Comparison of Microbiological and Radiometric Assays for Determining Total Folacin in Spinach

Several commercially available forms of spinach were analyzed for total folacin content by the microbiological assay using Lactobacillus casei and a radiometric assay. Types of products included frozen uncooked, fresh raw, microwave and conventionally cooked fresh and creamed strained spinach. Folacin content ranged from 0.62 mcg/g for strained spinach to 2.50 mcg/g for uncooked frozen spinach, when assayed microbiologically. With the radiometric assay, folacin values were significantly higher (P<0.05) than with the L. casei assay. The microbiological assay appears more suitable for determination of total folates in complex food matrices than the radioassay.     

NUTRIENT QUALITY OF SELECTED VEGETABLES PREPARED BY CONVENTIONAL AND COOK-FREEZE METHODS

Selected vegetables (spinach, broccoli, sweet potatoes, and collard greens) prepared in 2.27 kg (5 lb) quantities by boiling, were frozen and stored for six months at ?18°C. Zinc, iron, β-carotene, and ascorbic acid were determined on the raw vegetable immediately after cooking and after reheating in a microwave oven subsequent to 6 months frozen storage. The greatest nutrient loss occurred for water soluble nutrients during boiling. Nutrient comparison between cooked samples (conventional method) and samples microwaved after 6 months frozen storage (cook-freeze method) indicated that differences existed only in ascorbic acid content of spinach. Data indicated that vegetables prepared by cook-freeze, a method used by health care institutions, were generally equal in nutrient quality to conventionally prepared vegetables.     

Nutrient retention in microwave cooked germinated legumes

The effects of germination on the cooking quality and nutrient retention in pressure and microwave-cooked Bengal gram, green gram and horse gram were studied. Ungerminated (UGL) and germinated legumes (GL) cooked in a microwave oven, and under pressure were analysed for moisture, protein, ash, iron, thiamin, ascorbic acid, in vitro protein digestibility (IVPD) and starch digestibility (IVSD) and bioavailable iron. Results revealed that microwave cooking required more water and time than did pressure cooking. The range of analysed constituents on dry weight basis in UGL and GL legumes, respectively, were as follows: protein, 18.2–23.5 and 19.4–25.7 g, ash, 2.1–2.9 and 2.2–2.9 g, iron, 5.4–7.3 and 7.3–10.3 mg, thiamin, 0.10–0.34 and 0.54–1.83 mg, ascorbic acid, 2.4–3.9 and 3.1–25.6 mg/100 g. The effect of germination and method of cooking on nutrient retention varied, depending on nutrient and severity of heat treatment. Microwave cooking caused 36–57% reduction of ascorbic acid while pressure cooking caused 10–30% loss. The IVSD in raw samples ranged from 18.4% to 22.1% in UGL and 33.6% to 43.6% in GL. Cooking of UGL and GL, by both methods, increased the starch digestibility threefold. The IVPD of raw UGL ranged from 64.6% to 66.2% and that of GL was 72.4–73.9%. In cooked UGL the IVPD ranged from 70.9% to 82.3% and, in GL, from 78.4% to 84.2%, showing a significant difference in cooking methods only in UGL. The iron bioavailability ranged from 11.5% to 18.7% in raw UGL while it was 18.3–20.6% in GL. GL had a higher content of thiamin and ascorbic acid, higher protein and starch digestibility and bioavailable iron, even after cooking.     

Effect of cooking on total vitamin C contents and antioxidant activity of sweet chestnuts (Castanea sativa Mill.)

