Encapsulation of Ethylene Gas into Granular Cold-Water-Soluble Starch

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Encapsulation of Ethylene Gas into Granular ColdWater Soluble Starch: Structure and Release Kinetics Linfan Shi, Xiong Fu, Chin Ping Tan, Qiang Huang, and Bin Zhang J. Agric. Food Chem., Just Accepted Manuscript • DOI: 10.1021/acs.jafc.6b05749 • Publication Date (Web): 20 Feb 2017 Downloaded from http://pubs.acs.org on February 22, 2017

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Journal of Agricultural and Food Chemistry

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Encapsulation of Ethylene Gas into Granular

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Cold-Water Soluble Starch: Structure and Release

3

Kinetics

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Linfan Shi a, Xiong Fu a,b, Chin Ping Tan c, Qiang Huang a,b,*, Bin Zhang a,b,*

6 7 a

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School of Food Science and Engineering, South China University of Technology, Guangzhou 510640, PR China

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b

Guangdong Province Key Laboratory for Green Processing of Natural Products and Product Safety, Guangzhou 510640, PR China

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12 13

c

Department of Food Technology, Faculty of Food Science and Technology, Universiti Putra Malaysia, 43400 Serdang, Selangor, Malaysia

14 15 16 17 18 19 20 21 22

* Corresponding authors

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Tel.: +86 20 8711 3845; fax: +86 20 8711 3848.

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E-mail address: [email protected] (Q. Huang), [email protected] (B. Zhang).

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ACS Paragon Plus Environment


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ABSTRACT:

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Ethylene gas was introduced into granular cold-water soluble (GCWS) starches

28

using a solid encapsulation method. The morphological and structural properties of

29

the novel inclusion complexes (ICs) were characterized using scanning electron

30

microscopy, X-ray diffractometry, and Raman spectroscopy. The V-type single helix

31

of GCWS starches was formed through controlled gelatinization and ethanol

32

precipitation, and was approved to host ethylene gas. The controlled release

33

characteristics of ICs were also investigated at various temperature and relative

34

humidity conditions. Avrami’s equation was fitted to understand the release kinetics

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and showed that the release of ethylene from the ICs was accelerated by increasing

36

temperature or RH, and was decelerated by increased degree of amylose

37

polymerization. The IC of Hylon-7 had the highest ethylene concentration (31.8%,

38

w/w) among the five starches, and the IC of normal potato starch showed the best

39

controlled release characteristics. As a renewable and inexpensive material, GCWS

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starch is a desirable solid encapsulation matrix, with potential in agriculture and food

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applications.

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KEYWORDS: encapsulation, ethylene, granular cold-water soluble starch,

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controlled release

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2


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INTRODUCTION

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Ethylene, which is a natural ripener for fruits and vegetables that is present in the

48

tissues and organs of plants, is widely used in agriculture and food industry. It can

49

also enhance the color development of fruits, induct adventitious roots and root hairs,

50

and promote fruit flowering.1 As an active gas, ethylene is often stored in pressurized

51

cylinders for commercial uses, which has the major disadvantages of leakage and

52

explosion during the transport and storage. Encapsulating of gas into solid matrices

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with slow release properties can effectively avoid these defects.2 These solid matrices

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can be categorized into two groups using X-ray diffraction techniques:3 i) ordered

55

structures with well-defined pore size, such as carbon nanotubes4 and zeolites5, and ii)

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disordered structures with a wide range of pore diameters and surface area, e.g.,

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activated carbons6 and cyclodextrins.7 These solid matrices with low gas

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encapsulation capability normally need to be prepared under harsh conditions, which

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is a major drawback for industrial use. For example, Vela et al. encapsulated CH4 into

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single-walled carbon nanotubes at a pressure of 35.62 MPa and 0 °C, with a low CH4

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concentration of 4.0% (w/w).8

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Among the reported solid matrices, only cyclodextrin (CD) can be used as food

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grade material.3 The hydrophobic interior of the α-CD toroids (0.47-0.53 nm) was

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reported to encapsulate gases with low molecular weight such as CH4, C2H4, C3H8, Kr,

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Cl2, and CO2.9,10 However, the primary commercial limitations of CD are its high cost

66

and low encapsulated concentration.

3



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Amylose forms a left-handed single helix that is stabilized by hydrogen bonds, and

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has a hydrophilic outside surface and a hydrophobic inside helical cavity.11 Amylose

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single helices can pack together in a crystalline structure known as V-type crystalline

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structure.11 In previous studies, V-type complexes were used to prepare slowly

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digestible and resistant starches, to create a new delivery system to protect volatile

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and sensitive guest molecules, such as esters of vitamins, fatty acids and genistein.12,

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13

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fatty acids and alcohols with the aid of hydrophobic interactions.14 Chen and Jane

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prepared granular cold-water soluble (GCWS) starches through alcoholic-alkaline

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treatment, and achieved controlled release of atrazine, which was determined by the

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amylose content, particle size, and environmental temperature.15

V-type starch molecules are reported to host suitable guest molecules such as iodine,

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Although numerous attempts were made to entrap various gases in solid matrices,

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to the best of our knowledge no further details or discussions on encapsulated gases

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into starch have been reported.16,

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GCWS starches prepared from different botanical origins using a solid encapsulation

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method, and characterized the inclusion complexes (ICs) by scanning electron

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microscopy (SEM), X-ray diffractometry (XRD), and Raman spectroscopy. Avrami’s

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equation was used to study the controlled release kinetics of ethylene from ICs at

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various temperature and relative humidity conditions. Additionally, the mechanism of

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formation and stability of IC were discussed.

