Physiology and Microbiological Quality of Fresh-cut Mango Cubes as Affected by High-O2 Controlled Atmospheres

Preliminary study showed that among 40‐ to 100‐kPa O₂ atmospheres, 60‐kPa O₂ reduced the respiration of fresh‐cut ‘Carabao’ mango cubes the most when held at 5 °C or 13 °C for 42 h. Therefore, the effects of 60‐kPa O₂ on the physiology and microbial quality of fresh‐cut ‘Carabao’ and ‘Nam Dokmai’ mango cubes were determined and compared with those held in air. The high‐O₂ atmosphere reduced the respiration rate of ‘Carabao’ mango cubes stored at 5 °C but stimulated the rate after 2 d of storage at 13 °C. Browning of ‘Carabao’ cubes was accelerated by 60‐kPa O₂ at 13 °C. With ‘Nam Dokmai’ cubes, the high O₂ had no effect on respiration rate, browning, and incidence of water‐soaked appearance at 5 °C and 13 °C. The high O₂ did not affect texture or ascorbic acid content of ‘Carabao’ and ‘Nam Dokmai’ mango cubes at either temperature. Counts of lactic acid bacteria and molds were below the detection level (2.4 log colony‐forming units [CFU]/g) during storage at both temperatures. However, 60‐kPa O₂ stimulated the growth of mesophilic aerobic bacteria on ‘Carabao’ cubes and yeasts of ‘Nam Dokmai’ cubes at 13 °C. The increased microbial count may have been due to the higher pH of cubes stored in 60‐kPa O₂ at 13 °C than at 5 °C or in air. Within ‘Nam Dokmai’ mango cubes, the predominant genera in mesophilic aerobic bacteria were Enterobacter, Klebsiella, and Pantoea and in the yeasts were Candida, Cryptococcus, and Rhodotorula. These results indicate that 60‐kPa O₂ is not desirable for mango cubes when held at 13 °C.     

Low O2 Atmospheres Affect Storage Quality of Zucchini Squash Slices Treated with Calcium

Calcium chloride treated or nontreated zucchini squash slices were stored in air or low O₂ (0.25, 0.5 and 1%) at 10°C. Respiration rate, ethylene production, and development of browning/decay were reduced under low O₂. Slices stored under 0.25% O₂ had less weight loss and browning/decay, and greater shear force and L-ascorbic acid content than those stored in air. Microbial count, pH, and color at the end of storage were improved by low O₂. Calcium treatment had no additive effect on maintaining quality of zucchini squash slices stored in 0.25% O₂ atmosphere.     

Studies on flavonol degradation by peroxidase (donor: H2O2-oxidoreductase,EC 1.11.1.7): Part 1—Kaempferol

The peroxidatic degradation of kaempferol was studied at pH 5·5 under UV-spectrophotometric control. The reaction products obtained after incubation of kaempferol (dissolved in ethylene glycol monomethylether) with peroxidase (Boehringer, Mannheim)/H₂O₂ were fractionated in preparative scale by liquid chromatography on Sephadex LH-20. About twenty compounds were detected by analytical HPLC, from which four substances could be characterized by means of their spectroscopic data: 2,4,6-trihydroxybenzoic acid, 4-hydroxybenzoic acid, 2,2-dihydroxy-1(2,4,6-trihydroxyphenyl)-3(4-hydroxyphenyl)-1,3-propandione and 2-(4-methoxyphenyl)-5,7-dihydroxy-4H-1-benzopyran-4-one (acacetin).     

Supercritical CO2 Extraction of Oil from Atlantic Mackerel (Scomber scombrus) and Protein Functionality

Supercritical carbon dioxide (SC-CO₂) extraction temperature and pressure for oil removal from freeze-dried, fall Atlantic mackerel muscle were optimized. The effect of extraction conditions on pH and water-binding potential (WBP) of the protein residue was evaluated. For the temperature range (35–55°C) and pressure interval (20.7–34.5 MPa), 34.5 MPa/35°C gave highest oil yield and concentration of ω-3 fatty acids. SC-CO₂ extraction at higher pressure levels caused slight decreases in protein residue pH. WBP of residual proteins was maximal at 1.49g H₂O/g protein for 34.5 MPa/45°C. The high lipid removal and retention of protein functionality in the residue after oil extraction may make such processes useful for future food applications.     

