MOISTURE MIGRATION IN A POTATO STARCH PATTY DURING POST-FRYING PERIOD

The change in crispness of the crust region of a fried food due to water migration was studied duringfrving and post-frying period. Moisture distribution was determined immediately after frying and at different times during storage. A restructured starch system consisting of potato starch and distilled water 16 was prepared in the shape of a patty. the moisture distribution in the patty was determined during fiying and post-frying period. Experiments were conducted for two dfferent flying times, 10 and 20 mm, using an oil temperature of 180G. Moisture distribution also was determined in patties fried for 10 mm and stored at 4C in a sealed container for 0.5, 3, and 4.5 h.
The experimental moisture profiles were compared with those obtained with a mathematical model, based on the one-dimensional heat and mass transfer in the core and crust regions of an infinite slab. Changes in the moisture content were correlated with changes in the mechanical properties of the crust during storage.     

LIMPNESS OF FRIED POTATO SLABS DURING POST-FRYING PERIOD

The rupture stress (RS) of fried potato slices (1.60 mm thick) and of the crust of fried potato slabs (FPS) having lengths of 60 mm and sides of 8, 10 and 12 mm, was determined during the post‐frying period by a puncture test. The RS of fried potato slices decreased as water activity increased from 0.22 to 0.85. The RS of FPS diminished in the first 5–6 min when exposed to ambient conditions and remained almost constant thereafter. A novel videotape technique and image analysis were used to follow deflection of FPS in the post‐frying period. An apparent modulus based on the composite structure of FPS and calculated from beam mechanics decreased with time in a trend similar to that of the textural parameters. We concluded that changes in physical properties of the crust because of moisture accumulation are the major causes of loss of texture (limpness) in FPS during the post‐frying period.     

玉米淀粉的粉体综合特性研究

利用现代高分子材料科学的研究方法和手段,了解玉米淀粉的粉体综合特性,同时初步探讨微观形态和宏观粉体性能的相关性.结果表明:不同筛目的玉米淀粉的分散度(Ds)随着筛子目数的增加,而逐渐的增加;玉米淀粉的松装密度(Pa)随着筛子目数的增加,而逐渐的增加;玉米淀粉的振实密度(Pp)随筛子目数的增加而增加;玉米淀粉在甲苯作溶剂时所测的粒径(D)比较小.     

PHYSICOCHEMICAL CHANGES IN STARCH DURING DEEP-FAT FRYING OF A MOLDED CORN STARCH PATTY

Corn starch patties with an initial moisture content of 46.5% (wet basis) were fried in oil at 165C. The results indicated that oil content in the patty ranged from 10.6 to 12.5% in the crust region, and 1.5 to 3.9% in the core region. Starch gelatinization was significantly dependent on frying time and location of starch in the patty. Both, water absorption and water solubility indices of starch increased with frying time, with the starch contained in the crust exhibiting much higher water absorption ability and water solubility than that contained in the core region. Measurements of 'blue value'(the intensity of blue color of starch solution upon addition of iodide ion) and the absorbance spectra of starch samples indicated that amylose-lipid complexes were present in the fried materials. The degree of starch complexation was 10.9 to 13.2% in the crust and 0.3 to 6.6% in the core region. The puncture force on the surface of a food fried for no more than 5 min was close to that in the food center, although a significant increase in force was required for the crust region during the later stages of frying.     

MECHANICAL PROPERTIES OF AN IMMERSION FRIED POTATO STARCH-GLUTEN GEL DURING POSTFRYING PERIOD

Moisture profiles in fried samples of potato starch with different gluten contents were determined during postfrying storage. Over time, moisture migrated from the core to the crust of the sample, and the moisture content of the crust region increased. The addition of gluten caused a significant increase in oil uptake in the crust. The initial hardness of the crust significantly decreased as the gluten content increased to 10 and 30%, during the first 30 min of storage. With longer storage time (> 240 min), the crust hardness tended to increase, due to an increase in firmness of the starch sample. This behavior was less pronounced for samples with 10 and 30% gluten. The range of linear viscoelastic behavior (up to 14% strain) was determined from the initial linear zone of the stress-strain curves. Stress relaxation tests were performed in the linear and nonlinear viscoelastic regions, with a strain level of 5% and 40%, respectively. According to stress relaxation curves, samples became less elastic with the addition of gluten and more elastic with the time of storage.     