In this work the total vitamin C contents (ascorbic acid + dehydroascorbic acid) and antioxidant activity of raw and cooked chestnuts was evaluated. The vitamin C contents of raw chestnuts varied significantly between the different cultivars (cv) studied and it varied from 400 mg/kg dry weight (cv Lada) to 693 mg/kg dry weight (cv Martaínha). The different cultivars behave differently during the cooking process concerning the loss of vitamin C. A significant decrease in the vitamin C content of the chestnuts was observed, 25–54% for the boiling process and 2–77% for the roasting process. Boiled and roasted chestnuts can be good sources of vitamin C since it may represent 22.4%, 16.2%, 26.8% and 19.4%, respectively, of the recommended dietary intake for an adult man and woman. The cooking process significantly changed the antioxidant activity of the chestnuts. A difference was observed between the cultivars during the cooking processes, concerning the antioxidant activity. For the raw chestnuts the variation in vitamin C content of the chestnuts explains 99% of the antioxidant activity variation but for the roasted and boiled chestnuts this percentage significantly decreases to 51% and 88%, respectively. Although a high antioxidant activity is still present in the cooked chestnuts, the cause for this antioxidant activity is less dependent on the vitamin C content of the chestnuts, probably due to the conversion of ascorbic acid to dehydroascorbic acid. The increase in gallic acid during the cooking process, presumably transferred from the peels to the fruit, also contributes to the high antioxidant activity observed for the cooked chestnuts.     

Effect of cooking on the antioxidant properties of coloured peppers

Pepper (Capsicum annum L.) has long been recognized as an excellent source of antioxidants, being rich in ascorbic acid and other phytochemicals. This study was conducted to investigate the effect of different cooking methods on the antioxidant properties of coloured peppers. Six varieties of peppers were subjected to different cooking methods, such as microwave heating, stir-frying and boiling in water, for 5 min individually. The cooked and raw peppers were analyzed for radical-scavenging activity (RSA) and total polyphenol content (TP) using 1,1-diphenyl-2-picrylhydrazyl–high-pressure liquid chromatography (DPPH)–HPLC and Folin-Ciocalteu methods, respectively. The samples were also evaluated for ascorbic acid content (AsA) by HPLC. Total carotenoid content was determined spectrophotometrically. Results suggest that there is no significant (P > 0.05) difference in RSA, TP, AsA and total carotenoid contents between the cooked and raw peppers when processed for 5 min. However, the cooked peppers show marked differences (P < 0.05) in the RSA, TP and AsA when cooked for 5 min in boiling water with further reduction observed after boiling for 30 min. This may be due to the leaching of antioxidant compounds from the pepper into the cooking water during the prolonged exposure to water and heat. Therefore, it is vital to use less water and cooking time and also to consume the water used for boiling so as to obtain the optimum benefits of bioactive compounds present in peppers. It is concluded that microwave heating and stir-frying without using water are more suitable cooking methods for pepper, to ensure the maximum retention of antioxidant molecules.     

Effect of Preparation and Service on the Thiamin Content of Oven-Baked Chicken

Chicken breast halves were oven-baked and evaluated for thiamin content when prepared and served under a cafeteria-style foodservice system. After preparation, they were held on a steam table for 90 min, frozen stored for 4 wk and finally reheated using conventional and microwave ovens. Thiamin determinations were conducted on raw, cooked, hot-held, frozen-cooked and reheated samples. The mean total percent cooking losses for the freshly cooked chicken were 20.4 ± 10.9%. The steam table holding for 90 min resulted in 4.4 ± 0.7% evaporation losses. The mean percent evaporation losses for the microwave reheated chicken were not significantly different from those of the conventionally reheated samples. No significant differences were noted in the moisture and fat content among various treatments. The thiamin content of raw meat when calculated on a dry, fat-free basis was significantly higher than the thiamin content of the cooked meat. There were no significant differences in the thiamin content after various treatments.     

Effect of Heating Time of Soybean on Vitamin B-6 and Folacin Retention, Trypsin Inhibitor Activity, and Microstructure Changes

Heating treatments of boiling 20 min or autoclaving 5 min, 10 min, or 20 min, of soaked (25°C for 10 hr) soybeans, significantly influenced vitamin B-6, free folacin, trypsin inhibitor activity, water absorption, moisture content and blue, green and amber color values in the cooked soybeans. Analysis of covariance showed a relationship (P≤0.05) between water absorption after cooking with total folacin in cooked soybeans and water absorption after cooking with blue color values. Other relationships (P≤0.05) were observed in cooked soybeans between texture and total folacin, moisture and trypsin inhibitor activity, and trypsin inhibitor activity and free folacin.     

