Effect of pH and temperature on the formation of volatile compounds in cysteine/reducing sugar/starch mixtures during extrusion cooking

Mixtures of cysteine, reducing sugar (xylose or glucose), and starch were extrusion cooked using feed pH values of 5.5, 6.5, and 7.5 and target die temperatures of 120, 150, and 180 degrees C. Volatile compounds were isolated by headspace trapping onto Tenax and analyzed by gas chromatography--mass spectrometry. Eighty and 38 compounds, respectively, were identified from extrudates prepared using glucose and xylose. Amounts of most compounds increased with temperature and pH. Aliphatic sulfur compounds, thiophenes, pyrazines, and thiazoles were the most abundant chemical classes for the glucose samples, whereas for xylose extrudates highest levels were obtained for non-sulfur-containing furans, thiophenes, sulfur-containing furans, and pyrazines. 2-Furanmethanethiol and 2-methyl-3-furanthiol were present in extrudates prepared using both sugars, but levels were higher in xylose samples. The profiles of reaction products were different from those obtained from aqueous or reduced-moisture systems based on cysteine and either glucose or ribose.     

Effect of Single‐Screw Extruder Die Temperature,Amount of Distillers' Dried Grains With Solubles (DDGS), and Initial Moisture Content on Extrudates

Corn distillers' dried grains with solubles (DDGS) was extruded with corn meal in a pilot plant single‐screw extruder at different extruder die temperatures (100, 120, and 150°C), levels of DDGS (0, 10, 20, and 30%) and initial moisture contents (11, 15, and 20% wb). In general, there was a decrease in water absorption index (WAI), water solubility index (WSI), radial expansion, and L* value with an increase in DDGS level, whereas a* value and bulk density increased. Increase in extruder die temperature resulted in an increase in WSI and WAI but a decrease in L* and bulk density. Peak load was highest at 30% DDGS as compared with 0, 10, and 20% DDGS extrudates. Die temperature of 120°C and initial moisture content of 20% resulted in least peak load. The a* value remained unaffected by changes in extruder die temperature. Radial expansion was highest at extruder die temperature of 120°C. Maximum WAI, WSI, radial expansion, and L* value were obtained at 15% initial moisture content. An increase in initial moisture content, in general, decreased L* value and bulk density but increased a* value of extrudates.     

Effect of Extrusion Cooking on Extractable Lipids and Fatty Acid Composition in Sifted Oat Flour

Sifted oat flour was processed at 25.0, 27.5, and 30.0% moisture content in a twin-screw extruder at screw speed 300 rpm. The preset temperatures of the extruder barrel were 120, 150, or 180°C. Raw material and extrudates were analyzed for the content of diethyl ether-extractable lipids, with and without hydrolysis, and the content of chloroformmethanol-water saturated butanol (C/M/WSB) extractable lipids. The lipid extracts were analyzed for fatty acid (FA) composition. Percentage distribution of palmitic, oleic, and linoleic acids were significantly different in the different lipid extracts. Extrusion processing influenced the amounts of extractable lipids, while FA composition was not affected.     

Effects of water content on volatile generation and peptide degradation in the maillard reaction of glycine, diglycine, and triglycine

Peptides abundant in food and protein hydrolysates are known to be important to process flavors. The present study reports the volatile profile of the Maillard reactions of glycine, diglycine, and triglycine. The reaction with glucose was conducted at 0-100% water content in glycerol medium at 160 degrees C for 1 h. Volatile compounds were quantified by stir bar sorptive extraction-gas chromatography-mass spectrometry, and nonvolatile compounds were quantified by high-performance liquid chromatography-tandem mass spectrometry. The major volatiles produced from each of the reaction systems were trimethylpyrazine and 2,5-dimethylpyrazine. Volatile generation increased as water decreased, and the overall reactivity of the glycine and glycine peptides in volatile formation was glycine approximately triglycine > diglycine. Triglycine was very unstable and mainly degraded into cyclic Gly-Gly and glycine, whereas diglycine had a higher stability than triglycine toward hydrolytic cleavage of the peptide bond. The amounts of glycine, diglycine, cyclic (Gly-Gly), and triglycine in the peptide-glucose reaction mixtures at different water content were reported.     

