PRESERVATIVES


in-house microbiological investigations explored the extent of AV 406’s anti-fungal and anti-bacterial properties. This can be demonstrated most easily by its minimum inhibitory concentration (MIC) - the lowest concentration of an anti-microbial that will inhibit the growth of a microorganism. In-house studies showed promising


potency against yeasts such as Candida albicans and Malassezia furfur, with MIC values of ≤0.2%. AV 406 also gave encouraging MIC values of 0.25% against gram-positive bacteria (Staphylococcus aureus and Propionibacterium acnes), and 0.5–1.0% against gram-negative bacteria (Pseudomonas aeruginosa and Escherichia coli), as shown in Table 1. Higher MIC values against gram-negative


compared to gram-positive bacteria can be explained by examining the structure of the bacteria themselves. Gram-negative bacteria typically have notably higher tolerance to anti-bacterial agents as they are surrounded by a thin peptidoglycan cell wall, which is further enclosed by an outer membrane. It is this lipopolysaccharide layer which provides greater protection from anti-bacterial agents. In comparison, the absence of an outer


membrane in grampositive bacteria allows the penetration of the anti-bacterial agent to occur with greater ease. The broad spectrum of potency displayed was encouraging as it illustrates that end products containing AV406 may be self-preserving and therefore do not require a dedicated preservative. It is worth noting that due to the nature


of sodium caproyl/lauroyl lactylate and sodium citrate, the MIC values discussed were obtained using pH adjusted media, where the tryptic soy agar (TSA) or Sabouraud dextrose agar (SDA) had been adjusted to pH 5.5–6. In-house studies with AV406 have noted superior antimicrobial activity at lower pH levels. Media were adjusted using hydrochloric acid (10%) to obtain the desired pH. Table 1 shows the MIC values for TSA and SDA with and without pH adjustment. This is an important consideration, as the


formulator must consider whether AV 406 will be a suitable preservative and/or anti- microbial active in the final formulation where the pH is above 6. Preservative and anti- microbial effects are still observed where the pH is above 6, although the dosage will likely increase to offset the reduction in efficacy. To further validate anti-microbial activity,


these results have been proven in end formulations according to the American Society for Testing & Materials (ASTM) method E 2315. This is a standard time-kill test which measures the antimicrobial performance of a sample over a short period of time. The kill test quantifies the reduction in numbers of a known inoculum of microorganisms over specified contact times. Each product was tested from 30 seconds to


five minutes at regular intervals, which is within the expected time frame of a consumer using a soap or shampoo. Finished products included hand soaps with antibacterial properties and shampoo with anti-dandruff properties (Table 2).


www.personalcaremagazine.com


53


TABLE 2: TIME-KILL TEST RESULTS FOR EACH PRODUCT CONTAINING AV 406 ACCORDING TO ASTM E2315 Product


Soap bar* Liquid shampoo *Modified solid time-kill test.


TABLE 3: ATSM E2315-STANDARD TIME-KILL TEST FOR LIQUID SHAMPOO AGAINST M. FURFUR Entry


1


2 3 4 5 6 7 8 9


Active Ingredient AV 406 (0.5%) AV 406 (1.0%) Zinc pyrithione


Piroctone olamine Climbazole


AV 406 (0.5%) AV 406 (1.0%) Zinc pyrithione


Piroctone olamine In order to solidify the claim that the


observed anti-dandruff activity was the direct result of the AV 406, background studies and control samples with other common antidandruff actives, such as zinc pyrithione, climbazole, piroctone olamine in identical formulations, were conducted. These provided a frame of context and comparison against the tried and tested anti-dandruff additives which have dominated the market. Table 3, Entries 1–5 show results for neat


shampoo formulations against M. furfur. As expected, common anti-dandruff additives given in Entries 3–5 gave exceptional results, showing a reduction of 99.99% of M. furfur within a 30-second contact time. This result was matched by AV 406 when included in the formulation at levels as low as 0.5%. It is worth noting, that this is the percentage of aqueous blend of sodium caproyl/lauroyl lactylate and sodium citrate as supplied, and not the active content of product. In addition to testing products neat against


M. furfur, more stringent testing was conducted where products diluted to 20% with standard tap water were tested in order to replicate an ‘in-use’ model more accurately (Entries 6–10). Although AV 406-containing shampoos do see a reduction in anti-fungal activity once diluted, this is in the order of magnitude which can be expected from a 20% in-test dilution.


TABLE 4: FORMULATION OF LUPINE & COCONUT LIQUID SHAMPOO USED IN M. FURFUR TRIALS


INCI Name


Sodium Laureth Sulphate Cocoamidopropyl Betaine Lupine Extract Coconut Oil


Aevum Vita 406 Aqua


Hydroxyethylcellulose


w/w % 55.56 16.67 0.5 1.0


0.5


24.77 2.0


%


0.15 0.3 1.0 0.1


0.75 0.03 0.06 0.2


0.02


Reduction after time 99.99%-30 sec. 99.99%-30 sec. 99.99%-30 sec. 99.99%-30 sec. 99.99%-30 sec. 77.00%-2 min 88.50%-2 min 99.99%-30 sec. 99.99%-30 sec.


The reduction in efficacy between Entry 1 and 6 is 23%, whereas reduction in efficacy between Entry 2 and 7 is just 11%. Considering the extremely low active dose in AV 406 (0.5% as supplied resulting in 0.03% of active ingredient), a reduction in M. furfur of 77% in a two-minute contact time shows significant anti-microbial strength. Zinc pyrithione, piroctone olamine and climbazole did not show a reduction in efficacy once diluted. Results were particularly significant as zinc pyrithione is due to be banned from personal care applications in the EU from March 2022. A dilution of 20% for shampoo products was a result from inhouse testing, where it was found that on average, the ratio of shampoo to the mass of water retained by thoroughly soaked hair was around 1:4. In line with market and consumer trends,


AV 406 has also been formulated in water- free, packaging-free cosmetic products. In theory, water-free formulations may not always require preservation. However, in the case of a shampoo or soap bar, the product will become wet through normal use and may not fully dry out, making it susceptible to microbial growth. For this reason, AV 406 was added into shampoo bar formulations at 1–2% for self-preservation as well as for antibacterial effect (Figures 2 & 3). Formulations containing AV 406 without


any additional were challenge tested according to EP 7.0 standards. All formulations included in this article passed according to these standards, demonstrating the preservative efficacy of AV 406 from as low as 0.5%. Results from a wide range of


comprehensive studies show that this blend of sodium caproyl/lauroyl lactylate and sodium citrate can not only be used to create self-preserving formulations, but also as an anti-bacterial active. Depending on the formulation and dosage, this could introduce


July 2022 PERSONAL CARE


AV 406 (%) 1


0.5 Microorganism


Mixed bacteria M.furfur


Reduction after time 99.09%-1 min.


99.99%-30 sec. Potential Claim


Anti-bacterial Anti-dandruff


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56  |  Page 57  |  Page 58  |  Page 59  |  Page 60  |  Page 61  |  Page 62  |  Page 63  |  Page 64  |  Page 65  |  Page 66  |  Page 67  |  Page 68  |  Page 69  |  Page 70  |  Page 71  |  Page 72  |  Page 73  |  Page 74  |  Page 75  |  Page 76  |  Page 77  |  Page 78  |  Page 79  |  Page 80  |  Page 81  |  Page 82  |  Page 83  |  Page 84  |  Page 85  |  Page 86  |  Page 87  |  Page 88  |  Page 89  |  Page 90  |  Page 91  |  Page 92  |  Page 93  |  Page 94  |  Page 95  |  Page 96