*3.3. Soap Analysis*

Saponification with EVOO developed normally, as described in Spitz L. [8]; the soap paste, initially semi-liquid, slowly solidified.

NEFOO soaps have different characteristics from EVOO soaps. The sodium salts of fatty acids are formed very quickly in NEFO oil due to the high acidity, so the soap paste hardens very quickly. The saponification process was developed at low temperature and with slow addition of the basic solution to obtain a homogeneous product.

The maturation times of the soaps were determined considering three parameters: pH, color, and solubility.

Initially, the pH of NEFOO soaps was lower than EVOO soaps (Table 2), probably due to the high amount of free fatty acids that neutralize part of the sodium hydroxide very quickly [41].


**Table 2.** pH of the soap solutions produced for different maturation times.

The pH of NEFOO soaps was constant from the thirtieth day of ripening, while the pH of EVOO soaps was constant after the ninetieth day of ripening. The pH values shown in Table 2 are the average of the results obtained in triplicate.

EVO oil (Figure 2A) showed a more intense color than NEFO oil (Figure 2B) due to the greater quantity of chlorophylls, carotenoids, polyphenols, and flavonoids, which determine the initial color of the soaps [16,17,42].

Soaps whiten in the ripening phase due to oxidative processes that act on the pigments. The color of the soaps depends on the type of oil initially used and the maturation time, generally, the soaps marketed have a natural color between soft yellow and white.

blue).

**Days of** 

**Figure 2.** Comparison of EVO oil (**A**) and NEFO oil (**B**) used for the production of soaps. **Figure 2.** Comparison of EVO oil (**A**) and NEFO oil (**B**) used for the production of soaps.

Soaps whiten in the ripening phase due to oxidative processes that act on the pigments. The color of the soaps depends on the type of oil initially used and the maturation The colors of the soaps produced are shown in Table 3 with the models RGB (model that uses red, green, and blue as base colors) and CIELAB (color space l\* a\* b\*).

time, generally, the soaps marketed have a natural color between soft yellow and white. The colors of the soaps produced are shown in Table 3 with the models RGB (model **Table 3.** Report colors of soaps with RGB and CIELAB models (l\* brightness and a\* b\* mixture of red, yellow, green, and blue).


**Table 3.** Report colors of soaps with RGB and CIELAB models (l \* brightness and a \* b \* mixture of red, yellow, green, and NEFOO soaps after 30 days of maturation were white and this color was maintained up to 180 days of maturation, while EVOO soaps tended to soft yellow after 90 days of maturation and to white at 180 days (Table 3).

**Maturation EVOO Soap 0% EVOO Soap 5% NEFOO Soap 0% NEFOO Soap 5% RGB l\* a\* b\* RGB l\* a\* b\* RGB l\* a\* b\* RGB l\* a\* b\***  Considering the CIELAB parameters, EVOO soap with 0% free fatty acids had a more intense yellow-green color than EVOO soap with 5% free fatty acids, this difference was not observable for NEFOO soaps.

5 90.4 −24.8 87.2 93.3 −25.1 73.8 98.4 −9.3 29.1 98.8 −6.9 21.6 15 93.7 −22.5 74.1 95.4 −21.3 78.9 98.2 −2.62 8.5 97.7 −3.3 11.4 Soaps' solubility was determined considering the degree of clarity of the solutions with complete dissolution of the soap.

30 97.6 −14.4 48.7 95.8 −13.1 42.9 98.9 −0.3 1.0 96.9 −0.2 1.3 90 97.0 −3.6 9.2 97.0 −3.7 10.6 97.1 −0.4 0.9 96.1 −0.2 0.8 180 99.3 −0.3 0.7 98.1 −0.4 0.8 97.1 −0.3 0.8 97.4 −0.3 1.2 EVOO soaps, after 5 days of maturation, showed different turbidity (Figure 3A). After 15 and 30 days of maturation (Figure 3B,C) the turbidity rapidly decreased for soap with 0% of non-neutralized fatty acids, while it slowly decreased for soap with 5% of non-neutralized fatty acids.

Soaps' solubility was determined considering the degree of clarity of the solutions

EVOO soaps, after 5 days of maturation, showed different turbidity (Figure 3A). After 15 and 30 days of maturation (Figure 3B,C) the turbidity rapidly decreased for soap with 0% of non-neutralized fatty acids, while it slowly decreased for soap with 5% of

NEFOO soaps, after 5 days of maturation, had very similar turbidity (Figure 3D). After 15 and 30 days of maturation (Figure 3E,F) the turbidity of both soaps decreased

with complete dissolution of the soap.

non-neutralized fatty acids.

**Figure 3.** Images of the solutions of EVOO (**A**–**C**) and NEFOO (**D**–**F**) soaps in different ripening days 5 days (**A**,**D**) 15 days (**B**,**E**) and 30 days (**C**,**F**). **Figure 3.** Images of the solutions of EVOO (**A**–**C**) and NEFOO (**D**–**F**) soaps in different ripening days 5 days (**A**,**D**) 15 days (**B**,**E**) and 30 days (**C**,**F**).

After 90 and 180 days, all soaps showed a slight turbidity: this was more present in EVOO soaps (Figure 4A,B) than in NEFOO soaps (Figure 4C,D). This low turbidity for very long maturation times could be due to the initial rancidity of the soaps. NEFOO soaps, after 5 days of maturation, had very similar turbidity (Figure 3D). After 15 and 30 days of maturation (Figure 3E,F) the turbidity of both soaps decreased until clear solutions were obtained. **Figure 3.** Images of the solutions of EVOO (**A**–**C**) and NEFOO (**D**–**F**) soaps in different ripening days 5 days (**A**,**D**) 15 days (**B**,**E**) and 30 days (**C**,**F**).