17

In this study, we encapsulated ethylene into

87 88 4


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MATERIALS AND METHODS

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Materials. Normal maize (NMS) and potato (NPS) starches were purchased from

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Dacheng Company (Changchun, China). High-amylose starch (Hylon-7, HA7 and

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Hylon-5, HA5) was purchased from Ingredion (Shanghai, China), and waxy maize

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starch (WMS) was a gift from Lihua Co., Ltd. (Qinhuangdao, China). Other

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chemicals were commercial products of analytical reagent grade.

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CLDs of Starches. Starch debranching was performed as described by Wang et

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al.18 The SEC weight distribution of debranched starch was analyzed in duplicate

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using an Agilent 1100 series SEC system (Agilent Technologies, Waldbronn,

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Germany) equipped with a refractive index detector (Shimadzu RID-10A, Shimadzu,

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Kyoto, Japan). A series of SEC columns (GRAM precolumn and GRAM 100 and

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GRAM 1000 columns, Polymer Standard Services, PSS, Mainz, Germany) placed in

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an oven at 80 °C were used to separate the debranched starch molecules. The mobile

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phase was a DMSO/LiBr solution (0.6 mL/min) and pullulan standards were used for

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calibration to convert the SEC elution volume into the hydrodynamic volume Vh or

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the corresponding radius Rh using the Mark-Houwink equation.19 The molecular size

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distribution data were plotted as SEC weight distribution, w (log Vh), against the

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hydrodynamic radius (Rh/nm). The amylose content (AC) was calculated as the ratio

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of the area under the curve (AUC) of the debranched SEC distribution curves for the

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larger branches to the total AUC for all branches.20

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Preparation of GCWS starches. GCWS starches were prepared following a

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reported method with minor modification.21 The HA7, HA5, NMS and NPS samples 5



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(10.0 g, dry starch basis, dsb) were suspended in 70.0 g of an aqueous ethanol

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solution (40%, w/w), and NaOH (3 M) was added at 4 g/min. The mixture was stirred

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at 100 rpm for 30 min at 35 °C, and the additional ethanol solution (20 g, 40%, w/w)

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was slowly added. The mixture was centrifuged at 1800×g for 10 min and washed

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twice with ethanol solution (40%, w/w). The recovered starch was resuspended in

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ethanol solution (40%, w/w), and neutralized with HCl (3 M in absolute ethanol). The

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mixture was washed with ethanol solution (80%, w/w) followed by absolute ethanol,

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and oven-dried at 80 °C for 3 h. The dry material was gently crushed in a hand agate

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mortar and passed through a 150-mesh nylon sieve. The preparation of the GCWS

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starch from WMS was performed following the above steps, expect for the dispersion

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process (ethanol solution, 80%, w/w) and the washing step (ethanol solution, 95%,

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w/w). The mass ratios of alkali/starch (HA7, HA5, NMS, NPS and WMS, dsb) were

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1:8, 1:5, 1:4, 1:3.5, and 1:3, respectively. Further increasing the amount of NaOH led

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to starch gelation (data not shown).

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Encapsulation of Ethylene Gas. The encapsulation of ethylene into GCWS starch

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was investigated by a solid encapsulation method at a pressure of 1.2 MPa for 24 h at

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25 °C. The GCWS starch (10.0 g, dsb) was weighed into a 250 mL quartz container,

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and placed into a pressure vessel chamber (Yanzheng Biological Technology Co., Ltd,

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Beijing, China). After vacuum treatment, the vessel chamber was flushed with

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ethylene until the desired pressure level was reached. After 24 h of reaction, the

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residual ethylene in the vessel chamber was absorbed by bromine solution (3%, w/w),

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and the ICs were transferred to a -80 °C freezer for further analysis. The properties of 6


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the ICs were determined within 8 h.

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Encapsulation Capacity. The ethylene encapsulation capacity of GCWS starches

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was determined using headspace gas chromatography (HS-GC). ICs (20 mg) and

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distilled water (1 mL) were added into an amber vial, and the cap was sealed tightly

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immediately. The ICs were magnetically stirred at 600 rpm for 5 min to dissolve the

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ICs thoroughly.

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A GC system (Agilent, 7890A, CA, USA) and an automatic headspace sampler

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(DANI, HS 86.50, Cologno Monzese, Italy) were used for HS-GC measurement. The

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GC system was equipped with a thermal flame ionization detector (Agilent, CA,

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USA), and a DB-5 capillary column (30 m × 0.25 mm × 0.1 µm, J & W Scientiﬁc,

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USA). The carrier gas was nitrogen at 40 mL/min, and the column temperature was

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35 °C. The temperature of the oven and injector was set at 60 °C and 250 °C,

145

respectively. The peak area of the sampled ethylene was recorded and calculated as

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ethylene concentration based on the ethylene standard (o2si company, SC, USA).

