Evolution of oxidation parameters
During the fermentation stage (15 days), the parameters indicating lipid oxidation (TBARS) and proteins (thiol) were determined. Regarding the TBARS values, they went from 0.03 ± 0.03 to 0.15 ± 0.33 mg MDA/kg of sausage in the control batch, from 0.03 ± 1.09 to 0, 02 ± 0.001 mg MDA/kg of sausage in batch S1, and from 0.03 ± 0.001 to 0.01 ± 0.02 mg MDA/kg of sausage in batch S2 (Table 2a). These results show that the fermentation stage and the level of clove addition significantly affected the TBARS values (p > 0.05); since the TBARS values gradually decreased throughout the fermentation stage and with the level of clove addition. This trend could be attributed to the antioxidant effects of cloves. This observation is similar to the work of Sharma et al [10], who found that clove oil significantly decreased TBARS levels in sausages. Thus, the results obtained show that clove extracts were effective in protecting sausages against lipid oxidation during the fermentation phase.
Table 2: (a) physico-chemical and colorimetric parameters, (b) Secondary structure determined from MIR spectra of different sausage batches during the fermentation stage, (c) classification table of FDA with leave-one-out cross-validation for physico-chemical and colorimetric and MIR data sets of different sausage batches during the fermentation stage taking into account the fermentation stage , and (d) classification table of FDA with leave-one-out cross-validation for physico-chemical and colorimetric and MIR data sets of different sausage batches during the fermentation stage taking into account the formulation.
Table 2a:
Fermentation (day)
|
Control
|
S1
|
S2
|
|
Thiol (nmol mg/ protein)
|
1
|
2.58 ± 0.007 a
|
3.03 ± 0.001 b
|
3.04 ± 0.909 b
|
5
|
2.88 ± 0.21a
|
3.06 ± 0.43b
|
3.79 ± 0.21b
|
10
|
2.78 ±0 1.09a
|
3.00 ± 0.72b
|
3.01 ± 0.01b
|
15
|
2.45 ± 1.21a
|
3.00 ± 1.04b
|
3.00 ± 0.45b
|
TBARS (mg MDA / kg of sausages)
|
1
|
0.03 ± 0.03a
|
0.03 ± 1.09a
|
0.03 ± 0.001a
|
5
|
0.07 ± 0.01a
|
0.04 ± 0.32b
|
0.04 ± 0.01b
|
10
|
0.07 ± 0.01a
|
0.04 ± 0.03b
|
0.03 ± 0.01b
|
15
|
0.15 ± 0.33a
|
0.02 ± 0.001b
|
0.01 ± 0.02b
|
L*
|
1
|
42.97 ± 0.45a
|
40.59 ± 1.09b
|
41.86 ± 0.32b
|
5
|
38.14 ± 0.21a
|
41.28 ± 0.21b
|
40.87 ± 0.25b
|
10
|
38.14 ± 0.56a
|
41.28 ± 0.42b
|
41.42 ± 1.90b
|
15
|
36.83 ± 2.00a
|
39.85 ± 1.07b
|
40.07 ± 0.01b
|
a*
|
1
|
16.00 ± 0.12a
|
13.82 ± 1.04b
|
13.29 ± 1.08b
|
5
|
14.68 ± 0.25a
|
13.56 ± 0.60b
|
12.51 ±0.00b
|
10
|
13.68 ± 1.23a
|
12.56 ± 1.52b
|
12.66 ±0.01b
|
15
|
13.11 ± 0.43a
|
12.00 ± 1.21a
|
12.03 ± 0.21a
|
b*
|
1
|
37.48 ± 1.98a
|
33.53 ±1.104b
|
33.44 ± 1.12b
|
5
|
31.78 ± 0.09a
|
30.42 ± 0.21b
|
29.62 ± 1.09c
|
10
|
30.62 ± 0.43a
|
29.42 ± 1.53b
|
29.28 ± 1.21b
|
15
|
27.50 ± 0.54a
|
25.70 ± 2.09b
|
24.90 ± 1.07b
|
Means ± standard deviations; Different capital letters (A. B. C) represent statistical difference between the formulations (p < 0.05); Control: sausages with 80% chicken fillet, 18% veal fat and 2% sesame flour; S1: sausages with 80% chicken fillet, 17% veal fat, 2 % sesame flour, and 1% cloves; S2: sausages with 80% chicken fillet, 16% veal fat and 2% sesame flour, and 2% cloves
