干制对淀粉特性及其制品品质的影响

干制是淀粉原料及其制品加工的常用手段。淀粉原料（块根、块茎、籽粒等）通过干制预处理,不仅便于安全保藏和后续加工,而且显著提高了淀粉提取率和加工适性。在淀粉基食品（粉条、粉丝、虾味片等）生产中,干燥是必要环节,对产品品质有决定性作用。干制过程复杂,涉及水分迁移、热量传递以及其他物理化学变化（如淀粉分子链重结晶、淀粉与其他共存成分相互作用）,这使生产中干制的经验性仍多于科学性。因此,作者全面总结和分析了干制对原料中淀粉特性以及淀粉基食品品质的影响及规律,为通过选择干制方式及干制条件来改善淀粉原料加工适性及干制淀粉基食品的品质提供参考。     

Lactose crystallization delay in model infant foods made with lactose, beta-lactoglobulin, and starch

Handling and storage alter infant food powders due to lactose crystallization and interactions among components. Model infant foods were prepared by colyophilization of lactose, β-lactoglobulin (β-LG), and gelatinized starch. A mixture design was used to define the percentage of each mixture component to simulate a wide range of infant food powders. The kinetics of crystallization was studied by a gravimetric method (dynamic vapor sorption) at 70% relative humidity (RH). After freeze-drying, lactose was amorphous and crystallized at 70% RH. The delay before crystallization depends on the contents of β-LG and starch in the formulations. A mathematical model was proposed to predict crystallization time (delay) at 70% RH. For the formulation containing 50% lactose, 25% β-LG, and 25% starch, lactose was still amorphous after 42 h at 70% RH, whereas pure amorphous lactose crystallized after approximately 70 min. Calculated and experimental results of adsorbed moisture from the formulations were compared. Adsorbed water of formulation containing lactose could not be calculated from moisture sorption properties of each component at a given RH because β-LG and gelatinized starch prevented lactose crystal growth.     

Sorption isotherms,GAB parameters and isosteric heat of sorption

The diffusion–sorption drying model has been developed as a physics‐based way to model the decreasing drying rate at low moisture contents. This new model is founded on the existence of different classes of water: free and bound water. The transition between these classes and the corresponding thermodynamics form distinct components of the drying model. This paper shows that the characteristics of the different classes of water and of the transition between them can be deduced from the GAB sorption isotherm. The parameters in the GAB sorption isotherm support the theory of localised sorption, establishing the existence of different classes of water. Moreover, the sorption mechanism retrieved from the GAB parameters is in accordance with the sorption mechanism, which is obtained from the moisture dependence of the net isosteric heat of sorption. This holds for experimental sorption data of corn and starch as well as for literature data on five vegetables and four fortified cassava products. An extremum in the net isosteric heat of sorption coincides with the transition between bound and free water, and the partition moisture content corresponds with the monolayer value derived from the GAB equation. This confirms that the GAB monolayer value can be chosen as model boundary between bound and free water. Moreover, it reveals that this method can be developed into a technique to estimate the bound water content in foods. Copyright © 2005 Society of Chemical Industry     

Effect of preservatives on the functional properties of tapioca starch: analysis of interactions

The effect of different levels of potassium sorbate or sodium benzoate addition on the water sorption behavior and on the mechanical properties of freeze-dried tapioca starch gel was studied.It was observed that the addition of potassium sorbate or sodium benzoate to starch before the gelatinization process increased the amount of water sorbed by the system, but experimental moisture content of the mixture was lower than the one predicted by a mass balance, revealing the existence of an interaction between starch and the preservatives. In general, in the range of water activity 0.755-0.976, most of the preservative was bounded to starch. Mechanical properties of the powder obtained after freeze drying of gels were also influenced by the addition of the preservatives: an increase in bulk density, higher cohesiveness and initial Young modulus was observed after antimicrobial addition.Results obtained showed that sorbate and benzoate interact with tapioca starch and that this interaction has a great influence on system behavior.     

A New Model for Describing the Water Sorption Isotherm of Foods

This work investigated the applicability in the food area of a new sorption equation recently developed by Ferro Fontán et al. (1982). The equation may be written, 1n (γ/a_w) =α (m)^-r, where, γ, α and r are parameters to be determined, m is the moisture content, and a_w is water activity. It was found that the three parameter equation is able to describe the water sorption isotherm of 18 different foods in an extensive range of a_w (up to about 0.95) with only 2–4% error (average) in the predicted moisture contents. Foods examined comprised, among other, oilseeds, starchy foods, and proteins.     

