Postharvest decay control and quality retention in litchi (cv. McLean's Red) by combined application of modified atmosphere packaging and antimicrobial agents

The effects of modified atmosphere packaging (MAP) [bioriented polypropylene (BOPP-1 or BOPP-2)] in combination with antimicrobial agents Bacillus subtilis, 10⁷ colony-forming units (cfu) ml⁻¹; ethylenediamine tetraacetic acid, calcium disodium salt hydrate (EDTA) (0.1%); or 4-hexylresorcinol (4-HR) (0.15%) on postharvest decay control and quality retention of litchi cv. McLean's Red were assessed as possible replacements for commercial SO₂ fumigation. Fruits dipped in B. subtilis, EDTA or 4-HR (5 min) separately, blow dried (25 °C, 3 min), packed in BOPP-1, held for 18 d at 2 °C, 95% RH, and 2 d at 14 °C, 75% RH were significantly less decayed. The antagonist–BOPP-1 combination also promoted the best bacterial survival during storage. B. subtilis was observed to survive effectively in BOPP-1 (16% O₂, 6% CO₂; 90% RH), but its survival was adversely affected in BOPP-2 (5% O₂, 8% CO₂; 93% RH). Alternaria alternata and Cladosporium spp. were the major decay-causing fungi in BOPP-1 treatments, and Candida, Cryptococcus and Zygosaccharomyces were the predominant yeasts in BOPP-2 treatments. Combination treatments EDTA, 4-HR or B. subtilis in BOPP-1 inhibited polyphenol oxidase (PPO) and significantly reduced pericarp browning and severity. Although the combination treatments EDTA, 4-HR or B. subtilis in BOPP were equally effective in controlling decay and browning, the EDTA and 4-HR affected the natural pinkish-red colour of the pericarp by showing higher h° values (orange–pink). Among the combination treatments, B. subtilis+BOPP-1 had the best potential to control decay, retain the colour and the overall litchi fruit quality during a marketing chain of 20 d.     

Eradication of Clavibacter michiganensis subsp. michiganensis by incorporating fresh crop debris into soil: Preliminary evaluations under controlled conditions

A method for the eradication of Clavibacter michiganensis subsp. michiganensis was tested for its efficacy in three experiments carried out in the laboratory and greenhouse. In the first experiment, peat moss and sand mix in pots was amended with fresh tomato debris which was either artificially infected with the pathogen, or was not amended. Pots were enclosed in plastic bags or left open. Two temperatures (25 °C and 45 °C) were tested over a 6-week period. The pathogen was not detected in the amended soil after 4 weeks treatment at 45 °C, but was not eradicated after treatments in open pots at 25 °C.In the second experiment, the survival of C.m. michiganensis in either artificially infested soil or in artificially infected tomato plants was studied to determine the behaviour of the pathogen under these conditions. Strains of saprophytic bacteria in the genera Bacillus, Paenibacillus and Brevibacillus were identified under the experimental conditions. In vitro antagonism between Bacillus subtilis and C.m. michiganensis was observed. Finally, the recovery of C.m. michiganensis introduced into disinfected substrate was determined. Survival of C.m. michiganensis in plates artificially inoculated with substrate was greatly reduced after a 4-week treatment at 25 °C, or after 1 week at 45 °C.C.m. michiganensis remained pathogenic on plant tissue after 4 weeks of either thermal treatment.It is important to take these results into account with regard the effect of different soil disinfection techniques or ecological alternatives such as biofumigation, solarization, and the addition of organic matter, as well as for integrated pest management systems.     

