Coffee: Chlorogenic Acids — Content and Roasting Degradation

Chlorogenic acids (CGAs) are a family of phenolic ester compounds formed from quinic acid and one or more hydroxycinnamic acids (primarily caffeic, ferulic, and p-coumaric acids). They are the dominant polyphenol class in coffee and are responsible for a significant portion of coffee’s antioxidant activity, characteristic sour-acidic taste notes, and many of its studied health associations.

Structure and Isomers

The term “chlorogenic acid” refers to a family of related compounds, not a single molecule. The most important group is the caffeoylquinic acids (CQAs), of which 5-caffeoylquinic acid (5-CQA, formerly called chlorogenic acid specifically) constitutes the majority. Coffee also contains:

• Feruloylquinic acids (FQAs) — similar structure with a ferulic acid moiety
• Dicaffeoylquinic acids (diCQAs) — two caffeic acid groups esterified to a single quinic acid
• Mixed diesters (caffeoyl-feruloylquinic acids)

Together, approximately 40 distinct CGA isomers have been identified in coffee extracts.

CGA Content by Roast Level

Roasting is the primary determinant of CGA content in brewed coffee. The heat-driven hydrolysis and degradation of these esters is essentially irreversible.

Coffee State	CGA Content (% dry weight)	Notes
Green (unroasted) Arabica	6.0–7.0%	Highest CGA content
Green Robusta	7.0–10.0%	Robusta has more CGAs than Arabica
Light roast (Arabica)	3.0–4.0%	~50% degraded
Medium roast (Arabica)	1.5–2.5%	~65–70% degraded
Dark roast (Arabica)	0.5–1.0%	~85–90% degraded
French/Italian roast	<0.5%	>90% degraded

Data synthesized from Farah (2012) and Clifford (2000).

Degradation Kinetics During Roasting

CGA degradation begins above 180°C and accelerates sharply as bean temperature climbs through first crack (~196°C) and toward second crack (~224°C). Three main degradation pathways operate simultaneously:

1. Ester hydrolysis — quinic and caffeic acids are released; caffeic acid may further degrade
2. Lactonization — quinic acid cyclizes into quinolactone, contributing bitterness
3. Incorporation into melanoidins — CGAs bind with proteins and sugars during Maillard reactions, forming high-molecular-weight brown polymers

The quinolactone pathway is significant because it converts antioxidant CGAs into bitter compounds that contribute to dark roast’s characteristic harshness.

Health Research Context

The CGA content of coffee is a focus of health research because:

• CGAs are potent inhibitors of glucose-6-phosphatase, an enzyme involved in hepatic glucose release — mechanism proposed for coffee’s observed association with reduced type 2 diabetes risk
• CGAs exhibit antioxidant activity in vitro, though bioavailability in humans is an active area of investigation
• Epidemiological data (Higdon and Frei 2006; multiple meta-analyses) consistently associate habitual coffee consumption with reduced risk of type 2 diabetes, Parkinson’s disease, and certain liver conditions

Because light roasts retain significantly more CGAs than dark roasts, studies attempting to link CGA intake to health outcomes must account for roast level — a variable often poorly controlled in epidemiological work.

Contribution to Flavor and Acidity

CGAs directly contribute to perceived acidity and astringency in brewed coffee. As CGAs degrade during roasting:

• Quinic acid concentration increases, contributing sharp, dry astringency
• Caffeic acid is released, with its own bitter/sour character
• Further pyrolysis produces chlorogenic acid lactones, major contributors to dark roast bitterness

Light-roasted coffees, with their higher residual CGAs, tend to taste brighter and more complex-acidic. Dark roasts trade CGA-derived brightness for Maillard-reaction-derived body and bittersweetness.