PUNCTURE TESTING OF TIOGA STRAWBERRIES*

Forces required to puncture firm ripe Tioga strawberries were dependent on the shape and physical dimensions of the punch used. They increased as the area, circumference or total contact surface area of the punch increased. The physical dimensions of the punch were responsible for 83 to 85% of variations in puncture forces. Punch circumference, punch area, and punch total contact surface area were equally effective in estimating the force required to puncture Tioga strawberries.     

聚丙烯酸酯浆料的酯基对混合浆相分离的影响

以初显分离时间和沉降率为量化指标，研究了酯基类型和含量、PVA类型、淀粉含量对混合浆相分离的影响。实验结果表明：酯基类型及数量对淀粉／PVA混合浆液的相分离行为有明显影响，BA链节有利于混合浆液的稳定性，而MA和MMA则能获取相对较低的相分离程度。随着BA含量的增加，混合浆的相分离速度减小，但相分离程度却有所增大。所介绍的几种聚丙烯酸酯浆料有助于降低淀粉与部分醇解型PVA混合浆液的相分离速度，不能改善淀粉与完全醇解型PVA混合浆的相分离速度。     

MEASURING HARDNESS DISTRIBUTION OF COOKED RICE BY SINGLE-GRAIN PUNCTURE

A 0.71-mm-diameter punch mounted in the Instron Universal Testing Machine was used to measure hardness of 100 individual grains of 15 rices after cooking. A hardness distribution curve for each rice was obtained. The puncture forces of rices cooked at a fixed water:rice weight ratio of 2 were more variable than those for rices cooked in excess water for the optimum cooking time. High- and intermediate-amylose rices cooked using a water:rice ratio of 2 were harder than corresponding rices cooked in excess water. For waxy and low-amylose rices, the reverse was generally true. Pairs of rices with almost identical physicochemical properties but which differed in preference tests by consumers also differed in their hardness distribution profile.     

聚丙烯酸丁酯共聚浆料的合成与浆液、浆膜性能

研究了对涤、棉纤维均有较好吸附性的新型浆料。采用乳液聚合法合成了聚丙烯酸丁酯共聚浆料,测试不同比例单体的浆液、浆膜性能,并与变性淀粉浆料比较,丙烯酸丁酯共聚交料浆膜的耐磨性、伸长率明显优于酸解淀粉。     

MECHANICAL PROPERTIES OF TOMATOES AS RELATED TO PUNCTURE INJURY SUSCEPTIBILITY

The relation between mechanical properties of tomato ( Lycopersicon esculentum Mill.) and puncture injury susceptibility was investigated using two cultivars: Tradiro, which is moderately resistant and Blitz, which is very susceptible. Mechanical properties were determined using a universal testing machine and an acoustic firmness sensor. The susceptibility to puncture injury was measured by a pendulum test. By means of Partial Least Squares analysis (PLS), a relationship with a coefficient of determination (R²) of 0.78 was found between the mechanical properties and the puncture injury susceptibility of the tomato cultivar. High loadings were found for the force required to puncture the tomato with and without skin, the elasticity of the fruit, the toughness of the skin and the acoustic firmness of the tomato fruit, indicating that these mechanical properties affect the susceptibility to puncture injury. The obtained results directly imply that these mechanical properties should be used to screen for genotypes with lower susceptibility to puncture injury.     

THE EFFECTS OF TURGOR PRESSURE ON PUNCTURE AND VISCOELASTIC PROPERTIES OF TOMATO TISSUE

The effects of turgor pressure on puncture and viscoelastic properties of mature-green tomato pericarp were examined using tissue discs soaked in a range of osmotica (0.0–0.6 M mannitol) for at least 36 h at 4C. Turgor pressure was estimated from the osmotic potential of soaking solutions that induced incipient plasmolysis. Based on volume changes, the osmotic potential and turgor pressure of fresh tissue were estimated to be −0.56 ± 0.08 MPa and 0.20 MPa, respectively. However, puncture and viscoelastic properties corresponded to a turgor pressure of 0.15 MPa. The discrepancy between calculated and actual turgor pressures was attributed to the presence of apoplastic solutes. The data from this study revealed a general increase in cell wall stress, strain and elasticity with increasing turgor. With increases in turgor above that of untreated tissue both wall extensibility and elasticity became limiting and thus cell wall stiffness increased. Conversely, a decrease in turgor below that of untreated tissue led to an increase in viscoelasticity. Increases in bioyield and pseudoplastic bioyield strains with a variation in turgor from that of untreated tissue were consistent with cell debonding as a dominant mechanism of tomato tissue bioyielding. The reduced failure force, deformation and firmness with increasing turgor were consistent with cell rupture as a predominant mechanism of failure of mature-green tomato pericarp tissue.     