Dynamic viscoelastic, calorimetric and dielectric characteristics of wheat protein isolates

Dynamic oscillatory rheology of two wheat protein isolate (Prolite 100 and Prolite 200) doughs (≈48% moisture content, wet basis) were studied over a frequency range of 0.1–10 Hz during temperature sweep from 20 to 90 °C at a heating rate of 2 °C/min. Both doughs behaved similarly during heating; showed a threshold value and increased sharply, thereafter. Prolite 200 dough had a higher elastic modulus (G′) and lower phase angle (δ) whereas Prolite 100 showed a distinct gel point at 52.2 °C followed by significant increase up to 90 °C. Rheological data of doughs after isothermal heating at 90 °C for 15 min followed by cooling to 20 °C resulted in strong mechanical strength. However, Prolite 100 dough showed more viscoelastic characteristics with significant transformation from liquid-like to solid-like behavior after heating than Prolite 200. Thermal analysis of isolates indicated distinct endothermic peaks in wider temperature range (50–130 °C) at various moisture levels. Lower temperatures could be associated with denaturation of various fractions of proteins whereas higher temperature linked to glass transition temperature of isolates. SDS–PAGE did not show any clear distinction among protein subunits between two isolates. Dielectric measurements of isolates at frequencies from 500 to 3000 MHz and temperature range between 30 and 80 °C indicated Prolite 200 had higher dielectric constant (ε′) and loss factor (ε″) than Prolite 100. Isolates showed significant changes in dielectric properties above 50 °C indicating protein denaturation and supported rheological and calorimetric data.     

Comparison of two seed oils used in cosmetics, moringa and marula

Comparison of the seed oil of Moringa pterygosperma (moringa) and Sclerocarya birrea (marula) showed a marked difference in fatty acid composition and oxidative stability. Moringa, with 1000 ppm tocopherols, had an oil stability index (OSI) of 133 h at 110 °C while marula with 1000 ppm tocopherols yielded 37 h at 110 °C. This correlated well with the fatty acid composition of these two oils. Moringa had less than 1% polyunsaturates and marula had 6.7% of these oxidatively unstable materials. In addition, fatty acid compositions of seven species of moringa are presented. All of these species had levels of behenic acid ranging from 1 to 7% with oleic acid levels from 68 to 79%. The highest amount of polyunsatures was found in the moringa species was in Moringa drouhardii with 3.6%.     

Changes in wheat seed germination ability,soluble carbohydrate and antioxidant enzyme activities in the embryo during the desiccation phase of maturation

Soluble sugar contents and antioxidant enzyme activities were measured in the embryo of wheat (Triticum aestivum) seeds throughout the desiccation phase of maturation in 2003 and 2004 to investigate whether they were related to seed quality. Whatever the date of harvest after the end of filling, seeds tolerated artificial drying in the ears, and almost all of them germinated at 10 °C whereas they were dormant at 30 °C. Their sensitivity to 5 day accelerated ageing treatment (45 °C, 100% relative humidity) slightly decreased during desiccation. This phase of development was associated with an accumulation of sucrose and raffinose, and an increase in the raffinose/sucrose ratio in the embryo. Artificial drying in the ears resulted in an increase in both sugars, but especially raffinose, and in the maintenance of a high value (around 0.6–0.7) of the raffinose/sucrose ratio. Superoxide dismutase, catalase and glutathione reductase activities did not change markedly in the embryo after mass maturity. They were sufficiently active to maintain malondialdehyde and H₂O₂ contents at very low levels. No clear relationship existed between the antioxidant enzyme activities and seed quality, whereas seed tolerance to ageing seemed to be related to a high value of the raffinose/sucrose ratio.     

Direct lipase-catalyzed lipophilization of chlorogenic acid from coffee pulp in supercritical carbon dioxide

