Enzyme Inactivation Improves Stability of Self-Rising Corn Meals

Enzymes affecting corn lipids were inactivated by adjusting whole dent corn to 15% moisture and gradually heating it to 91° or 96°C during passage through a two-stage steam-jacketed conveyer, followed by cooling. Heat-processed and untreated products were then milled by a four-break, 96% extraction procedure. Processed and untreated meals were formulated into self-rising meals and stored at 37°C for 6 months. Processed meal formulations were significantly (P < 0.05) more stable during storage than those from untreated meal as indicated by lower fat acidity values and greater carbon dioxide retention. Corn bread prepared from stored enzyme-inactivated meal had greater volume and maintained more uniform shape than that from stored untreated meal.     

Comparison of microwave irradiation and conventional thermal heating on volatile profiles and degree of oxidation in corn oil

Volatile profiles and degree of oxidation in corn oils after microwave treatment for 50 min were compared to oils with conventional heating at 180°C for 4 h. Oil microwaved for 10 and 50 min showed a similar degree of oxidation compared to the oil heated at 180°C for 1 and 3 h, respectively, based on the primary and secondary oxidation products. However, the total volatile contents of 50 min-microwaved oil were significantly lower than that of corn oil heated for 1 h at 180°C (P < 0.05). Microwave treatment accelerated the rates of lipid oxidation by 4.6 times compared to 180°C thermal oxidation. Relatively short treatment with microwave irradiation may not provide sufficient time to generate volatiles from oil. Microwaved corn oil for 50 min had higher contents of hexanal and t-2-heptenal and lower contents of 2,4-decadienal and nonanal than the oils heated at 180°C for 3 h. Reactive oxygen species may be involved in volatile formation in microwave-irradiated oils.     

Is flint corn naturally resistant to Sitophilus zeamais infestation?

Sitophilus zeamais (maize weevil) is one of the most destructive pests of maize stored in tropical and subtropical regions. This study determined the resistance of flint corn and dent corn to infestation by S. zeamais (Motschulsky), the maize weevil. Improved King Philip hybrid flint corn and Fontanelle 6T-510 hybrid dent corn were used in this experiment. Two temperature conditions (10 °C and 27 °C) and two storage times (15 days and 30 days) were used. Results showed that flint corn was more resistant to insect damage than dent corn at 27 °C and 30 day storage time. After 30 days storage time and 27 °C death rate was significantly higher in flint corn (R² = 0.945) compared to (R² = 0.634) in dent corn. Damaged seed was 10% higher in dent corn then in flint corn at 27 °C and 30 days. However, no significant difference was observed for seed weight loss between flint corn and dent corn at the same storage conditions. Both dent and flint corn were extensively cultivated in developing countries It appears that storage of flint corn may be one promising solution to reducing corn damage infestation problems in the tropics and in developing countries, but more research is needed.     

Reduction of Moniliformin in Corn by Heat Processing

The effects of autoclaving, baking, extrusion, frying, and roasting on the stability of moniliformin (MON) in spiked (5 μg/g of MON) corn‐based food products were investigated. Roasting corn meal at 218 °C for 15 min had the most significant effect (p ≤ 0.05) on the reduction of MON (44.6%). Autoclaving creamed corn at 121 °C for 65 min resulted in only 10% reduction of MON. Reductions of MON ranging from 5.4 to 28.9% were observed when corn chips were prepared from spiked masa. MON was reduced by 42.2% when corn muffins were baked and by 26.7% when corn grits were extruded. Overall, MON showed heat stability similar to or greater than other Fusarium mycotoxins such as deoxynivalenol and fumonisin B₁     

Physicochemical properties of whey protein conjugated with starch hydrolysis products of different dextrose equivalent values

Conjugation of whey protein with maltodextrin (MD) or corn syrup solids (CSS) having dextrose equivalent (DE) values in the range 6–38 was achieved by heating solutions of 5% whey protein isolate and 5% MD or CSS, initial pH 8.2, at 90 °C for up to 24 h. Maximum conjugation, with production of limited colour and advanced Maillard products was achieved after 8 h of heating. The extent of conjugation increased with increasing DE value of the MD and CSS ingredients. Conjugation increased whey protein solubility at pH 4.5 from 9% for whey protein heated alone to 24% for whey protein heated in the presence of CSS38 at 90 °C for 8 h. Conjugation of whey proteins with MD6 or CSS38 enhanced the stability to heating of protein solutions at 85 °C for 3 min with 50 mm added NaCl.     

