Lovedeep Kaur

Morphological, thermal and rheological properties of starches from different botanical sources

Corn, rice, wheat and potato are the main sources of starches which differ significantly in composition, morphology, thermal, rheological and retrogradation properties. Cereal starches contain a significant quantity of phospholipids, while potato starch is rich in esterified phosphorus. Potato starch exhibits higher swelling power, solubility, paste clarity and viscosity than wheat, rice or corn starches. Morphological characteristics, such as shape and size of the starch granules, exhibit significant differences. Potato starch granules are smooth–surfaced, oval and irregular or cuboidal-shaped while corn, rice and wheat starch granules are angular, pentagonal and angular; and spherical and lenticular–shaped, respectively. Corn, rice and wheat starch granules are less smooth–surfaced than potato starch granules. Potato starch granules are largest (<110 μm) in size followed by wheat (<30 μm), corn (<25 μm) and rice (<20μm) starches. Gelatinization temperatures (To, Tp, Tc) and enthalpies of gelatinization (ΔHgel) of starches from different sources also differ significantly. Corn and rice starches generally show higher transition temperatures than wheat and potato starches while the ΔHgel values are higher for potato and wheat starches. Potato starch shows a higher tendency towards retrogradation than the cereal starches. The rheological properties, such as storage modulus (G′) and loss modulus (G″) of the starches from the different sources increase to a maximum and then drop during heating of all the starches. Potato starch shows highest peak G′, G″ and lower tan δ than corn, rice and wheat starches during the heating cycle.

Some properties of potatoes and their starches. I. Cooking, textural and rheological properties of potatoes

Abstract Three different potato cultivars (Kufri Jyoti, Kufri Badshah and Pukhraj) were analyzed for cooking, sensory, textural and rheological properties. Potato cultivars (Kufri Jyoti and Kufri Badshah) with higher mealiness scores had lower cooking times and compression forces than cultivars with lower mealiness scores (Pukhraj). Kufri Jyoti and Kufri Badshah potatoes also showed higher total solids loss and water uptake values during cooking than Pukhraj potatoes. The cooked potatoes from different cultivars were also evaluated by stress relaxation test and texture profile analysis (TPA). The stress relaxation test for Kufri Jyoti and Kufri Badshah cooked potatoes yielded higher Maxwell elastic moduli (E0, E1 and E3) than Pukhraj cooked potatoes. The viscous moduli (η1,η2 and η3) were found to be significantly lower for Kufri Jyoti cooked potatoes than for Kufri Badshah and Pukhraj. TPA parameters, such as hardness, fracturability, cohesiveness and adhesiveness values, were higher for Kufri Jyoti and Kufri Badshah and were found to be related to elastic factors, such as E0, E1 and E3.

Actinidin Enhances Gastric Protein Digestion As Assessed Using an in Vitro Gastric Digestion Model

Consumption of kiwifruit has long been claimed anecdotally to assist in gastric digestion. This has generally been assumed to be due to the presence of the proteolytic enzyme actinidin; however, there is little published evidence supporting this assumption. This paper reports the findings of an in vitro study that examined the effect of kiwifruit proteases (actinidin) on the digestion of a range of common food proteins under simulated gastric conditions. An extract from green kiwifruit containing actinidin was prepared. Several protein sources derived from soy, meat, milk, and cereals were incubated in the presence or absence of the kiwifruit extract using an in vitro digestion system consisting of incubation with pepsin at pH 1.9, simulating gastric digestion in humans. The digests were subjected to gel electrophoresis (SDS-PAGE). For some protein sources, simulated digestion in the presence of kiwifruit extract resulted in a substantially greater loss of intact protein and different peptide patterns from those seen after digestion with pepsin alone. As an example, the addition of actinidin extract enhanced the digestion of alpha-, beta-, and kappa-caseins in sodium caseinate by 37, 33, and 48%, respectively. Under simulated gastric conditions, kiwifruit extract containing actinidin enhanced the digestion of some, but not all, food proteins over and above that found with pepsin alone.

Actinidin Enhances Protein Digestion in the Small Intestine As Assessed Using an in Vitro Digestion Model

This paper describes an in vitro study that tests the proposition that actinidin from green kiwifruit influences the digestion of proteins in the small intestine. Different food proteins, from sources including soy, meat, milk, and cereals, were incubated in the presence or absence of green kiwifruit extract (containing actinidin) using a two-stage in vitro digestion system consisting of an incubation with pepsin at stomach pH (simulating gastric digestion) and then with added pancreatin at small intestinal pH, simulating upper tract digestion in humans. The digests from the small intestinal stage (following the gastric digestion phase) were subjected to gel electrophoresis (SDS-PAGE) to assess loss of intact protein and development of large peptides during the in vitro simulated digestion. Kiwifruit extract influenced the digestion patterns of all of the proteins to various extents. For some proteins, actinidin had little impact on digestion. However, for other proteins, the presence of kiwifruit extract resulted in a substantially greater loss of intact protein and different peptide patterns from those seen after digestion with pepsin and pancreatin alone. In particular, enhanced digestion of whey protein isolate, zein, gluten, and gliadin was observed. In addition, reverse-phase HPLC (RP-HPLC) analysis showed that a 2.5 h incubation of sodium caseinate with kiwifruit extract alone resulted in approximately 45% loss of intact protein.