The direct esterification of chlorogenic acid (5-CGA) by immobilized Candida antarctica lipase B (Novozym 435) in supercritical CO₂/t-butanol has been studied. The Taguchi approach was applied to evaluate the effects of temperature (35–55 °C), pressure (150–250 bar), t-butanol (2–10%, v/v), and the enzyme amount (10–30 mg/ml), on the ester concentration and overall conversion. Optimum reaction conditions were established at: 150 bar, 55 °C, 10% t-butanol (v/v), 20 mg/ml of lipase. Addition of 20 mg/ml of molecular sieves (3 Å) was also necessary to minimize the inhibiting effect of the increasing water concentration. Maximum conversions reached 77, 82 and 85% in 25 h using geraniol, pentanol and heptanol as aliphatic chain donors, respectively. HPLC analysis demonstrated the selective esterification of 5-CGA from a coffee pulp aqueous-methanolic extract, which reached a conversion to heptyl ester of 65% at the optimal condition. The supercritical CO₂ selectivity towards the esterified product was the working principle of this study, by which minimized interphase transport limitations and enhanced mass-transfer phenomena substantially improved the reaction kinetics.     

Purification and Characterization of a Glutenin Hydrolysing Proteinase from Wheat Damaged by the New Zealand Wheat Bug, Nysius huttoni

A glutenin hydrolysing enzyme (bug proteinase), present in New Zealand wheat damaged by Nysius huttoni, was purified 50000-fold by anion exchange, hydrophobic interaction, immobilized metal ion affinity and gel filtration chromatography. The enzyme had an apparent M_r of 14·1k as determined by gel filtration chromatography. SDS-PAGE showed a major protein band of M_r 30k and six minor bands of M_r 13·2-28·5k, none of which was a glycoprotein. Isoelectric focusing revealed two major enzyme active bands (pI 9·6 and 9·2) and three minor activity bands (pI 9·9, 8·8 and 8·2). IEF showed no protein contaminants in the most purified sample. The enzymes had optimum activity at pH 8·9 and 45°C. The activity was stable in the pH range 4·5-11 and at 50°C for 20 min at pH 8·9. The bug proteinase was shown to be a serine proteinase by inhibition with phenylmethylsulphonyl fluoride and potato proteinase inhibitors (POT-IC and POT-ID). Thirty other proteinaceous serine proteinase inhibitors did not inhibit the enzyme. Bread baking with partially purified enzyme produced loaves with the poor quality characteristics of loaves made with bug-damage wheat.     

Hydrothermal Processing of Barley (cv. Blenheim): Optimisation of Phytate Degradation and Increase of FreeMyo-inositol

Optimal conditions were developed for hydrothermal processing of whole barley kernels (cv. Blenheim) to degrade phytate (myo-inositol hexaphosphate) and to increase the content of freemyo-inositol. The hydrothermal treatment comprised of two wet steeps, where lactic acid solution of different concentrations was used, and two dry steeps followed by successive drying. Experiments were performed as a central composite design and evaluated by multiple linear regression. The variables in the experiments were temperature in the first wet and dry steep (T₁), temperature in the second wet and dry steep (T₂) and lactic acid solution concentration in both wet steeps (C) and mathematical models were developed in these variables. Optimal conditions for maximal phytate degradation and for maximal increase of freemyo-inositol wereT₁=48 °C,T₂=48–50 °C andC=0·8%, at these conditions the amount of phytate was reduced by 95–96% and the freemyo-inositol concentration was increased from 0·56 to 2·45 μmol/g d.m. We conclude that this hydrothermal process can be used to produce a barley product (cv. Blenheim) with a low phytate content and a high level of freemyo-inositol.     

Muffins with resistant starch: Baking performance in relation to the rheological properties of the batter

The effect on baked muffins of progressively replacing wheat flour with resistant starch (RS) was studied. Muffin volume and height and the number and area of gas cells decreased significantly when the RS level reached about 15% (by weight of total formulation) or higher. Rheological properties of the raw batters were studied: the mechanical spectra of batters at 25 °C, the evolution of the dynamic moduli (G′ and G″) with rising temperatures (from 25 to 85 °C) and the mechanical spectra at 85 °C were obtained from oscillatory rheological tests. The decrease in the viscosity and in the elastic properties of the muffin batter as the flour was increasingly replaced by RS was related to the baking performance of the final baked products.     

