Clifford J Studman

Computers and electronics in postharvest technology — a review

The article gives an overview of areas where computers and electronics have made a particular impact on the postharvest industry. These include environmental control and storage, quality monitoring, quality management, grading systems, inventory control, and management of product. Specific examples of the application of electronic systems have been given to illustrate the current state of postharvest technology, and some future predictions have been given. It is likely that consumer demand for improved quality, longer storage life, and guaranteed product safety will continue to grow. In a highly competitive market the industry will need to meet these demands, and electronic technology will play an increasingly important role. Improved sensors to assess quality are still needed, and handling and storage systems are likely to become increasingly sophisticated. In the latter half of the twentieth century technology has contributed much to improve the worlds food supply, but it has also generated problems for the wider society, which will require attention in the next millennium.

Bruising damage in apple-to-apple impact

A study of free normal impact between pairs of Granny Smith apples has been conducted. Bruising was generally more severe on one of the two fruit. Sometimes only one apple was damaged, and it was very rare for both fruit to be damaged equally. It is suggested that differences in the apparent ease of bruising of some varieties reported by growers may be more owing to variations of fruit physical yield strength around each fruit or between fruit in the same crop, than to absolute values of bruise susceptibility. It was found that the total bruise volume of the two fruit was linearly correlated with the energy absorbed. There was a non-linear relationship between the contact area and the impact energy, but the two were related by a 2/5 power law as predicted by elasticity theory. It was also found that the coefficient of restitution varied in a non-linear manner with impact energy, decreasing as the impact energy increased, to reach an asymptotic value of around 0·45. When the coefficient of restitution was above 0·7 very little damage was produced on the apples.

Fruit contact pressure distributions : equipment

A commercially available tactile sensing system allows the pressure distribution between contacting surfaces to be determined in real time. This sensor has been used to determine the pressure distribution between fruits, mainly apples, in contact with flat and curved surfaces. The sensor consists of a thin flexible plastic film containing a grid of sensitive material that responds according to the pressure at each point on the mesh. Details of the sensor and examples of experimental results obtained with the system are described. The device was found to have a non-linear output, and the data needed to be calibrated to improve the accuracy of the results. Examples of the surface pressure distribution generated in the contact area as apple fruit were loaded to failure, and the effects of commercial packaging materials on pressure distribution are presented.

A multi-purpose firmness tester for fruits and vegetables

Abstract A computer driven testing system has been developed to measure the firmness and other physical properties of fruit and vegetables rapidly and easily. The system has multiple functions and can be used for a range of crops in either destructive or non-destructive mode. Measurements made include skin firmness or rupture strength, flesh firmness at any given depth, compressibility, modulus of elasticity, energy absorption during a loading cycle, and compression strength between flat plattens. The system has the ability to instantaneously record both load and displacement, and then feed this information into the indenter movement control to make immediate alterations to the indenter movement. The system consisted of a computer with a multi-function input/output ( I O ) card and two computer controlled stepper motors which drove a vertical column at up to 4 mm s−1. Various indenters could be attached to the column to compress or crush the fruit sample. The specimen to be sampled was placed on a load cell under the indenter column, and the output from the load cell was fed to the computer at a sampling rate of 40 kHz through an analogue/digital ( A D ) converter. The computer was programmed to conduct the required test measurements as soon as the specimen was detected. In this way measurements could be taken by inexperienced personnel. Each test took under 30 s to complete, and results were fed back to the user immediately. Examples of measurements on tomatoes, apples and cherries are presented to demonstrate the type of output data obtained.

Non‐destructive measurement of kiwifruit firmness

Abstract Design and operation of two prototypes of an instrument for measurement of fruit softness and its application to characterisation of kiwifruit (Actinidia deliciosa) softening behaviour are described. The “softness meter” was used to measure deformation of the fruit surface beneath a small spherical probe under constant load with time and caused negligible damage to the tested fruit. Softness was quantified as a “softness coefficient”, estimated as the slope of the regression line of deformation on the natural logarithm of time. After an initial delay in softening, softness coefficients of kiwifruit increased approximately linearly with time in storage at 0°C and were inversely and hyperbolically related to penetrometer data obtained on the same fruit. Repeated measurements on individual fruit, made possible by the non‐destructive nature of the softness meter, will enhance control of experimental error in research on fruit softening behaviour.

