999). The total collagen content in the samples was measured by hydroxyproline determination. Soluble collagen was measured after heating the homogenized meat slurry prepared with a diluted Ringer solution at 77°C for 70 min. The chemical composition was estimated in triplicate at each sampling point. The WB shear force was determined using seven cylindrical samples of 14 mm in diameter and 15 mm in length cuts. The measurements were carried out for samples cut perpendicular to the fiber direction using a texturometer TA-XT2 (Stable Micro Systems, UK) and a WB knife with a triangular cut-out. The TPA analysis was conducted as described by Breene (1975) using a TA-XT2 texture analyzer with a 50-mm diameter cylindrical probe. Muscle samples of 14-mm in diameter and of 10-mm in length, cut lengthwise to the fibers, were compressed twice, parallel to the fiber direction to 70% of their original height at the probe travel rate before testing 5 mm/s, as well as during and after testing 2 mm/s, with a 3-s interval between the first and the second stroke. The TPA parameters of hardness and chewiness were chosen. Each measurement was repeated seven times. The results of the measurements were compiled with the use of the Stable Micro Systems Texture Expert software for Windows, version 1.05. The cold meats were evaluated based on a five-point scale which assumed the following levels of quality: 4.51–5.00 (very good); 3.51–4.50 (good); 2.51–3.50 (satisfactory); and 1.00–2.50 (unsatisfactory). The evaluation was conducted according to Polish standards (PN-ISO 4121, 1998) as well as (PN-ISO 6658, 1998) by a trained sensory panel of 16 people after the second and third month of ripening. The evaluated distinguishing features were assigned the following significance coefficients: 0.05 (overall impression), 0.05 (cross-section color), 0.10 (cross-section structure), 0.10 (odor intensity), 0.10 (odor desirability), 0.15 (juiciness), 0.15 (tenderness), 0.10 (saltiness), 0.10 (flavor intensity), and 0.10 (flavor desirability). The muscle tissue’s microstructure was analyzed with the use of Leo 435VP scanning electron microscopy (Carl Zeiss, Germany). Samples for the structure analysis were preserved by osmium tetrachloride and gluthar aldehyde and then, after dehydration with acetone, they were spread with gold (Cieciura, 1989). The statistical analysis was performed using the Statistica software for Windows, version 9.0 (USA). The effect of the ripening time on the chemical properties, texture parameters, and sensory quality was tested using a one-factor analysis of variance (ANOVA). The Scheffe and Duncan post-hoc tests were used for the comparison of the means (the significance of differences was investigated at p < 0.05).

Results and discussion

The changes in the chemical composition of the kumpia wieprzowa during the 3-month ripening are presented in Table 1. The product dried evenly and consequently a decrease in the water content, approximately 145 g/kg (p < 0.05), was simultaneous with an increase of protein, fat, and salt content of approximately 45 g/kg (p < 0.05), 70 g/kg (p < 0.05), and 26 g/kg (p < 0.05), respectively. A significant decrease of water activity (a_w) values, from 0.95 to 0.88 (p < 0.01), was associated with phenomena of slight drying, microstructural, and compositional modifications in the product during ripening (Martín-Sánchez et al., 2011). The same phenomenon was observed in other research (Węsierska et al., 2012), describing the changes of the biochemical properties of kumpia wieprzowa during ripening. The breakdown of some low molecular components by enzymatic reactions, additionally could favor the reduction of a_w in ripened product (Martín-Sánchez et al., 2011; Patrignani et al., 2007). A gradual decrease of pH value, from 5.8 to 5.4 (p < 0.01), was observed in kumpia wieprzowa during the first 2 months of ripening. At the third month of ripening, the value of pH did not change. As reported Spaziani, Del Torre, and Stecchini (2009) in some ripened meat products processed at low temperatures, fermentation can be limited and thus the pH does not decrease by more than 0.20–0.40 units. The qualitative changes that took place in the microstructure of the perimysium, endomysium, and myofibrils of kumpia wieprzowa during ageing are shown in Figures 1 and 2. The microstructure of the muscle and connective tissue, i.e. fibers and bundles of meat fibers as well as endo- and perimysium, was unspoiled after dry salting and smoking procedure (Figure 1). The myofibrills were strongly attached to each other by the endomysial connective tissue and the sarcolemma of those cells was still intact. The separation that can be seen between the muscle cells inside certain bundles was attributed to the effect produced by the chemical fixation and dehydration during preparation for scanning electron microscope (SEM). Other authors observed a similar effect in Teruel dry-cured ham at the beginning of production (Lepetit, 2007). Kumpia wieprzowa was characterized by the highest water content and a_w (Table 1) and the lowest WB shear force, TPA hardness, and TPA chewiness values (Table 2) at this stage of production.

