Structure and functional properties of taro starch modified by dry heat treatment

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International Journal of Biological Macromolecules 261 (2024) 129702

Available online 26 January 2024

Structure and functional properties of taro starch modied by dry

heat treatment

Gan Hui

, Peilei Zhu

, Mingchun Wang

Department of Food Science and Engineering, Anhui Engineering Laboratory for Agro-products Processing, Anhui Agricultural University, Hefei 230036, China

Institute of Horticulture, Anhui Academy of Agricultural Sciences, Hefei 230031, China

ARTICLE INFO

Keywords:

Taro

Starch

Dry heat

Structure

Functional property

ABSTRACT

Taro starch (TS) was modied by dry heat treatment (DHT) for different periods (1, 3, 5, and 7 h at 130 ◦C) and

temperatures (90, 110, 130, and 150 ◦C for 5 h) to expand its applications in food and other industries. The

structure and functional properties of DHT-modied TS were characterized. It was found that TS granules

became agglomerated after DHT, and the particle size, amylose content, solubility, and retrogradation enthalpy

change of TS increased with increasing dry heating time and temperature, whereas the relative crystallinity,

molecular weight, swelling power, gelatinization temperature, and enthalpy change decreased. The absorbance

ratio of 1047 cm

−1

/1022 cm

−1

for DHT-modied TS (except at 7 h) was higher than that of native TS. DHT

increased the contact angle of TS in a time- and temperature-dependent manner. At a moderate strength, DHT

increased the pasting viscosity, relative setback value, and storage modulus but decreased the relative break-

down value. Moreover, DHT (except at 150 ◦C) caused a decrease in the rapid digestive starch content and

estimated glycemic index of TS. These results suggested that DHT-modied TS could be used in foods with high

viscosity requirements, gel foods, and low-glycemic index starch-based foods.

1. Introduction

Starch is a degradable natural biomaterial and is widely used in food,

textile, and pharmaceutical industries as a thickener, stabilizer, water-

retaining agent, ller, adhesive, and glazing agent. Natural starch, due

to its inherent molecular structure characteristics, has many unfavorable

properties, including cold water insolubility, low shear resistance,

thermal decomposition, and retrogradation, all of which can limit its

application [1]. Accordingly, structural modication strategies are

typically applied to expand the applications of starch, improve the

inherent limitations of native starch, enhance its favorable properties,

and develop new functional properties [2,3]. Commonly employed

starch modication approaches include physical, chemical, and enzy-

matic modications, among which physical modications have attrac-

ted increased attention in recent years, given that the processes are

simple, safe, clean, and pollution-free [2,3].

Dry heat treatment (DHT), which refers to heat treatment of starch

with a moisture content of <10 % at a temperature of 60–200 ◦C, is a

standard physical method that alters the physical and chemical prop-

erties of starch [4,5]. As early as 1998, Chiu et al. [4,5] systematically

introduced a heat-inhibited granular starch and its preparation process

in a patent, and claimed that this type of modied starch functioned

similarly to chemically cross-linked starch, with high resistance to heat,

shear, and extreme pH. In recent years, more studies have been con-

ducted to investigate the inuence of DHT on the morphology, structure,

and functional properties of starch. It has been shown that DHT led to

the aggregation of starch granules and the appearance of cracks, de-

pressions, and holes on the surface of starch granules, instead of leading

to the disappearance of the granular structure of starch [6–8].

Furthermore, it has been determined that although the crystal type of

starch typically does not change with DHT, the integrity of the crystal-

line structure is altered, manifested by a decrease in relative crystallinity

as well as the gelatinization temperature and enthalpy change [9–11].

However, Zou et al. [12] found one exception for DHT-modied waxy

corn starch by demonstrating that DHT leads to an increase in the

crystallinity of waxy corn starch. This could be because of the rear-

rangement of damaged double helices and the partial reorganization of

the amorphous regions to form new crystal structures. As such, it has

been concluded that the change in starch structure directly affects its

digestibility, but the changes in starch digestibility under DHT differ for

* Corresponding author.

