Seok Ho Park

Non-destructive monitoring of apple ripeness using an aldehyde sensitive colorimetric sensor

We developed an on-packaging colorimetric sensor label that can detect the aldehyde emission of apples based on Methyl Red. The sensor label was constructed using printable inks on paper medium and relied on the change in basicity caused by the nucleophilic addition reaction between aldehyde and hydroxide via the Cannizzaro reaction. The sensor can be used to detect aldehyde in solution and vapor. Sensitivity and stability toward changes in humidity were achieved by altering the concentration of OH-. Under exposure to ripening apples, the label changed color from yellow to orange, and then to red. The degree of ripeness was estimated by a sensory test and texture analysis. The color change of sensor label had showed a similar tendency to the changes in the parameters of the sensory test, soluble solid content, and hardness. Therefore, the sensor label can be used for real time on-package ripeness monitoring of apples during their shelf life.

Effects of ultrasonic thawing on the physicochemical properties of frozen pork

This study was carried out to investigate the effects of ultrasonic thawing on physicochemical characteristics of frozen pork sirloin. To determine the velocity of an ultrasonic thawing machine, -80°C frozen pork sirloins were thawed using 132, 580, and 1,000 kHz ultrasonic thawing machines, and the physicochemical properties of pork sirloin thawed with 15°C tap water and those using the ultrasonic thawing machines were compared. As a result, thawing speed by ultrasonic thawing was three times faster than that of tap water, but drip weight loss rate is increased by about 5% during ultrasonic thawing compared to that during thawing in tap water. However, biochemical properties, such as pH, volatile basic nitrogen, thiobarbituric acid, and total aerobic bacteria, were not improved by ultrasonic thawing. Hunter values, such as total color change and redness, improved slightly after 580 kHz ultrasonic thawing. The hardness and chewiness of the pork sirloin decreased significantly after 580 kHz ultrasonic thawing; however, springiness was not changed. These results indicate that ultrasonic thawing is faster than thawing in tap water, but the physicochemical characteristics of frozen pork sirloin was not significantly improve by ultrasonic sound.