METABOLISM OF SOLANINE AND CHLOROPHYLL IN POTATO TUBERS AS AFFECTED BY LIGHT AND SPECIFIC CHEMICALS

SUMMARY— Chlorophyll and solanine syntheses as affected by cultivars, specific gravities, light intensities, and chemicals were studied in potato (Solanum tuberosum, L.) tubers. When exposed to 100 ft-c of while fluorescent light for 5 days, tubers of Bounty, Kennebec, Norchip and Red Lasoda were most sensitive to greening and solanine development. LaChipper and Platte tubers were resistant to the light effects. Chlorophyll synthesis was inversely related to specific gravity of tubers, while specific gravity did not affect solanine synthesis. The chlorophyll content of tubers exposed to 50 ft-c and 200 ft-c was significantly less than that of tubers exposed to 100 ft-c and 150 ft-c light intensities. The solanine synthesis was not influenced by the light intensities studied. Chemicals were applied at a concentration of 10,000 ppm by vacuum injection technique. Ethrel® and Alar® were effective in inhibiting chlorophyll and solanine formation. Ethrel was more effective in retarding the chlorophyll formation and alar was most effective in preventing solanine formation. Maleic hydrazide MH®-30 and Cyocel® were ineffective in controlling both chlorophyll and solanine formation.     

The biomass and total lipid content and composition of twelve species of marine diatoms cultured under various environments

Twelve species of purified marine diatoms were cultured in summer and in winter greenhouses and in an incubator. Subsequently, their biomasses were estimated, and their fatty acid components and contents were analysed using gas chromatography. Among the investigated diatoms, the biomasses ranged from (1.18 ± 0.059) × 10⁶ to (2.51 ± 0.0126) × 10⁷ cells/mL. The total lipid content (dry weight) ranged from 30.2 ± 1.59% to 45.1 ± 2.39%, and each diatom included from 12 to 19 different types of fatty acids from a total of 22 different kinds of fatty acids found. The diatoms cultured at varied temperatures (17-32 °C) and light intensities (122-655 μmol photons m⁻² s⁻¹) showed different trends of accumulation of PUFA and SFA.     

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.     

INFLUENCE OF WOUND INJURY ON ACCUMULATION OF PROTEINASE INHIBITORS IN LEAF AND STEM TISSUES OF TWO PROCESSING TOMATO CULTIVARS

Serine proteinase inhibitor(s) and small amounts of cysteine proteinase inhibitor were detected in both leaf and stem tissue 48 h after mechanical injury to the lower leaf of 21–25 day old tomato cultivars (cv). Leaves accumulated about 2–15 times more trypsin inhibitor than stem tissue. Approximately 10 times more trypsin inhibitor (TIU) accumulated in plants held at 30C in continuous light compared to plants held under ambient greenhouse conditions after injury. Uninjured plants held at 30C under continuous light accumulated less proteinase inhibitor(s) than injured plants. Holding Bonnie Best in the dark at 30C for 48 h resulted in less inhibitor(s) accumulation in response to mechanical wounding than holding plants at 30C in continuous light. TIU/g tissue recovered from injured plants held at 30C under continuous light varied with cultivar, i.e., for leaves: Bonnie Best (33.61), Alta (21.00; 25.43), Castlemart (16.00; 13.17) and Halley (1.96); and for stems: Castlemart (8.29), Alta (4.47) and Bonnie Best (2.59). SDS-PAGE assayed for inhibitor activity revealed the main trypsin and chymotrypsin inhibitor(s) in injured leaves both had a molecular mass (Mr) of 19.1 KD on SDS-PAGE substrate gels. Treatment of the inhibitors with 2.0% SDS at 100C prior to electrophoresis revealed a second major trypsin inhibitor (Mr = 16.4 KD) and two additional major α-chymotrypsin inhibitors (Mr = 16.4; 6.2 KD).     

EFFECT OF DEHYDRATION ON PHYSICOCHEMICAL PROPERTIES OF MUSTARD, MINT AND SPINACH

Mustard, mint and spinach were dehydrated in a sun and cabinet drier and were subsequently studied for rehydration characteristics. Dehydration ratio ranged from 12.37:1.0 to 23.37:1.0, while rehydration ratio varied from 1.0:2.84 to 1.0:3.76 for three green leafy vegetables. The bulk density of dried vegetables varied from 55.1 to 171.5 kg/m³, whereas the angle of repose was in the range of 33.2–52.4°. Color values L, a, b and ΔE were reduced with blanching and drying. Retention of chlorophyll, β‐carotene and ascorbic acid in dehydrated products varied from 41.87 to 61.35%, 22.26 to 55.16% and 13.36 to 37.53%, respectively. On rehydration, the ascorbic acid retention was further reduced to 4.17–11.55%.     

