Determining the effects of annealing time on the glass transition temperature of Pueraria lobata (Willd.) Ohwi starch

To probe the effects of annealing time on the glass transition temperature (T_g) and digestibility of Pueraria lobata (Willd.) Ohwi starch, the starch crystal structure and moisture distribution through the components of P. lobata (Willd.) Ohwi starch were investigated. Annealing times of 0, 1, 3, 6, 12 and 24 h were employed to determine the effect of starch T_g using differential scanning calorimetry (DSC) with the support of ¹H low‐field NMR, polarised light microscopy and ¹³C CP/MAS NMR. The T_g values of the starch increased with longer annealing times. The ¹H low‐field NMR results showed that the T₂ relaxation time decreased and starch–water interactions increased as the annealing time increased. Compared with native starch, annealed starch had higher contents of slowly digested starch (SDS) and resistant starch (RS). The starch crystal structure was not destroyed after annealing, but the relative crystallinity percentage increased slightly.     

The impact of desmin on texture and water‐holding capacity of ice‐stored grass carp (Ctenopharyngodon idella) fillet

The objective of this work was to analyse the role of desmin in texture softening and water‐holding capacity (WHC) of ice‐stored grass carp fillet. Results indicated that shear force of the fillet decreased sharply within 3 days, while drip loss increased during the whole ice storage. Water mobility and distribution were measured by low‐field ¹H NMR T₂ relaxation that revealed a positive correlation (P < 0.01) between WHC and the mobility of the immobilised water (T₂₁ relaxation time). Meanwhile, negative correlation could be established between intact desmin and drip loss (P < 0.01). Intact desmin was extremely correlated with shear force (P < 0.01) and positively correlated with calpains activity (P < 0.05). This study demonstrated that the degradation of desmin was involved in the mobility of the myofibrillar water and softening of grass carp fillet during ice storage. Furthermore, calpains autolysis seemed to result in desmin degradation.     

Mobility and Stability Characterization of Model Food Systems Using NMR, DSC, and Conidia Germination Techniques

Mold conidia germination was used as a microbial probe of food stability in sucrose, starch, and sucrose/starch systems. A group of nuclear magnetic resonance (NMR) and differential scanning calorimeter (DSC) techniques were used to fully characterize the water and solid mobility and glass transition temperature (Tg) of the systems, respectively. Water content, a_w, and ²H NMR R₁ and R₂ relaxation rates did not predict mold germination time. We concluded that the self-diffusion coefficient, (translational mobility of water), the DSC Tg (overall system mobility), and to a more limited extent, the ²H NMR R*₂ relaxation rate and the ¹³C T_1p (solids mobility), could provide alternative measures to supplement a_w for predicting food stability and safety.     

Effect of formulation on physicochemical properties and water status of nutritionally enhanced tortillas

BACKGROUND: Various nutritionally enhanced tortillas were developed by incorporating ingredients with nutritional functionality (carrot, soy, wholemeal kamut and their combination (CSK)) in a standard wheat tortilla formulation. The effect of these ingredients on the physicochemical properties and water status of the products was evaluated. RESULTS: Partial substitution of carrot juice for water in the tortilla formulation significantly reduced the macroscopic (water activity and moisture content) and thermal (‘frozen’ water (FW) content) properties and marginally reduced the ¹H molecular mobility (faster ¹H free induction decay (FID)) compared with the standard. Wholemeal kamut increased the FW content via a possible water redistribution among ingredients. Whole soy flour induced higher ¹H molecular mobility (T_2B relaxation rate, % ¹H T_2B population and single T₁), probably because a loose soy protein—water interaction and/or margarine. The water status of the CSK tortilla reflected the contribution of each ingredient in the respective prototype: fast ¹H FID (carrot), high FW content (kamut), high ¹H molecular mobility and low moisture content and water activity (soy). CONCLUSIONS: The changes in formulation used in this study to produce tortillas with enhanced nutritional value affected the water status of the products in a very interesting manner: the different ingredients altered the water status at different levels. Copyright © 2008 Society of Chemical Industry     

