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Einhorn-Stoll, U., Kastner, H., Hecht, T., Zimathies, A., & Drusch, S. (2015). Modification and physico-

chemical properties of citrus pectin – Influence of enzymatic and acidic demethoxylation. Food

Hydrocolloids, 51, 338–345. https://doi.org/10.1016/j.foodhyd.2015.05.031

Ulrike Einhorn-Stoll, Hanna Kastner, Theresia Hecht, Annett Zimathies,

Modification and physico-chemical properties of citrus pectin – Influence of enzymatic and

acidic demethoxylation

U. Einhorn-Stolla, H. Kastnera, T. Hechta, A. Zimathiesb, S. Druscha

Königin-Luise-Strasse 22, D-14195 Berlin, Germany

Richard-Willstätter-Str. 11, D-12489 Berlin, Germany

application conditions.

Two groups of model pectins, one with DM 57% and one with DM 42%, have been prepared from

one mother pectin (DM 68%) under exactly defined conditions. They were modified by an acidic and

two enzymatic methods. The enzymes were fungi (f) and plant (p) pectinmethylesterases (PME). All

pectins were treated similarly after demethoxylation. Thermal stability was tested by thermal

analysis and water uptake by a sorption and a capillary sucking method.

The enzyme-treated pectins were less thermal stable than the acidic-treated and their water uptake

was superior to the acidic-treated in the sorption method and inferior in the capillary sucking tests.

The differing pH during demethoxylation (1.5 for acidic, 4.4 for fPME and 7.4 for pPME) caused

varying intermolecular interactions of the pectin macromolecules in solution, resulting in different

range of food products. They can be tailored for specific applications by different modifications,

demethoxylation from high-methoxylatd pectins (HMP) to low-methoxylated pectins (LMP) is the

dominating process. The methoxyl group at C6 of the galacturonic acid (GalA) units of the pectin

molecule backbone is cleaved and a carboxyl group is formed. This was traditionally performed as a

chemical reaction under acidic or alkaline conditions. Nowadays it is mainly an enzymatic process

using fungi or plant pectinmethylesterases fPME or pPME (Rolin, 2002; Rolin, Chrestensen,

Hansen, Staunstrup & Sorensen, 2010) with only limited side reactions, such as depolymerisation,

and because it allows a better process control. The application of plant PME for the modification of

pectins for the milk industry in acidic dairy drinks (Laurent & Boulenguer, 2003) was an additional

example for the application of the enzymes. Whereas chemical demethoxylation and most fPME,

Interactions with water are essential for the physical stability of pectin and its application (Elizalde,

Pilosof, & Bartholomai, 1996). On the one hand, contact with moisture during transport and storage

of pectin considerably influences the powder properties (Einhorn-Stoll, Benthin, Zimathies, Görke, &

Drusch, 2015). On the other hand, pectin powders have to be dispersed and dissolved prior to any

application. Despite the good final solubility of pectins, several technological operations such as

mixing with sugar, stirring or heating are necessary in order to prevent lump formation and to

achieve quick pectin dissolution (Rolin, 2002). Different aspects of pectin-water interactions can be

tested by different methods. Nowadays, water sorption performed through the determination of

sorption isotherms is most commonly applied (Panchev, Slavov, Nikolova, & Kovacheva, 2010;

Galus, Turska, & Lenart, 2012; Kurita, Miyake, & Yamasaki, 2012; Basu, Shivhare, & Muley, 2013).

suspension and dissolution processes. The water can creep also into macro-capillaries and inter-

particle voids, the pectin particles can swell and start to dissolve (Elizalde et. al., 1996). The more

porous pectin particles are, the more water they can take up and, normally, the earlier their

dissolution starts. Thus, the capillary sucking method allows conclusions on the pectin dissolution

behaviour. The water uptake of pectin is generally assumed to depend on three main factors:

(I) The number of hydrophilic groups determines the amount of water that can be bound via

hydrogen bridges.

(II) Close contact of the dissolved pectin macromolecules during modification promotes the

formation of inter- and intramolecular bonds and a more compact structure of the

particles after drying.

(III) Small particles and a rough surface after drying, milling and sieving increase the water

uptake by sorption.

Dongowski, 2007) but, in a direct comparison, LMP demethoxylated under alkaline conditions were

thermally less stable than acidic-treated LMP. The difference was ascribed mainly to the reaction

conditions: Under acidic conditions (treatment with HCl at pH around 1) the newly formed free

carboxyl groups were mostly undissociated and able to form hydrogen bonds between neighboured

macromolecules. That caused a more compact structure in dry state. Under alkaline conditions

(modification with potassium carbonate at pH around 10) monovalent cations were bound to the

newly formed dissociated carboxyl groups and kept the dissolved pectin macromolecules in a

certain distance. That caused a less compact structure in dry state. A comparable effect was

described before for pectin containing apple fibre (Schalow & Kunzek, 2004).

In recent publications was reported that commercial modified pectins with similar molecular

Therefore, the aim of the present work is the examination of the influence of different well-controlled

pectin demethoxylation procedures on the physico-chemical and techno-functional properties.

Model pectins were prepared from one commercially available high-metholxylated pectin, using

plant or microbial pectinmethylesterases and hydrochloric acid, respectively. These model pectins

were examined with respect to their thermal stability and their water uptake behaviour. It was

hypothesized that different molecular interactions in the liquid state during demethoxylation affect

the physical structure of the dried pectin, which leads to differences in thermal stability and water

uptake.

A commercially available non-standardised high-methoxylated (HM) citrus pectin (CP Kelco, Lille

Skensved, Denmark), named as original pectin OP68 C, was demethoxylated in order to prepare

different model pectins of high and low DM and a varying (block-wise or statistical) distribution of the

free carboxyl groups. According to the demethoxylation method they are coded with P for treatment

reference pectin in the presented work and is named as OP68. All chemicals used were of

analytical grade.

2.1. Preparation of model pectins

For enzymatic demethoxylation, two types of pectinmethylesterase (PME) were used, fungal PME

(fPME) Fructozym Flot from Aspergillus niger (Erbslöh, Geisenheim, Germany) and orange plant

PME (pPME), prepared from orange peel in the laboratory according to Arbaisah, Asbi, Junainah, &

Jamilah (1997) and Kim, Teng, & Wicker (2005). A pH-stat method, based on Williams, Foster, &

Schols (2003) and Limberg, Körner, Buchholt, Christensen, Roepstorff, & Mikkelsen (2000) was

applied, using a 902 Titrando with a 800 Dosino and a 50 mL dosing unit (Deutsche METROHM

GmbH & Co. KG, Filderstadt, Germany). The pH of the pectin solution (1%) was adjusted with

The model pectins from both procedures were precipitated from the solution with 95 vol% ethanol

(ethanol:water = 4:1) and the precipitate was washed at least five times with 95 vol% ethanol for