Robert K. Prange

Improving the thiobarbituric acid-reactive-substances assay for estimating lipid peroxidation in plant tissues containing anthocyanin and other interfering compounds

Abstract. The occurrence of malondialdehyde (MDA), a secondary end product of the oxidation of polyunsaturated fatty acids, is considered a useful index of general lipid peroxidation. A common method for measuring MDA, referred to as the thiobarbituric acid-reactive-substances (TBARS) assay, is to react it with thiobarbituric acid (TBA) and record the absorbance at 532 nm. However, many plants contain interfering compounds that also absorb at 532 nm, leading to overestimation of MDA values. Extracts of plant tissues including purple eggplant (Solanum melongena L.) fruit, carrot (Daucuscarota L.) roots, and spinach (Spinacia oleracea L.) leaves were assessed for the presence of MDA and other non-MDA compounds absorbing at 532 nm. A method described herein corrects for these interferences by subtracting the absorbance at 532 nm of a solution containing plant extract incubated without TBA from an identical solution containing TBA. The reliability and efficiency of this spectrophotometric method was assessed by altering the relative ratios of exogenous MDA additions and/or extracts of red cabbage (Brassica oleracea L.) leaves containing interfering compounds and then measuring MDA recovery. Reliability was also validated through high-performance liquid chromatography and high-performance liquid chromatography-mass spectrometry techniques. Results indicated that over 90% of exogenously added MDA could be recovered through the improved protocol. If there were no corrections for interfering compounds, MDA equivalents were overestimated by up to 96.5%. Interfering compounds were not detected in vegetables such as lettuce (Lactuca sativa L.) and spinach which had low or negligible concentrations of anthocyanidin derivatives. Comparisons between the TBARS method presented here and two currently accepted protocols indicated that the new modified method exhibits greater accuracy for quantifying TBA-MDA levels in tissues containing anthocyanins and/or other interfering compounds. This modified protocol represents a facile and rapid method for assessment of lipid peroxidation in virtually all plant species that contain interfering compounds.

Oxygen concentration affects chlorophyll fluorescence in chlorophyll-containing fruit

Abstract The effect of lowering O2 concentration on chlorophyll fluorescence was continuously monitored in apple (Malus x domestica Borkh.), pear (Pyrus communis L.), banana (Musa L. Cavendish subgroup), kiwifruit (Actinidia deliciosa (A. Chev.) C.F. Liang et A.R. Ferguson), mango (Mangifera indica L.), and avocado (Persea americana Mill.) fruit, using a large surface-area sensor. In all of the six fruit, there were specific O2 concentrations at which the Fo and Fv/Fm chlorophyll fluorescence values suddenly increased and decreased, respectively. When the O2 concentrations were increased, the Fo and Fv/Fm signals returned to their previous values. Since the O2 concentrations at which this phenomenon occurred were close to known low O2 thresholds for these fruit, it may be that chlorophyll fluorescence can rapidly and non- destructively determine the lowest acceptable O2 concentration for stored chlorophyll-containing plant products.

Effects of ethylene and 1-methylcyclopropene on potato tuber sprout control and fry color

