APPLICATION OF AN IN-LINE RHEOLOGICAL CHARACTERIZATION METHOD TO CHEMICALLY MODIFIED AND NATIVE CORN STARCH

The application of an in‐line ultrasonics‐based rheological characterization method for measuring the rheological properties of 6% (w/v) acid‐thinned and native corn starch suspensions and gels was studied. The measurements were performed in steady, laminar pipe flow using a 5 MHz frequency transducer to determine the radial shear rate distribution. Two pressure transducers were used to measure the pressure drop allowing the shear stress distribution to be calculated through the conservation of linear momentum. It was possible to obtain shear viscosity over a range of shear rates, 1–50 1/s, from a single velocity profile. A comparison of the shear viscosity function at different flow rates showed that this method could be a valid method of process rheometry during the manufacturing of starch‐based products. Both ultrasonics and rotational rheometry results showed that acid‐thinned and native corn starch suspensions exhibited Newtonian behavior before heat treatment and non‐Newtonian behavior after heating. Power law consistency index and flow behavior index of the acid‐thinned corn starch gel at 39°C were 0.60 Pa.s ^0.68 and 0.68, respectively; whereas those of the native corn starch were 5.90 Pa.s ^0.37 and 0.37 at 38C. Their consistency index increased and flow behavior index decreased with cooling and a thermoreversible change in the flow behavior index was observed in the native corn starch after storage.     

RHEOLOGICAL BEHAVIOR AND TIME-DEPENDENT CHARACTERIZATION OF ICE CREAM MIX WITH DIFFERENT SALEP CONTENT

The effect of salep concentration on the rheological characteristics of ice cream mixes (0.5–1.5% salep content), prepared from nonfat cow's milk and sugar, was studied using a controlled stress rheometer. The flow curves and time‐dependent flow properties of the ice cream mixes were assessed at different temperatures. The ice cream mixes’ samples showed slightly thixotropic behavior, which was reduced as the salep content decreased. The forward and backward measurements of the flow curves of ice cream mixes were modeled with the power law model. The ice cream mixes showed pseudoplastic flow behavior after destruction of the thixotropic structure. In mixes that were first presheared at a high shear rate flow properties could also be described by the power law model. The second‐order structural kinetic, first‐order stress decay and Weltman models were applied to model the time‐dependent flow properties of the ice cream mixes. Among these, the first‐order stress decay model was found to fit well the experimental data.     

BRAZILIAN HULL-LESS AND MALTING BARLEY GENOTYPES: I. CHEMICAL COMPOSITION AND PARTIAL CHARACTERIZATION

Barley represents an important source of total dietary fiber (TDF) and β‐glucans. The chemical composition and partial characterization of two Brazilian barley experimental lines, hull‐less and malting, are reported. The range in diameter of the A‐ and B‐type granules was similar in both barley lines, 15 to 28 µm and 8 to 10 µm, respectively. Higher values for total starch, damage starch, ash, TDF and insoluble dietary fiber (IDF) were observed in the malting line while β‐glucan content was similar in both samples. The malting barley line had higher values of total isolated starch, as well as residual protein and total lipids in starch. The starch from the hull‐less barley line had lower swelling power and higher solubility than malting barley.     

干酪质地及流变学特性的研究进展

介绍了有关干酪的成分及工艺过程对质地和流变学特性影响的研究。在干酪成分中，蛋白质是影响产品流变学特性的主要因素，酪蛋白空间形成的网状结构构成了干酪流变学的基础。在加工过程中，pH、温度、钙浓度、蛋白水解等所有对干酪成分分子产生变化的因素都可能使干酪的流变学特性和质地发生变化。因此，干酪流变学特性的研究对更好地控制质地，生产出质优价廉的干酪，具有重要的意义。最后，研究状况进行了展望。     

HTCA—丙酮溶液流变行为与可纺性关系的研究

用气压式毛细管流变仪研究了高温法二醋酸纤维素（ＨＴＣＡ）—丙酮纺丝溶液的非牛顿指数ｎ，结构粘度指数△η和粘液活化能△Ｅη与可纺性的关系．结果表明，ｎ值的增大和△η的减小有利于改善ＨＴＣＡ—丙酮溶液的可纺性，但难以作为可纺与不可纺的判据．而△Ｅη能较好地表征ＨＵＣＡ—丙酮溶液的可纺性，△Ｅη值越高．流动性和可纺性越差，实验表明△Ｅη高于８０ＫＪ／ｍｏｌ时．其溶液不可纺．在ＨＴＣＡ—丙酮溶液中加入１０—１５％左右的助溶剂Ｄ，可提高丙酮的溶解能力，使ｎ值增大，△η和△Ｅη降低，从而改善了可纺性。     

