Scientia et Technica Año XXVIII, Vol. 28, No. 03, julio-septiembre de 2023. Universidad Tecnológica de Pereira. ISSN 0122-1701 y ISSN-e: 2344-7214

150

Effect of extraction conditions on obtaining

pectin from agroindustrial coffee by-products

Efecto de las condiciones de extracción en la obtención de pectina a partir de

subproductos agroindustriales del procesamiento del Café

W. Pérez-Mora ; J. Mojica-Gómez

DOI: https://doi.org/10.22517/23447214.25163

Scientific and technological research article

Abstract— Pectin is a product of industrial interest that uses

agroindustrial residues to obtain it. To address the reduction of

waste generated in coffee agroindustrial production and explore

potential applications of by-products, this study investigates the

impact of various physical factors (pH, temperature, and reflux

time) on the extraction of pectin from discarded coffee husks

(Coffea arabica) in the San Juan de Rioseco area, following the

desiccation process. The extraction process involves hydrolysis in

an acidic medium using hydrochloric acid, followed by coagulation

with 96% ethanol, filtration, and subsequent drying at 45°C. The

quality of the obtained pectin is assessed through infrared

spectrophotometry to determine the degree of esterification and

extraction yields under different conditions. Wet material yields

high methoxyl pectin, with esterification levels ranging from 56%

to 75%, while the yield remains below 1%. Analysis of the main

components and surface graphs reveals an inverse relationship

between temperature and esterification degree, as well as a direct

relationship between time and yield. Based on these findings, the

optimal extraction conditions are determined to be pH 2.0, a

temperature of 90°C for 1 hour. Overall, the results suggest that

byproducts from the coffee agroindustrial process hold promise as

a source of pectin.

Index Terms— acid hydrolysis, coffee byproducts, degree of

esterification, pectin, response surface methodology, solid-liquid

extraction, waste management.

Resumen— La pectina es un producto de interés industrial que usa

residuos agroindustriales para su obtención. Para abordar la

reducción de residuos generados en la producción agroindustrial

del café y explorar posibles aplicaciones de subproductos, este

estudio investiga el impacto de varios factores físicos (pH,

temperatura y tiempo de reflujo) en la extracción de pectina a

partir de cáscaras de café desechadas (Coffea arabica) en el área

de San Juan de Rioseco, después del proceso de desecación. El

proceso de extracción implica la hidrólisis en un medio ácido

utilizando ácido clorhídrico, seguido de la coagulación con etanol

al 96%, filtración y posterior secado a 45°C. La calidad de la

pectina obtenida se evalúa mediante espectrofotometría infrarroja

para determinar el grado de esterificación y los rendimientos de

extracción bajo diferentes condiciones. El material húmedo

produce pectina de alto contenido de metoxilo, con niveles de

esterificación que oscilan entre el 56% y el 75%, mientras que el

rendimiento se mantiene por debajo del 1%. El análisis de los

This manuscript was sent on August 17, 2022 and accepted on July 28,

2023. This work was supported by Centro de Gestión industrial – SENA and

Sistema de Investigación, Innovación y Desarrollo Tecnológico - SENNOVA

code SGPS-8493-2021.

componentes principales y los gráficos de superficie revela una

relación inversa entre la temperatura y el grado de esterificación,

así como una relación directa entre el tiempo y el rendimiento.

Basándose en estos hallazgos, las condiciones óptimas de

extracción se determinan como un pH de 2.0, una temperatura de

90°C durante 1 hora. En general, los resultados sugieren que los

subproductos del proceso agroindustrial del café tienen potencial

como fuente de pectina.

Palabras claves— Extracción sólido líquido, grado de

esterificación, hidrólisis ácida, manejo de residuos, metodología de

superficie de respuesta, pectina.

I. INTRODUCTION

OFFEE is one of the most important agricultural products in

the world and Colombia is internationally recognized for

its coffee quality, aroma, and flavor. There are mainly two

methods for the treatment of coffee fruits: wet processing and

dry processing. Approximately half of the world coffee harvest

is processed by the wet method in which the coffee berry is

subjected to mechanical and biological operations in order to

separate the seed from the exocarp (husk), the mesocarp

(mucilaginous pulp), and the endocarp (seed). This is the

preferred method for processing in Colombia [1], [2].

