Introduction

Fermented sausage is one the most important meat products in the world. And Turkish-style fermented sausage, also known as sucuk, on the other hand, is the most commonly consumed meat product in Turkey. Sucuk is produced from beef, fat, various spices and curing agents. The fat content of the sucuk is substantially high (30–40%), and fats perform significant technological and sensory functions in sucuk (Yıldız-Turp and Serdaroglu 2008). However, it is suspected that the consumption of processed meat products increases the risk of developing some disorders, such as colorectal cancer and coronary artery disease, due to their high-fat level and curing agents (salt, nitrite, nitrate) (Ferguson 2010; Thøgersen and Bertram 2021). To minimise these negative effects, it is highly encouraged to improve meat products by altering the components used in the product formulation or adding certain healthy ingredients to those products.

One possible alternative to increase healthy food consumption is the use of dietary fibre. Dietary fibre, an indigestible carbohydrate, is classified as either soluble or insoluble (Verma and Banerjee 2010). Dietary fibre has received a great deal of attention from researchers since becoming known as a nutraceutical, which may be used in meat technology from a health point of view. Studies have shown that dietary fibre is vital for preventing diverticular disorders, normalising intestinal motility, lowering serum cholesterol levels, and reducing the risk of hypertension and diabetes (Garau et al. 2007; Wen et al. 2020). Therefore, it is beneficial to consume food that contains dietary fibre, daily.

Dietary fibre is present at high concentrations in cereals, vegetables and fruits. Among all dietary fibre, particularly citrus fibre and albedo are appropriate for meat technology to enhance cooking efficiency; improve textural, colour, and sensorial properties; act as a fat substitute; function as a natural antioxidant, and hold water and oil (Aleson-Carbonell et al. 2004). Albedo is a spongy, light coloured and cellulosic compound consisting in large part of citrus peel (Fernández-Ginés et al. 2004). As a high-fibre component of citrus fruits, albedo can be considered as a potential fibre source. Albedo is not only a good source of dietary fibre but also a source of bioactive components, such as vitamin C, flavonoids and other antioxidants, which increase its effectiveness (Aleson‐Carbonell et al. 2003). Therefore, many studies have focused on the use of fibre and albedo in unfermented and fermented sausage. For instance, in their study, Aleson‐Carbonell et al. (2003) used lemon albedo in dry‐cured sausages. In another study, Aleson-Carbonell et al. (2004) examined some parameters of a non-fermented sausage supplemented with lemon albedo. Similarly, Fernández-Ginés et al. (2003) investigated the effects of citrus fibre on quality parameters of bologna sausages. Furthermore, Yalınkılıç et al. (2012) studied the effects of different concentrations of fibre on some quality characteristics of fermented sausage. Coksever and Saricoban (2010) studied the effects of bitter orange albedo addition on some parameters of fermented Turkish-style sausages. The addition of albedo or fiber indicated that decreasing residual nitrite levels, delayed oxidation, increased cooking yield and lightness values, and improved texture and sensory evaluation.

Even though there are some research conducted on the effects of various types of fibre and albedo, to the best of our knowledge, none of them in the literature focused on the use of pre-treated bitter orange albedo in fermented sausage. Among citrus fruits, the bitter orange is one of the most popular. Bitter oranges, also known as sour oranges, belong to the Citrus genus and Rutaceae family. Bitter orange is referred to as Citrus aurantium L. and cultivated in Mediterranean countries. It is widely used in the perfumery, flavouring and food technology industries, especially in fruit juice processing (Farag et al. 2020; Farahmandfar et al. 2020). Due to their acidity and bitter taste, bitter oranges are not consumed as fresh fruit. These oranges contain slightly more pectin than sweet oranges (Farag et al. 2020). Because of the reasons mentioned above, pre-treated bitter orange albedo is considered a good choice for a dietary fibre source for sucuk production. Considering its benefits, this research aims to assess the effects of the pre-treated bitter orange albedo on the physicochemical, textural and sensory properties of Turkish-style fermented sausages (sucuk).

