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1.
Bioprocesses were developed to enhance the value of proteins from deoiled corn germ. Proteins were hydrolyzed with trypsin, thermolysin, GC 106, or Flavourzyme to generate the bioactive peptide sequences. At an enzyme to substrate ratio of 1:100, protein hydrolysis of wet-milled germ was greatest using thermolysin followed by trypsin, GC 106, and Flavourzyme. For the dry-milled corn germ, protein hydrolysis was greatest for GC 106 and least for Flavourzyme. Electrophoretic patterns indicated that the hydrolysis conditions used were adequate for generating low molecular weight peptides for both germs. Unhydrolyzed dry- and wet-milled corn germ did not appear to contain angiotensin I converting enzyme (ACE)-inhibitory peptides. After hydrolysis with trypsin, thermolysin, and GC 106 but not Flavourzyme, ACE inhibition was observed. ACE inhibition was greatest for the GC 106 hydrolysate for both wet- and dry-milled corn germ. Denaturing the protein with urea before hydrolysis, in general, increased the amount of ACE-inhibitory peptides found in the hydrolysate. Membrane fractionations of both the wet- and dry-milled hydrolysates indicated that most of the ACE-inhibitory peptides were in the <1 kDa fraction. Examination of the control total protein extracts (before treatment with proteases) from wet- and dry-milled germ revealed that neither had ACE-inhibitory properties. However, when both total corn germ control protein extracts were fractionated, the <1 kDa fraction of wet-milled corn germ proteins exhibited ACE inhibition, whereas the comparable low molecular weight fraction from dry-milled corn germ did not.  相似文献   

2.
An alkali corn wet-milling process was developed to evaluate the process as a method to produce high purity corn starch and coproducts with added value. Using a single hybrid (R1064 × LH59), the effects of alkali concentration (0.18–0.82% NaOH), time (29–61 min), and temperature (36–75°C) were investigated. Starch yield was not affected by steep time or temperature. Starch yield was optimal at 65.2% using 0.5% alkali. Increasing the concentration of alkali to 0.82% or decreasing it to 0.18% caused a decrease in starch yield of 8–10 percentage points. Other wet-milling products (fiber, germ, and gluten) also were affected. Steep conditions of 0.5% NaOH, 60 min, and 45°C gave optimal starch yield. Comparisons between alkali and sulfur dioxide wet-milling processes, using 1-kg sample size, were performed on 10 commercial yellow dent corn hybrids. The alkali process averaged 1.7 percentage points more starch than the sulfur dioxide process. Each hybrid had a higher starch yield when wet-milled with the alkali method. Alkali wet-milling produced pure corn starch with <0.30% protein (db).  相似文献   

3.
调质大米半干法磨粉制备鲜米粉及其品质测定   总被引：4，自引：1，他引：3  
为考察半干法磨粉对鲜米粉品质的影响,该研究选用旋风磨和布勒磨对调质后含水率为28%和30%的大米进行磨粉,分析大米粉的白度、凝胶特性及糊化特性,对加工鲜米粉的质构特性、蒸煮特性和感官品质进行了分析。结果显示:调质大米可以减小磨粉仪器机械力和热能对大米粉品质的破坏,其中调质大米经布勒磨粉碎后的白度显著高于湿磨粉白度(P0.05);旋风磨含水率为30%调质粉的凝胶硬度最大为3.45 N/cm2,与湿磨粉的无显著差异(P0.05);2种调质粉相比于湿磨粉其崩解值较小,其中布勒磨含水率为30%调质粉回生程度较低,与湿磨粉无显著差异(P0.05)。对于鲜米粉的品质,筛选得到的旋风磨含水率为30%鲜米粉的硬度为35.10 N/cm2,弹性为0.97,较湿磨米粉更柔软弹滑,感官评价总分和蒸煮特性与湿磨米粉无显著差异。以上结果表明,含水率为30%的大米经旋风磨粉碎后能够制得与湿法磨浆相媲美的鲜米粉,可为解决湿磨法废水量大、产品得率低等问题提供参考。  相似文献   

