APPLE POSTHARVEST PRESERVATION IS LINKED TO PHENOLIC CONTENT AND SUPEROXIDE DISMUTASE ACTIVITY

The postharvest preservation of apples indicated that well-preserved varieties of apples had increased superoxide dismutase (SOD) activity initially, and the activity declined during later storage as apples deteriorated. The increased SOD activity linked to better preservation correlated with higher phenolic content and free-radical scavenging-linked antioxidant activity. Well-preserved varieties were able to maintain a more stable pentose phosphate pathway (measured by the activity of glucose-6-phosphate dehydrogenase) throughout the storage period. Proline content increased with proline dehydrogenase (PDH) activity in the initial storage period, indicating proline catabolism supporting potential adenosine 5'-triphosphate (ATP) synthesis. During later storage, succinate dehydrogenase activity increased, while PDH activity declined indicating a shift to tricarboxylic acid cycle and likely nicotinamide adenine dinucleotide hydrogen (NADH) generation for ATP synthesis. This shift, coupled with the declining SOD activity, coincides with rapid deterioration. The guaiacol peroxidase activity generally declined in late stages, indicating postharvest deterioration.

PRACTICAL APPLICATIONS

Understanding the phenolic-linked antioxidant response during postharvest preservation of apples has implications for understanding critical control points for preservation and determination of better biochemical markers associated with preservation and long-term storage. These insights would also help elucidate markers such as high phenolic content and antioxidant enzyme response pathways that would allow for selection and breeding of varieties that would preserve better. Higher phenolic content not only improves the postharvest storage of apples but have also shown human health benefits.     

HEALTH BENEFITS OF APPLE PHENOLICS FROM POSTHARVEST STAGES FOR POTENTIAL TYPE 2 DIABETES MANAGEMENT USING IN VITRO MODELS

An increasing number of studies indicate that regular intake of fruits and vegetables have clear links to reduced risk of chronic diseases like diabetes and cardiovascular disease. The beneficial effects in many cases have been attributed to the phenolic and antioxidant content of the fruits and vegetables. Apples are a major source of fiber and contain good dietary phenolics with antioxidant function. Previous epidemiological studies have indicated that intake of apples reduces the risk of developing type 2 diabetes. Our studies indicate that this reduced risk is potentially because of the modulation of postprandial glucose increase by phenolics present in apples via inhibition of α -glucosidase. Phenolic content was evaluated during 3 months of postharvest storage of four varieties of apples and results indicated positive linkage to enhanced postharvest preservation and α -glucosidase inhibition. These in vitro results along with existing epidemiological studies provide strong biochemical rationale for further animal or human clinical studies.

PRACTICAL APPLICATIONS

The understanding of phenolic-linked antioxidant enzyme responses during postharvest storage of apples has implications for using the same phenolic functional ingredients toward health benefits such as α-glucosidase inhibition linked to glycemic index control associated with type 2 diabetes. Therefore strategies to understand phenolic-linked postharvest preservation and natural treatments to extend this preservation in selected varieties, such as McIntosh and Cortland in this study, can be basis for food ingredient design for health benefits. These strategies can then be extended to prolong postharvest preservation and enhance phenolic linked human health benefits of a wide variety of fruits and vegetables.