Physical and Chemical Attributes of a Ready-to-Eat Meat Product during the Processing: Effects of Different Cooking Methods

The effects of cooking time (10–50 min) and treatments (atmospheric, pressure, and microwave cooking) on Kavurma (a ready-to-eat meat product) were investigated. Atmospheric and pressure cooking technique had more desirable quality attributes than microwave cooking technique on kavurma production. Color, texture, moisture content, pH, and 2-thiobarbituric acid reactive substance values were followed during processing. Moisture content, pH, 2-thiobarbituric acid reactive substance, hardness, and chewiness values of microwave cooked samples were significantly different (p < 0.05) than that of atmospheric and pressure cooked samples. The microwave cooking method had the greatest influence on lipid oxidation compared to others. While the level of 2-thiobarbituric acid reactive substance was lower which was under the threshold value of 1 mg MA/kg in atmospheric and pressure cooking, it was higher in microwave cooking. On the other hand, among Hunter color values, lightness value increased (p < 0.05) for atmospheric cooked samples while it decreased by time for pressure and microwave cooked samples. However, a* and b* values of microwave and pressure cooked samples were significantly higher than atmospheric cooked samples.     

Change in proximate, amino acid and fatty acid contents in muscle tissue of rainbow trout (Oncorhynchus mykiss) after cooking

Changes in proximate, amino acid and fatty acid composition of farmed, commercially important rainbow trout (Oncorhynchus mykiss) after conventional and microwave cooking were analysed. Rainbow trouts cooked in microwave ovens had statistically significant higher total protein, total fat, and ash than electrical oven‐cooked samples. The amounts of essential and nonessential amino acids were not different between cooking methods, but the difference between raw and cooked samples was significant. Lysine, leusine, methionine, threonine, valine, arginine and histidine were found most in microwave‐cooked rainbow trouts whereas isoleucine, tyrosine and phenylalanine were found most in electrical oven‐cooked samples. As total saturated fatty acid and total monounsaturated fatty acids amount were not statistically different between the cooking methods, the difference between raw and cooked fillets was found statistically significant (P < 0.05). There was no statistically significant difference between raw and cooked fillets in total n‐3 and n‐6 contents.     

Traditional cooked vegetable dishes as important sources of ascorbic acid and beta-carotene in the diets of Indian urban and rural families

BACKGROUND: Fresh vegetable produce is abundant during the winter season in Punjab. It is an important source of vitamins and minerals in the Punjabi diet, but the availability of ascorbic acid and beta-carotene from the vegetables is altered to varying degrees when they are subjected to traditional household processing methods. OBJECTIVE: To determine the importance of traditional cooked vegetable dishes as sources of ascorbic acid and beta-carotene among urban and rural families during the winter. METHODS: Information about vegetable consumption, storage, and cooking practices was collected from 60 families, 30 each from urban and rural areas of Ludhiana District, Punjab, India. Samples of the common cooked vegetable dishes were prepared in the laboratory by methods ascertained from the survey and analyzed for ascorbic acid and beta-carotene. RESULTS: The average total daily per capita consumption of vegetables by urban and rural families was 411.7 and 365.9 g, respectively. Cooked vegetable dishes provided 68.7% of the total vegetable intake for urban families and 85.0% for rural families. On average, the edible portion constituted 78.9% of the weight of the vegetables. Ten cooked vegetable dishes that were most frequently consumed by the families (mustard saag, potato-spinach, potato-fenugreek, potato-brinjal, potato-cauliflower, potato-capsicum, potato-carrots, potato-beans, potato-peas, and cabbage-peas) were selected for preparation in the laboratory and nutritional analysis. The average concentrations of ascorbic acid and beta-carotene in the cooked vegetable dishes were 46.0 mg/100 g and 794.2 microg/100 g fresh weight, respectively. The percentage losses of ascorbic acid and beta-carotene during preparation and cooking were 26.1% and 25.9%, respectively. CONCLUSIONS: For adult Indian men and women, the recommended dietary allowance of ascorbic acid is 40 mg, and that of beta-carotene is 2,400 microg. Cooked vegetable dishes provided 269.9% and 77.5% of the recommended dietary allowances of ascorbic acid and beta-carotene, respectively, indicating that these dishes are good sources of these nutrients in the diets of both urban and rural families during the winter season.     

