Jacob B. Biale

The Postharvest Biochemistry Of Tropical And Subtropical Fruits

Publisher Summary This chapter emphasizes respiration as the central process affecting the behavior of the harvested fruit. It discusses several aspects in the physiology and biochemistry of fruits rather than to present a complete account for each fruit. Physiological and chemical changes that influence the quality and vitality of fruits are related to patterns of respiration. A distinction has been made between fruits that do and fruits that do not exhibit a characteristic upsurge in respiratory activity before the onset of senescence. The role of ethylene in fruit ripening and its relationship to the climacteric rise have been discussed. The idea is advanced that ethylene is a product, rather than a causal agent, of the ripening process. The biochemical changes characteristic of living cells in general are examined and found to play an important role in fruits. Mitochondria1 oxidations and phosphorylations have opened up a new avenue of approach to old problems. Studies with cytoplasmic particles coupled with investigations on proteins, enzymatic activities, and metabolic pathways suggest that active synthesis characterizes fruits during the climacteric rise.

Protein synthesis in avocado fruit tissue.

The question wag raised whether enhanced protein synthesis was associated with the rise in respiration of the avocado fruit which occurs at the end of maturation and is known as the “climacteric rise.” The methodology consisted of following the incorporation of 14 C- L -valine and 14 C- L -leucine into proteins of tissue slices secured from fruits at several stages of the climacteric. It was found that the incorporation of these amino acids rose sharply during the early stage of the climacteric rise and declined rapidly thereafter. Incorporation was virtually absent in tissue of fruit at the peak of the climacteric rise. Puromycin effectively inhibited the incorporation of valine and leucine into proteins of climacteric tissue, but did not affect the oxygen uptake of the discs. It was concluded that oxygen uptake along the rise was not directly related to protein synthesis.

Carbon dioxide effects on fruits

Summary1.The first products of C14O2 fixation by lemon fruit in the dark were found to be malic, citric and aspartic acids. It is presumed that exalacetic is actually the first product to be labeled but that it is converted rapidly to the three other acids.2.Malonic acid was identified as one of the products of exposure to C14O2.3.Aconitic, fumaric and α-ketoglutaric acids could not be detected in the extracts of lemon peel, thus raising the possibility of the existence of at least two pools for the products of CO2 fixation.4.The suggestion was advanced that accumulation of citric acid in the vacuole leads to a deficiency of oxalacetic acid and thus limits overall oxidation. Carbon dioxide stimulates respiration by increasing the supply of oxalacetic acid.