Chemical Analysis of Moldavian Dragonhead Bagasse
Moldavian dragonhead bagasse (MDB) is obtained by pressing oil from seeds contained 5.43% of fat (
Table 2). MDB is characterized by unique content of fatty acids. Over 90% of the fatty acids present in these MDB are unsaturated, of with over 80% are polyunsaturated fatty acids [
7]. Linolenic acid ALA 18:3 (62.21%), belonging to the omega-3 group, had the highest share in the fat fraction. Linoleic acid LA (
n-6) 18:2 in the tested MDB constituted more than 20% of fatty acids, and the content of oleic acid (
n-9) 18:1 was approximately 10%. Similar results were obtained by Abdel-Raheem [
31], Matwijczuk [
7], and Stuchlik and Žak [
32]. Comparing the obtained results, e.g., with high-linolenic oils, such as linseed oil and chia, the content of linolenic acid in MDB was higher than in linseed (50%) and chia (62%) oils. The
n-3 to
n-6 ratio (3.5) was higher than that of flax (3.3) and chia (3.2) oils [
7]. The human body cannot synthesize linolenic acid, and therefore, it is known, along with linoleic acid, as an essential fatty acid. Due to the high content of this fatty acid and high ratio of
n-3/
n-6, Moldavian dragonhead seed, the extracted oil, and bagasse can be used as a food supplement, where enrichment with omega-3 fatty acids is needed. MDB contained 23.97% protein. According to Hanczkowski et al. [
33] the seeds of the blue variety of D. moldavica L. contain approx. 21.03% protein, 24.02% fat, 11.23% fiber, and 4.91% ash. Protein is characterized by a favourable amino acid composition and high nutritional value. It contains a lot of sulphur amino acids (methionine and cystine) [
33].
The chemical composition of ice cream enriched with MDB is presented in
Table 3. The obtained ice cream had a high dry matter content, ranging from 40.56 g (100 g)
−1 to 41.02 g (100 g)
−1. Increasing the dry matter content in the ice cream mixture reduces the diameter of the ice crystals, which is very desirable and improves the consistency of the ice cream. In addition, the dry matter content affects the degree of aeration in ice cream [
34]. In general, formulations with a high dry matter content produce a better quality ice cream. According to Clarke [
1], typical ice cream should contain between 28% and 40% dry matter with a fat content between 7 and 15%. However, according to Goff and Hartel [
35], low fat ice cream should contain dry matter in the range of 28–32% with a milk fat content of 2–5% and in the case of light ice cream, dry matter is in the range of 30–35% with a fat content of min. 5–7%.
The protein content in the ice cream supplemented with MDB changed significantly (
p < 0.05) from 10.16 g (100 g)
−1 for the LW1.0 sample to 12.07 g (100 g)
−1 for ice cream with 3.0% MDB addition. The importance of protein in ice cream is justified by the ability of this compound to stabilize the emulsions after the homogenization process. Proteins also have a large influence on the water-holding capacity of products, improving the viscosity of the mixtures, reducing ice formation, and increasing the melting resistance of ice creams [
1]. According to Clarke [
1], standard ice cream generally has a protein content of around 4–5%, lower than the values obtained in the present study.
The fat content of ice cream samples is given in
Table 3. All results differed significantly (
p < 0.05) from each other. That with the increase in the percentage of MDB in the ice cream, the content of fat and fatty acids increases significantly (
Table 4). These values for fat ranged from 2.19 g (100 g)
−1 (LW1.0) to 5.33 g (100 g)
−1 (LW3.0). The fat content affects the degree of aeration in the ice cream. Many authors define fat content limits in cream ice cream at the level of 8 and 12%, at which the best air entrainment effect is obtained [
1,
35]. The ratio of fat content to dry matter content is also important and depends on the type of ice cream. For ice cream made with sucrose, the fat content is three times less than the dry matter content with 70% aeration, and for ice cream with inulin the fat content is almost five times less than the dry matter content with 43% aeration [
36].
As verified in
Table 3, the ash content for all the ice cream formulations were similar; however, ice cream sample LW3.0 contained higher amounts (2.06 g (100 g)
−1 (
p < 0.05).
