Bernard Goyette

Effect of Barometric Pressure on Flight Initiation by Trichogramma pretiosum and Trichogramma evanescens (Hymenoptera: Trichogrammatidae)

Abstract The effect of barometric pressure changes on flight initiation of female Trichogramma evanescens Riley and Trichogramma pretiosum Westwood (Hymenoptera: Trichogrammatidae) was studied in a flight chamber over a 6-h period. Six different barometric pressure regimens were tested for their impact on flight initiation of both species: constant 975 and 1,025 mbar (stable regimens), and 50 mbar increase or decrease in pressure between 975 and 1,025 mbar either within 1 (rapid increase or decrease) or 6 h (slow increase or decrease). Both Trichogramma species did not respond to stable or slow changes in barometric pressure, but rapid barometric changes significantly reduced the flight initiation of females. The effect of rapid barometric pressure changes was almost immediate and independent of its direction, whether it was increasing or decreasing. The reduction in flight initiation was lifted rapidly when the barometric pressure became stable again, immediately for T. pretiosum and 1 h later for T. evanescens. These results are in agreement with the hypothesis of an adaptive response to rapidly changing climatic conditions and associated higher risks of mortality during flight for small insects like Trichogramma. The higher flight initiation observed for T. evanescens females also agrees with field results where they displayed higher dispersal capacity than T. pretiosum females under adverse climatic conditions. The effects of barometric pressure on parasitoid foraging behavior deserve more attention because this climatic variable may play a significant role in their population dynamics.

Effect of hyperbaric treatments on the quality attributes of tomato

Goyette, B., Vigneault, C., Charles, M. T. and Raghavan, V. G. S. 2012. Effect of hyperbaric treatments on the quality attributes of tomato. Can. J. Plant Sci. 92: 541–551. An experimental hyperbaric system was conceptualized, designed and built to explore the effect of hyperbaric treatment on the quality attributes of tomato. Tomato fruits at the early breaker stage were subjected to hyperbaric pressures of 1, 3, 5, 7 or 9 atmabs for different durations (5, 10 or 15 d) at 13°C. The effect of hyperbaric treatment on postharvest quality of tomato fruit was evaluated with an emphasis on weight loss, firmness, color, titratable acidity (TA) and total soluble solids (TSS). Hyperbaric treated tomato fruit ripened more slowly and were characterized by lower respiration rate than fruits kept under ambient conditions. Significant differences in weight loss, color, lycopene concentration and firmness were found between hyperbaric treated and control tomato fruit. No significant difference was found in the sugar/acid ratio (TSS/TA).

Invited review: Engineering aspects of physical treatments to increase fruit and vegetable phytochemical content

Vigneault, C., Leblanc, D. I., Goyette, B. and Jenni, S. 2012. Engineering aspects of physical treatments to increase fruit and vegetable phytochemical content. Can. J. Plant Sci. 92: 373–397. The levels of phytochemicals in fruit and vegetables are affected by many preharvest and postharvest factors, such as cultivars, farming practices, environmental conditions, harvest techniques, and postharvest handling and treatment. Postharvest factors are generally the easiest to manage since produce handling takes place mainly under controllable conditions. Although specific physical treatments, such as heat and ultraviolet radiation, have been developed to increase the phytochemical content of horticultural produce, very little information is available on the engineering aspects of these treatments. A review of the engineering aspects related to phytochemical-enhancing physical treatments was undertaken to identify the process parameters required to obtain repeatable results, the basic information required for scale-up of the process, and the key parameters required to ensure appropriate monitoring and control of commercial applications. The uniformity, efficiency, efficacy, ease of control and ease of scale-up of various physical treatments were compared to support the development of a new phytochemical-enhancing treatment for potential commercial application. These treatment methods were considered independently of the physical characteristics of the produce treated (type of produce, size, shape, and positioning) to reduce the number of parameters to be studied with a view to scale-up processes, following identification of the optimal processing conditions through laboratory-scale testing.

Effect of Hyperbaric Treatment on Quality Attributes of Tomato Fruits

An experimental hyperbaric system was conceptualized, designed and built to explore the effect of hyperbaric treatment on the quality attributes of tomato.

Design of a computer controlled pressure chamber for insect behavioral studies

A cylindrical chamber was designed and built to evaluate the effects of barometric pressure on insect behavior. The chamber, 200 mm diameter by 550 mm high, is made of an acrylic pipe and two acrylic covers. The system is computer controlled using an electronic barometer, solenoid valves, a vacuum pump, and compressed air connected to a data acquisition unit. The chamber is pressurized and maintained using compressed air; a vacuum pump is used to decrease pressure. The performance of the system was tested by lowering the pressure from 1050 to 950 mbar and then increasing it to 1050 mbar within 1 h, following a sinusoidal pattern. The maximum difference between the instantaneous set point pressure and the recorded pressure was 1.1 mbar, which represents a maximum error of 1.1% over the range tested. This system was able to simulate adequately the range of pressure to which insects are normally subjected in their natural environment.