PRODUCTION OF CO2 AND C2H4 AFTER GAMMA IRRADIATION OF STRAWBERRY FRUIT

Strawberry fruit (Fragaria ananassa, Duch. cv ‘Kent’) were irradiated at doses from 0 to 4 kGy and stored at 10°C to verify whether irradiation at very low doses could delay postharvest ripening while causing minimal damage to the tissues. CO₂ and C₂H₄ production were used as stress indicator. Anthocyanins and titratable acidity were measured as maturity parameters. CO₂ and C₂H₄ production increased six hours after irradiation. The increase in CO₂ production was proportional to the dose of irradiation and was highest at 4 kGy. Maximum C₂H₄ production was reached at 1 kGy. The different response of CO₂ and C₂H₄ production to irradiation suggests that the membrane system supporting C₂H₄ production was more sensitive to gamma rays than mitochondrial CO₂ production. Irradiation at 0.3 kGy slightly delayed color development in the fruit. Overall, the results indicated that it may be possible to use irradiation at a low dose to delay ripening while causing only minimal tissue damage.     

Effects of Short-term Exposure to Low O2 and High CO2 Atmospheres on Quality Attributes of Strawberries

Strawberries (Fragaria ananassa Duch., cv. ‘Selva') were stored 10 days in 1.0%, 0.5%, or 0.25% 0₂ or air + 20% CO₂; or 6 days in air + 50% or 80% CO₂ at 0 or 5°C without detrimental effects on quality. Decay and softening were reduced by treatments. An untrained taste panel, under ordinary eating conditions, did not consistently differentiate ‘Pajaro’ strawberries kept in 0.25% 0₂ from those stored in air. A trained taste panel, under controlled conditions, perceived slight off-flavor in ‘G3’ strawberries kept in 0.25% or 0% 0₂. This correlated with ethanol, ethyl acetate, and acetaldehyde in juice. The 50% or 80% CO₂ treatments caused injury after 8 to 10 days, while 20% CO₂ treatments did not. All high CO₂ treatments caused increase in pH of juice.     

Formation of Cholesterol-5,6-Epoxides during Spray-drying of Egg Yolk

An indirect heated spray dryer with an evaporative capacity of up to 7 kg H₂O/hr was used to identify factors responsible for formation of cholesterol-5,6-epoxides (CEs) in spray-dried egg yolk. CEs were not formed under various operating conditions without addition of H₂0₂ to liquid yolk. At 10% H₂O₂, 90° and 150°C outlet temperatures, concentrations of CEs were 27 and 37 ppm, respectively. At 5% H₂O₂, 90° and 150°C outlet temperatures, concentrations of CEs were undetected and 16 ppm, respectively. Antioxidants appeared to lower CEs. Small amounts of CEs were formed in products dried in the presence of low concentrations of nitrogen oxide gases (NO_x). CEs increased greatly during storage of products dried from liquid yolk containing H₂O₂.     

Protein-Protein Interactions Between Soybean Beta-conglycinin (B1-B6) and Myosin

Protein-protein interactions between soybean beta-conglycinin (B₁- B₆) and myosin were studied by turbidity, solubility and SDS-poly- acrylamide gel electrophoresis (SDS-PAGE) analysis. Turbidity and solubility studies showed that, under the experimental conditions used, these proteins interacted at temperatures between 60° and 100°C, while SDS-PAGE analysis indicated that the interaction also occurred at 50°C. The interasction was such that no detectable complexing between these two proteins was observed. The presence of beta-conglycinin resulted in diminished aggregations of myosin heavy chains between 50° and 100°C.     

