QUENCHING MECHANISMS AND KINETICS OF CAROTENOIDS IN RIBOFLAVIN PHOTOSENSITIZED SINGLET OXYGEN OXIDATION OF VITAMIN D2

The oxidation of vitamin D₂ in a solution of 12% water, 88% acetone and 15 ppm ribqflavin under light or dark was studied by measuring the headspace oxygen. Ribofiavin accelerated the oxidation of vitamin D₂ by singlet oxygen under light, but did not affect vitamin D₂ oxidation under dark. Quenching mechanisms and kinetics within the range of 0–20 ppm β‐cawtene or fucoxanthin and with 0–80 ppm retinyl acetate or retinol on 15 ppm riboflavin photosensitized singlet oxygen oxidation of vitamin D₂ were also studied. The rate of singlet oxygen formation by 15 ppm riboflavin was 1.78 umole oxygen/mL headspace‐hour. The reaction rate constant of vitamin D₂ with singlet oxygen was 2.2 times 10⁷ M^?1A s^?1. The carotenoids minimized the oxidation of vitamin D₂ by quenching singlet oxygen. The total quenching rate constants of retinol, retinyl acetate, jucoxanthin and ft‐carotene were in the order of 1.22 times 10⁸, 5.98 times 10⁸, 1.78 times 10⁹ and 5.00 times 10⁹M^?1. s^?1 respectively, which suggests that as the number of double bonds of carotenoids increases, the quenching rate constant ofcarotenoid increases.     

CHARACTERIZATION OF THE DIFFERENT STATES OF MYOGLOBIN IN PORK USING COLOR PARAMETERS AND REFLECTANCE RATIOS

Because color is becoming more important to the food industry, color studies are being conducted to improve the control of both raw materials and processes. Several studies have pointed to the importance of the different states of myoglobin in determining the color changes which take place during processing. The aim of this study was to characterize the color parameters (CIE LAB coordinates, reflectance spectrum and reflectance ratios) of the three myoglobin forms (deoxymyoglobin, oxymyoglobin and metmyoglobin) in pork Subscapularis muscle. The deoxymyoglobin present in fresh pork lean meat was converted into the pure states, and color parameters (lightness, redness, yellowness, hue, chroma and a*/b* ratio), reflectance spectrum (400–700 nm) and reflectance ratios (R560/R500, R650/R570, R630/R580 and R630-R580) were obtained. All the color parameters and reflectance ratios (except redness values) varied according to the state of the myoglobin.     

EFFECTS OF LOW CONCENTRATIONS OF H2O2 ON LIPID OXIDATION AND OF STORAGE AND pH ON NONHEME IRON CONTENT OF RAW BEEF MUSCLE

Ground beef samples were prepared from semimembranosus muscles, and beef muscle residue devoid of heme pigments was prepared by repeated washing of the ground muscle with distilled-deionized water. When ground muscle, or muscle residue samples treated with metmyoglobin-H₂O₂ (4 mg metmyoglobin/g muscle residue; 1:0.1 to 1:1 for molar ratio of metmyoglobin to H₂O²) were stored at 4°C for 0 or 6 days, no changes in nonheme iron content were observed. Similarly, nonheme iron content of stored samples was not affected by pH (5.5, 6.0 or 6.5). While metmyoglobin-H₂O² added to water-extracted beef muscle residue catalyzed the oxidation of the indigenous lipids, treatment of the residue with H₂O² alone had no effect on the oxidation.     