The study examined the efficacy of 1-methylcyclopropene (1-MCP), an anti-ethylene compound, as a preventative treatment for ethylene-induced fry color darkening in potato (Solanum tuberosum L.) tubers, without reducing the effectiveness of ethylene as a tuber sprouting control agent. The experiment was conducted for two years with ‘Shepody’ and ‘Russet Burbank.’ Tubers of each cultivar from four separate growers received one of the following treatments: Air (control), Air + 1-MCP (1 (μL.L-1 for 48 h), isopropyl N (3-chlorophenyl) carbamate (chloropropham; CIPC; 1% a.i. [v/v]); continuous ethylene (4 μL.L-1) in air; continuous ethylene pre-treated with 1-MCP once; continuous ethylene pre-treated with 1-MCP and repeated monthly; and continuous ethylene pre-treated with 1-MCP and repeated bi-monthly. Treatment started after suberization and cooling to 9 C, and samples were evaluated at 3-wk (year 1) or 4-wk (years 2 and 3) intervals thereafter until April (Shepody) or June (Russet Burbank). Sprout growth (sprout fresh weight per tuber), fry color (Agtron reflectance units), tuber weight loss, incidence of disease infection and internal disorders were evaluated. Weight loss, tuber infection, and the occurrence of disorders were not affected by any of the treatments. Sprout growth was controlled by the continuous ethylene supply in both cultivars, and single or multiple additions of 1-MCP to the ethylene treatment did not affect the ethylene control of sprouting. As expected, ethylene treatment alone enhanced fry color darkening in both cultivars. In Russet Burbank tubers, fry color was not darkened in any of the ethylene + 1-MCP (once, monthly, or bimonthly) treatments. In Shepody, fry color was not darkened in the ethylene + 1-MCP monthly or bimonthly treatments, but started darkening 4 wk after exposure in the single ethylene + 1-MCP treatment. It is concluded that 1-MCP can be used to control fry color darkening induced by ethylene without blocking ethylene control of tuber sprouting. However, the number of 1-MCP applications required may vary with the cultivar, e.g., one application was sufficient in Russet Burbank but not in Shepody.ResumenSe examinó la eficacia del 1-metilciclopropeno (1-MCP), que es compuesto anti-etileno como tratamiento preventivo del oscurecimiento de tubérculos de papa (Solanum tuberosum L.) después de ser fritos, sin reducir el efecto del etileno como controlador del brotamiento de los tubérculos. El experimento se condujo por tres años con ‘Shepody’ y dos años con ‘Russet Burbank’. Tubérculos de cada cultivar provenientes de cuatro productores diferentes recibieron uno de los siguientes tratamientos: Aire (testigo); Aire + 1-MCP (μL.L-1 por 48 horas); isopropil N-(3 clorofenil) carbamato (cloroprofano); CIPC1% i.a. (v/v); etileno continuo (4 (μL.L-1) en el aire; etileno continuo y pre tratamiento con 1-MCP por una sola vez; etileno continuo y pre tratamiento con 1-MCP cada mes y etileno continuo, pre tratamiento con 1-MCP cada 2 meses. El tratamiento comenzó después de la suberización y enfriamiento a 9 C y las muestras fueron evaluadas a intervalos de 3 semanas (el primer año) o a intervalos de 4 semanas (el segundo y tercer año) y luego en abril (Shepbody) o junio (Russet Burbank). Se evalué el crecimiento de los brotes (peso fresco de los brotes por tubérculo), color de la fritura (unidades de reflejo Agtron), pérdida de peso del tubérculo, incidencia de infecciones por enfermedades y desérdenes internos. La pérdida de peso, la infección del tubérculo y la presencia de desórdenes no fue afectada por ninguno de los tratamientos. El desarrollo de los brotes fue controlado por el continuo suministro de etileno y la adición simple o multiple de 1-MCP al tratamiento con etileno en ambos cultivares y no afectó el control ejercido por el etileno sobre el brotamiento. Como se esperaba, el tratamiento con etileno sólo intensificó el oscurecimiento de la papa frita en ambos cultivares. Los tubérculos de Russet Burbank, no se oscurecieron por fritura en ninguno de los tratamientos de etileno + 1-MCP (por una vez, mensual o bimensual). En tubérculos de Shepody el color de la fritura no se oscureció en los tratamientos con etileno + 1-MCP mensual o bimensualmente, pero comenzó a oscurecer a las 4 semanas después de expuestos al tratamiento simple de etileno + 1-MCP. Se concluye que el 1-MCP puede ser usado para controlar el oscurecimiento del color al ser fritos inducido por el etileno, sin bloquear el control ejercido por el etileno sobre el brotamiento. Sin embargo, el número de aplicaciones requeridas de 1-MCP puede variar con el cultivar, por ejemplo, una aplicación fue suficiente en Russet Burbank pero no en Shepody.