FORMATION OF RESISTANT STARCH DURING DEEP-FAT FRYING AND ITS ROLE IN MODIFYING MECHANICAL PROPERTIES OF FRIED PATTIES CONTAINING CORN, RICE, WHEAT, OR POTATO STARCH AND WATER

Resistant starch (RS) was determined in patties (5.1 cm diameter, 1.27 cm high) prepared by mixing starch (corn, rice, wheat, or potato) in distilled water and immersion fried in canola oil (at 170 ± 3C). The RS content (expressed as % of total starch) in corn starch increased from 4.25 to 5.43% (±0.11) in the core region of a patty, whereas in the outer crust region the RS level was constant throughout the frying process. Similar trend was observed in potato, rice, and wheat starch patties. Upon varying the amylose content in the corn starch from 21 to 70%, the initial RS content (prior to frying) increased from 3.47 to 22.74 (±0.11%), following a linear relationship. Maximum force (MF) to puncture the crust of each starch patty was determined for frying duration of 3 to 15 min. Patties exhibiting higher RS content prior to frying, developed crusts with higher MF to puncture the crust, exhibiting a linear relationship between those two variables.     

THE EFFECTS OF FLAXSEED, SOY AND CORN FLOURS ON THE TEXTURAL AND SENSORY PROPERTIES OF A BAKERY PRODUCT

The objective of this study was to assess the effects of some healthy ingredients on the properties of a ring‐shaped bagel/pretzel‐type bakery product to offer an alternative product satisfying consumer demand. For this purpose, ground flaxseed, defatted soy flour and corn flour were blended at a weight basis with wheat flour at 5, 10 and 15%. The taste score decreased upon increasing the level of substitution of flaxseed, soy and corn flours. Samples containing 15% of flaxseed were rated poorest in taste. No significant difference was observed in crust color except 15% level of flaxseed. The control sample had highest crust color value. The crispness scores of control and other samples containing 5% corn flour were higher than that of other samples. The samples with 5% flaxseed flour had lower crust L values. Flaxseed, soy and corn flour showed significant effects on the hardness, cohesiveness, springiness, gumminess, fracture force and stiffness values (P < 0.05). Samples with 15% corn flour had the highest hardness value. The results of the present study suggest that flaxseed, soy and corn flours could be added to a typical snack formulation up to levels of 10% with a reasonable acceptance offering promising nutritious and healthy alternative to consumers.     

INFLUENCE OF FLAVORING ON THE VISCOELASTIC PROPERTIES OF STARCH GELS DURING GELATION AND LONG-TIME RETROGRADATION

The effect of three different aroma compounds on the texture of starch dispersions during gelation and retrogradation was studied. Oscillatory measurements were used to follow gelation and to check the structure of the starch dispersions after retrogradation up to 28 days. Rheological tests did not indicate any effect of the presence of any of the aroma compounds on the mechanism of gelation. During long‐time retrogradation, some added aroma compound did. We assume that this is a consequence of the ability of aroma compounds to form a complex or to show another type of interaction with starch molecules like entrapment in the amorphous regions of starch. Linalool is known to form complexes with amylase, but did not induce texture modifications, probably because, in our experiments, the added amount of this compound was too low. Isoamyl acetate, which according to literature interacts with amylopectin, exhibited a weak effect after 3 or 4 weeks, depending on the amount added. Octanal also increased gel stiffness after 3 weeks. This phenomenon is consistent with the observation that this aroma compound can form complexes with starch as demonstrated by X‐ray diffraction in this study.     

TRIAL METHOD FOR MEASURING THE EFFECT OF LIPIDS ON THE RHEOLOGICAL PROPERTIES OF STARCH PASTE DURING THE GELATION PROCESS

An attempt was made to measure the effect of lipid components on the viscosity and thixotropy of wheat starch paste in a short aging time after gelatinization. Viscometry was used to follow periodically the changes in apparent viscosity (at 76.8 s⁻¹) of the mixed paste of wheat starch and one of a series of lipids in a cone-plate viscometer for 210 min after gelatinization, i.e. a procedure of eight cycles of measurement with a sample. Each cycle of the measurement consisted of viscometry for 3 min and a rest period for 27 min at 30°C. The apparent viscosity of all the samples decreased greatly during the 3 min measurement due to thixotropic breakdown of the macroscopic structure in the samples. The results suggest that the presence of a small amount of free fatty acid and monoglyceride may play a role in reducing starch paste gelation.     

