Germplasm Enhancement of Maize

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Project Overview
Objectives

Progress in 2005

Table 1
Table 2
Table 3
Table 4

GEM - 2005 Public Cooperator's Report

NOTE: The information in this report is shared cooperatively. The data are not published, but are presented with the understanding that they will not be used in publications without specific consent of the public cooperator.

 

Project Title: Value-added Utilization of GEM Normal and High-amylose Line Starch

 

Jay-lin Jane and Li Li

Department of Food Science and Human Nutrition

Iowa State University, Ames, IA 50011

Project Overview

This research project is aiming to characterize starches produced by the GEM projects and to develop value-added utilization of these starch lines.  Two types of starch, normal maize starch extracted from GEM lines supplied by the GEM Coordinator, Dr. Mike Blanco, and high-amylose maize starch developed from GEM amylomaize project of Dr. Mark Campbell at Truman State, were the main genotypes used in the study.  Starch lines that displayed unique thermal properties (e.g., low or high gelatinization temperature and retrogradation rate) were selected and analyzed for their chemical structures and physical properties.  These selected starch lines were also investigated for their enzyme digestibility. The results of enzyme digestibility of the starch lines will enable GEM researchers to select desirable end uses of the starch lines, for example, easily digestible starch lines for baby chicken feed, and quickly retrograded/less digestible starch lines for making healthy foods to control body weight and for diabetic patients.  The enzyme digestibility of the starch was also correlated to its chemical structures and physical properties to reveal structure-function relationships.  Understandings of these structure-function relationships will assist maize breeders to produce value-added maize starch lines for specific market needs and to develop efficient screening techniques to identify desirable starch lines. 

Objectives

Objectives of this research project are to identify starch lines of desirable characteristics and to develop value-added utilization of GEM starch.  Specific objectives of the study during 2005 are:

  1. To investigate enzyme digestibility of GEM normal maize starch lines and to identify lines that are easily digestible, suitable for small animal feed and lines that are quickly retrograded and suitable for slowly digestible healthy-food ingredients.
  2. To characterize high-amylose maize starch and select desirable lines for resistant starch production.

Progress Made in 2005

Objective 1. To investigate enzyme digestibility of GEM normal maize starch lines. 

Starch samples that displayed high percentage retrogradation or low onset gelatinization temperatures were selected for the enzyme digestibility study and structure analyses.  Enzymatic digestibility tests were run using porcine pancreatic alpha amylase, and results are shown in Table 1.   Two promising GEM genotypes were found with 65% percent digestibility (AR17056:N2025-574 and DKB844:S1601-289) and both lines were increased by selfing in the GEM Ames nursery, and crossed together for future yield trials and digestibility research.  These lines are candidates for highly digestible starch desired for animal feed.  The amylopectin branch chain-lengths of these starches were analyzed to understand how structure affects the digestibility of starch.  The correlation coefficients (R) of the percentage enzyme digestibility (%ED)/the average branch chain length was -0.394; R of %ED/% content of amylopectin branch chains with DP>36 was -0.35; R of %ED/%retrogradation was 0.331; R of %ED/onset gelatinization temp was 0.0041.  These results indicated effects of the amylopectin branch chain length on the enzyme digestibility of starch and also showed a relationship between the rate of starch retrogradation and enzyme digestibility, but there was no correlation found between the onset temperature of starch gelatinization and the enzyme digestibility of starch (R=0.0041).  Starch that displayed larger percentage of enzyme digestibility, in general, consisted of shorter branch chain lengths. 

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Table 1. Enzyme digestibility of selected GEM normal maize starch linesa

 

 

 

 

 

 

Sample

 

 

% Digestion

 

 

Inventory #

Pedigree

Rep1

Rep2

Average

STDEV

Normal maize

 

58.9

62.6

60.7

2.6

02GEM00880

AR17056:N2025-574-1-B-B

65.0

66.2

65.6

0.8

03GEM00448

CUBA164:S15-118-6-9-B-B-B

 

 

 

 

02GEM00403

CUBA164:S15-7-9-1-B-B

47.5

49.6

48.6

1.5

04GEM00242

DKB844:S1601-206-1-B-B-B-B

55.3

57.7

56.5

1.7

04GEM00243

DKB844:S1601-289-1-B-B-B-B

67.2

63.3

65.3

2.7

02GEM00325

DKB844:S1601-3-2-B-B

61.3

59.2

60.2

1.5

03GEM00401

AR16026:S17-237-2-B-B-B

53.9

50.2

52.1

2.6

04GEM00234

AR17056:N2025  Select # 10-B-B-B-B

56.4

55.4

55.9

0.7

04GEM00241

CUBA164:S2008a-377-B-B-B-B

58.2

61.3

59.8

2.2

02GEM00412

CUBA164:S15-81-7-2-B-B

60.7

62.0

61.4

0.9

 

 

 

 

 

 

a Starch (20mg) was suspended in 9ml phosphate buffer (0.1M, pH6.9) containing 120 unit of porcine pancreatic alpha amylase. Samples were incubated for 24 hours at 37 degree C with shaking at 120 strokes/min. The reaction was stopped by the addition of 2ml of a 1M NaOH. The supernatant was collected by centrifugation at 500g for 10min. The extent of hydrolysis was determined by using DNS method.

