We review recent applications of atomic force microscopy (AFM) to characterize microstructural and textural properties of food materials. Based on interaction between probe and sample, AFM can image in three dimensions with nanoscale resolution especially in the vertical orientation. When the scanning probe is used as an indenter, mechanical features such as stiffness and elasticity can be analyzed. The linkage between structure and texture can thus be elucidated, providing the basis for many further future applications of AFM. Microstructure of simple systems such as polysaccharides, proteins, or lipids separately, as characterized by AFM, is discussed. Interaction of component mixtures gives rise to novel properties in complex food systems due to development of structure. AFM has been used to explore the morphological characteristics of such complexes and to investigate the effect of such characteristics on properties. Based on insights from such investigations, development of food products and manufacturing can be facilitated. Mechanical analysis is often carried out to evaluate the suitability of natural or artificial materials in food formulations. The textural properties of cellular tissues, food colloids, and biodegradable films can all be explored at nanometer scale, leading to the potential to connect texture to this fine structural level. More profound understanding of natural food materials will enable new classes of fabricated food products to be developed.
Background and objective
Generally, most milled rice is consumed as cooked grain. Nevertheless, a steady increase in new processes and products involving rice flour as a fundamental ingredient can be observed, which imposes a need for deeper knowledge of the properties of milled rice flours. The objective of this study is to investigate the effects of combinations of milling speed (750, 950, and 1,050 r/min) and milling time (20, 40, and 60 s) on the rheological and gel textural properties of waxy, low‐, and high‐amylose rice of flour.
Findings
Steady shear rheological measurements revealed that a positive relationship exists between milling revolution (speed × time) and the consistency coefficient values or hysteresis area of rice flour pastes; that is, the more the total milling revolutions, the higher the viscosity and stronger the thixotropic properties. During rheological measurement, waxy and low‐amylose rice flour pastes from milled rice with higher storage moduli and lower the ratio of storage moduli and loss moduli δ exhibited more elastic properties and higher gel strength than those from unmilled rice, indicating that a more rigid structure was formed. As milling speeds and durations increased, the hardness of waxy and low‐amylose rice flour gels increased, but the adhesiveness decreased.
Conclusions
This study showed that milling speed had more pronounced effects on the extent of change than did milling time regarding steady flow and textural properties. Meanwhile, both milling speed and duration could change the properties of rice flour to different extents.
Significance and novelty
These findings provided fundamentals for the effects of combinations of milling speed and milling time on the rheological and gel textural properties of the flours produced from waxy, low‐, and high‐amylose rice grains. Moreover, this research may help enable rice millers to produce improved functional rice products with minimal processing by precise control of suitable milling conditions.
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