The comparative evaluation of the nutrient composition and sensory attributes of four vegetables cooked by different methods

The following four vegetables; beans (Phaseolus vulgaris var. vulgaris), brinjal (Solanum melongena var. esculentum), knol‐khol (Brassica oleracea var. caulorapa) and radish (Raphanus raphanistrum satvius) were processed either by conventional, pressure or microwave cooking methods and were analysed for their nutritional and sensory profile. Raw samples were used as controls. Microwave cooking resulted in greater moisture loss when compared with vegetables cooked by other methods. The protein, fat, total ash, calcium, phosphorus, iron, and dietary fibre contents of the vegetables did not differ significantly in raw or cooked vegetables. Ascorbic acid was destroyed to the greatest extent by pressure cooking followed by microwave and conventional method. The sensory attributes of cooked vegetables, as evaluated by a paired preference test, revealed that there were no significant differences between cooked radish and knol‐khol but, in the case of beans and brinjal, microwave and conventionally cooked samples were preferred over pressure cooked ones.     

高温水煮和酸煮对猪骨硬度及化学成分的影响

为研究高温水煮和酸煮对猪骨硬度及化学成分的影响。以猪骨为实验对象,研究120℃条件下猪骨在水中煮制不同时间(40、50、60、70、80 min)和不同体积分数(0.0%、0.2%、0.4%、0.6%、0.8%、1.0%)的醋酸溶液中煮制80 min后猪骨硬度的变化。用凯氏定氮法和电感耦合等离子体原子发射光谱法测定未煮制猪骨、120℃条件下水中和1.0%醋酸溶液中煮制80 min后猪骨蛋白含量、钙、磷元素含量和钙、磷元素溶出量,用扫描电子显微镜观察猪骨粉碎后微观结构,测定猪骨红外吸收光谱,探究煮制后猪骨成分和结构的变化。结果表明,高温煮制能使猪骨硬度下降,水煮时间从40 min延长到80 min,猪骨硬度从(16 445±867)g下降到(10 995±546)g,醋酸溶液体积分数从0.0%增加到1.0%,猪骨硬度从(10 995±546)g下降到(6 003±153)g。高温煮制能使猪骨蛋白含量降低,猪骨表观钙、磷含量增加,钙、磷溶出量增加。水煮后猪骨蛋白含量为(28.5±2.3)g/100 g,降低了7.4%;猪骨表观钙、磷元素含量分别为(210.0±8.2)mg/g和(96.0±4.0)mg/g,分别增加了11.8%和8.9%;猪骨钙、磷含量溶出量分别为(0.57±0.04)mg/g和(0.17±0.01)mg/g。1.0%醋酸煮后猪骨蛋白含量为(25.9±0.9)g/100 g,降低了10.0%;猪骨表观钙、磷元素含量分别为(230.0±6.4)mg/g和(100.0±2.3)mg/g,分别增加了18.3%和14.8%;猪骨钙、磷元素溶出量分别为(1.73±0.01)mg/g和(0.75±0.01)mg/g。经扫描电子显微镜观测发现,煮制后的猪骨易粉碎,1.0%醋酸煮后的猪骨最容易粉碎。红外光谱发现,煮制后猪骨成分发生了变化,图谱的峰比未煮制简单,成分比未煮制猪骨单一,而加水煮制和加酸煮制后猪骨图谱的峰相似,煮制后猪骨红外光谱图更接近人工合成的羟基磷灰石晶体。高温水煮和酸煮均能引起猪骨蛋白、钙元素和磷元素等化学成分含量的变化,导致猪骨硬度显著下降(P0.05)。     

Effects of Four Cooking Methods on the Proximate, Mineral and Fatty Acid Composition of Fish Fillets

