Antioxidant activity of barley as affected by extrusion cooking

Grit from different hulled barley cultivars was subjected to extrusion cooking and the effect of extrusion moisture and temperature on the antioxidant properties was studied. A significant decrease in the total phenolic content (TPC) and total flavonoid content (TFC) was observed upon extrusion and a further decrease of 8-29% in TPC and 13-27% in TFC was observed when both the feed moisture and extrusion temperature were increased. The antioxidant activity (AOA) increased significantly upon extrusion and this increase was the highest (36-69%) at 150 °C and 20% feed moisture. The increase in feed moisture and temperature significantly increased the metal chelating activity. The reducing power decreased significantly upon extrusion as compared to their corresponding control samples. Extrusion lead to a greater increase in non-enzymatic browning (NEB) index however, increasing the moisture content of feed decreased the NEB index by 3-29% (at 180 °C) and 1-17% (150 °C), while increasing the temperature increased the NEB significantly.     

Antioxidant properties of tomato juice as affected by heating

The changes in the overall antioxidant properties of tomato juice samples and model solutions as a consequence of heat treatments were studied. The antioxidant properties were evaluated both through the measurement of the chain breaking and the oxygen scavenging activities. While a decrease in the antioxidant potential was found for short heat treatments, a recovery of these properties was measured by prolonging heating times. Results suggested that the initial reduction in the overall antioxidant activity can be attributed not only to the thermal degradation of naturally occurring antioxidants but also to the formation of early Maillard reaction products (MRP) with pro‐oxidant properties. The gain in antioxidant activity coincided with the formation of brown MRP. © 1999 Society of Chemical Industry     

Carotenoid concentrations of native Andean potatoes as affected by cooking

The effect of boiling on the concentrations of total and individual carotenoids was determined by spectrophotometry and HPLC, in a group of native Andean potato accessions with diverse intensities of yellow flesh colours. Changes in concentrations due to boiling varied significantly among accessions. Boiling significantly reduced the violaxanthin and antheraxanthin concentration of all the accessions. However, the lutein and zeaxanthin concentrations of boiled tubers were not affected or were higher than the concentrations in raw tubers. The intermediate yellow fleshed accession 701862 showed the highest lutein concentration (above 200 μg/100 g, FW) and the deep yellow fleshed accession 704218 showed the highest concentration of zeaxanthin (above 1000 μg/100 g, FW) in raw and boiled tubers. Boiled potatoes of deep yellow fleshed varieties are a significant source of zeaxanthin (above 500 μg per 100 g fresh weight basis).     

Antioxidant properties of tartary buckwheat extracts as affected by different thermal processing methods

The effects of roasting, pressured-steam heating and microwave heating on total phenolics, total flavonoids, and antioxidant properties of whole-meal flour from tartary buckwheat (Fagopyrum tataricum Gaertn.) were investigated. The total phenolics were evaluated by Folin-Ciocalteau assay, total flavonoids by aluminum nitrate colorimetric assay whilst antioxidant properties were based on free radical scavenging activity of flour extracts against hydroxyl and superoxide anion radicals, and inhibition of lipid peroxidation in vitro. This study showed that thermal treatment of buckwheat flour caused a decrease in total phenolics, total flavonoids and antioxidative activities. The changes in trend of the antioxidant activities due to the thermal treatment were positively correlated with the content of phenolics (R² = 0.8401-0.9909). Therefore, it can be suggested that special care should be taken when processing method is selected for the exploration of tartary buckwheat products.     

Lipid oxidation in chicken as affected by cooking and frozen storage

Oxidative rancidity in fresh, frozen and cooked chicken breast and leg meat was evaluated by measuring malondialdehyde (MDA) in fat from meat with an improved 2-thiobarbituric acid (TBA) assay with antioxidant protection, and by measuring the relative fluorescent products of organic and aqueous layers from Folch extracted meat. Fresh samples were frozen for 3 and 6 months at ?18 °C and cooked in convection and microwave ovens. Frozen storage for 3 and 6 months either before cooking or after convection and microwave cooking substantially increased MDA concentrations in fat from meat, whereas cooking was more effective in generating fluorescent products. There were no significant differences in free MDA concentrations or TBA numbers in chicken meat between convection and microwave cooking methods. The certain secondary fluorescent products were significantly higher in meat cooked by convection oven. The initial levels of either MDA or fluorescent products in meat are of primary importance in determining the final MDA and fluorescence levels after processing.     