Postharvest CO2 and Ethylene Production and Quality Maintenance of Fresh-Cut Kiwifruit Slices

The quality attributes and gas production of fresh-cut kiwifruit slices (Actinidia deliciosa cv. Hayward) were studied to identify the optimum ranges of storage temperature, relative humidity, and atmospheric composition. Also the effects of wounding, C₂H₄ addition or removal, and chemical treatments (calcium, ascorbic acid, citric acid) on deterioration rate were investigated. Flesh softening was the major quality loss of stored fresh-cut kiwifruit slices. Fresh-cut kiwifruit slices had a shelf-life of 9–12 days if treated with 1% CaCl₂ or 2% Ca lactate, and stored atO-2°C and >90% relative humidity in an C₂H₄-free atmosphere of 2 to 4 kPa O₂ and/or 5to10kPaCO₂.     

Optimisation of process parameters for the degradation of caffeic acid in sugar solutions

Fenton oxidation has been used to study the degradation of caffeic acid (CA), a colour precursor in sugar cane juice, in water and sucrose solutions. Central composite design and response surface methodology were used to evaluate the relationships between % CA degradation and the process parameters (i.e. CA and sucrose concentrations, pH, reagent dosages, reaction temperature and time). A quadratic polynomial model was developed for CA degradation and indicated that the initial sucrose and CA concentrations significantly affected the amount of CA degraded. Numerical optimisation was used to determine the optimum process parameters. It showed that in water at 35 °C, 80% CA was degraded at pH 5.49, 0.72 mm Fe²⁺ and 9.44 mm H₂O₂. However, in a synthetic sugar solution under similar conditions to that of factory mixed cane juice containing 13 mass% sucrose, only 61% of CA was degraded.     

Dynamic Changes of Headspace Gases in CO2 and N2 Packaged Fresh Beef

Two independent experiments were conducted to examine the effects of initial packaging/product conditions and storage conditions on in-package headspace pressure changes for modified atmosphere packaged beef during 12 hr storage. Headspace-to-meat volume ratio 1.8 to 5.9, surface area 200--800 cm², sample volume 0.22–0.75L, storage at 3–13°C and initial gas composition 20–100% CO₂ balanced with N₂ were studied. Headspace-to-meat volume ratio was the most important packaging parameter, but surface area and meat volume also affected headspace CO₂ changes. Decreased storage temperature reduced CO₂ concentration remaining in headspace. Higher initial CO₂ concentration resulted in greater concentration changes.     

Enzyme and silicone treatments on jute fibre. Part I: Effect on textile-related properties

The present study relates to broad-based assessment of softening of raw jute and selectively pretreated jute fibres under the action of mixed enzymes (cellulase, xylanase and pectinase) and a textile grade aminosilicone softener and to further assess how such selective treatments finally contribute in enhancing some textile-related properties. Application of 4% mixed enzyme on jute fibre at 55°C for 2 h at pH 4.8 offers much finer, softer, cleaner and brighter jute fibre with some lowering of bundle tenacity. However, pretreatment of jute fibre under combined oxidative action of 3% H₂O₂ and 0.75% K₂S₂O₈ for 2 h at 30°C (pH 11) followed by subsequent treatment with 1% mixed enzyme offers a better balance of textile-related properties covering moisture regain, fineness, bundle tenacity, flexural rigidity, surface reflectance, whiteness index, yellowness index and brightness index. Treatments of jute fibre with 0.5–1% aminosilicone softener under a specified condition also make jute fibre much softer, smoother, brighter and cause noticable reduction in coefficient of friction without much change in bundle tenacity. However, keeping all textile-related properties in view, a preatment of conventional 3% H₂O₂ bleaching for 2 h at 85°C (pH 11) or an oxidative treatment under combined action of 3% H₂O₂ and 0.75% K₂S₂O₈ for 2 h at 30°C (pH 11) prior to 1% aminosilicone treatment of jute fibre were found to be much useful for textile purpose.     