Table 1. Physico-chemical properties of kumpia wieprzowa during ripening (mean, standard deviation, n = 3).

Propiedades físico-químicas de kumpia wieprzowa durante la maduración (media, desviación estándar, n = 3).

Ripening period (month)	0	1	2	3
Water (g/kg)	627.00 ± 0.11^a	594.00 ± 0.10^b	564.40 ± 0.13^c	479.30 ± 0.25^d
Protein (N x 6.25) (g/kg)	207.00 ± 0.03^a	218.60 ± 0.13^b	230.10 ± 0.58^c	250.80 ± 0.21^d
Fat (g/kg)	97.00 ± 0.04^a	113.00 ± 0.27^b	125.20 ± 0.35^c	168.00 ± 0.51^d
Salt (g/kg)	47.10 ± 0.02^a	53.30 ± 0.05^b	64.00 ± 0.37^c	73.30 ± 0.08^d
Total collagen (g/kg)	9.90 ± 0.04^a	10.20 ± 0.05^ab	10.40 ± 0.05^ab	10.50 ± 0.01^b
Soluble collagen (% of total collagen)	5.50 ± 0.25^a	6.10 ± 0.03^b	13.40 ± 0.10^c	15.10 ± 0.04^d
aw	0.95 ± 0.01^a	0.94 ± 0.01^b	0.90 ± 0.01^c	0.88 ± 0.01^d
pH	5.80 ± 0.02^a	5.69 ± 0.04^b	5.37 ± 0.04^c	5.35 ± 0.01^c

Note: ^a,b,c,dAll values in a row with different superscripts are different at p < 0.05.

Figure 1. The structure of kumpia wieprzowa at the beginning of ripening.

La estructura de kumpia wieprzowa al iniciarse la maduración.

Table 2. Influence of ripening on WB shear force, TPA hardness, and TPA chewiness of kumpia wieprzowa (mean, standard deviation, n = 3).

Influencia de la maduración en la fuerza de corte wb, dureza apt y masticabilidad apt de kumpia wieprzowa (media, desviación estándar, n= 3).

Ripening period (month)	0	1	2	3
WB shear force (kG/cm^2)	6.97 ± 0.67^a	8.46 ± 1.15^b	10.23 ± 0.32^c	13.04 ± 0.27^d
TPA hardness (N)	57.56 ± 1.90^a	61.95 ± 3.90^b	88.35 ± 2.98^c	134.63 ± 3.05^d
TPA chewiness (N)	10.01 ± 0.61^a	14.29 ± 0.70^b	18.40 ± 1.46^c	60.26 ± 1.99^d

Note: ^{a, b, c, d}All values in a row with different superscripts are different at p < 0.05.

In consequence of the first month of ripening, the increase of protein and fat content was accompanied by an increase of the WB shear force and the highest cohesion value (unpublished data). The salt content was 53 g/kg at that time of ripening and increased. According to Ruiz-Ramírez, Arnau, Serra, and Gou (2005), the muscles with higher NaCl content present a higher hardness. Larrea et al. (2007) suggested that the 14 days, in which the pieces are in contact with curing salts, are sufficient time to be penetrated. Presumably, the cause of these results is the compaction of the myofibrillar structure (Kemp, Sensky, Bardsley, Buttery, & Parr, 2010).

The increase of the solubility of intramuscular collagen of the kumpia wieprzowa was particularly visible at the second month of ageing and slightly rose during the following month. The results correlated with the observations of Węsierska et al. (2012), that an almost two-fold increase of free amine groups as protein degradation products was observed in kumpia wieprzowa between the first and at the second month of ripening.