1H NMR studies of molecular mobility in wheat starch

Pulsed ¹H NMR was used to determine moisture content and molecular mobility of wheat starch suspensions at water activity (a_w) values between 0 and 0.93. Moisture determination by NMR agreed well with gravimetric determinations (R²=0.99). Transverse proton relaxation (T₂) of the systems were identified using single pulse and CPMG experiments. T₂ associated with starch molecules increased linearly from 7.1 to 10.1 μs as a_w increased from 0 to 0.93, due to plasticizing effects of water. T₂ associated with water molecules showed a linear increase up to a_w of 0.69. Results indicated that ¹H NMR could be employed to determine moisture content of starch suspension and to identify and quantify the molecular motion of starch chains and water molecules of starch suspensions at low moisture levels.     

Phytochemical stability in dried apple and green tea functional products as related to moisture properties

In this study, apple products made with and without added green tea extract were freeze-dried and stored for up to 45 days at 30 °C in low and intermediate moisture environments (water activity, a_w, 0.11, 0.22, 0.32, 0.57, and 0.75). Kinetic models were developed for the changes in color and decreases in contents of selected green tea and apple monomeric and polymeric flavanols and ascorbic acid. Moisture isotherms were developed for each product. At various moisture levels, the glass transition temperature (T_g) was measured by DSC and water mobility by ¹H NMR. Chemical changes were related to T_g, a_w, and water mobility in the products.Phytochemical degradation occurred more rapidly at higher moisture contents, except for caffeine which was stable. In the product containing apple with green tea, the content of monomeric flavan-3-ols decreased by 34% and 39% after 45 days of storage at a_w of 0.56 and 0.75, respectively. Phytochemical degradation correlated with increasing a_w, T_g, and water mobility. This study showed that, in general, storage at a_w 0.75 most affected phytochemical stability and color.     

Behaviour of water in different types of goats' cheese

Semi-hard, hard, and extra-hard goats' cheeses were analysed for water mobility by nuclear magnetic resonance relaxometry (NMR) and thermal properties by differential scanning calorimetry (DSC). In extra-hard cheese, the amount of bulk water as a proportion of the total water was the lowest, which indicated that the water was strongly entrapped in the proteolipidic network and bound by the water-soluble substances arising after increased proteolysis. The bulk water fraction is mainly a component of water-in-fat emulsions. The increase in H⁺ ion concentration limits the mobility of bound water protons. Both the peak temperature and enthalpy progressively decreased with the lowering of moisture. A strong correlation was found between the NMR parameter T₁ (spin–lattice relaxation time) and the DSC freezable water content.     

Water dynamics in white bread and starch gels as affected by water and gluten content

Three levels of water (180, 220 and 260 g/345 g flour) and three levels of gluten (giving 11.2, 13.0 and 14.2 g protein/100 g flour) were used to study the effects of water and gluten on water mobility in white bread using ¹H nuclear magnetic resonance (NMR) relaxometry. Changes in the transverse relaxation time (T₂) were related to water mobility. The three water levels resulted in three different moisture contents in the finished bread (0.55-0.77 g H₂O/g solids). Distributed exponential analysis showed two distinct regions of T₂ (30-600 μs and 1-60 ms), associated with multiple domains of water in the bread crumb. There was no significant difference in peak T₂ values with different gluten content, but significant differences were observed with different moisture content. The results suggested that the mobility of water associated with starch decreased dramatically because of gelatinization. To further investigate the effect of gluten on starch gelatinization, NMR measurements were made directly on model systems containing starch and various gluten amounts. The starch-gluten gels had higher T₂ values than pure starch gels, indicating less swelling of starch granules and absorption of water. This was attributed to less water available to starch in the presence of gluten.     

