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1.
Optimisation of a microwave-assisted methanolysis was performed to obtain cafestol and kahweol directly from green coffee oil (Coffea arabica). A two-factor (the methanolysis period and temperature), three-level, factorial experimental design (32) was adopted. The methanolysis procedure was performed under microwave irradiation, using closed vessel and accurate fast responding internal fibre-optic temperature probe. The effects on the responses were measured by HPLC. After 3 min of microwave irradiation (hold time) at 100 °C, with 500 mg of green coffee oil, a yield higher than 99% was obtained. The yield of this reaction is 26% after 2 h when working under conventional heating. The methods described in the literature lead to long reaction times, poor yields and formation of side products. The microwave-assisted technique proved to be faster, avoided undesired side products and gave better conversion, when compared to conventional heating process.  相似文献   

2.
Carboxymethyl potato starch was synthesised with the aid of microwave. Optimal degree of substitution (DS) of 0.32 was obtained at 45 °C in 25 min using aqueous ethanol media with water/solvent of 0.15 at 200 W. The molar ratio of sodium hydroxide and monochloroacetic acid to anhydroglucose unit for optimal DS were 2.5 and 1.0, respectively. FT-IR spectrometry revealed the carboxymethyl starch to show new bands at ν = 1614 cm−1 and ν = 1429 cm−1. Wide angle X-ray diffractometry and DSC revealed a remarkable reduction in starch crystallinity after carboxymethylation, which was consistent with destroyed surface observed in SEM. The digestibility of carboxymethyl starch (CMS) was lower than that of native starch. With similar DS, there was no difference in digestibility of carboxymethyl starch prepared with and without microwave. As DS increased from 0.05 to 0.32, the amount of resistant starch in microwave-assisted carboxymethyl starch was elevated from 14.6% to 20.0%, which was much higher than that of native starch (10.8%).  相似文献   

3.
The effect of mild heat treatment (below gelatinization temperature) towards the susceptibility of granular starch to enzymatic hydrolysis was investigated. Tapioca and sweet potato starches were subjected to enzymatic hydrolysis with a mixture of fungal α-amylase and glucoamylase at 35 °C for 24 h. Starches were hydrolyzed in native (granular) state and after heat treatment below gelatinization temperature (60 °C for 30 min). The dextrose equivalent (DE) value of heat-treated starch increased significantly compared to native starch, i.e., 36–50% and 27–34% for tapioca and sweet potato starch, respectively. Scanning electron microscopy examination showed that enzymatic erosion occurred mainly at the surface of starch granules. Hydrolyzed heat-treated starch exhibited rougher surface and porous granules compared to native starch. X-ray analysis suggested that enzymatic erosion preferentially occurred in amorphous areas of the granules. The amylose content, swelling power and solubility showed insignificant increase for both starches. Evidently, heating treatment below gelatinization temperature was effective in enhancing the degree of hydrolysis of granular starch.  相似文献   

4.
Waxy and non-waxy rice starches adjusted to 20% moisture (wet basis, w.b.) were heat-moisture treated in a microwave oven to determine the effects of the microwave heating characteristics on digestibility, pasting, and morphological properties of the heated starches. Microwave heating produced only minimal changes in digestibility as well as the physical characteristics of heated starches. Significant changes in viscosity properties after microwave heat treatment were observed for both waxy and non-waxy starches heat-treated in a microwave oven, relative to non-treated samples. Non-waxy starch heated in microwave oven showed an increase in breakdown viscosity from 29.8 RVU (non-treated starch) to 35.8 RVU after heating for 60 min. However, for waxy starch, breakdown viscosity decreased from 112.7 to 35.9 RVU after 60 min of microwave heat treatment, reflecting an increased stability of microwave heat-treated starch under cooking. The data obtained in this study indicate that there was much higher re-aggregation of starch granules in waxy starch after microwave heat treatment than occurred in non-waxy starch, suggesting a re-association of amylopectin branch chains in the heat-treated waxy starch.  相似文献   

