Agricuture/ 4. Technology of storage and processing of agricultural products

Gulnazym Ospankulova, Natalya Nechay

Kazakh Research Institute of Processing of Agricultural Products, Kazakhstan

E-mail: bulashevag@mail

Study of the properties of cereal starches to obtain the sugary matters

As of now, there is an interest to develop innovative complex technologies for the processing various agricultural recourses. In addition, it is of interest for manufacture of high-quality and called-for starches and sweeteners.

Our current study was devoted to comparative study on the physicochemical properties of cereal starches from local Kazakhstan crops; in particular wheat and barley. Such parameters as size distribution of starch granules, as well as the viscosity of starch gels and the susceptibility to hydrolysis by α-amylase and glucoamylase were determined.

Starch from barley has unique nutritional properties. It is an additive for Vitargo^® nutrient, designed specially for athletes. The susceptibilities of the starch derived from barley (ten barley genotypes) – waxy, normal and high-amylose hull-less barley, to hydrolysis by porcine pancreatic α-amylase were studied [1,2]. The starch conversion reached 91-97% after 72 h. It was shown that the outer layers of normal and high-amylose starch granules produced from hull-less barley were more resistant to enzymatic hydrolysis. It was found, that the hydrolysis rate both in meal and pure starches followed the order: waxy>normal>increased amylose. The parameters of the gelatinization temperatures, pasting characteristics and susceptibilities to enzymatic hydrolysis were studied for normal, high-amylose and low-amylose barley starches in the range of 48–72°C [3]. It was shown that normal starches were the most readily soluble in water at 48–60°C in the presence of a mixture of α-amylase, b-amylase and dextrinase and were most readily to be hydrolyzed by these enzymes. High-amylose starch was the most resistant to enzymatic hydrolysis [3].

Wheat starch is widely used in bakery, and its physicochemical properties are well-known. Wheat starch granules have a bimodal size distribution with type A (10–40 μm) and type B (110 μm) [4]. (Yonemoto et al., 2007). Independently of the cultivar used, the large granules had average diameter of 22 μm and were lentil-shaped, while small granules had average diameter of 6 μm and were spherical. The large granules had lower lysophospholipid and higher amylose contents and lower index of crystallinity than the small granules. Despite the higher crystallinity, small granules were more susceptible to enzymatic hydrolysis than large ones, suggesting that the susceptibility of the small granule fraction was related to its larger surface area. It was shown, that if the stable complexes of lipids with amylose were formed in wheat starch, the swelling and dissolving capacity, as well as the water binding capacity decreased [5,6]. Amylose-lipid complexes were more susceptible to the attack of cellulase and xilanase (Spezyme^® type) than to the digestion by α-amylase and glucoamylase. It was shown that high-amylose wheat was a promising raw material for processing bakery and extrusion food products with a reasonably high content of resistant starches [7].

Quantitative elemental C,H,N-analysis was performed on automated analyzers Carlo Erba 1106 (Italy) and Euro EA 3000 (Italy) with an accuracy of ± 0.2-0.3 abs% [8]. Protein content analysis was performed in the instruments Behrotest InKjei M (Germany) and BUCHI Kjeldahl Systems (Switzerland). Data on the chemical composition of starches studied were presented in Table 1.

Table 1 - Chemical composition of the cereal starches

	Wheat starch	Barley starch
Dry-weight substances, wt%	88.3	88.5
Moisture, wt%	11.7	11.5
Ash content, wt%	0.33	0.40
Carbon content, wt%	40.59	39.99
Hydrogen content, wt%	6.66	6.40
Nitrogen content, wt%	<0.3	<0.3
Protein content, wt%	0.25*	0.31*
	0.49**	0.36**

*– Determination of protein using BUCHI Kjeldahl Systems (Switzerland)

** – Determination of protein using Behrotest InKjei â M (Germany)

As may be seen from data of Table 1, the cereal starches did not contain ash and proteins (within the accuracy of the analysis).

Shapes of starch granules were examined using a digital microscope Motic DMBA 300/310 (Spain). The measurements of the starch granules’ size at the range of 0.03–1000 μm were performed using the SHIMADZU instrument SALD-2101 Laser Diffraction Particle Size Analyzer (Japan). The size of the both barley and wheat ranged between 10 mm and 100 mm, with the peak at 22 mm. The data were presented in Table 2.

Viscosity (in mPa•s) of starch gel (3 wt%) was determined using Rheotest instrument Heppler Visco ball (Germany). Fluidity was repeatedly (>3 times) determined and the results were averaged.

Table 2 - The parameters of the cereal starches studied

Parameter	Wheat starch	Barley starch
The size of granules, μm	22.2	22.3
Viscosity (0)*, mPa·s (20°C)	25.4	32.9
Fluidity (0)*, s	16	18
Fluidity (1)**, s	358	205
Amylose content,%	26	26
The rate constant of α-amylolysis, k, min–1	1.05	0.90
The initial rate of dextrin’ hydrolysis by glucoamylase (0)*, V0, mmol · l–1 ·min–1	12.0	10.0
The complete starch conversion,%	97	78

* – (0) – freshly prepared starch gel or dextrin

** – (1) – starch gel aged at 10–15^оС for 1 day

Amylolytic enzymes (Novozymes) – α-amylase Amylexâ and glucoamylase SAN Super 360L with activity 360 U/ml, were used. α-Amylolysis of starch suspensions (5 wt%) were conducted at 85^оС. The spectrum characteristics of colored hydrolysates were analyzed in spectrophotometer Genesys 6 (Germany) in a 0.2 mm cuvette at the wavelength range of 350–700 nm. For drawing kinetic curve optical density recorded at a wavelength corresponding to the OD peak was measured. It should be noted that the value of λpeak varied from 585 to 475 nm over starch hydrolysis occurred. The rate constant (k) was evaluated by fitting kinetic curve by the first order exponential decay with the help of software Origin7.5G.

