Sinapic Acid (Hydroxycinnamic Acid · UV Photoprotection · Neuroprotective)

Compound	Sinapic Acid
Chemical class	Polyphenol — Hydroxycinnamic Acid (3,5-Dimethoxy-4-hydroxycinnamic Acid)
CAS	530-59-6
Primary source	Brassica spp. (mustard, rapeseed), Sinapis alba (white mustard)
Key applications	Antioxidant, neuroprotective, anti-anxiety, photoprotective
Claim strength	Moderate
Typical form	Mustard/rapeseed extract; sinapine (sinapic acid choline ester); isolate
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Name origin: From Sinapis (mustard genus), the primary botanical source. Sinapic acid is the 3,5-dimethoxy-4-hydroxy analogue of caffeic acid — the most methoxylated of the common hydroxycinnamic acids. It is found primarily as sinapine (the choline ester) in mustard seed and rapeseed, and as sinapoyl esters in Brassicaceae cell walls. Traditional use: Mustard preparations have been used in Ayurveda and European herbalism for warming/counterirritant applications (topical) and as digestive and respiratory tonics (oral). Sinapic acid specifically has not been a traditional therapeutic target; it is characterised through modern phytochemical research. Research trajectory: Sinapic acid has attracted research for anxiolytic activity (GABA-A modulation), neuroprotection, antioxidant capacity, and UV photoprotection. Its dimethoxy-hydroxycinnamic structure gives it unique physicochemical properties including UV absorption at longer wavelengths than caffeic acid. Commercial source: Available as a constituent of Brassica seed preparations; isolated sinapic acid and sinapine are available from specialist chemical suppliers. Contact Herbuno for availability assessment.

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Evidence for Sinapic Acid Applications

Anxiolytic activity: Sinapic acid modulates GABA-A receptors and reduces anxiety-related behaviour in rodent models (elevated plus maze, open field test) at 5–25 mg/kg oral doses. The GABA-A modulation mechanism parallels other flavonoid anxiolytics (chrysin, vitexin) but from the hydroxycinnamic acid structural class — an unusual anxiolytic mechanism for a phenolic acid. Claim strength: Moderate (preclinical; no human trials).

Neuroprotective: Sinapic acid inhibits acetylcholinesterase, reduces amyloid-beta aggregation, and suppresses neuroinflammation in cell and animal models. Memory improvement in scopolamine-induced amnesia models is documented. Relevant for cognitive support and neuroprotection formulations. Claim strength: Moderate.

Antioxidant and UV photoprotection: Sinapic acid absorbs UV radiation at 326 nm (UV-A range) with high molar extinction coefficient, making it one of the most effective natural UV absorbers among hydroxycinnamic acids. Radical-scavenging capacity is high due to the 4-hydroxyl and dimethoxy electron-donating groups. Relevant for both internal antioxidant formulations and topical UV-protection applications. Claim strength: Moderate.

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Dosage & Formulator Specification

No established human supplement dose for sinapic acid. Preclinical effective doses: 5–25 mg/kg for anxiolytic and neuroprotective applications; human equivalent doses are approximately 0.3–2 mg/kg (21–140 mg/day for a 70 kg adult). Sinapic acid is not commercially available as a supplement ingredient at scale; Contact Herbuno for availability assessment for research formulation contexts.

Sinapine (sinapic acid choline ester) is more abundant in commercial rapeseed and mustard press cakes than free sinapic acid. Sinapine hydrolyses to sinapic acid and choline in the gut, making sinapine-rich seed preparations a potential delivery vehicle for sinapic acid with the additional benefit of choline co-delivery. Rapeseed press cake is an industrial by-product with potential as a sinapine source.

Sinapic acid has good aqueous solubility (better than ferulic acid). Stable at acidic to neutral pH. UV absorption at 326 nm makes it light-reactive — amber packaging required. Thermostable to 100°C for short durations.

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Frequently Asked Questions — Sinapic Acid

Is sinapic acid found in common dietary plants?
Yes. Sinapic acid and its esters are ubiquitous in Brassicaceae (mustard family) vegetables — broccoli, Brussels sprouts, cabbage, and kale all contain significant sinapoyl esters. Dietary exposure from Brassica vegetable consumption is meaningful (1–5 mg/day from regular vegetable intake). It is also present in citrus peel and several other botanical sources outside the mustard family.

What makes sinapic acid a better UV absorber than ferulic acid?
Both absorb UV, but ferulic acid absorbs primarily at 320 nm (UV-A/UV-B border) while sinapic acid absorbs at 326 nm with higher molar extinction coefficient in the UV-A range. The two dimethoxy groups in sinapic acid extend conjugation and shift the absorption maximum, giving superior UV-A coverage. The combination of ferulic acid + sinapic acid would theoretically provide broader UV photoprotection than either alone.

Is sinapic acid from mustard seed safe for mustard allergy sufferers?
Mustard is a declared allergen in EU food labelling (one of the 14 major allergens). Mustard allergy is primarily a protein-mediated IgE reaction to 2S albumin and other seed storage proteins, not to sinapic acid. Isolated sinapic acid from mustard extraction (which removes proteins) would not be expected to trigger mustard protein allergy; however, cross-contamination risk and absence of dedicated safety data for sinapic acid in mustard-allergic individuals means this should be declared on product labels and tested appropriately.

Can sinapic acid be combined with ferulic acid for a broader-spectrum topical antioxidant?
Yes — the complementary UV absorption spectra (ferulic acid at 320 nm, sinapic acid at 326 nm) and shared antioxidant mechanisms make the combination rational for broad-spectrum topical photoprotection. Research on the ferulic-sinapic acid combination for topical use is limited but the mechanistic basis is sound. The well-established CE Ferulic formulation architecture could theoretically incorporate sinapic acid for additional UV-A coverage.

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Claim-strength scale – High = multiple human RCTs; Moderate = limited trials or strong preclinical convergence; Emerging = early-stage lab or animal data.

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