Tung-Ching Lee

Antioxidant activity and phenolic compounds of Swiss chard (Beta vulgaris subspecies cycla) extracts

The antioxidant activity (radical scavenging and thiocyanate method), total phenolic contents (gallic acid equivalents) and phenolic composition (coulometric array detection) in methanol extracts of different parts and tissue types of hydroponically grown Swiss chard (Beta vulgaris subspecies cycla) were determined. Significant differences (P <0.01) in the antioxidant activity were found between leaves and stems. Phenolic content and composition of the leaves and the stems also were found to be different. A positive linear correlation (R=0.943) was demonstrated between radical scavenging activity and total phenolic content of each extract. The major phenolic acid and flavonoid in leaves of Swiss chard were syringic acid and kaempferol. Coulometric array detection showed good reproducibility (CV, 0.06–1.05%) and sensitivity (1 ng/ml, detection limit) for simultaneous detection of 13 phenolics. Our data indicates that Swiss chard has potential as a good dietary source of phenolic antioxidants.

Reducing the brittleness of zein films through chemical modification.

Zein protein is a major coproduct of biofuel from corn. To reduce the brittleness of zein films, a new type of zein-based biomaterial, was synthesized by chemical modification of zein with lauryl chloride through an acylation reaction. The final products were confirmed by (1)H NMR, FT-IR analysis, and SDS-PAGE. Thermal analysis detected no microphase separation in the synthesized polymer matrix. As the content of lauryl moiety increased, the glass transition temperatures of modified zein decreased by as large as 25.8 °C due to the plasticization effect of the lauryl moiety. In addition, mechanical and surface properties of cast films from acylated zein were also investigated. The elongation at break of modified zein sheet was increased by about 7-fold at the high modification level with some loss of mechanical strength. The surfaces of modified zein films were as uniform as unmodified zein film but more hydrophobic, further suggesting that no microphase separation happened during the film formation process. This work indicated the potential of these new biomaterials in the development of biodegradable food packaging materials and delivery systems.

Improved mechanical property and water resistance of zein films by plasticization with tributyl citrate.

Pure zein film is intrinsically rigid and brittle and lacks necessary mechanical properties for industrial processing. In addition, pure zein film is sensitive to high relative humidity, which limits its application in food packaging. To improve these properties, tributyl citrate (TBC) was incorporated into zein film to the mass ratios from 10% to 50%. A significant decrease in Youngs modulus was observed, from 409.86 MPa in pure zein films to 136.29 MPa in zein films with 50% TBC. Among all films, those containing 10% TBC are most flexible and toughest. Both DSC and microscopy methods suggested that the TBC may be loaded up to 20% to avoid microsized phase separation. Through modeling with experimental data, incorporating 50% TBC reduced the water absorption capacity to 12.94% compared to 31.78% by pure zein film. More importantly, the integrity of zein/TBC film was maintained at high relative humidity and even after immersion in water. However, more than 20% TBC in zein films led to microsized phase separation, which was harmful to mechanical properties.

Variation for antioxidant activity and antioxidants in a subset of AVRDC—the World Vegetable Center Capsicum core collection