Sensory and instrumental analyses of volatiles generated during the extrusion cooking of oat flours

Three batches of oats were extruded under four combinations of process temperature (150 or 180 degrees C) and process moisture (14. 5 and 18%). Two of the extrudates were evaluated by a sensory panel, and three were analyzed by GC-MS. Maillard reaction products, such as pyrazines, pyrroles, furans, and sulfur-containing compounds, were found in the most severely processed extrudates (high-temperature, low-moisture). These extrudates were also described by the assessors as having toasted cereal attributes. Lipid degradation products, such as alkanals, 2-alkenals, and 2, 4-alkadienals, were found at much higher levels in the extrudates of the oat flour that had been debranned. It contained lower protein and fiber levels than the others and showed increased lipase activity. Extrudates from these samples also had significantly lower levels of Maillard reaction products that correlated, in the sensory analysis, with terms such as stale oil and oatmeal. Linoleic acid was added to a fourth oat flour to simulate the result of increased lipase activity, and GC-MS analysis showed both an increase in lipid degradation products and a decrease in Maillard reaction products.     

Effect of extrusion parameters on conjugated linoleic acids of corn extrudates

The effects of extrusion temperature, 150-190 degrees C, and torque, 50-70%, on the content and configuration of conjugated linoleic acids (CLA) in corn extrudates were analyzed by GC and HPLC. At a temperature of 150 degrees C, CLA content increased from 1.2 mg/g of oil in feed to 7.8 mg/g of oil in corn extrudates. A decrease in total CLA (P < 0.05) was obtained when the product temperature was further increased to 190 degrees C. Alteration of CLA geometrical configuration was observed at higher extrusion temperatures. trans,trans-CLA significantly increased (P < 0.05) from 10.2% in feed to 11.9% of CLA at the extrusion condition of 190 degrees C and 70% torque. The highest expansion of extrudates was found at the product temperature of 150 degrees C and 70% torque. This extrusion condition also gave the maximum total CLA content and minimum trans,trans-CLA formation.     

Extrusion of Regular and Waxy Barley Flours for Production of Expanded Cereals

Grains of two regular and two waxy barley cultivars were milled into break and reduction stream flours using a wheat milling mill, granulated to facilitate feeding and flow through the barrel, and extruded to form expanded products using a modified laboratory single‐screw extruder. As moisture content of barley granules decreased from 21 to 17%, the expansion index of extrudates increased from 1.81 to 2.68, while apparent modulus of compression work (AMCW) decreased from 17.1 × 10⁴ to 7.8 × 10⁴ N/m². Break stream flours of both regular and waxy barley produced extrudates with higher expansion index (2.72–3.02), higher water absorption index (WAI), and lower AMCW than extrudates from reduction stream flours. Extrudates produced from regular barley had generally higher expansion and lower density than those produced from waxy barley. The specific mechanical energy (SME) was greater during extrusion of regular than of waxy barley. Barrel temperatures of 130, 150, and 170°C for the feeding, compression, and metering sections, respectively, resulted in higher SME, higher expansion index, lower water absorption index and lower AMCW of extrudates compared with a constant extruder barrel temperature of 160°C. Increased screw speed generally resulted in larger expansion index and increased WAI of extrudates. With increased feed rate from 89 to 96 g/min, the expansion index of extrudates decreased from 3.20 to 2.78 in regular barley and 3.23 to 2.72 in waxy barley, and harder extrudates were produced.     