The effects of baking, broiling, deep frying and cooking in a microwave oven on the proximate, mineral and fatty acid composition of grouper (Epinephelus morio), red snapper (Lutjanus campechanus), Florida pompano (Trachinotus carolinus) and Spanish mackerel (Scomberomorus maculatus) were determined. The lipid content of low fat species was not significantly changed by cooking, but lipid was lost from fatty fillets during cooking. The fatty acid composition of all fillets was not significantly changed by baking, broiling or microwave cooking. Deep fried fillets absorbed the major fatty acids in the cooking medium, and as the fillet lipid content increased the extent of absorption of fatty acids from the cooking medium decreased. Sodium, potassium and magnesium levels were decreased when low fat species were cooked, but these minerals were not lost when raw fillets containing higher lipid levels were cooked. Cooking did not significantly affect the concentration of the microelements, zinc, copper, iron and manganese.     

不同烹饪方式对盐渍鱼干风味和微观结构的影响

本文对比研究了微波烹饪、空气炸锅烹饪、烘烤烹饪和蒸煮烹饪4种常用烹饪方式对盐渍鱼干咀嚼性(质构)、滋味(游离氨基酸),风味(挥发性物质)和微观结构的影响。结果表明:4种烹饪方式均可通过显著降低盐渍鱼干的硬度和咀嚼性、增加弹性来改变其质构特性;微波烹饪、空气炸锅烹饪和烤箱烹饪都能不同程度的降低盐渍鱼干的游离氨基酸总量,而蒸煮烹饪提高了氨基酸总量,从原始量586.66 mg/100 g增加至631.45 mg/100 g;4种烹饪方式均可使鱼干样品中醛酮类物质和酯类物质含量显著上升,烷烃类物质含量显著下降,其中空气炸锅烹饪处理鱼干样品中醛酮类物质含量最高,达到37.07%;烹饪处理使盐渍鱼干肌肉纤维严重皱缩,纤维束间充满了烹饪用油,空气炸锅和烘烤烹饪处理后盐渍鱼干纤维束间的空隙较明显。     

Effects of cooking methods on the proximate,mineral and fatty acid composition of European eel (Anguilla anguilla)

The influence of microwave cooking and traditional cooking methods such as baking, grilling and frying on the nutritional composition of eels (Anguilla anguilla) was studied. All methods reduced moisture and increased the protein and fat content. Although the potassium and sodium content of fish cooked by different methods decreased significantly (P = 0.000), the calcium and magnesium content increased. The zinc content of the fish was not affected by cooking. The manganese and iron content significantly increased only in fried fish. The copper content was increased by grilling and microwave cooking. The proportion of saturated fatty acids and monounsaturated fatty acids in cooked fish decreased. Omega‐3 polyunsaturated fatty acids were increased by all cooking methods. The grilling and microwave‐cooking methods were the most suitable considering the n3/n6 ratio and eicosapentaenoic acid levels. The increase in the docosahexaenoic acid level of fried fish enhanced its nutritional value.     

不同烹饪处理对芹菜感官和营养品质的影响

以本芹、西芹为原料,研究4种烹饪方法(漂烫、蒸、微波、炒)对芹菜感官品质和营养品质的影响。研究了不同烹饪加热方式对两种芹菜的硬度、色泽、叶绿素、抗坏血酸、多酚类物质和抗氧化能力的影响。结果表明:烹饪处理后,西芹的硬度和色泽得以较好地维持,感官品质优于本芹,但其功能成分、营养价值均低于本芹。漂烫处理有明显的护色作用,但营养成分损失较大。相比于漂烫、微波和炒,蒸能够更好地保持芹菜的脆性和绿色色泽等感官品质,且抗坏血酸保留率最高,本芹、西芹分别为84.95%、73.90%。微波和油炒使芹菜中总酚含量增加,抗氧化能力升高。烹饪后,黄酮类化合物含量显著降低(P<0.05)。人们在日常食用芹菜时,应根据自己的需求选择合理的烹饪方法。     

