S.R. Drake

Dielectric properties of fruits and insect pests as related to radio frequency and microwave treatments.

Information on dielectric properties of commodities and insect pests is needed in developing thermal treatments for postharvest insect control based on radio frequency (RF) and microwave energy. Dielectric properties of six commodities along with four associated insect pests were measured between 1 and 1800 MHz using an open-ended coaxial-line probe technique and at temperatures between 20 and 608C. The dielectric loss factor of fresh fruits and insects decreased with increasing frequency at constant temperatures. The loss factor of fresh fruits and insects increased almost linearly with increasing temperature at 27 MHz radio frequency, but remained nearly constant at 915 MHz microwave frequency. Both dielectric constant and loss factor of nuts were very low compared to those of fresh fruits and insects. The temperature effect on dielectric properties of nuts was not significant at 27 MHz. The large difference in the loss factor between insects and nuts at 27 MHz suggests possible differential heating of insects in nuts when treated at the same time in a RF system.

Development of a saline water immersion technique with RF energy as a postharvest treatment against codling moth in cherries

‘Sweetheart’ sweet cherries (Prunus aium L.) immersed in 0.15% saline water were treated with radio frequency (RF) energy. The dielectric and ionic conductivity properties of the immersion water and that of fruit were matched to obtain a relatively uniform temperature distribution within and among fruits during RF heating. With immersion in saline water of 0.15% NaCl, the mean temperature of the water and that of the cherries differed by 0.6 °C, while the maximum temperature variation within and among fruits determined within 1 min after RF treatment completion was 1.0 °C of the set temperatures of 48 and 50 °C. The saline water immersion technique helped overcome the markedly high temperature differential problem within and among fruits, normally associated with treatments in air (without immersion) during RF heating. More than 99% mortality of the 200–400 codling moth larvae or 589–624 eggs was obtained at 50 °C when treated for between 7 and 10 min (heating 2–5 min and holding 5 min). Most quality parameters analyzed were better, or are comparable with methyl bromide fumigated fruit. Saline–water-immersion treatment in RF may be used to overcome the problem of slow conventional hot air or water heating, as well as the non-uniformity of temperature associated with electromagnetic heating in air, for developing alternative quarantine treatment for fruits.

Quarantine treatment of cherries using 915 MHz microwaves: temperature mapping, codling moth mortality and fruit quality

Sweet cherries (Prunus a6ium L.) were treated by 915 MHz microwaves in a pilot-scale multimode microwave system with an auxiliary hot air heater to determine heating characteristics and the effect of treatments on insect mortality and fruit quality. Quality parameters of the microwave-treated ‘Bing’ cherries were compared with control fruit and those subjected to methyl bromide fumigation. When heating cherries to average pit temperatures of 45, 50 and 55°C, the cherry pits heated faster than the surface, and larger cherries heated more quickly than smaller ones. Cherry temperature increased linearly with time with heating rates dependent on the microwave power, sample weight, cherry size and radial location inside the cherry. With a 2 min holding and 5 min hydrocooling protocol after microwave treatments, adjusted percentage 3rd instar codling moth (Cydia pomonella L.) mortality ranged from 5 to 62% and 39 to 98% without and with 1‐2 days cold storage, respectively. A higher mortality rate was obtained for insects in ‘Bing’ than ‘Rainier’ fruit. Firmness, percentage soluble solids content, titratable acidity, fruit weight, and objective fruit colour of microwave-treated ‘Bing’ fruit were comparable with these properties of control fruit and to those of cherries fumigated with methyl bromide. Stem greenness colour was reduced after the microwave and dry hot air combined treatments. Microwave energy may provide an alternative non-chemical quarantine treatment against codling moth in export cherries, but further study is needed to optimize the treatment protocol for insect control and fruit quality.

Comparison of alternative postharvest quarantine treatments for sweet cherries

Abstract The effects of controlled atmosphere heat treatments (CATTS) and irradiation on sweet cherry fruit quality were compared to fumigation with methyl bromide. ‘Bing’ and ‘Rainier’ sweet cherry varieties were tested from the Yakima and Wenatchee, WA growing areas. Irradiated cherries had overall quality better than methyl bromide-treated cherries. CATTS-treated ‘Rainier’ cherries, but not ‘Bing’, had more pitting and bruising after 14 days of storage than fruit from other treatments. Both cultivars treated with methyl bromide had poorer stem quality than controls. CATTS-treated ‘Bing’ fruits had poorer stem quality after 7 and 14 days of storage than the controls. This research demonstrated that both irradiation and CATTS have potential for alternative quarantine treatments for sweet cherries.

Effects of preharvest calcium sprays on apple and pear quality

Abstract Fruit from apple (Malus domestica Borkh.) and pear (Pyrus communis L.) trees sprayed with calcium chloride (CaCl2) had higher fruit calcium (Ca) concentrations by 10% or more than the unsprayed control trees. In ‘Delicious’ and ‘Golden Delicious’ apples, the incidences of bitter pit, scald, and internal breakdown were substantially reduced with CaCl2 sprays. In most instances, firmness, total acidity, and juiciness ratings of apples were improved with CaCl2 sprays. In ‘Anjou’ pears, the incidence of cork spot was reduced with CaCl2 sprays. Only sprays of NutriCal and CaCl2 + Regulaid showed substantial increases in fruit firmness of ‘Anjou’ pear. In 1991, yield of ‘Anjou’ pear trees was increased by 36% with CaCl2 sprays compared with the control trees.

