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.     

EFFECTS OF COOKING METHODS ON SENSORY QUALITIES AND CAROTENOID RETENTION IN SELECTED VEGETABLES1

The effects of induction boiling, conventional boiling and microwave steaming on the sensory qualities and carotenoid retention of broccoli, carrots, green beans and sweet potatoes were investigated. Significantly higher cooking yields were obtained for vegetables that were induction and conventionally boiled. No differences in the retentions of alpha‐carotene (α‐carotene), beta‐carotene (β‐carotene) and lutein/zeaxanthin were observed for vegetables by the cooking method, with the exception of β‐carotene retention in broccoli and sweet potatoes where retentions were higher for those that were induction boiled (90.3 and 86.1%, respectively) than those that were microwave steamed (62.2 and 66.4%, respectively). A trained panel judged the color scores of three vegetables by the cooking method as similar. The mean flavor scores (1 = extremely bland; 9 = extremely intense) for three vegetables that were conventional (4.7–5.4) and induction (5.3–5.5) boiled were lower than those that were microwave steamed (5.9–7.0). The mean texture scores (1 = extremely mushy/tender; 9 = extremely firm/tough) for all induction‐boiled (5.0–6.0) vegetables were higher than those that were conventionally boiled (3.4–5.2) and lower than those that were microwave steamed (5.1–6.6).     

CAROTENOID RETENTION AND SENSORY CHARACTERISTICS OF SELECTED VEGETABLES PREPARED BY INDUCTION STIR‐FRYING*

ABSTRACT

The effects of induction stir‐frying on carotenoid retention and sensory characteristics of selected vegetables (carrot, green spring onion, red pepper, snow pea, white spring onion and yellow pepper) were investigated. Cooking times ranged from 4 to 6 min, and cooking yields from 70.9 to 92.0%. The stir‐fried vegetables retained (w/w) more than 85% (mean) of each of their carotenoids (β‐carotene, lutein, zeaxanthin, α‐carotene, β‐cryptoxanthin and lycopene). Over three‐quarters of the 78 consumer panelists reported liking extremely/liking very much or liking moderately/liking slightly the appearance, color, flavor, texture and overall acceptability of carrot, green spring onion, red pepper, snow pea and yellow pepper; whereas, half to three‐quarters reported similarly for white spring onion. Few differences in attribute responses were observed by gender. Induction stir‐fried vegetables had excellent carotenoid retention, and the consumer panelists indicated liking them slightly to extremely.

PRACTICAL APPLICATIONS

This study indicates that vegetables that are cooked by induction stir‐frying retained (w/w) over 85% of their carotenoid content and had sensory characteristics that the consumer panelists liked. Perhaps individuals, specifically college students, might be inclined to consume more cooked vegetables if they liked the appearance, color, flavor, texture and overall acceptability of the vegetables. Consuming vegetables containing higher amounts of the carotenoids may also be beneficial.

     

SENSORY ATTRIBUTES AND THIAMINE CONTENT OF ROASTING CHICKENS COOKED IN A MICROWAVE, CONVECTION MICROWAVE AND CONVENTIONAL ELECTRIC OVEN

Fresh whole roasting chickens were cooked to an internal temperature of 79°C (175°F) in either a microwave, convection microwave or conventional electric oven. The sensory attributes of breast meat samples from chickens cooked in the three ovens were evaluated by untrained and laboratory panels. Untrained panelists found convection microwave cooked samples to be more acceptable in terms of juiciness than microwave cooked samples. Laboratory panelists rated the chicken cooked in the conventional oven as significantly more tender and juicy but similar in flavor intensity to chicken cooked in the microwave ovens. Thiamine retention on a dry weight basis ranged from 77% in conventionally cooked chicken breasts to 98% in microwave cooked chicken legs.     

RETENTION OF VITAMINS IN FRESH AND FROZEN BROCCOLI PREPARED BY DIFFERENT COOKING METHODS

Fresh and frozen broccoli were analyzed for retention of ascorbic acid, riboflavin and thiamine by semi-automated fluorometry before and after steaming, boiling or microwave cooking for 5 min. Retention of vitamins in general was higher for fresh than for frozen broccoli. Steamed fresh broccoli retained most ascorbic acid, riboflavin, and thiamine. Boiled fresh samples retained least riboflavin and ascorbic acid and microwaved samples, the least thiamine. In frozen broccoli, microwaved samples retained most ascorbic acid and riboflavin, and steamed samples retained most thiamine.     