Structural Transformation of Sago Starch by Heat‐Moisture and Osmotic‐Pressure Treatment

Sago starch was modified by osmotic‐pressure treatment (OPT) and heat‐moisture treatment (HMT) and physicochemical characteristics were compared. In OPT, sago starch was suspended in saturated sodium sulfate solution and heated for 1 h at 100, 110 and 120°C, corresponding to a calculated osmotic pressure of 32,728, 33,640 and 34,552 kPa (assuming sodium sulfate dissociates completely), respectively, and in HMT, sago starch with 20% moisture content was used. Change of X‐ray diffraction pattern from C‐type to A‐type was obtained for OPT and HMT starch at 110°C and 120 °C, respectively. RVA viscograms of both OPT and HMT starch exhibited a decrease of peak and breakdown viscosity but increase of final viscosity and pasting temperature. Onset (T_o), peak (T_p), and conclusion temperature (T_c) of gelatinization of both OPT and HMT starch increased significantly with increase of treatment temperature. Biphasic broadening of T_p was observed for HMT starch indicating an inhomogeneous heat transfer during HMT. The observed narrow peaks of DSC curves indicated better homogeneity of OPT. These properties suggest that OPT starch is more suitable for large‐scale production.     

Preparation,characterization, and water resistance of cationic acetylated starch‐g‐poly(styrene‐butyl acrylate) surfactant‐free emulsion

Cationic acetylated starch‐g‐poly(styrene‐butyl acrylate) surfactant‐free emulsion (CAS‐g‐poly(St‐BA)) was synthesized by graft copolymerization of styrene (St) and butyl acrylate (BA) onto CAS using FeSO₄–H₂O₂ redox initiator. The maximum graft of 55.68% was derived when H₂O₂ concentration, monomer concentration, and St/BA ratio were 9%, 130%, and 1:1, respectively. The results obtained from FTIR, NMR (H¹ NMR and C¹³ NMR), XRD, SEM, and thermogravimetric analysis (TGA‐DTG) confirmed graft copolymerization of St and BA onto CAS. And it was demonstrated that film‐forming properties of starch were greatly improved via grafting St and BA onto starch. It was also found that paper sized with CAS‐g‐poly(St‐BA) exhibited higher ring crush index and bursting strength than paper sized with cationic potato starch (CS) and CAS, as well as much lower water absorption, which is further verified by contact angles results.     

Effect of Heat‐Moisture Treatment on Structural and Thermal Properties of Rice Starches Differing in Amylose Content

Starches from glutinous rice (1.4% amylose), Jasmine rice (15.0% amylose) and Chiang rice (20.2% amylose) were exposed to heat‐moisture treatment (HMT) at 100 °C for 16 h and at different moisture levels (18, 21, 24 and 27%). The effect of heat‐moisture treatment on structural and thermal properties of these three rice starches was investigated. The HMT did not change the size, shape and surface characteristics of rice starch granules. The A‐type crystalline pattern of rice starches remained unchanged after HMT. The relative crystallinity (RC) and the ratio of short‐range molecular order to amorphous (RSA) of heat‐moisture treated glutinous and Jasmine rice starches decreased with increasing moisture level of the treatments. In contrast, the RC of the treated Chiang rice starch remained practically unchanged. A peak of crystalline V‐amylose‐lipid complexes was clearly presented in all treated Chiang rice starches. The peak became progressively stronger with increasing moisture level of the treatment. Differential scanning calorimetry (DSC) of all treated rice starches showed a shift of the gelatinization temperature to higher values. Increasing moisture level of the treatments increased the onset gelatinization temperature (T_o) but decreased the gelatinization enthalpy (ΔH) of rice starches. A broad gelatinization temperature range (T_c‐T_o) with a biphasic endotherm was found for all treated Chiang rice starches and Jasmine rice starch after HMT₂₇ (HMT at 27% moisture level). Additionally the (T_c‐T_o) of treated Chiang rice starches increased linearly with increasing moisture level of the treatments.     

