An investigation was carried out to establish the basic relationship between mechanical resonance, firmness, chemical composition and ethylene production during the maturity time and the ripening time of peach fruit. The stiffness factor calculated by a non-destructive frequency response technique was compared with biological properties obtained by measurement of chemical composition, firmness and ethylene production in the internal atmosphere of tested fruit. The correlation between the biological multifunction and the mechanical resonance frequency of peach fruit can be expressed by an exponential relationship. Multifactorial index seems to describe the rupture point that for peach fruit coincides with the beginning of climacteric developmental stage, detected by ethylene production. The harmonic signal from PULSE signal generator is swept over the frequency range 50 Hz -1.6 kHz. Fig. 2 presents a typical frequency response of tested peach. The highest peak from the spectrum was used for further processing and calculation of stiffness factor S using (1). The mass of each tested peach fruit was measured with precision balance. Sampling of peach fruitsSouth Haven peach fruits grown in an orchard of the research center were used for measurements. Peaches were harvested in the afternoon, transferred to the room temperature and all the parameters were measured next day. Harvesting intervals started from mid-June with the constant interval of one week during five weeks. 12 peach fruits were measured on each of these five measurement days.At the end of the measurements the ripest peach fruits from the last period were stored at a room temperature, numbered from 1 to 12 and their mechanical properties were measured every day from early ripe stage to late ripe stage (4 days). Measurement of texture propertiesThe peach texture was measured as a penetration test with cylindrical plunger of 8 mm diameter and constant speed 10 mm/min, 8 mm deep into tissue. Force deformation curves from penetration tests were plotted to express the skin resistance of tested peach fruits. The firmness of the tissue of tested peach is obtained from the rupture point. Each fruit was penetrated at the opposed locations to obtain skin deformation curve. The compression force expressed as the firmness for skin and flesh of tested peach was sampled and saved in the hard disk of the computer. The mean of four measurements was used to represent the firmness of each tested peach. Measurement of ethylene in atmosphere of impacted fruitA partial vacuum was applied to the tissue submerged in an aquatic solution. Gas bubbles leave out the fruit, rise in the solution and accumulate at the top of the submerged container. A sample (1 ml) of extracted gas was injected in the stainless steel column (1.2 m × 3 mm) packed with Porapak Q (60-80 mesh). Ethylene concentration was determined using an external standard of 110.7 µl/l ethylene calibration gas certified by Linde Products, Czech Republic. Measurement of chemical compositionTwelve fruits were...
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