Ca2+-Induced Gelation of Pre-heated Whey Protein Isolate

Addition of CaCl₂ to pre-heated whey protein isolate (WPI) suspensions caused an increase in turbidity when pre-heating temperatures were ≥ 64°C. Pre-heating to ≥ 70°C was required for gelation. WPI suspensions which contained CaCl₂ became turbid at 45°C and formed thermally induced gels at 66°C. Thermally and Ca²⁺-induced gels showed significant time/temperature effects but the penetration force values in the Ca²⁺-induced gels were always lower. However, Ca²⁺-induced gels were higher in shear stress at fracture. The Ca²⁺-induced gels had a fine-stranded protein matrix that was more transparent than the thermally induced gels, which showed a particulate microstructure.     

Unraveling a mechanism of honey antibacterial action: Polyphenol/H2O2-induced oxidative effect on bacterial cell growth and on DNA degradation

Several compounds with antibacterial activities were identified in honey however, a mechanism by which they lead to bacterial growth inhibition and bacterial death remains still unknown. We recently found that honeys possess DNA degrading activity mediated by honey hydrogen peroxide and an unknown honey component(s). Here we provide evidence that active honeys (MIC₉₀ of 6.25–12.5% v/v) possessed significantly higher levels of phenolics (p < 0.02) of higher radical scavenging activities (p < 0.005) than honeys of average activity. Removal of H₂O₂ by catalase eliminated bacteriostatic activities caused by both phenolics and H₂O₂ suggesting that the growth inhibition resulted from the coupling chemistry between these compounds. Both phenolics and H₂O₂ were involved in DNA degradation by honeys. Treatment of plasmid DNA with H₂O₂ alone did not affect the DNA integrity but H₂O₂ removal from honey by catalase prevented DNA degradation. Polyphenols extracted from honeys degraded plasmid DNA in the presence of H₂O₂ and Cu(II) in the Fenton-type reaction. The extent of DNA degradation was inversely related to the polyphenol concentration in this system as well as in honeys. At low content, honey polyphenols exerted pro-oxidant activity damaging to DNA. In conclusion, honey phenolics with pro-oxidant activities were necessary intermediates that conferred oxidative action of H₂O₂. Phenolic/H₂O₂-induced oxidative stress constituted the mechanism of honey bacteriostatic and DNA damaging activities.     

Decomposition of sinigrin by methanol/ammonia/water treatment in model systems and mustard (Brassica nigra L.) seed meal

 Sinigrin (allylglucosinolate) was stored at 20  °C, 40  °C, and 60  °C in solutions containing 10% ammonia in 95% methanol (CH₃OH/NH₃/H₂O). The individual samples were analyzed for their contents of sinigrin, its decomposition product allyl isothiocyanate (AITC) and other reaction products. The major reaction products were allyl thiourea, methyl ester of N-allyl thiocarbamoyl acid and allyl cyanide. A newly identified decomposition product of sinigrin was ethylcyanide. Defatted Brassica nigra seed meal was treated by the CH₃OH/NH₃/H₂O mixture to simulate the procedure used for rape and mustard seed meal detoxification. suspensions of the meal in the above mixture of solvents were heated at 20  °C, 40  °C and 60  °C, respectively. The major reaction products were the same as those arising from sinigrin. Minor products identified were 4-hydroxybenzyl isothiocyanate formed from sinalbin and 2-hydroxy-butenyl cyanide which arises from progoitrin. In all cases, AITC was very rapidly decomposed. Mechanisms explaining sinigrin decomposition are presented and discussed. Received: 3 May 1999     

Enterotoxin C2 Production by S. aureus in Entree Salads

Staphylococcus aureus strain 361 was inoculated into salads containing chicken, macaroni, potato, or artificially flavored soy product. Egg was added to some. The pH averaged 6.2 in the control made with water dressing rather than vinegar, 4.7 with home-style cooked salad dressing, and 4.9 with commercial salad dressing. Following incubation at 37°C for 8 or 24 hr, pH, total counts, and enterotoxin C₂ were determined. Enterotoxin was detected at 8 hr in all macaroni and potato dressing types. At 8 hr, enterotoxin was not detected in most soy product or chicken salads. By 24 hr the lowest levels were in the soy product salads but all products contained toxin. When the inoculum level was reduced below the 10⁵ CFU per g used in the main study, enterotoxin production was delayed but occurred at 8 hr if the inoculum level was 10³.     