TEXTURE MEASUREMENT OF INDIVIDUAL COOKED DRY BEANS BY THE PUNCTURE TEST

TEXTURE MEASUREMENT OF INDIVIDUAL COOKED DRY BEANS BY THE PUNCTURE TEST. M.C. BOURNE. J. Food Sci. 37, 751–753 (1972)-The Instron Universal Testing Machine was set up to puncture test a large number of cooked dry beans, one bean at a time, by using the distance cycling controls on the machine. The punch is caused to cycle between two preset distance limits at a predetermined speed, permitting the operator to devote full attention to placing and removing beans in the puncture cup. 10 beans per minute can be conveniently tested by this procedure. The number of peak force heights in 20 selected force ranges are counted off from the chart, making for rapid retrieval of data. Tests on cooked dry beans show that the number of beans in each texture range follows approximately a normal distribution pattern, except for the presence of a few exceptionally hard beans which cause the distribution curve to tail off into the high puncture-force range.     

ORAL SIZE PERCEPTION OF PARTICLES: EFFECT OF SIZE, TYPE, VISCOSITY AND METHOD

We investigated how different parameters affect oral size perception of small particles of SiO ₂ and polystyrene particles of varying sizes (2–230 μm). Eighteen healthy subjects assessed the size of the particles by rubbing the sample between the tongue and the palate. The importance of size and type were studied by direct scaling and forced choice ranking and the results of the two methods were compared. To assess the relative importance of the tongue and the palate in oral size perception topical anesthesia was applied. The size and characteristics of particles are of importance for perception of particle size, where hard and irregular particles are perceived as larger than soft and round particles of similar size. The two methods of size perception, direct scaling and forced ranking produce very similar results on oral size perception. Topical anesthesia of either the tongue or the palate had no significant effect.     

INFLUENCE OF THE SKIN ON PUNCTURE PROPERTIES OF CHILLED AND NONCHILLED TOMATO FRUIT

The puncture properties (firmness, toughness) of tomato skin and its influence on the overall puncture properties of mature-green fruit during ambient temperature (22C) ripening or chilled (5C) storage were estimated from the difference between whole fruit puncture force-deformation behaviour and that measured with the skin removed. Although the firmness of the skin of nonchilled fruit did not change significantly (p > 0.05) over 28 days of ripening, its contribution to overall puncture firmness increased from about 25 to 70%. Both skin toughness and its contribution to overall puncture toughness doubled within the first week of ripening of nonchilled fruit. The firmness of chilled fruit skin decreased (p > 0.05) only after 16 days of storage, but its contribution to overall puncture firmness remained constant at 25–30%. Both the toughness of the skin of chilled fruit and its contribution to overall puncture toughness remained constant during storage. Possible artifacts in the measurement of puncture properties of chilled fruit are discussed. The results are consistent with a toughening of tomato skin during early stages of ripening of nonchilled fruit that somewhat compensates for a rapid reduction in pericarp tissue integrity, and with an increase in firmness or rigidity of tomato skin and underlying tissue(s) during chilled storage of fruit.     

聚丙烯酸酯浆料在浆纱中的应用

提高T/C高支高密织物织造效率。以丙烯酸酯浆料对T/C高支高密纱及织物上浆,可增加纱线强度,提高织物上浆率、织造效率和一等品率,降低成本。     

INFLUENCE OF GRANULE SIZE ON VISCOSITY OF CORNSTARCH SUSPENSION

The influence of granule size and size distribution in gelatinized suspensions of 2.6% cornstarch heated at fixed temperatures between 70–90C on the power law viscosity was measured by laser diffraction. In the early stages of gelatinization, where the granule size standard deviation was less than 12 μm, dilatant behavior was observed over the shear rate range 200–1100 _S ⁻¹. At constant starch concentration and without granule rupture, suspension consistency, K, increased exponentially with granule mean diameter while the flow behavior index, n, decreased linearly with increase in the extent of gelatinization and the standard deviation of the granule size. The variation of K with granule size and that of n with standard deviation were found to be independent of temperature over 70–90C. In the later stages of gelatinization, where the granules lose their integrity, suspension viscosity progressively decreased as granule rupture continued.     

国外纺织浆料的研究与进展

介绍了国外研究得较多的接枝淀粉浆料和PVA的改性、回收利用、生物降解方面的进展，对聚酯浆料的研究也逐渐趋向成熟，并借鉴相关领域的先进技术在纺织经纱上浆方面也开展了许多工作．     

EFFECT OF PARTICLE SIZE AND SAMPLE SIZE ON LIPID STABILITY OF MILLED FLAXSEED (Linum usitatissimum L.)

Experiments were conducted to determine the effect of sample size and particle size on lipid oxidation of milled flaxseed. An initial experiment showed that most of the lipid oxidation detected in milled flaxseed samples occurred on the surface that was exposed to the air during storage. In a subsequent experiment, milled flaxseed at 100, 200 and 300 g were stored in the dark in rectangular pans for 8, 24 and 48 days at 50C. Lipid oxidation, as determined by surface lipid content, peroxide value and α-linolenic acid content, was lower in the 300 g samples than in the 100 g samples of milled flaxseed. Large versus small samples had less apparent lipid oxidation because of their inherently lower surface to volume ratio. In a third experiment, oxidation was lower in lipid extracted from coarse ( > 600 µm) than fine particles ( < 600 µm), after 48 days of storage.