Morphology of starch in surimi gels

 The purpose of this work was to study the changes undergone by starch during heat-induced surimi gel preparation either with or without added egg white, and their effects on the structure of gels using light and scanning electron microscopy. Gels were made from SA-grade Alaska pollack (Theragra chalcogramma) surimi with: (1) salt (3%, w/w); (2) salt and waxy corn starch (3% and 5%, respectively w/w); or (3) salt, waxy corn starch and egg white (3%, 5% and 5%, respectively, w/w). Final moisture was adjusted to 73% or 83%. The gels were prepared by prior setting (40°C, 30 min, followed by 90°C, 30 min) or cooking (90°C, 30 min). The prepared gel was frozen and stored at –20°C (±1°C) until analysis. Samples were observed by light and scanning electron microscopy. The results show that the starch granules alter according to the processing conditions, with the predominance of crystalline or amorphous morphology depending upon the availability of heat and water. Large cavities formed in the protein gel matrix during setting can trap water; as a result, water availability is limited for starch to swell and gelatinize even in the high-moisture gel. Received: 13 March 1997     

Antioxidative potential of melanoidins isolated from a roasted glucose–glycine model

The antioxidative activity of the total water soluble fraction (sol A), high molecular weight (HMW; MW>12,400 Dalton), low molecular weight (LMW) and the insoluble fraction (IS) of a glucose–glycine model system roasted at 120°C was studied in hydrophilic solutions (PBS buffer, fruit juices; addition: 0.01–0.1%) at ambient temperature and lipophilic (coconut fat, triolein and corn oil; addition: 0.01–0.5%) matrices at 60°C and frying conditions at 200°C. The hydrophilic reducing power in the water-soluble fractions was evaluated with the ABTS [2,2′-azino-bis(3-ethylbenz-thiazoline-6-sulfonic acid)] method. Fat stability was determined by observing the development of the peroxide value and conjugated dienes. All fractions increased the hydrophilic reducing power in the water-soluble fractions as a matter of concentration with highest effects for the 0.1% enrichment. In PBS buffer the HMW was most effective, in fruit juices the IS. A slight antioxidative effect in fats was observed only for 0.5% IS and 0.5% sol A in corn oil. Neither in coconut fat at 200°C nor in triolein at 60°C Maillard reaction products (MRPs) were able to extend shelf life. The results performed describe MRPs as highly antioxidative in water-soluble but less effective in water-insoluble fractions.     

Structural properties of protein-stabilized starch-based supercritical fluid extrudates

Supercritical fluid extrusion, a low temperature and low shear process, was used to produce pre-gelatinized corn and potato starch-based extrudates, containing 4–10% thermosetting egg white (EW) or whey protein concentrate (WPC-34), and dried at 22–100°C. Addition of proteins reduced shrinkage of high-moisture extrudates, as indicated by increases in expansion ratio by up to 140 and 341% when the drying temperatures were 22 and 100°C, respectively. Products containing 7% EW or WPC-34 and dried at 85°C expanded best while maintaining an intact structure, with expansion ratio (∼12) and bulk density (∼0.10 g/cm³) comparable to steam extrudates. The products had a unique composite and uniform microcellular structure, with average cell sizes in the range of 50-250 μm and cell density of the order of 10⁶ cells/cm³. The classical nucleation theory and a qualitative model for cell growth and shrinkage based on glass transition temperature were used to explain the microcellular structure.     

Effect of Temperature on Properties of Extrudates from High Starch Fractions of Navy, Pinto and Garbanzo Beans

High starch fraction (HSF) isolated from three legumes were extruded at different temperatures. Extruded products were evaluated for expansion, density, color and some functional properties. The highest value of expansion was noted for pinto bean, and the lowest for garbanzo, extruded at 132°C. Extrudates from HSF expanded significantly (P < 0.05) less than corn extrudates. Oil absorption capacity increased slightly with increasing temperature and values were lower for navy and garbanzo beans than for pinto HSF and corn. Oil emul-sification capacity of- bean samples was about two times higher compared to corn. Water absorption index (WAI) of pinto and navy beans significantly increased (P < 0.05) from 110°C to 132°C.     