Material and methods

Material

Beef (boneless rounds) was purchased from a local butcher (Konya, Turkey). Spices and collagen casings (Fibran, Girona, Spain) were obtained from a local market in Konya. Albedo was obtained from bitter orange (Citrus aurantium L.) fruits, which were imported from the Mediterranean Region of Turkey (Adana). The debittering method used by Turgut et al. (2016) was applied to bitter albedo, with minor modifications. Firstly, the albedo layer was removed from the fruit. Then, it was heated at 80 °C for approximately 10 min, and the processing water was changed after 12 h. After staying in the water for approximately one day to eliminate its bitter taste, the aqueous albedo was filtered and then dehydrated at 21 °C for 10 days. The main purpose of the dehydration process was to enhance the shelf life of albedo by decreasing its water content. Processed and dehydrated albedo was homogenised with a Waring Commercial Blender (USA) to obtain the appropriate particle size.

Sucuk preparation

For sucuk production, beef meat and tallow fat were cut into pieces. All additives were prepared as follows: NaCl (2.00%), garlic (1.15%), red pepper (0.75%), black pepper (0.45%), cumin (0.50%), sucrose (0.50%), sodium nitrate (0.010%) and sodium nitrite (0.015%). This mixture was added to the meat and tallow fat, and then they were minced in a grinder (Arı Makina, Turkey) through a 3-mm plate (Coksever and Saricoban 2010). Sucuk batter was divided into four equal parts, (1) control (without albedo), (2) pre-treated bitter orange albedo (1%), (3) pre-treated bitter orange albedo (2.5%) and (4) pre-treated bitter orange albedo (5%), and mixed again separately. Each sucuk batch was stuffed into casings (diameter 38 mm) with a stuffing machine (VEMAG Maschinenbau GmbH, Germany). The sucuk samples were naturally fermented without a starter culture and ripened for 21 days at ambient temperature with 70–85% relative humidity (RH).

Sampling

Sucuk samples were removed after the stuffing process (day 0) and during the ripening period on days 1, 3, 5, 7, 9, 14 and 21. pH, titratable acidity, weight loss, texture and colour were monitored throughout the ripening period. Water activity (aw), oxidative rancidity, penetrometer and microbial analysis were carried out on days 0, 7, 14 and 21 of ripening. Fat, protein and moisture analyses were carried out on the first and final samples. Sensory analysis (colour, total acceptability, texture, appearance and flavour) was done on the final sample after processing. Two samples were randomly selected (each approximately 100 g in weight) from each sucuk group for each analysis. Experiments were carried out in two replications. The analyses were repeated in triplicate for each analysis method.

Proximate analysis

The moisture, protein and fat content of the sucuk samples were measured according to standard procedures of the AOAC (2000). The equipment used for these analyses were as follows: hot air oven (Nüve, Turkey), Kjeldahl nitrogen/protein analysers (Velp Scientifica, Italy) and Soxhlet extractor, respectively. The pH value was determined by the Ockerman (1985) method, with a pH meter (pH 315i/SET WTW, Germany).

Physicochemical analysis

The titratable acidity values of the samples were determined according to Gökalp et al. (2012). The pH of the sucuk was measured with a pH meter (pH 315i/SET WTW, Germany), then the samples were titrated (0.1 N NaOH) to an endpoint of pH 8.30. To determine the total acidity, the meq of NaOH were converted to and expressed as per cent lactic acid.

Water activity was determined with a water activity system (Testo 650, Germany). Weight loss was observed according to Coksever and Saricoban (2010). Penetrometer values were measured using standard methods with a penetrometer (K 19,500 model, Koehler Instrument Company Inc, USA) (Candoğan and Kolsarıcı 2003). Colour properties L* (lightness), a* (± red–green) and b* (± yellow–blue) were determined with a chromameter CR-400 (Konica Minolta, Inc., Osaka, Japan) according to the CIE Lab. Direct evaluation of the sucuk was carried out six times.