Original article: Characterisation of water species revealed in the drying operation of Todarodes pacificus Steenstrup using water proton NMR analysis

For the discrimination of water molecules during the squid‐drying process, the water distribution was characterised by water proton NMR and moisture diffusivity (De) analysis methods as a function of the water content (W₀). The proton NMR spectrum showed three peaks indicating three different species (species‐A, ‐B, and ‐C) distributed in the squid muscle, each of which had a characteristic behaviour of the relaxation time (T₂) as a function of the W₀. The 1/T₂ of species‐A was drastically varied at W₀ = 120%‐d.b., indicating two further categories, i.e., species‐A₁ and ‐A₂. Species‐A₁ is available at W₀ > 120%‐d.b. and was characterised as having De = 5.1 × 10^?10 m² s^?1, activation energy of moisture diffusivity (E_D) = 17 kJ mol^?1, and relaxation rate 1/T₂ = 74 s^?1, as evaluated by the proton NMR spectrum without depending on W₀. Species‐A₂ is available at W₀ < 120%‐d.b., indicating a distribution of De = 4.8 × 10^?10–1.7 × 10^?10 m² s^?1, E_D = 25–35 kJ mol^?1 and 1/T₂ = 1.8 × 10³–1.5 × 10² s^?1 with increasing W₀. Species‐A₁ and ‐A₂ were assigned as weakly restricted water and strongly restricted water, respectively.     

Characteristics and oil absorption in deep‐fat fried batter prepared from ball‐milled wheat flour

BACKGROUND: The porous structure generated during frying influences oil absorption and textural qualities. The alteration in physical properties of wheat flour is suspected to affect the structure formation. The present study investigated the effect of physicochemical changes in wheat flour by the ball‐milling process on structure formation and consequently oil absorption of a fried wheat flour batter model. RESULTS: Batter models containing 600 g kg^?1 moisture were made of 0–10 h ball‐milled wheat flour and then fried in frying oil at 150 °C for 1–7 min. The samples made of milled flour possess larger pores and exhibit lower oil absorption than sample made of 0 h milled flour. The fracture force of a fried sample prepared from 5 and 10 h milled flour is lower than that of a sample prepared from 0 h milled flour. CONCLUSION: The decrease in glass transition temperature (T_g) and melting temperature (T_m) of milled flour affect the microstructure formation in the fried wheat flour batter. The microstructure is responsible for oil absorption and fracturability in fried food. The samples made of flour of longer ball‐milling time have lower oil absorption and higher crispness. Ball‐milling may be a tool to produce mechanically modified wheat flour which can reduce oil absorption for fried batter. Copyright © 2009 Society of Chemical Industry     

The antioxidant activity and transcellular pathway of Asp‐Leu‐Glu‐Glu in a Caco‑2 cell monolayer

Asp‐Leu‐Glu‐Glu (DLEE) is one of the antioxidant peptides purified from Chinese dry‐cured Xuanwei ham in our previous study. In the current work, the stability in a simulated digestion system, the transportation pathway and the antioxidant ability of DLEE were further investigated in a Caco‐2 cell monolayer. In the simulated gastrointestinal digestion system, no oligopeptides were generated. In the transport trial, the inhibitors cytochalasin D increased the transport of DLEE across the Caco‐2 cell monolayer, with P_app values of 3.22 × 10^?6 cm s^?1. A decreased expression occludin was observed with the DLEE incubation in the cell monolayer, and the antioxidant activity showed to be increased gradually in basolateral side. This study indicates that the absorption of DLEE could mainly occur via paracellular transport and provides information about its antioxidant activity after being absorbed across a cell monolayer.     