4.
Zein isolation by aqueous ethanol extraction from dry-milled corn produces a mixture of zeins, covalently linked polymers (dimers, tetramers, etc.) and higher-molecular-weight aggregates, some of which were not soluble in aqueous alcohol. The insoluble particles were identified as protein aggregates which form when the extraction solution is heated, particularly under alkaline conditions. The insoluble protein aggregates were not present in zein isolated by the same method from corn gluten meal. Zeins extracted from corn gluten meal and dry-milled corn were fractionated (by differential solubility) to identify differences in their polypeptide compositions. Using polyacrylamide gel electrophoresis, beta- and gamma-zeins were detected in dry-milled corn, but only trace amounts of beta-zein were found in corn gluten meal. Treatment of dry-milled corn with 0.55% lactic acid and 0.2% sulfur dioxide at 50 degrees C for 6 h before ethanol extraction resulted in a 50% increase in zein isolate yield with high solubility (98%). This pre-extraction treatment cleaved disulfide linkages of the beta- and gamma-zeins and significantly reduced insoluble aggregates in zein isolates.  相似文献   

5.
Ethanol fermentation of dry‐fractionated grits (corn endosperm pieces) containing different levels of germ was studied with the dry‐grind process. Partial removal of the germ fraction allows for marketing the germ fraction and potentially more efficient fermentation. Grits obtained from a dry‐milling plant were mixed with different amounts of germ (2, 5, 7, and 10% germ of the total sample) and compared with control grits (0% germ). Fermentation rates of germ‐supplemented grits (2, 5, 7, and 10% germ) were faster than control grits (0% germ). Addition of 2% germ was sufficient to achieve a high ethanol concentration (19.06% v/v) compared with control grits (18.18% v/v). Fermentation of dry‐fractionated grits (92, 95, and 97% grits) obtained from a commercial facility was also compared with ground whole corn (control). Fermentation rates were slower and final ethanol concentrations were lower for commercial grits than the control sample. However, in a final experiment, commercial grits were subjected to raw starch hydrolyzing (RSH) enzyme, resulting in higher ethanol concentrations (20.22, 19.90, and 19.49% v/v for 92, 95, and 97% grits, respectively) compared with the whole corn control (18.64% v/v). Therefore, high ethanol concentrations can be achieved with dry‐fractionated grits provided the inclusion of a certain amount of germ and the use of RSH enzyme for controlled starch hydrolysis.  相似文献   

6.
Three streams of corn dry-milled products (corn grits, corn cones, and corn flour) from three different commercial corn dry-millers were further separated by particle size according to the major portion of each stream. They were separated into corn grits (1.190 and 0.841 mm), corn cones (0.595, 0.420, and 0.297 mm), and corn flour (0.297 and 0.210 mm). Besides separation, corn grits were also ground and then separated into ground corn grits (0.297 and 0.210 mm). The original streams, streams with additional separation, and streams with additional grinding were analyzed for protein content, ash content, crude fat content, and color properties. Duncan's significant difference tests (P < 0.01) showed that additional separation and grinding of the commercial corn grits, corn cones, and corn flour affected protein, crude fat content, and color parameter (L, a, and b) distribution of the products. The tristimulus parameters (L, a, and b) were good indicators of the protein content of the corn dry-milled streams studied.  相似文献   

7.
The distribution of Fusarium molds and fumonisins was determined in commercial and experimental dry-milled corn fractions. Fusarium infection of the commercial whole corn samples ranged from 10 to 28%; F. moniliforme was the predominant species. Fusarium counts in corn fractions were <100 colony-forming units (CFU)/g in flaking grits, <100 - 6.4 × 104 CFU/g in bran, <100 − 1.6 × 104 CFU/g in germ, and <100 − 2.7 × 103 CFU/g in flour. Fumonisin concentrations were ≤0.1 μg/g in flaking grits, 0.2–1.1 μg/g in flour, 0.1–2.0 μg/g in germ, and 1.5–3.2 μg/g in bran. Yellow, blue, and white dent corns naturally contaminated with varying levels of fumonisins (25.4, 3.9, and 0.3 μg of fumonisin B1 per gram) and Fusarium molds (3.9 × 106, 8.0 × 105, and 2.6 × 104 CFU/g) were experimentally dry milled with a horizontal drum degermer. Number 5 grits contained significantly lower Fusarium counts and fumonisin concentrations than the whole kernel corn. Fusarium counts and fumonisins increased as grit size decreased, and high Fusarium counts and fumonisin concentrations were found in germ, bran, and fines.  相似文献   

