Fabrication and study on dually modified starch embedded in alginate hydrogel as an encapsulation system for Satureja essential oil

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Carbohydrate Polymers 322 (2023) 121331

Available online 25 August 2023

Fabrication and study on dually modied starch embedded in alginate

hydrogel as an encapsulation system for Satureja essential oil

Shahriyar Sahraeian, Mehrdad Niakousari

, Mahboubeh Fazaeli,

Seyed Mohammad Hashem Hosseini

Department of Food Science and Technology, School of Agriculture, Shiraz University, Shiraz, Iran

ARTICLE INFO

Keywords:

Double encapsulation

Double modication

Enzymatic modication

Esterication

Modied starch

ABSTRACT

This study aimed to investigate how the types and order of modications inuence the structure and physico-

chemical characteristics of modied porous starch. The work focuses on the encapsulation of essential oil in

hydrophobic microcapsules embedded in sodium alginate hydrogels. FTIR spectra indicated successful esteri-

cation of starch with OSA. 1047:1022 cm

−1

and 1022:995 cm

−1

band ratios of FTIR spectra revealed increased

crystallinity due to enzymatic modication, supported by XRD patterns. Porous-OSA (PO) starch had 1.5 times

higher degree of substitution (DS) than OSA-porous (OP) starch, conrmed by the intense peak at 0.85 ppm in

NMR spectra. SEM images displayed larger particles and smaller pore diameter in OP compared to PO and porous

starch, indicating amylolytic enzyme inhibition by OSA. Loading efciency (LE) showed no signicant difference

between OP and PO microcapsules (≈70 %), both signicantly higher other starch microcapsules. OP and PO

microcapsules exhibited sustained release, with enhanced antibacterial activity. Alginate hydrogels preserved

about 60 % antioxidant and 90 % antibacterial activities of SEO against 2 h of UV radiation. These ndings

suggest that the order of modication could not affect the functional properties of nal microcapsules. Addi-

tionally, the importance of alginate hydrogels as the protective and second wall material was disclosed.

1. Introduction

In recent years, scientists tend to exploit modied starch as wall

materials and vehicles to encapsulate and deliver food bioactives and

nutraceuticals (Chen et al., 2021; Zhong et al., 2022). Physical, chemi-

cal, and enzymatic modication of starch has been applied to extend the

application of starch in encapsulation processes. Chemical modication

of starch includes crosslinking, substitution, and conversion (Chen et al.,

2018). The substitution of hydroxyl groups of starch with octenyl suc-

cinate groups has been widely investigated among chemically modied

starches, including starch acetate and starch ether, due to its amphi-

philic nature. (Labelle et al., 2020). Additionally, enzymatic modica-

tion is used to enhance the encapsulation capacity of starch granules

through an increase in their surface area (Chen et al., 2021; Latip et al.,

2021).

In the food industry, alginate has been widely exploited as a thick-

ening agent, stabilizer, and encapsulation system in the food and phar-

maceutical industries (Saberi Riseh et al., 2021). The latter application

which includes hydrogels as encapsulation systems has been profoundly

investigated (Bennacef et al., 2021). Alginates endow several advan-

tages including crosslinking properties, pH responsivity, biocompati-

bility, and biodegradability extensively exploited as wall materials in

encapsulation systems to deliver food bioactives and nutraceuticals. The

development of hydrogels using alginates can be achieved through

either external gelation or internal gelation. For example, external

gelation or diffusion method includes using calcium solution to develop

gels. In detail, alginate dispersions are usually extruded into a calcium

solution and calcium molecules form intermolecular linkages among

alginate building blocks and hydrogels are formed (Saberi Riseh et al.,

2021). On the other hand, it is possible to add the calcium solution into

an alginate dispersion and from hydrogels. The latter technique is called

“inverse spherication” (Bennacef et al., 2021).