Starch Retrogradation: A Comprehensive Review

Starch retrogradation is a process in which disaggregated amylose and amylopectin chains in a gelatinized starch paste reassociate to form more ordered structures. Starch retrogradation has been the subject of intensive research over the last 50 years, mainly due to its detrimental effect on the sensory and storage qualities of many starchy foods. However, starch retrogadation is desirable for some starchy food products in terms of textural and nutritional properties. To better understand the effect of starch retrogradation on the quality of starchy foods, measurement methods of starch retrogradation and factors that influence starch retrogradation have been studied extensively. This article provides a comprehensive review of starch retrogradation including the definition of the process, molecular mechanisms of how it occurs, and measurement methods and factors that influence starch retrogradation. The review also discusses the effect of retrogradation on the in vitro enzyme digestibility of starch. Spectroscopic methods such as FTIR and Raman are considered to be very promising in characterizing starch retrogradation at a molecular level, although more studies are needed in the future.     

Examination of the additivity of moisture contents of components in simple model food systems

Additivity behavior in moisture sorption was examined for simple model food systems. Protamine, sucrose and starch were chosen as components and protamine-starch and protamine-sucrose mixtures were taken as simple model foods. Equilibrium moisture contents of individual components and food models were measured at four water activities between 0.2 and 0.8, and at two temperatures, 25°C and 35°C. Moisture contents of mixtures were also predicted from experimental moisture contents of components. For the mixtures, observed moisture content values were found to be higher than corresponding predicted ones. This showed that the additivity rule may not be applied for the systems studied and this was attributed to specific interactions between components.     

挤压对淀粉微观结构和理化性质影响的研究进展

挤压是一种常见的淀粉物理改性及食品加工方式,了解淀粉在挤压中及挤压后微观结构和理化性质的改变有利于淀粉类食品的创新生产和挤压机的有效应用。本文主要综述了挤压工艺对淀粉的直链淀粉含量、结晶特性、消化性、热特性、糊化特性、凝胶特性和流变特性的影响,以期为淀粉类食品加工的深入开发提供参考。     

The microstructure of starchy food modulates its digestibility

ABSTRACT

Starch is the main carbohydrate in human nutrition and shows a range of desired food properties. It has been demonstrated that fast digestion of starchy food can induce many health issues (e.g., hyperglycaemia, diabetes, etc.); therefore, how to modulate its digestion is an interesting topic. Previous studies have revealed that the microstructure and digestibility of starchy food of different botanical origin or from multiple processes are quite different; modulating starch digestion by retaining or altering its microstructure may be effective. In the present review, the current knowledge of the relationship between microstructural changes to starchy food and its digestibility at molecular, cell and tissue, and food processing levels is summarized. New technologies focused on microstructure studies and ways to manipulate food microstructure to modulate starch digestibility are also reviewed. In particular, some insights focusing on the future study of microstructure and the digestibility of starchy food are also suggested.     

Study of starch-lipid complexes in model system and real food produced using extrusion-cooking technology

The formation of starch-lipid complexes during extrusion of model system (rice starch added with oleic acid) and real food (rice starch added with pistachio nut flour) was evaluated. Both formulas were extruded at the same processing conditions (temperature profiles, screw speed and water feed content).The formation of starch-lipid complexes in real food, is strongly dependent on water feed content. In fact, at barrel temperature of 128 °C, the highest melting enthalpy of real food (6.7 J/g) was obtained only at 21% of water feed content whereas in the model system it was obtained both at 16 and 21%.These results point out the importance to consider all components present in the extruded food in order to study biopolymers modifications that occur during processing.

Industrial relevance

Additions of lipids alter the physical and chemical properties of starchy foods. The changes brought about by them in starchy foods have been attributed to the formation of complexes between amylose and lipids. These changes in the functionality of starch are of interest to the food industry and for human nutrition. Lipid complexation with starch is a very important reaction in extrusion cooking that affects structure formation and texture of the extruded products. Most studies on the starch-lipid complex formation during extrusion of model systems like starch and free fatty acids have been carried out, instead very little is known about starch-lipid complex formation during extrusion of flour blends containing fatty meal. This paper points out the importance to consider all components present in the food extruded in order to study biopolymers modifications that occur during processing. For this reason it is very important to use model systems that are not very different to real food and anyhow it would be advisable to verify the obtained results on real food, above all when a relation between macromolecular modifications and quality characteristics of extruded products would be studied.     