Study of the effect of hydrothermal process conditions on pasta quality

The effect of hydrothermal treatment on the pasting, hydration properties and colour quality of commercial fresh pasta were studied following an Instantaneous Controlled Pressure Drop treatment. This hydrothermal procedure involves a physical modification at high temperature (<144 °C) and restricted moisture content (<30%) during a very short time (15–40 s) followed by a rapid pressure drop to a vacuum (50 mbar). Two process variables (steam pressure level and processing time) were investigated using response surface methodology. Steam pressure level had the greatest effect on hydration and pasting parameters. Increased pressure resulted in elevation of mass ratio between cooked and uncooked pasta (W_i/W₀)_{100 °C} and reduction of for all treated pasta. The optimum cooking time of untreated pasta was 7 min (W/W₀=2.4), whereas for the same ratio it was less than 1 min for pasta treated at pressures ranging between 2.5 and 3.5 bar. The viscosity at 10 min (V₁₀) increased linearly when the pressure level increased. V₁₀ was 146 cP for untreated pasta whereas it reached 2659 cP for pasta treated at 3.9 bar (144 °C) for 25 s. The cold paste viscosity and setback viscosity decreased when the pressure varied from 1 to 3.9 bar.     

Starch gelatinization and amylose–lipid interactions during rice parboiling investigated by temperature resolved wide angle X-ray scattering and differential scanning calorimetry

Starch gelatinization and formation of crystalline amylose–lipid complexes during the heat/moisture treatment step in rice parboiling were studied with temperature resolved wide angle X-ray scattering (WAXS) and differential scanning calorimetry (DSC) using flour from Puntal (24% apparent amylose) and Jacinto (12% apparent amylose) rice samples [66, 40 or 25% moisture content (mc)]. Temperature resolved WAXS showed that the crystallinity index (CI, i.e. the relative amount of A-type crystals) of non-parboiled rice flours at 66% mc, monotonically decreased between 65 °C (Puntal) and 70 °C (Jacinto) and 90 °C (both Puntal and Jacinto). These temperatures were in agreement with the respective onset and conclusion temperatures of the M₁ endotherm measured by DSC. At 40% mc, the CI decreased monotonically from 65 °C (Puntal) and 70 °C (Jacinto) until 105 °C. In DSC both M₁ and M₂ endotherms were present. The conclusion temperature of the M₂ endotherm was higher than 105 °C. At 25% mc, the CI decreased very gradually and A-type crystals were no longer present at 145 °C. Under these conditions, no DSC endotherms were detected. No type II amylose–lipid complexes were formed during heating at 66% mc. In contrast, at 40 and 25% mc, V_h-type crystals were formed from 100 and 130 °C, respectively. Non-parboiled white rice flour had a strong A-type pattern. Mildly parboiled rice had a clear A-type, with a weak V_h-type and B-type pattern. Severe parboiling resulted in partially crystalline systems with superimposed A-type, V_h-type and B-type crystals. It was concluded that the rice variety, the combination of mc and the moisture distribution in the rice kernel and the temperature during parboiling all impact the level and the types of crystals in the parboiled rice.     

Effect of jet-cooked wheat gluten/lecithin blends on maize and rice starch retrogradation