8.
A very small scale laboratory procedure (≈10 g) is needed to test wet‐milling characteristics of corn when amounts of corn available for testing are quite limited. The objective of this study was to downscale 100‐g laboratory wet‐milling methods already widely used to measure wet‐milling properties of 10 g of corn. A Standard 100‐g procedure, a Modified 100‐g procedure, and an Experimental 10‐g procedure were compared using three corn hybrids with known differences in wet‐milling properties. All three procedures ranked most fraction yields (all except for germ) of the three hybrids the same. Germ separation was conducted differently for each procedure and probably accounts for these differences. Flotation and screening methods were likely affected by germ density and germ size, and hand‐picking the germ was efficient in recovering a pure germ fraction. The two 100‐g procedures were performed very similarly except for fiber recovery. The Modified 100‐g procedure was more efficient in recovering fiber because of intensive washing. Hybrid effects on the starch/gluten separation were more pronounced when the Experimental 10‐g procedure was used, which may allow for more discrimination among hybrids. Although most fraction yields are too small to run replicates for analytical tests, the Experimental 10‐g procedure will be useful in measuring milling efficiency of early generations of corn hybrids where limited samples are available, such as when valuable recombinant proteins are expressed for therapeutics and industrial enzymes.  相似文献   

9.
A new process was developed to recover corn fiber from the mash before fermentation in dry-grind ethanol production. In this process, corn is soaked in water (no chemicals) for a short period of time and then degermed using conventional degermination mills. In the remaining slurry, corn coarse fiber is floated by increasing the density of the slurry and then separated using density differences. The fiber recovered is called quick fiber to distinguish it from the conventional wet-milled fiber. This study evaluated the percent of quick fiber recovery for a normal yellow dent and high oil corn hybrid. The quick fiber was analyzed for levels of corn fiber oil, levels of ferulate phytosterol esters (FPE) and other valuable phytosterol components in the oil and compared with conventional wet-milled corn coarse and fine fiber samples. Fiber samples were also analyzed and compared for yields of potentially valuable corn fiber gum (CFG, hemicellulose B). Comparisons were made between the quick fiber samples obtained with and without chemicals in the soakwater. An average quick fiber yield of 6–7% was recovered from the two hybrids and represented 46–60% of the total fiber (fine and coarse) that could be recovered by wet-milling these hybrids. Adding steep chemicals (SO2 and lactic acid) to the soakwater increased the quick fiber yields, percent of FPE recoveries, and total percent of phytosterol components to levels either comparable to (for the dent corn hybrid) or higher than (for the high oil corn hybrid) those recovered from the total conventional wet-milled fiber samples. CFG yields in the quick fiber samples were comparable to those from the wet-milled fiber samples. CFG yields in the quick fiber samples were not significantly affected by the addition of chemicals (SO2 and lactic acid) to the soakwater.  相似文献   

10.
Adhesive properties on glass of commercial zein and an inexpensive zein-lipid mixture isolated from dry-milled corn were investigated. A method was developed for uniformly preparing bonded glass panels and measuring the amount of pull required to separate the panels. The adhesive strength of commercial zein to glass was greater at 29% than at 52% relative humidity (RH). Bonded samples prepared from zein isolates were less sensitive to changes in RH. Bonds using commercial zein formulations containing plasticizer reached a maximum strength at 10% poly(ethylene glycol) regardless of RH. Formulations that required the least amount of ethanol (35-42%) were obtained by adjusting its pH to 3 or 10 with a volatile acid or base. These formulations completely bonded to the glass panels at low sample concentrations as estimated by 100% cohesive failure and exhibited lower Young's Modulus values than most of the other bonding materials tested. Samples bonded with a polyvinyl acetate emulsion adhesive were not as strong as the zein-bonded samples and were sensitive to changes in RH.  相似文献   