Table 2b:
Fermentation time
|
Control
|
S1
|
S2
|
|
α-helix (%)
|
1
|
17.41a
|
17.63b
|
17.66c
|
5
|
17.50a
|
17.54b
|
17.39c
|
10
|
17.50a
|
17.39b
|
17.40c
|
15
|
17.50a
|
17.28b
|
17.40c
|
|
β-sheet (%)
|
1
|
36.37a
|
35.99b
|
36.40b
|
5
|
37.70a
|
37.65a
|
37.95a
|
10
|
37.23a
|
37.29a
|
38.80a
|
15
|
37.22a
|
38.70a
|
38.80a
|
|
β-turn (%)
|
1
|
37.98a
|
36.76b
|
37.56b
|
5
|
34.80a
|
34.80a
|
34.80a
|
10
|
34.60a
|
34.63a
|
34.70a
|
15
|
34.50a
|
34.70a
|
34.70a
|
|
Random coil (%)
|
1
|
6.23a
|
7.98b
|
6.67c
|
5
|
9.10a
|
9.15a
|
9.10a
|
10
|
9.20a
|
9.20a
|
9.20a
|
15
|
9.20a
|
9.30b
|
9.30b
|
Control: sausages with 80% chicken fillet, 18% veal fat and 2% sesame flour; S1: sausages with 80% chicken fillet, 17% veal fat, 2 % sesame flour, and 1% cloves; S2: sausages with 80% chicken fillet, 16% veal fat and 2% sesame flour, and 2% cloves
Table 2c :
|
Physico-chemical and textural measurements
|
Predicted \Observation
|
S1
J1
|
S1
J10
|
S1
J15
|
S1
J5
|
S2
J1
|
S2
J10
|
S2
J15
|
S2
J5
|
Control J1
|
Control J10
|
Control J15
|
Control J5
|
Total
|
% correct
|
S1J1
|
3
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
3
|
100.00%
|
S1J10
|
0
|
3
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
3
|
100.00%
|
S1J15
|
0
|
0
|
3
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
3
|
100.00%
|
S1J5
|
0
|
0
|
0
|
3
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
3
|
100.00%
|
S2J1
|
0
|
0
|
0
|
0
|
3
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
3
|
100.00%
|
S2J10
|
0
|
0
|
0
|
0
|
0
|
3
|
0
|
0
|
0
|
0
|
0
|
0
|
3
|
100.00%
|
S2J15
|
0
|
0
|
0
|
0
|
0
|
0
|
3
|
0
|
0
|
0
|
0
|
0
|
3
|
100.00%
|
S2J5
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
3
|
0
|
0
|
0
|
0
|
3
|
100.00%
|
Control J1
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
3
|
0
|
0
|
0
|
3
|
100.00%
|
Control J10
|
0
|
1
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
2
|
0
|
0
|
3
|
66.67%
|
Control J15
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
3
|
0
|
3
|
100.00%
|
Control J5
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
3
|
3
|
100.00%
|
Total
|
3
|
4
|
3
|
3
|
3
|
3
|
3
|
3
|
3
|
2
|
3
|
3
|
36
|
97.22%
|
|
|
Mid infrared measurements (4000-900 cm-1)
|
S1J1
|
3
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
3
|
100.00%
|
S1J10
|
0
|
3
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
3
|
100.00%
|
S1J15
|
0
|
0
|
3
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
3
|
100.00%
|
S1J5
|
0
|
0
|
0
|
3
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
3
|
100.00%
|
S2J1
|
0
|
0
|
0
|
0
|
3
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
3
|
100.00%
|
S2J10
|
0
|
0
|
0
|
0
|
0
|
3
|
0
|
0
|
0
|
0
|
0
|
0
|
3
|
100.00%
|
S2J15
|
0
|
0
|
0
|
0
|
0
|
0
|
3
|
0
|
0
|
0
|
0
|
0
|
3
|
100.00%
|
S2J5
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
3
|
0
|
0
|
0
|
0
|
3
|
100.00%
|
Control J1
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