5.
The present study was performed to investigate the possibility of using 4-α-glucanotransferase (4αGTase)-treated starch in W/O/W emulsions to increase their encapsulation efficiency (EE) and stability. Emulsions were prepared using soybean oil, polyglycerol polyricinoleate (PGPR), 4αGTase-treated starch and Tween 20. The mean diameter of W/O/W droplets ranged from 4 to 10 μm depending on the sonication time. When the dye was loaded in the internal water phase, the emulsion prepared by sonication for 1 and 2 min showed a high EE of the dye (>90%). The W/O/W emulsion prepared by sonication for 3 min showed an EE of <90%, but this EE was improved by adding 4αGTase-treated starch to the internal water phase. 4αGTase-treated starch was added to the internal water phase of W/O/W emulsions prepared with a low concentration of PGPR, and the PGPR concentration required to maintain an EE >90% was reduced. W/O/W emulsions containing 4αGTase-treated starch also showed better stability against heating and shearing stresses. These results indicated that 4αGTase-treated starch could be used in the preparation of W/O/W emulsions, which would allow the formulation of W/O/W emulsions with a reduced surfactant concentration.  相似文献   

6.
The objective of this research was to verify the effect of drying conditions on thermal properties and resistant starch content of green banana flour (Musa cavendishii). The green banana flour is a complex-carbohydrates source, mainly of resistant starch, and quantifying its gelatinization is important to understand how it affects food processing and the functional properties of the flour. The green banana flour was obtained by drying unripe peeled bananas (first stage of ripening) in a dryer tunnel at 52 °C, 55 °C and 58 °C and air velocity at 0.6 m s−1, 1.0 m s−1 and 1.4 m s−1. The results obtained from differential scanning calorimetry (DSC) curves show a single endothermic transition and a flow of maximum heating at peak temperatures from (67.95 ± 0.31) °C to (68.63 ± 0.28) °C. ANOVA shows that only drying temperature influenced significantly (P < 0.05) the gelatinization peak temperature (Tp). Gelatinization enthalpy (ΔH) varied from 9.04 J g−1 to 11.63 J g−1 and no significant difference was observed for either temperature or air velocity. The resistant starch content of the flour produced varied from (40.9 ± 0.4) g/100 g to (58.5 ± 5.4) g/100 g, on dry basis (d. b.), and was influenced by the combination of drying conditions: flour produced at 55 °C/1.4 m s−1 and 55 °C/1.0 m s−1 presented higher content of resistant starch.  相似文献   

7.
Edible film from water-soluble fish proteins were developed by casting film solution on leveled trays and effects of pH (9.5, 10.0 and 10.5), heating temperature (60, 70 and 80 °C), and heating time (10, 20 and 30 min) of the film solution on various film properties were determined using Response Surface Methodology (RSM). The impact of pH and heating temperature of film solution was more significant, overall, on the film's properties than heating time. Contour plots of tensile strength and elongation at break was highest at pH of 10.0 at 70 °C (2.75-3.02 MPa) but low in elongation at break (6.35-9.16%), while water vapor permeability and oxygen permeability were at their lowest (58.55-65.96 g mm/m2 d kPa and 351.33-624.18 cm3 μm/m2 d kPa). There was a direct correlation between the films’ and proteins’ solubility on one hand, and heating temperature of film solution on the other, which reversed with change in pH of film solution. Film color was darker and more yellowish with increase in the pH of film solution.  相似文献   

8.
Soy protein isolate (SPI) was mixed with lactose, maltose, dextran or soluble starch (SS) and heated (temperature ?90 °C) by microwave irradiation. Compared to the classical heating, the microwave heating (MH) speeded up the graft reactions of SPI with sugars. From the results calculated, the rate constants of free amino groups in the grafts of SPI with lactose, maltose, dextran and SS by MH were, respectively, 6, 7, 57 and 12.3 times of those by classical heating. After heating by microwave, the lysine and arginine decreased and from, the FTIR spectroscopy of SPI and its grafts by MH, the absorbance of –C–O stretching and –OH deformation vibrations (1050–1150 cm−1) and free –OH form (3643–3630 cm−1) in SPI grafts increased compared to SPI. The temporal development of the graft reactions of SPI with sugars by MH was also shown by SDS–PAGE.  相似文献   