Thiobarbituric acid (TBA) values

The TBA method was applied to measure oxidative rancidity of the sucuk groups (Gökalp et al. 2012; Ockerman 1985). Ground sucuk samples were mixed with distilled water. Then, 48.5 mL of water and 2.5 mL of HCl were added to this mixture. The collected distillate was transferred to TBA reagent and incubated in a water bath. The absorbance was read with a spectrophotometer (UV-160 A, UV-Visible Spectrophotometer, Shimadzu, Tokyo, Japan). The TBA numbers of the sucuk samples were expressed as milligrams of malonaldehyde per kilogram of sample.

Lactic acid bacteria (LAB) count

A 25 g sample was removed aseptically from each of the sucuk samples, transferred into sterile pouches containing 225 ml peptone water (0.1%) (Merck, Germany) and homogenised in a stomacher (Lab Blender, Seward, London). After homogenisation, serial decimal dilutions were carried out in the same diluent. LAB counts were performed using MRS Agar (Merck). Plates were incubated at 30 °C for 48 h (Baumgart et al. 1993).

Texture analysis

Textural parameters were measured with a texture analyser (TA.HD Plus texture analyser, 50 kg load cell, test speed 2 mm/sec, trigger force 5 g, Stable Micro Systems, England) by using a computer software program (Palamutoglu and Saricoban 2016). The sucuk samples were cut into cylinders and equilibrated at room temperature (21 °C). A cylinder probe (36 mm) was used to determine the texture measurement, applying 50% compression (strain).

Sensory analysis

Sensory analysis of the sucuk groups was performed by the experienced panellists consisting of 10 staff members from the Food Engineering Department at Selcuk University. Preparation to sensory evaluation the samples were removed from the casings, cut into 0.5-cm-thick slices and cooked for 60 s per side, with a total grilling time of 120 s. The sucuk samples were coded with four-digit random numbers and placed in random order. The panellists participated in two sessions, and in each session, eight samples (two pieces from each sample group) were presented to each panellist. Then, the samples were served to the panellists, who evaluated their appearance, colour, texture, flavour and total acceptability. The scores for each sample were given on a hedonic scale of 1 (worst) to 9 (best). Between samples, the panellists used unsalted bread and water to clean and neutralise their palate. Analyses were repeated twice, and the samples were selected randomly (Gökalp et al. 2012).

Statistical analysis

All data were subjected to statistical analysis using MINITAB for Windows Release 16.0. The collected data were analysed by two-way analysis of variance (ANOVA) with the ripening period and pre-treated bitter orange albedo (PA) concentration (0% PA (control), 1.0% PA, 2.5% PA and 5.0% PA) as factors. The mean values were compared by using Tukey’s Multiple Comparison Test. Each parameter was tested in triplicate samples with two replications.

Results and discussion

Proximate analysis

Table 1 indicates the results of proximate analysis of the sucuk samples. The moisture and fat contents were significantly (P < 0.05) affected by the PA concentration at the beginning and end of ripening. While the moisture values of the initial samples decreased with the addition of PA, the moisture values increased in the final samples. Among the final sucuk groups, the control group (20.01%) had the lowest moisture values. This may be related to the fact that albedo increases the water holding capacity of fermented sausage due to the pectin component of citrus fruits. Aleson‐Carbonell et al. (2003) supported this argument indicating that the use of lemon albedo increased the moisture levels of dry-cured sausages. Analyses also showed that the addition of PA decreased the fat content. In terms of health, a decrease in the fat proportion can be considered as a positive aspect of sucuk consumption. Looking at the protein content, it was found that the PA level had no significant (P > 0.05) effect on the protein content of final sucuk. This result contradicted with the Fernández-Ginés et al.'s (2004) findings. According to their study, the protein levels of bologna sausages increased when lemon albedo concentration was increased.

Table 1 Moisture, protein and fat contents of sucuk samples at the begining and end of ripening
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Finally, when the initial and the final sucuk samples were compared, it was observed that the moisture values of the sucuk samples decreased, whereas their protein and fat values increased. Similar to our findings, Ercoskun, Tagi, and Ertas (2010) reported that the fat and protein contents of the samples increased during fermentation due to the drying of sucuk.

