What is saponification and how does it relate to soap

The surfactant molecules reversibly assemble into polymolecular aggregates called micelles. By gathering the hydrophobic chains together in the center of the micelle, disruption of the hydrogen bonded structure of liquid water is minimized, and the polar head groups extend into the surrounding water where they participate in hydrogen bonding.

These micelles are often spherical in shape, but may also assume cylindrical and branched forms, as illustrated on the right. Here the polar head group is designated by a blue circle, and the nonpolar tail is a zig-zag black line. The oldest amphiphilic cleaning agent known to humans is soap. Soap is manufactured by the base-catalyzed hydrolysis saponification of animal fat see below.

Before sodium hydroxide was commercially available, a boiling solution of potassium carbonate leached from wood ashes was used.

Soft potassium soaps were then converted to the harder sodium soaps by washing with salt solution. The importance of soap to human civilization is documented by history, but some problems associated with its use have been recognized.

One of these is caused by the weak acidity pKa ca. Solutions of alkali metal soaps are slightly alkaline pH 8 to 9 due to hydrolysis. If the pH of a soap solution is lowered by acidic contaminants, insoluble fatty acids precipitate and form a scum. A second problem is caused by the presence of calcium and magnesium salts in the water supply hard water. These divalent cations cause aggregation of the micelles, which then deposit as a dirty scum. We note that we were unable to determine what saponification process or superfatting level lye discount was used to manufacture the soaps in the referenced study [ 2 ].

Also, in our study, we specifically focused on natural soaps with vegetable oils used as the source of the soap feedstock. These factors could account for the variation in quantitative levels of unsaponified fatty acids present in the natural herbal soaps evaluated in our study.

Though we observed that the exact quantity and quality of the unsaponified fatty acids present in the end products were not significantly affected by the additives used in the formulation following manufacturing by cold saponification Table 2. We observed significant percent changes in the retention of unsaponified fatty acids in the final products when additives were used in the formulation Figure 3.

Essential oils and clay included as additives in the formulation reduced the percent retention of unsaponified Cn3 and Cn9 fatty acids in HA Figure 3. Conversely, rosemary extract appears to enhance the retention of C unsaponified fatty acid in BBR Figure 3. Taken all together, these findings suggest the use of additives as essential oils or plant extracts in natural soap formulation did not significantly alter the composition and levels of unsaponified fatty acids in the finished products following manufacturing by cold saponification.

However, the additives significantly altered the percent change or retention of the feedstock fatty acids as unsaponified fatty acids in the finished products. The majority of the C, Cn9, Cn6, and Cn3 fatty acids present in the feedstock remained as unsaponified fatty acids in the final products.

That is, they were not converted to fatty acid salts saponified during the soap making process. In particular, the unsaturated fatty acids were not saponified when soaps were manufactured by cold saponification. This resulted in significant levels of unsaponified unsaturated fatty acids in the final products. This is of relevance because unsaponified fatty acids can modulate the quality and performance [ 2 ], as well as the shelf life of natural soaps.

The effects of cold saponification and natural additives on the percent change in a saturated and b unsaturated unsaponified fatty acids in different commercial natural soaps. Considering we observed that the majority of unsaturated fatty acids present in the natural soap feedstocks were retained as unsaponified fatty acids in the soaps produced, we wanted to assess the antioxidants, phenolics, and oxidants levels in the soaps to determine if they would have any relationships with preserving the unsaturated unsaponified fatty acids in natural soaps.

Cold saponification was used to manufacture the natural herbal soaps evaluated in this study Figure 1. This method of saponification is preferred by artisanal soap makers because it offers more creative flexibilities with the choice of natural ingredients that can be used in the formulation, as well as potentially preserving the antioxidants, free fatty acids, essential oils, and plant extracts used as additives in the formulation [ 1 , 3 ].

In the present study, we evaluated the phenolic, antioxidant, and oxidant content of natural herbal soaps formulated with high-quality plant-based feedstock vegetable oils and additives plant extracts and essential oils.

We observed cold saponification resulted in the retention of hydrophilic HPC , lipophilic LPC , and the total phenolic content TPC in all the natural herbal soaps evaluated in this study Figure 4 a—c. Hydrophilic compounds phenolic, antioxidants, or oxidants are soluble in water or aqueous solvents. Lipophilic compounds, on the other hand, are soluble in organic solvents [ 9 ]. The plant oils soap feedstock and extracts used as additives to formulate the natural soap products are excellent sources of polyphenols [ 10 ], and as such, contributed to the hydrophilic, lipophilic, and total phenolic content remaining in the natural soaps after cold saponification.

One interesting observation was that the H soap formulation poorly retained the phenolics, particularly the lipophilic phenolics following cold saponification Figure 4. The use of additives rosemary extract and essential oils , on the other hand, increased the TPC content in BB and FG natural soaps manufactured using cold saponification. Polyphenols are known to have potent antioxidant activities [ 9 , 10 , 11 ]. Additionally, the additives and plant oils used as ingredients to formulate the natural herbal soaps could also contain compounds, such as vitamin E, carotenoids, etc.

