Granular and Molecular Changes of  Native and Chemically Modified  Aponogeton natans (Linn.) Engl. & Krause Tuber Starch During Heating

 

Sujit Dash*, Amaresh Chandra Sahoo, Stutee Das, Jayasmita Swain, Monalisa Rout, Sushma Soni

Institute of Pharmacy and Technology, Salipur, Cuttack-754202, Odisha, India.

*Corresponding Author E-mail: discoversujit@gmail.com

 

ABSTRACT:

Starch gelatinization is a process associated with the disruption of starch granular structure causing starch molecules to disperse in water. This study was designed to study Aponogeton natans Linn.  native and acetylated modified tuber starch granules as they were heated in water, and their resulting morphological traits. Aponogeton natans Linn. tuber starch in 100 ml of distilled water were treated at specific temperatures (ranging from 35°C to 90°C at 5°C increments) for 30 min in 250 mL conical flasks in a water bath.The results indicate that starch gelatinization is a more complex process than the previously suggested order-to-disorder transition. The energy absorbed by the granules facilitates the rearrangement or formation of new bonds among molecules prior to the temperatures normally associated with the melting of amylopectin crystallites during gelatinization. It is also evident that amylose plays an important role during the initial stages of corn starch gelatinization.

 

KEYWORDS: Aponogeton natans, Starch, gelatinization, temperature, disruption,

 

 

INTRODUCTION:

Starch is a semicrystalline material that means the granules contain crystalline and amorphous regions [1−3]. These crystalline regions are majorly made up of amylopectin polymers of which the outer branches are hydrogen bonded to each other to form crystallites that unravel during gelatinization [4−6]. The amorphous regions of granules are mainly composed of amylose amylopectin branch points [7].Starch gelatinization is associated with the disruption of granular structure causing starch molecules to dissolve in water and, as such, is one of the starch’s most important and unique properties[8]. Thre are many food products which contain partially cooked starch that contribute to their functional and structural properties.

 

Therefore, it is important to understand the time and temperature dependence of starch structural changes in water to characterize the gelatinization processes, especially how the granular structure changes and how amylose and amylopectin which constitutes the starch granule behave at different water temperatures.

 

MATERIALS AND METHODS:

Preparation of the specimen for microscopical examination:

The plant specimen for the proposed study was collected from Salipur, Cuttack, Odisha, India. Care was taken to select the healthy plant and organs. The required samples of different organs were cut and removed from the plant and fixed in FAA (Formalin -5ml+ Acetic acid-5ml+ 70% Ethyl alcohol-90 ml). After 24 hour of fixing, the specimens were dehydrated with graded series of tertiary – butyl alcohol[9]. Infiltrations of the specimens were carried by gradual addition of paraffin wax (melting point 58-60˚C) until TBA (tertiary – butyl alcohol) solution attained super saturation. The specimens were cast into paraffin blocks. The paraffin embedded specimens were sectioned with the help of rotary microtome. The thickness of the section was 10-12 µm. Microscopic descriptions of tissues were supplemented with the micrographs wherever necessary. Photographs of different magnification were taken with Nikon labphoto 2 microscopic units.

 

Extraction of starch:

The starch was extracted using hot water method. 100 g of tubers were soaked in 1000 cm3 beakers in a thermostatic water bath at a constant temperature of 40oC for about 24 hours. One part of soaked tubers and three parts of distilled water were blended for 3 min at medium and high speed. The resultant slurry was passed through double layer of muslin cloth and then centrifuged at 5000 rpm for 20 minutes. The supernatant was discarded and the sediment resuspended in excess 0.02 % sodium hydroxide to remove any residual proteins and phenolic compounds. After standing for 4 hours the supernatant was discarded. This procedure was repeated 6-8 times until the supernatant becomes colourless. The final sediment was suspended in distilled water and then subjected to filtration through 0.045 mm sieve, neutralized to pH 7.0, filtered on Buchner funnel and thoroughly washed with distilled water. The filtered cake was dried overnight at room temperature, ground to powder and stored in an air-tight glass bottle before further analysis[10, 11].

 

Preparation of Starch Acetate:

Starch acetate will be prepared by slight alteration of the method described by Sodhi and Singh [12]. 100 grams of isolated Starch was dispersed in 225 ml of distilled water and stirred for 1 hour at 300C. The pH of the slurry was adjusted to 8.0 using 3% sodium hydroxide solution. Acetic anhydride (8 g) will be added drop-wise to the stirred slurry, while maintaining the pH within the range 8.0–8.4 using 3% NaOH solution. This reaction was allowed to proceed for 10 minutes after the completion of acetic anhydride addition. The slurry was then adjusted to pH 4.5 with 0.5 M Hydrochloric acid. The slurry was washed twice with distilled water and once with 95% ethanol, filtered, and oven-dried at 400C [12]

 

Particle size Determination:

The starch mean particle size of samples of the Aponogeton natans Linn. was determined microscopically with the aid of a calibrated eyepiece. The particle size of each sample dispersed in glycerol was calculated.