Effect of drying temperatures on starch-related functional and thermal properties of acorn flours

The application of starchy flours from different origins in food systems depends greatly on information about the chemical and functional properties of such food materials. Acorns are important forestry resources in the central and southern regions of Portugal. To preserve these fruits and to optimize their use, techniques like drying are needed. The effects of different drying temperatures on starch-related functional properties of acorn flours obtained from dried fruits of Quercus rotundifolia (QR) and Quercus suber (QS) were evaluated. Flours were characterized for amylose and resistant starch (RS) contents, swelling ability, and gelatinization properties. Drying temperature mainly affected amylose content and viscoamylographic properties. Amylograms of flours from fruits dried at 60 °C displayed higher consistency (2102 B.U. and 1560 B.U., respectively, for QR and QS). The transition temperatures and enthalpy were less affected by drying temperature, suggesting few modifications in starch structure during drying. QR flours presented different functional properties to those obtained from QS acorn flours. The effect of drying temperatures were more evident in QR.     

Analysis of a Model for Water Sorption Phenomena in Foods

The validity of the physical model on which the Hailwood and Horrobin (Trans. Far. Soc. 42B: 84; 1946) isotherm equation was developed was investigated. The results indicate that although the equation may fit sorption data for almost any type of food, it satisfies thermodynamic requirements (i.e. prediction of the temperature dependence) only for proteins and starchy foods. The results also show that plotting enthalpic changes against entropic changes for water sorption satisfies the enthalpy/entropy compensation phenomenon.     

含水量对湿热处理荸荠淀粉性质的影响

为有效开发利用荸荠淀粉,以荸荠淀粉为原料,将荸荠淀粉的含水量分别调节为20%、25%、30%、35%,利用鼓风干燥烘干箱在105℃下湿热处理2 h,研究湿热处理对荸荠淀粉糊化特性、流变特性、溶解度与膨胀度的影响。结果表明:随着湿热处理淀粉含水量的增大,淀粉糊峰值黏度和衰减值均有所降低;谷值黏度有所升高,淀粉颗粒的溶解度和膨胀度均有一定程度的下降;剪切稀化现象减弱;损耗角正切值越来越小,荸荠淀粉在湿热处理后所形成的凝胶为弱凝胶。     

STUDIES ON THE EFFECT OF TEMPERATURE ON THE MOISTURE SORPTION CHARACTERISTICS OF POTATOES

An understanding of the moisture sorption characteristics of food systems is an important objective in food engineering, in particular with respect to the mass transport phenomena during drying. A standard gravimetric technique was employed to examine the influence of temperature on the adsorption and desorption behavior for potatoes. The type II sorption isotherms were analysed using the Guggenheim-Anderson-de Boer model, with the observed hysteresis phenomena displaying a temperature dependence. The moisture dependent net isosteric heats of sorption were determined using the Clausius-Clapeyron equation.     

Starch-guest inclusion complexes: Formation,structure, and enzymatic digestion

Abstract

Starch/amylose-guest inclusion complexes, a class of supramolecular host-guest assemblies, are of critical importance in the processing, preservation, digestion, nutrients/energy uptake, and health outcomes of starch-containing foods. Particularly, the formation of inclusion complex has been suggested to lower the rate and extent of enzymatic digestion of starch and starch-containing foods. Compared with rapidly digestible starch, starch inclusion complex may fall into the category of slowly digestible starch, providing sustained glucose release and maintaining glucose homeostasis. Therefore, the ability of starch-guest inclusion complex to alter the digestive behavior of energy-dense starchy foods has been of interest to many researchers and has the potential to be developed and formulated into functional foods. In this article, we provide a comprehensive and critical review on the current knowledge of the in vitro and in vivo enzymatic digestion of starch-guest inclusion complexes, by emphasizing the structure-digestibility relationship. We examine the preparation methods employed, crystalline structures obtained, and physicochemical properties characterized in previous reports, which all have implications on the digestive behavior reported on the starch-guest inclusion complexes. In addition, we give suggestions on future research to elucidate the digestive properties of starch-guest inclusion complexes and to develop functional structures based on these complexes for use in foods and nutrition.     

Moisture migration by magnetic resonance imaging during eggplant drying: a preliminary study

The paper investigated the effect of hot‐air drying (50, 60 °C) on the physical properties of cylindrical eggplant samples. Drying kinetics, water profiles along longitudinal and transversal sample sections through nuclear magnetic resonance imaging (MRI) and volumetric shrinkage were determined. During the drying process at 50 °C, the volume of removed water was found lower than the reduction in sample volume, while at 60 °C it was higher. MRI showed that the water migration mainly occurs transversally than longitudinally. The curves of mass water loss obtained by both the standard weighting method and MRI showed conformity. Experimental data of moisture ratio and of shrinkage volume were fitted using empirical models available in the literature. This preliminary study showed that the nondestructive MRI technique offers the possibility to study water distribution in food during drying processes. The quantitative moisture distribution maps allow future development and verification of models for prediction of mass transport phenomena in foods during drying.     

