Recent insights into polysaccharide-based hydrogels and their potential applications in food sector: a review

1.1.4. Starch-based hydrogels 
Starch is a polysaccharide made of several glucose units linked via 
α
-
D
-(1–4) and/or 
α
-
D
-(1–6) bonds. Amylose and amylopectin are the 
primary compounds of starch. Amylopectin is highly branched whereas 
amylose is helical in structure and tightly packed. Amylose/Amylo-
pectin proportion highly influences crystallinity, gelatinization process, 
and molecular order 
[79]
. Starch via a three-step thermal treatment can 
easily hydrate or retrograde 
[80]
. In the first treatment, starch absorbs 
enough water with subsequent swelling of the starch granule. Gelatini-
zation occurs due to the destruction of starch granule and amylose 
leaching via heating followed by cooling which leads to the preparation 
of starch hydrogel due to retrogradation, recrystallization, and restruc-
turing of starch. 
Polydimethylsiloxane (PDMS) was added to strengthen the physical 
properties of starch-based hydrogel 
[81]
. Polydimethylsiloxane was 
incorporated into the starch hydrogel to raise the count of hydrogen 
bonds, to form stretchy elastomer for wound treatment. Furthermore, 
starch hydrogels can achieve characteristics like controlled release and 
sensitivity to external stimuli when physically integrating sodium algi-
nate or chitosan 
[82]
. 
Besides the abovementioned characteristics, starch-based hydrogels 
affect the environment to the least amount hence we can call these 
environment-friendly bio-renewable resources and could harvest the 
water thereby boosting the economy due to the water-absorbing prop-
erty acquired through the presence of OH group in its structural setup. 
1.1.5. Xanthan gum-based hydrogel 
Xanthan gum (XG), is produced by fermentation of sucrose, glucose, 
or lactose and is widely used in the food industries due to its biode-
gradability, non-toxicity, biocompatibility and low cost. Montmoril-
lonite (MMT), with the formula Al
2
Si
4
O
10
(OH)
2
yH
2
O, was extensively 
used to strengthen chemically cross-linked polymer hydrogels 
[83]
. 
Huang et al. 
[51] 
used Fe ions, XG, and MMT nanosheets as physical 
cross-linkers to create a newer hydrogel. The hydrogel networks are held 
together by ionic coordination, hydrophobic contacts and hydrogen 
bonds interactions between the COO of XG chains and Fe
3+
ions. Others 
utilize radiation or chemicals to penalize a three-dimensional network. 
The hydrogel was able to effectively disperse energy and achieve 
remarkable fatigue resistance and self-healing characteristics with the 
interactions between multiple crosslinking agents. Furthermore, due to 
the presence of COO from the XG chains, the hydrogels exhibit pH- 
dependent swelling characteristics. The hydrogel has outstanding me-
chanical and conducive properties at the same time. The XG/MMT/ 
PAAm hydrogels' tensile and compressive strengths might be 0.48 MPa 
and 5.9 MPa, respectively. They were able to regain their appearance 
after the applied force was removed, demonstrating their exceptional 
shape recovery, elasticity, and fatigue resistance abilities. Xanthan gum 
(XG) based hydrogels are also reported as non-toxic, biodegradable, and 
stimuli sensitive besides being explored as antibacterial agents through 
their co-polymerization with other compounds such as polyacrylic acids 
with the help of radiations such as microwaves 
[84]
. This study also 
witnessed the potential role of XG hydrogels in agriculture for the 
controlled release of agrochemicals such as urea. Moreover, XG-based 
hydrogels can also be employed for drug delivery systems, and wound 
healing and may have the fate of dye removal properties besides being 
quite biocompatible and stable with high adsorption potential by syn-
thesizing novel semi-interpenetrating polymer networks (semi-IPNs) 
through cross-linking 
[85]
. Additionally, XG hydrogel, through its 
encapsulation property, plays an distinguish role in controlled drug 
release thereby keeping the drug structural integrity intact along with 
resisting any change in functionality as witnessed in the encapsulation of 
ciprofloxacin drug into hydrogel of N-trimethyl chitosan/sodium car-
boxymethyl xanthan gum 
[86]
. XG along with poly N-vinyl imidazole 
hydrogel aid in the delivery of other nutrients such as proteins. XG-based 
hydrogels are potential candidates for applications in fields such as 
wastewater treatment, tissue engineering, and food packaging in addi-
tion to drug and protein delivery. Food packaging applications involve 
the use of hydrogel films carved out from XG in association with other 
polysaccharides with improved properties. In this concern, a synergistic 
film was developed from XG, k-Carrageenan, and Gellan gum for 
enhancement in morphological and structural properties 
[87]
. Time has 
witnessed several modifications in these hydrogels credited to certain 
limitations including poor mechanical properties, low surface area and 
thermal stability, and sometimes bacterial invasion. The modifications 
involve hydrogel synthesis, advanced chemical treatment, grafting 
procedures, etc. 
[88]
.