H4-KH23-B iary cooling is requiredPG PGD x f or PGD x f PG Helical gear units H4

Flender/Flender Gear Units/Helical gear units H4

ion is blocked; the importance of alternative respiration in vivo is stillunclear (. Oxidative reactions are not solely due to respiratory activity in either fresh or mini- mally processed produce. Residual respiration is term often used for 2-consuming pro- Postharvest Physiology of Fresh Produce 4 cesses involving enzymes such as polyphenoloxidase (PPO) and peroxidase. Such en- zymes are involved in wound repair reactions and in defense against intrudingmicroorganisms. PPO, possibly the most studied enzyme in harvested fruits and vegeta-bles, is responsible for the browning of plant tissues. In minimally processed produce,which is chopped, cut, sliced, or peeled, the level of tissue injury is much higher than in whole produce. Consequently, the level of metabolic activity and thus the respiration rate of minimally processed produce is often orders of magnitude higher than that of wholeproduce. Enzymes such as PPO will also be more active when present and may causevisible browning of cut surfaces. Similar to alternative respiration, residual respiration does not result in ATP produc- tion. In avocado tissues, alternative and residual respiration can account for 6 to 7% of the total 2consumption (. Although these numbers seem high, it is likely that both alternative and residual respiration contribute consistently to 2consumption. The three O2-consuming pathways also respond differently to variations in gas concentrations (7,, resulting in varying ratios between ATP-producing and nonATP-producing 2consump- tion. These ndings indicate that 3 molecules of ATP per 2molecule consumed is not consistently accurate for estimations of real-life ATP production. Therefore, when energy metabolism is quantied, factor should be introduced to indicate the percentage of 2 consumption resulting in ATP production. 2.1.2 Respiration Measurements The rate at which fruits and vegetables ripen or senesce can be inuenced and controlled by environmental factors such as tempe