Introduction
Self-standing solid-like structures from liquid vegetable oil, the
so-called oleogels, has recently received significant attention due to
its potential to replace trans-fat and reduce saturated fats in
confectionery, baked products, and processed meats
(Marangoni, Van Duynhoven, Acevedo,
Nicholson and Patel, 2020) In conventional oleogels, the
structure-forming agents are typically small molecule oleogelators, such
as plant waxes, fatty esters, monoacylglycerols, and ethyl cellulose
(Patel and Dewettinck, 2016,
Singh, Auzanneau and Rogers, 2017).
However, with more attention towards ‘clean label’ and ‘healthy’
alternatives, the use of food hydrocolloids such as gums, and proteins
as oleogelators has recently gained more consideration
(Doan, Van de Walle, Dewettinck and Patel,
2015, Gravelle, Blach, Weiss, Barbut and
Marangoni, 2017, Gravelle and Marangoni,
2018, Lim, Hwang and Lee, 2017).
However, these hydrophilic biopolymers are unable to form a crosslinked
network via intermolecular interactions if directly added into the oil;
therefore, indirect approaches are required to form a structured oil
phase. DeVries and coworkers successfully converted whey protein
stabilized hydrogels into oleogels by a step-wise solvent exchange
process (de Vries, Hendriks, van der Linden
and Scholten, 2015, de Vries, Wesseling,
van der Linden and Scholten, 2017). κ-Carrageenan stabilized hydrogels
were also converted into aerogels using supercritical carbon dioxide and
then into oleogels by allowing the aerogel to adsorb liquid oil
(Manzocco, Valoppi, Calligaris, Andreatta,
Spilimbergo and Nicoli, 2017). Combinations of surface active and
non-surface active biopolymers, such as hydroxypropyl methylcellulose
(HPMC) or methylcellulose (MC) with xanthan gum
(Patel, Cludts, Bin Sintang, Lewille,
Lesaffer and Dewettinck, 2014); and soy protein isolate with
κ-carrageenan (Tavernier, Patel, Van der
Meeren and Dewettinck, 2017) were also used to develop
emulsion-templated oleogels by removing the water using freeze-drying or
vacuum-drying process. Patel and coworkers were the first to use an HPMC
foam-templated approach to obtain oleogels
(Patel, Schatteman, Lesaffer and
Dewettinck, 2013). The freeze-dried HPMC foam was able to hold an oil
98 % of the foam weight. However, one of the most popular biopolymers,
pulse proteins, such as those from pea, lentil and faba bean have not
been explored significantly for oleogelation, despite their nutritional
and functional quality and higher consumer acceptance.
Our recent studies demonstrated that freeze-dried foams stabilized by
combinations of a pea or faba bean protein concentrates with xanthan gum
(XG) can be used to structure canola oil (CO)
(Mohanan, Tang, Nickerson and Ghosh,
2020). The foams prepared with 5 wt% faba bean protein concentrate
(FPC) or pea protein concentrate (PPC) with 0.25 wt% XG at pH 7 and pH
9 were able to hold an oil more than 20 – 30 times of their weight.
However, about 30-40% of the added oil was leaked out of the oleogel
upon centrifugation (Mohanan, Tang,
Nickerson and Ghosh, 2020). Due to the poor oil binding capacity of the
protein foam-templated oleogels, their rheological properties were
unreliable. Higher oil leakage during rheology measurements of the
oleogels led to a significantly higher storage modulus (G’) compared to
the oleogels with higher oil content (or higher oil binding capacity).
Also, the baking quality of the cakes baked using the oleogels was poor
due to significantly higher hardness and chewiness compared to a cake
baked using conventional high-melting shortening
(Mohanan, Tang, Nickerson and Ghosh,
2020). Therefore, the objective of the present study was to improve the
oil binding properties of the pulse protein foam-templated oleogels
using small quantities of conventional oleogelators, such as
high-melting monoacylglycerols (MAG) and candelilla wax (CW). We
hypothesized that the oleogelators would act as fillers in the protein
network to reduce the oil loss (OL) and improve the rheology of the
oleogels and therefore improve the textural properties of the cakes. The
overall goal was to see how much of the conventional high-melting
shortening functionality can be mimicked by the pulse protein-based
oleogels.