Determination of Sweet Potato Starch Mixed in Kudzu Starch by Moisture Sorption Method

Moisture sorption isotherms of kudzu starch, sweet potato starch, and their mixtures were measured at 20°C by a gravimetric method with a vacuum apparatus. Correlation was found between the mixture ratio of sweet potato starch to kudzu starch and moisture content of the mixed starches at a water activity of 0.750; the correlation coefficient was 0.9955. The moisture sorption method could be used to determine the amount of sweet potato starch mixed in commercial kudzu starch.     

A PHYSICO-CHEMICAL STUDY OF THE MECHANICAL PROPERTIES OF LOW AND INTERMEDIATE MOISTURE FOODS*

A number of textural properties of precooked, freeze-dried beef were examined by a cutting-extrusion test (force) and by a compression test (seven different properties). The tests were performed at different points of the moisture sorption isotherm over the complete range of water activity, A_w. In cutting-extrusion experiments (Allo Kramer Shear Press), a maximum in the force vs. A_w curve was observed at about A_w= 0.85. In compression experiments (Instron Universal Testing Apparatus), important changes of the textural properties were found in the range A_w= 0.15–0.30. These changes were paralleled by changes in the thermodynamic functions of water vapor sorption, especially in the standard differential entropy. Thermodynamic theory and mechanical measurements were used to interpret the textural changes in terms of increased crystallinity and subsequent swelling of the food structure.     

Experimental investigation and theoretical modelling of absolute convective drying of starch

Starch is a granular, hygroscopic, capillary-porous material with an intricate structure. It is known that drying starch till 0% moisture is a physical treatment that modifies starch properties. However, depending upon the heat and mass transfer mechanisms prevalent in the drying system, starch properties are modified in a unique manner. Therefore, the drying operation itself needs to be thoroughly understood. Potato starch was treated in an oven at three high-temperature levels (110, 130 and 140 °C) and for three sample thicknesses (2.8, 5.6 and 11.2 mm). It was observed that drying of starch with moisture content in the hygroscopic range occurred only in the 2nd falling rate period. Two existing theoretical, drying models, one based upon the Krischer Theory and the other based upon the Percolation Approach, were considered apt for modelling the oven drying. Both models describe the experimentally measured moisture profiles well. During drying, transition from one water sub-population to another was smooth. The effective diffusion coefficient decreased with moisture content and increased with temperature, but did not follow Arrhenius’ Law above 130 °C.     

Structural characteristics and rheological properties of plasma-treated starch

Corn starch was treated by a dielectric barrier discharge plasma, and the changes in the granule morphology, crystalline structure, and molecular structure, as well as the rheological properties, were investigated using diverse techniques. Dielectric barrier discharge plasma could change not only the granule surface but also the internal structures of the starch granule through its pinholes. Specifically, after the plasma treatment, as the pinhole diameter increased, the relative degree of crystallinity decreased, accompanied by molecular chain oxidation, i.e., the generation of carboxyl groups, and degradation, i.e., molecular weight reduction. Therefore, the rheological behavior changed from pseudo-plastic to Newtonian with a decrease in the paste viscosity. The results indicate that dielectric barrier plasma could be used to produce modified starch with low viscosity at a high concentration for food and non-food applications.Industrial relevanceAs an eco-friendly and non-thermal physical technique, dielectric barrier discharge plasma has attracted great attention in polymer modification due to the interest in reducing generated wastes during modification and producing polymer products with high safety. Starch is traditionally a main material for foods and has been widely used in food and non-food industries. For improving the properties of starch and thus widening its industrial applications using a specific technique, it is indispensible to understand how the technique affects starch's structure and property. The present work revealed that not only was the surface of starch granules altered by the dielectric barrier discharge plasma but also the internal structure was affected, since the pinholes promoted the penetration of the plasma into granule interior. In particular, along with a reduced degree of crystallinity, molecular chain oxidation and degradation occurred, as confirmed by the generation of carboxyl groups and the molecular weight reduction. Then, the rheological behavior of starch paste changed from pseudo-plastic to non-Newtonian, together with a decreased paste viscosity. These results have demonstrated that dielectric barrier discharge plasma could be used as a new physical method to modulate the structure and rheological properties of starch, for the production of starchy food products with relatively low viscosity at a high concentration.