The coffee pulp is one of the main by-products in the coffee-

making process and constitutes between 40 and 50% of the wet

weight of the fruit (including the husk)[1], [2]. This residue is

rich in carbohydrates, proteins, minerals, and appreciable

amounts of tannins, caffeine, and potassium [1], [3], [4]. These

wastes are generally underutilized. Its disposal in tropical

coffee-producing countries creates a problem because its

elimination causes environmental contamination, due to the

putrefaction of organic matter. This is why the need arises to

develop and implement adequate management mechanisms for

this waste material [1].

In the framework of a circular economy, efforts have been

W. P. M. Author is with the Centro de Gestión Industrial – SENA, Bogotá,

Colombia. (e.mail: whperez@sena.edu.co),

J. M. G. Author was with Centro de Gestión industrial – SENA. She is now

with the Tecnoparque, SENA, Bogotá, Colombia. (e-mail:

jamojica@sena.edu.co),

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made to develop mechanisms for the treatment and

management of coffee waste, including its use as raw material

for the production of food, beverages, vinegar, biogas, caffeine,

pectic enzymes, proteins, compost, and pectin, etc. [1], [5]. This

last product, pectin, is the central topic of this article.

Pectin is a natural biopolymer with various applications in

the food, pharmaceutical, and biotechnology industries; and has

been commonly used as a thickening, gelling, and colloidal

stabilizer agent in food and beverages [6], [7]. It is a complex

heteropolysaccharide composed of d-galacturonic acid residues

linked by α-1-4 bonds that form homogalacturonan chains [6],

[8]; and it is found commercially, almost exclusively, as a

derivative of citrus peel or apple pomace [9], [10], both by-

products in the manufacture of apple juice (or cider). However,

taking into account the growing industrial demand for pectin in

global markets (more than 5% per year) due to the wide variety

of technological and biological applications of this

polysaccharide [6], [11], it is important to find new sources that

are unconventional and have competitive and economic yields,

to obtain this product of industrial interest [10].

Obtaining pectin from various sources has been a widely

studied and published topic, but it is difficult to characterize this

as a model system due to the heterogeneous nature of the

polymer and the particular characteristics of each plant. A

useful tool that can be used for both statistical modeling and

experimental design is the response surface methodology

(RSM). From this methodology a model is obtained that allows

the establishment of the best conditions in the extraction

process by evaluating parameters such as pH, temperature and

extraction time, the degree of esterification and the extraction

performance. The response surface methodology has been

previously reported for the adequacy of the pectin extraction

process from other plant sources such as banana peel [12],

Pectin extraction from coffee by-products

Pectin extraction was carried out by acid hydrolysis using

hydrochloric acid in a closed reflux with a condensation system

according to what was reported [9], [10], [20]. A ratio of 1

portion of coffee residue to 4 portions of water was used. In the

extraction, the effect of three variables was measured:

the pH was adjusted by adding 1 mol L

-1

hydrochloric acid

with a potentiometer (between 1.5 and 3.5 pH units),

the hydrolysis time (between 15 minutes and 90 minutes),

and

the hydrolysis temperature is controlled in a thermostated

water bath (between 70⁰C and 90⁰C).

The extraction conditions evaluated were selected based on

the literature review conducted in the previously referenced

articles where the Response Surface Methodology (RSM) is

used as a method for optimizing conditions.

The warm, acidified extract was cooled to room temperature

and centrifuged at 6000 rpm for 15 minutes. The supernatant

was precipitated with 96% ethanol in a 1:1 v/v ratio and then

allowed to stand for one hour to allow the pectin to float. The

floating pectin was filtered off and rinsed with 96% ethanol.

The resulting pectin was dried in a forced convection oven at

45°C for 12 h. The extraction yield was calculated

gravimetrically and reported as the percentage of pectin

extracted compared to the total weight of the raw material used.

The following formula (equation 1), was used to determine

pectin yield:

pomegranate peel [13], passion fruit peel [14], pea hulls [15],

citrus peel [16], cocoa peel [17], [18], mango peel [9], guava

[19], jackfruit [20], and others. With the aim of generating a

% 𝑌𝑖𝑒𝑙𝑑 𝑜𝑓 𝑝𝑒𝑐𝑡𝑖𝑛 =

𝑊𝑒𝑖𝑔ℎ𝑡 𝑜𝑓 𝑝𝑒𝑐𝑡𝑖𝑛

𝑊𝑒𝑖𝑔ℎ𝑡 𝑜𝑓

𝑏𝑦𝑝𝑟𝑜𝑑𝑢𝑐𝑡𝑠

∗ 100 (1)

proposal for the utilization of residues in the agro-industrial

sector within the framework of the circular economy, in this

study, the effect of the extraction conditions on the efficacy of

obtaining pectin and its degree of esterification from

agroindustrial coffee residues is reported, using a response

surface methodology.