3
|
0
|
0
|
0
|
3
|
100.00%
|
Control J10
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
3
|
0
|
0
|
3
|
100.00%
|
Control J15
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
3
|
0
|
3
|
100.00%
|
Control J5
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
3
|
3
|
100.00%
|
Total
|
3
|
3
|
3
|
3
|
3
|
3
|
3
|
3
|
3
|
3
|
3
|
3
|
36
|
100.00%
|
Control: sausages with 80% chicken fillet, 18% veal fat and 2% sesame flour; S1: sausages with 80% chicken fillet, 17% veal fat, 2 % sesame flour, and 1% cloves; S2: sausages with 80% chicken fillet, 16% veal fat and 2% sesame flour, and 2% cloves
Table 2d:
Physico-chemical and textural measurements
|
Predicted \Observation
|
S1
|
S2
|
Control
|
Total
|
% correct
|
S1
|
5
|
1
|
6
|
12
|
41.67%
|
S2
|
3
|
9
|
0
|
12
|
75.00%
|
Control
|
6
|
0
|
6
|
12
|
50.00%
|
Total
|
14
|
10
|
12
|
36
|
55.56%
|
Mid infrared measurements (4000-900 cm-1)
|
S1
|
6
|
6
|
0
|
12
|
50.00%
|
S2
|
3
|
9
|
0
|
12
|
75.00%
|
Control
|
0
|
1
|
11
|
12
|
91.67%
|
Total
|
9
|
16
|
11
|
36
|
72.22%
|
Control: sausages with 80% chicken fillet, 18% veal fat and 2% sesame flour; S1: sausages with 80% chicken fillet, 18% veal fat, 2 % sesame flour, and 1% cloves; S2: sausages with 80% chicken fillet, 16% veal fat and 4% sesame flour, and 2% cloves
The levels of thiol content found in the Control, S1 and S2 batches for 1, 5, 10 and 15 days decreased significantly during the fermentation stage, since these values were 2.58 ± 0.007, 2.88 ± 0.21, 2.78 ± 0 1.09, and 2.45 ± 1.21 nmol mg/ protein in the Control batch, 3.03 ± 0.001, 3.06 ± 0.43, 3.00 ± 0.72, and 3.00 ± 1.04 nmol mg/ protein in S1 batch and 0.04 ± 0.909, 3.79 ± 0.21, 3.01 ± 0.01, and 3.00 ± 0.45 nmol mg/ protein in S1 batch (Table 2a). No significant difference was observed between S1 and S2 batches (p > 0.05) compared to Control batch; in agreement with the findings of Zhang et al. [11] who depicted that the addition of Salvia officinalis decreased the loss of thiol groups. These results indicate that the addition of clove had a positive effect on retarding protein oxidation in sausages.
Regarding the color measurements (Table 2a), it appeared that the incorporation of clove induced a decrease of L* values. Indeed, L* values at 1 day for Control, S1 and S2 batches were 42.97 ± 0.45, 40.59 ± 1.09 and 41.86 ± 0.32, respectively. While at 15 days, these values were 36.83 ± 2.00, 39.85 ± 1.07, and 40.07 ± 0.01, respectively, and no significant difference (p > 0.05) was observed between the S1 and S2 batches compared to the Control batch. Another explanation for this decrease would be due to the polyphenolic compounds present in the clove being able to oxidize into the relevant quinines and then into darker compounds in the sausages, in agreement with the observations of Zhang et al. [12] who observed a decrease in the value of L* with the addition of clove extract. Considering a given formulation in relation to fermentation time, a gradual decrease was observed. This trend shows both the clove effect and the fermentation time.