9.
A transgenic rice line (TRS) enriched amylose and resistant starch has been developed by antisense RNA inhibition of starch branching enzymes. In this study, gelatinisation and crystalline properties, swelling power, water solubility, morphological and structural changes of starches from TRS and its wild-type Teqing (TQ) were carefully investigated during heating. Compared to TQ, TRS starch showed higher gelatinisation temperatures, lower gelatinisation enthalpy and swelling power. Morphological and structural changes showed that TQ starch drastically swelled after 70 °C, then gradually disrupted with increasing heating temperature. The surrounding band of TRS starch restrained granule swelling, though the subgranules disrupted to form the cavity. The results of spectroscopic analyses indicated that A-type crystalline of TQ changed to amorphous starch after 75 °C, while C-type crystalline of TRS gradually changed to B-type crystalline after 75 °C, then became amorphous starch at 95 °C. These results add to our understanding of the effect of heating on the high-amylose rice starch.  相似文献   

10.
Radio frequency (RF) treatment holds potential as a pasteurization method to control Salmonella in almonds without causing a substantial loss of product quality. Thermal resistance of Salmonella can be reduced by increasing water activity, thus a soaking process was designed prior to RF treatments. A pilot-scale 27 MHz, 6 kW RF heating system was used to rapidly heat 1.7 kg washed in-shell almonds with hot air heating at 55 °C. To achieve appropriate heating rate, constant drying temperature and short time cooling, the RF treatment protocol was obtained using an electrode gap of 13 cm for heating, 14 cm for drying, and followed by forced room air cooling of 5-cm thick samples. The results showed that almond temperatures above 75 °C at 23% moisture contents for 2-4 min RF heating could meet the requirements to achieve 5-log reduction of Salmonella. The RF treatment process for 20 min reduced the moisture content to 5.7% w.b. Peroxide value, fatty acids values and kernel colors of the RF treated almonds met good quality standard used by nut industry.  相似文献   

11.
There is a great variability in cooking time and final texture among cassava cultivars and one factor in determining these characteristics is the age of roots at harvest. Final texture after cooking is an important attribute for the acceptability of cassava and starch gelatinization has a role in softening the tissue. Two cassava cultivars at two different harvest maturities were cooked at 90 °C and at boiling water temperature (98 °C) and the extent of gelatinization was determined using an iodine colorimetric method. A generalized model for starch gelatinization, considering temperature and cooking time as continuous variables and age at harvest as qualitative variable, was used to model the cooking process and applied for each cultivar. At 90 °C IAPAR-19 Pioneira reached maximum gelatinization in 32 min for the 12 month old sample and 88 min for the 25 month old sample, while double the time was needed for Catarina Amarela. At 98 °C Pioneira gelatinized in 12 min for the 12 month and 32 min for the 25 month old sample while Catarina Amarela needed 28 and 56 min. Calculated activation energy for starch gelatinization was 122.3±5.2 and 98.6±4.7 kJ/mol for cultivar IAPAR-19 Pioneira and Catarina Amarela, respectively.  相似文献   

12.
The digestibility of starch provided by coarsely ground corn is often low, which reduces the digestible energy (DE) concentration of the diet. We hypothesized that adding exogenous amylase to diets based on coarsely ground dent corn would increase dietary DE resulting in greater milk production. Total-tract nutrient digestibility was measured in a partially replicated Latin square experiment (6 cows and 4 periods) with a 2 × 2 factorial arrangement of treatments. Diets had 26 or 31% starch with or without exogenous amylase (amylase was added to the concentrate mixes at the feed mill). In the low and high starch diets, coarsely ground dry corn (mean particle size = 1.42 mm) provided 43 and 62% of total dietary starch (corn silage provided most of the remaining starch). No treatment interactions were observed. High starch diets had greater dry matter (DM), organic matter, and energy digestibility than low starch diets, and diets with amylase had greater neutral detergent fiber digestibility than diets without amylase. Digestibility of starch averaged 88% and was not affected by treatment. A long-term (98-d) lactation study with 48 Holstein cows (74 d in milk) was conducted using 3 of the diets (low starch diets with and without amylase and the high starch diet without amylase). Addition of amylase to a diet with 26% starch did not affect intake, milk yield, milk composition, body weight, or body condition. Cows fed the diet with 31% starch had greater DM and DE intakes; yields of milk, fat, and protein; and feed efficiency than those fed diets with 26% starch. Milk composition was not affected by starch concentration. Adding exogenous amylase to a lower starch diet did not make the diet nutritionally equivalent to a higher starch diet.  相似文献   