Effect of temperature and pH on the generation of flavor volatiles in extrusion cooking of wheat flour

Extrusion temperature (120, 135, and 150 degrees C) and quantity of added sodium hydroxide (0, 3, and 6 g/kg feedstock) were used as variables to study flavor generation in extrusion cooking of wheat flour. In total, 127 volatile components were identified in the extrudates, of which 51 contained sulfur. The levels of pyrroles, thiophenes, thiophenones, thiapyrans, and thiazolines increased at higher extrusion temperatures, whereas furans and aldehydes decreased. The addition of sodium hydroxide also affected the formation of volatile compounds. However, thiophenes, thiophenones, polythiacycloalkanes, thiazoles, thiazolines, pyrroles, and some pyrazines tended to increase with the more alkaline extrusion conditions. Some compounds from lipid-Maillard interactions were identified in the extrudates. Analysis of the volatile components by gas chromatography-olfactometry showed sulfur- and nitrogen-sulfur-containing heterocycles as possible contributors to the sulfury and rubbery odors observed in extrudates produced at the higher temperature and more alkaline conditions.     

Effects of Calcium Hydroxide and Processing Conditions on Corn Meal Extrudates

The effects of added calcium hydroxide (0.0, 0.15, 0.25, and 0.35%) and processing conditions, feed moisture content (mc) (16, 18, and 20%) and barrel temperature (130 and 150°C) on characteristics of corn meal extrudates were studied. Extruder screw speed was maintained at 130 rpm. Corn meal was extruded with a single-screw extruder (Brabender model GNF 1014/2) with a screw compression ratio of 3:1. The highest values (P < 0.05) for radial expansion and the lowest values for density and breaking force of extrudates were found for the treatment with 0.00% calcium hydroxide extruded at 16% feed mc and 130°C barrel temperature. This treatment was statistically different from the other treatments. Best values for radial expansion of samples extruded with added calcium hydroxide were for the samples with 0.15% calcium hydroxide at 18% feed mc and 130°C barrel temperature, followed by the sample with 0.35% calcium hydroxide at 16% feed mc and 130°C barrel temperature. Water absorption index and water solubility index were affected by calcium hydroxide and extrusion conditions evaluated. Extrudates had large numbers of flattened and sheared granules. Increases in calcium hydroxide increased extrudate yellowness. The combined action of calcium hydroxide and extrusion conditions completely modified the organized structure of the starch and suggest the formation of a starch-calcium complex (crystalline region). The texture of the extruded products was crispy after puffing.     

Physical Characteristics,Nutritional Quality,and Antioxidant Potential of Extrudates Produced with Polished Rice and Whole Red Bean Flours

In Brazil, rice (Oryza sativa L.) and beans (Phaseolus vulgaris L.) are the basis of the population's diet, and their consumption together is a good strategy to improve protein biological value. The aim of this study was to produce extruded products with whole red bean (WRBF) and polished rice (PRF) flours and to evaluate the effects of extrusion temperature (T) and feed moisture content (FM) on technological properties and total phenolic compounds content. The extrudates were elaborated in a twin‐screw extruder following a 2² central composite rotatable design with FM (15–23%) and T (120–160°C) as independent variables. WRBF and PRF were used at a 1:3 ratio. Amino acid content and profile were evaluated in the optimum extrudate (produced at FM = 19% and T = 140°C). The total phenolic content identified in extruded products was provided by the red bean seed coat, and its quantification suggested the release of bound phenolics with the extrusion process (not temperature dependent). The extrusion of PRF and WRBF, in combination, produced extruded products of high protein quality, being complete in essential amino acids for the diets of people at least 48 months old. The results indicate that legume flours such as WRBF incorporated into rice flour can cause a positive impact on technological, nutritional, and functional quality of extrudates.     