Encapsulation systems are exploited to protect bioactive compounds

and nutraceuticals from degradation caused by environmental and

gastrointestinal harsh conditions. One of the most susceptible bioactive

food ingredients is essential oil. Essential oils possess therapeutic

properties and are extracted from aromatic plants by hydrodistillation

techniques. The Satureja species, a member of the mint family and often

* Corresponding author.

E-mail address: niakosar@shirazu.ac.ir (M. Niakousari).

Contents lists available at ScienceDirect

Carbohydrate Polymers

journal homepage: www.elsevier.com/locate/carbpol

https://doi.org/10.1016/j.carbpol.2023.121331

Received 5 July 2023; Received in revised form 6 August 2023; Accepted 22 August 2023

Carbohydrate Polymers 322 (2023) 121331

known as mountain savory, is the source of Satureja essential oil.

Mountain Savory essential oil may have antifungal, antibacterial, anti-

rheumatism, anti-arthritis, and hair and scalp health-benecial proper-

ties (Asadi-Yousefabad et al., 2022; Ebadollahi et al., 2021). However,

essential oils are highly susceptible to environmental conditions such as

heat, light, and pH variations, which can degrade their potency and

stability over time. Therefore, the application of an encapsulation sys-

tem can be an effective technique to inhibit environmentally detrimental

effects on essential oils.

Given the limited investigations conducted on the dual modication

of starch, recent studies have demonstrated that this approach can be

highly effective in developing protective encapsulation systems with

desired delivery properties (Punia Bangar et al., 2022; Wang et al.,

2020). In general, two consecutive modications of starch using phys-

ical, chemical, or enzymatic approaches are considered homogeneous

dual modications, while the use of physical-chemical, physical-enzy-

matic, or chemical-enzymatic methods is considered a heterogeneous

dual modication. (Ashogbon, 2021; Sahraeian et al., 2023). A research

conducted by Chen et al. (2023) resulted in a dually-modied micro-

capsule with enhanced functionality. The porous starch was modied

through esterication with caffeic acid. The dually-modied starch

exhibited strong adsorption and antioxidant capabilities. Additionally,

microcapsules signicantly protected linoleic acid from oxidation, sug-

gesting its potential utility. Chlorogenic acid was encapsulated in

hydroxypropyl tapioca starch followed by embedding in alginate

hydrogels. A sustained release of chlorogenic acid was achieved,

demonstrating a prolonged release compared to that from both hydrogel

and modied tapioca alone (Lozano-Vazquez et al., 2015). Until now,

many research on dual modication of starch has focused on creating

functional ingredients with multiple functionalities. However, limited

attention has been given to the development of encapsulation systems

for susceptible bioactive compounds, particularly essential oils.

One of the key advantages of dual modication is the ability to

achieve synergistic effects that are not attainable with single modica-

tions. By combining different modication methods, it becomes possible

to tailor starch properties more precisely and efciently. This approach

allows researchers and industries to design starch-based materials with

specic functionalities, such as controlled release, improved thermal

stability, and protection properties. Interestingly, the preparation of

hydrophobic porous starch, an aspect of dual modication, remains

relatively unexplored in the existing literature. This presents an oppor-

tunity to investigate and develop new methodologies for creating hy-

drophobic porous starch. Additionally, directing attention toward

examining the inuence of the order of modication on the ultimate

encapsulation system could prove advantageous. This particular

perspective has also been overlooked in previous investigations. This

study also delved into the impact of the modication order, examining

variations in the degree of substitution, morphology, and

crystallography.

In summary, while the potential of dually modied starch granules

was evaluated, this study investigated how the order of enzymatic and

OSA modications impacts the functional properties of the nal

encapsulation systems, encompassing essential oil loading efciency,

release rate, as well as antioxidant and antimicrobial activities.

Furthermore, alginate was used as second wall material to embed the

dually modied microcapsules, and the protective properties of alginate

hydrogels against prolonged UV radiation were evaluated.