In order to study starch’s susceptibility to hydrolysis by glucoamylase dextrin suspensions (20 wt %) were prepared. The content of Amylexâ corresponded to 1-3 U per 1 g of starch. pH of dextrin solution was adjusted to 4.6. The solutions were filtered through nylon filters. Freshly prepared dextrin suspensions were used immediately for further hydrolysis by glucoamylase. After storage in refrigerator for a few weeks the friable sediments were formed in dextrin suspensions. The supernatant became transparent, but concentration of dry substances determined in this supernatant using refractometer did not change.

Hydrolysis of dextrin (20 wt %) was carried out at 50^оC during a period of several min to 6 h. To do this, the SAN Super 360Lâ was added to dextrin at the amount of ~3 U of glucoamylase per 1 g of starch. The kinetics of hydrolysis of dextrin was studied by determining the concentration of glucose using glucometer OneTouch Select® (USA), as well as spectrophotometer Genesys 6 (Germany) with the glucose oxidase-method [9]. Before measurements, the glucometer was calibrated using 3-4 standard glucose solutions, and regression coefficient was calculated, in most cases the coefficient was equal to 1.8.

Starch conversion (x,%) was calculated as ratio of glucose concentration measured during enzymatic hydrolysis to glucose concentration calculated theoretically as amount of glucose monomers in polymer starch molecule.

Viscous properties of starch gels depended on crops. As seen from Table 2, after aging at refrigerator for 1 day the gels’ fluidities increased 11 and 22 times for barley and wheat starch, respectively.

The kinetics of α-amylolysis was studied under control by the iodine reagent coloring. Common knowledge is that amylose and dextrin with a degree of polymerization n > 47 are bright blue colored, with n = 39–46 are blue-violet colored, with n = 30–38 are red-purple colored, with n = 25-29 are red, with n=21-24 are brown, and with n < 20 are yellow colored look like a dilute solution of iodine. Yellow color characterized the end of starch α-amylolysis. The color scale “blue → violet → red → brown” was observed for α-amylolysis of potato starch not for cereal starches. During α-amylolysis of all studied cereal starches red and brown colors were completely absent, as well as bright blue color were observed only for barley and wheat starches with higher amylose content (26 wt%).

The highest rate of hydrolysis was observed for barley and wheat starches (k = 0.90 and 1.05 min–1, respectively) with the highest amylose content (26 wt %), and with a maximum size of starch granules (22 μm) (Table 2). This observation differed from the result [3] that high-amylose starch was the most resistant to enzymatic hydrolysis. These observations may be explained by differences of reaction conditions, namely, we conducted simultaneously the starch gelatinization and hydrolysis at 85°C as described above.

The total starch conversion in the consecutive hydrolysis by α-amylase and glucoamylase depended on the crops (Table 2). It was found that wheat starches were hydrolyzed completely to glucose (x > 95%), while barley were hydrolyzed only at ~80-85 %.

Thus, we conclude that the most suitable for sugary matters is the wheat starch.

References:

1 Asare, E. K., Jaiswal, S., Maley, J., Baga, M., Sammynaiken, R., Rossnagel, B.G., & Chibbar, R. N.(2011). Barley grain constituents, starch composition, and structure affect starch in vitro enzymatic hydrolysis. Journal of Agricultural and Food Chemistry, 59, 4743–4754.

2 Li, J. H., Vasanthan, T., Hoover, R., & Rossnagel, B. G. (2004). Starch from hull-less barley: V. In-vitro susceptibility of waxy, normal, and high-amylose starches towards hydrolysis by alpha-amylases and amyloglucosidase. Food Chemistry, 84, 621-632.

3 MacGregor, A. W., Bazin, S. L., & Izydorczyk, M. S. (2002). Gelatinisation characteristics and enzyme susceptibility of different types of barley starch in the temperature range 48-72°C, Journal of the Institute of Brewing, 108, 43-47.

4 Yonemoto, P. G., Calori-Domingues, M. A., Franco, C. M. L. (2007). Effect of granule size on the structural and physicochemical characteristics of wheat starch. Ciencia e Tecnologia de Alimentos, 27, 761-771.

5 Nebesny, E., Rosicka, J., & Tkaczyk, M. (2002). Effect of enzymatic hydrolysis of wheat starch on amylose-lipid complexes stability, Starch, 54, 603-608.

6 Nebesny, E., Rosicka, J., & Tkaczyk, M. (2002). The stability of lipid-amylose complexes upon enzymatic hydrolysis of wheat starches of different chemical composition, Zywnosc, 9, 9-16.

7 Wasserman, L. A., Kiseleva, V. I., Schiraldi, A., Blaszczak, W., Fornal, J., Sotnikova, E.V., Gapparov, M. M. G., &Yuryev, V. P. (2004). Microstructure, thermal properties and susceptibility of the high amylose wheat starch to enzymatic hydrolysis: a new material for resistant starch (RSIII) production. Polish Journal of Food and Nutrition Sciences, 13, 151–155.

8 Fadeeva, V.P., Tikhva, V. D., & Nikulicheva, O.N. (2008) Elemental analysis of organic compounds using automatic CHNS-analyzers. Journal of Analytical Chemistry (Rus), 63, 1197–1210.

9 Kovalenko, G. A., & Sokolovskii V.D. (1989) Determination of glucose in an enzymatic biosensor based on minireactors with immobilized glucose oxidase. Journal of Analytical Chemistry (Rus), 44, 1323–1328.