 

Granular and molecular changes of native and acetylated modified Aponogeton natans (Linn. ) Engl. and Krause tuber starch during heating.

6 grams of native and acetylated modified Aponogeton natans Linn. tuber starch in 100 ml of distilled water was treated at specific temperatures (ranging from 35 to 90°C at 5°C increments) for 30 min in 250 mL conical flasks in a water bath. The starches were filtered through Whatman no.1 filter papers, and the residue was dried under vacuum pressure. 0.1 g in 25 ml of water, Aponogeton natans Linn. tuber starches samples was heated in a glass petri dish on a hot plate for 5−10 min (depending on the desired end temperature). After reaching the experimentally specified temperature between 30 and 85°C at 5°C intervals, the petri dish was promptly viewed using a light microscope using Nikon Labphot 2 Microscopic Unit and observed at a 1 × 400 magnification. Sample temperatures was monitored using an infrared thermometer before and during microscopic observation.

 

Results Microscopy of the tuber:

Rhizome powder viewed under polarized light microscope. Starch grains were seen in abundance in the ground tissue. Starch grains appear bright against dark background under polarized light [Figure: 1(A)]. The starch grains are circular and concentric. The hilum was in the centre. The starch grains vary in size. The larger starch grains are up to 20µm in diameter [Figure: 1 (B)]

Granular and molecular changes of Aponogeton natans Linn. tuber starch during heating.

 

During heating in water, both native starch granules and acetylated modified starch granules remained intact up to 50°C [Figure 2 and 3]. It appears that the outermost layers of the native starch and acetylated modified starch granules tend to maintain granular integrity during heating to 45°C and 50°C respectively though some of the starch granules swelled up due to the bond of the amylopectin with water molecule, before they disintegrate as the internal structure and free movement of starch polymers destabilize the granule’s internal structure. The native starch granules starts to lost their integrity and formed a molecular network at 55°C whereas acetylated modified starch granules lost their integrity and formed a molecular network at 60°C. The result further showed that complete granular disruption and the formation of a gelatinized solution for native starch and acetylated modified starch did not occur below 78°C and 81°C respectively. As observed by light microscopy, the large native starch granules swelled first and began to break apart at around 55−65°C; the large acetylated modified starch granules swelled first and began to break apart at around 60−65°C. The small native starch and acetylated modified starch granules did not start to disintegrate until 70°C and 75°C respectively.

DISCUSSION:

Due to acetylation , hydrophilic hydroxyl groups are substituted with hydrophobic acetyl groups and water molecules, a treatment such such as acetylation of amylose molecules, a treatment such as acetylation which eliminate crystallization will effect stabilization of starch solution. Acetylation also prevent or minimizes association of amylopectin outer branches[13] and also  increases the gelatinization temperature of acetylated modified starch over native starch of Aponogeton natans Linn .

 

CONCLUSION:

Initially gelatinization occurs in the amorphous regions, as opposed to the crystalline regions, of the granule, because hydrogen bonding is weaker in these areas. The differences in transition temperatures between the different starches may be attributed to the differences in the degree of crystallinity. The gelatinization properties are controlled in part by the molecular structure of amylopectin (unit chain length, extent of branching, molecular weight, and polydispersity). This is of practical value in industrial and food application because such association cause cloudiness and syneresis in aqueous dispersion of starches. Consequently, the gelatinization temperature ranges become smaller and this has important implication on the energy and time required to gelatinize the starch for specific industrial use.

 

 

 

A. Transverse section of the tuber

B. Transverse section showing starch in the cortical cell

 

 

10°C

 

20°C

 

30°C

 

 

45°C

 

 

55°C

 

 

65°C

 

 

78°C

 

Figure 2. Light microscopic images of Aponogeton natans Linn. tuber starch granules in water mixtures heated to specific temperatures (numbers represent the temperature (°C).

 

 

 

20°C

 

 

30°C

 

 

40°C

 

 

50°C

 

 

60°C

 

 

70°C

 

 

 

 

 

 

81°C

 

Figure 3. Light microscopic images of Aponogeton natans Linn. tuber acetylated modified starch granules in water mixtures heated to specific temperatures (numbers represent the temperature (°C).

 

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Received on 23.02.2016                              Modified on 20.03.2016

Accepted on 10.04.2016                             © RJPT All right reserved

Research J. Pharm. and Tech. 9(4): April, 2016; Page 459-462

DOI: 10.5958/0974-360X.2016.00085.8