Summary
Some 109tonnes of chlorophyll are destroyed each year on land and in the oceans. The fate of these chlorophylls is, however, largely unknown. This review describes the developmental stages at which chlorophyll breakdown occurs in aquatic and terrestrial biological systems, and the destruction arising from herbivory, disease, pollution and other physical hazards. At the cellular level, an attempt is made to separate the breakdown of chlorophyll during senescence from the many other events associated with cell destruction and death.

A consideration of the more important chemical and biophysical properties of chlorophylls and their derivatives is provided, together with data on their spectral properties. The biosynthetic and biodegradative pathways of chlorophyll metabolism are, so far as is possible, described with some predictions as to the likely fate of the missing tonnes. Two types of degradation are recognized; the first involves up to five defined enzymes concerned with the early stages, the second covers the less well defined enzymic and non-enzymic destruction of the macrocyclic structure. These degradative reactions are compared with the reactions implicated in the breakdown of other porphyrins including haems in plants and animals.

A brief description is given of the occurrence of breakdown products of chlorophyll in past biomass, including those of geological significance and those in a more recent archaeological context.

Finally, the economic significance of chlorophyll breakdown is considered in the context of agriculture and horticulture, veterinary and medical sciences, food colouring and cosmetic industries, and the multi-million-dollar attraction of autumn leaf fall to tourism.

The degradation of chlorophyll — a biological enigma

Digestion, absorption, and cancer preventative activity of dietary chlorophyll derivatives

The natural color of foods is due primarily to carotenoids, anthocyanins, betanin and chlorophylls, either as inherent food constituents or as food or feed additives. These compounds have drawn considerable attention in recent years, not because of their coloring properties, but due to their potential health-promoting effects. Their occurrence and levels in foods, along with the factors that influence the composition, have been widely investigated. Processing effects have been actively studied. In spite of the intense search for plant and microbial sources and efforts to increase yield, few natural food color additives have reached the market. Lack of stability is a major deterrent; microencapsulation and nanoencapsulation are being advocated to minimize this problem.

Natural food pigments and colorants

Effect of pH on chlorophyll degradation and colour loss in blanched green peas

Kinetics of colour change of double concentrated tomato paste during thermal treatment

Pyropheophytins a and b were determined as predominant chlorophyll derivatives in heat processed spinach. Chlorophylls a, b, pheophytins a, b and pyropheophytins a, b were quantitated in fresh, blanched and heat processed spinach at 116, 121 and 126°C. First order degradation rate constants were determined to calculate activation energies of 25.2 and 22.5 Kcal/mole for chlorophylls a and b and 20.7 and 15.7 Kcal/mole for pheophytins a and b, respectively. Based on the results, the suggested mechanism for the decomposition of chlorophyll during heat processing of vegetables is: Chlorophyll Pheophytin Pyropheophytin. Pyropheophytins a and b were major chlorophyll degradation products found in all commercially canned vegetable products surveyed.

J. H. Elbe

Papers

Kinetics of Chlorophyll Degradation to Pyropheophytin in Vegetables