The antioxidant capacity and polyphenol content of organic and conventional retail vegetables after domestic cooking

Vegetable consumption is associated with health benefits. Organic foods are thought to have higher contents of antioxidant substances. The objective of this work is to quantify soluble and hydrolyzable polyphenols, ascorbic acid, and the antioxidant capacity of fresh conventional and organic retail vegetables (potato, carrot, onion, broccoli, and white cabbage) while evaluating the effect of boiling, microwaving, and steaming on these parameters. The recovery rate for soluble and hydrolyzable polyphenols was variable according to the vegetable analyzed. However, soluble polyphenols resulted in lower recovery rates than did hydrolyzable phenolics after cooking. Organic vegetables showed higher sensitivity to heat processing than did conventionally grown vegetables. In general, cooking was found to lead to reductions in the antioxidant capacity for most vegetables, with small differences between the cooking methods applied. Even with the alterations in their content, polyphenols showed a positive correlation with antioxidant capacity in raw and cooked vegetables from both types of agriculture.     

Effect of different precooking methods on chemical composition and lipid damage of silver carp (Hypophthalmichthys molitrix) muscle

The influence of three precooking methods (steaming, oven‐baking and microwave‐cooking) on the chemical composition and lipid quality of silver carp fillets was evaluated. The changes in protein, fat and moisture were found to be significant for all the treatments (P ≤ 0.05). The iron content in the samples subjected to steam‐cooking increased; however, the other precooking methods did not change the mineral contents (P ≥ 0.05). The free fatty acid content of the fillets did not change by the different precooking methods, while thiobarbituric acid (TBA) values increased for oven‐ and microwave‐cooked fillets and remained constant in the steam‐cooked samples. Conjugated diene and browning colour formation levels significantly increased in the oven‐baked fillets. Oven‐baking and microwave‐cooking marginally affected the fatty acid composition of the silver carp. On comparing the raw and precooked fillets, steam‐cooking was found to be the best precooking method on retaining nutritional constituents.     

Effect of processing on the amino acid content of New Zealand spinach (Tetragonia tetragonioides Pall. Kuntze)

The aim of this work was to evaluate the effect of processing on the amino acid content and protein quality of New Zealand spinach (Tetragonia tetragonioides Pall. Kuntze). In this research, fresh and cooked New Zealand spinach as well as two frozen products prepared for consumption, one obtained using the traditional method (blanching–freezing–storage–cooking) and the other a convenience food product obtained using a modified process (cooking–freezing–storage–defrosting and heating in a microwave oven), were analysed. Glutamic acid was the dominant amino acid in fresh New Zealand spinach, and the limiting amino acids were cystine and methionine. Technological and culinary processing caused a significant increase in amino acid content in 100 g of edible portion, with the exception of methionine and cystine in frozen products prepared for eating. Changes in amino acid content expressed in g/16 g of N (which corresponded to 100 g tissue protein) were not significant, with the exception of the lower glutamic acid content in the frozen product obtained using traditional processing method.     

Effects of RN genotype and silage feed on fat content and fatty acid composition of fresh and cooked pork loin

This study aimed to establish effects of RN genotype and feed (red clover silage) on intra muscular fat content (IMF) and fatty acid composition (FA) of fresh and cooked pork loin (M. longissimus dorsi). Raw loins from silage-fed pigs compared with those from conventionally fed pigs had lower IMF, lower relative levels (rel.%) of saturated (SAFA) and monounsaturated (MUFA) fatty acids, and higher rel.% of polyunsaturated fatty acids (PUFA, ω6, ω3). Cooked loins, from silage-fed pigs compared with those of conventionally fed pigs, had higher rel.% of ω3, and lower ω6/ω3 ratios. IMF and cooking influenced FA concentrations in a pork portion. The differences in concentrations of SAFA, MUFA, PUFA and ω6 between raw loins of silage-fed pigs and conventionally fed pigs did not remain in cooked loins. The ω6/ω3 ratio, however, remained low, and thus more beneficial in loins from silage-fed pigs after cooking.