Degradation of the Amadori compound N-(1-deoxy-D-fructos-1-yl)glycine in aqueous model systems

The fate of the Amadori compound N-(1-deoxy-D-fructos-1-yl)glycine (DFG) was studied in aqueous model systems as a function of time and pH. The samples were reacted at 90 degrees C for up to 7 h while maintaining the pH constant at 5, 6, 7, or 8. Special attention was paid to the effect of phosphate on the formation of glycine and the parent sugars glucose and mannose, as well as formic and acetic acid. These compounds and DFG were quantified by high-performance anion-exchange chromatography. The rate of DFG degradation increased with pH. Addition of phosphate accelerated this reaction, particularly at pH 5-7. The rate of glycine formation increased with pH in both the absence and presence of phosphate. High glycine concentrations (60-70 mol %) were obtained, preferably at pH 6-8 with phosphate. However, the yield of glycine formed from DFG decreased at the advanced reaction stage for all pH values studied, both in water and in phosphate buffer. The rate of parent sugar formation increased from pH 5 to pH 7 in the absence of phosphate, leading to glucose and mannose in a constant ratio of 7:3. Addition of phosphate accelerated this reaction, yielding up to 18% parent sugars, most likely formed by reverse Amadori rearrangement. The formation rate of acetic and formic acid increased with increasing pH. The sum of both acids attained 76 mol %. However, the acetic acid concentrations were much higher than those of formic acid.     

Thermal degradation studies of glucose/glycine melanoidins

Nondialyzable and water-insoluble melanoidins, isolated from a glucose/glycine model reaction mixture, which was prepared in a standardized way according to the guidelines of the COST Action 919, were heated at different temperatures ranging from 100 to 300 degrees C. Among the volatile compounds, which were analyzed by SPME and GC-MS, pyrazines, pyridines, pyrroles, and furans were detected. In general, total amounts of volatile compounds increased with the temperature. When water-insoluble melanoidins were heated, especially at higher temperatures, this resulted in a higher diversity of isolated compounds. For furans, pyrroles, pyrazines, and carbonyl compounds a maximum was observed in the case of high molecular weight melanoidins around 200-220 degrees C. Pyridines and total oxazoles, however, were generated in higher yields with increasing temperatures. These results demonstrate the possibility of producing some flavor-significant volatiles from heated standard melanoidins at temperatures relevant to food preparation and contribute to the flavor aspects originating from melanoidins.     

Effect of Free Fatty Acids Addition on Corn Grits Extrusion Cooking

The influence of added fatty acids on extrusion cooking of corn grits and extrudate properties was studied. Samples with three average corn grits particle sizes were processed in a twin-screw extruder; fatty acids content (0.2–0.8%, wb) varied, and experimental conditions were kept constant (moisture content 18.4% wb, barrel temperature 150°C, screw speed 165 rpm). The effect of adding fatty acids was studied by analyzing water solubility and absorption indices, expansion indices, and mechanical (puncture test) and structural (computerized image analysis) extrudate properties. When fatty acids were added, water solubility and absorption indices decreased, radial expansion index decreased, longitudinal expansion index increased, number of cells increased, and mechanical resistance of extrudates decreased. The influence of added fatty acids was attributed to the formation of fatty acids-amylose complexes.     

Effects of Steam,Moisture, and Screw Speed on Physical Properties of DDGS‐Based Extrudates

A fractional factorial design with a replicated central composite point was used to investigate the effects of extrusion processing on physical properties of distillers dried grains with solubles (DDGS) based aquafeeds using a twin‐screw extruder. Extrusion cooking trials were performed with a nutritionally balanced ingredient blend for Nile tilapia, with two levels of screw speed (350 and 450 rpm), two levels of extruder water (0.236 and 0.302 kg/min), and two levels of conditioner steam (0.1 and 0.15 kg/min). The central point was 400 rpm screw speed, 0.271 kg/min extruder water, and 0.12 kg/min conditioner steam. Effects of these processing conditions on extrudate characteristics were extensively analyzed and included moisture content, water activity, thermal properties, expansion ratio, unit density, bulk density, color, water stability, sinking velocity, water absorption and solubility indices, and pellet durability index. Increasing the extruder water and conditioner steam resulted in a 5.3% decrease and nearly 8.6% rise in mass flow rate, respectively. As screw speed increased from 350 to 400 rpm, water stability and water activity increased by 13 and 58%, respectively. Increasing extruder water from 0.236 to 0.302 kg/min led to a significant increase in water stability by 12.5% and decreases in water absorption index, water activity, and expansion ratio by 13, 21, and 5.5%, respectively. As conditioner steam increased from 0.1 to 0.15 kg/min, sinking velocity and water absorption index decreased by 25 and 15%, respectively. Increasing conditioner steam from 0.1 to 0.12 kg/min resulted in 20, 5.5, 10, and 3% decreases in moisture content of the extrudates, brightness (L*), water stability, and expansion ratio, respectively. It also increased bulk density by 5.8% and unit density by 4.2%. Overall, all trials produced viable extrudates with properties appropriate for Nile tilapia feeding.     