Vital wheat gluten and lecithin (GL) (50:50, w/w) were dry blended in a coffee grinder and a 9.5% (w/v) aqueous slurry was jet-cooked (steam pressures of 65 psi/g inlet and 40 psi/g outlet) to disaggregate wheat gluten and facilitate better dispersion of the two components. The jet-cooked material was freeze-dried and stored at 0 °C for future use. The GL blend was added to pure food grade common maize and rice starch at concentrations of 0 (control), 6, 11, 16, and 21%. Starch gelatinization and retrogradation temperature transitions were determined using Differential Scanning Calorimetry (DSC). From the DSC profiles, the change in the ΔH value was used as an indication of starch retrogradation, where a higher ΔH value indicated higher retrogradation. The ΔH values of the blends at 4 °C had higher values than the −20 °C and the ambient (25 °C) storage temperatures. Overall, the 21% GL/starch blends reduced retrogradation by 50%. The lower amylose content of rice starch relative to maize starch was reflected in Rapid Visco Amylograph (RVA) measurements of peak viscosity, and similarly, Texture Analyzer (TA) measurements indicated that maize starch gel is firmer than rice starch gel. Retrogradation was also evaluated by observing G′, the shear storage modulus, as a function of time after running a standard pasting curve. Using this method, it appears that GL has a significant effect on maize starch retrogradation, since low concentrations (<0.4%, w/w) reduced G′ up to 40%. The opposite behavior was seen in rice starch, where G′ increased directly with added GL. It appears that the amylose level in the rice starch is too low to be affected by the GL, and the increase seen in G′ is most likely due to added solids.     

Protein extraction from defatted wheat germ by reverse micelles: Optimization of the forward extraction

In this work, the forward extraction of defatted wheat germ protein (DWGP) by reverse micelles was studied. The reverse micellar systems were formed by sulphosuccinic acid bis (2-ethylhexyl) ester sodium salt (AOT), isooctane and KCl solution. The effects of AOT concentration, pH, KCl concentration, extraction time, the amounts of defatted wheat germ flour (DWGF), W₀ (the molar ratio of water to surfactant, i.e. W₀ = [H₂O]/[AOT]) and temperature on the forward extraction efficiency of DWGP were tested. On the basis of single-factor experiments, the optimum extraction was achieved by response surface methodology (RSM). The experimental results lead to the conclusion that the highest forward extraction efficiency of DWGP was reached at the AOT concentration 0.06 g/mL, pH 8, KCl concentration 0.1 mol/L, time 30 min, the amounts of DWGF 0.500 g, W₀ 25 and temperature 36 °C. Under these conditions, the forward extraction efficiency of DWGP achieved 37%.     

In vitro release of angiotensin-converting enzyme inhibitors, peroxyl-radical scavengers and antibacterial compounds by enzymatic hydrolysis of glycated gluten

The combined effect of gluten glycation and proteolysis on the release of compounds exhibiting in vitro angiotensin-converting enzyme (ACE) inhibitory, antioxidant and antibacterial activities was investigated. Model systems consisting of wheat gluten and glucose were heated at 120 °C for 45 min, 150 °C for 30 min and 220 °C for 30 min to produce various Maillard reaction products mimicking reactions occurring in bread crusts. Progress of the Maillard reaction was estimated through indirect measurement of Amadori compounds as 2-furoylmethyl-amino acids. Glycation was followed by digestion with Pronase E and ultrafiltration. The anti-hypertensive activity was measured as the ability to inhibit the activity of angiotensin I-converting enzyme involved in hypertension regulation. The Oxygen Radical Absorbance assay was used to measure the peroxyl radical scavenging capacity of the products and their effect on microbial growth of Escherichia coli ATCC 25922 and Staphlococcus aureus ATCC 25923 was also studied. Advanced products of the reaction enhanced the antioxidant and antibacterial properties of gluten hydrolysates and decreased the overall ACE inhibitory activity. Ultrafiltration provided a useful method for separating compounds (< 3000 Da) with ACE inhibitory activity and advanced Maillard reaction products (>3000 Da) which scavenged peroxyl radicals and inhibited the microbial growth.     

