EFFECT OF IMMATURE AND OFF-COLORED SEEDS ON THE LIPID QUALITY OF MILLED FLAXSEED

The effect of visibly inferior flaxseed ( Linum usitatissimum L.) on the lipid quality of milled flaxseed was investigated. Flaxseed was aspirated and separated into low-, medium- and high-density fractions. All density fractions contained ≤ 0.1% broken seed, ≤ 0.4% contrasting seed and ≤ 0.25% extraneous material. The low-density fraction contained the most immature (2.8%) and off-colored seed (4.1%). Immature seed had a lipid content of 40.8%, a peroxide value (PV) of 2.69 meq/kg and a free fatty acid (FFA) content of 1.06%. The off-colored seed had a lipid content of 38.1%, a PV of 5.79 meq/kg, and a FFA content of 1.89%. Hand-cleaned seed (averaged across fraction density) had a lipid content of 41.4%, a PV of 0.41 meq/kg and FFA content of 0.37%. The removal of seed defects improved flaxseed quality and improved lipid quality in the low-density fraction.

PRACTICAL APPLICATIONS

Lipid oxidation is a major concern when using milled flaxseed as a food ingredient. These results indicate the importance of removing off-colored and immature flaxseed. Seed lots that contain immature and off-colored seed likely will have poor lipid quality and, when milled, be more susceptible to lipid oxidation during storage than will seed lots free of immature and off-colored seed.     

EFFECTS OF SCREW RESTRICTIONS ON THE PERFORMANCE OF AN AUTOGENOUS EXTRUDER

The Brady Crop Cooker is a low-cost autogenous extruder capable of manufacturing products suitable for human consumption in less developed countries (LDC). Versatility is achieved by the design of the extruder which directly affects its operation. One such design aspect is the inclusion of internal screw channel restrictions. The effects of location and number of restrictions on operation and product quality were studied. Results indicated that restrictions affected the location of the mechanical energy input and therefore temperature profiles along the screw. Increasing the number of restrictions also promoted cleavage of starch molecules due to the resulting higher shear in the screw channel.     

EFFECT OF PRESSING ON MOISTURE LOSS AND SENSORY PROPERTIES OF BEEF

Paired halves of top round (Semimembranosus and Adductor muscles) sub-primals were removed from each of ten, USDA Choice, approximately 272 kg steers, freezer wrapped, frozen, and stored at -24° C for approximately 1 month. Following freeze-tempering, each primal was divided longitudinally with one half being pressed at 344 Newtons/cm² to a specified shape in a Bettcher Model 70 Press, while the other half served as nonpressed control. Moisture loss and sensory properties were determined for 2.54 cm thick steaks. No significant differences were found in juiciness, flavor or Kramer shear values between pressed and non-pressed top round steaks, however, sensory tenderness scores were lower (P < 0.05) for steaks that were pressed than for those that were not pressed. Holding steaks at 2° C for 0, 1, 2, or 3 days did not significantly alter Kramer shear or sensory panel evaluations. Cooking loss, drip loss and total loss were not affected by pressing. Drip loss was lower (P < 0.05) and cooking loss was higher (P < 0.05) for steaks held one day at 2° C than for steaks held 2 or 3 days at 2° C. When drip loss and cooking loss were combined (total loss) there was no difference among the four storage times. Drip loss following portion cutting could result in a problem in fresh merchandising of freeze-tempered cuts.     

EFFECT OF FLAXSEED GUM ON QUALITY AND STABILITY OF A MODEL SALAD DRESSING1

Flaxseed gum was evaluated for its application as a stabilizer for salad dressing. It was found that for stabilization to occur the concentration of gum had to be higher than 0.45% (w/w). Solvent quality affected the stability of model oil‐in‐water emulsions. Flaxseed gum stabilized emulsions were stable at pHs greater than 2.8. Lower values caused the polysaccharide to have a compact configuration or caused cleavage of the polymer creating instability. Larger mean droplet size and creaming were observed when the pH was too low or the gum concentration was not sufficient for coverage. Salt addition greatly affected the rheological properties of the polysaccharide; however, the electrolyte improved the emulsifying capabilities of the egg yolk protein. Aging weakened the polymer network structure as shown by a decrease in Newtonian viscosity with a corresponding increase in phase angle confirming the transformation to a more fluid system.     