EFFECT OF NON-UNIFORM HEAT TREATMENT ON TOMATO RIPENING AND CHILLING INJURY

Abstract An experimental setup consisting of a forced-air-twin-chambers insulated device was built to generate a non-uniform (heterogeneous) heat treatment. The heterogeneous treatment insured that half part of tomato in one chamber to be exposed to warm air at a controlled temperature of 39.5°C and uniformly circulating at a velocity of 0.24m s-1, while the other half in the other chamber was exposed under unheated, controlled and stable conditions (23°C, 0.24m s-1). Temperature control for both chambers along with the desired fixed air flow rate is achieved using suitable instrumentation. The tested tomatoes were randomly divided into five lots: one was used as control, two were uniformly treated, and the other two were heterogeneously treated. Immediately after treatment the fruit were transferred to regular storage at 14°C, to ripening at 20°C or to chilling injury (CI) at 4°C. Color, firmness, titratable acidity (TA), total soluble solid (TSS) and severity of CI were measured or evaluated subjectively at designed time. Results indicated there existence of statistically significant difference between heated and unheated part for tested tomatoes in terms of color, and CI. As result of relative consistently higher value of TA and TSS, no significant difference in the taste indictor, suger:acid (TSS:TA) ratio, was noticed. The result implied that ripening process of heated part was delayed in particular period, and this delay was similar to the contrast between uniformly heated tomato and its control. The observed difference might be explained by the fact that the effect of heat treatment on tomato is localized rather than systemic. These findings addressed that ensuring uniform heat condition is of paramount importance to attain the desired effect. It is suggested to develop systems with media such as RF or microwave, or to optimize the layout of material treated with conventional media.

Effect of Thermodynamic Parameters on Tomato Ripening and Chilling Injury under Heterogeneous Heat Treatment

A forced-air-twin-chambers insulated device was built to generate heterogeneous heat treatment. This treatment insured that half part of tomato in one chamber to be exposed to effective warm air at a controlled temperature of 39°C and uniform circulation at a velocity of 0.24m s-1; while the other half in the other chamber was exposed to lower temperature of 36°C or 37°C under 0.24m s-1, or at 36°C under 0.12 m s-1. Temperature control for both chambers was achieved using suitable instrumentation, while the air velocity could be modified and fixed at a desired level. The tested tomato fruits were randomly divided into four lots: one was used as control, two were uniformly treated, and the other was heterogeneously treated. Immediately after treatment the fruits were transferred to regular storage conditions at 14°C, to ripening at 20°C or to chilling injury (CI) at 2°C. Under all storage conditions, relative humidity was maintained high at 90-93%. Color, firmness, titratable acidity (TA), total soluble solid (TSS) and severity of CI were measured or evaluated subjectively at designed time. Results indicated that temperature difference between two chambers has significant effect on the uniformity of color--especially on chroma and redness represented by hue, slightly on firmness, TA and sugar acid ratio in the temperature range investigated. Decreasing the temperature difference between the two chambers or relatively increasing the air flowrate of upper chamber significantly improved the uniformity of quality, addressing the importance of improving the uniformity of heating media around each individual treated fruit.

ASSESSMENT OF PRECOOLING TECHNOLOGIES FOR SWEET CORN

Three cultivars of sweet corn were precooled immediately after harvest using forced-air, vacuum and hydrocooling systems. Combinations of two air flow rates, 1 and 3 L•s-1•kg-1 of produce, and two water flow patterns, immersed and spray, with two cob orientations, parallel and perpendicular to the medium (air or water) flow were tested. Both precooled and room cooled corn cobs were stored for 7 and 21 days at 1oC and 90-95 % RH. Half cooling time and quality attributes were measured to assess the performance of all cooling systems. Cooling time was significantly reduced with perpendicularly oriented cobs, higher air flow rate (3 L•s-1•kg-1) and immersed-in-water type flow.. The highest decrease in cooling time was observed with vacuum with a production of a large mass loss, followed by forced-air. On the other hand, immersed-in-water treatment resulted in better maintenance of general quality index and of higher total soluble solids and moisture content over the period of survey. The three cultivars evaluated in the present study were shown to have differences in their storage ability and quality conservation. However, the selection of one cultivar over the others, for industrial application, will be governed by consumer’s preference and market supply.

Indirect Airflow Distribution Measurements in Horticultural Crop Packages

The airflow distribution through a porous medium such as horticultural crops is a great challenge. The development of a method allowing the measurement of the air velocity or its distribution would be of large interest. The applicability of using instrumented balls as an indirect measurement of air velocity was evaluated. A group of 64 instrumented plastic balls were used as horticultural produce simulators and strategically distributed in an orthogonal matrix along with other 448 plastic spheres to simulate precooling of column stacked produce. The ball matrix was submitted to cooling process under controlled conditions. Correlations were determined by measuring the half-cooling time of 64 simulators positioned at fixed locations inside of the two-end-fully-open ball matrix. The surrounding air velocity was inferred as a function of the simulator locations in reference with the air entrance. This method was then evaluated by comparing the data obtained for three package opening areas (0.67%, 2%, and 6%), and six airflow rates (ranging from 0.125 to 3.9 L•s-1•kg-1), and performing a mass balance. This comparison showed the capacity of this method in predicting the variation of the cooling rate as a function of the airflow rate and its capacity in inferring the mean air velocity through the ball matrix.