TASTE INTENSITY AS A FUNCTION OF STIMULUS CONCENTRATION AND SOLVENT VISCOSITY

The method of magnitude estimation was used to determine how viscosities imparted by sodium carboxymethylcellulose affect the taste intensities of various concentrations of glucose, citric acid, sodium chloride and quinine sulfate. For almost all levels of concentration across the four substances, an increase in the viscosity of the aqueous solvent produced decreases in taste intensity. A power function with a negative slope was chosen to describe the relation between the apparent viscosity (V, in centipoises) and the taste intensity (T): T=kV^?n, where n varied between 0.05 and 0.20. The relation between the concentration of the sapid chemical and the taste intensity, in most instances, also conformed to a power function, although some deviations occurred at low stimulus levels.     

Reduction ofEscherichia coliandSalmonella senftenbergon pork skin and pork muscle using ultraviolet light

The objective of this study was to evaluate the effect of ultraviolet (UV) light on the reduction ofEscherichia coliandSalmonella senftenberg. Microbial reduction was measured by determining total reduction and inactivation rates of surviving bacteria after exposure to different UV treatments. Surfaces of tryptic soy agar, pork skin and pork muscle were inoculated with eitherE. coliorS. senftenbergand exposed to 20, 50, 80, 100, 500 and 1000 microwatts per square centimeter (μW cm⁻²) of UV light. On the agar surface after 120 s, a >5-log reduction ofE. colion agar was obtained at intensities of 100μW cm⁻²or greater and, after 960 s, a >7-log reduction was observed at intensities of 80μW cm⁻²or greater forS. senftenberg. For fresh pork muscle and after 1920-s exposure, greatest logarithmic reductions (P<0.05) were achieved at intensities of 100μW cm⁻²or greater forE. coliand at intensities of 80μW cm⁻²or greater forS. senftenbergwhere a 1.5- and 2-log reduction was observed, respectively. For pork skin exposed at 1920 s, maximum logarithmic reductions forS. senftenbergwere observed at intensities of 100μW cm⁻². However, greatest logarithmic reduction ofE. colion pork skin was not observed until UV intensity reached 1000μW cm⁻². After exposure to 100μW cm⁻², UV D-values forE. coliwere 1370 s for pork muscle, 1282 s for pork skin, and 242 s for agar. WhenS. senftenbergwas exposed to 100μW cm⁻², UV D-values were 1163 s for pork muscle, 595 s for pork skin, and 15 s for agar. When surfaces were inoculated withE. coliand exposed to 1000μW cm⁻², UV D-values on muscle, pork skin and agar surfaces were 1205 s, 592 s, and 177 s, respectively. When surfaces inoculated withS. seftenbergwere exposed to 1000μW cm⁻², UV D-values were 1064 s, 490 s, and 21 s on muscle, skin and agar, respectively, In all cases,E. coliappeared to be more resistant to UV treatment compared toS. senftenberg. This study demonstrates that UV light can be used to reduce certain pathogens on pork meat surfaces. More research is needed to determine the antimicrobial activity of UV light exposure to meat carcasses or meat cuts in a food-processing environment.     

GLYCOALKALOID CONTENT OF NEWFOUNDLAND GROWN POTATO TUBERS AND POTATO WART TISSUE

Eight cultivars of potato tubers grown in Newfoundland were examined for total glycoalkaloids (TGA) at harvest and after 3, 6, 9 or 12 days exposure to 150 footcandles light. Freshly harvested tubers had TGA ranging from 0.9 to 15.4 mg/100 g of total tuber tissue. TGA increased as a result of long term light exposure in all cases; however, those cultivars surface-pigmented with red or blue anthocyanins were less responsive to light induction. TGA in light exposed tubers ranged from 52–71 mg/100 g for white cultivars, 26–46 mg/100 g for red varieties, and 23–40 mg/100 g for those pigmented with blue anthocyanins. Healthy tubers from plants afflicted with potato wart did not show abnormally high TGA; however, healthy cankers contained as high as 170 mg/100 g. Greening or decomposition of wart tissue was associated with a decline in TGA. Thin-layer chromatography revealed α-solanine and α-chanconine were the principal components in TGA extracts of both tubers and wart tissue.     