Low-temperature alcoholic fermentation by delignified cellulosic material supported cells of kefir yeast.

A novel system for low-temperature alcoholic fermentation of glucose is described. This system consists of kefir yeast immobilized on delignified cellulosic materials. Batch fermentations were carried out at various pH values, and the effect of temperature on kinetic parameters, in the range of 5-30 degrees C, was examined. At pH 4.7 the shortest fermentation time was obtained. The formation of volatiles indicates that the concentration of amyl alcohols (total content of 2-methylbutanol-1 and 3-methylbutanol-1) is reduced as the temperature becomes lower. Propanol-1 and isobutyl alcohol formation drops significantly below 15 degrees C. The percentage of ethyl acetate increases as the temperature is diminished. At 5 degrees C the content of total volatiles in the product was only 38% of the volatiles formed during fermentation at 30 degrees C.     

Formation of 2,5-dimethyl-4-hydroxy-3(2H)-furanone through methylglyoxal: a Maillard reaction intermediate

The caramel-like aroma compound, 2,5-dimethyl-4-hydroxy-3(2H)-furanone (DMHF) was quantified and verified by HPLC and GC-MS in the Maillard reaction based on methylglyoxal (MG). The reaction was performed in the 0.5 M phosphate buffer by heating MG with or without either glycine or cysteine at 120 degrees C for 1 h. MG alone or MG with cysteine could produce increased level of DMHF with pH increased, whereas MG with glycine had contrary trend. Experiments using a 1:1 mixture of [(13)C6]glucose and [(12)C6]glucose indicate that in the presence of glycine or cysteine, glucose skeleton kept intact during DMHF formation since a 1:1 mixture of [(13)C6]DMHF and [(12)C6]DMHF was formed. Acetylformoin was detected in the glucose with amino acid reaction system as a precursor of DMHF, while in the MG reaction systems, acetylformoin could not be identified. It is suggested different pathways of DMHF formation via MG and glucose.     

Effect of added caffeic acid and tyrosol on the fatty acid and volatile profiles of camellia oil following heating

Camellia oil is widely used in some parts of the world partly because of its high oxidative stability. The effect of heating a refined camellia oil for 1 h at 120 degrees C or 2 h at 170 degrees C with exogenous antioxidant, namely, caffeic acid and tyrosol, was studied. Parameters used to assess the effect of heating were peroxide and K values, volatile formation, and fatty acid profile. Of these, volatile formation was the most sensitive index of change as seen in the number of volatiles and the total area count of volatiles in gas chromatograms. Hexanal was generally the dominant volatile in treated and untreated samples with a concentration of 2.13 and 5.34 mg kg(-1) in untreated oils heated at 120 and 170 degrees C, respectively. The hexanal content was significantly reduced in heated oils to which tyrosol and/or caffeic acid had been added. Using volatile formation as an index of oxidation, tyrosol was the more effective antioxidant of these compounds. This is contradictory to generally accepted antioxidant structure-activity relationships. Changes in fatty acid profiles after heating for up to 24 h at 180 degrees C were not significant.     