Steroidal glycoalkaloids in potato foods as affected by cooking methods

Potato and its products have become indispensable foods and snacks for most people. Steroidal glycoalkaloids (SGAs) occur in all tissues of the potato, and consuming potatoes with a high SGA content harms human health. Therefore, the effects of different cooking methods on the SGA content in potato foods were investigated in this study. The results indicated that adding food-grade acetic acid during the manufacturing process did not affect the SGA content in stir-fried shredded potatoes or fresh mashed potatoes. However, the SGA content in potato food after peeling was significantly lower than that in non-peeled food, and the volume ratio of potato skin to flesh decreased with the increase of the potato tuber volume. Therefore, potato breeders and farmers should make the most hard to increase the proportion of commodity potato via corresponding science and technology. In addition, frying significantly reduced the SGA content in potato chips. Further research indicated that SGAs degraded slowly at 150°C, while they degraded rapidly at 190°C within 30 min. The temperature of rapeseed oil in the frying process can be as high above 200°C. Thus, frying significantly decreased the SGA content in potato chips, which could be attributed to temperature. These results will provide a theoretical basis and practical guidance for potato breeding and cooking.     

Antioxidant properties of Phyllanthus amarus extracts as affected by different drying methods

The total phenolic content (TPC) and antioxidant activity of fresh and dried Phyllanthus amarus plant materials were evaluated using the Folin-Ciocalteau method, 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging activity and ferric reducing antioxidant power (FRAP) assays. Different drying treatments led to significant reduction (P<0.05) in antioxidant properties of P. amarus methanolic extracts, with microwave drying causing the highest decrease in TPC and antioxidant activity exhibited by the reduction in both radical scavenging activity and FRAP. On the other hand, boiling water extracts appeared to exhibit significantly stronger antioxidant potentials (P<0.05) even in dried plant materials due to greater solubility of compounds, breakdown of cellular constituents as well as hydrolysis of tannins. Its strong free radical scavenging activity suggests that it has great potential in the food industry as functional food ingredient.     

Antioxidant properties of some commonly consumed and underutilized tropical legumes

The antioxidant properties of some commonly consumed [cowpea (Vigna unguiculata)] and underutilized [pigeon pea (Cajanus cajan) and African yam bean (Sphenostylis sternocarpa)] legumes were assessed with regard to their Vitamin C, total phenol, and phytate content, as well as antioxidant activity as typified by their reducing power and free radical scavenging ability. The Vitamin C content of the cowpeas ranged from 0.5 to 0.9 mg/100 g, while that of underutilized legumes were 0.9 mg/100 g for pigeon pea and 0.8 mg/100 g for African yam beans. The phenol content of the cowpeas were 0.3–1.0 mg/g, African yam bean had 0.7 mg/g total phenols, while pigeon pea contained 0.4 (white) and 1.2 mg/g (brown) total phenol content, respectively. The phytate content of all the legumes [cowpea (2.0–2.9%), pigeon pea (2.0–2.4%), African yam beans (2.4%)] analyzed were generally high, while the reducing power and free radical scavenging ability for all the legumes were very low except in African yam beans (23.6%), cowpea brown (29.9%), and pigeon pea brown (54.5%) that had a relatively high free radical scavenging ability. Therefore, one of the commonly consumed cowpea V. unguiculata (brown) and underutilized legumes C. cajan (brown) and S. sternocarpa could be considered as a functional food due to their relatively higher antioxidant activity (free radical scavenging ability and redox potential) which could be as a result of their relative higher total phenol content.     