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Because some ethylene dissolved in water, the ethylene concentrations in the ICs were

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calculated as the sum of two measurements: the ethylene in headspace and the

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dissolved ethylene in water. Dissolved ethylene in water was estimated based on the

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theoretical values from Henry’s Law22 as follows:

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Cw = 0.119 × Ch

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where Cw and Ch are the level of ethylene (cm3/m3) in water and headspace,

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respectively. The concentration ratio of ethylene in the ICs was presented as the

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quality ratio.

(1)

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Scanning Electron Microcopy. Scanning electron micrographs were obtained with

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an EVO18 scanning electron microscope (Zeiss, Oberkochen, Germany). Starch

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samples were mounted on an aluminum stub using double-sided tape, coated with a

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thin ﬁlm of gold (10 nm), and examined at an accelerating voltage of 10 kV.

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Raman Spectroscopy. Raman spectroscopy was recorded using a laser confocal

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micro-Raman scattering spectrometer (LabRAM Aramis, HJY Company, France) in

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the range of 500-4000 cm-1. The wavelength was 532 nm and the resolution was 2

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cm-1.

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X-ray Diffractometry. The X-ray diffractometer (D8 Advance, Bruker, Germany)

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was operated at 40 kV and 40 mA with Cu Kα radiation (λ = 0.154 nm). The

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measurements were scanned at a scan rate of 0.5°/min (angular angle 2θ = 4-35°)

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with a 0.02° step interval. The crystallinity of the starch was calculated using a MDI

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JADE software (version 6.5, Materials Data Inc., Livermore, California, USA).

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Crystallinity of the starch was calculated using the following equation: 23

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Crystallinity (%) = 100% × Ac / (Ac + Aa)

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where Ac is the crystalline area on the X-ray diffractogram and Aa is the amorphous

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area.

(2)

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Release Kinetics. Release kinetics of ethylene gas from ICs was investigated under

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different temperature or relative humidity (RH) conditions. The storage and

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transportation of fruits were usually carried out below room temperature. Therefore,

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ICs (1.0 g, dsb, moisture content ~ 9.0%) were weighed into a sealing bag and stored

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at four selected temperatures (-80, -20, 4 and 25 °C) over prolonged time periods. RH 8


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was controlled at 52.9% and 75.5% using a saturated magnesium nitrate or sodium

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chloride solution at 25 °C, respectively.24 ICs were analyzed for ethylene

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concentration using HS-GC. The ratio of ethylene release (X) was defined as in Eq.

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(3):

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X = (Ci - Ct) / Ci

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where Ci is the initial concentration of ethylene in the ICs and Ct is the concentration

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of ethylene in the ICs at time t (h).

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(3)

Avrami’s equation is a mathematic model used extensively to describe release

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kinetics, and can be described as follows:25

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X = 1 - exp (-kt n)

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where X is the ratio of active release at time t (h). k is the release rate constant and n is

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the Avrami parameter or release mechanism. Both k and n express the magnitude of

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release and are empirically determined. Eq. (4) can be rewritten using a double

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logarithm to obtain Eq. (5):

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In(-In(1-X))= lnk + nlnt

192 193 194

(4)

(5)

A linear plot of In(-In(1-X)) versus lnt in Eq. (4) allows the release rate constant k (intercept) and release parameter n (slope) to be determined. Activation energy Ea are widely applied to evaluate temperature effects on the

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release kinetics from ICs, and it can be expressed as follows:26

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k = k0 exp (-Ea/RT)

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where, k is the release rate constant and k0 is the pre-exponential factor related to k. Ea

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is the activation energy parameter, T is the absolute temperature (K) and R is the

(6)

9



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universal gas constant (8.314 × 10-3 kJ mol-1 K-1).

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Eq. (6) can be linearized as follows:

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lnk = lnk0 - Ea/RT

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(7)

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Ea can be determined by a linear plot of lnk versus 1/T and the slope equals (Ea/R).

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Statistical Analysis. The results are recorded as the means ± standard deviation

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(SD), and the significance of the differences between groups was tested using t-test

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analysis. The significance level was set at p < 0.05. Statistical analysis was conducted

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using SPSS version 19.0 software (SPSS, Inc., Chicago, IL).

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RESULTS AND DISCUSSION

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CLDs of Starches. The SEC weight CLDs profiles of five native starches are

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presented in Figure 1. The debranched SEC weight distribution can be empirically

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divided into two regions representing amylopectin (AP) chains (DP ~ 100).18 The SEC weight CLDs of all debranched

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starches showed three typical peaks. The first peak (denoted by AP1) included the

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shorter AP branches (peak Rh ~ 1.5 nm or DP ~ 12), which are usually confined to

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single lamella. The second peak (denoted by AP2) represented the longer AP branches

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(peak Rh ~ 2.5 nm or DP ~ 50), which are normally crossed through more than one

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crystalline lamella. The third peak (denoted by AM) represented the AM branches

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with a board distribution (Rh ~ 3.5-80 nm or DP ~ 100-30000). Some mutants of

