WATER BINDING CAPACITY OF STARCHES, THEIR DERIVED PRODUCTS AND OTHER CEREAL COMPONENTS

Abstract

Attached

This thesis describes the moisture biI1ding capacities and gelatinization characteristics of several commercial native starches and some of their derivatives. The main techniques uEed in the investigation were Differential Scanning Calorimetry and Scanning Electron Microscopy. The introduction presents a general review of starch-water relati0~s and the significance of these relations to food systems. A brief discussion of the aim of t.he project is also pre sent.ed to show the relevance of the research. 'I'he literature review attempts to introduce the nature of water , its involvement in ce rt.ai,n forms of food spoilage, the concept of bound wat.er and t.he COI!lmOn methods used in t.he determination of bound water. The chemistry, structure and properties of the starch substance ara also considered, with brj.ef references ~n outstanding contributions to the understanding of the behaviour of this industrially useful cornmod Lty . The process of starch gelatiniza·tion and the usual methods of its estimat.ion are also described, and in doing so brief discussion of water behav i.o o r in dough has been inel ude d . 'I'hestarch samples used in the st.udywere ana l.y sed for their moisture, protein, fat and ash contents. EC2h starch was ana lysed for eight metals using atomic observation spectrometry. Calcium, po t.e.s sLum and lTli:ignesimwen rc present in all samples. J.'>. few of t.he starches contained traces of zinc and copper. Aluminium was present in the al~~inium octinyl derivatives of both wheat and maize starches. This metal was also found in the canna and maize starches. Calorimetric studies investigating the moisture binding capacities of the starches showed native starches to have different moisture binding capacities. Substitution, cross-linking, oxidation, dextrinization, and acid hydrolysis of starches resulted in lower levels of moisture binding capacities compared with the parent starch. The only exception was the pre-gelatinized form which could bind more water than the parent starch. The time of mixing of wheat flour doughs was found to have no effect on the level of moisture bound in doughs. Sucrose was found to increase the level of bound water in starch-water system whereas salt had no effect'on the moisture binding level of the starches. Using the D.S.C. procedure, each native and derivatised starch had a characteristic gelatinization endotherm from which an enthalpy of gelatinization as well as a gelatinization range for which temperatures of on se t , peak and conclusion were measurable. In all cases, modification reduced the qelatinization energy. A minimum level of water in the available or free state was needed to initiate gelatinization. Sucrose reduced the gelatinization energy with increasing concentration, however wi h salt the effect was complex. The geJ,atinization energy decreased initially and then bGg~n to rise slowly with increase& salt concentration. The extent of gelatinization was found to be dependent on both temperat.ure and time of axpo sur e , Studies using scanning electron microscopy showed marked differences of granular disruption and solubilisation between the native starches. The processes of cross-linking were seen to retard granular disruption and dispersion of the starch materials. Substitution increased ease of dispersion and the _dried out gel appeared as a strandular network. Starches which had been dextrinized or oxidized or hydrolysed showed different behaviour again except for the oxidized tapioca form which gave a gel st.ruccu re similar to a substituted starch. Conditions such as temperature of heating and also time of heating were seen to affect each modification type differently. In general, the substituted forms were found to r be disrupted and dispersed after :lower heat t.r-e a.t.mnet; t.han the cross-linked forms with the cross-linked form being most resistant of all to dispersion. Studies using a sedimentation procedure indicated the same situation wifh substi tuted forms swelling g:t~eatlyand dispersing easily, while the cross-linked forms showed limited swelling. Electron microscopy showed that dextrinized, hydrolysed and the oxidized forms svreLl.ed and dispers8·4 but may have undergone some degree of retrogradation compared to the substituted fOL~s.