2. Materials and methods

2.1. Materials

Native corn starch was supplied by Khoosheh Zar Starch Industry in

Shiraz, Iran. Octenyl succinate (OSA) reagent was purchased from

Sigma-Aldrich Inc., and alginate (CAS No. 9005-38-3, MW:

250,000–350,000 Da, mannuronate: guluronate =25:75) was

purchased from the same supplier. Dextrozyme® DX 1.5X (DX), which

contains glucoamylase (255 AGU/g) and pullulanase (510 NPUN/g),

and Liquozyme® Supra (LS), which is an alpha-amylase (135 KNU/g),

were purchased from Novozymes in Denmark. Satureja hortensis L.

essential oil (SEO) was purchased from Deve Herbes company (New

Delhi, India). Dialysis bag was purchased from Shanghai Qiaoxing

Trading Co (Molecular weight cut-off of 5 kDa, Shanghai, China). All of

the other reagents used in the experiments were of analytical grade.

2.2. Preparation of granular OSA-modied starch

The preparation of granular OSA-modied starch was carried out

using the method described by Lopez-Silva et al. (2019). Briey, 50 g of

corn starch was accurately weighed and dispersed in 150 mL of distilled

water and gently stirred for 15 min. NaOH (1 M) was used to adjust the

pH value of the suspension to 8.75. A certain amount of OSA (%3 w/w of

the dried starch) was diluted 5 times in absolute ethanol and then added

slowly during the rst 1.5 h, at controlled pH values in the range of

8.70–8.78 throughout the modication process. The reaction was car-

ried out for 6 h at room temperature and was terminated by adding 1 M

HCl solution until the pH value reached 7. The suspension was centri-

fuged (8000g, 10 min) and then washed three times with excess distilled

water. After that, it was washed once with acetone and then again with

excess ethanol to remove OSA residue. Finally, samples were ltrated

and dried at 35 ◦C for 18 h. To obtain uniform samples, they were

crushed and passed through a 35-mesh sieve with a mesh size metric of

500

2.3. Enzymatic modication

Citrate-phosphate buffer was prepared (800 mL, pH =5.2) using a

proper amount of 0.1 M citric acid monohydrate and 0.2 M dipotassium

hydrogen phosphate and equally divided into three 400 mL beakers. 50

g of native starch was dispersed into two beakers and 50 g of granular

OSA starch was dispersed in another beaker. The suspensions were then

mixed for 15 min and allowed to be hydrated. Subsequently, enzymes (%

2 w/w of starch) with the portion of DX: LS =1:6 (w/w) were prepared

and added to the suspensions. The enzymatic reaction was carried out

for 8 h at 42 ◦C in a shaking incubator (50 rpm). At the end of the re-

action process, 0.1 M of NaOH was slowly added to the beakers, and the

pH value of the suspensions was adjusted to 10 in order to cease the

reaction. After the neutralization of samples, washing with distilled

water and centrifugation (8000g, 10 min) was repeated three times.

Sediments were then separated and dried in an oven at 35 ◦C overnight

Subsequently, the dried sediments were crushed and passed through a

35-mesh sieve (Zhang et al., 2012). Therefore, porous starch and OSA-

porous starch (OP) were obtained.

2.4. Preparation of OSA-modied porous starch

The method used for modifying corn porous starch with OSA was the

same as the procedure mentioned in Section 2.2. The product of this

reaction was named porous-OSA (PO) (Lopez-Silva et al., 2019).

2.5. Degree of substitution (DS)

Determination of the degree of substitution (DS) was carried out

according to the method described by Lopez-Silva et al. (2019) with

slight modications. Briey, 1.25 g of starch sample was dispersed in

12.5 mL of HCl solution (0.1 M) and was stirred (100 rpm) for 30 min

prior to centrifugation at 3000g for 10 min. The sediment was washed

once with ethanol and twice with distilled water. The sample was sus-

pended in 70 mL of distilled water and placed in a water bath containing

boiling water for 10 min. Afterward, it was allowed to cool down to

ambient temperature. Titration of suspension was carried out with 0.05

M NaOH until a pH value of 8.3 was achieved. Finally, the DS was

S. Sahraeian et al.

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