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starches, e.g. high-amylose maize starches, particularly HA7, consist of a large

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amount of intermediate materials, of which the branch chain length (Figure 1, Rh ~ 3 10


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nm or DP ~ 55-80) and the density of branching points27 are between AM and AP

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molecules. To compare the fine structure between starches, a set of empirical

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parameters was defined, such as the DP at the maximum of each peak (DPAP1, DPAP2

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and DPAM), and the relative height of each peak to AP1 (hAP2/AP1 and hAM/AP1). The DP

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at the maximum of each peak represents the relative chain length in each group of

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branches, and the height ratio of each peak maximum to AP1 reflects the relative

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amount of chains in each group of branches.18 The structural parameters of starches

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are summarized in Table 1. The DPAM values followed the order NPS > NMS > HA5 >

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HA7, whereas the opposite trend was observed for hAM/AP1 values and AC. Cereal

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starches normally have a considerably lower DPAM values than those from roots and

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tubers.28 The DPAP1, DPAP2 and hAP2/AP1 values of HA7 were highest, followed by

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HA5 and NPS (in decreasing order), showing that HA7 has longer branch chains of

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AP (peak Rh ~ 1.5-2.5 nm or DP ~12-50). The DPAP1, DPAP2 and hAP2/AP1 values of

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WMS did not have much statistically significant differences (p > 0.05) compared to

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those of NMS, suggesting that the AP structure of NMS was similar to WMS.

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Ethylene Gas Concentration in the ICs. To confirm whether the ICs were able to

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release ethylene completely in water, IC powder was dissolved in distilled water, and

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freeze-dried for further ethylene detection. We found no ethylene peak was detected

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by HS-GC analysis (data not shown), indicating that all ethylene was released from

240

the ICs.

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The ethylene concentrations in ICs are shown in Figure 2. The concentrations in

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ICs followed the order of their botanical origins: HA7 > HA5 > NMS > NPS > WMS. 11



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Notably, the highest ethylene concentration in HA7-IC was 31.8% (w/w). The

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NMS-IC sample had a similar ethylene concentration to NPS-IC, and WMS-IC

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showed the lowest values (2.3%, w/w). The ethylene concentrations in ICs of five

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starches had differed significantly (p < 0.5), indicating that the ethylene

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concentrations in ICs was positively dependent on the specific variety of starches. The

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amylose content of HA7, HA5, NMS, NPS and WMS was 69.8%, 48.6%, 26.5%,

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19.5% and 0.2%, respectively (Table 1). Thus, ethylene concentrations in ICs are

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associated with the AC of GCWS starches (correlation coefficient was 0.997 in Table

251

2).

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Morphology. The SEM images of the native, GCWS and IC samples are shown in

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Figure 3. HA7 and HA5 (Fig. 3A1 and B1) showed round to elongate shape with 7-10

254

µm in size, and NMS and WMS (Fig. 3C1 and E1) exhibited polygonal granules with

255

diameters of 10-20 µm. NPS (Fig. 3D1) appeared ellipsoidal with a size of 15-75 µm,

256

in agreement with a previous report.29 The GCWS starches had characteristic

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microscopic features that depended on their botanical origins. The size of GCWS

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starches prepared through alcoholic-alkaline treatment was approximately 2-4 times

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larger than that of the native counterparts. The majority of starch granules were still

260

intact with a slightly wrinkled surface, and minor granules bursting from the surface

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(Fig. 3D2).30 The AM can maintain the integrity of the starch granules, and the

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swelling is primarily a property of AP. WMS (Fig. 3E2), which has a high AP content

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( >~ 99%), suffered higher swelling expansion and more severe deformation. The

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expansion of NPS (Fig. 3D2) was due to an appreciable amount of phosphate 12


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monoester groups, which are negatively charged and linked to AP molecules.31 The

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resulting charge repulsion effect helps untangle the individual branches, and increases

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the swelling of granules.32 Additionally, it is noticeable that ethylene encapsulation

268

did not appear to change their morphological structure, indicating that the

269

macromolecular architecture of GCWS starches does not play a major role in the ICs.

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Raman Spectroscopy Analysis. To confirm the formation of the starch-ethylene

271

complex, HA7-IC was chosen as a representative. Compared with uncomplexed

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GCWS starch, the characteristic peaks at 1630-1600 cm-1 and 1500-1200 cm-1 were

273

higher in intensity for IC (Figure 4). The vibration at 1615 cm-1 in the Raman

274

spectrum has been reported to be associated with the C=C bond in ethylene.33 In

275

addition, the band at 1623 cm-l was assigned to the coordinated C=C stretching

276

mode.34 Therefore, Raman spectroscopy changes at 1630-1600 cm-1 indicate the

277

ethylene adsorption in the HA7-IC sample, in line with the ethylene concentration

278

results (Fig. 2). Additionally, the peaks were sharper and higher in intensity for the IC

279

compared with the uncomplexed GCWS starch at 1500-1200 cm-1, which was

280

assigned to C-H and H-C-H bending. This is in line with a previous study suggesting

281

that the bands at 1340 cm-1 and 1440 cm-1 represented the deformation vibration for

