Physical and enzymatic modification of starch
Abstract
As a functional ingredient in foods and other products, starch should exhibit desirable properties related to its digestibility, ability to swell and absorb water, retain its functionality as an ingredient and exhibit enhanced processing and storage stability. The principle aim of this research is to produce starch materials to meet these standards with modified swelling factor, retrogradation, pasting properties and digestibility utilizing physical and enzymatic treatments. For the first part of this study, normal corn, waxy corn and wheat starch were adjusted to 40.0% moisture by the addition of deionized water, then subjected to a step-wise thermal treatment up to 95.0 °C. After thermal treatment, beta-amylolysis was conducted for all three starches at 2, 10, and 24 hours alongside thermal controls which weren't subjected to enzyme treatment. Ordered structure, digestibility, chain organization, and pasting behavior of starches were evaluated using HPSEC, Englyst digestibility tests, DSC and x-ray powder diffraction and RVA and swelling factor tests. Results of these assays indicated that the step-wise thermal treatment partially gelatinizes starch, leading to overall reduced ordered structure, enrichment of starch crystallites, enhanced susceptibility to beta-amylase, and reduced swelling factor at room temperature. Based on RVA data, increasing enzymatic treatment leads to further reduced peak viscosity and reduced break down and set-back. Beta-amylolysis does not appear to significantly change the RVA onset temperature compared to hydrothermal treatment alone suggesting that beta-amylolysis has a negligible effect on starch's resistance to heating. The second area of this study utilized exhaustive beta-amylolysis of amylose containing starches at low starch swelling for reduced digestibility, enriched amylose content and increased branch density. The impact of beta-amylolysis and repetitive autoclave treatment on starch fine structure for all starch types in this study demonstrated that amylose content and branch density were enhanced. This, along with an enrichment of amylose-amylose chain associations resulted in a reduced swelling factor observed after cooking for treated starch as opposed to native counterparts after cooking. The autoclave treatment applied in this study eliminated some of the ordered structure attributed to amylopectin, but allowed further refined the formation of more highly ordered crystalline structure attributed to amylose-amylose interactions. The digestibility of starch treated by autoclave cycling and beta-amylolysis appears to have been reduced overall in this study. There was some change in crystallinity in starch as a result of autoclave treatment, but a lack of significant change in digestibility profile between starches as a result of receiving additional autoclave treatment. It is apparent that the physical state of amylose and amylopectin does not majorly contribute to altering of digestibility of these starches. Thus, the reduction in digestibility observed may be attributed to changes in starch affected by beta-amylolysis. The end result of applying an autoclave cycling pre-treatment coupled with beta-amylolysis is a high-purity maltose product using potentially less enzyme and less purification. The high molecular weight starch material also produced by this treatment has a reduced swelling factor and reduced viscosity development upon cooking as compared with untreated starch.
Degree
M.S.
Advisors
Yao, Purdue University.
Subject Area
Food Science
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