II. METHODS

A. Agroindustrial material

The agroindustrial coffee residues were obtained from coffee

farms in the municipality of San Juan de Rioseco in the

department of Cundinamarca, Colombia. These residues were

All procedures were performed in triplicate.

Determination of the degree of esterification

Fourier transform infrared spectra (FTIR-ATR) were

obtained from pectin obtained in the frequency range of 4000-

800 cm-1 in a Shimadzu IR PRESTIGE-2 spectrophotometer.

The samples were placed in a reflectance attenuator (ATR). The

empty glass was used as a reference. The degree of

esterification was calculated by the equations (2) and (3) of

Pappas et al. [21], according to that reported by Minjares-

Fuentes et al. [22]:

crushed to reduce their particle size, and preserved by freezing

at -80⁰C. The sampling unit for the experiments was selected by

waste quartering method, and consisted of 100 grams of residue

for each experimental replicate.

DE  124R  2.2013

R 

1740



1630

(2)

(3)

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Scientia et Technica Año XXVIII, Vol. 28, No. 03, julio-septiembre de 2023. Universidad Tecnológica de Pereira

Where DE is the degree of esterification, A1740 y A1630

were defined as the absorbance intensities of the bands caused

by vibrations of the esterified and unesterified carboxyl groups

at 1740 cm

-1

and 1630 cm

-1

[22].

Experimental design and statistical analysis

A central compound design (CCD) with three independent

variables (temperature, time and pH) was used for the

experiment. The response surface methodology (RSM) was

used to evaluate the effect of the study variables and determine

the best conditions for the extraction of pectin from

agroindustrial coffee residues, using as dependent variables the

pectin extraction yield and the degree of esterification. With the

results, a complete second-order model was tested according to

equation 3.

� = �

+ �

� + �

�� + �

�

+ �

�

��

�

�� + �

�� + � (3)

Where y is the answer; ki, βi and αi are constant; t and T are

the extraction time and temperature respectively; and e is the

random error associated with the model. The RSM analysis,

principal component analysis, and residues plots was performed

in the trial version of Minitab 17.

III. RESULTS AND DISCUSSION

Pectin is a natural biopolymer with various applications in

food, pharmaceutical and biotechnology industries. In this

work, the obtaining of this industrially valuable product from

agro-industrial coffee by-products was proposed.

The degrees of esterification of the pectin obtained under

working conditions ranged between 60% and 75% and makes it

possible to classify them as high methoxyl pectin. Pectin can be

characterized by different parameters, the most important being

the degree of methoxylation or degree of esterification (GE),

which refers to the percentage of methoxylated C atoms in the

galacturonic acid skeleton, and is related to the gelation

properties [12]. Pectin can be classified as high methoxy

content if the degree of esterification is greater than 50%, and

low methoxy pectin content for degrees of esterification less

than 50% [12], [23]. This percentage is the one that determines

the possible use of pectin in the industry. Pectin with a high

degree of esterification is preferred.

Lower temperatures and times, and higher pH values produce

pectin with greater methoxylation that agrees with that reported

in pectin from other plant sources [9], [12], [13]. Another

parameter of interest is the yield percentage that was relatively

low compared to other plant sources reported in the articles that

have been cited, finding results between 0.14% and 2.0% under

the study conditions.

In order to optimize the extraction, the response surface

methodology using Minitab 17 was used to define the

conditions that produced a maximum percentage of yield while

maintaining a high degree of methoxylation. Based on the

results of the surface model of responses for the degree of

esterification and the percentage of yield, equations 4 and 5

were formulated and three-dimensional graphs were built (Fig.

1 and 2 where two variables are represented in a 3D surface

graph while that the other variable remained constant).

%𝑅 = −1,90 − 0,75𝑝𝐻 + 0,783𝑡 + 0,057𝑇 − 0,177 𝑝𝐻

−

0,173𝑡

− 0,00053𝑇

+ 0,0180𝑝𝐻 ∗ 𝑇 (4)

𝐷𝐸 = 323 − 52,0 𝑝𝐻 + 1,1𝑡 − 4,69𝑇 + 1,28 𝑝𝐻

−

3.52𝑡

+ 0,0211𝑇

+ 0,528 𝑝𝐻 ∗ 𝑇 (5)

The three-dimensional graphs are the graphical

representations of the regression models that provide a method

to visualize the relationship between the responses and

experimental levels of each variable and the type of interactions

between pairs of variables for the responses percentage of yield

(Fig. 1) and degree of esterification (Fig. 2).