11.
Different corn types were used to compare ethanol production from the conventional dry‐grind process to wet or dry fractionation processes. High oil, dent corn with high starch extractability, dent corn with low starch extractability and waxy corn were selected. In the conventional process, corn was ground using a hammer mill; water was added to produce slurry which was fermented. In the wet fractionation process, corn was soaked in water; germ and pericarp fiber were removed before fermentation. In the dry fractionation process, corn was tempered, degerminated, and passed through a roller mill. Germ and pericarp fiber were separated from the endosperm. Due to removal of germ and pericarp fiber in the fractionation methods, more corn was used in the wet (10%) and dry (15%) fractionation processes than in the conventional process. Water was added to endosperm and the resulting slurry was fermented. Oil, protein, and residual starch in germ were analyzed. Pericarp fiber was analyzed for residual starch and neutral detergent fiber (NDF) content. Analysis of variance and Fisher's least significant difference test were used to compare means of final ethanol concentrations as well as germ and pericarp fiber yields. The wet fractionation process had the highest final ethanol concentrations (15.7% v/v) compared with dry fractionation (15.0% v/v) and conventional process (14.1% v/v). Higher ethanol concentrations were observed in fractionation processes compared to the conventional process due to higher fermentable substrate per batch available as a result of germ and pericarp fiber removal. Germ and pericarp yields were 7.47 and 6.03% for the wet fractionation process and 7.19 and 6.22% for the dry fractionation process, respectively. Germ obtained from the wet fractionation process had higher oil content (34% db) compared with the dry fractionation method (11% db). Residual starch content in the germ fraction was 16% for wet fractionation and 44% for dry fractionation. Residual starch in the pericarp fiber fraction was lower for the wet fractionation process (19.9%) compared with dry fractionation (23.7%).  相似文献   

12.
The fate of DNA during steeping, wet-milling, and subsequent processing of maize was examined using a sensitive polymerase chain reaction (PCR-based) detection system. The system used specific amplification of maize DNA sequences by primers generated toward plant nuclear- and chloroplast-encoded genes. The PCR method facilitated analysis of DNA content in food products, which is an important issue in use of genetically modified organisms. In a conventional laboratory wet-milling countercurrent steep system, DNA was detected in maize kernels throughout the process but was not found in steepwater. After kernels were wet-milled, DNA was detected in the starch, germ, coarse fiber, and wet gluten fractions but not in the fine fiber fraction. When dried by heating at 135°C for 2 hr, DNA was degraded to undetectable levels in the wet-milled gluten fraction and hydrated kernels. DNA was not detected in feed pellets, starch, dextrose, sorbitol, or high-fructose maize syrup made from industrial wet-milled samples. Although DNA could be detected in laboratory wet-milled fractions, some degree of degradation occurred after extended exposure to steepwater. Countercurrent steepwater samples from the later stages of the steeping process were able to degrade DNA. The level of DNA degradation appeared to correspond to the presence of sulfur dioxide and may represent a physiochemical rather than an enzyme-mediated process. Our results indicate that some steps in the steeping and wet-milling process can degrade maize genomic and plastid DNA.  相似文献   

13.
A procedure based on the resistance and capacitance (RC) properties of corn to calculate a displacement value (DV) was evaluated for detection of corn that had reduced wet-milling quality. In 1991 and 1992, three hybrids were dried at air temperatures between ambient and 115°C in batch dryers. Additional samples, obtained from commercial elevators in 1992, had been dried with air temperatures ranging from 52 to 136°C. A baseline reference relationship was developed between log10-resistance and capacitance with data from ambient-dried samples. A DV was defined as the horizontal distance along the capacitance axis from a sample RC data point to the baseline reference. RC properties of samples dried at air temperatures >50°C were compared to the baseline and the DV determined. Selected drying treatments were wet-milled by a laboratory-scale procedure to verify milling quality and correlation with DV. The effects attributed to hybrid and harvest moisture content on the RC properties of ambient-dried samples were small, allowing the baseline reference to be applied to a wide range of corn samples. In 1992, the baseline shifted upward from the 1991 baseline by 0.5 units on the log10-resistance axis. DV increased significantly at drying air temperatures >50°C for batchdried samples. While DV correlated with drying temperature in batchdried samples (r = 0.66), it did not correlate with starch yield or recovery of commercial samples (r ≤0.10). Although the specific causes could not be determined, the shift in the baseline indicates the method would be difficult to implement on a practical scale. Although not indicated by DV, starch recovery decreased significantly for samples batch-dried at air temperatures ≥70°C. All samples dried at 115–136° had significantly lower starch recoveries.  相似文献   

