3.1. Proximate Composition of Butter Cookies
The moisture content ranged from 3.19 to 4.54%; wheat flour cookies with 4% mulberry leaf additive had the highest moisture content, while wheat flour cookies with 8% mulberry leaf additive had the lowest (3.19%) (
Table 4). Andresen et al. [
42] investigated the effect of baking time and temperature on moisture content in butter cookies and found that the contents of this parameter ranged from 1.1% to 9.4%. According to the literature, a high moisture content reduces the shelf life of cookies and causes a delay in the caramelization and Maillard reactions [
43].
A higher content of protein was found in all treatments of wheat flour cookies (from 5.75% to 6.77%), compared with rice flour cookies (from 2.96% to 4.76%) (
Table 4). The replacement of wheat and rice flour with mulberry leaf powder had a significant effect on the protein content. Wheat flour cookies with 8% and 12% mulberry leaf additive had the significantly highest amount of this compound, while rice cookies without mulberry leaf additive had the significantly lowest amount. Wheat flour is a high-protein food that contains more protein than white rice [
44]. Tian et al. [
44] reported that the protein content of different rice flours was 27.24–43.04% lower than that of common wheat. Mulberry leaf powder is also high in protein, with levels ranging from 18.41 to 24.63% depending on genotypes [
45].
With increasing amounts of mulberry leaf additive, the quantities of fiber and ash in both wheat and rice cookies significantly increased. Replacing wheat flour with 4–12% mulberry leaf additives led to an increase in fiber from 13.80% to 62.20% and in ash from 51.06% to 84.04%. Compared with rice cookies without additive (control), the content of ash in rice cookies with 4–12% mulberry leaf additive increased from 22.56% to 87.84%, and the content of fiber increased from 16.81% to 47.06%. Wheat and rice cookies with a 12% mulberry leaf additive had significantly higher contents of these compounds compared to other cookie samples. According to the literature, in dried mulberry leaves, ash ranged from 14.59 to 17.24% [
15] and fiber ranged from 11.46 to 16.61% [
28]. Therefore, we can use mulberry leaf additives to increase the amounts of the mentioned compounds in various types of food products. The pH values of the butter cookies varied from 6.58 to 7.57. The pH values of the wheat and rice cookies increased as the added amounts of mulberry leaf increased. The maximum values of this parameter were found in the wheat and rice cookies with a 12% mulberry leaf additive (7.57 and 7.50, respectively).
Sayuti et al. [
32] evaluated the nutritional value of wheat flour cookies containing mulberry leaf (10, 20, and 30%) and mulberry leaf extract (10, 20, and 30%). It was discovered that increasing the amounts of mulberry leaf and extract in cookies increased the ash and protein content. This could be due to the high mineral and protein content of mulberry leaves, according to the authors. Makchuay et al. [
33] investigated the effect of mulberry leaf tea powder on the protein and fiber content of rice noodles. The addition of powder at 5 to 25% increased crude fiber content by 5–8 times and the protein content of noodles by 1.16–1.55 times compared with rice noodles without additives.
3.2. Mineral Elements Evaluation of Butter Cookies
The contents of macroelements such as P, K, Ca, and Mg varied significantly depending on the flour used and the addition of mulberry leaf powder. P was the most abundant element in all of the cookie samples tested, followed by K, Ca, and Mg (
Table 5). All rice flour cookie samples demonstrated 8.37–30.71% higher P values when compared to wheat flour cookies. We found the highest concentrations of this mineral in rice flour cookies containing 4%, 8%, and 12% mulberry leaf additive (380.47, 390.82, and 390.91 mg 100 g
−1, respectively), with no significant difference between them.
The addition of mulberry leaf powder as an additive also increased the contents of K and Ca in butter cookies. Both the wheat and rice cookies with a 12% mulberry leaf additive had the significantly highest amounts of K (170.22 and 160.22 mg 100 g−1, respectively) and Ca (170.45 and 160.68 mg 100 g−1, respectively), while the control wheat and rice cookie samples recorded the lowest contents of these minerals. All treatments of rice flour cookies showed a higher Mg content (from 24.91 to 42.33 mg 100 g−1) compared to wheat flour cookies (from 13.24 to 32.21 mg 100 g−1). Rice flour cookies with 8% and 12% mulberry leaf additive had the highest content of 36.21 and 42.33 mg 100 g−1, respectively, while wheat flour cookies without additive had the lowest content of 13.24%.