The base bar formulated with rosemary extract BBR as an additive contained the highest total antioxidant activity The hydrophilic antioxidants accounted for the largest component of the total antioxidant activities Figure 4.

Cold saponification is considered a milder form of soap saponification [ 1 ] and is preferred by some artisanal soap makers because it can be effective in retaining the fragrance and antioxidants present in the soap ingredients used to formulate natural soaps [ 3 ], consistent with the findings observed in this study.

This is the first time to our knowledge that this relationship is reported in natural herbal soaps manufactured using cold saponification. The results indicated that significant oxidation existed in the natural soaps evaluated in this study, with the hydrophilic oxidants being the major contributor to the total oxidant status Figure 4. The lowest oxidation status was observed in BB A significantly higher oxidation status was observed in FG One of the major functions of antioxidants is to suppress oxidation [ 9 , 11 ].

Polyunsaturated fatty acids present in the natural soaps as unsaponified fatty acids are highly susceptible to lipid oxidation [ 3 , 12 ]. Consequently, we determined if the observed soap polyphenols or antioxidants were associated with suppressed oxidation, thus enhancing the retention of unsaturated unsaponified fatty acids in the natural soaps following cold saponification.

The same observation was noted for the association between the shorter chain C—C unsaponified saturated fatty acids and TAA. Overall, these findings suggest phenolics and antioxidants present in the natural ingredients used to formulate herbal soaps were effectively retained by cold saponification, and that both the antioxidants and phenolics present in the feedstocks or additives were associated with the retention of Cn9 and Cn3 unsaturated unsaponified fatty acids in natural herbal soaps.

These findings are of major significance to artisanal production of natural herbal soaps because antioxidants, polyphenols, and unsaponified unsaturated fatty acids appear to be major influencers or determinants of soap quality, consumer perception, and preference of the final products. Total phenol, antioxidant, and oxidant content in natural soaps following cold saponification.

Scatter plots showing relationships between the phenolic content and antioxidant activities in different commercial natural soaps after cold saponification. Scatter plots showing relationships between the phenolic content and unsaponified fatty acids in different commercial natural soaps after cold saponification.

Scatter plots showing relationships between the antioxidants activities and unsaponified fatty acids in different commercial natural soaps after cold saponification. Considering the levels and composition of unsaponified fatty acids were similar between the samples with and without additives Table 2 , we decided to focus our attention on determining the sensory perception of BB, FG, and H, as well as to determine if there was any relationship between sensory attributes and soap quality parameters based on the unsaponified fatty acid composition.

Color and fragrance are two main sensory perceptual indicators of soap quality [ 3 ]. The BB had the highest color preference 7. This was very interesting because the base bar was formulated as part of the experimental design, where it was used as a control bar to compare the effects of soap formulation across samples. The other soaps were formulated with exotic essential oils as additives, but this did not translate to superior overall acceptance.

Shape, lather, moisturizing ability, and estimated price were also evaluated in this study. However, there was no significant difference between the soap types and these sensory parameters. As such, the overall perception and preference were similar between all three soap types Table 3.

These relationships suggest that an appealing smell had the greatest influence on consumer preference, and that color and appealing smell influenced perceived pricing of the natural soaps evaluated in this study.

Pricing, smell fragrance , and color are major affective response indicators reported in the literature. Affective response is used as an instrument to measure market potential [ 13 ].

Surprisingly, lather and moisturizing characteristics major indices of natural soap quality [ 1 , 2 , 3 ] had very little influence on the overall consumer ratings of the three natural soaps evaluated in this study. However, the overall preference or affective response was similar between the three natural soaps Table 3. Consequently, we sought to determine whether the unsaponified fatty acids observed in the natural soaps had any influence on the sensory qualities or attributes of the soaps evaluated in this study.

Overall, when sensory attributes, antioxidant activities, phenolic content, and oxidation status were used to cluster or differentiate the three natural soaps, the soaps clustered in different quadrants of the biplot following PCA analysis Figure 8. The BB was grouped in quadrant 1 based on the lather ability, appealing shape, overall rating, appealing smell, and the level of HPC. Similarly, when the unsaponified fatty acids were added to the model and PCA analysis conducted, H, FG, and BB segregated into separate quadrants of the biplot Figure 8 b.

BB was not segregated based on unsaponified fatty acids. Color, LPC, price, smell, and overall preferences were instead observed as the parameters segregating BB in quadrant 2 of the biplot.

Interestingly, BB consistently had the best overall preference of the soaps formulated in this study Figure 8. Sensory attributes of different commercial natural soaps manufactured using cold saponification. The BB had superior color ratings and appealing smell compared to the other soaps following sensory evaluations. Overall, when unsaponified fatty acids, antioxidants, phenolics, oxidation status, and sensory attributes were used to group the natural soaps, BB had the best overall preference.