RETENTION OF VITAMIN C,IRON, AND β-CAROTENE IN VEGETABLES PREPARED USING DIFFERENT COOKING METHODS1

The true retention of vitamin C, iron, and β-carotene in five vegetables cooked by household microwave-steaming, stir-frying with oil, stir-frying with water, and boiling to equal degrees of overall acceptability were compared. Vegetables prepared by microwave-steaming and stir-frying with oil had significantly higher (means of 1.31 – to 1.83 fold) vitamin C retention values than those which were boiled. Iron retention was significantly higher (means of 1.17-to 1.34-fold) in four of five vegetables cooked by microwave-steaming rather than by boiling. β-carotene retention in four of five vegetables cooked by the different methods was similar. Overall, higher retention values were observed in vegetables cooked by microwave-steaming and stir-frying with oil.     

SELECTED SENSORY AND CHEMICAL ATTRIBUTES OF CHICKEN BREAKFAST SAUSAGES FROM DIFFERENT ANIMAL FAT SOURCES

Four breakfast sausage formulations were prepared to contain: (1) chicken lean + chicken fat (CF), (2) chicken lean + beef fat (BF), (3) chicken lean + pork fat (PF), or (4) chicken lean + high-oleic pork fat (PO). Formulations were targeted to contain 15% fat. Acceptability, tenderness, juiciness and flavor scores for each of the formulations as measured by a consumer taste panel (n = 71), were not different (P> 0.05). Sausages prepared with CF had a higher (P < 0.05) cooking loss and lower fat content than those prepared with BF. Thibarbituric acid (TBA) values for PO were significantly lower than those containing BF, PF, or CF. Sausage products containing chicken fat exhibited the highest TBA values during 9 days of storage at 4°C. These results suggested that chicken, beef, pork or high-oleic fats can be used as the fat source in low-fat chicken breakfast sausages without affecting the product acceptability.     

PHYSICOCHEMICAL CHARACTERISTICS AND SENSORY ATTRIBUTES OF WHEAT-BASED "PAPADS" INCORPORATED WITH GREEN LEAFY VEGETABLES

Papads are cereal or legume‐based preserved products which are consumed after deep fat frying. They were chosen for value addition with two types of green leafy vegetables (GLV). Wheat‐based papads were prepared using refined wheat flour, cumin seeds, salt and GLV, that is, shepu (Peucedanum graveolens) and kilkeerae (Amaranthus tricolor) at different levels in fresh (15 and 20%) and dehydrated forms (5 and 10%). Greens were analyzed for their proximate principles, selected minerals and vitamins. In the fried papads, fat uptake and expansion volume were determined. The fried papads were subjected to sensory analysis by a panel of 100 members. Expansion volume of papads with fresh greens and 5% dehydrated greens were satisfactory, but differences existed between the greens. Fat uptake of kilkeerae papads was similar to that of control papads but shepu‐incorporated papad showed slightly lower absorption. Papads with 15–20% fresh greens and 5% dehydrated greens scored above 6 on a scale of 10 indicating acceptability of papads incorporated with greens. Mineral, vitamin and fiber content of greens‐incorporated papads increased remarkably. Acceptability of papads in terms of physicochemical characteristics, sensory attributes and nutritional quality suggests the suitability of papads incorporated with greens.     

STRUCTURAL FAILURE IN SELECTED RAW FRUITS AND VEGETABLES1

A torsion test was developed for studying the structural failure of selected raw fruits and vegetables. Apple, melon and raw potato flesh were tested at a shear strain rate of approximately 0.26s^-1 in torsion and uniaxial compression. Low strain modulus values were determined in addition to shear stresses and normal strains at failure. Results corroborated the maximum normal strain failure criterion proposed by Segerlind and Dal Fabbro (1978) for apples and suggested its application to potatoes and melons if true strains are used rather than engineering strains. The maximum shear stress theory also seemed to be a possible failure criterion for potatoes. Results comparing compressible and incompressible materials suggest that bulk strain affects the shear stress at failure. The observed failure planes supported the quantitative results for stresses at failure. Scanning electron micrographs indicated that the cellular failure occurred in the cell wall, regardless of whether it was due to tension, Varying specimen lengths or diameters had negligible effects on the uniaxial compression modulus but did affect the shear stress at failure in a manner yet to be satisfactorily explained.     