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Fig. 1. Surface graphs for the variables studied. A Yield (%) as a function of

pH and time. B: Yield (%) as a function of pH and temperature. C: Yield (%)

as a function of time and temperature. The surface plots were made in Minitab

17.

Fig. 2. Surface graphs for the variables studied. A: Degree of esterification

(DE) as a function of pH and time. B: Degree of esterification (DE) as a function

of pH and temperature. C: Degree of esterification (DE) as a function of time

and temperature. The surface plots were made in Minitab 17.

Similar to that of pectin obtained from grape residues [22],

pectin from banana peel [24], and pectin from walnut

processing wastes [6], we found that the pH is the parameter

that most affects the performance in the extraction of pectin in

agroindustrial coffee residues.

The pectin yield decreases with increasing pH at different

extraction temperatures. This indicates that extraction is

favored by acidity. However, in an environment that is too

acidic, pectin will over-hydrolyze, degrease and be subject to

cleavage [16], obtaining lower yields, so an extraction pH of

close to 2 is recommended for the process.

At constant pH, it was determined that the longer the time

and the higher the temperature the yield for obtaining pectin

was higher. However, the product obtained decreases in quality,

since it has lower degrees of esterification. This is due to the

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fact that high temperatures and long exposure times favour

hydrolysis reactions of glycosidic bonds, demethylation

reactions, and polymer breakdown [16].

In the residual plot (Fig. 3A and 3B), it can be observed that

the residuals are randomly distributed around zero, without

showing a discernible pattern. This suggests that the statistical

model adequately captures the variability of the experimental

data and that there is no systematic trend in the residuals.

Therefore, we can infer that the model is a good representation

of the data. The Principal Component Analysis (PCA) confirms

the findings of the response surface model. Fig. 3C shows the

PCA projection plot. Principal Component 1 explains 33.6% of

the variance and confirms the positive relationship between

extraction time and pectin yield, while the degree of

esterification shows a negative relationship with extraction time

and temperature.

According to the model obtained through response surface

methodology, it was determined that the optimal conditions for

coffee pectin extraction, in relation to the response variables,

are pH 2, an extraction temperature of 90°C, and a hydrolysis

time of one hour. The suitability of the models in predicting the

responses was tested by conducting pectin extraction under the

selected optimal conditions. The experimental values aligned

with the predicted values (Table I). Overall, it was observed that

the model adequately predicts the response variables, as evident

from the correlations between the predicted and experimentally

obtained results, as depicted in the residual plots. The adjusted

model provides a better approximation for predicting the degree

of esterification, exhibiting only a 1.5% difference compared to

the values predicted by the model for the optimal extraction

conditions.

TABLE I

EXPERIMENTAL AND PREDICTED RESULTS OF THE STUDY VARIABLES

ACCORDING TO THE EQUATION OF THE RESPONSE SURFACE MODEL.

Experimental

(%)

Predicted (%) Difference %

Fig. 3. Model verification: Residue between the experimental results and the

results predicted by the response surface model for A. The yield, and B. The

Yield 0.58 ± 0.04 0.62 6.4

degree of esterification (DE). C. PCA projection plot

Degree of

esterification

65.6 ± 0.5 66.6 1.5

The pectin extracted under the response surface model

The results presented correspond to the best conditions for the extraction of

coffee pectin with respect to the response variables (pH 2, an extraction

temperature of 90°C and a hydrolysis time of one hour). The experimental

results are presented as the mean ± standard deviation for an n=3

conditions was characterized by infrared FTIR

spectrophotometry. The infrared spectrum of the pectin

extracted from the coffee husk under the extraction conditions

resulting from the response surface model is shown in Fig. 4. A

wide absorption around 3321 cm

-1

of polysaccharides caused by

stretching of hydroxyl groups is observed, as well as two peaks

between 3000 cm

-1

and 2850 cm

-1

that corresponded to the

asymmetric and symmetric stretching of the CH bond in the

galacturonic ring of aliphatic carbons. The absorption at 1732

-1

corresponded to the stretching vibration of the C=O bond

of the esterified carboxyl group, while the absorption at

approximately 1647 cm

-1

was attributed to the vibration

stretching of the carboxylate ion bond (non-esterified carboxyl

group). The relationships of these absorptions are used to

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calculate the degree of esterification, according to those

reported by Minjares-Fuentes et al. [22] and according to

equation 2, showing a degree of esterification that classifies

pectin as high methoxy by being greater than 50% [10], [25].