14.
The effect of adding lactic acid and sulfur dioxide at different times from the start of batch steeping on corn starch yields was studied. Five commercial hybrids were steeped with 0.5% lactic acid or 0.2% sulfur dioxide added over the first 15 hr of steeping and wet-milled following a 100-g corn wet-milling procedure. No significant differences were observed in starch yields when lactic acid was added to the steep solution (SO2 and water) from 0 hr (start of steeping) to 15 hr. Addition of SO2 to the steep solution (lactic acid and water) resulted in significantly higher average starch yields when SO2 was added between 5 and 15 hr compared with addition at 0 hr (SO2 and lactic acid for full 24 hr of steeping). Based on the results of the first experiment, a second experiment was done in which one of five original hybrids was steeped for 24 hr, during which lactic acid or SO2 was added until 23.9 hr (i.e., 5 min before milling) after the start of steeping. Similar results were found in the second experiment. Residual protein in starch samples did not exceed 0.85%. Steepwater protein content decreased with delays (16–20 hr) in adding either chemical to the steep solution. A significant effect on starch pasting properties of chemicals and duration of chemicals in steep-water was observed. Testing these findings using a larger scale (1,000 g) corn wet-milling procedure produced results similar to those obtained with the 100-g corn wet-milling procedure.  相似文献   

15.
The phenolic acid composition and concentration of four manually separated fractions (pericarp, aleurone layer, germ, and endosperm fractions) as well as whole grains of yellow corn, wheat, barley, and oats were analyzed by HPLC‐MS/MS following microwave‐assisted alkaline aqueous extraction. Phenolic acid compositions in whole grains and their fractions were similar, with minor differences among the grain fractions. Significant differences (P < 0.05), however, were observed in phenolic acid concentrations among cereal types, within cereal varieties, and among grain fractions, with yellow corn exhibiting the highest values. The concentrations of p‐coumaric and syringic acid in the pericarp were 10‐ to 15‐fold and 6‐ to 10‐fold higher, respectively, in yellow corn than in wheat, barley, and oats. In the aleurone layer, sinapic and vanillic acids in yellow corn were about 8‐ and 30‐fold more than in wheat. The germ fraction of wheat had 1.8 times more syringic acid than yellow corn germ. Grain fractions, excluding endosperm, had enhanced levels of phenolic acids compared with whole grain. Sinapic acid was more concentrated in the pericarp and germ of wheat, whereas isoferulic acid was concentrated in the germ of purple barley. Syringic and vanillic acids were concentrated in the pericarp and sinapic acid in the aleurone layer of yellow corn. These findings are important in understanding the composition and distribution of phenolic acids, and they act as a guide in identification of grain fractions for use as food ingredients. In addition, yellow corn fractions (aleurone and pericarp) may be potential alternative phenolic‐rich functional food ingredients in grain‐based food products.  相似文献   

16.
We recently reported that corn fiber oil contains high levels of three potential cholesterol-lowering phytosterol components: ferulate-phytosterol esters (FPE) (3–6 wt%), free phytosterols (1–2 wt%), and phytosterol-fatty acyl esters (7–9 wt%). A previous study also indicated that corn bran oil contained less phytosterol components than corn fiber oil. The current study was undertaken to attempt to confirm this preliminary observation using more defined conditions. Accordingly, oil was extracted from corn fiber and corn bran prepared under controlled laboratory conditions, using the same sample of corn hybrid kernels for each, and using recognized bench-scale wet-milling, and dry-milling procedures, respectively. After extraction, the chemical composition of the phytosterol components in the oil were measured. This study confirmed our previous observation—that FPE levels were higher in corn fiber oil than in corn bran oil. During industrial wet-milling, almost all of the FPE are recovered in the fiber fraction (which contains both fine and coarse fiber). During laboratory-scale wet-milling, ≈60–70% of the FPE are recovered in the coarse fiber (pericarp) and 30–40% are recovered in the fine fiber. During laboratory-scale dry-milling, <20% of the FPE are recovered in the bran (pericarp), and the rest in the grits. The recoveries of the other two phytosterol components (free phytosterols and phytosterol-fatty acyl esters) revealed a more complex distribution, with significant levels found in several of the dry- and wet-milled products.  相似文献   

17.
An improved means of isolating zein is needed to develop new uses for corn zein. We have measured the yield of zein and evaluated the ability of acetic acid to remove zein from corn gluten meal, distillers dried grains, and ground corn using acetic acid as solvent. Acetic acid removed zein more quickly, at lower temperatures, and in higher yields when compared with alcoholic solvents. After 60 min at 25°C, ≈50% of the zein in corn gluten meal was removed. A step change in yield from 43 to 50% occurs as the extraction temperature is increased from 40 to 55°C after mixing for 30 min at 25% solids. The protein composition of the zein removed from corn gluten meal using acetic acid is very similar to that of commercial zein by SDS‐PAGE. The zein obtained from corn gluten meal using acetic acid had higher amounts of fatty acids and esters according to IR analysis, leading to slightly lower protein content. Films made from zein extracted from corn gluten meal using acetic acid had lower tensile strength (≈60% lower) than films produced from commercial zein. Fibers with very small diameter (0.4–1.6 μm) can be produced by electrospinning using the AcOH solution obtained after corn gluten meal extraction.  相似文献   