Dietary fiber profile of barley flour as affected by extrusion cooking

Barley grains, Phoenix and CDC-Candle, were extruded in a twin-screw extruder at 90−140 °C and 20–50% moisture level. Effects of extrusion conditions on total (TDF), soluble (SDF), and insoluble dietary fiber (IDF) were determined. The content of SDF and TDF increased upon extrusion cooking of both types of barley flours. The changes in IDF content were found to be variety-dependent. Only a minor decrease in IDF content of CDC-Candle barley was found, but an increase in IDF content of Phoenix was observed at all extrusion temperatures. The increase in SDF, in both barleys, could be due to the transformation of some IDF into SDF during extrusion and the formation of additional SDF by transglycosidation. The increase in IDF in Phoenix flour could be due to the formation of retrograded amylose [resistant starch (RS3)] during extrusion cooking and subsequent cooling.     

Polyphenols of chickpea and blackgram as affected by domestic processing and cooking methods

The effects of soaking, cooking, autoclaving and sprouting on the polyphenol contents of eight cultivars of chickpea (Cicer arietinum) and four of blackgram (Vigna mungo) were studied. All the treatments reduced the polyphenols of the legume seeds, but to a varying extent. Sprouting and autoclaving had the most pronounced effect; ordinary cooking and soaking were relatively less effective.     

Cowpea cooking characteristics as affected by micronisation temperature: a study of the physicochemical and functional properties of starch

Bechuana white cowpeas were micronised to three temperatures (130, 153 and 170 °C). Cooking properties of the cowpea seeds and the role of starch‐related properties were studied. In all cases, micronisation significantly reduced the cooking time and thus the time required for the cowpea seeds to attain a suitably soft texture. This was attributed in part to the significant improvement in rate of water absorption during cooking and starch pre‐gelatinisation, as evidenced by loss of birefringence and increased susceptibility of the cowpea starch to α‐amylase digestion. However, micronisation to 170 °C resulted in a severe deterioration in pasting properties of the cowpea flour, possibly due to starch depolymerisation and/or amylose‐associated crosslinking. Owing to these changes, cowpea seeds micronised to 170 °C required a longer cooking time than the other two micronised samples. Flour prepared from cowpea seeds micronised to 170 °C may have limited starch functionality. Copyright © 2006 Society of Chemical Industry     

Zinc bioavailability in different beans as affected by cultivar type and cooking conditions

Zinc bioavailability was studied in five cultivars of beans (Phaseolus vulgaris, L): white (Ouro Branco), black (Diamante Negro), and brown (BRS Radiante, Pérola and Talismã) cooked with or without soaking water. The cooked bean flours or ZnCO₃ were added to the test or control diets to provide 15 mg Zn/kg diet and were fed to weaning Wistar male rats for 42 days. Blood and femur were collected for analyses of plasma and erythrocyte Zn, bone weight and bone/dietary mineral ratio. Zinc bioavailability of Ouro Branco bean cooked with soaking water was higher than the other cultivars and similar to the control diet. Talismã without soaking water showed the lowest values for most of the parameters analyzed. Zinc bioavailability was not affected neither by the cooking process itself nor by the contents of phytate, tannins and dietary fiber, but it varied according to the bean cultivar and the phytate × calcium:zinc molar ratio.     

Physicochemical,milling and cooking quality of rice as affected by sowing and transplanting dates

The physicochemical, milling and cooking characteristics of three commercial varieties of paddy viz. Jaya, PR 106 and Pb. Basmati no. 1 as affected by different dates of sowing nursery and transplanting, were investigated. Grain yield was adversely affected with late sowing and transplanting dates. Significant differences were recorded on the yield of head rice and brokens in the three varieties grown under different sowing and transplanting dates. The effect of normal and late dates of sowing on 1000-kernel weight and grain dimensions was significant for both paddy and milled rice. Protein content of rice was not affected by sowing dates but late transplantings resulted in higher values. Free fatty acids in rice and bran were significantly increased with late sowing and transplanting dates, however, the amylose content decreased under these situations. Late transplanting dates decreased the minimum cooking time but increased the solid losses in gruel. The late transplantings deteriorated the organoleptic properties of cooked rice and had higher values for clearing and spreading.     