Pepper ( Capsicum sp.) is important in human diets in many parts of the world and a major source of several antioxidants, including carotenoids, ascorbic acid, tocopherols and phenolics. More information on genetic diversity within Capsicum for antioxidant (AO) content and antioxidant activity (AOA) could contribute to improved human health. We evaluated 46 Capsicum accessions from AVRDC—the World Vegetable Center Capsicum core collection for content of nine AO (five carotenoids, ascorbic acid, tocopherols α and γ, and total phenolics) and two AOA assays for 2 years in south Taiwan. Ample genetic diversity exists within C. annuum to increase AO content. Based on dry weight values, non-pungent C. annuum entries as a group were significantly greater than pungent entries for contents of β-cryptoxanthin (36%), ascorbic acid (65%), total phenolics (36%) and α-tocopherol (11%). Group means of the brown-fruited entries exceeded the means of red-fruited entries for capsanthin (34%), zeaxanthin (37%), lutein (36%), β-cryptoxanthin (71%), β-carotene (82%), ascorbic acid (19%) and α-tocopherol (40%). Red-fruited C. annuum entries ‘Verdano Poblano’ and ‘Guajillo Ancho’ from Mexico ranked among the entries highest for all carotenoids, ascorbic acid and α-tocopherol. The inhibition of lipid peroxidation (ILP) assay could be adopted for AOA characterization or selection because of high variation among entries and consistent entry performance over years. ILP was positively correlated with phenolics ( r =0.72**) and ascorbic acid ( r =0.58**) contents. Significant positive correlations were detected between most carotenoids as well as a significant positive correlation between ascorbic acid and total phenolics contents ( r =0.78**).

Nutritional and Toxicologic Effects of Nonenzymatic Maillard Browning

The Maillard nonenzymatic browning reaction is known to cause serious reduction in the nutritionai value of foods. The reduced nutritionai value does not seem to be limited to the loss of amino acids, as supplementation of the diet with those amino acids does not completely restore its biologic value. When rats were fed a browned egg albumin diet and a control diet of equal protein quality for up to 12 mo, the rats fed browned diet showed enlarged cecums, livers, and kidneys and reduced weight gain. In addition, intestinal digestive enzyme activities decreased, and serum alkaline phosphatase and serum glutamic oxaloacetic transaminase (GOT) activities increased compared to the control group. The livers of the rats fed browned protein showed histopathologic changes including fatty change and an unknown pigment accumulation. The data indicate a possible cumulative toxic effect due to the long-term feeding of Maillard browned compounds. The mutagenic activity of Maillard browned egg albumin was also tested. No mutagenic effect was observed. The products of the nitrosation of the Amadori compound fructosyl-L-trytophan were mutagenic, however, in strains TA 1535 and TA 100 of the Salmonella/mammalian microsome mutagenicity assay.

Effect of Maillard Browning Reaction on Nutritional Quality of Protein

The Maillard reaction, or non-enzymatic browning reaction, between reducing sugars and proteins (amino acids), is known to cause serious deterioration of food quality during processing and storage. Increasing evidence shows that these compounds formed under mild conditions substantially reduce the availability of amino acids and proteins. Data obtained by ourselves and others has shown there is a significant decrease in the nutritional value of foods which undergo the Maillard reaction beyond that accounted for in the loss of biologically available lysine. In the present investigation, a mixture of egg albumin and glucose was used as a model system. The nutritional quality of egg albumin as a function of the extent of Maillard browning with periods of less than 10 days of storage was evaluated by in vivo and in vitro methods. A substantial decrease in nutritional quality of protein was observed even at the initial period of storage (less than three days) and most available in vitro methods could not reveal this change. The result of a three-month rat feeding experiment indicated that there were physiological and biochemical changes in rats fed with browned protein diet. It is extremely inportant at the present time to have information on the nutritional value and aspects of food safety of browned food products with respect to nutritional labelling policy. Therefore, in addition to the development of new food products with high protein quality, the practical applications of this study are also discussed.

Structure and physical properties of zein/pluronic f127 composite films.

Triblock copolymer Pluronic F127 has been used to form composites with zein, a corn protein and coproduct of the bioethanol industry, to alleviate its natural brittleness. At low F127 loadings (0-35%), the plasticizing effect was dominant, and the elongation at break of zein composite film containing 35% F127 was about 8-fold higher than that of the zein film with 10% F127. At high F127 loadings (50-100%), a large number of lamellae crystals were formed in the film matrix as verified by a combination of differential scanning calorimetry (DSC), atomic force microscopy (AFM), and small-angle X-ray scattering (SAXS). The F127 crystallization surpassed its plasticizing effect, resulting in an increased brittleness of zein film with the further increase of F127 loading. Compared with the flat-on lamellae of pure F127, F127 chains folded into branch-like lamellar structures in the zein composite film containing 50% F127 due to the confinement of amorphous zein. Besides, the crystals in zein films were composed of extended chain integral folding (IF = 0) and once-folded chain (IF = 1) polyethylene oxide (PEO) crystals, and the portion of once-folded chain (IF = 1) PEO crystals increased with F127 loading. Thus, through investigation of the competition of plasticizing effect and crystal formation under different F127 loadings, the optimized F127 loading in zein/F127 composite film with a good overall performance was determined to be at around 35%.

