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J. Cosmet. Sci., 74.5, 289–300 (September/October 2023)
*Address all correspondence to Georgia E. Tsotsou, gtsotsou@uniwa.gr
Extraction-Free, In Situ Analysis of Glucose in Cosmetic
Formulations Based on Digital Image Colorimetry by
Smartphone
GEORGIA ELENI TSOTSOU AND ANASTASIA KYRIAKI TSARA
Department of Biomedical Sciences, University of West Attica, Egaleo, Greece (G.E.T., A.K.T.)
Cosmetic S.A., Karellas, Koropi, Greece (G.E.T)
Accepted for publication September 26, 2023.
Synopsis
We are proposing an extraction-free methodology for in situ quantifying glucose in cosmetic formulations
including oil-in-water (O/W) emulsions, shampoos, or gels. Quantification is based on the known glucose
oxidase/peroxidase reaction which is employed directly into the cosmetic formulation to generate a colored
product. Digital image colorimetry is then used to capture, calibrate, and quantify responses by the image-
processing software ImageJ. We have demonstrated a linear relationship between smartphone camera-
captured color intensity of the treated formulation and glucose concentration in all studied formulations.
Upon methodology validation, favorable technical characteristics were obtained for glucose analysis in an
O/W emulsion: the linearity range under the conditions employed was between 0 and 6.4*10−3% weight
per weight concentration of glucose in the formulation. Additionally, analysis of two quality control samples
yielded a coefficient of variation ≤11.6%, while bias was not higher than ±11.1%. Last, we successfully applied
the proposed analysis setup in combination with a standard addition procedure to quantify spiked glucose in
O/W emulsions, including colored emulsions, where bias was found between ±3.2% and ±15.9%. The above
results indicate acceptable reproducibility and accuracy for the proposed methodology and accountable matrix
effect. This study may open the route for routine glucose quantification in cosmetic or food emulsions and
galenic ointments.
INTRODUCTION
Glucose is a hygroscopic molecule, component of the natural moisturizing factor (NMF)
and is often used for its humectant/skin conditioning properties in skin care applications
either added directly to the formulation or indirectly, as component of natural extracts. In
addition, it has a role in certain formulations as a flavoring agent. Glucose is commonly
present in bath products, cleansing products, skin care products, makeup, and hair care
products. Moreover, it is also used in skin whitening products thanks to its indirect anti-
melanogenic effect at 2% weight per weight concentration (w/w).1 Glucose concentration in
cosmetic products ranges widely, from 10−4% to 91% in leave-on products and from 10−4%
to 84% in products intended for dermal contact.2

290 JOURNAL OF COSMETIC SCIENCE
Topical application of glucose may promote skin homeostasis by maintaining the
skin microbiome i.e., functioning as a prebiotic.3 It has not been clearly established,
though, a topical glucose effect on the microflora involved in skin diseases such as
Propionibacterium acnes (acne), or Malassezia spp. (folliculitis, dandruff and pityriasis)
etc. Other prebiotics have been demonstrated to inhibit the inflammation-causing
bacterium Propionibacterium acnes, in favor of beneficial species of the skin.4,5 It has
been manifested that excess glucose in hyperglycemic abscesses can significantly
enhance S. aureus virulence potential, thus worsening infection.6 Since glucose often
enters cosmetic formulations through added extracts, it is not always mentioned in the
product’s list of ingredients. In such specific applications, the existence of an analytical
method for glucose quantification in the frame of quality control may potentially be
important.
In the area of topical pharmaceuticals, the availability of a direct method to inform on
glucose content may be important for specific applications/patient groups: Although
systemic hyperglycemia prevents wound healing, topical preparations of sugar-based
compounds and honey have provided, in specific studies, promising results as a means
toward wound repair.7,8 No contribution to systemic hyperglycemia was observed.8 Another
study indicated that high glucose inhibits keratinocyte and fibroblast migration as well
as wound healing in vivo, in a concentration-dependent manner.9 Last, in the domain of
nutrition, there is a need to quantify glucose in emulsions used for the purpose of parenteral
nutrition.10
The glucose oxidase-based photometric method is commonly used for determining glucose
in solution11, either in biological fluids or food extracts, and presents the advantages of
increased specificity and ease of analysis, since several commercial kits relying on this
principle are available. A large number of alternative methods have been published
including spectrophotometric, electrophoretic and chromatographic methods.12 In general,
chromatographic methods (usually HPLC or GC) and mass spectrometry are the gold
standard methods of analysis of organic analytes in cosmetics and personal care products.13
Although specific and sensitive, they present the drawback of requiring strong analytical
expertise, expensive equipment, and typically extensive sample preparation.14 A number
of spectrophotometric methods are also commonly used such as Raman, IR, UV-Vis13,
which although simpler, still require sample preparation prior to analysis, which may
often involve toxic waste generation. Additionally, immunological analytical techniques
have been proposed for quantification of a number of analytes in cosmetics and personal
care products15, which are highly specific and sensitive, however they suffer from high
analysis cost.
We here describe a low-cost and low-waste, extraction-free, smartphone-based
methodology for in situ analysis of glucose in cosmetic formulations. The methodology
relies on the glucose oxidase (GOD)-catalyzed specific glucose conversion to a colored
product through peroxidase (POD)11 inside the cosmetic preparation. Smartphone-
based digital image colorimetry is then employed to capture, calibrate, and quantify
responses. Smartphone-based image analysis is emerging as an increasingly popular
technique, with applications over a range of domains.16 The greatest advantage of the
proposed method over existing analysis setups is the lack of a pretreatment step. The
format’s simplicity and the lack of need for analytical equipment also make the method
very attractive.