Water, the most abundant constituent of natural foods, is a ubiquitous plasticizer of most natural and fabricated food ingredients and products. Many of the new concepts and developments in modern food science and technology revolve around the role of water, and its manipulation, in food manufacturing, processing, and preservation. This article reviews the effects of water, as a near-universal solvent and plasticizer, on the behavior of polymeric (as well as oligomeric and monomeric) food materials and systems, with emphasis on the impact of water content (in terms of increasing system mobility and eventual water "availability") on food quality, safety, stability, and technological performance. This review describes a new perspective on moisture management, an old and established discipline now evolving to a theoretical basis of fundamental structure-property principles from the field of synthetic polymer science, including the innovative concepts of "water dynamics" and "glass dynamics". These integrated concepts focus on the non-equilibrium nature of all "real world" food products and processes, and stress the importance to successful moisture management of the maintenance of food systems in kinetically metastable, dynamically constrained glassy states rather than equilibrium thermodynamic phases. The understanding derived from this "food polymer science" approach to water relationships in foods has led to new insights and advances beyond the limited applicability of traditional concepts involving water activity. This article is neither a conventional nor comprehensive review of water activity, but rather a critical overview that presents and discusses current, usable information on moisture management theory, research, and practice applicable to food systems covering the broadest ranges of moisture content and processing/storage temperature conditions.

Beyond water activity: recent advances based on an alternative approach to the assessment of food quality and safety

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.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/1541-4337.12143

Starch retrogradation: a comprehensive review

Methods for the study of starch retrogradation

The double-helical nature of the crystalline part of A-starch.

Descriptions of the functional significance of carbohydrates based on the familiar equilibrium thermodynamics of very dilute solutions fail for pragmatical time scales and conditions, which are far from equilibrium. This is not too surprising, since limiting partial-molar properties reflect the independent behavior of solute in the limit of infinite dilution where free volume is maximum at a given temperature, while Tg′-Wg′ properties reflect the cooperative behavior of solute-plasticizer blends at the limiting minimum value of free volume to observe relaxation within experimental time scales. Carbohydrate-water systems, with well-characterized structure and MW above and below the entanglement limit, provide a unique framework for the investigation of non-equilibrium behavior. Thermal analysis by DSC reveals the central role of water as a plasticizer for carbohydrates and of the glass transition as a physicochemical parameter that governs their properties, processing, and stability. A classical polymer science approach is used to study structure-property relationships of carbohydrates as water-compatible food polymers, which are treated as homologous systems of polymers, oligomers, and monomers with their plasticizers and solvents. Mechanical relaxation behavior is described by a “transformation map” of the critical variables of moisture content, temperature, and time. The glass curve is a reference contour, which represents the limiting isogram for free volume, local viscosity, relaxation rates, and rotational and translational mobility. Map domains are discussed as aspects of “water dynamics,” to dispel the myth of “bound water,” and “glass dynamics,” to relate to macroscopic structure and collapse phenomena. A particular glass with invariant composition and Tg (prepared by freeze-concentration) is identified as a pivotal and practical reference state. The Tg observed during DSC analysis is often an effective Tg, resulting from instantaneous relative relaxation rates and non-uniform distribution of total sample moisture. Non-equilibrium melting, annealing, and gelation/recrystallization of kinetically metastable, partially crystalline carbohydrate systems exhibit non-Arrhenius kinetics which depend on the magnitude of ΔT above the appropriate Tg, as defined by WLF relaxation transformations. Thermally reversible aqueous gels (crystallized from an under-cooled, rubbery melt) are described by a “fringed micelle” structural model for a three-dimensional polymer network, composed of microcrystalline junction zones crosslinking plasticized amorphous regions of flexible-coiled, entangled chain segments.

A food polymer science approach to structure-property relationships in aqueous food systems: non-equilibrium behavior of carbohydrate-water systems.

A sensitive method to determine the change of degree of gelatinization during storage of starch products was studied. A new enzyme system consisting of beta-amylase-pullulanase was established for this purpose and named as BAP method. Beta-amylase is known not to react on raw starch and pullulanase is also known to be strongly affected by the degree of dispersion of amylopectin molecule in a solution. The new enzyme system clearly differentiates the velocity of hydrolysis between gelatinized starch and retrograded one compared with the conventional glucoamylase system. This enzyme system is particularly useful to determine the retrogradation of starchy food during storage.

New Enzyme System-Beta-Amylase-Pullulanase-To Determine the Degree of Gelatinization and Retrogradation of Starch or Starch Products

To determine the structure of retrograded starch, 10% solutions of normal-and waxy corn starches were treated by repeated freeze-thaw cycles to obtain extremely retrograded starch samples . These starch samples were examined for the determination of the degree of gelatinization, iodine binding, acid and enzyme hydrolysis etc. The residual carbohydrates after acid and enzyme treatment were completely different from each other in molecular weight and shape, determined by the gel filtration of Toyopearl HW-50. We proposed three different domains (A, B and C) existing in retrograded starch, which are schematically illustrated in the text .

Structural Studies on Retrograded Normal and Waxy Corn Starches

Studies on the Retrogradation of Starchy Foods (Part 1)

デンプンの糊化による構造変化および糊化度の近赤外法による計測について検討を行い,以下の結果を得た.(1) 糊化度の異なるデンプンの近赤外吸収スペクトルを調べたところ, 1204, 1368, 1436, 170O, 1748, 1784,1924, 2088, 2280, 2320および2348nm近傍の吸収度の変動(分散)が大きかった.特に, 2088および2280nm近傍のスペクトルは,糊化の進行に伴い複雑な変動を示した.(2) BAP法の糊化度またはデンプンの粒度をそれぞれ目的変数とし,吸光度の2次微分値を説明変数とする回帰分析を行ったところ,ともに1807および2095nmで高い相関が得られた.(3) デンプンの吸収帯が存在しないことから, 1807nmにおける高い相関は,その原因の1つとして粒度などの物理的な要因に基づくものと考えられた.(4) 糊化度と粒度の間には,高い正の相関(r=0.96)が認められた.糊化度が進むにつれて,デンプンの粒子が大きくなるものと考えられた.(5) 2100nm近傍のスペクトルデータは,粒度などの情報とデンプンの構造変化の情報が重なっていることから,主成分分析により,情報の分離を行ったところ,得られた第2主成分スコアと糊化度との間に高い直線性(r=0.98)が認められた.以上のことから,近赤外法によりデンプンの糊化度を計測できることが明らかとなった.

Analysis of Geiasinization of Starch by Near Infrared Spectroscopy

(1) 加熱経歴の異なる炊飯過程の糊化度を追跡することにより炊飯のよい条件を検討した。(2) 急速加熱は緩慢加熱に比べ昇温中の糊化度の進行はおくれるが,仕上がり飯では差はない。(3) モデル実験による米粒の糊化度の限界は,60℃・10時間で18%, 70℃・5時間で80%, 80℃・5時間で94%, 90℃・2時間で98%, 100℃・1時間で98%となった。(4) 60℃で20分保ち米に十分に吸水させたのち,急速に加熱する二段昇温加熱による炊飯の結果は,糊化度の向上と官能検査によるよい食味の結果を得た。

Akiko Matsunaga

Papers

New Enzyme System-Beta-Amylase-Pullulanase-To Determine the Degree of Gelatinization and Retrogradation of Starch or Starch Products

Structural Studies on Retrograded Normal and Waxy Corn Starches

Studies on the Retrogradation of Starchy Foods (Part 1)

Analysis of Geiasinization of Starch by Near Infrared Spectroscopy

Degree of Gelatinization of Starch during the Cooking Process of Rice