PREPARATION AND CHARACTERIZATION OF AFLATOXIN B2a-HEMIGLUTARATE AND ITS USE FOR THE PRODUCTION OF ANTIBODY AGAINST AFLATOXIN B1

Hemisuccinate (HS) and hemiglutarate (HG) of aflatoxin B_2a (afla B_2a) were prepared by refluxing afla B_2a with the corresponding anhydride and 4-N, N-dimethylaminopyridine in tetrahydrofuran. Two epimers of the respective HS or HG which show different chromatographic behavior and physiochemical properties were isolated and characterized. Afla B_2a-HS hydrolyzes very rapidly in aqueous solution and was not used for further study. Afla B_2a-HG hydrolyzes at a much slower rate and was selected for the coupling to protein. Using the mixed anhydride method, as much as 12 moles of afla B_2a-HG were conjugated to each mole of bovine serum albumin (BSA). The antibody obtained from rabbits immunized with afla B_2a-HG BSA is most specific to afla B₁ and shows little cross reaction with afla G₁ and aflatoxicol. The lower limit for detection of afla B₁ by radioimmunoassay using this antibody is in the range of 30–50 pg per assay.     

THE INTERACTION OF DORMANCY AND WATER-SENSITIVITY OF BARLEY WITH TEMPERATURE

Newly-harvested Scotch barley was dried and put into storage at 90, 100, 110 and 120° F. One sample at each temperature was cooled at a slow rate (2° F./week) and one at a fast rate (2° F/day). The loss of dormancy and water-sensitivity was followed throughout the drying and storage periods. Dormancy and water-sensitivity were lost most rapidly at high drying and storage temperatures. The optimum drying and storage conditions produced a non-water-sensitive, non-dormant barley within 14 days of harvest. Calculation of regression coefficients for percentage loss of dormancy and water-sensitivity per day at average storage temperatures enabled activation energies to be calculated for the two processes. These were 17·5 and 18·3 kcal/mole respectively. Two very similar processes are therefore involved in dormancy and water-sensitivity and their removal.     

EFFECT OF SALICYLHYDROXAMIC ACID (SHAM) ON DL-DOPA OXIDATION BY MUSHROOM TYROSINASE AND BY NaIO4

Salicylhydroxamic acid (SHAM) inhibits very effectively the rate of DL‐DOPA oxidation by mushroom tyrosinase. SHAM also affects the spectrum of the initial produces) formed when DL‐DOPA is oxidized by mushroom tyrosinase or by NaIO4. Moreover, at certain concentrations, SHAM prevents the polymerization of dopaquinone formed enzymaticatty or nonenzymatically probably due to a chemical interaction between dopaquinone and SHAM.     

THE USE OF CO2 IN PACKAGING OF FRESH RED MEATS AND ITS EFFECT ON CHEMICAL QUALITY CHANGES IN THE MEAT: A REVIEW

The antimicrobial effect of carbon dioxide (CO₂) is well documented but comparison of the large number of often contradictory studies investigating the effect of CO₂ on chemical quality changes is lacking. The amount of absorbed CO₂ varies from 0 - 1.79 L CO₂/kg meat depending on the applied packaging and storage conditions, which clearly demonstrates the necessity of optimizing these conditions with respect to the required amount of CO₂. Absorption of large amounts of CO₂ in meat tissue can cause a minor decrease in pH due to the dissociation of the produced carbonic acid to bicarbonate and hydrogen ions. A decrease in pH might affect other chemical quality parameters but this is not observed to be the case in the reviewed studies and general detrimental effects of CO₂ cannot be found for color, weight loss or lipid oxidation. However, elevated CO₂ levels can cause pore formation in cooked meat.     

THE EFFECTS OF FEEDING ELEVATED LEVELS OF VITAMINS D3 AND E ON BEEF QUALITY

Yearling (12 Angus, 12 Wagyu ≥ Angus) and 2-year old heifers (12 Angus, 12 Wagyu ≥ Angus) were fed elevated levels of Vitamin D ₃ and/or Vitamin E to evaluate beef quality. Warner-Bratzler shear force (WBS) and sensory characteristics were determined on steaks from the Longissimus lumborum (LL) aged 21 days and on steaks from the Gluteus medius (GM) and Psoas major (PM) aged 7 days. Steaks were cut from all muscles, displayed for 5 days then L * value and hue angle were determined. Vitamin E supplemented heifers received the highest sensory tenderness and juiciness scores, while no differences were observed among other treatments. D ₃+ E supplemented Angus LL had higher WBS values than other treatments and breeds. Display time affected both color measures for all muscles, but especially hue angles of GM and PM. Vitamin treatment affected LL and GM color measures in yearlings to a greater extent than in 2-year olds.     