Potato Starch and Its Modification

Publisher Summary This chapter provides information on important physicochemical and functional characteristics of native potato starch in comparison with some cereal starches. It also discusses various modification techniques being used to modify potato starch, with an emphasis on the post-modification changes in its morphological, physico-chemical, rheological, and thermal behavior. The various factors that influence potato starch modification are also discussed. Progress in understanding the high value of chemically modified starches has encouraged the starch industry to produce modified starches using different modification reagents and starch sources. Some factors such as starch composition, concentration and type of reagent, and reaction conditions may affect the reactivity of starch during chemical modifications such as acetylation, hydroxypropylation, and cross-linking. The heterogeneity of the granule population within a single starch source may also affect the extent of modification. The changes observed in the morphological, physico-chemical, pasting/rheological, and gelatinization and retrogradation (thermal) properties of the starches after modification may provide a crucial basis for understanding the efficiency of the starch modification process at industrial scale.

Characterization of Gum Ghatti (Anogeissus latifolia): A Structural and Rheological Approach

Gatifolia, a commercial gum ghatti (Anogeissus latifolia) product was studied for its structural, thermal, and rheological characteristics. This study may prove helpful for the use of gum ghatti in a diverse range of food applications. The molecular weight (M(W)) and R(g) (radius of gyration) for gum ghatti were calculated to be approximately 8.94 x 10(7) g/mol and 140 nm, respectively, using high-performance size exclusion chromatography (HPSEC) system combined with multi-angle laser light scattering (MALLS). Gum ghatti solutions exhibited pseudoplastic behavior (as determined by flow experiments), which became more prevalent with increasing concentrations. Gum ghatti also displayed time-dependent shear-thickening behavior and showed negative hysteresis during up-down flow measurements. Under the measurement conditions at the range of frequencies and temperatures studied, the gum did not behave as a typical viscoelastic gel.

Impact of structural characteristics on starch digestibility of cooked rice.

To examine the impact of structural characteristics of cooked rice grains on their starch digestibility, a simulated in vitro gastro-small intestinal digestion technique was applied to intact and homogenised cooked rice samples. The starch hydrolysis percentage increased during simulated small intestinal digestion, in which approximately 65% and 24% of the starch was hydrolysed within the first 5min, for homogenised and intact cooked rice, respectively. The kinetic constant of homogenised cooked rice, which was regarded as an estimated digestion rate, was ∼8 times higher than the intact cooked rice. The homogenised and intact samples were also examined for any microstructural changes occurring during the in vitro digestion process using fluorescent and scanning electron microscopy. In the intact samples, the aleurone layers of the endosperm remained as thin-film like layers during in vitro digestion and thus may be regarded as less digestible materials that influence cooked rice digestibility.

Food microstructure and starch digestion.

Microstructural characteristics of starch-based natural foods such as parenchyma or cotyledon cell shape, cell size and composition, and cell wall composition play a key role in influencing the starch digestibility during gastrointestinal digestion. The stability of cell wall components and the arrangement of starch granules in the cells may affect the free access of amylolytic enzymes during digestion. Commonly used food processing techniques such as thermal processing, extrusion cooking, and post-cooking refrigerated storage alter the physical state of starch (gelatinization, retrogradation, etc.) and its digestibility. Rheological characteristics (viscosity) of food affect the water availability during starch hydrolysis and, consequently, the absorption of digested carbohydrates in the gastrointestinal tract. The nonstarch ingredients and other constituents present in food matrix, such as proteins and lipids interact with starch during processing, which leads to an alteration in the overall starch digestibility and physicochemical characteristics of digesta. Starch digestibility can be controlled by critically manipulating the food microstructure, processing techniques, and food composition.

Starch – A Potential Biomaterial for Biomedical Applications

The unique physicochemical and functional characteristics of starches isolated from different botanical sources such as corn, potato, rice and wheat make them useful for a wide variety of biomedical and pharmaceutical applications. Starch properties such as swelling power, solubility, gelatinization, rheological characteristics, mechanical behaviour and enzymatic digestibility are of utmost importance while selecting starch source for distinctive applications such as bone fixation and replacement. Starches can also be used as carriers for the controlled release of drugs and other bioactive agents. The chemically modified starches with more reactive sites to carry biologically active compounds are useful biocompatible carriers, which can easily be metabolized in the human body. This chapter reviews the physico-chemical, morphological and thermal characteristics of different starches that may be of importance during their use in specific biomedical and pharmaceutical applications

Impact of the degree of cooking on starch digestibility of rice - An in vitro study.

The impact of cooking degree on the starch digestibility of a non-waxy, cooked rice was examined through a simulated gastro-small intestinal in vitro digestion model. The starch hydrolysis of both non-homogenised and homogenised cooked rice samples during simulated digestion was also compared in order to examine the impact of grain structure on starch digestibility. Polished rice grains were cooked in boiling water for 10min (partially cooked) and 20min (fully cooked) to obtain samples of different cooking degree. No significant differences in the equilibrium starch hydrolysis (%) were observed among the partially and fully cooked grains, although significant differences were observed among the uncooked and cooked samples. The equilibrium starch hydrolysis (%) of homogenised rice was higher than its non-homogenised counterpart. These results showed that rice starch digestibility should not be affected by the cooking degrees related to starch gelatinisation, but was influenced by the modification/destruction of the grain structure during mechanical processing.