MICROWAVE AND CONVENTIONAL BLANCHING EFFECTS ON CHEMICAL, SENSORY, AND COLOR CHARACTERISTICS OF FROZEN BROCCOLI

Broccoli (cv. Empress) obtained from a local supplier was blanched within 15 h of harvest. It was blanched by four methods in covered containers: conventional boiling water (1900 mL, 4 min) (BW), steam (300 mL water, 4 min) (ST), microwave heated in 1 L glass containers (60 ml water, 4 min, 700 W) (MW), and microwave heated in 1 L Seal-a-Meal^TM bags (45 ml water, 4 min) (MWB). Aliquots were frozen at -18C for 4 weeks. Fresh unblanched broccoli peroxidase activity ranged from 389 to 829 units/min; activity was essentially zero immediately after all blanching treatments. The highest reduced ascorbic acid (RAA) content occurred in fresh unblanched broccoli. Some peroxidase regeneration occurred during frozen storage. Immediately after blanching, all blanched broccoli had lower RAA content than control broccoli. MW-blanched broccoli retained the greatest amount of RAA and had appearance, visual color, texture scores, and chroma of florets and stems equivalent to ST-blanched broccoli. MW-blanched broccoli had flavor and general acceptability scores similar to BW-blanched broccoli. After 4 weeks in frozen storage, MW-blanched broccoli had the highest RAA content.     

EFFECT OF HEATING METHODS ON THIAMINE RETENTION IN FRESH OR FROZEN PREPARED FOODS

SUMMARY— Thiamine retentions were determined in beef stew, chicken a la f or newburg and peas in cream sauce, which ware 11 freshly prepared and held for 1, 2 or 3 he ld 180°F (82.2°) or 2) freshly prepared, frozen at −10°F (−23.3°C) and reheated to reheated using microwaves, infrared heating or boiling water immersion. Similar treatments had the on the thiamine retention in the various products. The average thiamine retentions Boy de n products (based on 100% for the freshly prepared foods) were 93.5% in the frozen-microwave heated products; 90% in the frozen-infrared heated products; 86% in the frozen-immersion hot products versus 78% in the fresh hot products after 1 hr, 74% after 2 hr and 67% after 3 hr.     

THERMO-PHYSICAL PROPERTIES OF SELECTED VEGETABLES AS INFLUENCED BY TEMPERATURE AND MOISTURE CONTENT

Thermo‐physical properties of selected vegetables (cassava, eggplant, ginger, green pepper, white radish and zucchini) were evaluated under different conditions of temperature (5 to 40C) and moisture content (30 to 94% wb). Test samples were equilibrated to a given temperature and moisture content prior to use. The thermal conductivity and heat capacity were measured using the line heat source probe and the differential scanning calorimeter, respectively. Depending on the state, temperature, moisture content and the type of vegetable, average heat capacity varied from 1.5 to 4 kJ/kgC, while the thermal conductivity varied from 0.08 to 0.60 W/mC. Heat capacity of the unfrozen vegetables was found to be approximately twice as much as values obtained for the frozen ones. Although both temperature and moisture affected the thermal conductivity, the latter had the greater influence. Generally, differences in measured data and responses to both temperature and moisture content were attributed to differences in structural characteristics and composition. Correlations were developed for estimating thermo‐physical properties of several vegetables.     