282

=C-H in ethylene gas.35

283

Crystalline Structure. Figure 5 shows the X-ray diffraction profiles of native,

284

GCWS and IC samples. The native NMS and WMS samples clearly showed the

285

A-type polymorph with major peaks at ~15°, 17°, 18° and 23° 2θ, whereas the native

286

HA7, HA5 and NPS samples showed a typical B-type diffraction pattern with 13



287

characteristic peaks at ~5°, 17°, 22° and 24° 2θ.36 The crystallinity of native HA7,

288

HA5, NMS, NPS and WMS was 24.1%, 26.1%, 33.5%, 44.6% and 48.0%,

289

respectively, consistent with a previous report.37 All GCWS and IC samples except for

290

WMS had a clear V-type crystalline structure with major peaks at ~7°, 13° and 20°

291

2θ.38 When starch molecules were placed in a strong alkaline solution, the protons of

292

the -OH group were dissociated, leaving negative charges on the starch molecules.

293

The repulsion between negative charges resulted in swelling of starch granules (Fig.

294

3A2-E2).21 The swelling power exerted a tension on neighboring crystallites of starch

295

molecule.39 Further swelling led to the uncoiling or dissociation of the double helix

296

structure, and the order of crystallites was destroyed (Fig. 5).40 Ethanol restricts the

297

swelling of granules due to dehydration effect, and also forms complexes with AM

298

and longer branch chains of AP molecules to generate the V-type single helix structure

299

(Fig. 5). The V-type crystallinity of GCWS starches followed the order HA7 > HA5 >

300

NMS > NPS. It was noted that the V-type crystallinity increased with increasing of

301

AC, and decreased with increasing DPAM values. Pearson’s correlations showed that

302

the ethylene concentrations in ICs were also positively and significantly correlated

303

with AC (Table 2). This is because AM changed to V-type single helices during the

304

alcoholic-alkaline treatment, and hosted ethylene gas to form the ICs. In addition,

305

long branch chains of AP also contributed to the content of V-type crystalline structure

306

during ethanol precipitation,38 supported by the fact that ICs from NPS and NMS with

307

different ACs (19.5% cf. 26.5%, Table 1) had similar ethylene concentrations. There

308

was no obvious change in the characteristic XRD peaks between GCWS starches and 14


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ICs. The crystallinity slightly increased, likely due to the formation of ethylene

310

complexes.

311

Release Kinetics. The time course of ethylene release from ICs at different

312

temperature and RH conditions is shown in Figure 6. The release ratio expressed the

313

relative amount of ethylene released from the ICs at different time intervals. At -80 °C

314

and -20 °C, the ethylene release ratio was below 0.15 after 120 h of storage (Fig. 6A

315

and B), probably due to the low kinetic energy of ethylene gas. After 120 h of storage

316

at 4 °C (Fig. 6C), the encapsulated ethylene gas in the ICs of HA7, HA5, NMS and

317

WMS almost completely released (release ratio > 0.99), and the release ratio of

318

NPS-IC was only 0.75. Ethylene gas showed a significantly faster release rate at

319

25 °C (Fig. 6D) among the four temperature conditions. A high temperature promotes

320

the molecule's speed (kinetic energy), thus, ethylene molecules will migrate faster

321

inside the cavities of GCWS starches resulting in an increase in diffusion rate.41

322

Similar temperature effects on release have been reported for CD encapsulated

323

eugenol from ICs.42

324

The release of ethylene gas from the ICs accelerated markedly with increasing RH.

325

After 4 hours of storage, a release ratio of 0.99 was found for all ICs at 52.9% RH

326

(Fig. 6E), and the same release ratio was monitored after 1.2 h at 75.5% RH (Fig. 6F).

327

Rising RH induced high moisture absorption into GCWS starches during storage,

328

resulting in the marked dissolution of single helices of GCWS starches. The release of

329

ethylene was related to the presence and concentration of water molecules

330

surrounding the ICs, in line with a previous study.43 15



331

Avrami’s equations were used to analyze release kinetics, and fitted the ethylene

332

release kinetics very well (r2 > 0.9, Table 3). The ethylene release rate constant k and

333

release parameter n from the ICs are summarized in Table 3. The release parameter n

334

fell within the range of 0.30-0.90, indicating that the release of ethylene corresponded

335

to the diffusion limited mode for different temperatures. Similarly, the release

336

parameter n for various RH values ranged between 0.90 and 2.00, showing a

337

first-order kinetics mode. That means the major physical process was ethylene gas

338

diffusion from the solid phase into the gas phase at various temperatures, whereas RH

339

had a marked effect on the release kinetics of ethylene. The release rate constant k can

340

be an important index to indicate the rate of ethylene gas liberate from ICs depending

341

on storage temperature or RH. It should be noted that kHA7 ˃ kHA5 ˃ kNMS ˃ kNPS for

342

same the temperature and RH, likely due to different DPAM values for GCWS starches.