Water dynamics of turbot flesh during frying,boiling, and stewing processes and its relationship with color and texture properties: Low‐field NMR and MRI studies

Water dynamics in turbot flesh during frying, boiling and stewing was assessed by nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) techniques. Protons associated with different types of water were distinguished by T₂ relaxation spectra, and significant differences of water mobility were detected. Principle component analysis revealed a clear discrimination between samples of different cooking methods. MRI provided further visualization of internal information for turbot flesh during cooking. The linear regression analysis demonstrated a strong correlation between the NMR parameter A₂₃ and b* value (R² = .972) during frying process, A₂₃ and L* (R² = .963), T₂₂ and b* (R² = .991) during boiling process, T₂₂ and b* (R² = .883) during stewing process. Moreover, a good correlation was found between A₂₁ and cohesiveness (R² = .924) during the frying process, A₂₃ and resilience (R² = .879) during boiling process, as well as between A₂₃ and chewiness (R² = .946) during stewing process.

Practical applications

Water mobility and distribution can significantly affect turbot flesh physical and biochemical status leading to change the texture, color, tenderness and taste during cooking process. Therefore, it is very important to develop a fast, nondestructive method to monitor the water dynamics, reduce the cooking time, save energy and visualize the structure change of turbot flesh during cooking. In this study, a rapid and nondestructive NMR and MRI method were developed to analyze the water dynamics of turbot flesh during frying, boiling and stewing for the first time. The water states, distribution and mobility were analyzed by the NMR and MRI. Different cooking methods displayed different water dynamics in turbot flesh, which could be identified when NMR combined with chemometrics principal component analysis. The facile method by using both NMR and MRI for analysis of turbot flesh may have great potential for rapid and nondestructive analysis of other food processing.     

Physico‐chemical Characterization of Floridean Starch of Red Algae

The current work reports on isolation and physico‐chemical characterization of floridean starch from three species of agarophytic macro red algae. As determined by ¹H‐NMR spectroscopy, the average chain length and degree of branching frequency of this starch were 18 and 4.8, respectively. According to its amylopectin chain length distribution obtained by Dionex analysis, the crystalline polymorph of floridean starch from the red alga Gracilariopsis lemaneiformis was deduced to be C‐type and this was further supported from its X‐ray crystallographic pattern. Enzymatic analysis of its glucose 6‐phosphate content showed that floridean starch had a low level of covalently linked phosphate (1 nmol per milligram starch) and this was further confirmed by ³¹P‐NMR. The absorbance peak of floridean starch with iodine occurred at 527—530 nm and the blue value was low (0.1), indicating the absence of amylose, which was confirmed by differential scanning calorimetry (DSC). Floridean starch exhibited low gelatinization temperature, low viscosity, high clarity and little or no retrogradation upon repetitive freeze‐thaw cycles, as studied by DSC and rapid viscosity analysis (RVA). These results are discussed in light of the functional properties and the structure of floridean starch.     

Rehydration of Freeze‐Dried and Convective Dried Boletus edulis Mushrooms: Effect on Some Quality Parameters

ABSTRACT: Quality of rehydrated products is a key aspect linked to rehydration conditions. To assess the effect of rehydration temperature on some quality parameters, experiments at 20 and 70 °C were performed with convective dried and freeze‐dried Boletus edulis mushrooms. Rehydration characteristics (through Peleg's parameter, k₁, and equilibrium moisture, W_e), texture (Kramer), and microstructure (Cryo‐Scanning Electron Microscopy) were evaluated. Freeze‐dried samples absorbed water more quickly and attained higher W_e values than convective dried ones. Convective dehydrated samples rehydrated at 20 °C showed significantly lower textural values (11.9 ± 3.3 N/g) than those rehydrated at 70 °C (15.7 ± 1.2 N/g). For the freeze‐dried Boletus edulis, the textural values also exhibited significant differences, being 8.2 ± 1.3 and 10.5 ± 2.3 N/g for 20 and 70 °C, respectively. Freeze‐dried samples showed a porous structure that allows rehydration to take place mainly at the extracellular level. This explains the fact that, regardless of temperature, freeze‐dried mushrooms absorbed water more quickly and reached higher W_e values than convective dried ones. Whatever the dehydration technique used, rehydration at 70 °C produced a structural damage that hindered water absorption; consequently lower W_e values and higher textural values were attained than when rehydrating at 20 °C.     