A dairy refrigeration heat recovery unit and its effects on refrigeration operation

Abstract Concern about increased energy costs prompted an investigation into refrigeration heat recovery as one conservation alternative for reducing water heating costs on farm dairies. A theoretical energy balance was conducted, from which the potential for recovery of refrigeration condenser heat was estimated to be up to 60% of the water heating energy requirements. Preliminary tests with heat exchangers led to the development and testing of a tube-in-tube, counter flow heat exchanger, with fins on the refrigerant side and cores on the water side to improve the heat transfer characteristics. The exchanger, designed to provide 300 l of water at 60°C from a 2·25 kW refrigeration system which cooled 2100 l of milk per day, had a surface area on the refrigerant side of 0·84 m 2 , and an overall thermal conductance of 750 W m −2 °C −1 . It was inserted between the compressor and the condenser of the refrigeration plant and tested with two condensing systems (air and water), together with varying conditions of condenser pressure and milk temperatures at inlet and final cooling. In addition, tests on the receiver pressure and suction superheat were performed to determine their effect on the overall system performance. Increasing the condenser pressure from 6·5 bar to 12 bar increased cooling times. In extreme circumstances the system failed to comply with the New Zealand milk cooling regulations. The average coefficient of performance (C.O.P.) of the refrigerator (with the heat exchanger in the circuit) decreased with increasing pressure, varying from 3·0 to 2·3 over this range of pressures for the water cooled condenser system. Values for the air cooled condenser system were 0·3 to 0·4 lower due to fan power consumption.

Analysis of damage thresholds in apple-to-apple impacts using an instrumented sphere

Abstract Fruit-to-fruit impacts on commercial packing lines were simulated in the laboratory for pairs of fresh ‘Gala’, ‘Splendour’, ‘Fuji’, ‘Braeburn’, and ‘Granny Smith’ apples by dropping one apple onto the other from a range of heights. Bruising was generally more severe on one of the two apples, and it was quite common for only one apple to be damaged. Contact areas above 1 cm2 were closely related to bruise areas. Below this level bruising rarely occurred. Some bruises produced in apple-to-apple impacts were not visible unless the apple skin was removed. ‘Braeburn’ apples required a greater drop height to produce a significant bruise than other varieties. An Instrumented Sphere (IS), 89 mm in diameter with a mass of 0.336 kg, which recorded acceleration magnitudes above an adjustable pre-programmed threshold, was used to characterise impacts onto fruit. When the results of apple-to-apple and IS-to-apple impacts were compared, it was found that the area of the larger of the two bruises produced in fr...

The performance and economics of a dairy refrigeration heat recovery unit

Abstract The results of a series of experiments on a refrigeration heat recovery unit designed to provide 300 1 of 60°C water from a 2·25 kW refrigeration system cooling 21001 of milk per day are presented. The unit was inserted between the compressor and condenser of the refrigeration plant and tested with two condenser systems (air and water), four condenser pressures (6·5 bar, 7·5 bar, 10 bar and 12 bar), two milk inlet temperatures (23°C and 18°C), and two milk final temperatures (4°C and 7°C). In addition, tests on receiver pressure and suction superheat were performed to determine their effect on the overall system performance. Increasing condenser pressure caused the gross heat recovery to rise from 15·1 MJ (4·2 kWh) d−1 m−3 to 29·2 MJ (8·1 kWh) d−1 m−3 of milk for the water cooled system, while water outlet temperatures rose from 45°C to 64°C. The corresponding ranges for the air cooled condenser were 13·7 MJ (3·8 kWh) d−1 m−3 to 23·8 MJ (6·6 kWh) d−1 m−3, and 38°C to 55°C. Changing milk inlet and final temperatures gave a proportional change in cooling times and total heat recovery, but had no effect on C.O.P. or heat recovery rates. Suction superheating increased the total heat recovery by approximately 3·2 MJ (0·9 kWh) d−1 m−3, and water outlet temperatures by 5°C. Although increasing condenser pressure resulted in an increase in gross heat recovery, these gains were offset by the additional compressor power required. The net heat recovery varied between 13·7 MJ (3·8 kWh) d−1 m−3 at 6·5 bar, to 19·1 MJ (5·3 kWh) d−1 m−3 at 12 bar for the water cooled system. For the air cooled condenser system the net heat recovery remained fairly constant at approximately 11·5 MJ (3·2 kWh) d−1 m−3. Based on these figures, the annual savings have been calculated under various conditions. At 10 cents per kWh, the heat recovery unit used in a system with a water cooled condenser operating at 12 bar, with suction superheat, on a farm producing 2100 1 per day, could save

A once-through solar water heater system for farm dairies

NZ453 per annum. For a 210 cow dairy farm, such a system would cost around

An experimental study of the ability of sheep to penetrate artificial barriers

NZ5000 (including the cost of the water cooled condenser), making the installation marginally uneconomic. However, heat recovery systems on larger farms are likely to be more attractive financially, because the increase in return is not matched by a similar increase in cost. The optimum operating conditions may vary if the electricity tariffs are altered. Methods of increasing the net heat recovery are considered and other techniques for reducing hot water power consumption are discussed.