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Maintenance of textural integrity in frozen, shredded vegetables

Maintenance of textural integrity in frozen, shredded vegetables. Li Ni, PhD Danny Lin, M.S. Diane Barrett, PhD Food Science & Technology University of California, Davis. Outline. Background Texture measurement of vegetables Optimization of LTLT pretreatment

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Maintenance of textural integrity in frozen, shredded vegetables

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  1. Maintenance of textural integrity in frozen, shredded vegetables Li Ni, PhD Danny Lin, M.S. Diane Barrett, PhD Food Science & Technology University of California, Davis

  2. Outline • Background • Texture measurement of vegetables • Optimization of LTLT pretreatment • Optimization of exogenous CaCl2 concentration • Color improvement of green vegetables

  3. Textural integrity of frozen vegetables • Structure and condition of the raw vegetable • Maturity at harvest • Blanching, freezing, thawing and cooking conditions used for preparation • Interaction of the structural components at cell walls and cell membranes

  4. Cell walls of vegetable tissues • 3-dimensional network of cellulose, hemicellulose, pectin, lignin and proteins • Cemented together by middle lamella • consists of calcium salts of galacturonic acid polymers that have been partially esterified with methyl alcohol cell wall cell membrane middle lamella

  5. Softening of vegetablesby thermal processing • Resistance to deforming forces • Turgor • Cell wall rigidity • Breakage of cell walls accompanied by release of vacuolar contents • Separation of one cell from another - failure at the adhesive layer between the cells

  6. Pectin molecule polymer of galacturonic acids which may be partially esterified

  7. Calcium ions polygalacturonic acid chains (pectins) Calcium interaction • Interaction with cell walls and middle lamella: “Egg-box” model

  8. ++ ++ Calcium interaction • Interact with cell membranes and affect turgor pressure Calcium ions Phospholipid bilayer

  9. Pectinmethylesterase (PME) • Hydrolyzes the methyl ester linkages in pectin molecules and releases methanol and free galacturonic acid moieties • Free carboxyl groups then form Ca-bridges between pectin molecules • Activity • Inactive at temperatures  50C • Activated  50C and reacts with cell wall pectins • rapidly deactivated at  70C

  10. Objective • Improve texture integrity and crispiness of frozen vegetables • Activation of PME • LTLT pretreatment • Calcium binds free carboxyl groups • Addition of Ca2+ • Improve color of pretreated frozen vegetables • 3-step-blanching • Addition of Zn2+ • Increased pH - calcium lactate

  11. Vegetables

  12. Materials & Methods Shredded vegetables LTLT pretreatment (60, 65, 70, 75C for 5, 10, 15, 30, 45 min) Blanching (100C for 2.5 min) Cooling (ice bath) Equilibrate to ambient temperature Analysis

  13. Thermal processing

  14. Thermal processing

  15. Texture analysis Texture Technologies TXT2 Analyzer (Kramer shear compression)

  16. Texture analysis Texture Technologies TXT2 Analyzer (Kramer shear compression) 45 angle Original Sharpened

  17. Texture analysis Texture Technologies TXT2 Analyzer (load cell)

  18. Texture measurement Parameters for TXT2 Analyzer (Kramer shear compression)

  19. Texture measurement Parameters for TXT2 Analyzer (Kramer shear compression)

  20. Texture change of thermally processed vegetables Broccoli 30 min 5 min

  21. Texture change of thermal processed vegetable Sugar snap pea 5 min 30 min

  22. Optimization of LTLT pretreatment Optimum temperature of preheating for 5 min Vegetable Size T (C) Bok choy 1-1/2 " L x 1/4" W 65 Chinese cabbage 1-1/2 " L x 1/4" W 60 Cabbage 1-1/2 " L x 1/4" W 65 Carrots 1-1/2 " L x 3/8” W 65 Green pepper 1-1/2 " L x 3/8" W 70 Red pepper 1-1/2 " L x 3/8" W Broccoli 3/4 " floret head x 1-1/2 "long 60 Sugar snap peas whole 65

  23. PME activity • Endogenous in raw • Residual (after pretreatment) • Exogenous - add PME as ingredient

  24. Bok choy

  25. Carrots

  26. Optimization of Ca2+ addition Exogenous Firmness (Kg) Ca2+ % Green pepper Red pepper Broccoli Carrot Control 34.432.47 36.323.74 22.110.96 11.381.28 0 38.852.45 45.533.7632.672.06 0.5 39.532.95 38.722.93 48.216.25 34.723.55 1 40.051.77 42.171.98 45.114.07 35.423.27 2 41.063.0145.392.5451.205.11 37.263.31 3 37.972.93 42.013.80 51.763.99 40.004.83 4 37.541.33 44.033.06 49.224.46 39.922.22 5 40.555.34 41.192.49 52.612.50 44.265.37

  27. Optimization of Ca2+ addition Exogenous Firmness (Kg) Ca2+ % Chinese cabbageCabbageSugar snap peaBok choy Control 19.021.53 29.852.24 23.481.21 17.670.56 0 26.161.02 46.693.20 36.203.59 26.703.40 0.5 27.153.93 45.304.95 34.102.22 28.922.40 1 26.703.00 43.424.03 34.353.42 30.701.47 2 28.065.22 43.726.16 33.841.72 33.452.48 3 27.213.85 46.663.05 32.593.15 29.152.34 4 30.561.80 42.343.48 32.902.80 29.152.34 5 29.632.67 43.606.96 32.043.27

  28. Addition of CaCl2 • Improved firmness • Higher conc. (5%) of CaCl2 contributed a firmer texture in carrots • 2% of CaCl2 resulted in a firmer texture for bell peppers, broccoli, and bok choy • 4% of CaCl2 contributed a firmer texture for Chinese cabbage • Addition of CaCl2 did not increase the firmness of cabbage and sugar snap pea

  29. Improvement of green color • 3-step-blanching • HTST-LTLT-Blanching • Addition of Zn2+ • ZnCl2 • Increased pH • Calcium lactate

  30. CaCl2 ZnCl2 Calcium lactate (0, 0.5, 1, 2, 3, 4, 5%) 3 step blanching 100C for 3, 6, 9, 12, 15 sec Materials & Methods Shredded vegetables LTLT pretreatment (60, 65, 70, 75C for 5, 10, 15, 30, 45 min) Blanching (100C for 2.5 min) Cooling (ice bath) Equilibrate to ambient temperature Analysis

  31. Pretreatment for vegetables • Bok choy • LTLT (65C, 5min) with 4% calcium lactate • Chinese cabbage • LTLT (60C, 5min) with 1% calcium lactate • Cabbage • LTLT (65C, 5min) • Sugar snap pea • LTLT (65C, 5min) with 2% calcium lactate • 3-step (100C, 122s + LTLT)

  32. Pretreatment for vegetables • Broccoli • LTLT (60C, 5min) or 3-step (85C, 2s + LTLT) • Carrot • LTLT (65C, 5min) with 5% calcium lactate • Green pepper • LTLT (70C, 5min) with 3% calcium lactate • Red pepper • Addition of 2% CaCl2 in blanching H2O without pretreatment

  33. Firmness changes during frozen storage Bok choy

  34. Firmness changes during frozen storage Carrots

  35. Unit operation Raw material LTLT pretreatment Blanch Microwave Thaw/cook Freeze Frozen storage

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