Purification and Characterisation of Ascorbate Oxidase from Flour and Immature Wheat Kernels

White flour from wheat was shown to contain basic-ascorbate oxidase (AOX) enzymes (pI 7·6–9·6) and acidic-AOX enzymes (pI 5·1–6·6) in a ratio of 0·4:1, based on chromatography data. Immature wheat kernels (two weeks post-anthesis) contained about 12 times more AOX activity (units/g dry weight) than flour from mature grain, and the ratio of basic- to acidic-AOX was 5:1. Acidic-AOX was purified 90-fold from flour by hydrophobic interaction, gel filtration and anion exchange chromatography. Basic-AOX was purified 20 000-fold from immature wheat by hydrophobic interaction, anion exchange, cation exchange and gel filtration chromatography in a yield of 5%. The acid-AOX had a M of 140 k, was optimally active at pH 6·3 and 40 °C, and was stable in the pH range 5–9 and at 30 °C for 0·5 h at pH 6·2. The Km values were 0·26 m for L-ascorbic acid and 0·93 m for D-iso ascorbic acid. The basic-AOX had a M of 139 k and subunit M of 72 k. The enzyme was optimally active at pH 6·2 and 50 °C, and was stable in the pH range 5–9 and at 40 °C for 0·5 h at pH 6·2. The Km values were 0·30 m for L-ascorbic acid and 0·53 m for D-iso ascorbic acid. The absorption spectrum of basic-AOX had absorption maxima at 280 nm and 607 nm of similar magnitude to those measured in AOX fromCucurbita species (squash). This indicates that wheat AOX contains protein-bound copper similar to other plant AOX.     

Physical properties of chia (Salvia hispanica L.) seeds

Physical properties of Salvia hispanica L. seeds were investigated and their application was also discussed. Physical properties were assessed for white and dark seed separately, except for the angle of repose and static coefficient of friction, which were determined for the seed mixture. The mean moisture content was 7.0% (dry basis). The average for the three characteristic dimensions, length, width and thickness was 2.11, 1.32 and 0.81 mm for dark seeds and 2.15, 1.40 and 0.83 mm for white seeds, respectively. The bulk density, true density and the porosity were between 0.667 and 0.722 g cm⁻³, 0.931 and 1.075 g cm⁻³, and 22.9 and 35.9%, respectively. The equivalent diameter ranged from 1.32 to 1.39 mm. The volume of single grain and sphericity ranged between 1.19 and 1.42 mm³, and 62.2 and 66.0%, respectively. The geometric mean diameter ranged between 1.31 and 1.36 mm for dark and white chia seeds, respectively. This parameter could be used for the theoretical determination of seed volume and sphericity. One thousand seed mass averaged 1.323 g for dark seeds, and 1.301 g for white seed. The angle of repose varied between 16° and 18° whereas the value of static coefficient of friction was 0.28 on galvanized sheet and 0.31 on mild steel sheet.     

Mass transport studies of model migrants within dry foodstuffs

Cereals are widely consumed foodstuffs and it is therefore important to take them into account when estimating consumer exposure to packaging-related chemicals. The mass transport of three model migrants (diphenylbutadiene, triclosan and BHT) from low-density polyethylene (LDPE) within dry foodstuffs of different particle size (rice and wheat flour) was studied because of the relationship between consumer exposure and possible harmful effects on human health. The conditions that most affect the mass transport of substances within dry foods are evaluated and discussed. The diffusion coefficients (D_F) for diphenylbutadiene (DPBD) and triclosan in the studied foodstuffs were estimated. The D_F values for DPBD and triclosan in wheat flour at 25 °C were 7.1 × 10⁻⁸ cm²/s and 3.3 × 10⁻⁸ cm²/s, respectively. The D_F values for DPBD and triclosan in rice at 25 °C were 4.7 × 10⁻⁸ and 4.3 × 10⁻⁸ cm²/s, respectively. BHT displayed different behaviour and other tests were therefore carried out to elucidate the associated mass transport process.     

Influence of chemical and biological treatments on volatile oil composition of Artemisia annua Linn.