Sprout development and processing quality changes in potato tubers stored under ethylene: 1. Effects of ethylene concentration

Ethylene effectively inhibits sprouting of potatoes (Solanum tuberosum L.) during storage, but it often darkens fry color. The objective of the work described here was to determine if altering the concentration of ethylene applied would reduce the darkening while retaining adequate sprout inhibition. Trials were conducted over three consecutive years (1991–1992, 1992–1993, and 1993–1994). Tubers of cv Russet Burbank (ca 150–300 g) were stored at 9 C for 25 wk in closed chambers in a refrigerated room under continuous exposure to 0.4, 4, 40, or 400 µL L−1 ethylene gas delivered with the ventilation airstream (ca 0.5 air exchanges per h, for 6 h each day). Untreated control and chlorpropham-treated (CIPC) check tubers were stored under the same conditions but without ethylene supplementation. Sprout number, length, and biomass, fry color, loss of tuber mass, disease, and dry matter content were evaluated at 5-wk intervals. Dose-dependent effects (400>40>4>0.4 µL L−1) of ethylene on sprout growth and fry color were observed. The 400, 40, and 4 µL L−1 ethylene treatments inhibited sprout growth as effectively as CIPC, whereas in 0.4 µL L−1 ethylene sprouting was midway between CIPC and the untreated control. Sprout mass and maximum sprout length in all ethylene treatments were significantly lower (P<0.05) than in the untreated control. Compared with the initial value (57.3 Agtron reflectance units [ARu]), after 5 wk of storage fry color was up to 5 ARu darker in the ethylene treatments, but recovered steadily at the subsequent evaluation dates. At 25 wk of storage the fry color of tubers from the 40 and 4 µL L−1 ethylene treatments were, however, still darker than tubers stored with CIPC. Inhibition of sprout growth was slightly more effective in the 400 and 40 µL L−1 ethylene treatments than in 4 µL L−1, although there were no significant differences (P<0.01) in fry color between these treatments. In comparison with the other ethylene treatments, fry color in 0.4 µL L−1 ethylene was lighter, but inhibition of sprout growth was significantly (P<0.05) poorer. There were no differences in tuber disease incidence or dry matter content between the treatments. At 25 wk, the untreated tubers had ca 50% greater loss of tuber mass than any other treatment, attributable to their heavy sprouting. Loss of tuber mass in the ethylene treatments was not significantly different (P<0.001) from that in the CIPC treatment.ResumenEl etileno inhibe eficazmente el brotamiento de la papa (Solanum tuberosum L.) durante el almacenamiento, pero a menudo oscurece el color de la fritura. El objetivo de este trabajo fue determinar si alterando la concentración de etileno aplicado se puede reducir el oscurecimiento, reteniendo una adecuada inhibición del brotamiento. Las pruebas se realizaron durante tres años consecutivos (1991–1992, 1992–1993, y 1993–1994). Tubérculos del cultivar Russet Burbank (ca.150–300 g) se almacenaron a 9EC por 25 semanas en cámaras cerradas en un cuarto refrigerado bajo continua exposición a gas etileno 0.4, 4, 40 y 400 µL L−1, repartido con la corriente de aire de ventilación (ca. 0.5 de cambios de aire, por 6 horas diarias). Los tubérculos sin tratar y los testigos tratados con cloroprofan (CIPC) fueron almacenados bajo las mismas condiciones pero sin suplemento de etileno. A cinco semanas de intervalo se evaluó el número de brotes, largo y biomasa, color de fritura, pérdida de masa del tubérculo, enfermedad y contenido de materia seca. Se observaron los efectos dependientes de la dosis de etileno (400>40>4>0.4 µL L−1) sobre el crecimiento del brote y el color de la fritura. Los tratamientos de etileno 400, 40 y 4 µL L−1 de etileno inhibieron el crecimiento del brote tanto como el CIPC y el testigo sin tratamiento, mientras que en 0.4F µL L−1 el brotamiento con etileno fue la mitad entre CIPC y el testigo sin tratamiento. La masa de los brotes y la longitud máxima en todos los tratamientos con etileno fueron significativamente menores (P<0.05) que en el testigo sin tratar. Comparado con los valores iniciales (57.3 unidades Agtron de reflectancia [ARu]), después de cinco semanas de almacenamiento, el color de fritura estuvo hasta 5 ARu más oscuro en los tratamientos de etileno, pero se recuperó regularmente en las siguientes fecha de evaluación. A las 25 semanas de almacenaje, el color de fritura de los tratamientos 40 y 4 µL L−1 de etileno, fue, sin embargo, todavía más oscuro que los tubérculos almacenados con CIPC. La inhibición de crecimiento del brote fue ligeramente más efectiva en el tratamiento con etileno 400 y 40 µL L−1 que en 4 µL L−1, aunque no hubo diferencias significativas (P<0.01) en el color de fritura entre estos tratamientos. En comparación con los otros tratamientos de etileno, el color de fritura en etileno 0.4 µL L−1 fue más ligero, pero la inhibición de brotamiento fue significativamente (P<0.05) menor. No hubo diferencias en la incidencia de enfermedades del tubérculo o contenido de materia seca entre los tratamientos. A las 25 semanas, los tubérculos sin tratar tuvieron 50% más pérdida de la masa del tubérculo que ningún otro tratamiento, atribuible a su intenso brotamiento. La pérdida de masa del tubérculo en los tratamientos con etileno no fue significativamente diferente (P<0.001) del tratamiento con CIPC.