PSYCHOPHYSICAL AND PSYCHOMETRIC EVALUATION OF COMMERCIAL APPLE JUICES

Psychophysical and psychometric relationships of five commercial apple juices were evaluated. Sugar content of apple juices ranged from 9.6 to 10.6%, acid content from 0.40 to 0.51% and phenolic content from 0.12 to 0.23%. Sweetness intensity (log) correlated with sugar content (r = 0.92), sourness intensity (log) with acid content (r = 0.93) and sugar-acid ratio (r = 0.92), and bitter/astringent taste (log) with phenolic content (r = 0.95) and the acid content (r = 0.91). The expected correlation between sweetness intensity and sugar acid ratio was absent. Preference (like/dislike) scores for thefive brands of apple juices were significantly different at p < 0.05 and ranged from 5.70 to 7.90. Preference did not correlate with any chemical contents, ratios or sensory intensities. Preference for apple juice was adequately described by multivariate equations combining aroma intensity either with sugar content (r²= 0.91) or sweetness intensity (r²= 0.99).     

Spatial distribution of light-induced lipid oxidation in semi-hard yellow cheese as detected by confocal microscopy

The migration of oxidative damage in semi-hard yellow cheese resulting from surface exposure to 436 nm monochromatic light with an intensity of 2.5 × 10¹⁷ quanta min⁻¹ cm⁻² for 0, 5, 10, and 15 min was followed by confocal laser scanning microscopy using labelling with the lipophilic fluorescence ratio probe C₁₁-Bodipy (581/591). From 5 × 5 × 5 mm cubes of cheese exposed to light on one plane 35 μm was sliced off and fluorescence of oxidised and non-oxidised probe recorded simultaneously on the surface of the slice reaching 250 μm inwards from the exposed surface. From the emission of the fluorescence ratio probe light-induced lipid oxidation could be followed with time of exposure to light. The penetration of light inwards in the cheese with time expressed as quanta cm⁻², as calculated from light transmittance at 436 nm determined spectrophotometrically for cheese slices of up to 300 μm thickness, together with light intensity as determined by actinometry, could alone account for the inwards migration of oxidation. Diffusion of radicals seems of less importance for spatial dispersion of light-induced oxidation in semi-hard cheese.     

THERMAL PROPERTIES OF RADISH AND ALFALFA SEEDS

Thermal conductivity, specific heat, and density were measured in a temperature range of 30C to 80C, and moisture content of 4.6% to 6.5% for radish seeds, 5.0% to 7.3% for alfalfa seeds typically encountered in the radio frequency dielectric heating for seeds. Thermal conductivity and specific heat were determined using a linear heat source probe and a modified calorimeter method, respectively. Thermal conductivity of radish and alfalfa seeds ranged from 0.050 to 0.091 W/mC (SD: 0.011) and 0.075 to 0.120 W/mC (SD: 0.012), respectively. Specific heat was in the range of 0.290 to 0.479 kJ/kgC (SD: 0.051) for radish seeds and 0.333 to 0.593 kJ/kgC (SD: 0.076) for alfalfa seeds. Density of radish and alfalfa seeds ranged from 684 to 675 kg/m³ (SD: 5.592) and 819 to 804 kg/m³ (SD: 8.921), respectively. Thermal diffusivity of the seeds was also determined, and the values varied from 25.13 × 10^?8 to 34.47 × 10^?8 m²/s for radish seeds and 27.14 × 10^?8 to 29.73 × 10^?8 m²/s for alfalfa seeds. Regression models were fitted to the experimental data for each thermal property, and showed second order polynomial relationships with temperature and moisture content.     

Polycyclic aromatic hydrocarbons and lead in roadside lettuce and rye grain

Thirty-eight samples of lettuce and three samples of rye from an experimental site close to a highway were analysed for 20 polycyclic aromatic hydrocarbons (PAH) and lead. The lettuce plants were grown 8–65 m from the road and collected after 5,9 and 11 weeks of exposure. The levels of benzo[a]pyrene (BaP) and lead varied from 0.1 to 1.3 μg kg^?1 and from 0.18 to 1.6 mg kg^?1, respectively. The plants grown close to the road and with long exposure times showed the highest levels. The positive gradients for PAH and lead with exposure time and closeness to the road were nearly identical, but in different concentration ranges. Lettuce plants grown in a cold frame showed lower levels than those grown in the open. In rye sampled at 7–25 m from the road, BaP was not detected and lead levels ranged from 0.07 to 0.11 mg kg^?1. The results suggest that the Swedish National Food Administration/National Environmental Protection Board recommendations, i.e. not to grow leafy vegetables closer than 25 m from roads with intense traffic, are sufficient at traffic flows of up to 12 000 vehicles per day.     