The Control batch samples showed higher a* values (p > 0.05) than S1 and S2 batches (Table 2a). Throughout the fermentation stage, the a* value for Control batch decreased significantly compared to the S1 and S2 batches. From these results, it appeared that cloves could have a preventive effect on the discoloration of sausage samples during the fermentation stage. These results are similar to the work of Kong et al. [13] who noted that pork patties with clove extract significantly decreased the a* value compared to the Control batch. Our results are also in agreement with studies carried out by Zhang et al. [12] who also found that clove extract considerably affected the value of a* in sausages.
Regarding the b* value, the control batch showed values ranging from 37.48 ± 1.98 to 27.50 ± 0.54 during fermentation, while batches S1 and S2 showed values ranging from 33.53 ± 1.104 to 25.70 ± 2.09 and from 33.44 ± 1.12 to 24.90 ± 1.07, respectively (Table 2a). In batches S1 and S2, significant differences (p > 0.05) compared to the control batch at days 1, 10 and 15 were observed. The results found show that the addition of cloves significantly impacted the b* value, due to the addition of cloves. Indeed, Zhang et al. [12] noted that the discoloration of sausages could be attributed to the antioxidant properties of phenolic compounds present in cloves which exhibit an antioxidant effect in sausages ([15].
In order to extract the information contained in the physico-chemical and colorimetric data, principal component analysis (PCA) was applied to the normalised data (Fig. 1). The map defined by PC1 and PC2, respectively 62 and 15.8% of the total variance, allowed to clearly differentiate sausage samples according to their stage of fermentation and, to a lesser extent, their recipes. This trend was confirmed by a discriminant factor analysis (FDA) with leave-one-out cross-validation carried out on the 5 PCs of the PCA. Thus, an overall correct classification of 97.22% was obtained (Table 2c). Moreover, by applying the FDA according to the level of addition of the clove, overall rates of 55.56% were obtained (Table 2d).
Evolution of MIR spectra of sausages during fermentation
The MIR spectra recorded on samples from Control and S1 and S2 batches are mentioned in Fig. 2. The spectra were characterized by a strong absorption band around 3330 cm− 1 due to the presence of O–H stretching and N–H stretching vibrations as described by Pavli et al. [16]. A second small peak was observed at 2920 cm− 1 which was attributed to the saturated aliphatic C–H stretching [17]. This observation is similar to that of Pebriana et al. [18] who reported that the –CH2 functional group presented peaks at 2920, and 2922 and 2853 cm− 1 consecutively as the results of asymmetrical and symmetrical vibration. The peak observed at: i) 2852 cm− 1 could be due to the asymmetric and symmetrical stretching methylene (−CH2−) group [18; 19]); ii) 1743 cm− 1 could be attributed to the carbonyl groups (C=O); and iii) 1640 cm− 1 could be related to the cis stretch C = C and H–O–H stretch of the water and/or Amide I group [16]. Our results are in agreement with those of Pedersen et al. [17] who stated that the carbonyl (C = O) group of the triglyceride ester presented a peak at 1744/1745 cm− 1. Pedersen et al. [17] also reported that the peak at 1711 cm− 1 was assigned to C = O group of free fatty acid substituted trans and cis olefin absorbed near 1674 cm− 1 and 1659 cm− 1 as the result of C = C stretching vibration, respectively [17]. Another peak was observed at 1551 and 1403 cm− 1 which can be due to C–H deformation of CH2, CH3 asymmetric deformation or bending, CH2 scissoring or bending [18]. Those observed at 1246 cm− 1 and 1162 cm− 1 could be attributed to the Amide III band and amines, free amino acids and C–N stretch, respectively [18].