Minor Strecker degradation products of phenylalanine and phenylglycine

Phenylalanine (Phe) was oxidized with either potassium peroxodisulfate or glyoxal. Volatile reaction products were isolated and analyzed by GC/FID and GC/MS. Nonvolatile products were derivatized with diazomethane and analyzed by the same methods. Under the experimental reaction conditions (equimolar ratio of reactants, 100vv°C, 1 h), the decomposed amount of amino acid was 28% (glyoxal) and to 74% (peroxodisulfate), respectively. Sixteen volatile compounds having their origin in the amino acid molecule were detected and identified. The major compound was phenylacetaldehyde (208 mg/peroxodisulfate, 11 mg/glyoxal), followed by bibenzyl, benzaldehyde, and benzyl alcohol. Other products were present in concentrations lower then 0.1 mg. For comparison, the lower homologue of Phe, phenylglycine, was oxidized under the same conditions. Analogously, 21% (glyoxal) and 65% (peroxodisulfate) of this amino acid decomposed, predominantly to benzaldehyde (242 mg/peroxodisulfate, 95 mg/glyoxal). A minor decomposition product was benzoic acid (2.9 mg), other ten products arose at levels lower then 0.1 mg. The formation of minor oxidation products during Strecker degradation of amino acids suggests the importance of radical reactions. In systems comprising glyoxal, ten heterocyclic compounds arose as minor products (3-furancarbaldehyde, 5-methyl-2-furancarbaldehyde, 2-pyrrolcarbaldehyde, 3-phenylpyridine, pyrazine, methyl-, ethyl-, vinyl-, and 2-phenylethylpyrazine).     

Gelatinization and Liquefaction of Starch with a Heat Stable α-Amylase

Sweet potato and corn starches were gelatinized and liquefied to dextrose equivalent (DE) 10 in a steam-jacketed kettle or in a twin-screw extrusion cooker in a single step process with a heat stable ex-amylase. The time required to gelatinize and liquefy 20% starch slurries in a kettle at 95°C was 45 to 50 sec. Starch powder (10 kg/hr) and water (2-6 kg/hr) were fed to an extrusion cooker to adjust the moisture contents of the starch from 20 to 55% (wet basis) and gelatinized and liquefied to DE 10 at a barrel temperature of 120°C or above with 2 to 3% (w/w) a-amylase added. The optimum conditions for the operation were to feed starch with water to maintain 50% moisture and 2% heat stable a-amylase at a barrel temperature of 120°C.     

Kinetics of Starch Gelatinization During Extrusion Cooking

Ordinary corn (30% amylose) and waxy corn (1% amylose) were extruded at 17.8, 20, 30, 40 and 42.2% product moisture contents (d.b.) and extruder barrel temperatures of 116°, 120°, 140°, 160° and 164°C. Screw speeds of 93.5, 100, 130, 160 and 166.5 rpm were used to generate different residence times. The extruded products were evaluated for extent of starch gelatinization. Results indicate that the degree of gelatinization decreased with increasing moisture content but increased with increasing temperature. Starch gelatinization exhibited pseudo-zero-order reaction kinetics with higher rate constants for waxy corn than for high amylose corn. The rate constants decreased with decreasing temperature.     

Effects of Prolonged and Adverse Storage Conditions on Levels of Cholesterol Oxidation Products in Dairy Products

The effects of normal and adverse environmental holding conditions on the formation of cholesterol oxidation products (COPS) in powdered cheeses and salted and unsalted butteroil were investigated. Little or no change in COPS levels was noted in a variety of powdered dairy products stored at 4, 21, or 38°C for up to 6 months. Storage for 18 mo at 4°C resulted in a three-fold increase in the levels of COPS. Cheddar cheese powder continuously exposed to light (1611 lx) displayed increases in α-epoxide and 7-ketocholesterol through week 3, thereafter declining to a level at week 9 of about one-half of that seen at week 3. Continuous heating of butteroil (110°C) caused large increases in COPS' levels, with unsalted butteroil exceeding levels found in salted butteroil by 2- to 3-fold.     