STUDIES ON THE EFFECT OF SURFACTANT, BLANCHING AND OSMOTIC PRETREATMENTS ON THE CONVECTIVE DRYING OF POTATOES

Moisture removal from solids is an integral part of food processing. To approach the drying process of a given product it is necessary to have a knowledge of the drying kinetics. However, foodstuffs are often subjected to certain chemical and physical treatments, such as surfactant impregnation, osmotic dehydration or blanching, prior to convective drying. The drying behavior of potatoes was monitored within an experimental air tunnel dryer, with the mechanism of internal moisture migration being identified as diffusion. This was subsequently evaluated on the basis of the liquid diffusion theory. Experimental data revealed osmotic concentration as a favorable process. A 29±2% reduction in diffusion coefficient was observed following osmotic dehydration with a salt/sugar solution, however, this provided a 63±3% reduction in drying time. Structural modifications were induced by blanching, with this rendering a 10±1 and 27±2% lowering of the moisture transfer rate during drying at 30 and 60C, respectively.     

预处理脱除木质素的研究

通过比较预处理富含木质素原料的3种方法:酸法、稀碱和碱性H2O2预处理,得出碱性H2O2预处理玉米芯和棉籽壳木质素脱除率最高,且相对应的木聚糖含量也较高.     

THE EFFECT OF WORT pH ON COPPER FINING PERFORMANCE

Copper fining trials with ale and lager worts under conditions whereby the pH of wort was artificially manipulated prior to fining, demonstrated that the optimal copper fining rate decreased with increasing values of wort pH. Clarification of acidified worts (pH<4.5) was poor regardless of the rate of copper finings addition. These results suggest that the mechanism of fining action cannot be explained by a simple electrostatic model of interaction between positively charged groups present on wort poly-peptides (lysine, arginine and histidine) and negatively charged sulphonyl groups of carrageenan. Manipulation of wort pH may be exploited to ensure batch consistency in fining performance without the requirement for variation in the rate of addition of copper finings.     

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.     

EFFECT OF FRICTION ON THE PERFORMANCE OF TEXTURE TEST CELLS*

The relationship was measured between the normal contact force and the force required to overcome friction between food samples and a surface simulating a typical texture test cell. Peas produced frictional behavior that combined the characteristics of dry friction and fluid flow. Friction coefficients for selected foods ranged from 0.04 to 0.52. Friction force was linearly related to the normal contact force and non-linearly to the area of contact between the sample and the surface, and the speed of the sample relative to the surface. This verifies the fact that, with empirical texture test devices, these test variables must be held constant. The estimated friction forces represented a significant amount of the total force required to operate a wire extrusion cell and a back extrusion cell. It was concluded that standardization of the test cell would be easier to achieve if the contact area between the sample and the cell surfaces was minimized and if low friction materials were used to construct the cells.     

EFFECT OF PRETREATMENTS AND PROCESSING CONDITIONS ON THE CHEMICAL, PHYSICAL, MICROBIOLOGICAL AND SENSORY CHARACTERISTICS OF GARLIC PASTE

The influence of storage temperature of garlic bulb and chemical additives (including ascorbic acid, citric acid and potassium sorbate) on the chemical, physical, microbiological and sensory characteristics of garlic paste was evaluated. Formation of undesirable greenish pigment was avoided by storing fresh garlic bulbs at 25 and 40C. Moreover, heating bulbs to 40C a few minutes before processing facilitated skin removal. Garlic paste was processed, packed and thermally treated at 85C for 5 min. The color of garlic paste was affected by chemical treatment, temperature and storage period. The rate of color difference (ΔE) increase was divided into two linear periods with different slopes. Garlic paste exhibited pseudoplasticity with yield stress and flow adequately described by the Herschel–Bulkley model (r² > 0.990). Both consistency index and apparent viscosity decreased with increase in temperature.     

亚麻籽蛋糕的研制

研究了以亚麻籽粉和面粉为主要原料的营养蛋糕的研制，通过实验确定了亚麻籽蛋糕的最佳配方为：面粉95％，亚麻籽粉5％，糖100％，鸡蛋120％。     

EFFECT OF CELL SIZE ON THE PERFORMANCE OF THE SHEAR-COMPRESSION TEXTURE TEST CELL

Shear compression cells were manufactured to have dimensions 0.75, 0.5 and 0.25% that of the standard cell and used to test a range of foods. Maximum force and energy increased nonlinearly with increasing cell size and sample weight. The results demonstrate that cells of various sizes are practical for testing foods.
Friction in the cell is dependent on alignment of the cell components in the test machine. To obtain comparable readings the cell body must be oriented in the machine the same way for every test.