Water distribution and mobility in herring muscle in relation to lipid content,season, fishing ground and biological parameters

Low‐field ¹H nuclear magnetic resonance transverse relaxation profiles were measured on muscle samples from herring differing in catch season (summer or winter), fishing ground (Baltic Sea, North Sea, Skagerrak or Kattegat), biological parameters (maturity status, sex and spawning type), lipid and water content, and catching vessel (the institute's research vessel Dana or commercial fishing vessels). Water mobility and distribution in herring muscle samples were calculated from the NMR signals by the use of multi‐way analysis. The distribution and mobility of water in samples from herring caught by Dana differed according to season, samples from summer herring having two water pools (with T₂‐values of 37 and 75 ms) and samples from winter herring having three water pools (with T₂‐values of 41, 58 and 102 ms). This difference in number of water pools was also found in samples from herring caught by commercial vessels. It is suggested that samples from herring caught during winter contain an extra pool of inter‐myofibrillar water not present in the samples from herring caught during the summer due to their higher lipid content. The water and lipid content significantly affected the water distribution in both summer and winter herring. The differences in water pools were also reflected in the sensory quality of a marinated herring product. The leaner winter herring corresponding to samples with three water pools were more firm and had less fatty mouth feel than the more fatty summer herring, corresponding to samples with only two water pools. Copyright © 2005 Society of Chemical Industry     

Water Binding of Wheat Flour Doughs and Breads as Studied by Deuteron Relaxation

Water mobility in wheat flour doughs and breads was investigated by deuteron relaxation using pulsed NMR. Water was replaced by deuterium oxide in dough and bread at different concentrations. Mixograms indicated that wheat flour associated more strongly with D₂O than it did with H₂O. Varying the D₂O:H₂O ratio of flour doughs had no effect on the longitudinal (T₁) or transverse (T₂) relaxation times of deuteron. Hard wheat and soft wheat flour doughs showed similar increases in T₁ and T₂ with increasing moisture content. Staling of bread crumb was accompanied by decreased T₁ and T₂, indicating an overall decrease in water mobility and increase in water binding. The decrease in water mobility of bread crumb with storage time was shown to be independent of reduction in moisture content.     

Low‐field NMR: A tool for studying protein aggregation

Low‐field nuclear magnetic resonance (NMR) spin–spin relaxation (T₂) measurements were used to study the denaturation and aggregation of β‐lactoglobulin (β‐LG) solutions of varying concentrations (1–80 g L^?1) as they were heated at temperatures ranging from ambient up to 90 °C. For concentrations of 1–10 g L^?1, the T₂ of β‐LG solutions did not change, even after heating to 90 °C. A decrease in T₂ was only observed when solutions having higher concentrations (20–80 g L^?1) were heated. Circular dichroism (CD) spectroscopy and fluorescence tests using the dye 1‐anilino‐8‐naphthalene sulfonate (ANS) on 0.2 and 1 g L^?1 solutions, respectively, indicated there were changes in the protein's secondary and tertiary conformations when the β‐LG solutions reached 70 °C and above. In addition, dynamic light scattering (DLS) showed that protein aggregation occurred only at concentrations above 10 g L^?1 and for heating at 70 °C and above. The hydrodynamic radius increased as T₂ decreased. When excess 2‐mercaptoethanol was added, the changes in both T₂ and the hydrodynamic radius followed the same trend for all β‐LG protein concentrations between 1 and 40 g L^?1. These observations led to the conclusion that the changes in T₂ were due to protein aggregation, not protein unfolding. Copyright © 2007 Society of Chemical Industry