343

The linear AM chains contribute to the V-type crystalline structure formation in

344

GCWS starches, whereas the single helices of V-type crystalline structure are

345

unstable.44 Longer AM chains, impart greater stability to complexes. Starch with high

346

DPAM values can generate ICs with good organization and stability.45 The melting

347

temperature, stability and crystalline structure of amylose-lipid complexes increased

348

generally with DPAM values.46 NPS-IC showed better thermal stability and controlled

349

release characteristics than other starches, and released ethylene gas continuously at

350

4 °C for 192 h, likely due to its highest DPAM value (3156). Activation energy can be

351

interpreted as the relative index of the binding strength of granular cold-water soluble

352

starch with ethylene.47 The activation energy of ethylene release from ICs followed 16


Page 16 of 35

Page 17 of 35


353

the order: NPS > NMS > HA5 > HA7 (Table 3), indicating that the binding strength

354

between ethylene and GCWS starch prepared from NPS was stronger than other

355

starches.

356

ethylene from NPS-IC. The release of ethylene from WMS-IC did not obey any rule,

357

due to the low ethylene concentration in IC. Therefore, the activation energy of

358

WMS-IC based on the release rate constant is not calculated in Table 3). However, the

359

improvement of IC stability and potential loss of ethylene gas during longer-term

360

storage are under study and will be reported in the future.

These data were consistent with the controlled release characteristics of

361

In conclusion, GCWS starch showed its capacity to encapsulate ethylene gas. The

362

ethylene concentrations in ICs followed the order HA7 > HA5 > NMS > NPS > WMS,

363

and the maximum ethylene concentration in HA7-IC was up to 31.8% (w/w). The

364

results from XRD, HS-GS and Raman spectroscopy confirmed that the double helices

365

of AM and longer AP branch chains of GCWS starches changed to single helices that

366

can host ethylene gas. Avrami’s equation was used to analyze the release kinetics of

367

ethylene gas from ICs, and the results showed that all treatments showed diffusion

368

release mechanisms in temperature experiments, whereas the release mechanism in

369

RH experiments resembled first-order kinetics. The release rate of ethylene gas from

370

ICs accelerated with rising temperature or RH, and decreased with increasing DPAM.

371

NPS-IC showed better controlled release characteristics than other starches, and

372

released the ethylene gas continuously at 4 °C for 192 h. GCWS starch is a potential

373

solid matrix for gas encapsulation in agriculture and food industry, with applications

374

such as fruit ripening and food shelf-life regulation. 17



375

AUTHOR INFORMATION

376

Corresponding Author

377

*(Q.Huang) Telephone: +86-20-8711-3845. Fax: +86-20-8711-3848. E-mail:

378

[email protected]

379

*(B.Zhang) Telephone: +86-20-8711-3845. Fax: +86-20-8711-3848. E-mail:

380

[email protected]

381

Notes

382

The authors declare no competing financial interest.

383

ABBREVIATIONS USED

384

AM, amylose; AP, amylopectin; AUC, area under the curve; CD, cyclodextrin; CLD,

385

chain length distribution; DMSO, dimethyl sulfoxide; DP, degree of polymerization;

386

GCWS, granular cold-water soluble, HA5, Hylon-5; HA7, hylon-7; HS-GC,

387

headspace gas chromatography; IC, inclusion complex; NMS, normal maize starch;

388

NPS, normal potato starch; RH, relative humidity; SD, standard deviation; SEM,

389

scanning electron microscopy; SEC, size exclusion chromatography; SPSS, statistical

390

product and service solutions; WMS, waxy maize starch; XRD, X-ray diffractometry.

391

ACKNOWLEDGMENTS

392

The authors thank the financial support received from NSFC-Guangdong Joint

393

Foundation Key Project (U1501214), Natural Science Foundation of Guangdong

394

Province, China (2014A030313236), and the Fundamental Research Funds for the

395

Central Universities of China (2015ZZ107).

396 18


Page 18 of 35

Page 19 of 35


397

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properties. J. Agric. Food Chem. 2014, 62, 760-771.

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for calculating starch crystallinity and its correlation with double helix content: a

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combined XRD and NMR study. Biopolymers 2008, 89, 761-768.

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alpha-amylase hydrolysis of hydroxyethylated amylose and specificity of subsite

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binding. Biochemistry 1984, 23, 5795-5800.

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adsorption kinetics on mesoporous silica under wide range of pressure and

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β-cyclodextrin and its controlled release characteristics. Food Chem. 2007, 103,

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461-466.

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(44) Dries, D. M.; Gomand, S. V.; Goderis, B.; Delcour, J. A. Structural and thermal

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transitions during the conversion from native to granular cold-water swelling

514

maize starch. Carbohydr. Polym. 2014, 114, 196-205.

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(45) Godet, M. C.; Bizot, H., Buléon, A. Crystallization of amylose-fatty acid

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complexes prepared with different amylose chain lengths. Carbohydr. Polym.

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1995, 27, 47-52.

518

(46) Putseys, J. A.; Lamberts, L.; Delcour, J. A. Amylose-inclusion complexes:

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formation, identity and physico-chemical properties. J. Cereal Sci. 2010, 51,

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521

(47) Agbenin, J. O.; Raij, B. V. Kinetics and energetics of phosphate release from

522

tropical soils determined by mixed ion-exchange resin. Soil Sci. Soc. Am. J. 2001,

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65, 1108-1114.