PRACTICAL APPLICATIONS

This research has practical applications to the flaxseed milling and food industries. These results show that assessment of lipid oxidation in milled flaxseed needs to consider sample size (collection). Milled flaxseed oxidized predominantly at the sample surface where a polymerized layer of flaxseed particles formed over time. Relatively little oxidation occurred in the interior of the sample. Thus, sampling from the surface or interior of a milled flaxseed sample will end in different results and conclusions. Similarly, results will vary with surface : interior ratio of milled flaxseed. Food manufacturers may want to discard the top layer of milled flaxseed that has been exposed to air. Lipid oxidation was less with coarse than fine particles. Thus it would be prudent not to use milled flaxseed with a finer particle size than is necessary for acceptable end-use quality.     

凝聚法合成固态丙烯酸酯浆料

聚丙烯酸酯固态浆料可通过乳液凝聚方法制得，凝聚时溶液PH和凝聚试剂是工艺关键，而浆料高分子构成则是制固态浆料的本质性决定因素，适当的分子构成能使浆料既成固态，又成膜强韧，吸湿低，并保持该类浆料其他特性。     

ROLE OF GRANULE SIZE AND SIZE DISTRIBUTION IN THE VISCOSITY OF COWPEA STARCH DISPERSIONS HEATED IN EXCESS WATER

The role of granule size and size distribution, measured by laser diffraction, in affecting the flow behavior and yield stress of cowpea starch dispersions (2.6% w/w) heated for various time intervals at 67, 70, 75 and 80C was studied. Flow data on the dispersions at 20C were fitted to the power law flow equation. The standard deviation of the granules described the transition of flow behavior from shear thickening (dilatant) in the early stages of gelatinization to shear thinning (pseudoplastic) in the latter stages. It was an important variable for also correlating the critical shear rate, λ˙c, for the onset of shear thickening in starch dispersions. The granules swelled to a maximum of about 3.5 X raw starch granule mean diameter and a granule mass fraction of 65%. The consistency index of the dispersions increased with granule mean diameter.     

EFFECT OF SUBSTRATE SIZE ON THE ACTIVITY OF TOMATO POLYGALACTURONASE

SUMMARY— Three polygalacturonic acid preparations with widely differing molecular weight distributions were obtained by controlled enzymatic hydrolysis of pectic acid. A study of the action of tomato polygalacturonase on the polygalacturonic acids and pectic acid revealed that the activity h dependent on the molecular size of the substrate. Pectic acid was hydrolyzed optimally at pH 5, with little activity below pH 4. Decreasing the molecular weight of the substrate resulted in a progressive shift of the pH optimum to the acid side. For the smallest substrate, the activity extended to below pH 2. Monovalent cations enhanced the activity at low pH, and this effect was also dependent on the molecular weight of the substrate. Below pH 4, pectic acid inhibited 70% of the hydrolysis of low molecular weight substrates by tomato polygalacturonase. The incomplete inhibition is attributed to the presence of a polygalacturonase isoenzyme which is not inhibited by high molecular weight polygalacturonic acids.     

DELINEATION OF PUNCTURE FORCES FOR EXOCARP AND MESOCARP TISSUES IN CUCUMBER FRUIT 1

A puncture test was used to differentiate exocarp (skin) and mesocarp tissues of fresh cucumbers for resistance to penetration. Optimum instrumental test conditions were a punch size of 3.15 mm diameter and crosshead speed of 5 cm/min. The force required to penetrate the exocarp of whole fruit was determined and was deemed to represent a composite of the exocarp and the underlying tissue. By placing 7 mm thick, longitudinal slices skin down on a die plate, failure forces representing the mesocarp and exocarp tissues were determined in fruit ranging from 2.5–5.5 cm diameter. Exocarp force measurements were not influenced by slice thicknesses greater than 1 mm. Mesocarp measurements were lower with thicker slices, and required uniformity of thickness to maximize precision. The exocarp was found to represent about 60% of the composite force required to penetrate whole cucumbers, regardless of fruit size. Toughness of both exocarp and mesocarp increased with fruit size. The relative contributions of exocarp to penetration of seven other fruits varied from 58 to 88%.     

CHANGES IN SIZE OF GAS CELLS IN DOUGH AND BREAD DURING BREADMAKING AND CALCULATION OF CRITICAL SIZE OF GAS CELLS THAT EXPAND

Microscopic observation showed that a group of small air cells entrained during the early stage of mixing is the original cause of cell structure of bread. At the beginning of fermentation, about 3 × 10⁸/m² gas cells with diameters between 3 × 10⁻⁶ and 8 × 10⁻⁴ m were entrained in the dough. The distribution curve of cell size was approximately normal on a logarithmic scale. During fermentation and proofing, a great portion of carbon dioxide was released into cells larger than about 10⁻⁴ m in diameter that was equivalent to a few percentages of total number of gas cells. After baking, gas cells smaller than 10⁻⁴ m in diameter were not observed and the total number of cells in baked bread reduced to about 10⁶/m² with diameters between 10⁻⁴ and about 5 × 10⁻³ m. The critical cell size to expand generally agreed with the calculated value using an equation, rc'= 3s/E (re': critical radius to expand, s: surface tension, E: elasticity), and cited value of s and E.