CHEMICAL CHARACTERIZATION OF DIFFERENCES BETWEEN ALES AND LAGERS

The chemical identification of the substances responsible for differences between ales and lagers has been investigated, using new as well as established techniques. The two types of beer are broadly similar in composition, but lagers are characterized particularly by higher levels of certain sulphur compounds, and ales by higher levels of certain heterocyclic compounds. Several compounds have been identified for the first time as beer components.     

EFFECT OF ADDITIVES ON RHEOLOGICAL CHARACTERISTICS AND QUALITY OF WHEAT FLOUR PAROTTA

Effects of oxidizing agents (potassium bromate [20 and 40 ppm], ascorbic acid [100 and 200 ppm] and potassium iodate [20 and 40 ppm]), reducing agents (potassium metabisulphite [100 and 200 ppm] and cysteine hydrochloride [50 and 100 ppm]), enzymes (fungalα‐amylase [10 and 20 ppm] and protease [10 and 20 ppm]) and dry gluten powder (1, 2 and 3%) on rheological characteristics of dough and quality of parotta were studied. Addition of oxidizing agents and dry glutenincreased values for farinograph stability, extensograph and mixograph areas, apparent biaxial extensional viscosity, compressive stress, hardness and cohesiveness, while reducing agents and enzymes decreased the aforementioned characteristics and increased force decay parameter and adhesiveness of the dough. Among the different additives studied, incorporation of 100‐ppm potassium metabisulphite, 50‐ppm cysteine hydrochloride and 10‐ppm protease increased the overall quality score of parotta.     

EFFECT OF PROCESSING CONDITIONS ON THE COMPOSITION AND RHEOLOGICAL PROPERTIES OF APPLESAUCE

The relation between the composition and rheological properties of applesauce was studied in two ways. For artificial applesauces, reconstituted from isolated applesauce particles and applesauce serum, the residual shear stress increases exponentially with pulp content. Below a particle size of 0.625 mm the values of residual shear stress and apparent viscosity are lower for smaller particles. The effect of the processing conditions (finisher screen openings and cooking time) and raw material (apple variety and ripeness) on particle size and pulp content was studied on sauce made in a pilot plant. The particle size and pulp content of these applesauces affect the rheological properties in the same way as was shown for the artificial applesauces.     

RHEOLOGICAL CHARACTERIZATION OF ASEPTICALLY PACKAGED PUDDING

The flow behavior of commercially available, aseptically packaged vanilla pudding was measured using a Thermo Haake RheoStress rheometer (RS1, Thermo Electron Corporation, Waltham, MA) with a concentric cylinder system. Six different shear rates, ranging from 1 to 100/s, and three reasonable serving temperatures were investigated using constant shear rate tests. A time‐dependent, Herschel–Bulkley model characterized the thixotropic nature of pudding. The model's five parameters were related to temperature. The model was validated at three constant shear rates and at two different temperatures, and was found to predict viscosity well as a function of time, shear rate and temperature.     

MORPHOLOGY AND CHEMICAL COMPOSITION OF BARLEY ENDOSPERM CELL WALLS

Cell walls have been isolated from barley endosperm and found to contain a microfibrillar phase which is embedded in an amorphous matrix. The microfibrillar phase probably consists of cellulose, together with tightly bound arabinoxylan and polysaccharides rich in mannose. The matrix material is arabinoxylan (approx. 25%) and β-glucan (approx. 75%). Pectic polysaccharides are absent from the isolated cell walls. After successive removal of the matrix polysaccharides with water and 1-M NaOH, only 6% of the wall remains. The intra-cellular surfaces of the wall fragments are extensively pitted, probably as a result of adpression of starch granules into the cell wall material during endosperm development. Although polysaccharides are the major components of the cell walls, some nitrogen (less than 1%) is present. Phenolic compounds may also be wall constituents, but hydroxyproline could not be detected.