Quality Advantages of Food Grade Soybeans from the Upper Midwest: storage perspective. Sam K. C. Chang. Ph.D., Professor; IFT Fellow

Transcription

1 Quality Advantages of Food Grade Soybeans from the Upper Midwest: storage perspective Sam K. C. Chang Ph.D., Professor; IFT Fellow Department of Cereal and Food Sciences North Dakota State University Fargo, ND Phone:

2 United States No. 1 Soybean Producer Most of food-grade soybeans are shipped to Asian countries for soy food making.

3 Soybeans: Functional Food 40-45% protein 17-21% oil 34% carbohydrate 5% ash Lower heart disease (FDA, 1999) Cancers Ideal food for long duration space flight

4 Consumers Benefit from High Quality Soy Food Products

5 Soymilk: Quality Differences Color, Aroma, Taste, Mouthfeel, Viscosity

6 7S, β-conglycinin: 35% of Total Soy Protein (Maruyama et al., 2003)

7 11S, Glycinin: 40% of Soy Proteins 3 orthogonal views (Adachi et al., 2003)

8 Soybean Quality Factors affecting soybean quality Raw materials: Cultivars Storage: Seeds are alive.

9 Storage and Shipping Soybeans go through transportation and storage before processing 9 Storage bins Rail and Cargo Ships

10 Storage Warehouse

11 1 Ton Bags

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13 First Experiment: Color Changes During Storage To design a rapid method for predicting food quality by using a simple color monitor. Farmers, shippers, and manufacturers can monitor food quality during storage. Help in marketing soybeans. Soy Foods Soymilk Tofu Fermented soy foods Bean sprouts Vegetable oils

14 Research Objectives 14 A systematic approach (wide ranges of RH and temperature) to understand the changes in soybean color and protein during soybean storage. How color changes can be mathematically related to protein recoveries, and soymilk and tofu making quality.

15 Soybean Varieties Studied Proto: high protein Vinton: higher lipid content than Proto IA2032: Lipoxygenases-null

16 Storage Conditions, and Sampling Schedules (Kong, Chang and others, 2008, JFS 73:S134)

17 Storage Devices Incubator and glass jars Each jar held 700 to 800 grams of beans. Used saturated salt solution to control relative humidity. Opened jars regularly (one or two weeks) to allow fresh air circulation Institute of Food Technologists 17

18 Moisture Color: Soybean Quality Measurements Hunter L, a, b scales, Color Difference, Δ Ε

19 Quality Attributes of Soymilk and Tofu 19 Soymilk ph, protein and solids. Color: Hunter s L, a, b scales. Tofu Coagulant mixing time in sec. Tofu yield and solids content. Tofu textural properties by Instron. Firmness. Elasticity. Brittleness.

20 Soymilk and tofu methods Soybean Soaked Coagulated Stirred Add CaSO 4.2H 2 O Overnight Drained Ground and Filtered Soymilk Incubated 8 min Transferred Pressed Keep boiling, 5 min Boiled Cooled to 87 C Tofu 64.4 g/cm 2, 15 min g/cm 2, 15 min Reference: Cai TD, Chang KC

21 Raw and Stored Soybean Samples 65% RH and 40C, 0-12 Months Institute of Food Technologists

22 Changes in Soybean Color, L value - Whiteness

23 Changes in Soybean Color- a Value: Redness

24 Soybean Storage Decreased ph of Soymilk

25 Soymilk Protein Recovery Decreased During Storage

26 Coagulant Mixing Time Decreased by Storage at 70%RH, 40C

27 Tofu Yield Decreased at High Temperatures of Storage

28 Equations between Soybean Color and Soymilk/Tofu Making Properties

29 Regression Equations Among Soymilk and Tofu Making Properties

30 Multiple Factorial Regression Equations Between Soybean Color and MC, RH, T, t Equation 6 (Kong and Chang, 2009) Equation 7 (Kong and Chang, 2009) R 2 =0.8979

31 Kinetic Parameters between Soybean Color and Solid Extractability for Proto and Vinton, 70%RH, 22-40C

32 Conclusions on Color Quality 1. Rapid color analysis can predict soybean quality for making soy foods. 3. In this study, temperature played the most important role followed by time and RH. 5.Variety effect is important. (Vinton has higher lipid, higher deterioration rate). 3. Soymilk/tofu quality can be predicted from the kinetic equation or linear regression equation.