Physicochemical analysis

The pH and titratable acidity (TA) contents of the sucuk samples were significantly affected by the albedo concentration and ripening period (P < 0.01). The lowest pH (5.45) and highest TA (1.81%) values were observed with the addition of 5% PA. The addition of PA decreased the pH values of the sucuk groups. Aleson‐Carbonell et al. (2003) indicated that the pH values of the sucuk samples ranged between 5.63 and 6.01. In another study, it was found that the addition of dehydrated cooked lemon albedo decreased the pH values of dry-cured sausages (Aleson-Carbonell et al. 2004). Fernandez-Lopez et al. (2007) also reported that the pH of dry-cured sausages decreased with the addition of orange fibre. This decrease might be related to the acidic compounds in orange fibre. Nevertheless, Fernández-Ginés et al. (2003) found that citrus fibre did not significantly affect the pH values of bologna.

As seen in Table 2, increasing the ripening time decreased the pH of the sucuk samples significantly. In the first seven days of ripening, the pH decreased from 5.99 to 4.64. Thereafter, the pH values of samples began to increase along with the ripening period. Similar findings were reported in the literature. In their study, Bozkurt and Bayram (2006), Bozkurt (2007), and Cicek and Polat (2016) found that the pH values of fermented sucuk initially decreased and then increased towards the end of ripening. According to Wanangkarn et al. (2012), a sharp decrease in pH in the first days of ripening is key to the quality and safety of fermented meat products.

Table 2 pH, titratable acidity, weight loss and colour (L*, a*, b*) properties of sucuk samples during ripening
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The drop in the pH value in the sucuk groups was related to lactic acid production, which changed during the ripening period due to lactic acid accumulation (Fernandez-Lopez et al. 2008). Throughout the ripening period, the highest TA (2.04%) was on the seventh day of ripening.

Table 2 shows the weight loss (WL) values of the samples. The albedo level and ripening period had a significant (P < 0.05) impact on the WL values. Among the treatments, the lowest WL was found with the addition of PA to the sucuk group. The same effect was reported by the Sánchez-Zapata et al.'s study (2013) indicating that the tiger nut fibre addition reduced the weight loss of Chorizos. This situation may be associated with the high water-holding capacity of albedo due to the pectin component of citrus fruits (Fernández-Ginés et al. 2004). An increased ripening period resulted in greater weight losses due to the drying process in the fermentation time, as expected. This effect was in accordance with the findings of Coksever and Saricoban (2010).

Colour results

Colour properties (L*, a*, b*) of the sucuk groups were presented in Table 2. The albedo concentration and ripening period had significant (P < 0.05) effects on the L* (lightness) values of the samples. The lightness value increased when PA was added to the sucuk. Similar results for the L* value were observed by Yalınkılıç et al. (2012), who reported that the L* value increased with the concentration of orange fibre. Likewise, Fernández-Ginés et al. (2003) stated that L* values increased when fibre was added to bolognas. They explained that the observed increase could be high in white parts of citrus albedo.

Besides, our results showed that the L* values increased from 48.24 to 51.84 throughout the initial seven days of the ripening period. Then, these values began to decrease in the sucuk samples. This result was consistent with other studies reporting that the lightness of the samples increased during the first six days of ripening, then decreased during the remaining ripening time (Bozkurt 2007).

In our study, the addition of albedo did not change the redness (a*) values of the sucuk group, while yellowness (b*) was significantly affected by the addition of albedo. Similarly, Fernandez-Lopez et al. (2007) also reported that the increased b* values of sausages could be attributed to the presence of yellow pieces of the bitter orange albedo which could not be cleaned fully in the albedo preparation.