According to the data of this study, the freeze-dried mulberry leaf additive increases the contents of the analyzed macroelements in cookies due to the high amount of these elements in the leaves, which is much higher than in wheat or rice flour. Mulberry leaf powder is an excellent source of some important minerals, particularly calcium (2870.08 mg 100 g
−1), potassium (1630.14 mg 100 g
−1), phosphorus (430.88 mg 100 g
−1), and magnesium (270.68 mg 100 g
−1) [
29]. However, in the scientific literature, there is no information about the mineral element contents of butter cookies enriched with mulberry leaf powder. Kim et al. [
30] evaluated the macroelement content of jelly with various levels of mulberry leaf powder (0.5, 1, 1.5, and 2%). They revealed that increasing the amount of mulberry leaf powder added significantly increased the contents of K, Ca, and Mg. In a study conducted by Kulaitienė et al. [
29], yogurt bites with 1% mulberry leaf powder contained 41.24% significantly higher amounts of K, 21.14% more Ca, 38,08% more P, and 139.70% more Mg than the yogurt bites without additives.
The amounts of Fe, Zn, Mn, Cu, and B in the cookie samples also varied depending on the flour used and the amount of mulberry leaf additive (
Table 6). The Fe content in rice flour cookies (control) was significantly (64.37%) higher than in wheat flour cookies (control). In wheat cookies with a 12% mulberry leaf additive, the mineral content increased by 12.41% compared to control wheat cookies. However, the replacement of rice flour with mulberry leaf powder had a negative effect on the Fe content of rice flour cookies. Zn content was lower in wheat flour cookies (from 5.28 to 6.02 mg kg
−1) than in rice flour cookies (from 9.88 to 12.25 mg kg
−1). In wheat flour cookies, the mulberry leaf additive did not significantly influence the Zn content. However, rice flour cookies with 12% powder contained the significantly highest amount of this element among the rice cookie samples. The mulberry leaf supplementation had a negative effect on the cookie’s B content. The significantly highest content of B was in the control wheat flour cookies (9.12 mg kg
−1). The Mn and Cu content in rice flour cookies were also higher than those in wheat flour cookies. Mn varied from 1.95 to 3.40 mg kg
−1 and Cu from 0.73 to 1.00 mg kg
−1 in wheat flour cookies. In rice flour cookies, Mn ranged from 5.25 to 6.28 mg kg
−1, and Cu from 1.65 to 1.95 mg kg
−1. The content of these minerals in both wheat and rice cookies increased with increasing levels of mulberry leaf powder. Wheat and rice flour cookies with a 12% leaf additive showed significantly higher content of Mn and Cu, while wheat and rice flour cookies without the additive had the lowest.
Our results are consistent with previous researchers’ findings that the incorporation of mulberry leaf powder in food products increases some microelement content. The addition of mulberry leaf powders to the formulation of yogurt bites allowed for a significant increase in the amount of Fe, Zn, and Mn in the final products [
29]. Wheat flour masala biscuits enriched with 7.5% mulberry leaf powder contained 3.75 mg zinc, 19.66 mg iron, 3.19 mg manganese, and 5.68 mg copper, while control biscuits without mulberry additive had 2.34 mg zinc, 19.31 mg iron, 2.06 mg manganese, and 3.65 mg copper [
31]. Also, our results showed that rice is a great gluten-free alternative to wheat flour. Rice has higher levels of Fe, Zn, Mn, and Cu than wheat, making it suitable for processing into flour and use in various beneficial food products [
46,
47].
3.3. Evaluation of Total Chlorophyll, Phenolic Amount, and Antioxidant Activity in Butter Cookies
The conducted studies showed that the total amount of total chlorophyll in butter cookies ranged from 2.81 to 17.92 mg 100 g
−1 (
Figure 1). The results showed that adding mulberry leaf powder to butter cookies increased the amount of total chlorophyll. Wheat flour cookies with a 12% mulberry leaf additive showed six times a significantly higher amount of total chlorophyll compared to wheat cookies without the additive. Cookies made from wheat and rice flour without the additive had the significantly lowest amount of total chlorophyll.
Other researchers conducted a study on semolina pasta enriched with 0, 1, 2, 3, 4, and 5% nettle leaf supplement. The study showed that the lowest total chlorophyll content of 0.98 mg 100 g
−1 was found in the no-added noodles, while the highest total chlorophyll content was found to be 23.76 mg 100 g
−1 with the additive [
48].