Crystallization Kinetics of Concentrated α,α-Trehalose and α,α-Trehalose/Salt Solutions Studied by Low-resolution 1H-Pulsed NMR

Crystallization kinetics of concentrated trehalose and trehalose/salt solutions were followed by proton ¹H) pulsed nuclear magnetic resonance (¹H p‐NMR). Three concentrations (66,70, and 72.5%) of trehalose and with the addition of ZnCl₂.2H₂O, CaCl₂.2H₂O, and MgCl₂.2H₂O were crystallized at 5,10,15,20, and 25 °C. Supercooling and molecular diffusion determined the crystallization rates. The highest rate of crystallization of 66,70, and 72.5% trehalose occurred at 20 °C, whereas the lowest rate occurred at 25 °C. The maximum solid content was higher at lower temperatures, as expected based on the higher supercooling values. Crystallization was delayed by the addition of salts and especially of CaCl₂.2H₂O.     

Degradation of anthocyanins in sour cherry and pomegranate juices by hydrogen peroxide in the presence of added ascorbic acid

Effects of hydrogen peroxide in the presence of ascorbic acid on the degradation of sour cherry and pomegranate juice anthocyanins were studied at three H₂O₂ concentrations (4.65, 6.98 and 9.31 mmol l⁻¹) and two ascorbic acid concentrations (60 and 80 mg l⁻¹) at 20 °C. Degradation of anthocyanins by H₂O₂ was fitted to first-order reaction kinetics in sour cherry and pomegranate juices. A similar degradation pattern was found at the 60 and 80 mg ascorbic acid levels for pomegranate juice. Degradation of sour cherry anthocyanins at the 60 mg ascorbic acid level was fitted to a second-order reaction kinetic, whereas it was a first-order reaction kinetic after a lag period occurred at the 80 mg level. Ascorbic acid, at 80 mg l⁻¹, markedly accelerated the degradation of anthocyanins in sour cherry juice at all the H₂O₂ concentrations studied. In contrast, ascorbic acid, at both 60 and 80 mg l⁻¹, protected the anthocyanins from the degradation by H₂O₂ in pomegranate juice.     

Influence of NaCl and CaCl2 on Cold-Set Gelation of Heat-denatured Whey Protein

Heat‐denatured whey‐protein isolate (HD‐WPI) solutions were prepared by heating a 10 wt% WPI solution (pH 7) to 80 °C for 10 min and then cooling it back to 30 °C. Cold‐set gelation was initiated by adding either NaCl (0 to 400 mM) or CaCl₂ (0 to 15 mM). Both salts increased the turbidity and rigidity of the HD‐WPI solutions. Gelation rate and final gel strength increased with salt concentration and were greater for CaCl₂ than NaCl at the same concentration because the former is more effective at screening electrostatic interactions and can form salt bridges.     

Effects of sodium metabisulphite,hydrogen peroxide and heat on aflatoxin B1 in lafun and gari - two cassava products

Sodium metabisulphite and hydrogen peroxide alone or in combination with heat (50–70°C) were found to be effective in degrading aflatoxin B1 (AFB1) in lafun and gari. Hydrogen peroxide (H₂O₂) at a concentration of 3 % in the aqueous phase gave a 12.5 % degradation of aflatoxin B1 in lafun and at 50°C, degradation levels of 25 % and 50 % were obtained with 6.0 and 9.0 % H₂O₂, respectively. When sodium metabisulphite was applied during the production of gari (a fermented cassava product heated to 50-70°C during production) AFB1 degradation levels were found to be 65.8 %, 60.9 %, 41.5 % and 36.6 %, respectively, for sodium metabisulphite levels of 1.0 %, 0.8 %, 0.5 % and 0.3 %.