Amylo-Oligosaccharide Formation from B. stearothermophilus α-Amylase Action on Starches

The action of α-amylase from Bacillus stearothermophilus on starches is distinguished by early dominant quantities of maltohexaose (DP₆), followed by its erosion and increases in amylo-oligosaccharides with various degrees of polymerization (DP): maltose (DP₂), maltotriose (DP₃) and maltopentose (DP₅). Amylolysis of the starches at high substrate concentrations (20-30%) and elevated temperature (95°C) gave yields of 11–31% maltohexaose in the hydrolysate compositions. The a-amylolysis of jet-cooked ordinary, waxy and high-amylose corn starches is greater with the high-amylose starch than with the starches containing increasing quantities of amylopectin. Starch derivatives with hydroxypropyl groups greatly reduced amylolysis, but these groups did not alter the action patterns.     

Some Characteristics of Whole Corn: Whole Soybean (70:30) and Rice: Whole Soybean (70:30) Mixtures Processed by Simple Extrusion Cooking

Mixtures of corn or rice with dehulled soybeans (70:30) were extruded at three cone openings. Processing temperatures were inversely correlated with cone opening. As cone opening increased fat retention and nitrogen solubility index increased, while dispersibility, protein nutritive value and acceptability (as “atole”) by school children decreased. The PER and NPR of the mixtures were significantly (P < 0.05) correlated with processing temperature (r = 0.90 for both) and sensory score (r = 0.83 and 0.82, respectively). No correlation was observed between protein nutritive value and residual antiphysiological factors of the products. After storage of mixtures for 12 wk at 4° and 25° C, fat acidity values were lower than 2%; those stored at 35°C showed nearly 10%. All samples were equally acceptable.     

Effect of a Di-Thermal Storage Regime on Quality and Nutritional Changes and Energy Consumption of Frozen Boxed Beef

Seven types of beef products were commercially packaged, frozen, and stored at top corner pallet positions in three rooms for a year. The storage temperatures were: (1) -23°C, constant; (2) -23°C and -21°C; (3) -21°C and -18°C. Compared to the -23°C, constant room (as reference), a net energy saving of 6 and 14% was obtained for the two di-thermal storage rooms by maintaining the temperatures at the lower levels for one 12-hr period followed by the higher levels for another 12-hr period. The weight loss for most products was negligible, except for bulk-packed hamburger patties which lost over 1%. The results on sensory, nutritional, and other quality attributes of frozen boxed beef products showed no serious quality damage from both constant and di-thermal storage after 1 yr, except for MPB and beef patties whose practical shelf life was limited to 6 months.     

Low‐ and Medium‐DE Maltodextrins From Waxy Wheat Starch: Preparation and Properties

The goal of the research was to prepare maltodextrins (MD) from waxy wheat starch and waxy corn starch (control). Waxy wheat starches with 0.2% protein, 0.2% lipid and ∼1% amylose were isolated from two flours by mixing a dough, dispersing the dough in excess water, and separating the starch and gluten from the resultant dispersion. The mean recoveries were 72% for the starches and 76% for the gluten fraction with 80% protein. Maltodextrins having low‐dextrose equivalence (DE) 1—2 and mid‐DE 9—10 were prepared by treatment of 15% slurries of waxy wheat starch and waxy corn starch at 95 °C for 5—10 min and 20—50 min, respectively, with a heat‐stable α‐amylase. Denaturing the enzyme and spray‐drying produced MD's with bulk densities of 0.3 g/cm ³. The powdery MD's were subjected to an accelerated‐rancidity development test at 60 °C, and an off‐odor was detected after 2 days storage for the low‐DE MD's from the two waxy wheat starches (WxWS₁‐MD 1.2 and WxWS₂‐MD 1.5), but not for the low‐DE waxy corn maltodextrin (WxCS‐MD 2.2) or a commercial waxy corn MD with DE 1. None of the mid‐DE 9—10 MD's developed off‐odor after 30 days storage at 60 °C. The experimental products WxWS₁‐MD 9.2, WxWS₂‐MD 9.9 and WxCS‐MD 9.1 showed high water‐solubility and gave 1—10% aqueous solutions of high clarity with no clouding upon cooling.     