DETERMINATION OF VARIABLE DIFFUSION OF SODIUM DURING DEBITTERING OF GREEN OLIVES

Time‐variable average effective diffusion coefficients of sodium in the skin and flesh were determined using Macroscopic Mass Balances from experimental data obtained during debittering of green olives, variety Arauco at temperatures of 15, 20 and 25C and lye concentrations of 1.50, 2.25 and 3.00% of NaOH. The effective diffusion coefficient of sodium increased with treatment time at both surfaces of the skin, while it varied very little within the flesh, and in many cases, remained almost constant during the debittering process. In general, the diffusion coefficients determined in the present study were within an order of magnitude of 10^?10 m²/s for the flesh during most of the treatment time, while for the skin, they were of the order of 10^?12 m²/s for the initial treatment times. Macroscopic mass balances are a simple mathematical method that can be used in lieu of more common numerical techniques, to evaluate variable diffusion coefficients providing accuracy and greater detail of the whole phenomena.     

INFLUENCE OF TEMPERATURE AND LIGHT EXPOSURE ON SENSORY SHELF-LIFE OF A COMMERCIAL SUNFLOWER OIL

The objectives of the present work were to: (1) correlate consumer acceptability measured with a consumer panel versus oxidized flavor measured with a trained sensory panel to thus define the sensory failure of a commercial sunflower oil; and (2) study the effect of storage temperature and light exposure on the sensory shelf‐life of sunflower oil bottled in polyethylene tetraphtalate (PET) with nitrogen in the headspace. Of the consumers, 15% unexpectedly preferred the more oxidized oil samples than the fresh ones. Their data were not considered in sensory failure calculations. By correlating the consumer data with the trained sensory panel data, a sensory failure point of 3.6 on a 0 to 10 oxidation flavor scale was obtained. Both storage temperature and exposure to light had a significant effect on shelf‐life. Estimated shelf‐lives at an ambient temperature of 20C were 281 days for light exposed oil, and greater than 2 years for oil kept in the dark.     

Heat and light stability of three natural blue colorants for use in confectionery and beverages

The stabilities of three natural blue colorants—gardenia blue, phycocyanin and indigo—toward heat and light were studied in simple solutions of various pH. Gardenia blue was found to be stable at temperatures up to 80 °C in aqueous solution at pH 3, 5 and 7. Exposure to light of 3×10⁵ lux for 24 hours resulted in approximately 50% degradation of gardenia blue in aqueous solution. Phycocyanin was found to be unstable to heat and light in aqueous solution. Phycocyanin is insoluble in acidic solution (pH 3) and denatures at temperatures above 45 °C at pH 5 and 7, leading to a color change. Exposure to light of 3×10⁵ lux for 24 hours in aqueous solution at pH 5 and 7 caused ~80% degradation. Indigo was found to be stable in medium-chain-triglyceride oil for temperatures up to 90 °C, but to photodegrade (by approximately 70% after five hours of exposure to 3×10⁵ lux), corresponding to a quantum yield of 1.8×10^–4 mol Einstein^–1 for visible light and 1.4×10^–2 mol Einstein^–1 for UV, as determined for monochromatic light of 600 and 313 nm, respectively. Exploratory studies have been carried out with the three blue colorants in application media such as soft drink, jelly gum, hard candy and sugar coating for soft candy. Despite its lower stability towards heat and light, phycocyanin was concluded to be the more versatile blue food colorant among the three studied, showing a bright blue color in jelly gum and coated soft candy.     

Characterization of the Photodegradation of β-Carotene in Aqueous Model Systems

The photodegradation of β-carotene in model dispersions was studied to gain a better understanding of carotene stability in foods. Aqueous dispersions were exposed to 250 ft-c of light at varied times and temperatures. Analysis was by HPLC and spectrophotometry. Degradation reactions fit a first-order kinetic model. Temperature, physical state and β-carotene microenvironment had some influence on degradation rates. cis-isomers of β-carotene were present and the relative amounts of cis-isomers increased with time of exposure.     

