The impact of heat-moisture treatment on the molecular structure and physicochemical properties of normal and waxy potato starches

Abstract

Heat-moisture treatment (HMT) is a physical modification technique that modifies starch structure and properties without destroying its granular structure. HMT has been shown to cause starch chain interactions and crystallite disruption/reorientation within the amorphous and crystalline domains. However, the part played by amylose (AM) during HMT of starches is not properly understood. Furthermore, a systematic study has not been carried out to examine how variations in HMT temperatures influence molecular structure, physicochemical properties and digestibility of normal potato (NP) and waxy potato (WP) starches. Thus, the objective of this study was to determine changes to molecular structure, physicochemical properties and digestibility ofNP and WP starches on HMT at different temperatures (80,100,120 and l30°C) for 16 h at 27% moisture. Structural changes on HMT were monitored by scanning electron microscopy (SEM), confocal laser scanning microscopy (CLSM), polarized light microscopy (pLM), wide angle X-ray scattering (WAXS), attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopy, fluorophore assisted capillary electrophoresis (FACE) and KlS spectra. Changes to physicochemical properties on HMT were determined by granular swelling, amylose leaching, gelatinization parameters and pasting properties. Digestibility of normal and waxy potato starches before and after HMT by porcine pancreatic a-amylase (PPA) was monitored by measuring initial velocity and by exarninationofthe granular structure at different stages of hydrolysis by SEM, CLSM and PLM. The results showed that structural changes on HMT were influenced by differences in starch chain mobility at different temperatures of HMT. Starch chain mobility, in turn, was influenced by the interplay between the extent to which B-type crystallites were transformed into A+B-type crystallites, kinetic energy imparted to starch chains and amylose content. The main type of structural changes influencing physicochemical properties at different temperatures of HMT were starch chain interactions (at 80 and IOO°C), disruption of hydrogen bonds between amylose-amylopectin and amylopectin-amylopectin (at 120 and l30°C), disorganization of amylopectin chains near the vicinity of the hilum (at 100, 120 and l30°C)andformationofinterruptedhelices(atl30°C).The susceptibility ofNP and WP starches towards a-amylase decreased at 80°C, but increased in the range 100 to l30°C. NPand WPstarches exhibited heterogeneity in degradation (NP>WP) Most studies have been on the impact ofHMT on the thermal properties, crystallinity and pasting propertiesofnorrnalstarches. Some researchers (Hoover and Manuel, 1996; Kweon el al., 2000;Zavareze et al., 2010) have attempted to explain the impact of HMT on the structure and physicochemical properties of starches varying in amylose content. However, the part played by amylose during HMT of starches is still not properly understood. Unlike in cereal starches, amylose has been shown to be co-crystallized with amylopectin...

Rice starch vs. rice flour: Differences in their properties when modified by heat–moisture treatment

“…It was observed that the protein bodies were deformed and spread over the lumps of starch granules. Due to their fragile nature (Varatharajan, Hoover, Liu, & Seetharaman, 2010), protein bodies can easily be denatured by heating at 100 • C. The enlarged photo (1000×, Fig. 2 inset) of HMT rice flour with 30% moisture content reveals that the denatured protein bodies spread over, and adhered to, the surfaces of the starch granule clumps.…”

Understanding Starch Structure: Recent Progress

“…WAXS powder diffractograms of many starch granules, especially from cereals, show a characteristic peak at 20 • 2θ, which is attributed to V-amylose-phospholipid complexes [17,[158][159][160]. However, it should be noted that a peak near 20 • 2θ also is found in other than cereal starches with only low amylose content-even in amylose-free potato starch [44,160,161], and thus it can not solely be attributed to amylose-lipid complexes. Nevertheless, 13 C-cross-polarization/magic-angle spinning nuclear magnetic resonance ( 13 C CP/MAS NMR) studies confirmed that a part of the amylose in cereals is complexed with lysophospholipids [162].…”

“…However, the granule integrity remains intact because the backbones of the amylopectin molecules stretch in all directions (compare with a balloon) and, only when they loose contact with each other the granules disintegrate [252]. In the presence of amylose, starch granules are more stable than waxy granules [161,259,260]. The stabilising effect is possibly due to amylose intermixed with amylopectin backbones in the amorphous lamellae [203], which decreases their flexibility and retards the swelling.…”

Changes in physicochemical properties and in vitro digestibility of common buckwheat starch by heat-moisture treatment and annealing

“…Therefore, CBS should be modified in order to meet the processing requirements in food production. In general, starch can be modified chemically (acid hydrolysis, oxidation and cross-linking) and physically (pre-gelatinization, heat-moisture treatment [HMT] and annealing [ANN]) (Varatharajan, Hoover, Liu, & Seetharaman, 2010). HMT is usually carried out in a relatively low moisture (<35%) and high temperature (90-120 • C) condition.…”