Luybov A. Wasserman

The influence of heating rate and annealing on the melting thermodynamic parameters of some cereal starches in excess water

Some normal (maize, wheat, barley, rye) and high amylose (barley) starches were studied using the method of differential scanning microcalorimetry (DSC). It was shown that a decrease of heating rate from 3 K/min to 0.25 K/min for 1% aqueous dispersions of starch does not lead to changes of the thermodynamic melting parameters of crystalline lamellae irrespective of the origin of starches. With the exception of the results for maize starch, the same behavior is observed for melting of amylose-lipid complexes. For maize starch, a decrease of heating rate and an annealing of crystalline lamellae lead to an increase of melting enthalpy of amylose-lipid complexes but does not change their melting temperature. The melting cooperative units for crystalline lamellae of the cereal starches were calculated. Using the average value of the melting cooperative unit, the lamellar thickness was determined. It is practically equal to the thickness of crystalline lamellae in the amylopectin model proposed by Robin. It was shown that the temperature dependence of the heat capacity for starch maize lipids has a negative increment. Some concepts concerning melting mechanisms of crystalline lamellae and amylose-lipid complexes are discussed.

Molecular basis of the gelatinisation and swelling characteristics of waxy barley starches grown in the same location during the same season. Part II. Crystallinity and gelatinisation characteristics

Abstract Nine waxy barley samples (grown at the same site during the same season) were investigated to identify those molecular aspects of amylopectin structure and architecture which define the order and gelatinisation characteristics. Using 13C CP-MAS/NMR it was confirmed that the number of double helices within the starches were approximately constant although differences in crystallinity were identified by X-ray diffraction. These differences in terms of amount of crystalline order correlated well with gelatinisation temperatures. The onset (To), peak (Tp) and conclusion (Tc) gelatinisation temperatures were 53.4, 59.2 and 68.1 °C on average with the associated enthalpy (ΔH) of 11.0 and 13.5 J g−1 on a starch and amylopectin basis. Annealing of the starches below To elevated To, Tp and Tc by +11.9, +8.2 and +5.1 °C on average and sharpened the gelatinisation range (Tc−To). Acid hydrolysis after annealing increased To, Tp and Tc (especially Tc) by +2.3, +17.4 and +34.7 °C on average. Annealing in the presence of α-amylase elevated similarly the gelatinisation parameters by +10.2, +7.1 and +2.8 °C for To, Tp and Tc, respectively. Crystalline lamellae lengths were found to be 5.2±0.7 and 6.2±0.4 nm using high sensitivity differential scanning micro-calorimetry and differential scanning calorimetry, respectively.

Changes of Thermodynamic and Structural Properties of Potato Starches (Udacha and Acrosil Varieties) during Biosynthesis

Starches isolated from two potato varieties (Udacha, Acrosil) at different stages of maturation were investigated using X-ray diffraction and high sensitivity differential scanning microcalorimetry methods. Applying some physico-chemical approaches, the thickness of the crystalline lamellae and the thermodynamic parameters characterizing their surface faces were determined. The thickness of crystalline lamellae is practically equal to the corresponding value in an amylopectin model proposed by Robin et al. The values of the thermodynamic parameters for the face sides of the starch crystalline lamellae are one order of magnitude smaller than the corresponding values for polyethylene crystals. Some concepts concerning structural changes during biosynthesis if starch potato granules are discussed.

The Application of Different Physical Approaches for The Description of Structural Features in Wheat and Rye Starches. A DSC Study

Starches isolated from wheat (Rapoports variety) at different stages of maturation and from completely maturated rye (Viatka-2 variety) were investigated in excess of water and in 0.6 M KCl using high sensitivity differential scanning microcalorimetry (HSDSC). Applying some physico-chemical approaches, the starch polymorphous structure, the thickness of the crystalline lamellae and the thermodynamic parameters characterizing their surface faces were determined. It has been established that wheat and rye starches belong to the A-type starches. It is suggested that during biosynthesis of granules the formation of the A-type structure is accompanied by an accumulation of crystal defects. This process leads to a decrease in the melting temperature of starches.

Changes of Thermodynamic and Structural Properties of Wrinkled Pea Starches (Z‐301 and Paramazent varieties) During Biosynthesis

Starches isolated at different stages of maturation (milky, waxy, complete maturation) of wrinkled peas were investigated by differential scanning calorimetry (DSC) and X-ray diffraction (XRD). It was shown that the maturation of wrinkled peas is accompanied by changes in the structural and thermodynamic properties of starches. The melting process of milky starches could be approximated by means of a “two-state” model. The melting process of the waxy and completely maturated starches was described as the melting of a mixture of low and high temperature populations of double-helical type crystallites, denoted as B- and B*-types, as well as the melting of Vh -type crystallites. The relative amounts of the three structures were determined by deconvolution of the calorimetric peaks. The values of the melting cooperative units ( ϑ ) and the thickness of the crystalline lamellae (pitch heights) for starches were determined using mathematical models describing the melting processes. The values of the ϑ for milky, waxy, and completely maturated starches were calculated as 18 and 29 anhydroglucose residues, respectively. The thickness of the crystalline lamellae of B-type crystals in the milky, waxy, and completely maturated starches were calculated. Structural changes in starch granules during maturation of wrinkled pea are discussed.