33 Second Experiment: Biochemical changes during storage 33 A systematic approach to understand the changes in soy protein s molecular structures, and other biochemical changes during soybean storage. How these changes are correlated to soymilk and tofu making quality

34 Soybean and storage conditions 34 Soybeans: Cultivar Proto (ND) Four storage conditions: Adverse conditions: 84% RH, 30 C Mild conditions: 57% RH, 20 C Cold storage: in a walk-in-cooler, 3~4 C (86% RH) Ambient conditions: in a garage (temperature not controlled)

35 Storage time Storage time: 9 months for adverse conditions 18 months for other three conditions 35

36 Chemical Analysis of Soybeans 36 Moisture, Protein, Lipid, Ash, Carbohydrate. Titratable acidity Total free sugar Phytate Isoflavones Soymilk protein recoveries Tofu quality

37 Soybean Chemical Composition 37 For the cold conditions (4 C) (RH 86% in cooler) Moisture increased due to high humidity in cooler. Lipid, protein, and total free sugar no significant changes. Phytate degradation occurred slowly with storage time. Titratable acidity increased slightly along with storage time.

38 Soybean Chemical Composition 38 For the uncontrolled ambient conditions (Garage) Moisture equilibrated at 8.8~9.4% after 3 months. Lipid, protein, and total free sugar no significant changes. Phytate degradation occurred slowly with storage time. Titratable acidity increased slowly along with storage time.

39 Soybean Chemical Composition 39 For the mild conditions (57% RH, 20C) Moisture was equilibrated at % in 3 months. Lipid and protein showed no significant changes. Total free sugar changed slightly with no trend. Phytate decreased slightly with storage time. Titratable acidity increased slowly along with storage time.

40 Results: Chemical Compositions of Soybeans For the adverse conditions (84% RH, 30 C) 40 Moisture increased along with storage time. Titratable acidity increased along with storage time (from 0.73% to 2.03%). ph of soy flour slurry decreased significantly (from 6.6 to 5.5). Phytate degraded along with storage time (from 1.33% to 0.87%). Total free sugar degraded along with storage time (from 11.5% to 6.4%).

41 Results: Soymilk protein content decreased by storage of soybeans at 30 C and 84% RH protein of soymilk solids of soymilk solids of tofu Percentage M 1 M 2 M 3 M 4 M 5 M 6 M 7 M 8 M Storage months Figure 3-1. Protein and solids content in soymilk and tofu made from soybeans stored under adverse conditions

42 Scanning Electron Microscopic Image of Tofu (Yuan and Chang, (Chang and 2004) Yuan, 2004)

43 Tofu yield from soybeans stored in 84% RH 30 C 43

44 Tofu yield in other storage conditions 44

45 Protein Isolation and Purification (Hou and Chang, 2004, 2005) Glycinin and -conglycinin were isolated by fractionation method and purified by chromatographies. 45 Purified proteins were dialyzed and freezedried for characterization

46 Results (SDS-PAGE of 11S) Lane #1: control raw; #2: control 0 month; # 3~#10: 84% RH 30 C, 1~8 months; # 11: 57% RH 20 C, 18 months; # 12: cold 4 C, 18 months; # 13: uncontrolled ambient temp.18 months; # 14: molecular markers. 46

47 Results (SDS-PAGE of 7S) 47 Lane #1: control raw; #2: control 0 month; # 3~#10: 84% RH 30 C, 1~8 months; # 11: 57% RH 20 C, 18 months; # 12: cold 4 C, 18 months; # 13: uncontrolled ambient temp.18 months; # 14: molecular markers.

48 11S & 7S protein isolation yield In the adverse conditions: 0 m ~ 9 m 11S yield: decreased from 14.5% to 0%. 7S yield: decreased from 12.6% to 0.2%. 48 In the other conditions: 18 months 11S yield: 14% 7S yield: 12%

49 Characterization of purified glycinin and -conglycinin 49 Subunit & purity: SDS-PAGE Molecular size: gel filtration Glycosylation: total sugar content SH/SS interchange: DTNB reagent Hydrophobicity: fluorescence probe ANS Secondary structure: circular dichroism (CD) Amino acid composition: HPLC Denaturation-phase transition: DSC

50 Conclusions on 11S protein structure studies Structural changes occurred to 11S from the conditions of 84% RH 30 C 50 Glycosylation with storage time Total free SH S-S bonding Hydrophobicity Beta-sheet structure In adverse conditions, the 11S structure tended to unfold and might have lower hydrophobic interactions and less hydrogen bonding.