Stability of the Stevia‐Derived Sweetener Rebaudioside A in Solution as Affected by Ultraviolet Light Exposure

Rebaudioside A is a natural noncaloric high‐potency sweetener extracted from the leaves of Stevia rebaudiana. With rebaudioside A use increasing in foods, understanding the factors affecting its stability is necessary. This project evaluated the degradation rate constants of rebaudioside A in water, 0.1 M phosphate buffer, and 0.1 M citrate buffer at pH 3 and 7 as a function of ultraviolet (UV) light intensity (365 nm, 0 μW/cm² for dark conditions, 27 μW/cm² for low intensity, and 190 μW/cm² for high intensity) at 32.5 °C. Rebaudioside A stability was adversely affected by light exposure. The pseudo‐1st‐order degradation rate constants increased significantly (P < 0.05) with increasing light intensity in all solutions. Under dark conditions, rebaudioside A in phosphate buffers was more susceptible to breakdown than in water and citrate buffers at both pH levels. However, exposure to UV light resulted in rebaudioside A degradation occurring approximately 10 times faster in citrate than in phosphate buffers at both pH levels. The sensitivity of rebaudioside A to UV light was greater in citrate buffers than in water or phosphate buffers. The use of light‐protective packaging for beverages containing rebaudioside A will improve its stability.     

High carbon dioxide pressure inactivation kinetics of Escherichia coli in broth

The inactivation kinetics of Escherichia coli by high pressure carbon dioxide was investigated. Inactivation rates increased with increasing pressure (25, 50, 75 and 100 atm), temperature, and exposure time. Microbial inactivation followed first order reaction kinetics, with inactivation rates (k) and decimal reduction times (D) that varied from 0·0848 to 0·4717 min⁻¹and from 4·90 to 27·46 min, respectively, at treatment temperatures (20, 30 and 40°C). The inactivation rates of E. coli were described by the apparent activation volume (ΔV^*) and a ‘pressure z value’, and they were greatly dependent on both temperature and pressure.     

ENUMERATION OF AEROMONAS FOR VERIFICATION OF THE HYGIENIC ADEQUACY OF SWINE CARCASS DRESSING PROCESSES1

Populations of Aeromonas spp. and aerobic bacteria from dehairing equipment and from carcasses passing through different processing steps in a swine slaughtering plant were evaluated to identify the hygienic risks of each operation. Sponge samples were taken from the scraper flails in dehairing machines and the surface of the shackling table at pre‐ and post‐operation times, with 20 samples from each location being collected at each time. Increased post‐operation levels of Aeromonas spp. indicated a buildup and possible spread of these bacteria to carcasses. The belly skins of 40 dehaired carcasses were each sampled at five points along the process line which were after the shackling, after the final singeing, after the final polishing, after the final wash and after chilling. The levels of microbial contaminants on carcasses varied at each processing step. The heaviest contamination of carcasses with Aeromonas (1.88 log CFU/cm²) and aerobic bacteria (2.66 log CFU/cm²) occurred after shackling. Counts were reduced at other steps as a result of singeing, washing and chilling operations. However, singed carcasses were recontaminated with Aeromonas and aerobic bacteria during the polishing operation. Aeromonas hydrophila were the most prominent motile aeromonads (74.1%) recovered at the plant. The findings for Aeromonas spp. were similar to those for aerobic bacteria (r²= 0.9995) which suggested that Aeromonas spp. are appropriate indicators for assessing carcass dressing processes.     

KINETICS AND HYDROLYSIS PARAMETERS OF TOTAL FRUCTOOLIGOSACCHARIDES OF ONION BULBS: EFFECTS OF TEMPERATURE REGIMES AND CULTIVARS

This work studied the percentage of hydrolysis, observed hydrolysis rate constant (k_obs), half‐life time (t_1/2) and kinetics of degradation of the total fructooligosaccharides (FOS) of three different onion bulb cultivars (Yellow Spanish, Red Amposta and Tenshin) kept during 6 months under three temperature regimes, 10, 15 and 20C. The percentage of hydrolysis of FOS was higher at 20C than at 10C and ranged from 47 to 58% at 10C, from 63 to 68% at 15C and from 74 to 83% at 20C. The k_obs ranged from 27 × 10^?3 to 36 × 10^?3/week at 10C and from 41 × 10^?3/week to 47 × 10^?3/week at 15C, while at 20C, it was high and was about k_obs 56 × 10^?3/week.. The t_1/2 decreased when temperature increased, and varied from 19.5 to 26.0 weeks at 10C, from 14.6 to 16.8 weeks at 15C and from 9.4 to 12.3 weeks at 20C, indicating that high degree of polymerization (DP) FOS have shorter lives than low DP FOS. Linear regression and kinetics of hydrolysis have shown that FOS hydrolysis is higher at 20C, with a coefficient of regression ranging between 0.87 and 0.99. Apparently, FOS hydrolysis is temperature independent, and storage time had more effect on the higher DP FOS than on the lower DP FOS.