EFFECT OF MICROWAVE POWER LEVEL AND TIME ON ASCORBIC ACID CONTENT, PEROXIDASE ACTIVITY AND COLOR OF SELECTED VEGETABLES

The objective of these studies was to evaluate the effects of blanching at various microwave power levels (30%, 55%, 70%, 100%) for times (0, 1, 2, 3, 4 min) on peroxidase inactivation, and ascorbic acid and color preservation in broccoli, green beans and asparagus. As power level and time increased, moisture losses increased. Actual ascorbic acid concentration (mg/100 g) increased, but when adjusted for moisture loss, it decreased. Microwave treatment at any power level for as little as 1 min reduced peroxidase activity. However, at higher powers (70% and 100%), less time was required to achieve the maximum reduction. Microwave heating at 70% or 100% caused some darkening (decreased L* value). Hue angle decreased (less green) at 55 %, 70% and 100% power after 1 min of treatment. Overall, microwave power level and time had greater effects on moisture, RAA content and on peroxidase activity than on color.     

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).     

PHENOLIC COMPOUNDS AND ANTIOXIDANT POWER IN MINIMALLY PROCESSED SALAD

ABSTRACT

Phenolic content and antioxidant power of Lactuca sativa var. capitata (L.), Cichorium indivia var. latifolium (L.) and Eruca sativa (Mill.) were determined in fresh‐cut products during storage at 4C. In fresh‐cut leaves, storage did not affect the antioxidant power in escarole, whereas after 24 h, lettuce exhibited a transient rise in ferric‐reducing antioxidant power value (+50%), which was associated with increased phenol content. In rocket salad, the antioxidant power increased significantly just 1 h after cutting. The major phenols determined in escarole and lettuce hydroxycinnamic derivatives were chlorogenic acid, di‐caffeoylquinic and caffeoyltartaric acids, which increased significantly in fresh‐cut products of both species during storage. In rocket salad, only hydroxycinnamic and kaempferol derivates were found, and their content was not influenced by processing and storage even if it is probably related to the higher antioxidant power found for this species.

PRACTICAL APPLICATIONS

Many phenolic compounds are antioxidants that may contribute to reduce human diseases (e.g., cancer and heart diseases). The beneficial effects of a diet rich in vegetables have been partially attributed to an increased consumption of phenols with high antioxidant capacity. Processing vegetables (e.g., salad) for minimally processed products influences the antioxidant capacity of the tissues with different effects in relation to the species used.     

EXTRUSION COOKING OF RICE: EFFECT OF AMYLOSE CONTENT AND BARREL TEMPERATURE ON PRODUCT PROFILE

The effect of amylose content (5.0–28.6%) of rice and barrel temperature (80–120C) on extrusion system parameters torque and net specific mechanical energy and extrudate characteristics extrudate bulk density (ED), water solubility index, expansion ratio (ER) and Warner–Bratzler shear stress were studied using a twin‐screw extruder. The feed rate (15 kgh^?1), moisture content (20.0% ± 0.2) of feed and the screw speed (400 rpm) were kept constant. ED and ER of the product suggested that a barrel temperature of 120C was desirable to generate an expanded extrudate rice product from low‐amylose rice cultivar. Experimental data on system parameters and extrudate characteristics fit to second‐degree polynomial regression equations (r ≥ 0.904, P ≤ 0.01) with the amylose content of rice and barrel temperature of the extruder.