The a* values increased significantly during the three days of ripening and then began to decrease the following day. The increase in a* values depended on the conversion of colour pigment. It was likely that nitrosomyoglobin pigment was forming on the first days of fermentation (Lücke 1994). This result was consistent with Yalınkılıç et al. (2012). Pérez-Alvarez et al. (1999) also stated that redness values of dry-cured Spanish sausages increased in the initial fermentation time and then decreased in the remaining days of the ripening period.

As seen in Table 2, the yellowness values of the samples decreased during the ripening period. Similar decreases in b* values have been reported by some researchers (Ercoskun, Tagi, and Ertas 2010; Pérez-Alvarez et al. 1999; Yalınkılıç et al. 2012). The reduction in yellowness values has been attributed to myoglobin conversion (Aleson-Carbonell et al. 2004).

TBA, water activity and penetrometer values

The albedo concentration and ripening period had significant (P < 0.05) effects on the oxidative rancidity value of the sucuk samples (Table 3). When the levels were investigated, using 1% PA decreased TBA values, but generally, TBA values increased as PA levels increased. In a study on the sucuk supplemented with orange fibre, it was specified that orange fibre addition increased the TBARS values of the sucuk samples (Yalınkılıç et al. 2012). Similar results were also found by Aleson-Carbonell et al. (2005), that the TBA values of beef burger increased with lemon albedo addition.

Table 3 TBA, water activity (aw), penetrometer values and lactic acid bacteria counts of samples
Full size table

It was observed that TBA values increased significantly (P < 0.05) with increasing ripening time. TBA values ranged between 0.24 and 0.37 mg MA/kg in the ripening period. Yalınkılıç et al. (2012) also found that lipid oxidation increased during the fermentation period. In our study, TBA results of fermented sucuk samples were lower than the references levels (P < 0.01); therefore, Yıldız-Turp and Serdaroglu (2008) reported that the acceptable maximum lipid oxidation level of samples should be lower than 1.0 mg MA/kg sample.

As shown in Table 3, the aw of the samples was not significantly (P < 0.05) affected by the albedo concentration. As Yalınkılıç et al. (2012) also indicated the aw of the sucuk samples had not been affected by the addition of orange fibre. However, increasing the ripening time decreased the aw values (P < 0.01). The aw values ranged between 0.910 and 0.798 in the sucuk groups.

The penetrometer values of the sample group were significantly affected (P < 0.05) by the use of PA. Increasing the albedo level decreased the penetrometer values of the samples. Comparing the two groups, it can be easily observed that the penetrometer values were lower in the albedo-supplemented sucuk group than the control group. Aleson‐Carbonell et al. (2003) evaluated the effects of different raw and cooked lemon albedo levels of the sausages. Parallel to our results, they observed that the highest hardness value was found in the sausages with 5% added lemon albedo. Similarly, Coksever and Saricoban (2010) and Fernández-Ginés et al. (2003) stated that adding fibre resulted in a firmer texture.

The ripening period had a significant (P < 0.05) effect on the penetrometer values. Penetrometer values decreased from 189.02 to 75.94. The decrease in this value was potentially due to the drying of the sucuk samples during the ripening period. That, in turn, may increase the hardness of the sucuk. Throughout the ripening period, water was lost from the samples.

Lactic acid bacteria (LAB) counts

The effect of the albedo level and ripening period on LAB counts was statistically significant (P < 0.05). As seen in Table 3, the highest LAB count was observed in the sucuk group with 5% PA, which possessed the lowest pH value (5.45). The same effects on sucuk were reported by Yalınkılıç et al. (2012). They found that the use of orange fibre significantly decreased the pH value. They also reported that the higher LAB counts in samples containing orange fibre were likely due to the pH-lowering influence of the fibre or the possible stimulatory influence of the fibre on LAB.

The LAB counts increased during 14 days of ripening, then decreased to 5.82 log cfu/g at the end of the ripening period. Similar results were found for LAB counts by some researchers (Ercoskun et al. 2010; Sayas-Barberá et al. 2012), whereas LAB counts in the present study were lower than in those studies. It is thought that this situation is likely due to the efficiency of the starter culture and ripening conditions. Lactic acid bacteria indicate important growth throughout fermentation and begin to occur as the dominant microflora in the sucuk. As Capita et al. (2006) also pointed out the lactic acid bacteria were the predominant microorganisms with the capability to adapt in fermented foods during storage.