Physicochemical and fatty acid characteristics of stewed pork as affected by cooking method and time

This study was designed to investigate the effects of cooking on physicochemical and fatty acid characteristics of stewed pork. Pre‐fried or raw pork belly cubes were stewed for 60, 90, 120, 150 or 180 min. After cooking, proximate chemical composition, texture, sensory evaluation, lipid oxidation, fatty acid profiles and cholesterol content were determined. Prolonged cooking time resulted in higher percentages of dry matter, fat and fat loss in stewed cubes (P < 0.01), and pre‐frying also increased fat loss. Tenderness and elasticity values of texture profile analysis and sensory scores were the highest for the cubes stewed for 180 min or by pre‐frying combined with stewing for 150 min. Pre‐frying and extended cooking time significantly increased lipid oxidation (P < 0.01). Cooking modified fatty acid profiles which altered the derived cardiovascular indices, and reduced cholesterol content. Prolonged stewing improved eating quality and most nutritional values of pork belly.     

Sensory evaluation and in vitro protein digestibility of mung bean as affected by cooking time

Heat treatment is particularly important in the preparation of mung bean for consumption, from the point of view not only of acceptability but also of improvement on protein digestibility. Sensory evaluation of cooked mung bean in terms of taste, colour, aroma and texture has an organoleptic panel indicated that there was no significant difference (P < 0.05) between mung bean cooked for 25, 30, 35, 40 and 45 min. An in vitro protein digestibility assay was used to examine the effect of cooking time on protein digestibility. The applied non-linear mathematical model indicated a high correlation coefficient between experimental and predicted data (R² ≥ 0.999). A maximum improvement in in vitro protein digestibility (IVPD) of 4.83% was obtained by cooking for 38.6 min. No remarkable changes in most amino acids were found between raw and cooked samples except that tryptophan was decreased by 4.69% and a 10.29% loss of threonine occurred with the optimum cooking time. © 1999 Society of Chemical Industry     

Microstructural changes of starch in cooked wheat grains as affected by cooking temperatures and times

The changes of starch microstructure in soft and hard wheat grains after cooking in a pressure cooker were investigated using a scanning electron microscope (SEM) and a light microscope (LM) in conjunction with image analysis. The conditions studied included variation of the cooking times (20-120 min) at the constant temperature (120 °C) and with variable temperatures (110-140 °C) for constant time (40 min). SEM images showed that steam induced changes in the intact starch granules of cooked wheat grains, with the microstructure becoming more in mud-like structure, with increased cooking time or temperature. The swelling and gelatinization of starch granules could contribute to this change. Suspensions of cooked wheat flour were selectively stained with iodine, for observation using the LM. The image analysis software was used for quantitative analysis of the images captured from the LM, providing both the number and area of the starch granules (determined from the dark-blue spots) per fixed image size. With increased cooking time or temperature, the number of starch granules decreased and the area increased as a result from the swelling and melting of starch granules. This study demonstrated the use of SEM and LM for the investigation of starch granules in cooked wheat grains without prior starch isolation.     

Composition and physicochemical characteristics of restructured beef steaks containing walnuts as affected by cooking method

The study was conducted to determine the influence of various cooking methods - conventional oven, microwave oven, electric grill and pan-frying on the composition and physicochemical characteristics of restructured beef steaks formulated as low fat (L, 2.0% fat), medium fat (M, 13.0% fat) and 20% added walnut (W, 12.6% fat). Composition, retention coefficients for different compounds, cooking loss (CL) and texture were affected by both formulation and cooking. There was considerable retention of moisture, fat and minerals (as ash) in W samples after cooking. CL was highest (P<0.05) in M sample and lowest (P<0.05) in W samples. Microwaved restructured steaks had higher (P<0.05) kramer shear force (KSF) and bind strength (BS), while pan-fried and conventionally oven-cooked steaks had lower (P<0.05) KSF. The thiobarbituric acid-reactive substances (TBARS) content was low in all restructured steaks but was affected by both cooking and formulation. Although cooking can change the proximal composition of steaks, lipid retention (>90%) was greatest in the case of the W sample, thus assuring that the ultimate objective of these restructured meats, namely to provide a source of walnut and walnut fat, would be successful.