The secondary structure of proteins determined on sausage samples during the fermentation stage is presented in Table 2b. The range of 1600–1700 cm− 1 was used to determine the Amide I band. The different peaks could be attributed to different secondary structures, including α-helix (1654–1662 cm− 1), β-sheet (1611–1640 cm− 1), β-turn (1665–1693 cm− 1) and random coil (1642–1650 cm− 1). The results obtained show that the protein structure of sausages changed significantly with the fermentation stage. The levels of α-helix decreased significantly in all formulations with the increase in the fermentation stage. The total ratio of α-helix in Control, S1 and S2 batches did not change significantly (p < 0.05); since it varied from 17.41 to 17.50%, 17.63 to 17.28% and 17.66 to 17.40% respectively. On the other hand, the α-helix levels in all 3 formulations increased with the level of clove addition, except for days 5, 10 and 15, where it remained relatively stable. These results indicate that the α-helix levels were affected by both clove and fermentation stage. Interestingly, for a formulation considered in relation to the fermentation stage, the α-helix levels remained relatively stable. This trend indicates that the level of clove addition showed the greatest effect
In S1, S2 and Control batches, the β-sheet levels varied from 36.37 to 37.22%, 35.99 to 38.70% and 36.40 to 38.80%, respectively. Moreover, on day 1, the β-sheet levels were significantly higher (p > 0.05) in batches containing clove, on the other hand, they remained stable on days 5, 10 and 15, since no significant difference was observed between batches. Regarding the β-sheet and random sheet, the same trend was observed throughout the fermentation stages since except on day 1, the β-sheet and random sheet levels remained statistically unchanged (p < 0.05).
The PCA applied in order to extract information from the MIR spectra clearly allowed to differentiate Control, S1 and S2 batches (Fig. 2b). This trend was confirmed by the FDA since 100% correct classification was obtained for all formulations (Table 2c). Moreover, when FDA was applied only considering the level of clove addition, an overall rate of 72.22% was obtained (Table 2d). From the obtained results, it appeared that MIR allowed better discrimination of sausages according to their formulation and fermentation stage than the physico-chemical and textural measurements.
Prediction of some chemical parameters from mid infrared spectra
Partial least squares regression (PLSR) was applied to predict TBARS and thiol levels using the range of 4000 − 900 cm− 1 (Table 3). Considering the calibration set as shown in Table 3, the prediction levels of TBARS (R2 = 0.94, RPD = 1.00; RMSEC = 0.02) and thiols (R2 = 0.97, RPD = 2.74; RMSEC = 0.43) can be considered as good. The level of thiols (R2 = 0.88, RPD = 2.50; RMSEP = 0.35 (Table 3a) and TBARS (R2 = 0.87, RPD = 0.87; RMSEP = 0.03 (Table 3a; Fig. 3c)) was obtained. The developed model demonstrated the potential use of MIR as a tool to predict the physico-chemical composition of sausages enriched with sesame flour and cloves extracts throughout the fermentation stage.
Table 3
Cross-validation results of TBARS and thiol contents using PLSR of the calibration and validation models
Data
|
Calibration
|
Validation
|
R2
|
RPD
|
RMSEC
|
R2
|
RPD
|
RMSEP
|
Thiols ( nmol mg/ protein)
|
0.97
|
2.74
|
0.43
|
0.88
|
2.50
|
0.35
|
TBARS ( mg MDA / kg of sausages)
|
0.94
|
1.00
|
0.02
|
0.87
|
0.87
|
0.03
|
RMSEC: Root mean square error of calibration; |
RMSEP: Root mean square error of prediction; |
RPD: Ratio of prediction deviation; |
TBARS: Thiobarbituric acid reactive substances |