Texture profile results

Table 4 demonstrates the textural parameters of sucuk samples. Ripening time and albedo concentration significantly (P < 0.01) increased the hardness, springiness, gumminess and chewiness values of the sucuk. Hardness increased during the ripening time in all of the sucuk groups. Similarly, Bozkurt and Bayram (2006) observed that sample hardness increased during the 16 days of ripening. This results could be explained as a decrease in the level of moisture and coagulation of proteins at acidic pH values. Gumminess and chewiness values also increased during the ripening time. Szczesniak (2002) found that increased chewiness and gumminess values led to a tougher structure during ripening.

Table 4 Hardness, adhesiveness, springiness, gumminess, and chewiness results of sucuk samples during ripening
Full size table

Albedo addition altered the textural properties of the sucuk samples, except for the adhesiveness value. As with the penetrometer values, hardness increased as the PA addition level increased. Albedo concentration had a significant effect on the hardness, springiness, gumminess, and chewiness values of the samples. As the PA concentration increased, the values of these parameters also increased (P < 0.05) throughout ripening. Compared to the control group, hardness, gumminess, and chewiness were higher in the albedo-supplemented groups. Similar result was also found by Aleson‐Carbonell et al. (2003) in dry-cured sausages formulated with cooked albedo. Sánchez-Zapata et al. (2013) stated that the springiness, gumminess and chewiness values of the samples increased when tiger nut fibre was added to dry sausages. They also reported that textural parameters of meat products changed depending on the fibre type. This was probably because the consistency of meat products could be increased using insoluble fibre due to its capacity to modify the products’ textural characteristics. (Sánchez-Zapata et al. 2013).

Sensory analysis

Figure 1 shows the appearance, texture, colour, flavour and total acceptability of the albedo-supplemented sucuk samples. The addition of PA had a significant (P < 0.05) effect on the appearance, texture, colour, flavour and total acceptability of the sucuk groups. According to Tukey’s multiple range test for sensory parameters, the highest scores were in samples with PA, relative to the control group. The panellists generally accepted the use of PA in sucuk samples. As the PA level increased, the mean scores for appearance also increased. Although the highest mean score for texture was observed in the 2.5% inclusion group, the differences between other sucuk groups were not statistically significant, except for the control group. Considering the mode of sucuk consumption, hard texture and firm structure are the properties that generally desired (Kilic 2009). As shown in the penetrometer results, penetrometer values were higher in the samples with albedo than in the control group (Table 3). Since sucuk has a distinctive colour and flavour, adding an excessive amount of albedo could have reduced the colour and flavour scores. According to the total acceptability scores, 1% and 2.5% PA should be used in sucuk samples. Aleson‐Carbonell et al. (2003) also reported that the highest general quality was determined in sausages with the addition of 2.5% lemon albedo.

Fig. 1
figure 1

Sensorial results of final sucuk groups

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Conclusion

The addition of pre-treated bitter orange albedo improved the physicochemical, microbiological, textural and sensory properties of fermented sausages. When PA was added as an ingredient in fermented sausages (sucuk), it decreased the pH and fat value of the final product. The lowest weight loss was found with the addition of PA to the sucuk group. L* and b*values of the sucuk group increased with the concentration of PA. Albedo addition affected the growth of lactic acid bacteria. The level of albedo added in the samples had no inhibitory effect on lipid oxidation. However, PA addition altered the textural properties of the sucuk groups. The albedo concentration increased the hardness, springiness, gumminess and chewiness of sucuk. In sensory analysis, higher scores were obtained for samples with PA than in the control group. Overall, results indicated that adding PA (2.5%) to sucuk is recommended to improve healthy sucuk consumption. PA would be considered an alternative dietary fibre source, and in addition to all, further research would be needed to improve the quality of the processed meat product.