This is a significant finding because the base bar was included in this study as the control and was not a part of the more sophisticated formulations using specialty plant oils as feedstock , exotic essential oils, or plant extracts as additives that the industry partner typically used to make their natural soaps for commercial sales. The use of these ingredients did not translate to superior consumer preference or acceptance. These findings suggest some of the more exotic additives and specialty oils used as feedstock in manufacturing natural soaps may not be producing the perceived consumer acceptance or preference, and considerations should be given to their use during manufacturing of hand-made natural soaps.

This could have implications in the cost of materials used for production and potential profitability. Three natural herbal soaps designated base bar BB , forest grove FG , and hibiscus rose hip H were manufactured using cold saponification. The health Canada compliant numbers for each of the natural soaps are as follows: , 0. Aliquots 8 g of the melted oils and butter from each soap batch were obtained to determine the chemical composition of the soap feedstock prior to cold saponification.

Four separate batch replicates were independently made for each soap type. The saponification value for all oils used in the composition of the different soaps were determined using a commercial lye calculator. The cold process method herein referred to as cold saponification was used for soap production where lye pure sodium hydroxide was used as the base in the saponification process.

The amount of sodium hydroxide required determined from the lye calculator was mixed with water and left to cool for 60 min. The cooled lye and water was added to the melted oils and butter for each soap type see above , and the subsequent mixture was blended until thickened about the consistency of thick cream , but before trace point where the saponification process is almost complete was reached the consistency of pudding.

The mixture was used to fill parchment paper-lined molds, and the soaps were left to complete saponification at room temperature for 24 h. A total of eight batches for each soap type were made for both chemical and sensory perception analyses.

Each soap type was designated as follows: base bar BB , forest grove FG , and hibiscus rose hip H based on their formulation. To evaluate the effects of additives on the unsaponified fatty acid composition of BB, FG, and H herbal soaps following cold saponification, natural plant additives were added to each of the soaps as follows: To the base bar and forest grove soaps, 0. To both hibiscus and forest grove, a second combination of natural additives consisting of a combination of naturally sourced colored clays for color and essential oils for fragrance were added.

Specifically, 0. This soap bar was designated FGA. To hibiscus, French pink clay, filtered hibiscus rose hip tea steeped in boiled water for 1—3 h for color, aesthetic appeal, and fragrance , and an essential old blend containing sweet orange, pink grape fruit, bergamot, vanilla, cinnamon bark, cedar leaf, ylang ylang, cananga, lavender, and palmarosa were added as additives.

This soap bar was designated HA. As such, 0. The additives were added to the mixture and thoroughly mixed just before molding. The same cold saponification method noted above was used to manufacture the soaps with additives. Extraction was carried out according to the methods of Thomas et al. The supernatant was filtered with glass wool, and the filtrate was used without further dilution to determine the lipophilic antioxidant activity and the organic phenolic content of the soaps.

The undisturbed pellets were re-suspended in 1 mL of cold 50 mM sodium phosphate buffer pH 7. The supernatant was diluted with 50 mM sodium phosphate buffer.

This diluted supernatant was used to determine the hydrophilic antioxidant activity and aqueous phenolic content. The hydrophilic and lipophilic phenolic content were determined separately using a fold diluted solution of Folin—Ciocalteu reagent with quercetin as a standard in the range of 0—1. The microplates with the mixture were incubated in the dark at room temperature for 30 min, and the absorbance was measured at nm using a Synergy HT microplate reader Biotek, Fisher Scientific, Mississauga, ON, Canada.

The results were expressed as micromole quercetin equivalents per gram of soap. Four replicates were analyzed per standard concentration or sample treatment. Values for total phenolic content were determined by summation of the aqueous hydrophilic and organic lipophilic phenolic values.

The hydrophilic and lipophilic antioxidant activities were determined according to the methods of Jimenez-Alvarez et al. The working solution reaction mix was prepared fresh daily by adding 25 mL of 30 mM acetate buffer pH 3. A standard solution of 1 mM of Trolox was made using 6. The sample mixture was incubated in the dark for 30 min and the absorbance was measured at nm using a Synergy HT microplate reader Biotek, Fisher Scientific, Mississauga, ON, Canada. The results were expressed as micromole Trolox equivalents per gram soap.

Values for total antioxidant activity were determined by summation of the aqueous hydrophilic and organic lipophilic antioxidant values. This analysis was conducted using the established method of Erel [ 16 ]. Sodium hydroxide NaOH is used to produce hard soaps like bar soap. Whereas, potassium hydroxide KOH is used to make liquid or soft soaps. You can add a variety of ingredients to your soap including oatmeal , fruit and herbs , and flowers. The other ingredients that you put in the soap can provide additional benefits toward your skin care, though not necessarily with lathering and cleansing abilities.

How well the soap lathers and cleanses also depends on the oils used for the soap and their reaction with the lye, so you can get a variety of soaps using different ingredients. When you are making soap, you are testing—by trial and error—with chemistry.

Soap is one of those crafts that also have a scientific component and can be great for experimenting with different ingredients. Just make sure to thoroughly research the ingredients that you use, the proportions of oil to lye, and that you also follow safety precautions because lye is a volatile substance. Try it, and you will have beautiful soaps to use in your bathroom, sell at craft fairs, or give to friends.

What Is Saponification in Soap-Making?