CONCENTRATION OF ONION JUICE VOLATILES BY REVERSE OSMOSIS AND ITS EFFECTS ON SUPERCRITICAL CO2 EXTRACTION

Supercritical carbon dioxide extraction of onion oil at moderate temperatures produces aproduct which is characteristic of the fresh flavor of onions. It was attempted to improve extraction efficiency by concentrating the onion juice by reverse osmosis prior to supercritical CO₂ extraction. Reverse osmosis was carried out for all combinations of 600, 700, and 800 psi feed pressure and 25 and 35C. The juice was concentrated to 18 ^oBtix and then subjected to supercritical CO₂ extraction. The effect of concentration on the extraction process was evaluated by comparing the yields of extracts from concentrated juice with that of single strength juice. Concentration of onion juice by reverse osmosis improved the efficiency of supercritical CO₂ extraction of onion oil and did not alter its characteristic fresh aroma.     

EFFECT OF BENZOIC ACID AND SOME OF ITS DERIVATIVES ON THE RATE OF DL-DOPA OXIDATION BY MUSHROOM TYROSINASE1

Vanillic acid and salicylic acid inhibited the rate of dihydroxyphenylalanine (DL-DOPA) oxidation to dopachrome (γ_max=475 nm) by tyrosinase at all concentrations tested. Benzoic acid and p-hydroxybenzoic acid (PHBA), at relatively low concentrations, slightly stimulated the rate of DL-DOPA oxidation, whereas at higher concentrations each inhibited the reaction. p-Hydroxybenzoic acid methyl ester (PHBAME), at relatively low concentrations, had a pronounced synergistic effect on the reaction, whereas at relatively high concentrations it inhibited the rate of DL-DOPA oxidation. The synergistic effect of 1.6–6.6 mM PHBAME on the rate of DL-DOPA oxidation to dopachrome was found to be only an apparent effect due to the ability of PHBAME to be hydroxylated very slowly by tyrosinase to a yellow pigmented product(s) with DL-DOPA serving as a reductant (AH₂) for the hydroxylation reaction, thus hastening the conversion of PHBAME to pigmented product(s). Vanillic acid, salicylic acid, benzoic acid and PHBA could not be hydroxylated by tyrosinase.     

EFFECT OF CaCl2 AND CONVECTIVE-OSMOTIC DRYING ON TEXTURE AND PREFERENCE OF APPLE

Conventional air‐drying combined with osmotic dehydration was researched as a potential method for drying apple cubes of superior quality. Samples were pretreated with CaCl₂ at different temperatures and times. Pretreated apple cubes were dehydrated in a tray dryer. Then, osmotic dehydration with sucrose solutions was carried out. The curves for osmotic dehydration showed that the gain of solids was higher when 40% of water was removed by convective drying while the loss of weight was lower at the same level of dehydration at 65°Brix. Texture measurements indicated that the temperature of pretreatment affected the hardness and cohesiveness. Hardness values were higher at 40C, while cohesiveness values were lower at the same temperature. The CaCl₂ at a given temperature did not have a significant effect on texture. Sensory evaluation showed that samples pretreated at 25C and osmotically dried at 50°Brix had the higher preference by the judges.     

THE INFLUENCE OF OXYGEN ON THE PRODUCTION OF DIACETYL DURING FERMENTATION AND CONDITIONING

Although varying concentrations of oxygen in wort at pitching do not affect the production of diacetyl, its availability during fermentation has a significant effect. The enhanced production of diacetyl resulting from access of oxygen during fermentation is caused by its effect in increasing yeast growth and in altering the balance of amino acids relative to sugars and not by a direct oxidation of acetoin. Oxygen has no effect upon the concentration of diacetyl during storage and conditioning, provided that the beer is free from contamination.