The absorption peaks between 1010 cm

-1

and 1150 cm

-1

indicate that the sample contains pyranose similar to that

reported by Wang et al. [26]. The results found for coffee pectin

both in the form of the infrared spectrum and its absorptions

agree with those reported in pectin obtained from tomato

residues [25], in banana peel [12], in pomegranate peel [13],

and pectin extracted from grapefruit peel [26].

Fig. 4. FTIR spectrum for extracted pectin at pH 2 with closed reflux and

heating at a constant temperature of (90 ° C x 60 Minutes).

Taking into account that pectin is used as an additive

(thickening agent, gelling agent and colloidal stabilizer) [27],

[28], raw material that in Colombia must be exported from

producing countries such as Germany, Mexico, Brazil, China,

India among other producing countries [27], the results found

are an approximation to the possibility of generating a suitable

waste management proposal for the coffee agroindustry.

IV. CONCLUSION

The pectin was successfully extracted from agroindustrial

coffee by-products from the municipality of San Juan del Rio

Seco, Cundinamarca, under different conditions of pH,

temperature and extraction time. The high temperature and

strongly acidic pH conditions resulted in a higher extraction

yield, but at the cost of decreasing the degree of methoxylation

for a maximum of 75% for a minimum of 60%. The optimal

conditions for pectin extraction, defined as those that produced

a maximum extraction yield, while maintaining a degree of

methoxylation that classifies the pectin obtained as having a

high degree of methoxylation, were: 90°C, 1 h, pH 2.0.

The results suggest the potential for conducting a pectin

extraction process from this type of waste, aiming to achieve

proper waste management for the agroindustry. While the yield

results are lower compared to conventional pectin sources, it is

recommended to implement drying processes before extraction

to enhance this parameter. Additionally, future studies should

consider scaling up to a pilot plant to assess the process

efficiency and evaluate the characteristics of the product

obtained.

ACKNOWLEDGMENT

The authors thank to Centro de Gestión Industrial - Servicio

Nacional de Aprendizaje SENA in Bogotá and Sistema de

Investigación, Innovación y Desarrollo Tecnológico

(SENNOVA) for funding the project " Obtención de productos

aprovechables a partir de la valorización de residuos orgánicos

generados en plazas de mercado de Bogotá, en el marco de la

economía circular" code SGPS-8493-2021, the CGI - Neurona

Industrial Process research group, and the learners from the

Research Hotbed of Chemical Agroindustrial waste and Foods

- QuiRAl.

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Walter Pérez Mora was born in Bogotá,

Colombia in 1986. He received a bachelor’s

degree in Chemistry in 2009 from Universidad

Nacional de Colombia, in Bogotá, Colombia.

He received his Master in Science - Chemistry

in 2013 from Universidad Nacional de

Colombia, in Bogotá, Colombia. He is

currently pursuing a Ph.D. in Science - Chemistry in the same

University. He is an Instructor of technology in Chemistry

applied to industry in the Industrial Management Center to

Servicio Nacional de Aprendizaje SENA, where he is also a

member of the Research Group in industrial processes. He

is the author of a research book, four book chapters and 8

research papers. His research interests include, Plant

biochemistry, Environmental chemistry with emphasis on

circular economy and analytical Chemistry.

ORCID: http://orcid.org/0000-0002-7290-1874

Jaquelin Mojica Gómez was born in Bogotá,

Colombia in 1978. She received a bachelor’s

degree in Chemistry in 2004 from Universidad

Nacional de Colombia, in Bogotá, Colombia. She

is Specialist in Laboratory Management of the

Universidad Colegio Mayor de Cundinamarca

and received her master’s in science - Chemistry in 2021 from

Universidad Nacional de Colombia, in Bogotá, Colombia. She

has an extensive experience in the analytical area,

instrumentation management chemistry and design,

development, and analytical methodologies validations. She is

currently an instructor and researcher at the Centro de Gestion

Industrial of the Servicio Nacional de Aprendizaje SENA-CGI,

where she directs the hotbed of research in Agroindustrial

Waste Chemistry and Food QuiRAL. She is the author of a

research book and 2 research papers. Her research interests

include phytochemistry, analytical Chemistry and

environmental chemistry with emphasis on circular economy.

ORCID: https://orcid.org/0000-0002-4089-3750