Physiochemical Properties and Probiotic Survivability of Symbiotic Corn‐Based Yogurt‐Like Product

Corn is a major grain produced in northern China. Corn‐based functional food products are very limited. In this study, a symbiotic corn‐based yogurt‐like product was developed. Corn milk was prepared through grinding, extrusion and milling, and hydration processes. Corn extrudate was prepared under the optimized conditions of corn flour particle size <180 μm, moisture content of 15% and extrusion temperature at 130 °C. The corn milk was prepared from 8% corn extrudate suspension and then milled twice with 0.1% glyceryl monostearate and 0.1% sucrose ester as emulsifiers. The corn milk was mixed with sugar (5%), glucose (2%), soy protein isolate (0.75%), inulin (1%), polymerized whey protein (0.3%) and xanthan gum (0.09%) as thickening agents. The mixture was fermented at 35 °C for 6 h using a probiotic starter culture containing L. plantarum. Chemical composition (%) of the symbiotic corn‐based yogurt‐like product was: total solids (17.13 ± 0.31), protein (1.12 ± 0.03), fat (0.30 ± 0.05), carbohydrates (15.14 ± 0.19), and ash (0.16 ± 0.02), respectively. pH value of this symbiotic product decreased from 4.50 ± 0.03 to 3.88 ± 0.13 and the population of L. plantarum declined from 7.8 ± 0.09 to 7.1 ± 0.14 log CFU/mL during storage at 4 °C. SDS‐PAGE analysis showed that there were no changes in protein profile during storage. Texture and consistency were also stable during the period of this study. It can be concluded that a set‐type corn‐based symbiotic yogurt‐like product with good texture and stability was successfully developed that would be a good alternative to the dairy yogurt.     

Characteristics of mince from pond-bred silvercarp (Hypophthalmichthys molitrix) and preliminary experiments on its use in sausages

The quality of fresh, chilled and frozen mince made from the flesh of pond-bred silvercarp (Hypophthalmichthys molitrix (Val)) was evaluated. Flavour panel scores for all minces were acceptable and this quality did not deteriorate during storage for one week in a domestic refrigerator (5–6°C) or for one year at ?20°C. The levels of oxidative rancidity (2-thiobarbituric acid analysis) in the minces were consistent with this maintenance of quality. Aerobic plate counts at 25°C of fresh mince rose from 7–9 × 10⁴ to 1.1 × 10⁵ after 6 days' storage at 5–6°C. Coliform and psychrotroph counts rose from 1.0 × 10¹ and 7–8 × 10³ to 5–4 × 10² and 1.3 × 10⁴, respectively. The functional and textural properties of pond-bred silvercarp mince in terms of salt-soluble protein content, water binding capacity and penetrometer values were measured on fresh, refrigerated and frozen samples. All-fish sausages and frankfurters developed from pond-bred silvercarp mince were assessed in laboratory and consumer tests against commercial beef sausages and frankfurters. The fish products competed well and achieved levels of acceptance similar to those of the beef-containing products. Texture measurements revealed slight changes in the fish products during storage for 7 days at 5–6°C. No spoilage was detected in any of the products after a week at 5–6°C. The nutritional advantages of the fish sausages and frankfurters are discussed.     

Cationization of Waxy and Normal Corn and Barley Starches by an Aqueous Alcohol Process

When an aqueous alcoholic-alkaline solvent was used, cationization of normal and waxy corn and barley starches was achieved with high degrees of substitution (DS) and reaction efficiency (RE) in the absence of gelatinization inhibitor salts. Ethanol was a more effective solvent than methanol or 2-propanol, and alcohol concentrations could vary between 35–65%. Maintaining a starch to water ratio of 1:1 (w/w) was critical, but DS values were proportional to the concentration of cationic reagent, 3-chloro-2-hydroxypropyltrimethylammonium chloride. At 50°C, cationization was essentially complete within 6h but nearly the same DS could be achieved in 1h at 70°C.