After 90 and 180 days, all soaps showed a slight turbidity: this was more present in EVOO soaps (Figure 4A,B) than in NEFOO soaps (Figure 4C,D). This low turbidity for very long maturation times could be due to the initial rancidity of the soaps. After 90 and 180 days, all soaps showed a slight turbidity: this was more present in EVOO soaps (Figure 4A,B) than in NEFOO soaps (Figure 4C,D). This low turbidity for very long maturation times could be due to the initial rancidity of the soaps.

harder and more compact than EVOO soaps, especially in the early stages of maturation, with a consequent difficulty in their solubilization in water. **Figure 4.** Images of the solutions of EVOO (**A**,**B**) and NEFOO (**C**,**D**) soaps after different ripening days: 90 days (**A**,**C**) and 180 days (**B**,**D**). **Figure 4.** Images of the solutions of EVOO (**A**,**B**) and NEFOO (**C**,**D**) soaps after different ripening days: 90 days (**A**,**C**) and 180 days (**B**,**D**).

Considering the pH, color, and solubility, NEFOO soaps showed a correct maturation after 30 days from their production, while EVOO soaps had an optimal maturation after 90–180 days. Soaps with maturation after 30 and 180 days are shown in Figure 5. It is interesting to observe the hardness of the soaps: NEFOO soaps tended to be harder and more compact than EVOO soaps, especially in the early stages of maturation, with a consequent difficulty in their solubilization in water. It is interesting to observe the hardness of the soaps: NEFOO soaps tended to be harder and more compact than EVOO soaps, especially in the early stages of maturation, with a consequent difficulty in their solubilization in water.

Considering the pH, color, and solubility, NEFOO soaps showed a correct maturation after 30 days from their production, while EVOO soaps had an optimal maturation after 90–180 days. Soaps with maturation after 30 and 180 days are shown in Figure 5. Considering the pH, color, and solubility, NEFOO soaps showed a correct maturation after 30 days from their production, while EVOO soaps had an optimal maturation after 90–180 days. Soaps with maturation after 30 and 180 days are shown in Figure 5.

**Figure 5.** Soaps matured 30 days and 180 days. **Figure 5.** Soaps matured 30 days and 180 days.

There were no substantial differences, for the parameters considered in this study, between soaps with 0% and 5% of free fatty acids produced with the same oil. There were no substantial differences, for the parameters considered in this study, between soaps with 0% and 5% of free fatty acids produced with the same oil.

The stage of maturation is not strictly linked to the use of the product but represents an important parameter for its marketing. The stage of maturation is not strictly linked to the use of the product but represents an important parameter for its marketing.

#### **4. Conclusions 4. Conclusions**

This study highlighted that non-edible fermented olives can be used for soaps' production. This study highlighted that non-edible fermented olives can be used for soaps' production.

The high acidity of NEFOO determines different and shorter saponification processes than the normal procedures reported by Spitz L. [7,8]. The high acidity of NEFOO determines different and shorter saponification processes than the normal procedures reported by Spitz L. [7,8].

Considering the pH, color, and solubility data, NEFOO soaps ripen faster than EVOO soaps, while there are no substantial differences between soaps with 0% and 5% free fatty acids obtained with the same oil. Considering the pH, color, and solubility data, NEFOO soaps ripen faster than EVOO soaps, while there are no substantial differences between soaps with 0% and 5% free fatty acids obtained with the same oil.

The fermentation of non-edible olives makes it possible to easily and quickly recycle an undervalued food waste to produce a widely used product, such as olive oil soaps, with lower costs, production times, and maturation. The fermentation of non-edible olives makes it possible to easily and quickly recycle an undervalued food waste to produce a widely used product, such as olive oil soaps, with lower costs, production times, and maturation.

The study described could be used to produce "alternative" olive oils on a large scale, exploiting non-edible drupes currently used to produce fodder, natural fertilizer, and energy biomass. The study described could be used to produce "alternative" olive oils on a large scale, exploiting non-edible drupes currently used to produce fodder, natural fertilizer, and energy biomass.

**Author Contributions:** Conceptualization, A.T., A.F. and F.S.; Methodology, A.T., A.F. and F.S.; Formal Analysis, A.T., A.F. and F.S.; Investigation, A.T., A.F. and F.S.; Data Curation, A.T., A.F. and F.S.; Writing-Review and Editing, A.T., A.F. and F.S.; Supervision, A.T., A.F. and F.S.; Project Administration, A.F., A.T. and F.S. All authors provided critical feedback and helped shape the research, analysis, and manuscript. All authors have read and agreed to the published version of the manuscript. **Author Contributions:** Conceptualization, A.T., A.F. and F.S.; Methodology, A.T., A.F. and F.S.; Formal Analysis, A.T., A.F. and F.S.; Investigation, A.T., A.F. and F.S.; Data Curation, A.T., A.F. and F.S.; Writing-Review and Editing, A.T., A.F. and F.S.; Supervision, A.T., A.F. and F.S.; Project Administration, A.F., A.T. and F.S. All authors provided critical feedback and helped shape the research, analysis, and manuscript. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding. **Funding:** This research received no external funding.

**Institutional Review Board Statement:** Not applicable. **Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable. **Informed Consent Statement:** Not applicable.

**Conflicts of Interest:** The authors declare no conflict of interest. **Conflicts of Interest:** The authors declare no conflict of interest.