51 Conclusion on 11S Protein (Continued) Changed structure of 11S might lead to a weaker gel matrix in tofu, which caused a lower yield S structure had not significantly changed even soybeans were stored in the other three conditions for 18 months.

52 Conclusions on 7S Protein Structure 52 7S protein from the 84% RH 30 C for 9 months Slight glycosylation as compared to control Total free SH after 6 months S-S bonding after 6 months Hydrophobicity after 7 months α-helix structure within 3 months, then stable β-sheet structure within 3 months, then stable The other 3 selected storage conditions showed no significant influences on the structure of 7S protein as compared to the control.

53 Conclusion on Phytate 53 In the adverse conditions, phytate in soybean degraded significantly with storage time. In the other 3 conditions, phytate in beans showed slight reduction as storage up to 18 months. Phytate degradation only played an indirect and minor role in reducing tofu quality during storage. Soymilk acidity, protein extractability, and protein denaturation had more influences than phytate did.

54 Changes of Isoflavones 54 Isoflavones distribution in the initial beans 87% malonylglucosides 12% glucosides < 1% aglycones Isoflavones distribution in the adverse conditions for 9 months < 1% malonylglucosides 2% glucosides 97% aglycones

55 Changes of Isoflavones 55 Isoflavones distribution in the mild conditions for 18 months 66% malonylglucosides 31% glucosides < 2% aglycones Isoflavones distribution in the cold conditions for 18 months 87% malonylglucosides 12% glucosides < 1% aglycones

56 Isoflavones 56 Isoflavones distribution in the uncontrolled ambient conditions for 18 months 76% malonylglucosides 22% glucosides < 2% aglycones

57 Conclusion on Isoflavones Interconversion of isoflavones occurred dramatically in soybeans during adverse storage. 57 Glucosides and malonylglucosides were the dominant forms in the fresh soybean. Aglycones were the major forms as the soybeans aged during storage. The more aglycones the soybean had, the more deterioration the soybeans. Soybeans stored in ambient conditions did not change as much as the adverse conditions.

58 Overall Conclusions on the Effect of Storage on Biochemical effects and Tofu Yield and Quality 58 Under adverse conditions, soybeans could deteriorate significantly after 2 months. Protein solubility and structural changes contributed to the reduction in tofu yield and quality. Other factors such as acidity and phytate changes are also important. Under mild conditions, soybeans could remain good quality for making tofu for up to 18 months. In the US Northern Plain region, soybeans could be kept in the ambient conditions for up to 18 months without damaging its quality for tofu.

59 Onsite Storage of Soybeans 5 Soybean varieties were studied Stored on the farm storage warehouse Whapton-Breckenridge, MN (Brushvale) Casselton, ND (Sinner Brothers &Breshnahan) Prosper, ND (Peterson Farm) Results show no changes in soybean quality over one year of storage in North Dakota-Minnesota region. Average annual temperature in Fargo is 5 C. This provides a big advantage for keeping the soybeans fresh for food uses.

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61 North Dakota State University Cereal and Food Sciences

62 Storage Affects Biochemistry of Soybeans Protein structures & aggregation Secondary: alpha-helix, beta-sheets Tertiary and quaternary: glycosylations, -S-S-, hydrophobicity, aggregations Phytate: phytase Isoflavones : glucosidases, forms conversions. Sugars: Maillard reactions and degradations Lipids Oxidation: Off-flavor, rancid flavor Hydrolysis: Free fatty acids, acid values

63 Biochemical changes influence food and processing properties Color Taste Aroma Texture Tofu Processing ability Coagulant Mixing time

64 Optimal coagulant concentration (OCC, mm CaCl 2 ) of soymilk prepared from soybeans under various storage conditions (Liu and Chang, 2007) month 2 months 3 months %RH during storage

65 The Simple Titration Method for optimal coagulant concentration Liu and Chang (2002, 2003)

66 Effect of MgCl 2 Concentration on viscosity and swirl depth Liu and Chang (2002)