DOI: 10.25338/b8c91c
title: Acids in Coffee - A Review of Sensory Measurements and Meta-Analysis of Chemical Composition

description: This dataset contains information from the meta-analysis presented in
 "Acids in Coffee: A Review of Sensory Measurements and Meta-Analysis
 of Chemical Composition." Acid concentrations were extracted
 from a total of 121 publications for at least one of 26 different
 organic acids (OAs) or 23 different chlorogenic acids (CGAs), yielding
 7,509 distinct data points. Concentrations were collected for Coffea
 arabica, Coffea canpehora (robusta), and other types of coffee, for both
 green and different roast levels. 
description: To obtain a more complete picture on the acid composition in
 coffee, we conducted an extensive review and meta-analysis of the
 scientific literature. Web of Science, Google Scholar, and the University
 of California Library catalog were searched between April to December 2020
 for any publications that included data about the amounts of acid in
 coffee samples. This search focused explicitly on measurements of the
 concentration of individual CGAs and OAs in coffee, not the overall amount
 of acid in coffee (usually expressed as total titratable acidity). Access
 was limited to online versions of publications due to COVID-19
 restrictions during the time of the database search. Articles not
 available directly online were obtained through Interlibrary Loan
 requests. In the case of articles published in languages other than
 English, a translating website was used to read the article. Abstracts and
 full texts were examined for specific data about the absolute amounts of
 any chlorogenic or organic acids. Articles that only examined the
 presence, relative amounts, or formation pathways of CGAs or OAs were
 excluded. Papers that reported CGAs or OAs in units of mg/L without
 including the original mass of coffee used were excluded due to the fact
 that amounts in units of mg/L cannot be directly compared with amounts in
 units of mg/kg (comparing mass in wet basis versus mass in dry
 basis).  If the publication did contain specific
 amounts of CGAs or OAs that satisfied the preceding conditions, then all
 roast levels, extraction types, and coffee species were included, except
 for decaffeinated and instant coffee. The additional processing on
 decaffeinated and instant coffee complicates comparison with other
 coffees. If the publication listed data for store-bought samples, those
 were included as well. In some cases, roast level and coffee species were
 not specified, and these data points were categorized as “unspecified”.
 For the purposes of this review, Coffea arabica will be referred to as
 “arabica” coffee and Coffea canephora cv. robusta will be referred to as
 “robusta” coffee.  <br> A tremendous complicating factor is the
 roast level, which strongly affects acid concentrations but is very
 challenging to quantify precisely; subjective roast descriptions like
 “dark roast” have no universally accepted definition. For the purpose of
 the meta-analysis, we therefore performed a semi-qualitative
 classification of the reported roast levels into three categories – light,
 medium, or dark – using the following methodology.    
 The roast levels for specific data in publications was determined
 in one of four ways: (1) as the publication’s self-described roast level;
 (2) from the publication’s reported amount of water lost during roasting
 (11-13% = light, 14-16% = medium, 17-20% dark) or organic roast loss
 percentage (ORL%) (2-4% = light, 4.1-5.5% = medium, 5.6-7% = dark)
 (Perrone et al. 2008; Weers et al. 1995); (3) the publication’s reported
 L*a*b* color values of the roasted beans where L* of 30, 25, and 20
 correspond to light, medium, and dark, respectively (Chindapan, Soydok,
 and Devahastin 2019); or (4) as “unspecified” if the publication did not
 mention any of the above.  If the publication provided finer demarcations
 of roast level (e.g., a “light roast” and a “very light” roast), then we
 grouped their samples as appropriate into just our three broad categories.
 Lastly, samples that were labelled simply as “roasted” without giving any
 indication to the degree of roast kept the label of “roasted” and were
 included when comparing roasted coffee as a whole (Correia, Leitao and
 Clifford 1995; Agnoletti et al. 2019).   We emphasize that because roast
 level is very qualitative and methods of measuring roast level vary
 greatly, the roast level labels used in this paper are approximate, based
 on the information available in the cited publications. 
 Similarly, extraction of the acids for analysis varied widely
 among the different publications. If a chemical solvent such as methanol
 was used, the extraction type was labelled as “solvent”; soaking the
 coffee grounds in hot water was labelled as “immersion”; extraction types
 such as “French press” or “espresso” were explicitly mentioned in their
 respective publications and the labels were kept for data
 collection.  Lastly, all measurements were converted to
 mg/kg to simplify comparison.  Accordingly, the units reported in the
 publications often had to be converted, e.g., data reported in units of
 g/kg was multiplied by 1000 to match units of mg/kg. In cases, where
 publications reported concentration in terms of mmol/kg, the molecular
 weight of the specific acid was used to convert to mg/kg. Lastly, in
 articles that presented the data in units of mg/L and included the
 original brew recipe (grams of coffee and liters of water), the data was
 converted to units of mg/kg using the brew recipe, assuming full
 extraction from the dry coffee grounds. <br> Data for 23 different
 CGAs and 26 different OAs was collected and analyzed While thirty-eight
 OAs have been quantified in coffee (Maier 1999), many are present in trace
 amounts and not commonly reported. Those reported in fewer than 2
 publications and with amounts less than 0.01/kg were not included,
 accounting for the difference in total OAs analyzed in this
 review.  In chlorogenic acids the widely reported acids
 are total CQA, 5-CQA, 4-CQA, 3-CQA, total diCQA, and total FQA. Some
 publications would report only total concentrations of one class (“Total
 diCQA”) instead of quantifying each isomer, so three categories were
 created, “Total CQA”, “Total FQA”, and “Total di-CQA”, to compare across
 publications (Anthony, Clifford, and Noirot 1993). Each of these
 categories includes the sum of each isomer in that class; for example,
 “Total CQA” is a sum of 5-CQA, 4-CQA, and 3-CQA.  27 unique CGAs have been
 identified in coffee (Clifford et al. 2003; Clifford 2006). The limited
 recurrences (fewer than 2 publications) of some species led to their
 exclusion from data collection. <br>  
description: Chlorogenic acids and organic acid concentrations are
 presented in separate .csv files. A third separate .csv is included that
 details the full bibliographic information for the publications that
 provided the data for this dataset.