Nitrogen fertilization and elemental composition affects fruit quality of ‘Fuji’ apples

Abstract In 1989 to 1995, five rates of nitrogen (N) fertilizer were applied to ‘Fuji’ apple trees grafted on ‘Delicious’ and ‘Granny Smith’ interstems and grown on M.26 rootstock to determine fruit quality and yield. Fruit weight was increased by N fertilizer rate, but fruit production was not influenced appreciably by rate of N fertilizer, for the one year (1994) it was observed. Highest fruit quality was achieved with the lowest N fertilizer rate of 25 lbs.A‐1 (28.4 kg.ha‐1). Fruit quality was negatively related to N in leaves and fruit peel and cortex as well as leaf boron (B), fruit peel copper (Cu), magnesium (Mg) and fruit cortex Mg, and manganese (Mn) for both interstems. Lower rates of N fertilizer were related to lower concentrations of leaf and fruit N, “redder”; fruit skin color, greater fruit firmness and soluble solids concentration, higher fructose levels, and a lower incidence of bitter pit and scald than the higher rates of 100 or 150 lbs N A‐1 (113.6 or 170.5 kg N ha‐1).

TIME OF NITROGEN APPLICATION AND ITS INFLUENCE ON ‘GOLDEN DELICIOUS’ APPLE YIELD AND FRUIT QUALITY

Nitrogen (N) fertilization influences apple (Malus × domestica Borkh.) yield and quality, but less is known about the effect of rate and timing of fertilization on fruit quality. Rate and time of N fertilization (114 g/tree in Nov.+68 g/tree in May, 227 g/tree in Aug., 45 g/tree for 4 weeks starting in Aug., 136 g/tree in Aug., and 68 g/tree Aug. and May) affected N concentrations in flowers, bourse leaves, and in mid-terminal leaves of current seasons growth. Return bloom and yield were highest for trees with the highest rate of N applied in August and they were lowest for trees with the lowest rate of N applied in a split application in May and August. Fruit size, color, firmness, soluble solids, and titratable acids, either at harvest or after 90 days in regular atmosphere storage, were not influenced by all five relatively low rates of N application. The best N treatment for fruit quality was with the low rate of N application in August. Highest fruit firmness, soluble solids content, and titratable acidity after storage occurred in fruit from trees that were harvested in 1997 with the lowest yield, regardless of N application. Return bloom, flower, and leaf N were good predictors of yield. Due to alternate bearing tendencies yield was a better predictor of fruit firmness, soluble solids, and titratable acidity than leaf N. The best N treatment for highest yield without sacrificing fruit quality was a single application (227 g) in August each year.

Effect of calcium spray materials, rate, time of spray application, and rootstocks on fruit quality of 'Red' and 'Golden Delicious' apples

Abstract Calcium (Ca) spray materials improved fruit quality as measured by control of bitter pit, fruit finish (appearance), increased red skin color, reduced incidence of scald, increased juiciness, texture, and fruit firmness of ‘Red’ and ‘Golden Delicious’ apples (Malus domestica, Borkh.). Concentrations of Ca in leaf and fruit tissues were increased by Ca sprays, especially calcium chloride (CaCl2)‐containing spray materials. Improved fruit firmness and control of bitter pit occurred for either standard recommended or high rates of Ca spray materials. At high rates of application, the only significant difference that occurred between early and late applications of Ca spray materials was that less leaf injury occurred with the early applications. Unsprayed ‘Red Delicious’ fruit from M.7 rootstocks had greater fruit peel Ca concentrations and a lower incidence of bitter pit but smaller fruit than fruit from trees on M.26 rootstocks. The above information is strong evidence that Ca sprays are important for the improvement of apple quality.

Influence of mid‐summer boron sprays on boron content and quality indices of ‘delicious’ Apple 1

Abstract Boron (B) is required for optimal yield and quality of apple fruit (Malus domestica Borkh.) but may impair fruit quality if present in excessive amounts. A field experiment was conducted to examine the effects of a single mid‐July foliar B spray (0, 11.3, 22.6 g B/tree) on the B content and postharvest quality indices of 220‐gram ‘Starking Delicious’ apples. Fruit B concentration was positively related to B application rate and ranged from 9 to 55 mg/kg dry mass (1.3 to 7.7 mg/kg fresh mass). The relative B increases were greater in the core and inner cortex than in the outer cortex and skin, suggesting that some of the applied B entered the fruit through the tree vascular system. Increasing fruit B concentrations caused minor changes in fruit external color indices L and b and internal color index b but had no effect on firmness, soluble solids concentration, titratable acidity, starch index, external color index a, or internal color indices L and a. None of the effects were of horticultural sig...

Influence of different calcium materials and spray timing on mineral composition, yield, fruit quality, and control of fruit disorders of ‘anjou’ pears

Abstract During a six‐year period (1980, 1985–1989), 20 different calcium (Ca) materials were sprayed at an early (3X; June to July), late (3X; July to August), and an early plus late (5X; June to August) timing on 25‐year‐old ‘Anjou’ pear (Pyrus communis L.) trees. Calcium chloride (CaCl2) sprays increased fruit Ca in the cortex by an average of 10.5% greater than in unsprayed controls and cork spot was reduced by an average of six‐fold. Yield from trees sprayed with Ca materials averaged greater than 13% more crop load than the unsprayed control trees. Leaf and fruit injury from CaCl2 sprays in 1980 were near borderline acceptability, but injury was reduced slightly by halving the spray concentration rate to 681 g CaCl2 per 379 liters of water in 1985 to 1989. Due to temperatures above 26°C, leaf and fruit injury from Ca sprays, particularly calcium nitrate [Ca(NO3)2], were more severe for the late or early plus late sprays than for the early sprays. Fruit size was slightly larger on trees sprayed only ...