524

24


Page 24 of 35

Page 25 of 35


525

List of figure captions

526

Figure 1 SEC weight CLDs of debranched starches extracted from various starches.

527

Figure 2 Ethylene concentrations in inclusion complexes.

528

Figure 3 SEM photos of native (1), granular cold-water soluble (2) and inclusion

529

complex (3) samples. HA7 (A), HA5 (B), NMS (C), NPS (D) and WMS (E).

530

Figure 4 Raman spectroscopy of HA7 sample. (a) GCWS starch prepared from HA7,

531

(b) IC.

532

Figure 5 X-ray patterns of native (a), granular cold-water soluble (b) and inclusion

533

complex (c) samples. HA7 (A), HA5 (B), NMS (C), NPS (D) and WMS (E).

534

Figure 6 Release of ethylene from complexes at various temperature and RH

535

conditions. -80 °C (A), -20 °C (B), 4 °C (C), 25 °C (D), 52.9% RH (E) and 75.5% RH

536

(F).

25



Page 26 of 35

Table 1 Structural parameters obtained from SEC weight CLDs of various debranched starches a

537

Samplesb

AC(%)

HA7 HA5 NMS NPS WMS

69.8 ± 0.3 a 48.6 ± 0.9 b 26.5 ± 0.2 c 19.5 ± 0.3 d 0.2 ± 0.1 e

DP of peak maximum in SEC weight molecular size distribution of debrached starch DPAP1 DPAP2 DPAM a a 22.2 ± 0 48.3 ± 0.1 448 ± 2 a b b 20.7 ± 0.3 45.1 ± 0.1 539 ± 17 ab 16.2± 0.1 c 39.7 ± 0.1 c 821 ± 10 ac 19.3 ± 0.1 d 43.7 ± 0.1 d 3156 ± 212 d c c 16.4 ± 0.1 39.9 ± 0.2 -

Height of peak maximum in SEC weight molecular size distribution of debranched starch as a ratio to AP1 peak height hAP2/AP1 hAM/AP1 a 1.448 ± 0.006 1.816 ± 0.023 a b 1.163 ± 0.018 0.636 ± 0.325 b 0.580 ± 0.003 c 0.146 ± 0.001 c 0.918 ± 0.001 d 0.144 ± 0.004 d c 0.599 ± 0.006 -

538

a

539

small and/or broad to determine the local maximum, which appears as a shoulder of the adjacent larger peak. SEC: size exclusion

540

chromatography, CLDs: chain length distributions.

541

b

542

content, DP: degree of polymerization, AM: amylose, AP: amylopectin.

Mean ± standard deviation is calculated from duplicate measurements. "-" means the parameters cannot be identified, because the peak is too

Sample code: HA7: Hylon-7, HA5: Hylon-5, NMS: normal maize starch, NPS: normal potato starch, WMS: waxy maize starch, AC: amylose

26


Page 27 of 35


Table 2 Correlation coefficients between starch structures and ethylene concentrations in inclusion complexes (Y) a

543

Y AC DPAP1 DPAP2 DPAM hAP2/AP1 hAM/AP1 544

*

545

a

Y 1 0.997** 0.881* 0.890* -0.091 0.910* 0.900*

AC 1 0.858 0.872 -0.167 0.898* 0.919*

DPAP1

DPAP2

DPAM

hAP2/AP1

hAM/AP1

1 0.993** 0.091 0.992** 0.841

1 0.073 0.995** 0.886*

1 -0.014 -0.266

1 0.901*

1

Correlation is significant at the 0.05 level. **Correlation is significant at the 0.01 level.

Sample code: AC: amylose content, DP: degree of polymerization, AM: amylose, AP: amylopectin.

27



Page 28 of 35

546

Table 3 Release rate constants k, release parameters n, fitting degree r2 and activation energy Ea of ethylene from ICs based on Avrami’s equation

547

at various temperature and RH conditions a Temperature (°C)

RH (%)

Ea

b

Samples

-80

548 549 550

-20

4

25

(kJ/mol)

52.9

k×10-3 (h-1) 10.05 28.52 262.90 612.01 1650.37 HA7 n 0.52 0.35 0.51 0.68 18.24 1.12 2 r 0.981 0.988 0.984 0.994 0.997 k×10-3 (h-1) 7.43 23.03 158.98 546.62 1368.89 HA5 n 0.41 0.32 0.61 0.55 18.42 0.98 2 r 0.990 0.984 0.930 0.997 0.994 5.76 207.63 1004.01 k×10-3 (h-1) 13.31 123.94 NMS 20.49 n 0.45 0.48 0.63 0.87 1.26 2 r 0.948 0.995 0.957 0.986 0.992 -3 -1 k×10 (h ) 5.52 11.39 38.47 192.63 818.73 NPS n 0.39 0.41 0.76 0.61 36.97 1.51 2 r 0.938 0.990 0.980 0.992 0.979 -3 -1 8.70 14.12 122.21 214.17 k×10 (h ) 1236.15 N. A.c WMS n 0.44 0.41 0.66 0.83 0.95 2 r 0.997 0.945 0.995 0.999 0.979 a ICs: inclusion complexes, RH: relative humidity. b Sample code: HA7: Hylon-7, HA5: Hylon-5, NMS: normal maize starch, NPS: normal potato starch, WMS: waxy maize starch. c N.A.: not analyzed. 28


75.5 4763.58 1.01 0.994 4241.85 0.96 0.999 2989.18 0.91 0.993 2418.14 1.10 0.950 2462.06 0.99 0.993

Page 29 of 35


DP

w(logVh) [arb. units]

5 10 25

552

AM

2

AP2 AP1

10000 HA7 HA5 NMS NPS WMS

1

0 551

1000

100

1

10 Rh (nm)

100

Figure 1 SEC weight CLDs of debranched starches extracted from various starches.