Chlorophyll fluorescence of Delicious apples at harvest as a potential predictor of superficial scald development during storage

Abstract Chlorophyll fluorescence (Fv) of Delicious apples at harvest was evaluated as an indicator of superficial scald development during storage. The Fv of ‘Imperial’ and ‘Sturdeespur’ Delicious apples was determined at three weekly harvest intervals, and the apples were later evaluated for scald intensity after 2, 4 and 6 months of storage at 0 °C. ‘Sturdeespur’ apples had an overall higher incidence of scald than ‘Imperial’ apples. Fv at harvest was found to correlate positively with scald development in ‘Sturdeespur’ apples from Harvest 1. ‘Sturdeespur’ apples with low Fv ( 18) were most likely to develop severe scald. However, no such relationship was observed for ‘Imperial’ apples, or for some ‘Sturdeespur’ apples from harvests 2 and 3. The results of this study suggest that Fv at harvest may be a predictor of scald development.

The influence of crop-load, delayed cooling and storage atmosphere on post-storage quality of 'Honeycrisp'™ apples

Summary The influence of crop-load, delayed cooling and storage environment on fruit quality and disorder, and on the incidence of rot was investigated on 7 year-old ‘Honeycrisp’ apple (Malus domestica Borkh.) trees on ‘Malling 26’ rootstocks at three different sites during 2003 and 2004. Fruit from non-thinned (control) trees, or trees thinned to three, six or nine fruit cm–2 trunk cross-sectional area (TCSA) were harvested and: (1) immediately cooled over 24 h to 3°C [commercial (Comm)] then stored at 3°C in refrigerated air (RA) or in a controlled atmosphere (CA; 2.5 kPa O2, 1.0 – 1.5 kPa CO2); or (2) held at 20°C for 6 d, followed by 1 d at 3°C [= 7 d pre-storage warming treatment = delayed cooling (DC)] then stored at 3°C under RA or in CA storage. After 3 and 6 months of storage, fruit mass (g), firmness (N), colour (% red), soluble solids content (SSC; %), titratable acidity (TA; mg malic acid equivalents 100 ml–1 juice), “greasiness” (0–3 scale), the extent of disorders such as soft scald (%) and low temperature breakdown (LTB; %), as well as the incidence of rot (%) were assessed. In general, as crop-load increased fruit mass, firmness, colour, SSC and TA decreased regardless of the effects of DC and storage treatment. Crop-load did not influence fruit “greasiness” and had an inconsistent and less-pronounced effect on soft scald, LTB and rot. The 7 d pre-storage warming treatment reduced the incidence of soft scald and LTB, irrespective of crop-load, but had little influence on other fruit quality measurements. Although the storage environment did not consistently alter quality, CA-stored ‘Honeycrisp’ apples tended to be more acidic, less “greasy” and develop less soft scald. Overall, the data indicate that the highest fruit quality was attained by thinning ‘Honeycrisp’ trees as close to three fruit cm–2 TCSA as possible, by subjecting newly-harvested fruit to a 7 d pre-storage warming period of 20°C, followed by CA storage at 2.5 kPa O2, 1 – 1.5 kPa CO2 at 3°C.