玉米淀粉磷酸单酯制备条件的优化

以玉米淀粉为原料,与混合磷酸盐作用,采用湿法工艺制备淀粉磷酸单酯.选取酯化剂用量、pH值、酯化反应温度、反应时间、催化剂用量5个因素为变量,以产物的取代度DS为试验指标,通过5因素2次正交旋转组合试验得出5因素与DS的关系,并在此基础上确定最佳的制备工艺条件：酯化剂用量30%,pH值6-6.5,反应温度130-140℃,反应时间2-2.5h,催化剂用量6%-7%.     

RHEOLOGICAL PROPERTIES OF HEATED CORN STARCH + SOYBEAN 7S AND 11S GLOBULIN DISPERSIONS

At 10% solids content, magnitudes of G' and G" of soybean 7S dispersion were substantially lower than those of corn starch dispersion, while those of soybean 11S dispersion were much higher than those of starch. Profiles of G' at 30 Hz as a function of starch concentration of starch + 7S and starch + 11S gels were asymmetrical reflecting phase separation due to thermodynamic incompatibility. However, the starch concentration corresponding to the critical point below which no phase separation occurs for the starch + 7S dispersion was about 7% and for the starch + 11S dispersion it was about 3%. At equal starch fractions, values of G' at 30 rad s^-1 of corn starch + 7S dispersions were nearly equal to those of only corn starch. In contrast, at starch concentrations between 6–8%, G' values of the corn starch + 11S dispersions were much higher than those of only starch and a minimum value occurred at a starch concentration of about 5%. Based on frequency dependence of G' values, heated corn starch + 7S dispersions may be classified as weak gels, while heated corn starch + 11S dispersions may be classified as true gels.     

蜡质马铃薯淀粉的性质及应用

蜡质马铃薯淀粉具有比普通马铃薯和蜡质玉米淀粉更为优良特性。具有糊化温度低、膨胀容易,糊化时吸水、保水力大,糊液的粘度很高、透明度非常好,平均粒径大、粒径大小分布范围广等独特性质,蜡质马铃薯淀粉在食品工业具有广泛应用前景。     

LIPIDS OF WHEAT, CORN AND POTATO STARCH

The lipid constituents from wheat, corn and potato starches were analyzed, as was the composition of nonstarch compounds present in these lipid extracts. The lipids were extracted from starch granules using n- propanol-water (3:1, v/v) via cold and hot extraction into surface and internal lipid fractions, respectively; fatty acid profiles of the fractions so obtained were then carried out. The content of surface lipids was greatest from potato and wheat starches, whereas cornstarch was characterized as having the highest relative percentage of internal lipids. Hot extraction resulted in an increase in the lipid content for all extracts, and of the starches investigated, the lipids from cornstarch contained the highest percentage of polyunsaturated fatty acids. Unlike that of wheat starch, it was noted that the fatty acid, C20: 1 (n-9), could only be extracted from corn and potato starch granules by the hot extraction technique. Lysophosphatidylcholine (LPC) and some phenolics were found to bind to wheat starch granules, but not to those of corn and potato. Using HPLC-UV-DAD analysis, five phenolic compounds were detected in the lipids extracted from wheat starch by hot extraction. Maxima from UV-DAD spectra of the compounds were observed at a wavelength of 337.4 or 332.7 nm, and are characteristic of phenolic acids or their derivatives.     

红薯微孔淀粉的制备及性质研究

以红薯淀粉为原料，探讨α-淀粉酶用量、反应温度、反应pH值和反应时间等因素对其微孔化反应的影响，并对微孔淀粉的吸水率、吸油率和X射线衍射以及扫描电子显微镜结构表征进行了研究。     

VISCOELASTIC BEHAVIOUR DURING THE GELATINIZATION OF STARCH II. EFFECTS OF EMULSIFIERS

The viscoelastic behaviour during the gelatinization of starch in the presence of emulsifiers was studied in oscillatory shear. Glycerol-monostearate and sodium stearoyl-lactylate delayed the viscoelustic changes during gelatinization in a way which was intetpreted as related to the granules being stiffer in presence of these emulsifiers. Sodium abdecyl sulphate caused a destabilization of the granules, resulting in the rheological changes occurring at lower temperatures. Emulsifiers increased the viscous part of the rheological response. In a wary-starch variety, where the amount of amylase is small, emulsifiers had only a small effect on gelatinization. It was concluded that the formation of an amylose-lipid complex was of importance if an emulsifier was to exert an effect.