13.
Thermostable enzymes are currently being investigated to improve industrial processes of starch saccharification. A novel glucoamylase was purified to electrophoretic homogeneity from the culture supernatant of Fusarium solani on a fast protein liquid chromatographic system (FPLC). The recovery of glucoamylase after gel filtration on FPLC was 31.8% with 26.2-fold increase in specific activity. The enzyme had a molecular mass of 40 kDa by SDS-PAGE and 41 kDa by gel filtration. The glucoamylase exhibited optimum activity at pH 4.5. The Kcat and Km were 441/min and 1.9 mg/ml, respectively, for soluble starch, specificity constant (Kcat/Km) was 232. The enzyme was thermally stable at 50 °C and retained 79% activity after 60 min at this temperature. The half-life of the enzyme was 26 min at 60°C. The enzyme was slightly stimulated by Cu2+ and Mg2+ and strongly inhibited by Hg2+, Pb2+, Zn2+, Ni2+ and Fe3+.  相似文献   

14.
The effects of gelatinisation on slowly digestible (SDS) and resistant starch (RS) of native and modified canna starches were investigated. Starch slurries (10% w/w) were gelatinised at 100 °C for 5, 10, 20 and 40 min using a rapid visco analyzer (RVA). Significant change in the degree of gelatinisation (DG) values of all starch samples was observed during the initial 10 min of gelatinisation; after that the DG values increased gradually with gelatinisation time. The RS contents in all gelatinised starches decreased with increasing gelatinisation time, while the SDS values fluctuated. Chemical modification affected DG values as well as RS/SDS contents. The RS contents in 10% (w/w) acetylated, hydroxypropylated, octenyl succinylated and cross-linked canna starches gelatinised at 100 °C for 40 min were 26.6%, 32.0%, 45.3% and 19.8%, respectively, which were higher than that of the native starch (12.4%). Canna starch modified by crosslinking had the highest SDS content when gelatinised for 20-40 min. Modification of canna starch by heat-moisture treatment resulted in a lower content of RS for all treated samples. However, the Vt-HMT25 (canna starch containing moisture content of 25% during heat treatment) when gelatinised for 5-20 min contained a higher amount of SDS, compared to unmodified starch. The most effective modification method for RS and SDS formation was octenyl succinylation, where the sum of RS and SDS approached that of Novelose260.  相似文献   

15.
Microalgae represent an alternative and innovative source of natural ingredients that can be used in the development of novel food products. Biologically active compounds (e.g. carotenoids) are naturally encapsulated within microalgal cells, being able to resist harsh technological conditions involved in food technology processes. The aim of this work was to study the effect of adding Haematococcus pluvialis and Spirulina maxima microalgal biomass on the linear viscoelastic behaviour of vegetarian food gels prepared from pea protein, κ-carrageenan and starch. The gelation process was monitored in situ through dynamic oscillatory measurements, under different thermal profile conditions. Increasing temperature (70–90 °C, 5 min) resulted in more structured gels, while the effect of time (5–30 min, at 90 °C) was less pronounced. The effect of heating and cooling rates on gel setting was also studied. Haematococcus gels were highly structured and less dependent on gel setting conditions. Spirulina gels presented lower values of viscoelastic functions than the control (gel matrix without microalgae), but this was overcome when using lower heating/cooling rates.  相似文献   

16.
In vitro indicators of starch bioavailability were evaluated in freshly prepared maize tortillas and compared to those exhibited by 24, 48 or 72 h-stored samples. Storage took place either at room temperature (approx. 25 °C) or under refrigeration (4 °C). Potentially available starch (AS) content decreased from 670 g kg−1 in the control tortilla to 583 g kg−1 in 72 h-stored preparations. Concomitant increases in total resistant starch (RS) and retrograded resistant starch (RRS) were recorded upon storage. RRS content in 72 h-stored samples (35-39 g kg−1) doubled that of freshly prepared tortillas. Changes in AS, RS and RRS were not affected by storage temperature. Both initial rate and final point of starch hydrolysis by pancreatic amylase were reduced in samples kept for 48 and 72 h, without influence of storage temperature. Storage length is suggested as a major determinant of the bioavailability of starch in tortillas.  相似文献   