In consequence of the slight drying and the further dehydratation during the 3-month ripening, the myofibrillar bundles were compacted with a large number of empty spaces or gaps between neighboring myofibrils (Figure 2). The distance between the muscle fibers decreased and the connective tissue endomysium shrank. Larrea et al. (2007) observed the cells bounded tightly together but with practically no endomysial connective tissue in the ready-to-eat Protected Designation of Origin (PDO) Teruel dry-cured ham. Katsaras and Budras (1992) asserted that endomysium compared to perimysium is more sensitive to the lactic acid effect. The collagen fibrils in the endomysium are additionally shorter (47–48 nm) than in the perimysium (65–67 nm) (Lepetit, 2007), and hence the individual perimysial layers are stronger and they are the major contributors to toughness (Lepetit, 2008; Purslow, 2005). The well-preserved microstructure of kumpia wieprzowa corresponded with the TPA hardness and TPA chewiness. The highest TPA hardness value obtained in the present study was 134.6 N and correlated with a_w = 0.88 (p = –0.88) and with 1.5% content of soluble collagen (p = 0.91). The correlation between the protein content and the TPA chewiness (p = 0.87) was ascertained both after the second and third month of ripening. The consistence, slightly plastic at the beginning, became more elastic at the end of the ripening. Similar findings involving rheological features of dry-cured hams were made by Monin et al. (1997) and Serra, Ruiz-Ramírez, Arnau, and Gou (2005). According to Ruiz-Ramírez et al. (2005), a dry-cured muscle with a higher NaCl content showed a higher TPA hardness, TPA cohesiveness, and TPA springiness, especially in those with pH <5.7. The final value of kumpia wieprzowa’s pH was 5.3 (Table 1). Moreover, Monin et al. (1997) observed transverse myofibrils cracks and muscle fiber damage during the dry-cured hams processing. The mentioned changes were not confirmed in kumpia wieprzowa. The differences in TPA hardness and tenderness value, evaluated by a sensory panel in that time period (Table 3) were difficult to explain. In spite of the increase of TPA hardness and TPA chewiness, which could be a result of water loss, the perception of the juiciness did not change in the sensory estimation. Ruiz-Carrascal, Ventanas, Cava, Andrés, and García (2000) also did not find a significant relationship between the degree of dehydration (water content) and the sensory textural characteristics (hardness, dryness, and juiciness) in Iberian dry-cured hams, though Serra et al. (2005) described a significant negative correlation between moisture content and hardness (compression 50%) in several commercial dry-cured hams. Simultaneously, the saturation of kumpia wieprzowa proceeded as a result of the curing smoke compounds. Repeated smoking was not conductive to the degradation of the connective tissue, including the perimysium. Thanks to the tanning interaction of the curing smoke compounds, among others with the connective tissue proteins, they became more insensitive to the physico-chemical agents. Likewise, Okonkwo and Ledward (1992) considered that the long-lasting smoking causes an increase in the hardness of the meat products. The smoking influenced the sensory evaluation of kumpia wieprzowa – the flavor desirability as well as flavor and odor intensity obtained the highest grades in a 3-month product. Those features affected the increase of the overall evaluation from 4.3 to 4.4 points. The final product was characterized by a red-brown color and marbled cross section. The flavor was salty, characteristic for dry meat, and depended on a variety and proportion of spices used (the bay-leaf aroma was distinguishable). The changes of the cross-section color and the cross-section structure values in the sensory estimation were not statistically significant.

Figure 2. The structure of kumpia wieprzowa after 3rd month of the ripening.

La estructura de kumpia wieprzowa después de 3 meses de maduración.

Table 3. Sensory quality of kumpia wieprzowa during ripening (mean, standard deviation, n = 3).

Calidad sensorial de kumpia wieprzowa durante la maduración (media, desviación estándar, n = 3).

Ripening period (month)	0	1	2	3
Overall impression	–	–	4.25 ± 0.53a	3.77 ± 0.53b
Cross-section color	–	–	4.04 ± 1.08	3.68 ± 0.57
Cross-section structure	–	–	4.37 ± 0.71	4.14 ± 0.71
Odor intensity	–	–	4.25 ± 0.74a	4.73 ± 0.70b
Odor desirability	–	–	4.29 ± 0.81	4.09 ± 0.68
Juiciness	–	–	4.46 ± 0.66	4.45 ± 0.74
Tenderness	–	–	3.96 ± 0.69a	4.45 ± 0.67b
Saltiness	–	–	4.72 ± 0.44	4.77 ± 0.43
Flavor intensity	–	–	4.50 ± 0.64a	4.75 ± 0.40b
Flavor desirability	–	–	4.27 ± 0.67	4.50 ± 0.60
Overall evaluation	–	–	4.32	4.41

Note: ^{a, b, c, d}All values in a row with different superscripts are different at p < 0.05.

Conclusions

Although changes in the muscle fibers and connective tissue membranes configuration are visible, the perimysium had a well-preserved structure during ripening. Depending on the stage of ripening, the values of the WB shear force as well as TPA hardness and TPA chewiness increase equally, however the most considerable increase of TPA hardness and TPA chewiness is visible between the second and third month. These results correlate with the decline of a_w and the increase of the soluble collagen content. These findings also correspond with the increase of the protein, fat, and salt content due to the water loss and with changes in the muscle microstructure. In spite of the significant decline of the water content, the perception of the juiciness is not changed in the sensory evaluation. Smoking procedures, the composition of spices and the optimum treatment duration can affect the sensory quality of kumpia wieprzowa. Apart from the tenderness, the flavor desirability, saltiness as well as flavor and odor intensity obtain the highest grades in the 3-month product. Those features affect the increase of the overall evaluation of the ready to eat product.

Acknowledgements

The studies were supported by Grant No. NN312305740 from the Polish Committee of Scientific Research in Department of Animal Product Technology, University of Agriculture in Krakow, Poland.