CHEMICAL, NUTRITIVE AND SENSORY CHARACTERISTICS OF TOMATOES BEFORE AND AFTER CONVENTIONAL AND MICROWAVE BLANCHING AND DURING FROZEN STORAGE

The objective of this study was to evaluate the effects of microwave blanching on chemical, physical and sensory characteristics of tomatoes prior to and after frozen storage. Tomatoes were blanched (4 min) using four treatments: conventional boiling water (BW), steam (ST), microwaved in a glass container (MW), and microwaved in boilable bags (MWB). The lowest moisture content occurred in MW‐blanched tomatoes before (92%) and after (86%) frozen storage. These tomatoes had the highest reduced ascorbic acid (RAA) content and the highest RAA retention (> 23 mg/100 g, >91%) after blanching and after frozen storage. After blanching, MWB‐blanched tomatoes were the lightest, while after frozen storage, ST‐blanched tomatoes were the lightest. BW‐blanched tomatoes had generally higher flavor, texture and appearance scores. This study demonstrated that though visual color and sensory attributes were highest for BW‐blanched tomatoes, MW‐blanched tomatoes retained more nutritive value in the finished product.     

THE INFLUENCE OF BLANCH AND FREEZING METHODS ON THE QUALITY OF SELECTED VEGETABLES1

Microwave blanced vegetables were lower in color and ascorbic acid than water or steam blanched vegetables. Shear values for microwave blanched asparagus were higher than the values for water or steam blanched. Drip loss was higher for microwave blanched green beans and peas than water or steam blanched. The reverse was true for asparagus. Sensory preference scores for color and flavor were very low for the microwave blanched vegetables. Little or no difference in quality was found between water and steam blanched vegetables. Individually quick frozen vegetables displayed less drip loss than common blast frozen vegetables and shear values were lower.     

SENSORY AND MECHANICAL ATTRIBUTES OF GEL TEXTURE

Eighteen experienced judges evaluated the texture of gels varying in gelatin concentration (22-45 g/L) in terms of firmness by oral and manual shear and compression, cohesiveness, and extent of breakdown in the mouth. Manual compression and biting with the front teeth discriminated well across gel concentrations. All sensory measures except extent of breakdown increased with gelatin concentration. Instron (IUTM) measurements showed that increasing gelatin concentration resulted in an increase in maximum force and force/deformation, but had little effect on deformation at yield and rupture or in elasticity and cohesiveness. Results from mechanical measurements varied with the type of force applied (compression, shear or puncture), the loading rate (50 or 200 mm/min), and the extent of deformation attained (40–90%). The highest discrimination across gel concentrations was achieved with shear force at a rate of 200 mm/min and at greater deformations. Sensory responses correlated most highly with the following IUTM measurements: (1) Compression forces at yield and at deformations of 70 and 85% at the higher crosshead speed; (2) Compression forces below the yield point at the lower crosshead speed; and (3) Shear forces measured at maximum deformation (90%) at 200 mm/min.     

IDENTIFYING OBJECTIVE CHARACTERISTICS THAT PREDICT CLUSTERS PRODUCED BY SENSORY ATTRIBUTES IN COOKED RICE

From eight samples of raw-milled, 10 samples of parboiled and 2 samples of canned rice, appearance, texture and flavour were determined sensorily and related to instrumental parameters and clusters of different types of rice having common sensory perceptions were identified. The physico-chemical characteristics, enthalpy of amylose-lipid complex I, protein content, length of raw grain, elastic recovery, water uptake and the viscoelastic index, varied widely between rice samples. The most discriminatory sensory attributes were appearance and texture characteristics such as 'brown', 'elastic', 'long', 'firm' and 'shiny'. The instrumental measurements were highly correlated with sensory parameters. Parboiled rice samples, characterised by a brown colour, an elastic—firm—smooth texture and a broth flavour, were different from the raw-milled rice samples described as 'juicy', 'melting', 'shiny', 'aggregated and swollen grains', 'starch and milk' flavour. Canned rice samples were distinguished by a 'jute and earth' flavour, 'bitterness' and the presence of 'foreign matter'. Five clusters of types of rice could be distinguished which were characterised by a soft texture for the first, by a sticky-pasty texture for the second, by a brioche flavour and medium intensity characteristics of sticky and melting texture for the third, by the length of grain and a slight crunchy texture for the fourth, and by the firmness and elasticity for the last cluster. Five instrumental determined characteristics, enthalpy of amylose-lipid complex I, thickness of cooked grain, water uptake, browness index and protein content classed each rice into one of these 5 clusters with an error of 4%.