Effect of DDGS,Moisture Content,and Screw Speed on Physical Properties of Extrudates in Single‐Screw Extrusion

Three isocaloric (3.5 kcal/g) ingredient blends containing 20, 30, and 40% (wb) distillers dried grains with solubles (DDGS) along with soy flour, corn flour, fish meal, and mineral and vitamin mix, with net protein adjusted to 28% (wb) for all blends, were extruded in a single‐screw laboratory‐scale extruder at screw speeds of 100, 130, and 160 rpm, and 15, 20, and 25% (wb) moisture content. Increasing DDGS content from 20 to 40% resulted in a 37.1, 3.1, and 8.4% decrease in extrudate durability, specific gravity, and porosity, respectively, but a 7.5% increase in bulk density. Increasing screw speed from 100 to 160 rpm resulted in a 20.3 and 8.8% increase in durability and porosity, respectively, but a 12.9% decrease in bulk density. On the other hand, increasing the moisture content from 15 to 25% (wb) resulted in a 28.2% increase in durability, but an 8.3 and 8.5% decrease in specific gravity and porosity, respectively. Furthermore, increasing the screw speed and moisture content of the blends, respectively, resulted in an increase of 29.9 and 16.6% in extruder throughput. The extrudates containing 40% DDGS had 8.7% lower brightness, as well as 20.9 and 16.9% higher redness and yellowness, compared with the extrudates containing only 20% DDGS. Increasing the DDGS content from 20 to 40% resulted in a 52.9 and 51.4% increase in fiber and fat content, respectively, and a 7.2% decrease in nitrogen free extract. As demonstrated in this study, ingredient moisture content and screw speed are critical considerations when producing extrudates with ingredient blends containing DDGS, as they are with any other ingredients.     

Aging of whey protein films and the effect on mechanical and barrier properties

This work focuses on the aging of whey protein isolate (WPI) films plasticized with glycerol (G) and sorbitol (S). The films were cast from heated aqueous solutions at pH 7 and dried at 23 degrees C and 50% relative humidity (RH) for 16 h. They were stored in a climate room (23 degrees C, 50% RH) for 120 days, and the film properties were measured at regular intervals. The moisture content (MC) of the WPI/G films decreased from 22% (2 days) to 15% (45 days) and was thereafter constant at 15% (up to 120 days). This affected the mechanical properties and caused an increased stress at break (from 2.7 to 8.3 MPa), a decreased strain at break (from 33 to 4%), and an increased glass transition temperature (T(g)) (from -56 to -45 degrees C). The barrier properties were, however, unaffected, with constant water vapor permeability and a uniform film thickness. The MC of the WPI/S films was constant at approximately 9%, which gave no change in film properties.     

Water Solubility and Macromolecular Properties of Corn Meal Extrudates as Affected by Epichlorohydrin

Degermed corn meal adjusted to 18% moisture content (db) with epichlorohydrin (ECH) content at 0, 0.5, 1, or 2% (w/w) were extruded with a twin-screw laboratory extruder at a screw speed of 140 rpm. Compression and metering barrel zones were set at 100, 120, or 140°C. Water solubility (WS) of ground extrudates ranged from 7.6 ± 1.1% to 14.3 ± 1.3%. ECH content had a significant (P < 0.01) negative effect on WS, while barrel temperature and the interaction between barrel temperature and ECH content were not significant (P > 0.05). Presumably, ECH reduced WS of extrudates through cross-linking between hydroxyl groups on starch and protein molecules. Gel-permeation chromatography patterns for both 100 and 140°C barrel temperatures showed that high molecular weight carbohydrates in the extrudates decreased with increasing ECH content without a simultaneous increase in low molecular weight carbohydrates. This suggested that the decrease in high molecular weight fractions was due to insolubilization by cross-linking rather than degradation. SDS-PAGE revealed that two protein bands of ≈29 and 17.5 kDa disappeared, and a new band appeared at 45 kDa with increasing ECH content. This indicated that, most likely, ECH reacted with protein in addition to reacting with starch. However, glycoprotein and starch-protein complexes were not identified with electrophoresis.