Comparison of a new apple firmness penetrometer with three standard instruments

Abstract The performance of a newly developed firmness penetrometer (fruit quality tester — FQT), was evaluated over two growing seasons with poststorage apples against the Effegi, Magness-Taylor (MT) and electronic pressure tester with the speed control engaged (EPT-SC). The FQT was operated in the: (a) standard (FQT-Std); (b) MT (FQT-MT); and (c) EPT (FQT-EPT) modes with the latter two simulating the operation of the MT and EPT-SC devices, respectively. ‘Cortland’, ‘McIntosh’ and ‘Northern Spy’ fruit were stored for 3–14 months in controlled atmosphere (CA) conditions and were then held at room temperature for 1–7 days, following which firmness was measured by four operators with each of the six instruments or modes. The ten cultivar/storage/poststorage fruit lots were designated as either hard or soft if the poststorage firmness average for the lot was ≥ or

Improvement of quality of Elstar apples by dynamic control of ULO conditions

Abstract A comparison was made for Elstar apples between the current ULO (Ultra Low Oxygen) recommendation and an experimental hand-controlled DCS (Dynamic Control System). The oxygen content under DCS conditions was controlled by the ethanol content in the headspace. The DCS-stored fruits showed higher scores for firmness, colour and taste. Results will be discussed in relation to the possibilities of the development of a DCS (patent pending) system.

Determination of the optimal pre-storage delayed cooling regime to control disorders and maintain quality in ‘Honeycrisp’TM apples

Summary Several pre-storage time (0, 1, 2, 4, and 6 d) and temperature (3.5º, 10º, 15º, 20º, 25º, and 30ºC) delayed cooling (DC) treatments were tested on harvested ‘Honeycrisp’TM apples to determine which combination was optimal for reducing soft scald and low temperature breakdown (LTB), while maintaining the highest fruit quality [i.e., firmness, minimal mass loss, titratable acidity (TA), soluble solids content (SSC), absence of rot, and minimal skin greasiness] after 4 months of refrigerated air (RA) storage. Fruit were harvested from three separate Annapolis Valley (Nova Scotia) orchard sites in 2006 and in 2007. Multiple linear regression and surface response curves showed that fruit firmness and SSC generally increased throughout the DC treatment, but were affected curvilinearly by temperature, reaching a maximum at approx. 15ºC, then declining. Loss of fruit mass was positively related to a (day temperature2) interaction, indicating that it increased synergistically the longer and the warmer the DC treatment. Fruit acidity was affected only by temperature, with the highest TA values at approx. 15ºC, then declining at higher DC temperatures. Multiple logistic regression and surface responses demonstrated that the incidence of soft scald declined curvilinearly the longer and the warmer the DC treatment, while LTB declined curvilinearly with increasing DC temperature only. A positive (day2 temperature2) interaction indicated that fruit greasiness increased non-linearly as the duration and temperature of DC increased. Collectively, these results show that both soft scald and LTB were suppressed or eliminated by a DC regime of 25ºC for 1 – 2 d, or 30ºC for 1 d, without incurring a major reduction in fruit quality.

Fruit mass, colour and yield of ‘Honeycrisp’™ apples are influenced by manually-adjusted fruit population and tree form

Summary The influence of three manually-adjusted crop loads [3, 6 and 9 fruit cm–2 trunk cross-sectional area (TCSA)] on ‘Honeycrisp’™ apple (Malus domestica Borkh) quality and canopy volume were compared with unadjusted control trees. The crop-load treatments were applied at three sites over two consecutive seasons at 50 days after full bloom (DAFB). Sixteen trees at each site were selected annually, with the treatments being applied in a randomisedcomplete-block design. Fruit mass and fruit colour (%) were used to assess quality at harvest, while yield was determined by the mass (kg) of fruit cm–2 TCSA. The canopy volume (CV) for each tree was calculated following harvest and used as a covariate in determining its influence on fruit size and colour. As crop load decreased, harvested fruit mass and % red colour increased. For similar crop-load adjustments, larger tree CVs (in m3) resulted in greater fruit mass. Crop load and fruit-canopy density (fruit m–3 CV) were more highly correlated with fruit mass than with % fruit colour. The highest fruit quality occurred at the three and six fruit cm–2 TCSA. In addition, manually adjusting the crop-load at 50 DAFB did not eliminate the disposition of ‘Honeycrisp’™ towards biennial bearing in Nova Scotia’s climate.