Absence of overt toxicity from feeding the flavonol, quercetin, to rainbow trout (Salmo gairdneri)

The toxicity of the plant flavonol, quercetin, to rainbow trout (Salmo gairdneri) was investigated. Quercetin, which had been confirmed to be mutagenic in the Ames Salmonella/mammalian microsome test, was fed to trout at levels of 1 or 5% in the diet for 8 months. Survival, growth and feed conversion efficiency, selected haematological parameters and the relative weights of heart, liver and spleen were unaffected by the ingestion of quercetin, and there were no histopathological changes in any of the tissues examined.

Biodegradability of chitin- and chitosan-containing films in soil environment

The biodegradation of polyethylene-chitin (PE-chitin) and polyethylene-chitosan (PE-chitosan) films, containing 10% by weight chitin or chitosan, by pure microbial cultures and in a soil environment was studied. Three soil-inhabited organsims,Serratia marcescens, Pseudomonas aeruginosa, andBeauveria bassiana were able to utilize chitin and chitosan in prepared PE-chitin and PE-chitosan films after eight weeks of incubation at 25°C in a basal medium containing no source of carbon or nitrogen. In a soil environment, the biodegradation of those films was studied and compared with a commercial biodegradable film containing 6% by the weight of corn starch. In soil placed in the lab, 73.4% of the chitosan and 84.7% of the chitin in the films were degraded, while 46.5% of the starch in the commercial film was degraded after six months of incubation. In an open field, 100% of the chitin and 100% of the chitosan in the films were degraded, but only 85% of the starch in the commercial film was degraded after six months of incubation. The weight of controls, (polyethylene films), remained mainly stable during the incubation period. Both PE-chitin and PE-chitosan films degraded at a higher rate than the commercial starch-based film in a soil environment indicating the potential use of chitin-based films for the manufacturing of biodegradable packaging materials.

Effect of temperature perturbations on tomato (Lycopersicon esculentum Mill.) quality and production scheduling

Summary Controlled environment experiments were conducted to evaluate the effect of a 2-week change in air temperature imposed after first fruit-set on tomato production scheduling and on the quality of vine-ripened fruit. Experiments were conducted with hydroponically-grown tomato (Lycopersicon esculentum Mill., cv. ‘Laura’). Air temperature was altered from control day/night temperature values of 23°/18°C for a 2-week period starting 10 d after fruit-set. Plants were returned to the 23°/18°C temperature and a minimum of eight fruits per treatment were harvested at three ripening stages, breaker (when 25% of the fruit skin had acquired a red tint), breaker plus 3 d, and breaker plus 6 d. A perturbation of ± 5°C (28°/23°C and 18°/13°C) was used in two Experiments (E1 and E2) and ± 7°C (30°/25°C and 16°/11°C) was used in a third Experiment (E3). Fruits were more responsive to an increase than to a decrease in temperature. Reductions in days to harvest (from 3.1 – 8.5 d) and fruit fresh weight at later stages of vine-ripening were observed for the high temperature treatments. Colour indices, soluble solids contents (SSC), acidity and viscosity at each ripening stage were significantly affected by high temperature treatments. The results indicate that short-term temperature perturbations following first fruit-set can influence the rates at which changes occurred in the external appearance of fruit (colour) and in their internal characteristics. The results can be used to improve environmental control and management strategies for tomato growers.