Our studies showed that the phenolic content of the butter cookies ranged from 0.27 to 1.48 mg 100 g
−1 (
Figure 2). In both types of cookies, the addition of mulberry leaves significantly increased the content of phenolic compounds compared to the control. We found that the addition of 4, 8, and 12% mulberry leaf to both wheat and rice flour cookies significantly increased the content of phenolic compounds by 1.47, 2.1, 2.36, 2.62, 3.15, and 5.48 times, respectively, compared to the control treatment.
A comparison between wheat and rice flour cookies without additives showed significant differences. The wheat flour cookies were found to have a higher content of phenolic compounds, by as much as 96.30%. According to the literature, the addition of mulberry leaf powder to yogurt bites [
29], snacks [
49], and rice noodles [
33] significantly increased the total phenolic compound content.
Other scientists investigated that the addition of mulberry leaf extract also increased the content of phenolic compounds in bread [
50].
According to M. Polumackanyxz et al. [
51], antioxidant activity is an important parameter for determining the health benefits of foods. Our results revealed that the addition of mulberry leaves had a significant effect on the antioxidant activity of the cookies (
Figure 3). The antioxidant activity of the butter cookies ranged from 9.06 to 67.98%. The significantly lowest antioxidant activity was in both types of cookies without additives, while the significantly highest was in the rice flour cookies with a 12% additive. The addition of mulberry leaves increased the antioxidant activity of the wheat and rice flour cookies by an average of 3.70 and 5.39 times, respectively, compared to the control cookie samples.
A study by other researchers showed that the cookies with a 7% addition of mulberry leaf contained the highest antioxidant activity (31.11%), while the cookies with no addition had the significantly lowest (7.21%) [
6]. Thailand researchers’ results showed that antioxidant activity increased in four snack products (loaf bread, Thai steamed cupcakes, green coconut sweet pudding, and snow skin mooncake) supplemented with 10% mulberry leaf powder. Therefore, the bioactive properties of mulberry leaf powder suggest their possible use for supplementing healthy foods [
49].
3.4. Physical Characteristics of the Cookies
The texture, as well as the color properties of bakery products, play an important role in consumer acceptability [
52,
53].
The physical properties of butter cookies, such as hardness and color, were influenced by the addition of mulberry leaves and are summarized in
Table 7. A comparison of wheat and rice flour cookies’ L* color coordinates revealed significant differences between all treatments. The addition of mulberry leaf led to a significant darkening of the cookies, with the rice flour cookies containing a 12% addition being the darkest. The control cookies were significantly lighter compared to the cookies with additives.
Assessing the a* value, which indicates the red or green color, it was found that the wheat and rice flour cookies without additives were significantly reddest at 8.76 and 9.36, respectively, while the wheat flour cookies with a 12% addition were characterized by a* negative value (−1.26) (
Table 7). The intensity of the red color in wheat and rice flour cookies with additives decreased by an average of 6.95 and 37.44 times, respectively, compared to the control.
Our research revealed that b* color coordinates ranged from 32.49 to 39.80 in wheat flour cookies and 30.59 to 36.47 in rice flour cookies (
Table 7). After evaluating the b* value, it was found that the addition of mulberry leaves had a significant effect on the yellow-ness of the cookies, and wheat flour cookies with 8 and 12% mulberry leaves were significantly yellower compared to all treatments of samples.
A researcher Park [
6], performed a study where cookies were enriched with 0, 1, 3, and 7% mulberry leaf additive. The study’s result was similar to ours. The control cookies without additives were significantly lighter (75.51 NBS), while cookies with a 7% mulberry leaf additive were significantly darker (51.23 NBS). The significantly highest value of a* coordinate was (2.15) in cookies without additive and the significantly lowest (−1.83) in cookies with 7% mulberry leaf additive. Cookies with 7% mulberry leaf addition showed the significantly highest (40.11) b* value difference, while the control variant showed the lowest (16.10).
The cookies’ hardness varied from 19.96 to 42.70 N, depending on both factors (
Table 7). Wheat flour cookies were found to be significantly harder by 1.5 times compared to rice flour cookies. Both wheat and rice flour butter cookies with 12% leaf addition were significantly harder by 42.00 and 96.04% N, respectively, compared to the control. The addition of 4 and 8% mulberry leaves had no significant effect on wheat flour cookies, while this additive significantly increased the hardness by 41.93 and 56.01%, respectively, in rice flour cookies.
In a study conducted by Park [
6], wheat flour was replaced with 0, 1, 3, 5, and 7% mulberry leaf additive in cookies, and it was found that the addition of mulberry leaf powder increased hardness.