The effect of addition of MDB on the pH ice cream presented in
Table 3. pH value ranged between 5.80 and 5.88 and it was observed that the increasing proportion of MDB did not cause significant changes in the pH of the ice cream. The obtained pH values were lower than those obtained by other authors of the studies, 6.27–6.52 [
37], 6.17–6.48 [
38], and 6.65–7.05 [
39].
Supplementation of ice cream with MDB also influenced the physical properties of ice cream. The selected features are presented in
Table 5. The study of the time of the first drop appearance and the total melting time showed statistically significant differences (
p < 0.05) for the examined ice cream. The ice cream with a 3% share of MDB had the highest melting time (the total melting time was 38 min). The obtained values of 34.74–38.00 min indicate the high melting resistance of ice cream [
40]. Melting characteristics are an important parameter in assessing the quality of ice cream, the correct selection of technology and freezing parameters. The melting point is determined by a number of parameters, such as the dry matter content, the size of ice crystals, the number and size of fat particles, as well as the composition of the ice cream mixture [
41].
The hardness of the tested ice cream differed statistically significantly (
p < 0.05) and ranged from 9.25 N to 28.76 N. The highest hardness was recorded for ice cream with a 3.0% share of MDB (LW3.0) (
Table 5). Increasing the percentage of this additive in ice cream resulted in an increase in their hardness. Similar relationships were observed for the adhesiveness (stickiness). Adhesiveness is defined as the work necessary to overcome the attractive forces between the surface of the food product and the surface of other materials with which it comes in contact. Ice cream with a 1.0% share of MDB (LW1.0) had the lowest adhesiveness (−15.72 N·s), while that with a 3.0% share the highest (−44.47 N·s). Numerous factors such as the ingredients used [
42,
43], fat network, ice phase volume, ice crystal content and ice crystal size [
41] influence hardness. The effect of fat content and gum concentration on the adhesiveness of sample was found parallel to the results of the hardness; that may be due to change in ice phase volume, viscosity and texture [
43]. The similar trend for these parameters was reported by other researchers [
44,
45].
Apparent viscosity is a physical property of ice cream. According to Goff and Hartel [
35] viscosity is especially important for industry design but there is not a clear optimum value for viscosity.
Figure 2 shows the viscosity values for the five tested ice cream samples at variable speed. The study on the viscosity of ice cream with the addition of MDB showed non-linear characteristics, i.e., samples exhibited pseudoplastic behavior. The LW3.0 and LW2.5 samples showed the greatest decrease in viscosity for low speed gradients, while the LW1.0 and LW1.5 samples showed a very low initial viscosity value of 3.2 and 6.6 Pa∙s, respectively. The increase in viscosity along with the increase in the proportion of MDB in ice cream may be caused by the presence of fiber. El Nagar et al. [
46] noted that the increase in viscosity in low-fat ice cream with the addition of inulin may cause interactions between the dietary fiber and water as a component of the ice cream mixture.
Table 6 shows the values of the cryoscopic temperature and thermophysical properties (thermal conductivity—λ, heat capacity—C, thermal diffusivity—a) of ice cream with different percentages of bagasse from
D. moldavica L. seeds. The cryoscopic temperature of the tested samples did not differ statistically significantly and ranged from −3.5 °C to −4.0 °C. This parameter is one of the most important thermophysical properties of food. It is necessary to determine its value when designing and optimizing refrigeration technologies [
47,
48,
49].
The ice cream containing 2.5% (LW2.5) of MDB had a lower conductivity coefficient (1.06 W∙(m∙K)
−1) than ice cream with the share of 1.0% (LW1.0). The highest value of heat capacity (C = 2.72 MJ·(m
3∙K)
−1) was recorded for the sample with 1% addition of MDB (LW1.0). Agrawal et al. [
50] reported that thermal conductivity of ice cream ranged from 1.039 W·(m∙K)
−1 to 1.071 W·(m∙K)
−1 and heat capacity values from 2.516 MJ∙(m
3·K)
−1 to 2.542 MJ∙(m
3·K)
−1. Thermal diffusivity for ice cream containing 3.0% (LW3. 0) MDB was significantly higher than the other tested samples and amounted to 0.50 mm
2·s
−1. The main factor influencing the thermophysical properties is the amount of frozen water, which also depends on the final temperature of the product.