E-mail address: wmc@ahau.edu.cn (M. Wang).

Equal contributors.

Contents lists available at ScienceDirect

International Journal of Biological Macromolecules

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

https://doi.org/10.1016/j.ijbiomac.2024.129702

Received 26 July 2023; Received in revised form 14 January 2024; Accepted 22 January 2024

International Journal of Biological Macromolecules 261 (2024) 129702

starches with different structures and compositions [13,14].

Taro (Colocasia esculenta (L). Schott), belonging to the Araceae

family, is an edible tuber crop and widely cultivated in tropical and

subtropical regions of Asia, the Pacic Islands, Africa, and America

[15,16]. In China, taro is known as “yu tou” and is abundantly produced

in the east, south, and southwest regions. The edible corms and cormels

of taro are rich in starch, which accounts for 70–80 % of the dry basis

weight. This makes taro a potential source of starch for commercial

applications. Taro starch (TS) is a typical small granule starch with

irregular and polygonal shapes. The average granule size has been re-

ported to range from 1 to 5

m [16]. Because TS has small granules and

is easy to digest, it can be used in infant and gluten-free foods [17], as a

ller in biodegradable packaging lms [18], an emulsier for Pickering

emulsions [19], and a wall material for microencapsulation of functional

oils and avors [20,21]. Various researchers have studied TS extraction,

chemical composition, molecular structure, and physicochemical and

functional properties [16]. Moreover, some studies on TS modication

have reported improved and extended properties [16,20]. Compared

with traditional commercial starches, such as corn, potato, cassava, and

rice starch, TS has not been extensively studied despite the increase in

research interest. Thus, more studies must be conducted on the char-

acteristics and modications of TS to further expand the application

scope thereof in food and other industries, thereby allowing it to

compete with commercial starch.

In light of the increased interest in applying starch in emulsions and

emulsifying system-related foods [7,22–24], studies on the hydrophobic

modication of starch have attracted increasing attention. Our previous

studies [23,25] reported that DHT is a promising and effective approach

for improving the hydrophobicity of native starch and exogenous

protein-fortied starch, which is related to an increase in the hydro-

phobicity of endogenous and exogenous proteins in starch upon DHT,

thus also matching the ndings of previous studies [10,26]. Accordingly,

we aimed to explore a more effective and convenient preparation

method for hydrophobicity-modied starch using DHT in combination

with a native starch that has a relatively high endogenous protein con-

tent. It has been shown that water-extracted TS naturally contains a high

protein content [27], thus being an ideal candidate for preparing

hydrophobicity-modied starch.

To our knowledge, the hydrophobic modication of TS by DHT and

the characteristics of modied TS have yet to be systematically studied

[28]. Therefore, based on water-extracted TS with a relatively high

endogenous protein content (1.14 %, w/w), the objective of this study

was to explore the structure and functional properties of TS modied by

DHT for different periods (1, 3, 5, and 7 h at 130 ◦C) and temperatures

(90, 110, 130, and 150 ◦C for 5 h). In particular, the impact of DHT on

the hydrophobicity of starch and the contribution of endogenous pro-

teins within starch to enhance the hydrophobicity of DHT-modied

starch were veried by contact angle measurements and deproteiniz-

ing treatment, in addition to examining the DHT mechanism.

2. Materials and methods

2.1. Materials

Fresh taro corms were provided by Shandong Yimu Sweet Potato

Agricultural Technology Co., Ltd. (Rizhao, Shandong, China). Amylose

from potatoes was purchased from Sigma-Aldrich Chemical Co. (St.

Louis, MO, USA). Amylopectin from maize was purchased from Beijing

Solexpo Technology Co., Ltd. (Beijing, China).