 

Objective 2. To characterize high-amylose maize starch and select desirable lines for resistant starch production.

The resistant starch (RS) content and the amylose content of high-amylose maize starches are shown in Table 2. The RS content was measured by using AOAC method for total dietary fiber contents. The RS contents of samples 1, 2 and 3 were much larger than that of the other samples.  The amylose contents of the starch samples were determined by using gel permeation chromatography (GPC). The starch sample that had a larger RS content possessed a greater amylose content. The RS content of the starch sample was positively correlated with the amylose content of the starch with a correlation coefficient of 0.89.

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Table 2. Resistant starch and amylose contents of high-amylose maize starch lines

Sample

Pedigree

%RS

%Amylose

1

GUAT209:S13//OH43ae/H99ae  1-2-1-2

42.41.7

88.40.4

2

GUAT209:S13//OH43ae/H99ae  4-4-2-1-1

43.20.1

89.30.3

3

GUAT209:S13//OH43ae/H99ae  4-4-2-1-2

39.40.5

86.11.1

4

H99ae

19.10.5

66.50.9

5

OH43ae

14.00.5

74.60.6

6

B89ae

14.90.6

67.00.6

7

B84ae

11.51.4

67.70.7

 

The branch chain-length distributions of the high-amylose maize starch amylopectins are shown in Table 3. These amylopectins had less very short branch-chains (DP≤12) and more long branch-chains (DP≥ 37) than normal maize starch amylopectin. The RS content was positively correlated to the percentage of branch-chains of DP 13-24, with a correlation coefficient of 0.85. 

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Table 3. Branch chain length distribution of high-amylose maize starch amylopectin

Sample

Pedigree

DP≤12

DP13-24

DP25-36

DP≥37

Average CL

1

GUAT209:S13//OH43ae/H99ae  1-2-1

nda

nd

nd

nd

 

2

GUAT209:S13//OH43ae/H99ae  4-4-2-1

10.7

37.0

14.7

39.9

35.1

3

GUAT209:S13//OH43ae/H99ae  4-4-2-1

10.6

38.3

14.9

36.1

33.2

4

H99ae

8.4

36.0

13.6

42.1

37.3

5

OH43ae

10.5

34.7

14.1

40.7

35.8

6

B89ae

9.0

36.1

13.7

41.2

37.0

7

B84ae

10.1

35.4

13.3

41.2

36.4

a Not determined.

 

Thermal properties of the native high-amylose maize starches are shown in Table 4. All the starch samples displayed similar onset gelatinization temperature (63.8-65.0C).  Broader gelatinization temperature ranges, however, were observed for samples 1, 2, and 3.  The conclusion temperatures of samples 1, 2, and 3 varied from 104.8 to 106.7C, which were substantially higher than that of the other starch samples (92.8 94.2C).  The results indicated that starch granules of samples 1, 2, and 3 were not completely gelatinized after cooking at the boiling temperature. The high-amylose maize starches are from ae mutants; it is known that ae starches contain high amylose content, longer amylopectin branch chains, and display the B type polymorph.  How the branch-chains of amylopectin affect the resistant starch formation during processing, however, is not known.  We plan to process the high-amylose maize starch lines to further increase the resistant starch contents for manufacturing value-added healthy foods. 

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Table 4. Thermal properties of native high-amylose maize starch

Sample

Pedigree

To

Tp

Tc

DH

1

GUAT209:S13//OH43ae/H99ae  1-2-1a

63.71.7b

91.40.1

106.41.6

7.30.9

2

GUAT209:S13//OH43ae/H99ae  4-4-2-1

65.00.2

92.11.1

106.70.6

6.20.6

3

GUAT209:S13//OH43ae/H99ae  4-4-2-1

64.20.9

85.26.2

104.80.9

7.11.5

4

H99ae

64.40.1

77.70.0

94.22.6

12.61.0

5

OH43ae

64.80.3

77.00.5

94.01.5

15.61.4

6

B89ae

64.30.3

80.51.7

92.82.9

14.20.6

7

B84ae

65.00.8

77.12.5

94.00.5

13.30.3

 

a Samples (~3.0 mg,dsb) and deionized water (~9.0 mg) were used for the analysis; T0, Tp, Tc and DH are onset, peak, conclusion temperature, and enthalpy change, respectively.

b Other values were calculated form two replicates; : Standard deviation.

 

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We are grateful to our Cooperators for their support!

 


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