17.
A simple and fast method for the TMS derivatization of phenolic acids in a closed vial using microwave irradiation followed by GC/MS analysis is proposed. A full factorial design was used to investigate the effects of two independent variables, namely, time and power of microwave irradiation, on the yield of silylation reaction. The optimal conditions were tested against the classical heating derivatization procedure. No significant differences were found between the classical heating and microwave-assisted derivatization. Chromatographic separation of the nine phenolic acids examined was achieved in 16 min. The mass spectral fragmentation patterns of the derivatives obtained by the proposed method were identical to those from the classical heating. Four different batches of brewer’s spent grain were extracted and analyzed for the total phenolic acid content. Significant differences between the batches of spent grains were found for all analytes. The total phenolic acid content varied between 2688 and 4884 μg/g.  相似文献   

18.
Irfan Turhan  Mustafa Karhan  Fehmi Gurel 《LWT》2008,41(8):1396-1399
Honey producers have been heating honeys at mild temperatures below 100 °C chiefly in order to prevent post-bottling crystallization. In this study, we aimed to determine the effects of thermal treatment on the HMF content of honeydew and floral honey during the isothermal heating process at mild temperatures. Water content, formol number, total acidity, pH value and minerals were also determined in both honey types as their characteristics differ with composition, which is able to affect the rate of HMF formation. Potassium content and pH value were found as the distinguishing properties and both were greater in honeydew honey than in floral honey (p<0.01). Honeydew and floral honey samples were heated at 75, 90 and 100 °C for 15-90 min and analysed for HMF content by HPLC-RP. The Arrhenius model was used to calculate reaction rate constants and activation energies which were found to be different for each of the honey types. Heating at 90 °C for up to 90 min in floral honeys and up to 75 min in honeydew honeys did not cause a significant increase of HMF and not exceed the threshold level of 40 mg kg−1. Our results show that the excessive HMF content might be related to primitive storage conditions rather than overheating.  相似文献   

19.
The decomposition of betanin under dielectric heating (microwave irradiation, power: 25–200 W (3–24 kJ g−1)) follows first-order kinetics with a rate constant similar to that obtained during conventional conduction heating (half-life < 2 min at 100 °C). Color coordinate analysis indicates that betanin is bleached upon thermal treatment, whereas beetroot juice and spray-dried beetroot powder tend to form colored decomposition products. The antiradical capacity of betanin decreases upon heating, but is still much higher than that of standard antioxidants such as ascorbic acid and trolox. Betalamic acid, a high capacity antiradical, was detected by mass spectrometry and second-derivative absorption spectroscopy in betanin samples submitted to thermal treatment.  相似文献   

20.
Successful development of a thermal treatment protocol depends on reliable information on fundamental thermal death kinetics of targeted insects under different heating conditions. The effects of heating rates (1, 10, and 15 °C min−1), pre-treatment conditioning (30 °C+6 h), and the difference between long-term laboratory cultures and recently isolated cultures on thermal mortality of fifth-instar navel orangeworm, Amyelois transitella (Walker), were studied using a heating block system. There was no significant difference in insect mortality resulting from heating rates of 10 and 15 °C min−1. Temperature control at 1 °C min−1 was more uniform than for the other heating rates, resulting in reduced variability for insect mortality. The mean mortality at the heating rate of 1 °C min−1 was significantly lower than for the two faster heating rates only at 48 °C+30 min. The pre-treatment conditioning of fifth-instar Amyelois transitella enhanced their thermotolerance only at certain temperature-time combinations. Fifth-instars from long-term laboratory and recently isolated cultures were equally susceptible to elevated temperatures. Therefore, thermal death kinetic information obtained from the long-term laboratory cultures can be used to develop thermal protocols against field pests.  相似文献   

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