The relative abundance of isoprenoids and other volatile components in the aerial parts of Artemisia annua Linn. (Asteraceae) after different nutritional treatments was analyzed by GC and GC/MS. Hydro-distillation of untreated (control) plants yielded 0.28 ± 0.04% essential oil on fresh weight basis. Monoterpenes were predominant in the essential oil of which cis-limonene-1,2-epoxide (22.1%), artemisia ketone (11.5%), iso-pinocamphone (11.4%), thujyl alcohol (9.9%) and camphor (8.4%) were the major components. The essential oil distilled from A. annua treated with Azospirillum (2 ml/plant) amounted to 0.30 ± 0.03% of fresh weight and consisted mainly of neral (31.1%), β-caryophyllene (25.1%), artemisia ketone (10.0%), thujyl alcohol (9.4%), trans-bergamotene (8.5%) and spathulenol (4.8%). The essential oil from plants treated with basal N, P, K and S application (in the form of urea P₂O₅, K₂O and gypsum at a rate of 120, 50, 100 and 50 kg/ha, respectively) amounted to 0.32 ± 0.03% of fresh weight and consisted mainly of thujyl alcohol (33.3%), β-caryophyllene (15.5%), cis-undec-5-ene (14.4%), artemisia ketone (6.0%), trans-nerolidol (5.8%) and undec-4-ene (4.6%). The hydrodistillation of A. annua treated with Glomus (Mycorrhizal soil 50 g/plant) yielded 0.50 ± 0.02% essential oil on fresh weight basis. The sesquiterpenes were predominant in this essential oil and consisted of β-caryophyllene (51.2%), trans-bergamotene (15.4%), α-gurjunene (14.3%), germacrene D (5.1%) and ledol (4.5%) as major components. The only monoterpenes in the essential oil were neral, nerol and pulegone (each less than 1%). These findings suggest that A. annua treated with Glomus lacks glandular trichomes—the primary sites of synthesis of monoterpenes.     

Phospholipids and wheat gluten blends: interaction and kinetics

A model system comprising of lysophosphatidylcholine (LPC) and isolated gluten were used help understand the positive effect of PL on bread-loaf volume. The kinetics of the effect of gluten on the thermal properties of LPC were determined using DSC. Blends of PL and 3, 6, and 10% gluten were heated from 0 to 70 °C at rates between 3 and 19 °C/min and cooled to 0 °C. The onset and peak temperatures and ΔH were recorded. The peak temperature was used to calculate the activation energy (E_a) and Z value. The transition for pure LPC vesicle formation was detectable by DSC in the presence of gluten. Gluten increased the activation energy of LPC during vesicle formation and disruption. The increase in gluten content from 3 to 6% and then to 10% had a slight effect on the activation energy value of LPC during vesicle disruption, whereas during formation a steady increase was noticed with higher gluten additions. Overall, the ΔH of the blends showed a decrease at higher heating rate. The change in the PL activation energy in the presence of gluten is indicative of a form of interaction.     

Improved viscoelastic zein–starch doughs for leavened gluten-free breads: Their rheology and microstructure

Gluten-free bread was prepared from commercial zein (20 g), maize starch (80 g), water (75 g), saccharose, NaCl and dry yeast by mixing above zein's glass transition temperature (T_g) at 40°C. Addition of hydroxypropyl methylcellulose (HPMC, 2 g) significantly improved quality, and the resulting bread resembled wheat bread having a regular, fine crumb grain, a round top and good aeration (specific volume 3.2 ml/g). In model studies, HPMC stabilized gas bubbles well. Additionally, laser scanning confocal microscopy (LSCM) revealed finer zein strands in the dough when HPMC was present, while dynamic oscillatory tests showed that HPMC rendered gluten-like hydrated zein above its T_g softer (i.e. |G*| was significantly lower). LSCM revealed that cooling below T_g alone did not destroy the zein strands; however, upon mechanical impact below T_g, they shattered into small pieces. When such dough was heated above T_g and then remixed, zein strands did not reform, and this dough lacked resistance in uniaxial extension tests. When within the breadmaking process, dough was cooled below T_g and subsequently reheated, breads had large void spaces under the crust. Likely, expanding gas bubbles broke zein strands below T_g resulting in structural weakness.