-Amylase (58 U/mg)

and gluco-amylase (98 U/mg) were purchased from Hefei Bomei

Biotechnology Co., Ltd. (Hefei, Anhui, China). Dispase (100 U/mg) was

purchased from Shanghai Yuanye Biotechnology Co., Ltd. (Shanghai,

China). Poly(methyl methacrylate) (PMMA) standards (2710, 4950,

10,900, 29,960, 62,950, 122,300, 298,900, 679,000, and 1,677,000 g/

mol) were purchased from Agilent Technologies, Inc. (Santa Clara, CA,

USA). DMSO (HPLC grade) was purchased from Shanghai Macklin

Biochemical Technology Co., Ltd. (Shanghai, China). All other chem-

icals were of analytical grade and above.

2.2. Isolation of TS

To isolate TS from fresh taro corms, a water extraction method was

used. First, the washed taro corms were peeled and sliced, and after

grinding in a high-speed blender with deionized water (1:2, w/w) for

1.5 min, the resulting slurry was ltered sequentially through 100-mesh

(150

m) and 300-mesh (48

m) sieves to obtain a ltrate. Next, the

ltered residues were washed twice with deionized water (1:2, w/w),

and then, all the obtained ltrates were combined and centrifuged at

3000 r/min for 15 min. Furthermore, after removing the soft gray layer,

the starch cake was resuspended with deionized water and centrifuged

ve times. The nal starch cake was dried at 40 ◦C until the moisture

content was <10 %, and the dried starch cake was ground and passed

through a 150-mesh (106

m) sieve to obtain the TS sample. The protein

content of the TS sample was 1.14 %, which was determined using an

automatic Kjeldahl nitrogen protein analyzer (UDK 159, VELP Scientic,

Italy).

2.3. Preparation of deproteinized TS

The deproteinized TS was prepared by protease treatment to verify

the role of the endogenous proteins in the TS morphology and hydro-

phobicity during the DHT process. Briey, TS was suspended in an acetic

acid–sodium acetate buffer (0.05 mol/L, pH 7.5) with dispase (based on

the deproteinization results from the pre-experiments, the starch and

dispase concentrations were set to 10 % (w/v) and 500 U/g starch,

respectively). Thereafter, the starch suspension was incubated in a water

bath (45 ◦C) for 4 h with rotary shaking (150 r/min) and then centri-

fuged at 1500 r/min for 10 min. After removing the soft gray layer, the

starch cake was resuspended with deionized water and centrifuged ve

times. The nal starch cake was treated using the same drying and

grinding process described in Section 2.2 to obtain the deproteinized TS

sample, denoted as TS-DP. The protein content of TS-DP was 0.20 %.

2.4. DHT of starch samples

DHT of the starch samples and parameters were selected according to

the methods published in our prior report and by Chiu et al. [4,5,25]. TS

was dry heated in an oven at 130 ◦C for 1, 3, 5, and 7 h to obtain the dry-

heated samples TS-1 h, TS-3 h, TS-5 h, and TS-7 h, respectively. Three

other dry-heated samples, namely TS-90 ◦C, TS-110 ◦C, and TS-150 ◦C,

were dry heated for 5 h at 90, 110, and 150 ◦C, respectively. The sample

TS-130 ◦C was the same as the sample TS-5 h. The TS-DP sample was dry

heated at 110 ◦C for 5 h to obtain the dry-heated sample TS-DP-110 ◦C.

The TS and TS-DP samples without DHT were designated TS-N and TS-

DP-N, respectively.

2.5. Micromorphology observations

The micromorphologies of the starch samples were observed via

scanning electron microscopy (SEM, Hitachi S-4800, Tokyo, Japan). A

small starch sample was evenly placed on double-sided tape attached to

a specimen holder and then coated with a thin layer of gold. The

micromorphology images were captured at 1000×and 30,000×

magnication.

2.6. Particle size measurements

The particle sizes of the starch samples were measured using a laser

particle size analyzer (Mastersizer 2000, Malvern Instruments, Co., Ltd.,

Worcestershire, England) according to the method of Marefati et al. with

slight modications [29]. A starch sample (0.1 g) was pre-dispersed in

10 mL of deionized water using a high-speed disperser at 10,000 r/min

G. Hui et al.

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