553

Sample code: HA7: Hylon-7, HA5: Hylon-5, NMS: normal maize starch, NPS:

554

normal potato starch, WMS: waxy maize starch, DP: degree of polymerization, SEC:

555

size exclusion chromatography, CLDs: chain length distributions, AM: amylose, AP:

556

amylopectin.

29



Ethylene concentration (%)

35

a

30 b

25 20

c

15

c

10 5

d

0 HA7

HA5

NMS

NPS

WMS

557 558

Figure 2 Ethylene concentrations in inclusion complexes.

559


560

normal potato starch, WMS: waxy maize starch. Samples with different letters above

561

the columns are significantly different at p < 0.05.

30


Page 30 of 35

Page 31 of 35


A1

A2

A3

10µm

10µm

10µm

562

B1

B3

B2

10µm

10µm

10µm

563

C1

C2

C3

10µm

10µm

10µm

564

D1

D2

D3

30µm

30µm

30µm

565

E1

E3

E2

10µm

10µm

10µm

566 567 568

Figure 3 SEM photos of native (1), granular cold-water soluble (2) and inclusion

569

complex (3) samples. HA7 (A), HA5 (B), NMS (C), NPS (D) and WMS (E).

570


571

normal potato starch, WMS: waxy maize starch.

31


Intensity [arb. units]


Page 32 of 35

b a

4000

3500

3000

2500

2000

1500

1000

500

-1

572 573

wavenumber(cm

574

Figure 4 Raman spectroscopy of HA7 sample. (a) GCWS starch prepared from HA7, (b) IC.

575

)

Sample code: HA7: Hylon-7, GCWS: granular cold-water soluble, IC: inclusion complex.

576

32


Page 33 of 35


B

a

24.1%

b

29.2%

c

31.5%

5

10

577

15

20 25 2 Theta (°)

30



A

b

23.8%

c

25.2%

10

15

20 25 2 Theta (°)

30

35

D

a

33.5%

b

16.1%

c

17.0%

10

15

20 25 2 Theta (°)

30



578 579

26.1%

5

35

C

5

a

a 44.6%

b

14.5%

c

15.2%

5

35

10

15

20 25 2 Theta (°)

30

35


E a

48.0%

b

0.4%

c

0.5%

5

580

10

15

20 25 2 Theta (°)

30

35

581

Figure 5 X-ray patterns of native (a), granular cold-water soluble (b) and inclusion complex (c)

582

samples. HA7 (A), HA5 (B), NMS (C), NPS (D) and WMS (E).

583

Sample code: HA7: Hylon-7, HA5: Hylon-5, NMS: normal maize starch, NPS: normal potato starch,

584

WMS: waxy maize starch.

33



A

B HA7 HA5 NMS NPS WMS

0.10

0.05

0.00

0.15 Ethylene release ratio

Ethylene release ratio

0.15

0.10

20

40

585

60 80 Time (h)

HA7 HA5 NMS NPS WMS

0.05

0.00 0

Page 34 of 35

100 120

0

20

40

60 80 Time (h)

100 120

D

C

1.0 Ethylene release fraction


1.0 0.8 0.6 HA7 HA5 NMS NPS WMS

0.4 0.2 0.0

0.8 0.6

0.2 0.0

0

50

586

100 150 Time (h)

HA7 HA5 NMS NPS WMS

0.4

200

0

20

40

60 80 Time (h)

100 120

F

E

1.0 Ethylene release ratio


1.0 0.8 0.6 HA7 HA5 NMS NPS WMS

0.4 0.2 0.0

0.8 0.6

0.2 0.0

0

587

1

2 3 Time (h)

4

HA7 HA5 NMS NPS WMS

0.4

0.0

0.2

0.4 0.6 0.8 Time (h)

1.0

1.2

588

Figure 6 Release of ethylene from ICs at various temperature and RH conditions.

589

-80 °C (A), -20 °C (B), 4 °C (C), 25 °C (D), 52.9% RH (E) and 75.5% RH (F).

590


591

normal potato starch, WMS: waxy maize starch, RH: relative humidity, ICs: inclusion

592

complexes.

34


Page 35 of 35


Graphic abstract Encapsulation of Ethylene Gas into Granular Cold-Water Soluble Starch: Structure and Release Kinetics Linfan Shi, Xiong Fu, Chin Ping Tan, Qiang Huang, Bin Zhang


Encapsulation of Ethylene Gas into Granular Cold-Water-Soluble Starch

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