18.
Pup‐loaf bread was made with 10, 30, and 50% substitution of flour with wheat starch phosphate, a cross‐linked resistant starch (XL‐RS4), while maintaining flour protein level at 11.0% (14% mb) by adding vital wheat gluten. Bread with 30% replacement of flour with laboratory‐prepared XL‐RS4 gave a specific volume of 5.9 cm3/g compared with 6.3 g/cm3 for negative control bread (no added wheat starch), and its crumb was 53% more firm than the control bread after 1 day at 25°C, but 13% more firm after 7 days. Total dietary fiber (TDF) in one‐day‐old bread made with commercial XL‐RS4 at 30% flour substitution increased 3–4% (db) in the control to 19.2% (db) in the test bread, while the sum of slowly digestible starch (SDS) plus resistant starch (RS), determined by a modified Englyst method, increased from 24.3 to 41.8% (db). The reference amount (50 g, as‐is) of that test bread would provide 5.5 g of dietary fiber with 10% fewer calories than control bread. Sugar‐snap cookies were made at 30 and 50% flour replacement with laboratory‐prepared XL‐RS4, potato starch, high‐amylose (70%) corn starch, and commercial heat‐moisture‐treated high‐amylose (70%) corn starch. The shape of cookies was affected by the added starches except for XL‐RS4. The reference amount (30 g, as‐is) of cookies made with commercial XL‐RS4 at 30% flour replacement contained 4.3 g (db) TDF and 3.4 g (db) RS, whereas the negative control contained 0.4 g TDF and 0.6 g RS. The retention of TDF in the baked foods containing added XL‐RS4 was calculated to be >80% for bread and 100% for cookies, while the retention of RS was 35–54% for bread and 106–113% for cookies.  相似文献   

19.
Effects of phytase addition, germ, and pericarp fiber recovery were evaluated for the E‐Mill dry grind corn process. In the E‐Mill process, corn was soaked in water followed by incubation with starch hydrolyzing enzymes. For each phytase treatment, an additional phytase incubation step was performed before incubation with starch hydrolyzing enzymes. Germ and pericarp fiber were recovered after incubation with starch hydrolyzing enzymes. Preliminary studies on phytase addition resulted in germ with higher oil (40.9%), protein (20.0%), and lower residual starch (12.2%) contents compared to oil (39.1%), protein (19.2%), and starch (18.1%) in germ from the E‐Mill process without phytase addition. Phytase treatment resulted in lower residual starch contents in pericarp fiber (19.9%) compared to pericarp fiber without phytase addition (27.4%). Results obtained led to further investigation of effects of phytase on final ethanol concentrations, germ, pericarp fiber, and DDGS recovery. Final ethanol concentrations were higher in E‐Mill processing with phytase addition (17.4% v/v) than without addition of phytase (16.6% v/v). Incubation with phytases resulted in germ with 4.3% higher oil and 2.5% lower residual starch content compared to control process. Phytase treatment also resulted in lower residual starch and higher protein contents (6.58 and 36.5%, respectively) in DDGS compared to DDGS without phytase incubations (8.14 and 34.2%, respectively). Phytase incubation in E‐Mill processing may assist in increasing coproduct values as well as lead to increased ethanol concentrations.  相似文献   

20.
The mechanical properties of cross-linked edible films based on calcium caseinate and two type of whey proteins (commercial and isolate) were investigated. Cross-linking of the proteins was carried out using thermal and radiative treatments. Size-exclusion chromatography performed on the cross-linked proteins showed that gamma-irradiation increased the molecular weight of calcium caseinate, while it changed little for the whey proteins. However, heating of the whey protein solution induced cross-linking. For both cross-linked proteins, the molecular weight distribution was >/=2 x 10(3) kDa. Combined thermal and radiative treatments were applied to protein formulations with various ratios of calcium caseinate and whey proteins. Whey protein isolate could replace up to 50% of calcium caseinate without decreasing the puncture strength of the films. Films based on commercial whey protein and calcium caseinate were weaker than those containing whey protein isolate. Electron microscopy showed that the mechanical characteristics of these films are closely related to their microstructures.  相似文献   

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